Alipogene Tiparvovec: Gene Therapy for Lipoprotein Lipase Deficiency

Editorial Alipogene tiparvovec: gene therapy for lipoprotein lipase deficiency

1. Introduction † Anthony S Wierzbicki & Adie Viljoen 2. Lipoprotein lipase deficiency † Guy’s & St. Thomas’ Hospitals, Department of Metabolic Medicine/Chemical Pathology, 3. Therapeutics of LPL deficiency London, UK 4. Therapeutic applications of the enzyme LPL Homozygous lipoprotein lipase (LPL) deficiency is an ultra-orphan disease associated with increased rates of pancreatitis. Current treatments based on 5. Alipogene tiparvovec acute plasmapheresis allied with ultra-low fat diets are inadequate as 6. Expert opinion responses to fibrates or other triglyceride-lowering therapies tend to be poor. Alipogene tiparvovec is an adeno-associated virus type I (AAV1) gene

therapy using a hyper-functional LPL serine447-stop (S447X) insert adminis- tered intramuscularly under general anaesthetic with allied immunosuppression. Treatment results in histological muscle expression of LPL allied with a transient 40% reduction in triglycerides and improvements in postprandial chylomicron triglyceride content. Alipogene tiparvovec is the first possibly curative treatment for LPL deficiency.

Keywords: alipogene tiparvovec, chylomicronemia, gene therapy, lipoprotein lipase, triglyceride

Expert Opin. Biol. Ther. (2013) 13(1):7-10

1. Introduction

Severe hypertriglyceridaemia is the only emergency in lipidology [1,2]. It is associated For personal use only. with a risk of pancreatitis that increases markedly with plasma triglyceride (TG) concentrations above 20 mmol/L though most cases occur with TG > 35 mmol/L [3]. Its aetiology is complex [1] but includes a functional or genetic deficiency in lipoprotein lipase (LPL) allied with secondary factors that either increase TG production, for example, alcohol or impair the clearance of TG-rich lipoproteins, for example, insulin resistance or diabetes. Lipoprotein lipase is a liver and muscle- secreted enzyme present on the vascular endothelial surface that hydrolyses surface TG from particles that show low relative amounts of phospholipid in contrast with endothelial or hepatic lipases. The function of LPL as an enzyme is modulated by

Expert Opin. Biol. Ther. Downloaded from informahealthcare.com by Dr J Read on 03/06/13 apolipoprotein (apo) C2 as a cofactor, and by apoA5 and lipid maturation factor-1 (LMF-1) as a regulator of hepatic expression [4]. In addition, LPL transfer to the surface of TG-rich particles and a receptor---- glycosylphosphatidylinositol- anchored high-density lipoprotein-binding protein 1 (GPI-HBP1) is involved in clearance of these opsonised particles. Thus, deficiencies in any one of five proteins can cause functional LPL deficiency. Severe hypertriglyceridaemia associated with LPL deficiency occurs in 1 in 20,000 to 1 in 1,000,000 depending on the exact nature of the defect. Heterozy- gotes for LPL deficiency (actually 1% of the population) requires secondary factors such as age, smoking, insulin resistance or excess alcohol intake to cause a hypertri- glyceridaemic state [5]. The TG-rich particles in these cases consist mostly of very low density lipoproprotein (VLDL) with some chylomicron (CM) remnants and are associated with a type IV or V hyperlipidaemia. In contrast in homozygous LPL deficiency, CM metabolism is impaired and very little VLDL is produced by the liver, thus giving rise to a type I hyperlipidaemia.

