RevIeWS

One hundred years of therapy

Chantal Mathieu ✉ 1,2, Pieter-Jan Martens1,2 and Roman Vangoitsenhoven 1,2 Abstract | At the time of its first clinical application 100 years ago, insulin was presented as the cure for people with mellitus. That transpired to be an overstatement, yet insulin has proven to be the lifesaver for people with mellitus and an essential therapy for many with mellitus or other forms of diabetes mellitus. Since its discovery, insulin (a molecule of only 51 amino acids) has been the subject of pharmaceutical research and development that has paved the way for other protein-based therapies. From purified animal- extracted insulin and human insulin produced by genetically modified organisms to a spectrum of insulin analogues, pharmaceutical laboratories have strived to tailor the preparations to the needs of patients. Nonetheless, overall glycaemic control often remains poor as exogenous insulin is still not able to mimic the physiological insulin profile. Circumventing subcutaneous administration and the design of analogues with profiles that mimic that of physiological insulin are ongoing areas of research. Novel concepts, such as once-weekly or - dependent and oral insulins, are on the horizon but their real-world effectiveness still needs to be proven. Until a true cure for type 1 diabetes mellitus is found and the therapeutic arsenal for other forms of diabetes mellitus is expanded, insulin will remain central in the treatment of many people living with diabetes mellitus.

Insulin is a peptide hormone that is continuously hyperglycaemia, such as microvascular and macrovas- released in low concentrations by the pancreatic β-cells cular complications, or adverse neonatal outcomes, such to limit catabolism in the fasting state. Postprandially, as macrosomia. increased insulin secretion ensures energy storage as a result of the synthesis of complex carbohydrates, pro- The early years teins and lipids. Its most important glucose-lowering The first reference to diabetes mellitus dates back effect is stopping endogenous glucose production and, of to the Ebers Papyrus, written around 1550 BCE, with the course, the insulin signalling cascade induces the inser- mentioning of polyuria as a main symptom2. Until tion of glucose transporters into the cell membranes of the early twentieth century, the diagnosis of T1DM in muscle cells and adipocytes1. Since its first clinical appli- young people was a death sentence as the underlying cation in 1922, insulin has become a widely prescribed pathophysiology remained unknown and no true ther- glucose-lowering agent in people with many forms of apy was available. A strict ‘starvation’ diet, as advocated diabetes mellitus. In type 1 diabetes mellitus (T1DM) by the physicians Joslin and Allen3, could temporarily or other conditions leading to a complete loss of β-cells avoid symptomatic glycosuria and acute metabolic (such as total pancreatectomy), lack of insulin leads to a decompensation; however, patients would still deterio­ catabolic state, characterized by glycogenolysis and glu- rate and life expectancy was limited to a few years at coneogenesis in the liver, lipolysis in adipose tissue, and the most. protein catabolism in muscle. Insulin deficiency results A series of pioneering observations by von Mering in ketone production, muscle wasting and weight loss, and Minkowski4, Hédon5 and Opie6 in the late nine- 1Department of Endocrinology, culminating in an acute metabolic decompensation teenth century suggested that the islets of Langerhans University Hospitals Leuven, () and eventually death. Therefore, produced an ‘internal secretion’, or hormone, that could Leuven, Belgium. insulin replacement therapy saves the lives of people with regulate carbohydrate metabolism. This substance was 2 Department of Chronic T1DM. Type 2 diabetes mellitus (T2DM) and gestational termed ‘insulin’ by de Meyer in 1909 (ref.7). Several Diseases and Metabolism, 8 9 10 KU Leuven, Leuven, Belgium. diabetes are characterized by impaired insulin secretion researchers, including Zuelzer , Scott , Kleiner and 11 ✉e-mail:​ chantal.mathieu@ in the presence of insulin resistance. Here, insulin sup- Paulescu , tried to isolate this hormone and, to some uzleuven.be plementation therapy is needed only when other agents extent, succeeded in producing pancreatic extracts that https://doi.org/10.1038/ are insufficient or contraindicated, to control blood lev- had the potential to lower blood levels of glucose. In s41574-021-00542-w els of glucose, and to avoid the complications of chronic hindsight, they could all be considered as discoverers of

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Key points extraordinary­ achievement, Banting and Macleod were awarded the Nobel Prize in Physiology or Medicine the • Insulin has proven to be a lifesaver for people with type 1 diabetes mellitus and an following year, in 1923. However, this climax was over- essential therapy for many people with type 2 diabetes mellitus or other forms of shadowed by animosity over the award not only with diabetes mellitus. regard to the work of other researchers (as mentioned • Since its discovery, insulin has been the subject of extensive pharmaceutical research previously) but also within the Toronto team. Indeed, and development that has also paved the way for other protein-based​ therapies. Banting immediately announced that he would split • Initially, advancements were mainly focused on improving the quality of life by his prize money with Best and, in response, Macleod reducing the frequency of injections and reducing antigenicity. shared his portion with Collip. Banting, Best and Collip • Since the Diabetes Control and Complications Trial in 1993, the focus has shifted subsequently shared the patent for insulin, which they towards mimicking the physiological insulin profile. sold to the University of Toronto for one Canadian • The risk of hypoglycaemia remains a major burden of insulin therapy. dollar (Box 1).

insulin. However, they were hampered by having only Towards better insulins crude changes in glycosuria as an outcome parameter As the news of the discovery of insulin spread worldwide, and, therefore, were not able to prove the efficacy of their there was an urgent need to upscale its production. In a extracts. Methods to determine blood levels of sugar partnership with Eli Lilly and Co. and their chief chem- were available but it was not until the 1910s that the first ist George Walden, purity and yield were improved and micro-chemical method for measuring sugar levels in standardization was achieved by applying isoelectric pre- the blood was introduced by Lewis and Benedict12 (later cipitation and subsequent recrystallization21. To address optimized by Myers and Bailey13), which meant that inter-batch potency differences, biological assays for esti- this method could be used in practice. This innovation mating the ‘blood sugar-lowering’ potential of prepara- was crucial for the development of insulin as a ther- tions were introduced, leading to each vial of insulin being apy for people with diabetes mellitus as it enabled the labelled with the number of blood sugar-lowering ‘units’ quantification of blood sugar levels. it contained22. A practice that led to the use of ‘units’ for Moreover, besides demonstrating efficacy, the further dosing insulin that is still used in the present day. purification of the endocrine hormone from the exo- crine pancreatic tissue remained a crucial and complex Longer-acting insulins step in enabling the clinical use of insulin. This puri- In the early days of the clinical use of insulin, the dura- fication was the step that caused issues for all of the tion of action of the short-acting regular (also known before-mentioned researchers. The critical final hur- as ‘soluble’ or ‘Toronto’) insulin extracts was as short as dles were tackled by four researchers based in Canada: 4–6 hours, necessitating multiple injections of insulin Frederick Grant Banting, Charles Herbert Best, John per day, using glass syringes23. To reduce the number of James Rickard Macleod and James Bertram Collip. In the daily (and nightly) insulin injections, the development spring of 1921, Banting, an orthopaedic surgeon, set of a longer-acting insulin formulation was considered out to study the function of pancreatic islets, inspired the next step forward. Hagedorn and Jensen succeeded, by an article by Barron14. He was given office space, an in 1936, by combining insulin with protamine24, a fish allocation of dogs and a student assistant by Macleod, protein that crystallizes with insulin hexamers and the head of physiology at the University of Toronto, delays the release of the active insulin monomers into Canada. Banting and his student, Charles Best, showed the circulation. In the same year, Scott and Fisher that ligation of the pancreatic duct resulted in atrophy of proposed the addition of zinc to insulin to create a pro- the exocrine with preservation of the islets tamine zinc insulin complex25. However, it was only in of Langerhans and normoglycaemia15–17. Furthermore, 1946 that neutral protamine Hagedorn (NPH) insulin, Banting et al. found that glucose control could be with a maximum duration of action of 4–12 hours after restored in diabetic dogs using an alcohol-based extrac- injection, was introduced26. It was very popular as the tion from fresh , without the need for prior first user-friendly longer-acting insulin as it provided ligation or degeneration18. The contributions of Collip, more stable glucose profiles than previous insulins and a biochemist-pharmacist, to the optimization and puri- could be used in conjunction with the shorter-acting fication of the extraction procedure were critical in regular insulin27. Other attempts to create longer-acting producing a pancreatic extract that was both safe and insulins, such as insulin lente suspensions (semilente, effective for use in humans for the very first time15. lente and ultralente), in the 1950s28 did not produce On 11 January 1922, a boy with diabetes mellitus lasting products due to variability29 and instability when named Leonard Thompson was treated with the extract used with regular insulin30. Insulin lente suspensions produced by this group and recovered from a moribund eventually stopped being used in the 1990s because of state15–17 (Fig. 1). These clinical observations were first incompatibility with pen-injectors and fine needles. presented to peers in May 1922 during the meeting The self-reconstituted combinations of regular insulin of the Association of American Physicians19. Leonard and NPH insulin twice daily were the standard of care for Thompson went on to live for 13 more years. Elizabeth many years to obtain both basal and mealtime coverage23. Evans Hughes (the daughter of a politically powerful Subsequently, premixes were developed based on American family), who started insulin therapy later Western diets where most patients needed approximately in 1922 at the age of 14, lived a successful life until she 30% regular insulin and 70% NPH insulin31. However, died of pneumonia at the age of 73 years20. For their this whole concept of controlling glucose profiles with

