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Home , Biological activity, New chemical entity

Acta Poloniae Pharmaceutica ñ Research, Vol. 67 No. 6 pp. 579ñ586, 2010 ISSN 0001-6837 Polish Pharmaceutical Society

MINI REVIEW

PRECLINICAL

TERESA BRODNIEWICZ1 and GRZEGORZ GRYNKIEWICZ2*

1MTZ Clinical Research, PawiÒskiego 5, 02-106 Warszawa, Poland 2Pharmaceutical Research Institute, Rydygiera 8, 01-793 Warszawa, Poland

Abstract: Life sciences provide reasonably sound prognosis for a number and nature of therapeutic targets on which could be based, and search for new chemical entities ñ future new , is now more than ever based on scientific principles. Nevertheless, current very long and incredibly costly and development process is very inefficient, with attrition rate spanning from many thousands of new chemical structures, through a handful of validated drug leads, to single successful new drug launches, achieved in aver- age after 13 years, with compounded cost estimates from hundreds of thousands to over one billion US dollars. Since radical pharmaceutical innovation is critically needed, number of new research projects concerning this area is steeply rising outside of big pharma industry ñ both in academic environment and in small private com- panies. Their prospective success will critically depend on project management, which requires combined knowledge of scientific, technical and legal matters, comprising regulations concerning admission of new drug candidates to be subjects of clinical studies. This paper attempts to explain basic rules and requirements of drug development within preclinical study period, in case of new chemical entities of natural or synthetic origin, which belong to low molecular weight category.

Keywords: drug design discovery and development, new molecular entities, testing, phar- macokinetics, quality management, common technical document, preclinical phase

Development of new drugs is perceived as a personally, as project managers, researchers or very complex process, which can be described reviewers and experts. Following European integra- from many different points of view; science and tion, local scientists finally stand a chance to design business story behind a new drug launch do not and submit ambitious research projects in advanced necessary match. Brisk scientific discovery can , prospectively realized within end up in clinical study failure or even withdrawal international cooperation. It is obvious that such after launch ñ over 90% drug leads do not make it development puts considerable load of responsibili- to the market. ty on the entire environment of researchers within Therefore, general view of the contemporary life sciences. In particular, chemists, pharmacists is, despite of its some spec- and biochemists should strive for more effective tacular successes, that of certain dissatisfaction ñ communication with drug discovery and develop- globally, more is spent on drug discovery and devel- ment (DDD) area, which requires some specific opment every year and less is delivered, in terms of knowledge. We intend to recapitulate essentials of radical innovation (1ñ3), which remains in sharp DDD process as practiced under current legal contrast to incredible progress achieved in basic sci- requirements, with some focus on quality assurance ence research and phenomenal involvement of tech- systems and safety. In particular, an evolution of a nical potential, spanning from new information drug candidate will be explained in terms of knowl- technology to sophisticated robotics. Leaving aside edge accumulation and technical documentation fil- overwhelming economical R&D problems of big ling. In order to simplify this complex task, we will pharma industry with knowledge management and be concerned only with so called ìsmall moleculesî generating much needed innovation, we would like (basically synthetics, roughly below 1000 daltons), to discuss this part of drug research and develop- as opposed to ìbiologicalsî of either natural or ment, which our readers are likely to come across biotechnological origin (4).

* Corresponding author: e-mail: [email protected]