2. Lipoprotein lipase deficiency In acute management, cessation of food intake is also used to stop the production of postprandially secreted lipoproteins Most cases of LPL deficiency have a type IV -- type V pheno- from the gut. In very severe acute cases, excess TG-rich type and are caused by the interaction of heterozygosity for lipoproteins can be removed physically by plasmapheresis LPL deficiency with environmental factors [5]. These patients or haemodialysis. typically present at age 50 with either eruptive xanthomata In cases of severe LPL deficiency (sometimes homozygous) or pancreatitis. They often have insulin resistance or type 2 dietary therapy with extreme limitation of saturated fat intake diabetes. A bout of acute pancreatitis event is often triggered is the mainstay of treatment. Fibrates, omega-3 fatty acids and by a respiratory tract or other infection. Their cardiovascular niacin may have some effect but this is often reduced when com- risk is variable but often increased but the principal risk of pared with the effects seen in heterozygotes. As dietary fat is type 2 diabetes secondary to beta cell destruction secondary the source of the lipid incorporated into the CMs present in to episodes of acute and sub-acute pancreatitis. The develop- LPL deficiency, other approaches that interfere with either gut ment of diabetes exacerbates any underlying TG elevation absorption of fatty acids, or with CM synthesis may offer further. Most patients with this phenotype respond to a com- benefits in LPL deficiency. Orlistat, a gastric lipase inhibitor bination of fibrate; omega-3 fatty acid, niacin and statin which reduces fat availability, has been used successfully in the therapy allied with hypoglycaemic drugs [1]. treatment of moderate and severe LPL deficiency [9,10]. By contrast, patients with the type I phenotype present in childhood with hypertriglyceridaemia [6] allied with abdo- 4. Therapeutic applications of the minal pain and pancreatitis even with diets relatively low in enzyme LPL saturated fat and TGs. Unlike patients with type IV/V, they often show relative adipose tissue depletion with no evidence Numerous single nucleotide polymorphisms (SNP) have been of central obesity. Their cardiovascular disease risk is low identified in LPL and some have been associated with but they have a high probability of developing secondary increased TG concentrations and an increased risk of CVD type 2 diabetes. They pose a therapeutic challenge as their in epidemiological studies. However, one SNP---- S447X, pres- response to fibrates or other TG-lowering drugs is decreased ent in 20% of Caucasians, was found to be associated with or even absent. The mainstay of treatment in type I is a diet increased activity of the LPL enzyme caused by increased ultra-low in saturated fat (< 10 g/day) but they also show expression of LPL mRNA and reduced sensitivity to inhibi- reduced CM production after treatment with orlistat to tion by apoC3 [11]. This SNP was also associated with an reduce gastric lipase activity and intestinal fatty acid uptake. improved response to low fat diets and to fibrate therapy.

For personal use only. The very large CM particles present in type I and type V This LPL variant has been used as the basis of LPL gene ther- hyperlipidaemia cause a hyperviscosity syndrome and patients apies given its proven stability, efficacy and increased activity can complain of vasculitis and transient ischaemic attacks. compared to the normal form. Rates of subarachnoid haemorrhage are also increased in To investigate gene therapy, animal models are required patients with severe hypertriglyceridaemia. which mimic the human phenotype of disease accurately. Animal models of LPL deficiency exist including specific gene 3. Therapeutics of LPL deficiency knockout mice but also on a larger-scale LPL-deficient Burmese cats. All these animal models suffer from severe hyper- The primary therapy for moderate (heterozygous) LPL defi- triglyceridaemia associated with acute and chronic pancreatitis. ciency are fibrate drugs that activate peroxisomal proliferator Potential methods to rescue the phenotype in these animals Expert Opin. Biol. Ther. Downloaded from informahealthcare.com by Dr J Read on 03/06/13 activating receptor alpha (PPAR-a). This nuclear receptor and in man could include infusion of the deficient activates synthesis of LPL, often apo A-1 but also reduces enzyme---- analogous to treatments used for lysosomal storage the synthesis of apoC3 which acts as a negative regulator of disorders or Pompe´s disease but the half-life of LPL is 15 min LPL activity. Similarly, some thiazolidinedione drugs (i.e., in plasma. Alternatively, a novel source of active LPL could pioglitazone) have some PPAR-a as well as insulin-sensitising be provided. Liver transplantation for LPL deficiency using PPAR-g actions and can reduce TGs. Omega-3 fatty acids act cell infusion-based systems or lobe transplant remain a possibi- through a specific GPR120 receptor to reduce inflammation lity for treatment of LPL deficiency analogous to the approach and PPAR-g to insulin sensitise but also have other unclear used in homozygous-familial hypercholesterolaemia. However, effects that lead to reduced VLDL synthesis [7]. Niacin reduces these would only restore LPL activity to the liver and peripheral free fatty acid flux to the liver via GPR109 but mostly acts vasculature and there is also abundant LPL in muscle where it through diacylglycerolacyl transferase (DGAT)-2 to reduce may have a role in muscle-based lipid metabolism. lipidation of CM and VLDL precursors [8]. Statins reduce TGs by upregulating the LDL receptor whose principal 5. Alipogene tiparvovec actions are to enhance clearance of apoB-100 containing lipoproteins but also to clear particles containing apoE, that There have been previous attempts at gene therapy for is, TG-rich particles. inherited metabolic diseases. These have failed either due to