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Fig. 1 | A timeline of the major scientific and pharmaceu- Scientific discoveries First description of diabetes 1550 Pharmaceutical discoveries tical discoveries in the development of insulin with the mellitus in the Ebers Papyrus BCE approximate historical dates. While the disease diabetes mellitus was known for a long time2, its cause remained 1869 Langerhans unknown until the role of pancreatic β-​cells was identified CE describes islets 4 Minkowski and von Mering in the late nineteenth century . This finding resulted, in discover that islets of 1922, in the first successful administration of insulin to a Langerhans produce an 1890 human patient by Banting, Best, Macleod and Collip19. Since internal secretion then, insulin has been reinvented over and over again to This internal secretion is 1909 termed 'insulin' by de Meyer meet new challenges. Long-​acting insulin was created to reduce injection frequency24 and monocomponent insu- The first microchemical lins to reduce antigenicity35. In 1993, the Diabetes Control determination of sugar in the 1910 blood by Lewis and Benedict The first successful and Complications Trial showed the importance of tight administration of insulin in a glycaemic control for preventing chronic complications of 1922 human patient by Banting, hyperglycaemia33. This finding paved the way for insulin The first long-acting insulin was Best, Macleod and Collip analogues that were better able to mimic the physiological produced with the addition of 1936 insulin profile. Moreover, pharmaceutical discoveries go protamine (and zinc) NPH insulin facilitates hand in hand with scientific discoveries — after Banting and mixtures with regular insulin 1946 Macleod received the Nobel Prize in 1923, Sanger (in 1958) and Yalow (in 1977) received the Nobel Prize for their dis- Sanger receives the Nobel coveries regarding the insulin molecule and for the devel- 1958 Prize for unravelling the opment of a radioimmunoassay, respectively. NPH, neutral primary structure of insulin protamine Hagedorn. Monocomponent insulin developed 1973 Yalow receives the Nobel Prize 1977 for the development of a insulin as a result of its animal (bovine or porcine) origin radioimmunoassay for insulin as well as because of the protein additives in protamine Synthetic insulin was produced for the first time 1982 zinc insulin and NPH insulins. This feature led to the The Diabetes Control and formation of insulin antibodies and local injection site Complications Trial shows reactions that could develop into severe lesions, such as 1993 the importance of tight glycaemic control lipoatrophy. To solve this issue, highly purified insulins, The first synthetic termed monocomponent or single component insulins, human insulin analogue 1996 were being produced by 1973 (ref.35). Proinsulin had The first long-acting synthetic 2000 been identified as a major immunogenic contaminant human insulin analogue and its concentration was reduced from 50,000 parts per million to less than 1 part per million36. Despite not 2015 Second-generation long- acting synthetic human insulin being fully non-immunogenic, the change from previous Second-generation analogues are available generation insulins to these new highly purified insulins fast-acting synthetic human 2017 insulin analogues are available did result in a decrease in total insulin need (due to a fall in antibody titre)37. In 1963, insulin became the first human protein to be chemically synthesized38,39. In 1979, the laboratory synthesis of human insulin was achieved with genetic Future engineering40 using the recombinant DNA technology in • Liver-preferred insulins • Glucose-sensitive insulins Escherichia coli that had been established 2 years earlier to produce somatostatin41. In 1982, the first synthetic human insulin was commercially launched by Eli Lilly42. Other manufacturers followed (Novo Nordisk and one or two daily injections proved to be deleterious as it Hoechst) and the use of animal-based insulin quickly took insulin therapy further away from the normal insu- decreased43. lin physiology. This period of using long-acting insulins Insulin concentrations have varied over the years is seen by many as the Dark Ages of insulin therapy, with but concerted efforts worldwide have led to standard high rates of complications related to diabetes mellitus32. concentrations for insulin to increase safety22. For many It was only improved understanding of β-cell physiol- years, 40 units per millilitre and then 100 units per mil- ogy that led clinicians to comprehend the importance of lilitre were the standard concentrations. However, the tight glycaemic control in the prevention of complica- realization that people with severe insulin resistance tions through multiple daily injections32,33. This concept need to inject uncomfortably high volumes when using was finally demonstrated in the Diabetes Control and these concentrations led to the production of ultracon- Complications Trial (DCCT; see a later section). centrated forms of insulin. Concentrating human insu- lin, however, typically leads to protraction of its action44. Highly purified and recombinant human insulin Pharmacodynamic studies have shown that increasing As the frequency of daily injections was reduced, atten- the dose of the injected insulin also influences the action tion shifted towards the presence of impurities in com- profile of the insulin45. In addition, ultraconcentrated mercial insulins34 and the high level of antigenicity of human insulin (for example, human regular insulin

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Box 1 | What is insulin? and a twofold higher peak plasma concentration in the first hour after , resulting in a Early research focused on achieving the purest extrac- lower postprandial glycaemic peak49–51. Soon, insulin tion of insulin. However, at that time, nobody knew what aspart and followed. In , insulin was exactly. Only in 1924 was insulin recognized 147 proline is replaced with aspartic acid at residue 28 of the as being a protein , with its crystalline structure deter- 52,53 mined in 1926 (ref.148), its molecular weight determined B-chain . In insulin glulisine, asparagine is replaced in 1931 (ref.149) and its first visualization by X-​ray single- with lysine at position 3 and lysine is replaced with glu- 54 crystal photographs in 1935 (ref.150). The 51 amino acid tamic acid at position 29 of the B-chain . These changes sequence was determined by Sanger in 1955 (refs151–154), increase the rate of hexamer dissolution to dimers and for which he was awarded the Nobel Prize in 1958 monomers once diluted in subcutaneous tissue. In con- as insulin was the first protein to be fully sequenced. trast to and insulin aspart, insulin glulis- This work laid the foundation for insulin to become ine uses polysorbate 20 instead of zinc as an excipient to the first human protein to be chemically synthesized in achieve a slightly faster onset of action55. The removal of 38,39 1963 (refs ). In 1977, Yalow received the Nobel Prize zinc results in disruption of the insulin hexamer, thereby for the development of the radioimmunoassay for promoting absorption. In addition, polysorbate 20 is a insulin155, which was crucial to understanding glucose homeostasis. surfactant that is added as a stabilizing agent to balance the reduction in stability that occurs with the removal of zinc. The downside of using polysorbate 20 is that U500) has a pharmacokinetic profile that is intermediate insulin glulisine has been reported to result in more between that of U100 and NPH46. frequent catheter obstructions than insulin lispro and insulin aspart when used in the continuous subcutaneous Mimicking the physiological insulin profile infusion of insulin56. After the initial years of success with insulin therapies, The introduction of rapid-acting insulin analogues chronic complications of hyperglycaemia, such as retin- primarily offers more flexibility as they can be injected opathy, nephropathy, neuropathy and cardiovascular at the start of a meal because they rapidly appear in the disease, started to attract attention. In 1993, results of blood. In addition, a correction bolus can be given with the DCCT demonstrated that, in people with T1DM, a low risk of insulin stacking (that is, repeated correc- intensive insulin treatment with multiple daily injec- tional doses of rapid-acting insulin administered at close tions or continuous subcutaneous infusion of insulin intervals, with a risk of consequent hypoglycaemia)57. could prevent these chronic complications32,33. Intensive Rapid-acting insulin analogues also result in better over-