578 Preclinical Drug Development 579

Origin of new structures for DDD tiscale dynamic modeling of physiology takes over, the general idea of starting DDD process with bio- Although application of foreign substances logical descriptors screened against structural repre- (xenobiotics) in case of illness had been practiced sentations will stay in force (5, 6). Although since the time immemorial, modern pharmacy, oper- genomics as a single line of research did not fulfilled ating with defined chemical entities of reasonable its promise to deliver identified medicinal targets, chemical purity, is just a little more than a century there are many more ìomicî approaches, which sig- old. During that time there were two principal nificantly increase our knowledge how physiologi- sources of medicinal substances: a) natural products, cal processes are related and governed on a cellular obtained chiefly from plants or microbial sources, and organismal levels. The second big step in any and b) chemical synthesis, which basically took over DDD project or program is development of an activ- in the second part of the period. Currently, historical ity assay, in which new compounds can be tested, to view of an individual scientist discovering new eliminate inactive ones. Typically, for a given target drugs in his individual, modest laboratory, gave way two types of tests are made available: high through- to entirely different picture ñ that of a large organi- put, based on interaction with target proteins or zation, in which sophisticated logistics combines an selected cell lines, which allow to check effort of cohorts of various specialists into a pipeline affinity/activity of large libraries of compounds very of DDD, involving dozens of laboratories focusing quickly (within hours), and low throughput, run on on particular tasks within narrow technical special- tissues, organs or animals, in which preselected ties. At the same time a new source of pharmaco- compounds are investigated in more detailed proce- logically active substances emerged ñ biotechnolo- dures, for weeks or months. This system reflects gy, using biochemical methods on technical scale, incredible inefficiency of traditional way of pharma- providing secondary metabolites and recombinant ceutical industry screening, characterized by very proteins by mastering natural metabolic pathways high drop-out rate, amounting to many thousand and generating new ones. Biologicals and biosimilar failures per one successful drug candidate. Once products became a large branch of pharmaceutical proper target is defined and bioassays are estab- industry with its own specificity. It is generally lished and validated, medicinal chemistry enters the agreed, that the first step of the DDD process consist field, with a mission to provide a new chemical enti- of target identification and validation. While tradi- ty, which can interact with the target on the systemic tionally a disease or pathology was considered a tar- level in a drug-like manner. Moreover, prospective get, today molecular level of perception is new drug candidate must demonstrate: specificity employed, and identification of a faulty biochemical (defined ), potency (high affin- process and a macromolecule responsible is regard- ity for selected target), selectivity over other possi- ed obligatory. Typical targets are receptors, ble biological targets, and above all ñ safety for enzymes, elements within gene expression systems patients, which is to be demonstrated at the end of or particular events of intracellular signaling cas- DDD process, in carefully designed clinical trials, cades. Such reductionism is not entirely satisfactory, starting from early preclinicals (Fig. 1). but even if systems biology approach, with its mul- Additionally, the new drug candidate should also

Figure 1. Drug development diagram 580 TERESA BRODNIEWICZ and GRZEGORZ GRYNKIEWICZ fulfill some non medical criteria: 1) intellectual question: how to arrange for preclinical verification property rights for the active should be of selected is by no means sim- clearly defined and well protected; 2) the compound ple, as prospective therapeutical indications gener- should be available in reasonably priced and techni- ate great variety of pathology models, activity tests cally feasible process, easy to scale up and control, and other procedures. In general, the nonclinical affording consistently the active substance (API, team, is responsible for regulatory affairs strategy historically referred to as Bulk Drug Substances formulation, anticipating questions to be posed by [BDS]) of high chemical purity and desired physico- authorities examining future registration applica- chemical properties (7). These rather restrictive tion. Secondly, safety assessments are to be under- requirements concerning the new drug itself and the taken and manufacture of clinical supplies (both: way in which it is developed, are a matter of phar- API and pharmaceutical preparation) have to be maceutical law as well as numerous guidelines secured. All these activities should be coordinated issued by agencies regulating main markets of phar- and planned to minimize time to the first application maceutical products. Both: the law and the guide- to humans, without compromising safety. As all lines are currently a subject of harmonization tasks in the preclinical phase require the drug sub- between the main pharmaceutical markets: the US, stance, the critical question: ìwhen a new chemical Europe and Japan, highlighting safety and quality. entity studied becomes a drug candidate in sense of International Conference on Harmonization analytical specification?î, should be answered pre- (www.ich.org) regularly issues detailed guidances cisely and as early as possible. Initial in vitro bio- for pharmaceutical industry analogous to these emit- logical activity tests can be easily carried out on mil- ted by European (www.emea.europa.eu) and ligram quantities, while animal studies and American (www.fda.cedr.gov) agencies. in particular pharmaceutical development, can easi- ly elevate the active substance demand to a kilogram Quality criteria for a new drug candidate level (3). Chemical synthesis for the purpose of hit identification is usually performed on a fraction of The authors own experience indicate that large millimolar scale, without any consideration for proportion of projects concerning medicinal chem- process development. On the other hand, on the drug istry, with DDD elements carried out in our country lead and drug candidate level, chosen synthetic vari- during last decades, treated this ideology purely ant has to be examined in detail, particularly in declaratively without any intention to follow up terms of impurity formation, and then optimized. rules, regulations and to assume responsibility for Drug substance stability in time and under stress has money spent on rather chaotic studies and to be determined. This involves development and unplanned activities. New system of local science validation of analytical methods and identification funding and in particular participation in interna- of critical parameters of synthetic process, which tional programs will obviously require complete can frequently be derived from academic knowledge change in such attitude. The peer review system for about a reaction mechanism. Analytical specifica- the grant proposals will surely require professional tion for an API can be changed during development, level of DDD project design and management. The according to the best knowledge available, but it best advice for any project under drug discovery and should start at the reasonable level of chemical puri- development banner is: have a plan for entire action ty. For a , there is customary require- leading to complete registration file. In particular, ment of 99.8% of HPLC purity with no single clinical development plan (CDP), anticipating phar- unknown impurity crossing 0.1% level. For new maceutical formulation, dosage and patient popula- drug candidates, especially at preclinical study peri- tion should be treated as a cornerstone document, od, more flexible standards are possible e.g., with no from which a reasonable plan of preclinical studies individual purity present above 0.5%. At the same can be re-developed. To explain it further, we will time, based on advances in analytical techniques assume that hypothetical project starts from a point with coupled detection methods, it is reasonable to after principal discovery phase, in which biological assume, that no such thing as ìunknown impurityî target is defined, a new molecule is designed and should be included into specification. intellectual property rights for its application are The entire process of DDD is summarized for secured. To make it even more simple, let us assume purpose of filling a , in stan- that the compound in question is a low molecular dardized form of Common Technical Document weight synthetic chemical, for which an oral formu- (CTD), diagrammatically represented in form of a lation is envisaged. Even in such simplified case, the triangle (Fig. 2), containing five modules: 1. region- Preclinical Drug Development 581