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toxicity---- adenovirus-induced syncytial pneumonitis in trial in 6. Expert opinion cystic fibrosis, hepatic toxicity---- ornithine transcarbamylase deficiency or more frequently failed due to inadequate Homozygous LPL deficiency is an ultra-orphan disorder with efficacy with decline of expression of the constructs after no good modern treatment. It results in considerable burden 1 -- 2 months, for example, in homozygous familial hypercho- in morbidity due to pancreatitis and increased mortality related lesterolaemia. Novel viral vectors based on adeno-associated to both pancreatitis and hyperviscosity syndromes caused virus (AAV) have been engineered to give different tissue by CM plugs in capillary beds. Current dietary treatment is specificities and enhanced stability of expression [12]. inadequate, drug response is poor and plasmapheresis only Alipogene tiparvovec (AAV-LPL; Amsterdam Medical delivers transient benefits. Therapy with AAV-LPL does reduce Therapeutics (AMT), then uniQure) is an AAV1-based TGs transiently in patients with genetically proven LPL gene gene therapy containing the LPL S447X gene construct deficiency and also seem to improve CM metabolism but with a constitutive expression promoter. In animal models only in demonstrating reduced production rate of new CMs. of both mice [13] and cats [14] this therapy restored histolog- The data do not show an increase in CM clearance rates as ically detectable LPL activity, reduced TGs and improved might be expected for a highly efficacious therapy for LPL defi- lipoprotein turnover with few obvious side effects. Studies ciency. Clinically, the data to date show lower rates of pancre- have recently been conducted in man in eight patients with atitis based on a comparison of pre- and post-treatment homozygous LPL deficiency from the Netherlands using admission rates in a small number of subjects. The AAV-LPL two doses [15] and then at higher dose in 14 patients with treatment is suggested to reduce rates of pancreatitis admission homozygous LPL deficiency from the Netherlands and by 60 -- 70% compared with prior rates, but this type of cohort Quebec [16,17]. Patients with LPL deficiency in Quebec data can be confounded by other factors such as improved show a restricted mutation spectrum due to founder dietary adherence (or reduction in alcohol intake) under the effects [4]. Only patients with genetic LPL deficiency were close clinical supervision seen in clinical trial settings. The recruited for studies with AAV-LPL. Presence of apoC2, AAV-LPL treatment protocol is highly invasive and requires apoA5 or GPI-HBP1 mutations were specific exclusion crite- monitoring of the allied immunosuppressant therapy. The ria for the trials. The AAV-LPL trials were conducted at two use of a gene therapy requires special site licensing for storage different doses (3 Â 1011 or later mostly with 1 Â 1012 and administration of the vector and a specialist registry with genome copies/kg) with/without a 12-week course of immu- good follow-up is essential to monitor the long-term efficacy nosuppressants started prior to injection [17]. The therapy and safety of this intervention. The only patients’ studies so was given as 64 intra-muscular 1 ml injections in the major far have come from a limited mutation spectrum in the LPL ---- For personal use only. skeletal muscle groups under ultrasound guidance and gene mostly the four mutations found in Quebec and the performed with pain relief and under a general anaesthetic response of other LPL mutations to this treatment is unknown. as a day case procedure. Lipid profiles, lipoprotein turnover Though > 80% of LPL deficiency is caused by mutations in the and muscle biopsies were performed to monitor progress LPL gene, the utility of AAV-LPL therapy has not been over up to 1 year. The lowest dose of AAV-LPL reduced investigated in apoA5 deficiency where hepatic regulation of TGs transiently