insulin therapy improved glycaemic control compared all glycaemic control (lower HbA1c levels) and a reduced with conventional therapy (at that time one or two daily risk of hypoglycaemia compared with regular insulin 51,52,58 injections). The reduction in HbA1c from 9% in the con- in their respective clinical trials , with no relevant ventional group to 7% in the intensive insulin-treated differences between the rapid-acting insulins55,59–61. group resulted in dramatic reductions in the incidence Not taking cost or availability into consideration due of microvascular complications compared with the con- to regional differences, the number of injections might ventionally treated group, ranging from 35% to 76%32,33. be of great importance to some patients. Therefore, mix- Although the first insulin analogues, termed designer tures of NPH insulin with rapid-acting insulins have been insulins, had already been outlined in 1988 (ref.47), it manufactured. Combinations of rapid-acting insulin lis- was the results of the DCCT that redirected the focus pro and protamine insulin lispro as well as rapid-acting of diabetes mellitus management from trying to reduce insulin aspart and protamine aspart insulin are available the number of insulin injections per day to the devel- in different ratios as premixed insulins. These premixes opment of tools that would improve glycaemic control. are still popular, particularly in the treatment of people This notion led to the development of insulins that with T2DM who need insulin in many areas of the world, would allow improved mimicking of the β-cell insulin such as in south Asia62,63. The predominance of certain profile (insulin analogues), the introduction and wider premix ratios varies around the world, depending on use of improved insulin administration tools (pens and the regional carbohydrate intake64. As the pharmaco­ pumps) and, possibly most importantly, the manufac- kinetic and pharmacodynamic profile of the rapid-acting turing of tools that allow frequent measurements of component in the mixes remains unaltered65, they can blood levels of glucose (capillary blood glucose measure- be injected just before the meal. Of note, the benefits ments and eventually subcutaneous continuous glucose for glycaemic control and nocturnal hypoglycaemia are measurements). preserved with insulin lispro and insulin aspart mixtures compared with human insulin preparations that do not Rapid-acting insulin analogues. In 1996, the first have these benefits66,67. However, these premixes limit human synthetic insulin analogue — insulin lispro — flexibility and the presence of NPH contributes to the was launched48. In this analogue, the inversion of the variability of action of these products, which results in a neutral amino acid sequence of proline and lysine of higher frequency of hypoglycaemia and worse glycaemic the B-chain of insulin at positions 28 and 29 results in a control than with monotherapies68. reduced tendency for self-association and an increased In the past 5 years, the addition of excipients to dissociation into dimers and monomers and, thus, in expedite absorption from the subcutaneous space has faster absorption into the bloodstream than regular led to novel formulations of rapid-acting analogues. human insulin49. This alteration produces a faster peak The aim of these analogues is to more closely resemble

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the physiological mealtime insulin secretion by achiev- (in the vial). has a flatter pharmaco­ ing a faster onset of action together with a faster com- dynamic profile than NPH insulin, with a mean duration pletion of action. By contrast, the initial rapid-acting of action of 20 hours after a single first-dose administra- insulin analogues aimed to improve absorption by tion, which increases during maintenance therapy85,86. modifying insulin to more rapidly dissociate after injec- Switching from NPH insulin to insulin glargine results tion. Faster insulin aspart, launched in 2017, contains in better overall glucose control that is reflected by lower L-arginine as a stabilizer and niacinamide to increase fasting blood levels of glucose and a reduction in the absorption by increasing subcutaneous blood flow69. number of nocturnal hypoglycaemic events87. Compared with the original insulin aspart, this for- , which was launched in 2016, is a mulation results in a 5-minute earlier onset of action, pH-neutral insulin analogue where the threonine at a 74% greater early glucose-lowering effect in the first position 30 of the B-chain is removed and a 14-carbon half-hour after injection and a 14-minute earlier offset myristoyl fatty acid is added to lysine at position 29 of of the glucose-lowering effect70. In people with T1DM, the B-chain. This addition of a free fatty acid results

these effects result in a 0.08% reduction in HbA1c and in the self-association of the insulin hexamers into insulin improved postprandial glucose control with fewer dihexamers at the site of injection and an extended time in late hypoglycaemic events in comparison with insulin circulation in the bloodstream as a result of non-covalent aspart71–73. However, its use in the continuous subcutane- binding to albumin88 . The mean duration of action is ous infusion of insulin proved to be disappointing with a maximum of 23 hours in steady state, which often no improvement in overall glycaemic control74. necessitates twice-daily administration to cover basal The second ultra-rapid-acting insulin, ultra-rapid needs86,89. Compared with NPH insulin, insulin detemir lispro, contains additional citrate to increase absorption results in more stable glucose profiles, reflected in clin- by enhancing local vascular permeability and trepros- ical trials as better overall glycaemic control, with lower tinil to increase local vasodilatation75. First compared fasting blood levels of glucose and less nocturnal and to the original insulin lispro in the PRONTO-T1D severe hypoglycaemia90,91. A reduction in nocturnal study76 and later compared with all other rapid-acting and severe hypoglycaemia is also observed in comparison analogues (including faster insulin aspart)77, ultra-rapid with insulin glargine92. Despite insulin detemir resulting lispro was able to reach half-maximal dose concentration in a higher daily basal insulin dose, it is associated with 13 minutes after injection, which is 6 minutes earlier somewhat less weight gain than insulin glargine93. than faster insulin aspart, and achieved a greater reduc- Next, a more concentrated insulin glargine U300 was tion in postprandial glucose 2 hours after a meal than launched in 2015 with an extended duration of action faster insulin aspart. A small study with continuous sub- of 32 hours at steady state, which was attributable to a cutaneous infusion of insulin showed safety of use but, more compact subcutaneous depot with a smaller sur- again, no major effect on overall glucose control78. The face area than insulin glargine U100 (ref.94). A post hoc effect of these small differences in action profile on meta-analysis of the three EDITION studies in people the added value of using these formulations in clinical with T1DM, which compared insulin glargine U100

practice needs to be proven. The increased concen- to insulin glargine U300, showed similar HbA1c reduc- tration of ultra-rapid insulin lispro to 200 units per tions but a lower risk of severe hypoglycaemia for insulin millilitre does not alter its pharmacokinetic and phar- glargine U300, particularly during the first 8 weeks after macodynamic profile, allowing interchangeability with the start of treatment95. other insulin lispro formulations79. The most recent commercially available long-acting insulin analogue, , has a free fatty acid Long-acting insulin analogues. The original animal and chain attached to human insulin, similar to insulin human extended-acting insulins conferred a substantial detemir, but separated by a linker molecule. This for- variability in action due to the need for resuspension and mulation leads to a unique protraction mechanism that a non-flat pharmacokinetic profile with a peak activity forms a soluble and stable dihexamer in the vial in the 4–6 hours after injection80. These profiles resulted in an presence of phenol and zinc but, when injected, phe- increased risk in intermeal hypoglycaemia, particularly nol diffuses away and multihexamer chains are formed nocturnal hypoglycaemia80. Moreover, they failed to pro- at the injection depot96. Two concentrations of insulin vide 24 hours of insulin coverage80. The advent of the degludec with similar pharmacokinetic properties are first long-acting analogues reduced the risk of nocturnal available (U100 and U200)97. The duration of action hypoglycaemia, thus improving the safety and quality of insulin degludec is extended to 42 hours (half-life of of life for people with diabetes mellitus81, but leading to 25 hours) and insulin degludec is characterized by a sta- 44,98 an overall limited reduction in HbA1c compared with ble and evenly distributed glucose-lowering profile . NPH insulin82. Clinically, this profile results in a decreased risk of In 2000, insulin glargine became the first basal insu- nocturnal hypoglycaemia in comparison with insulin lin analogue approved for clinical use83. By the addition glargine U100 (ref.99). Studies comparing the pharma- of two arginine molecules to positions 31 and 32 of the cokinetic and pharmacodynamic profiles of insulin B-chain, together with substitution of asparagine with glargine U300 and insulin degludec show conflicting glycine at position 21 of the A-chain, the isoelectric point results, with the design of the studies mainly contribut­ of the molecule is shifted to pH 6.7 (ref.84). As a result, ing to the conflicting conclusions on the duration of precipitation only happens at neutral pH (at the injec- action and differences in day-to-day variability between tion site), whereas the molecule is soluble at acidic pH these two insulins100,101. Head-to-head comparisons

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between insulin glargine U300 and insulin degludec The need for parenteral administration remains have only been performed in people with T2DM, result- the most important hurdle to insulin therapy for many ing in overall similar glycaemic control102,103. However, patients and physicians. Inhalation has been explored the BRIGHT trial found that insulin glargine U300 had as an alternative and, in 2006, Exubera, the first a lower risk of hypoglycaemia during the titration period FDA-approved inhaled insulin, was introduced for use than insulin detemir, whereas the CONCLUDE trial ran in T1DM114. Although it was effective, high manufactur- into technical problems that hampered interpretation of ing costs and concerns about the long-term pulmonary its results102,103. The mixture of long-acting degludec with safety led to the early termination of the commercial rapid-acting aspart was approved in 2015 (the first and programme115. Later, Technosphere insulin became avail- only analogue–analogue insulin mixture without a pro- able, which is a dry powder formulation of human regular tamine component) and this formulation resulted in a insulin adsorbed onto microparticles that are inhaled116.