lytical Procedures, 3.2.S.4.4 Batch Analyses, 3.2.S.4.5 Justification of Specification, 3.2.S.5 Reference Standards or Materials, 3.2.S.6 Container Closure System, 3.2.S.7 Stability, 3.2.S.7.1 Stability Summary and Conclusions, 3.2.S.7.2 Post-approval Stability Protocol and Stability Commitment, 3.2.S.7.3 Stability Data. The list is exhaustive and practically self-explanatory, leaving little room for comments. It has to be understood that the format applies for new chemical entities as well as for generic drugs. In the first case situation is more dif- ficult for researchers, because there is no pharma- copoeial information on methods available, which in Figure 2. The Common Technical Document Elements (Source: case of generics greatly assists pharmaceutical ana- ìImplementation of the CTDî, FDA ICH Public Meeting, May 8, lytical services, and no back-up with reference stan- 2001) dards, so analytical methods have to be elaborated from scratch. It is obvious from the above, that char- acteristics of the API covers not only the chemical al and administrative information (concerning entity itself, but also the process for its manufactur- applying organization), 2. overviews and sum- ing, which is potentially confusing, because more maries, 3. quality, 4. nonclinical study reports and 5. often than not, synthetic methods evolve from inci- clinical study reports. Since one of us (T.B.) has dental laboratory preparation, through optimization recently characterized formalities and activities and scale up, to validated technical process, which involved in clinical trials (8), from CRO perspec- sometimes utilize entirely different synthetic strate- tive, this paper concentrates on the preclinical seg- gy, materials and conditions than its small laborato- ment of DDD, comprising CTD modules 3 and 4. ry scale predecessor. It is easy to postulate that all Module 3, dealing with quality of a drug sub- biological tests should be carried out on a substance stance and a drug product, is in its first part of par- obtained in a stable, validated technical process, but ticular interest to any project devoted to new drug at the time when test results are needed to guide design, discovery and development. Since final drug development decisions, such substance is unavail- active substance (frequently described as API, short able and will appear only many months down the for: active pharmaceutical ingredient) has to be pipeline. The question how to overcome this diffi- exhaustively and meticulously examined and its culty sounds tough, but the answer for a prospective properties fully characterized, in particular in project leader is easy: perceive DDD pipeline respect to stability and content of impurities, legiti- scheme as a learning process and mobilize your best mate question arises, when pharmaceutical quality scientific knowledge at every checkpoint. It stands requirements become critical within a pathway of to reason to concentrate on chemical purity of the biological testing. In order to solve this problem, par- substance of interest in the early phases of preclini- ticular points of the module 3 need to be discussed in cal testing period. It is reasonable to assume that test some detail. Content of the module, in its part devot- used for hit search are qualitative in character and ed to the substance, consists of the following points: 90% purity level can be considered satisfactory for 3.2.S.1 General Information, 3.2.S.1.1 Nomencla- such purpose. It is the toxicity testing platform, ture, 3.2.S.1.2 Structure, 3.2.S.1.3 General Proper- which requires pharmaceutical type specification of ties, 3.2.S.2 Manufacture, 3.2.S.2.1 Manufactur- tested substance, including impurity profile and er(s), 3.2.S.2.2 Description of Manufacturing impurity characteristics, therefore, well developed Process and Process Controls, 3.2.S.2.3 Control of analytical methods and proven manufacturing Materials, 3.2.S.2.4 Controls of Critical Steps and process have to be already in place. For an API Intermediates, 3.2.S.2.5 Process Validation and/or required chemical purity level is set at 99.8 % and an Evaluation, 3.2.S.2.6 Manufacturing Process De- unknown impurity should not exceed 0.1%. velopment, 3.2.S.3 Characterization, 3.2.S.3.1 Although these levels can be considered negotiable Elucidation of Structure and Other Characteristics, in the development phase, impurity profile can 3.2.S.3.2 Impurities, 3.2.S.4 Control of Drug become a critical factor ñ if changes in synthetic Substance, 3.2.S.4.1 Specification, 3.2.S.4.2 Ana- process scale up or optimization resulted in new lytical Procedures, 3.2.S.4.3 Validation of Ana- impurities, it could jeopardize validity of biological 582 TERESA BRODNIEWICZ and GRZEGORZ GRYNKIEWICZ tests, in particular lengthy and costly toxicology. prognostic for a lead compound success, provided Thus, importance of finalizing chemical route of proper metrics can be introduced. Since the matter synthesis early, with minimal number of steps and is reviewed comprehensively in numerous mono- elimination