by 20 -- 30% and showed poor muscle secretion seems to be the primary defect and in the milder expression. Subsequent studies using a higher dose, gave phenotype of ApoC2 deficiency---- where the lack of a cofactor demonstrable maintained injection site histological expres- for the active enzyme already present means it may not work. sion. Immunosuppression was added to the pretreatment Similarly, addition of extra LPL in patients lacking the LPL protocol to reduce T-cell-mediated anti-viral responses [18]. receptor---- GPI-HBP1 treatment with AAV-LPL---- is not likely Expert Opin. Biol. Ther. Downloaded from informahealthcare.com by Dr J Read on 03/06/13 These modifications resulted in an up to 40% reduction in to lead to benefit but again no studies have been performed the primary end point of plasma TGs at 3 -- 6 weeks from in animal models or later man for this indication. initial levels of 25 -- 40 mmol/L. However, this effect waned Alternative approaches not relying on gene therapy also exist and TGs returned to previous values after 12 weeks. More for the potential treatment of LPL deficiency. The most promi- detailed lipoprotein analysis showed a reduction in labelled sing are based on agents that reduce TG-rich particle synthesis. CM production and CM TG content with AAV-LPL but These agents though primarily directed at hepatic VLDL no obvious effect on CM clearance or VLDL production production also can reduce CM synthesis in enterocytes and or clearance [19]. Insulin sensitivity, non-esterified fatty acids; acute postprandial hypertriglyceridaemia. Microsomal transfer glycerol levels and safety markers (hepatic enzymes, creatine protein inhibitors (MTPIs) and especially those specifically kinase) were unchanged. A comparison of historic with directed to the gut (e.g., SurfaceLogix Slx-4090) reduce CM post-treatment rates of pancreatitis admission suggested a production and may have a role in the treatment of LPL defi- reduction in the number and possibly the severity of pancre- ciency [20]. However, no studies of MTPIs in LPL-deficient atitis events. These data for an ultra-orphan disorder with no patients exist as yet. Another approach that may have potential other efficacious treatment were sufficient for AAV-LPL to in reducing CM synthesis is the inhibition of diacylglycerol- be licensed by the European Medicines Evaluation Agency acyl-transferase-1 (DGAT-1) but again no human studies after an initial negative expert review. have been performed as yet [21].

Expert Opin. Biol. Ther. (2013) 13(1) 9 A. S. Wierzbicki & A. Viljoen

The proposed therapy using AAV-LPL is expensive with curative treatment. Long-term follow-up data will be essential costs likely to be in the range of e250,000 ($300,000) pay- to determine into which category AAV-LPL therapy fits and able for each of 5 years with additional costs for specialist thus as to whether it is a cost-effective intervention even using clinics and investigations. In health systems that use health the relaxed quality adjusted life year (QALY) criteria often economic models to determine willingness to pay thresholds, applied to inherited errors of metabolism and orphan diseases. the application for AAV-LPL will be controversial. Health economic models often have difficulties caused by wide confi- Declaration of interest dence intervals due to lifetime extrapolation errors for condi- tions treated in adolescence/young adulthood. Current health AS Wierzbicki served on the advisory board for Amsterdam economic cost effectiveness models also tend to use different Medical Therapeutics (now uniQURE BV) from 2008 to discount rates for treatments likely to be only disease modi- 2009. The authors have no other competing interests to fiers (typically 6%) from those that are potentially curative declare and have received no funding in preparation of the (3%) and it is uncertain whether AAV-LPL is a completely manuscript.

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