decreased risk of hypoglycaemia, particularly nocturnal Despite a proven non-inferiority in HbA1c effect and hypoglycaemia104. less hypoglycaemia compared with insulin aspart117, the success was again limited due to its increased cost and Insulin combinations. Combining a GLP1 agonist and concerns about long-term pulmonary safety118. basal insulin was done in an attempt to further reduce Another hard lesson to learn in the process of devel- the risk of hypoglycaemia, reduce the number of injec- oping novel insulins was the observation that some tions and limit weight gain associated with the use of molecular adaptations to the insulin analogue mole- insulin. Indeed, the combination of a GLP1 agonist with cule can alter off-target effects. For instance, during the a basal insulin was proved to be effective in patients development of insulin X10 (also called B10Asp), the with T2DM105–108. Currently, two mixtures of basal insu- histidine residue at the B10 position was replaced with lin together with a GLP1 agonist are commercially avail- aspartic acid to avoid self-association into hexamers47, able: insulin glargine with (IGlarLixi) and which successfully increased the rate of absorption by insulin degludec with (IDegLira). In patients 50%. However, the occurrence of mammary tumours with T2DM, both combinations result in an improve- in female rats during its testing phase halted the devel- (ref.119) ment in HbA1c compared with either of its components opment of insulin X10 . At least two molecular in monotherapy and a reduction of body weight by 1.5 kg characteristics could be responsible for this increased for iGlarLixi and 2.2 kg for IDegLira compared with its mitogenic potency, the first being a 28-fold increased insulin component in monotherapy105–108. binding to the IGF1 receptor compared with human insulin120 and the second being a decreased dissocia- Ups and downs of insulin development tion rate from the insulin receptor121. This obser­vation The road to the insulins we have in our hands today was increased the awareness of the potential threat of not one without obstacles. The current confidence that mitogenic adverse effects of novel insulin formations. many clinicians have in insulin therapy is only possi- Another obstacle emerged during the quest for ble through the lessons learned during careful drug liver-specific insulins. In an attempt to increase the liver discovery. to peripheral insulin exposure ratio to levels similar to The first concern for insulin therapy has been its the physiological first-pass effect, insulin peglispro co-dependence on advancements in the measurement (LY2605541) was designed. Aimed at exploiting the dif- of its effect: initially glycosuria and later laboratory- ference in endothelial permeability between liver and based blood levels of glucose13. Home self-monitoring peripheral capillaries, a polyethylene glycol polymer of blood levels of glucose was first developed in 1965 was attached to insulin lispro, which caused a delay in by Ames but only became available to the general public absorption from the subcutaneous tissue and a reduc- in the 1970s–1980s109. Fast and reliable capillary glucose tion in the glomerular filtration, making it a long-acting measurements­ are vital to orchestrating insulin dosage analogue with liver-preferred actions122. The IMAGINE 1 within a very narrow therapeutic index of intensive and 3 trials were very promising as insulin peglispro

insulin treatment. Undoubtedly, self-monitoring of resulted in a reduced HbA1c together with the expected 123,124 blood levels of glucose and the establishment of HbA1c weight reduction . However, insulin peglispro also as a glucose homeostasis marker110 indirectly led to the caused elevated transaminase and triglyceride levels, possibility to design and execute the DCCT33. resulting in the early termination of its development125. In turn, the DCCT accelerated the development of These studies led to insights on how to target the liver insulin delivery devices. For several decades, glass and but also opened the discussion about whether targeting then plastic syringes were the only method of insulin the liver in the absence of suppression of peripheral delivery, until insulin pens with replaceable prefilled lipolysis is a viable path. cartridges were introduced in 1985, allowing more practical and accurate multiple daily injections33. Since Challenges and future directions 1989, prefilled disposable insulin pens have started Towards fewer injections to replace the original reusable pens. These pens For most patients with T2DM, even a once-daily sub- resulted in reduced injection pain, further increased cutaneous self-injection of insulin is a major hurdle to lifestyle flexibility and increased dosing accuracy111. treatment intensification and many patients with T1DM These benefits improved the health-related quality hope to be able to reduce the number of daily insulin of life112, resulting in greater patient acceptability and injections without jeopardizing glycaemic control. compliance113. Therefore, even longer-acting basal insulins remain the

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subject of research and development. The most novel with T1DM are under way (such as the ONWARDS insulin, insulin icodec, promises a once-weekly injection programme, for example, NCT04848480, for T1DM). of basal insulin. It has been suggested to be safe, well Another approach to reducing the number of insu- tolerated, and to display the necessary pharmacokinetic lin injections is by oral administration of insulin. Initial and pharmacodynamic properties to enable once-weekly attempts were disappointing as insulin faced the same dosing in patients with T2DM126. Further efficacy and poor epithelial permeability and enzymatic degradation safety trials in larger study populations and in patients within the gastrointestinal tract as any protein therapy127.

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Fig. 2 | Past, current and future challenges of insulin. The main challenges of insulin are the reduction of hypoglycaemia, improving the quality of life of people with diabetes mellitus and improved mimicking of the physiological insulin profile as well as the cost of and access to insulin. Past (red), current (blue) and future (green) challenges are shown here. As there is considerable overlap between these subcategories, the challenges are often intertwined.

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However, an 8-week, randomized, double-blind phase II that the bioactivity of oligosaccharide insulins was trial has investigated the efficacy and safety of an oral glucose-sensitive in the circulation without subcutane- basal insulin (oral insulin 338) versus subcutaneous ous depots140,141. However, phase I clinical trials were not insulin glargine in insulin-naive patients with T2DM128. convincing and the programme has not been continued. Oral insulin 338 was non-inferior compared with insu- Nevertheless, intense research is ongoing to realize this lin glargine regarding glycaemic control and no safety concept138. issues for oral insulin 338 were reported128. This finding Another area of continued research is the develop- opens the door to oral insulins in clinical use; however, ment of liver-preferred insulins that would overcome the enthusiasm is somewhat curbed by the level of var- the relative peripheral overinsulinization that promotes iability in achieved plasma concentrations of insulin as insulin-induced weight gain, which remains a concern well as the low bioavailability129, which resulted in a high with currently used insulins. Despite initial setbacks cost of production and eventually caused the discon- and with continuous caution regarding the increased tinuation of development of oral insulin 338. However, risk of hypoglycaemia, encouraging reports are starting new preclinical oral insulin delivery techniques are being to emerge about a liver-preferred insulin (NNC0123- developed to increase bioavailability130,131. 0327). This is an insulin analogue with a C20 fatty diacid attached at position A22K that results in a high Overcoming hypoglycaemia and weight gain affinity for albumin in the serum, which suggests that One of the biggest challenges when using exogenous there could be a reduced transendothelial transport insulin is the absence of negative feedback and the sub- from plasma to periphery with a high hepatic insulin sequent risk of hypoglycaemia81. Hypoglycaemia (in receptor-mediated clearance142. Safety will have to be particular hypoglycaemia unawareness and consequent proven (particularly regarding hepatic steatosis and severe hypoglycaemia) not only diminishes the qual- hypoglycaemia) before these products hit the market. ity of life but also predisposes the individual to acute A final challenge that cannot be ignored is the price cerebrovascular disease, neurocognitive dysfunction, of these innovative insulins and access to this life-saving retinopathy and sleep disruption132. The introduction of therapy in general. Insulin is often in severely limited adjunct therapies in T1DM or the introduction of novel supply and prohibitively expensive in developing coun- therapies in T2DM can reduce the need for insulin but tries but, even in highly developed countries such as the does not offer a final remedy133. Replacement of the USA, access to insulin remains problematic143. This sit- β-cells by islet or pancreas transplantation is an inter- uation is remarkable, knowing that the original patent esting, but still niche, solution because of organ scarcity of insulin was sold for $1 to the University of Toronto as and the need for chronic immunosuppression134. By it was deemed to be unethical to profit from a discovery contrast, the advent of novel technologies, in particu- that would save lives. Banting famously stated, “insulin lar the ‘smart pumps’ that adapt insulin administration does not belong to me, it belongs to the world”144. In the by the pump to glucose levels measured by a sensor, is century since Banting’s statement, older insulins have rapidly changing how we treat people with T1DM in been replaced by continuously improved products cov- many countries135. Sensor-augmented pump therapy ered by new patents145, resulting in a near-exponential with automated insulin suspension reduces the com- increase in the cost of insulin in free markets146. bined rate of severe and moderate hypoglycaemia in Global measures are needed as it is unacceptable that a patients with T1DM136. The first reports on hybrid century-old, life-saving therapy remains inaccessible for closed-loop systems and real-world evidence on differ- so many people (Fig. 2). ent forms of closed loops have resulted in great optimism regarding these technologies137. In addition, the develop- Conclusions ment of multihormone pumps (delivering not only insu- The year 2021 marks the centenary of the discovery of lin but also glucagon) and the continuous improvements insulin as a therapy, leading to its first successful clinical in sensor technology suggest that these systems could be application and changing the lives of people with dia- a solution for the lack of feedback in present-day insulin betes mellitus. Its development process has been a per- therapy. However, the biggest unsolved issue remains a fect example of how small incremental steps can lead delay in sensing due to subcutaneous sensing and a delay to major breakthroughs. Moreover, the development in insulin response due to subcutaneous delivery. and refinement of insulin products and associated tools Probably the most exciting insulin optimization strat- in subsequent years has highlighted the indispensable egy is the concept of insulin with a glucose-dependent role of collaboration between clinicians, researchers and action. Since the 1970s, many have tried to produce pharmaceutical companies in improving the lives of peo- ‘glucose-sensitive’ insulin preparations and numerous ple with diabetes mellitus. While peripheral injections patent applications have been filed but none has yet and hypoglycaemia remain fierce challenges, exciting reached clinical usability138. The initial study139 and applications, such as automated insulin delivery systems, most published systems thereafter have used insulin are entering diabetes mellitus clinics world­wide and encapsulations in polymers intended for subcutane- smarter (for example, glucose-sensitive) insulins ous depots and include some sort of glucose-binding and novel administration routes (such as oral or inhaled or glucose-reactive motif to respond to glucose spikes. insulins) show great potential. Therefore, despite being a However, these systems are usually too slow to respond century old, the future for insulin is bright. to changes in glucose levels, making them unsuitable as Published online xx xx xxxx therapeutic products. Around 2010, it was discovered