of unknown impurities, is evident. graphs (9ñ11), we will only briefly tackle some Polish Pharmaceutical Law (Dz. U. 2008 Nr 45, poz. issues which are considered important for acceler- 271) and Directive from the Minister of Health ating DDD process. Absorption, distribution, dated November 4th 2008 (Dz. U. Nr 201, poz. 1247) metabolism and excretion (ADME), which are of require, that the form directed to the Clinical Trials utmost importance for any xenobiotic characteris- Registry (CEBK), contains detailed description of tics and reasonably well distinguish between drug- the active substance including physical and chemi- like and non drug-like compounds, are believed to cal characteristics, description of manufacturing be a function of simple physicochemical properties process, analytical methods, controls, standards as well as an affinity to various complex functional specification, stability etc., in line with the CTD for- biopolymers. Lipinskiís rule of 5 (RO5) is an exam- mat. These requirements correspond to the ple of generalization based on physicochemical Committee for Medicinal Products for Human Use descriptors, which gained wide recognition as use- ìGuideline on the Requirements to the Chemical ful exclusion criterion (12). It has been derived and Pharmaceutical Quality Documentation from observation that ca. 90% of orally active drugs Concerning Investigational Medicinal Products in has molecular weight below 500 Da, not more than Clinical Trialsî (CHMP/QWP/185401/2004 final; 5 hydrogen bond donors, not more than 10 hydro- London, March 31st, 2006). gen bonds acceptors, and log P value below 5. It It is of great importance to record changes in needs to be added, however, that this extremely quality management and regulatory agencies atti- useful rule works much better for synthetic com- tude towards applicants, which have taken place in pounds than for natural products. Since ADME recent years. Traditionally, quality control was car- refers to a rather broad set of physiological process- ried out off line, after manufacturing process com- es, many attempts have been made to secure quan- pletion, which could lead to rejection of ready made tifiable parameters for its measurement. In contem- batches of product. Current guidelines require, that porary DDD aqueous solubility, Caco-2 permeabil- process is designed in such a way, that quality is ity, volume of distribution, plasma protein binding, ascertained within, by proper control of critical blood-brain barrier penetration, oral , parameters. Process analytical technology (PAT) is intestinal absorption, P450 metabolic stability and a systemic tool allowing on line control of parame- elimination half life are routinely employed for ters, which efficiently eliminates generating batches drug quality assessment. Advances in analytical of product below specification requirements. methods and novel in vitro assays greatly facilitated Regulatory agencies not only encourage using best access to ADME data in comparison to historical process design for quality risk management but are times when most measurements were carried out visibly more inclined to dialog with an applicant, using radiolabelled compounds in rodent models. based on sound scientific knowledge, which is a rev- For example Caco-2 cells permeability, which is olutionary change from an early GMP period, in predictive for absorption of orally administered which any modification of DMF (drug manufactur- compounds, became widely accepted test on which ing file) recorded process was out of question on the permeation based classification system (PCS) of purely formal grounds. compounds was based (13). Currently expanded model, already adopted by the World Health Biological activity testing Organization, called Biopharmaceutics Drug Disposition Classification System (BDDCS) func- Dependence of biological activity on molecu- tions, which divides drugs into four classes, accord- lar structure is the key concept of medicinal chem- ing to solubility (low/high) and permeability istry, which has evolved through structure-activity (low/high) criteria. On such bases, Class one com- relationship (SAR) methodology into modern pounds (high solubility and high permeability) were bioinformatics allowing for prediction and model- singled out by the FDA for waiver of in vitro ing of biological properties as valuable support for bioavailability testing of immediate-release solid experimental in vitro and in vivo tests. dosage forms (14, 15). Pharmacodynamic proper- Contemporary process of new drug discovery and ties of drug leads and drug candidates are as a rule development relies to a high degree on selection of tested on several levels, from molecular (e.g., defined drug-like properties, which are considered receptor binding, microarrays) through cell lines, to Preclinical Drug Development 583 selected organ and model (e.g., knock-out) animals. AMS measurement. This technique, which can eas- On the lower levels there is increased use of imag- ily secure data for total mass balance of