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1. Petersen, M. C. & Shulman, G. I. Mechanisms of profiles of mixtures of short- and intermediate-acting 55. Heise, T. et al. Insulin glulisine: a faster onset of action insulin action and insulin resistance. Physiol. Rev. 98, insulins. Diabetologia 27, 558–562 (1984). compared with insulin lispro. Diabetes Obes. Metab. 2133–2223 (2018). 31. Turner, H. E. & Matthews, D. R. The use of fixed-mixture 9, 746–753 (2007). 2. Sanders, L. J. From Thebes to Toronto and the 21st insulins in clinical practice. Eur. J. Clin. Pharmacol. 56, 56. Kerr, D., Wizemann, E., Senstius, J., Zacho, M. & century: an incredible journey. Diabetes Spectr. 15, 19–25 (2000). Ampudia-Blasco, F. J. Stability and performance 56–60 (2002). 32. Nathan, D. M. The diabetes control and complications of rapid-acting insulin analogs used for continuous 3. Mazur, A. Why were “starvation diets” promoted for trial/epidemiology of diabetes interventions and subcutaneous insulin infusion: a systematic review. diabetes in the pre-insulin period? Nutr. J. 10, 23 complications study at 30 years: overview. Diabetes J. Diabetes Sci. Technol. 7, 1595–1606 (2013). (2011). Care 37, 9–16 (2014). 57. Heise, T. & Meneghini, L. F. Insulin stacking versus 4. von Mering, J. & Minkowski, O. Diabetes mellitus nach 33. Nathan, D. M. et al. The effect of intensive treatment therapeutic accumulation: understanding the pankreasextirpation. Centralblatt Klinische Med. 10, of diabetes on the development and progression of differences. Endocr. Pract. 20, 75–83 (2014). 393–394 (1889). long-term complications in insulin-dependent diabetes 58. Home, P. D., Lindholm, A. & Riis, A., European Insulin 5. Hedon, E. Diabète pancreatique. Travaux de Physiologie. mellitus. N. Engl. J. Med. 329, 977–986 (1993). Aspart Study Group.Insulin aspart vs. human insulin in (O. Doin, 1898). 34. Schlichtkrull, J. et al. Clinical aspects of insulin– the management of long-term blood glucose control 6. Opie, E. L. The relation of diabetes mellitus to lesions antigenicity. Diabetes 21, 649–656 (1972). in type 1 diabetes mellitus: a randomized controlled of the pancreas. Hyaline degeneration of the islands of 35. Bruni, B., D’Alberto, M., Osenda, M., Ricci, C. & Turco, trial. Diabet. Med. 17, 762–770 (2000). Langerhans. J. Exp. Med. 5, 527–540 (1901). G. L. Clinical trial with monocomponent lente insulins. 59. Plank, J. et al. A direct comparison of insulin aspart 7. De Meyer, J. Action de la sécrétion interne du pancréas Preliminary report. Diabetologia 9, 492–498 (1973). and insulin lispro in patients with type 1 diabetes. sur différents organes et en particulier sur la sécrétion 36. Sutcliffe, N. & Bristow, A. F. The proinsulin content of Diabetes Care 25, 2053–2057 (2002). rénale. Arch. Int. Physiol. 7, 96–99 (1909). commercial bovine insulin formulations. J. Pharm. 60. Homko, C., Deluzio, A., Jimenez, C., Kolaczynski, J. W. 8. Zuelzer, G. Ueber versuche einer specifischen Pharmacol. 36, 163–166 (1984). & Boden, G. Comparison of insulin aspart and lispro: fermenttherapie des diabetes. Z. f. exp. Pathologie u. 37. Alberti, K. G. & Nattrass, M. Highly purified insulins. pharmacokinetic and metabolic effects. Diabetes Care Theraphie 5, 307–318 (1908). Diabetologia 15, 77–80 (1978). 26, 2027–2031 (2003). 9. Scott, E. L. On the influence of intravenous injections 38. Katsoyannis, P. G., Fukuda, K. & Tometsko, A. Insulin 61. Dreyer, M. et al. Efficacy and safety of insulin glulisine of an extract of the pancreas on experimental peptides 9. Synthesis of a-chain of insulin and its in patients with type 1 diabetes. Horm. Metab. Res. pancreatic diabetes. Am. J. Physiol. 29, 306–310 combination with natural B-chain to generate insulin 37, 702–707 (2005). (1912). activity. J. Am. Chem. Soc. 85, 164–166 (1963). 62. Elizarova, S., Galstyan, G. R. & Wolffenbuttel, B. H. 10. Kleiner, I. S. The action of intravenous injections of 39. Zahn, H. & Schade, F. Chemische modifizierung von Role of premixed insulin analogues in the treatment pancreas emulsions in experimental diabetes. J. Biol. insulin, seidenfibroin, sehnenkollagen und wollkeratin of patients with type 2 diabetes mellitus: a narrative Chem. 40, 507–533 (1919). mit nitrophenylestern. Angew. Chem. Int. Ed. 75, 377 review. J. Diabetes 6, 100–110 (2014). 11. Paulescu, N. C. Recherche sur le role du pancreas (1963). 63. Home, P. et al. An observational non-interventional dans l’assimilation nutritive. Z. f. exp. 17, 85–109 40. Goeddel, D. V. et al. Expression in Escherichia coli study of people with diabetes beginning or changed (1921). of chemically synthesized genes for human insulin. to insulin analogue therapy in non-Western countries: 12. Lewis, R. & Benedict, S. R. A method for the Proc. Natl Acad. Sci. USA 76, 106–110 (1979). the A1chieve study. Diabetes Res. Clin. Pract. 94, estimation of sugar in small quantities of blood. 41. Itakura, K. et al. Expression in Escherichia coli of 352–363 (2011). J. Biol. Chem. 20, 61 (1915). a chemically synthesized gene for the hormone 64. Kalra, S. et al. Expert opinion: patient selection for 13. Myers, V. C. & Bailey, C. V. The Lewis and Benedict somatostatin. Science 198, 1056–1063 (1977). premixed insulin formulations in diabetes care. method for the estimation of blood sugar with some 42. Lilly, Six Generations of Caring and Discovery. Diabetes Ther. 9, 2185–2199 (2018). observations in disease. J. Biol. Chem. 24, 147–161 https://www.lilly.com/company/about-lilly/milestones- 65. Heise, T. et al. Time-action profiles of novel premixed (1916). of-caring-and-discovery (2021). preparations of insulin lispro and NPL insulin. 14. Barron, M. The relation of the islets of Langerhans to 43. Richter, B. & Neises, G. ‘Human’ insulin versus animal Diabetes Care 21, 800–803 (1998). diabetes with special reference to cases of pancreatic insulin in people with diabetes mellitus. Cochrane 66. Roach, P., Trautmann, M., Arora, V., Sun, B. & lithiasis. Surg. Gynecol. Obstet. 31, 437–448 (1920). Database Syst. Rev. 2003, CD003816 (2003). Anderson, J. H. Jr. Improved postprandial blood 15. Bliss, M. The Discovery of Insulin. (McClelland & 44. Heise, T. & Mathieu, C. Impact of the mode of glucose control and reduced nocturnal Stewart Inc., 1982). protraction of basal insulin therapies on their during treatment with two novel insulin 16. Banting, F. G. & Best, C. H. The internal secretion of pharmacokinetic and pharmacodynamic properties lispro-protamine formulations, insulin lispro mix25 the pancreas. J. Lab. Clin. Med. VII, 256–271 (1922). and resulting clinical outcomes. Diabetes Obes. and insulin lispro mix50. Mix50 Study Group. Clin. 17. Banting, F. G., Best, C. H., Collip, J. B., Campbell, W. Metab. 19, 3–12 (2017). Ther. 21, 523–534 (1999). R. & Fletcher, A. A. Pancreatic extracts in the 45. Gagnon-Auger, M. et al. Dose-dependent delay of the 67. Boehm, B. O., Home, P. D., Behrend, C., Kamp, N. M. treatment of diabetes mellitus. Can. Med. Assoc. J. hypoglycemic effect of short-acting insulin analogs in & Lindholm, A. Premixed insulin aspart 30 vs. premixed 12, 141–146 (1922). obese subjects with type 2 diabetes: a pharmacokinetic human insulin 30/70 twice daily: a randomized trial in 18. Banting, F. G., Best, C. H., Collip, J. B. & Macleod, J. J. and pharmacodynamic study. Diabetes Care 33, type 1 and type 2 diabetic patients. Diabet. Med. 19, R. The effect of insulin on the excretion of ketone 2502–2507 (2010). 393–399 (2002). bodies by the diabetic dog. Trans. R. Soc. Can. 16, 46. de la Pena, A. et al. Pharmacokinetics and 68. Bellido, V. et al. Comparison of Basal-Bolus and 43–44 (1922). Section V. pharmacodynamics of high-dose human regular U-500 premixed insulin regimens in hospitalized patients 19. Banting, F. G. et al. The effect produced on diabetes insulin versus human regular U-100 insulin in healthy with type 2 diabetes. Diabetes Care 38, 2211–2216 by extracts of pancreas. Trans. Assoc. Am. Physicians obese subjects. Diabetes Care 34, 2496–2501 (2015). 37, 337–347 (1922). (2011). 69. Kildegaard, J. et al. Elucidating the mechanism of 20. Cox, C. Elizabeth Evans Hughes — surviving starvation 47. Brange, J. et al. Monomeric insulins obtained by absorption of fast-acting insulin aspart: the role therapy for diabetes. Lancet 377, 1232–1233 protein engineering and their medical implications. of niacinamide. Pharm. Res. 36, 49 (2019). (2011). Nature 333, 679–682 (1988). 70. Heise, T., Pieber, T. R., Danne, T., Erichsen, L. & 21. Rosenfeld, L. Insulin: discovery and controversy. 48. FDA. FAD-approved drugs, Lilly. https://www. Haahr, H. A pooled analysis of clinical pharmacology Clin. Chem. 48, 2270–2288 (2002). accessdata.fda.gov/scripts/cder/daf/index. trials investigating the pharmacokinetic and 22. Lacey, A. H. The unit of insulin. Diabetes 16, cfm?event=overview.process&ApplNo=020563 pharmacodynamic characteristics of fast-acting 198–200 (1967). (2021). insulin aspart in adults with type 1 diabetes. 23. Donner, T. & Sarkar, S. Insulin – pharmacology, 49. Howey, D. C., Bowsher, R. R., Brunelle, R. L. & Clin. Pharmacokinet. 56, 551–559 (2017). therapeutic regimens and principles of intensive Woodworth, J. R. [Lys(B28), Pro(B29)]-human insulin. 71. Russell-Jones, D. et al. Fast-acting insulin aspart improves insulin therapy. https://www.ncbi.nlm.nih.gov/books/ A rapidly absorbed analogue of human insulin. Diabetes glycemic control in basal-bolus treatment for type 1 NBK278938/ (2000). 43, 396–402 (1994). diabetes: results of a 26-week multicenter, active- 24. Hagedorn, H. C., Norman Jensen, B., Krarup, N. B. & 50. Torlone, E. et al. Pharmacokinetics, pharmacodynamics controlled, treat-to-target, randomized, parallel-group Wodstrup, I. Promatine insulinate. JAMA 106, and glucose counterregulation following subcutaneous trial (onset 1). Diabetes Care 40, 943–950 (2017). 177–180 (1936). injection of the monomeric insulin analogue 72. Mathieu, C. et al. Efficacy and safety of fast-acting 25. Fisher, A. M. & Scott, D. A. The effect of various [Lys(B28),Pro(B29)] in IDDM. Diabetologia 37, insulin aspart in comparison with insulin aspart in type substances on the action of insulin. J. Pharm. Exp. 713–720 (1994). 1 diabetes (onset 1): a 52-week, randomized, treat-to- Ther. 58, 93 (1936). 51. Anderson, J. H. Jr. et al. Improved mealtime treatment target, phase III trial. Diabetes Obes. Metab. 20, 26. Krayenbuhl, C. & Rosenberg, T. Crystalline protamine of diabetes mellitus using an insulin analogue. 1148–1155 (2018). insulin. Rep. Steno Mem. Hosp. Nord. Insulinlab. 1, Multicenter Insulin Lispro Study Group. Clin. Ther. 19, 73. Pal, R., Banerjee, M. & Bhadada, S. K. Glycemic 60–73 (1946). 62–72 (1997). efficacy and safety of mealtime faster-acting insulin 27. Oakley, W., Hill, D. & Oakley, N. Combined use of 52. Lindholm, A., McEwen, J. & Riis, A. P. Improved aspart administered by injection as compared to regular and crystalline protamine (NPH) insulins in the postprandial glycemic control with insulin aspart. insulin aspart in people with diabetes mellitus: a meta- treatment of severe diabetes. Diabetes 15, 219–222 A randomized double-blind cross-over trial in type 1 analysis of randomized controlled trials. Diabet. Med. (1966). diabetes. Diabetes Care 22, 801–805 (1999). 38, e14515 (2021). 28. Hallas-Møller, K., Jersild, M., Petersen, K. & 53. Home, P. D., Barriocanal, L. & Lindholm, A. 74. Klonoff, D. C. et al. A randomized, multicentre trial Schlichtkrull, J. Zinc insulin preparations for single Comparative pharmacokinetics and pharmacodynamics evaluating the efficacy and safety of fast-acting insulin daily injection; clinical studies of new preparations of the novel rapid-acting insulin analogue, insulin aspart, aspart in continuous subcutaneous insulin infusion in with prolonged action. J. Am. Med. Assoc. 150, in healthy volunteers. Eur. J. Clin. Pharmacol. 55, adults with type 1 diabetes (onset 5). Diabetes Obes. 1667–1671 (1952). 199–203 (1999). Metab. 21, 961–967 (2019). 29. Owens, D. R. Insulin preparations with prolonged 54. Becker, R. H., Frick, A. D., Burger, F., Potgieter, J. H. & 75. Owens, D. R. & Bolli, G. B. The continuing quest for effect. Diabetes Technol. Ther. 13 (Suppl. 1), S5–S14 Scholtz, H. Insulin glulisine, a new rapid-acting insulin better subcutaneously administered prandial insulins: (2011). analogue, displays a rapid time-action profile in obese a review of recent developments and potential clinical 30. Heine, R. J., Bilo, H. J., Fonk, T., van der Veen, E. A. & non-diabetic subjects. Exp. Clin. Endocrinol. Diabetes implications. Diabetes Obes. Metab. 22, 743–754 van der Meer, J. Absorption kinetics and action 113, 435–443 (2005). (2020).