an injected ing technologies (e.g., fluorescent tags) to enhance drug sample, can be adopted to other isotopes of bio- specificity and sensitivity of biological test results. logically important elements (calcium, chlorine, There is constant tendency to save animals on ethic hydrogen) (16). principles and validity of animal models as human predictors is often criticized on purely scientific Toxicity testing principles. Preclinical pharmacological analysis of new Regulatory agencies (EMEA, FDA) require drug lead covers area from in vitro functional substantial evidence of safety and efficacy as the assays, through isolated cells and tissue studies, to basis for a new drug registration, significant part of in vivo animal pharmacokinetic (PK) and pharma- which is to be generated at preclinical stage. codynamic (PD) experiments. Responses to a dose Traditional term: toxicology for covering entire field of drug are quantified in terms of efficacy (maxi- of DDD, gradually fell out of fashion and finally mum strength of the effect) and potency (amount of was replaced by non-clinical safety assessment drug required for specific effect to occur; usually (NCSA). All tests in this area must be performed expressed as inverse of EC50). An issue of pharma- with certificate of appropriate ethical committee in cological profiling has been brought up relatively certified laboratories, under GLP conditions. recently. Since any drug candidate is likely to bind Studies in safety constitute continu- to multiple targets, distinct from the intended one, ous action carried out throughout DDD process with such lack of specificity should be seen as potential tasks like genetic toxicology, toxicokinetics, car- source of adverse effects and consequently failure cinogenicity and reproductive toxicity possibly in clinical trials. Efforts to identify as early as pos- overlapping with a clinical support period. sible the candidates with best target selectivity and Discovery phase is usually connected with multiple best safety profile include design of pharmacologi- administration protocol, lasting usually 4 weeks cal testing, with extensive use of bioinformatic (occasionally 6 months or even longer), carried out methods and target databases, like in silico screen- on two animal species, typically rats and non- ing of phylogenetic families of functional proteins rodents. Typically, three dose groups are formed, for possible binding. with a low dose close to pharmacologically effective Perhaps the most significant initiative for one, with purpose of establishing no observable future preclinical testing is called microdosing. This effect level (NOEL) and minimum toxic dose method, based on application of a single sub-phar- (MTD). Apart from close CNS (behavior, posture, macological dose of investigated compound to body weight, temperature etc.), respiratory and car- healthy volunteers, has recently passed proof of con- diovascular monitoring of experimental animals, cept set of experiments, comparing pharmacokinetic wide pathological assessment is performed (involv- (PK) results of such dosing with regular pharmaco- ing inter alia: heart liver, kidneys, spleen, brain, logical regimen. The power of microdosing, which pituary and adrenal glands, thyroids and parathy- is also called ìclinical trials phase 0î is based on roids, CV, GI and reproductive tracts). Considering sophisticated detection system with sensitivity in this, it comes as no surprise that 28-day toxicology attomole to zeptomole (10-18 ñ 10-21) range, provided experiment takes several months to complete, from by accelerator mass spectrometer. Investigated drug preparation to statistical elaboration of the raw data. sample is first enriched, by specific labeling during Reproductive toxicology is of special concern, fol- synthesis, with 14C long half-life radioactive isotope. lowing well known thalidomide tragedy. Just like in Accelerator mass spectrometry (AMS) allows for other areas of biological activity, there is a need for detection of heavier carbon isotope and determina- constant awareness to remember possible conse- tion of 12C : 14C ratio with exquisite precision, thus quences of genetic differences, even within the same can provide a wealth of pharmacokinetic and meta- species. Available study of clinical and post-market- bolic data from a single experiment. Typically, ca. ing adverse drug reactions in recent years indicate 100 microgram of a studied compound is adminis- that majority were reported in neurological, gas- tered to a human subject and after preselected time trointestinal, cardiovascular and hepatic areas (17). samples of blood, urine and sometime a biopsy sam- It can be assumed that although elimination of in ples are collected, analyzed and separated by HPLC, vivo assays in new drug safety evaluation is unreal- then analytes are converted into graphite in chemi- istic, the role of computational toxicology will grow cal oxidation-reduction sequence and subjected to systematically (18). 584 TERESA BRODNIEWICZ and GRZEGORZ GRYNKIEWICZ