Nature Reviews | Endocrinology

0123456789();: Reviews

76. Klaff, L. et al. Ultra rapid lispro improves postprandial 96. Jonassen, I. et al. Design of the novel protraction 116. Rave, K., Heise, T., Heinemann, L. & Boss, A. H. glucose control compared with lispro in patients with mechanism of insulin degludec, an ultra-long-acting Inhaled Technosphere insulin in comparison to type 1 diabetes: results from the 26-week PRONTO-T1D basal insulin. Pharm. Res. 29, 2104–2114 (2012). subcutaneous regular human insulin: time action study. Diabetes Obes. Metab. 22, 1799–1807 97. Korsatko, S. et al. A comparison of the steady-state profile and variability in subjects with type 2 diabetes. (2020). pharmacokinetic and pharmacodynamic profiles of J. Diabetes Sci. Technol. 2, 205–212 (2008). 77. Heise, T. et al. Ultrarapid lispro lowers postprandial 100 and 200 U/mL formulations of ultra-long-acting 117. Bode, B. W. et al. Inhaled technosphere insulin glucose and more closely matches normal insulin degludec. Clin. Drug Investig. 33, 515–521 compared with injected prandial insulin in type 1 physiological glucose response compared to other (2013). diabetes: a randomized 24-week trial. Diabetes Care rapid insulin analogues: a phase 1 randomized, 98. Heise, T., Nosek, L., Bottcher, S. G., Hastrup, H. 38, 2266–2273 (2015). crossover study. Diabetes Obes. Metab. 22, & Haahr, H. Ultra-long-acting insulin degludec has 118. Oleck, J., Kassam, S. & Goldman, J. D. Commentary: 1789–1798 (2020). a flat and stable glucose-lowering effect in type 2 why was inhaled insulin a failure in the market? 78. Bode, B. W. et al. Compatibility and safety of ultra diabetes. Diabetes Obes. Metab. 14, 944–950 Diabetes Spectr. 29, 180–184 (2016). rapid lispro with continuous subcutaneous insulin (2012). 119. Dideriksen, L. H., Jorgensen, L. N. & Drejer, K. infusion in patients with type 1 diabetes: PRONTO-pump 99. Ratner, R. E. et al. Hypoglycaemia risk with insulin Carcinogenic effect of female rats after 12 months study. Diabetes Technol. Ther. 23, 41–50 (2021). degludec compared with insulin glargine in type 2 administration of the B10Asp 79. de la Pena, A. et al. Bioequivalence and comparative and type 1 diabetes: a pre-planned meta-analysis of (abstract). Diabetes 41, 143A (1992). pharmacodynamics of insulin lispro 200 U/mL relative phase 3 trials. Diabetes Obes. Metab. 15, 175–184 120. Varewijck, A. J. & Janssen, J. A. Insulin and its to insulin lispro (Humalog(R)) 100 U/mL. Clin. (2013). analogues and their affinities for the IGF1 receptor. Pharmacol. Drug Dev. 5, 69–75 (2016). 100. Heise, T. et al. Comparison of the pharmacokinetic and Endocr. Relat. Cancer 19, F63–F75 (2012). 80. Owens, D. R., Matfin, G. & Monnier, L. Basal insulin pharmacodynamic profiles of insulin degludec and 121. Hansen, B. F. et al. Sustained signalling from the analogues in the management of diabetes mellitus: insulin glargine. Expert Opin. Drug Metab. Toxicol. 11, insulin receptor after stimulation with insulin what progress have we made? Diabetes Metab. Res. 1193–1201 (2015). analogues exhibiting increased mitogenic potency. Rev. 30, 104–119 (2014). 101. Heise, T. et al. Insulin degludec: lower day-to-day and Biochem. J. 315, 271–279 (1996). 81. Mathieu, C., Gillard, P. & Benhalima, K. Insulin within-day variability in pharmacodynamic response 122. Caparrotta, T. M. & Evans, M. PEGylated insulin analogues in type 1 diabetes mellitus: getting better compared with insulin glargine 300 U/mL in type 1 Lispro, (LY2605541)–a new basal insulin analogue. all the time. Nat. Rev. Endocrinol. 13, 385–399 diabetes. Diabetes Obes. Metab. 19, 1032–1039 Diabetes Obes. Metab. 16, 388–395 (2014). (2017). (2017). 123. Garg, S. et al. A randomized clinical trial comparing 82. Monami, M., Marchionni, N. & Mannucci, E. 102. Rosenstock, J. et al. More similarities than differences basal insulin peglispro and insulin glargine, in Long-acting insulin analogues vs. NPH human insulin testing insulin glargine 300 units/mL versus insulin combination with prandial insulin lispro, in patients in type 1 diabetes. A meta-analysis. Diabetes Obes. degludec 100 units/mL in insulin-naive type 2 diabetes: with type 1 diabetes: IMAGINE 1. Diabetes Obes. Metab. 11, 372–378 (2009). the randomized head-to-head BRIGHT trial. Diabetes Metab. 18, 25–33 (2016). 83. FDA. FDA-approved drugs, Sanofi Aventis US. https:// Care 41, 2147–2154 (2018). 124. Bergenstal, R. M. et al. Randomized, double-blind www.accessdata.fda.gov/scripts/cder/daf/index. 103. Philis-Tsimikas, A. et al. Risk of hypoglycaemia clinical trial comparing basal insulin peglispro and cfm?event=overview.process&ApplNo=021081 (2021). with insulin degludec versus insulin glargine U300 insulin glargine, in combination with prandial insulin 84. Rosenstock, J. et al. Basal insulin therapy in type 2 in insulin-treated patients with type 2 diabetes: lispro, in patients with type 1 diabetes: IMAGINE 3. diabetes: 28-week comparison of insulin glargine the randomised, head-to-head CONCLUDE trial. Diabetes Obes. Metab. 18, 1081–1088 (2016). (HOE 901) and NPH insulin. Diabetes Care 24, Diabetologia 63, 698–710 (2020). 125. Munoz-Garach, A., Molina-Vega, M. & Tinahones, F. J. 631–636 (2001). 104. Fulcher, G. R. et al. Comparison of insulin How can a good idea fail? Basal insulin peglispro 85. Lepore, M. et al. Pharmacokinetics and degludec/insulin aspart and biphasic insulin aspart [LY2605541] for the treatment of type 2 diabetes. pharmacodynamics of subcutaneous injection of 30 in uncontrolled, insulin-treated type 2 diabetes: Diabetes Ther. 8, 9–22 (2017). long-acting human insulin analog glargine, NPH a phase 3a, randomized, treat-to-target trial. 126. Rosenstock, J. et al. Once-weekly insulin for type 2 insulin, and ultralente human insulin and continuous Diabetes Care 37, 2084–2090 (2014). diabetes without previous insulin treatment. N. Engl. subcutaneous infusion of insulin lispro. Diabetes 49, 105. Rosenstock, J. et al. Efficacy and safety of LixiLan, J. Med. 383, 2107–2116 (2020). 2142–2148 (2000). a titratable fixed-ratio combination of Lixisenatide 127. Kumar, V. et al. Oral insulin: myth or reality. Curr. 86. Koehler, G. et al. Pharmacodynamics of the and insulin Glargine, versus insulin Glargine in type 2 Diabetes Rev. 14, 497–508 (2018). long-acting insulin analogues detemir and glargine diabetes inadequately controlled on 128. Halberg, I. B. et al. Efficacy and safety of oral basal following single-doses and under steady-state monotherapy: the LixiLan proof-of-concept randomized insulin versus subcutaneous insulin glargine in type 2 conditions in patients with type 1 diabetes. Diabetes trial. Diabetes Care 39, 1579–1586 (2016). diabetes: a randomised, double-blind, phase 2 trial. Obes. Metab. 16, 57–62 (2014). 106. Aroda, V. R. et al. Efficacy and safety of LixiLan, a Lancet Diabetes Endocrinol. 7, 179–188 (2019). 87. Chatterjee, S. et al. Glargine versus NPH insulin: titratable fixed-ratio combination of insulin Glargine 129. Mathieu, C. Oral insulin: time to rewrite the efficacy in comparison with insulin aspart in a basal plus Lixisenatide in type 2 diabetes inadequately textbooks. Lancet Diabetes Endocrinol. 7, 162–163 bolus regimen in type 1 diabetes–the glargine controlled on basal insulin and metformin: the (2019). and aspart study (GLASS) a randomised cross-over LixiLan-L randomized trial. Diabetes Care 39, 130. Abramson, A. et al. An ingestible self-orienting system study. Diabetes Res. Clin. Pract. 77, 215–222 1972–1980 (2016). for oral delivery of macromolecules. Science 363, (2007). 107. Gough, S. C. et al. Efficacy and safety of a fixed-ratio 611–615 (2019). 88. Havelund, S. et al. The mechanism of protraction combination of insulin degludec and liraglutide 131. Lamson, N. G., Berger, A., Fein, K. C. & Whitehead, K. A. of insulin detemir, a long-acting, acylated analog (IDegLira) compared with its components given alone: Anionic nanoparticles enable the oral delivery of of human insulin. Pharm. Res. 21, 1498–1504 results of a phase 3, open-label, randomised, 26-week, proteins by enhancing intestinal permeability. (2004). treat-to-target trial in insulin-naive patients with type 2 Nat. Biomed. Eng. 4, 84–96 (2020). 89. Porcellati, F. et al. Comparison of pharmacokinetics diabetes. Lancet Diabetes Endocrinol. 2, 885–893 132. Frier, B. M., Schernthaner, G. & Heller, S. R. and dynamics of the long-acting insulin analogs (2014). Hypoglycemia and cardiovascular risks. Diabetes Care glargine and detemir at steady state in type 1 diabetes: 108. Buse, J. B. et al. Contribution of liraglutide in the 34, S132–S137 (2011). a double-blind, randomized, crossover study. fixed-ratio combination of insulin degludec and 133. Warnes, H., Helliwell, R., Pearson, S. M. & Ajjan, R. A. Diabetes Care 30, 2447–2452 (2007). liraglutide (IDegLira). Diabetes Care 37, 2926–2933 Metabolic control in type 1 diabetes: is adjunctive 90. Heise, T. et al. Lower within-subject variability of (2014). therapy the way forward? Diabetes Ther. 9, insulin detemir in comparison to NPH insulin and insulin 109. Clarke, S. F. & Foster, J. R. A history of blood glucose 1831–1851 (2018). glargine in people with type 1 diabetes. Diabetes 53, meters and their role in self-monitoring of diabetes 134. Gruessner, R. W. & Gruessner, A. C. The current state 1614–1620 (2004). mellitus. Br. J. Biomed. Sci. 69, 83–93 (2012). of pancreas transplantation. Nat. Rev. Endocrinol. 9, 91. Frier, B. M., Russell-Jones, D. & Heise, T. A comparison 110. Koenig, R. J. et al. Correlation of glucose regulation 555–562 (2013). of insulin detemir and neutral protamine Hagedorn and hemoglobin AIc in diabetes mellitus. N. Engl. 135. Heinemann, L. et al. Insulin pump risks and benefits: (isophane) insulin in the treatment of diabetes: J. Med. 295, 417–420 (1976). a clinical appraisal of pump safety standards, adverse a systematic review. Diabetes Obes. Metab. 15, 111. Kadiri, A. et al. Comparison of NovoPen 3 and event reporting, and research needs: a joint statement 978–986 (2013). syringes/vials in the acceptance of insulin therapy of the European Association for the Study of Diabetes 92. Pieber, T. R. et al. Comparison of insulin detemir and in NIDDM patients with secondary failure to oral and the American Diabetes Association Diabetes insulin glargine in subjects with type 1 diabetes using hypoglycaemic agents. Diabetes Res. Clin. Pract. 41, Technology Working Group. Diabetes Care 38, intensive insulin therapy. Diabet. Med. 24, 635–642 15–23 (1998). 716–722 (2015). (2007). 112. Lee, I. T. et al. Improvement in health-related quality 136. Ly, T. T. et al. Effect of sensor-augmented insulin 93. Swinnen, S. G., Simon, A. C., Holleman, F., of life, independent of fasting glucose concentration, pump therapy and automated insulin suspension vs Hoekstra, J. B. & Devries, J. H. Insulin detemir via insulin pen device in diabetic patients. J. Eval. standard insulin pump therapy on hypoglycemia in versus insulin glargine for type 2 diabetes mellitus. Clin. Pract. 15, 699–703 (2009). patients with type 1 diabetes: a randomized clinical Cochrane Database Syst. Rev. 2011, CD006383 113. Lee, W. C., Balu, S., Cobden, D., Joshi, A. V. & trial. JAMA 310, 1240–1247 (2013). (2011). Pashos, C. L. Medication adherence and the associated 137. Bergenstal, R. M. et al. Safety of a hybrid closed-loop 94. Becker, R. H. et al. New insulin glargine 300 units.mL-1 health-economic impact among patients with type 2 insulin delivery system in patients with type 1 provides a more even activity profile and prolonged diabetes mellitus converting to insulin pen therapy: diabetes. JAMA 316, 1407–1408 (2016). glycemic control at steady state compared with insulin an analysis of third-party managed care claims data. 138. Hoeg-Jensen, T. Review: glucose-sensitive insulin. glargine 100 units.mL-1. Diabetes Care 38, 637–643 Clin. Ther. 28, 1712–1725 (2006). Mol. Metab. 46, 101107 (2020). (2015). 114. Skyler, J. S. et al. Efficacy of inhaled human insulin 139. Brownlee, M. & Cerami, A. A glucose-controlled 95. Danne, T. et al. Lower risk of severe hypoglycaemia in type 1 diabetes mellitus: a randomised proof-of- insulin-delivery system: semisynthetic insulin bound with insulin glargine 300 U/mL versus glargine concept study. Lancet 357, 331–335 (2001). to lectin. Science 206, 1190–1191 (1979). 100 U/mL in participants with type 1 diabetes: 115. Heinemann, L. The failure of exubera: are we beating 140. Lancaster, T. C., Zion T. C. Conjugate based systems a meta-analysis of 6-month phase 3 clinical trials. a dead horse? J. Diabetes Sci. Technol. 2, 518–529 for controlled drug delivery (patent). https://uspto. Diabetes Obes. Metab. 22, 1880–1885 (2020). (2008). report/patent/grant/10,398,781 (2010).

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141. Chen, Z., Lancaster, T. M., Zion, T. C. Drug-ligand, 149. Sjogren, B. & Svedberg, T. The molecular weight Competing interests conjugates, synthesis therof, and intermediated of insulin. J. Am. Chem. Soc. 53, 2657–2661 C.M. serves or has served on the advisory panel for Novo thereto (patent). https://patentscope.wipo.int/search/ (1931). Nordisk, Sanofi, Merck Sharp and Dohme Ltd., Eli Lilly and en/detail.jsf?docId=WO2012015681 (2012). 150. Crowfoot, D. X-ray single crystal photographs of Company, Novartis, AstraZeneca, Boehringer Ingelheim, 142. Edgerton, D. S. et al. Targeting insulin to the liver insulin. Nature 135, 591–592 (1935). Roche, Medtronic, ActoBio Therapeutics, Pfizer, Insulet and corrects defects in glucose metabolism caused by 151. Sanger, F. & Tuppy, H. The amino-acid sequence in the Zealand Pharma. Financial compensation for these activities peripheral insulin delivery. JCI Insight 5, e126974 phenylalanyl chain of insulin. I. The identification of has been received by KU Leuven; KU Leuven has received (2019). lower peptides from partial hydrolysates. Biochem. J. research support for C.M. from Medtronic, Novo Nordisk, 143. Cefalu, W. T. et al. Insulin Access and Affordability 49, 463–481 (1951). Sanofi and ActoBio Therapeutics; C.M. serves or has served Working Group: Conclusions and Recommendations. 152. Sanger, F. & Tuppy, H. The amino-acid sequence in the on the speakers’ bureau for Novo Nordisk, Sanofi, Eli Lilly Diabetes Care 41, 1299–1311 (2018). phenylalanyl chain of insulin. 2. The investigation of and Company, Boehringer Ingelheim, AstraZeneca and 144. Fralick, M. & Kesselheim, A. S. The US insulin crisis - peptides from enzymic hydrolysates. Biochem. J. 49, Novartis. Financial compensation for these activities has rationing a lifesaving medication discovered in the 481–490 (1951). been received by KU Leuven. R.V. serves or has served on the 1920s. N. Engl. J. Med. 381, 1793–1795 (2019). 153. Sanger, F. & Thompson, E. O. The amino-acid sequence speakers’ bureau for Novo Nordisk, Sanofi, Boehringer 145. Luo, J., Kesselheim, A. S., Greene, J. & Lipska, K. J. in the glycyl chain of insulin. I. The identification of Ingelheim, AstraZeneca and Mundipharma. Financial com- Strategies to improve the affordability of insulin in lower peptides from partial hydrolysates. Biochem. J. pensation for these activities has been received by KU the USA. Lancet Diabetes Endocrinol. 5, 158–159 53, 353–366 (1953). Leuven. P.-J. M. declares no competing interests. (2017). 154. Sanger, F. & Thompson, E. O. The amino-acid 146. Luo, J., Avorn, J. & Kesselheim, A. S. Trends in sequence in the glycyl chain of insulin. II. The Peer review information medicaid reimbursements for insulin from 1991 investigation of peptides from enzymic hydrolysates. Nature Reviews Endocrinology thanks the anonymous through 2014. JAMA Intern. Med. 175, 1681–1686 Biochem. J. 53, 366–374 (1953). reviewers for their contribution to the peer review of this work. (2015). 155. Yalow, R. S. & Berson, S. A. Immunoassay of 147. Somogyi, M., Doisy, E. A. & Shaffer, P. A. On the endogenous plasma insulin in man. J. Clin. Invest. Publisher’s note preparation of insulin. J. Biol. Chem. 60, 31–58 39, 1157–1175 (1960). Springer Nature remains neutral with regard to jurisdictional (1924). claims in published maps and institutional affiliations. 148. Abel, J. J. Crystalline insulin. Proc. Natl Acad. Sci. USA Author contributions 12, 132–136 (1926). The authors contributed equally to all aspects of the article. © Springer Nature Limited 2021

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