Issues concerning preparation of clinical batches searches, for which drug-like cluster mapping and other selection rules are already being designed As soon as a compound is selected for devel- (21). Pending further progress in bioinformatics, opment, dosage form design should start up. Since a there is an acute need for NCEs, which can be qual- majority of drug candidates are disqualified during ified as good leads for DDD. clinical testing, care should be taken to optimize In general, for admission of a new drug candi- design of preclinical studies in order to eliminate date to clinical studies, sound non-clinical data compounds which are likely to fail in further evalu- obtained under GLP conditions are needed, accom- ation. Besides, efforts should be mobilized, not to panied by a manufacturing process (comprising spend too much time and expenses on a risky invest- both: active pharmaceutical ingredient and pharma- ment in clinical batch preparation. On the other ceutical product) executed under proper quality con- hand, for certain drugs formulation might be trol and documented according to Common absolutely critical for drug efficacy. It seems rea- Technical Document format (3). There is an sonable to dissect physicochemical properties of a increased tendency to design drug-like properties in given new chemical entity into two parts: depend- silico, and also to use bioinformatics methods exten- ent, and independent of a solid state. In the first cat- sively for modeling and predictions, in all segments egory are such important properties like dissociation of biological activity testing. Despite of phenomenal constants, partition coefficients and stability in solu- progress in life sciences, including achievements of tions. In the second are: solubility, polymorphism, genomics and systems biology, there has been no solvent affinity and thermal parameters characteris- major change in the drug discovery and develop- tic for phase transitions. Traditionally, both cate- ment paradigm and the process of DDD remains gories were taken into account at the same time dur- painfully slow, exorbitantly expensive and dismally ing preformulation studies. Presently, it is required inefficient. DDD requires, more than ever, effective that pharmaceutical quality should be achieved by and timely coordination of chemical development, design, through well managed product and process safety assessment and pharmaceutical formulation, development (19). Although much of physicochem- as there is no foolproof blueprint when and how the ical characteristics mentioned in this paragraph is appropriate quality substance should emerge. The provided by analysts carrying out chemical develop- use of new pathology models, involving transgenic ment of API, there is no guarantee that a drug sub- animals facilitate same stages of preclinical studies, stance meeting specification mixed with excipients but a lack of proper biomarkers for organ toxicity, meeting specification will make a good tablet. It is particularly myocardial tissue damage, liver toxicity therefore understandable that provisional formula- and nephrotoxicity are serious drawbacks of the tions, like hard gelatin capsules containing only the present system. active ingredient, are often use for early phases of Fortunately for those involved in DDD proj- clinical trials. ects, there is a good supply of quality scientific lit- erature covering all details of preclinical develop- Conclusions ment, and recent volumes of Drugs and the Pharmaceutical Sciences series provide a good Neither target recognition nor lead identifica- example of it (22ñ25). Besides, there are topic-spe- tion has attained satisfactory level for successful and cific guidelines issued by EMEA and FDA, applica- productive new drug mining. Current therapy is ble to preclinical as well as clinical development, based upon less than 500 macromolecular targets (ca. which should be carefully studied beforehand, for 45% G-protein coupled receptors, 28% enzymes, every step of a DDD project. It is particularly satis- 11% hormones, 5% channels, 2% nuclear recep- fying, that scientific findings and arguments become tors), while functional genomics indicate an order of sufficient ground for a dialog with regulatory agen- magnitude higher number (20). Therefore, many cies in cases of postulated changes of process devel- more viable therapeutic targets are waiting to be dis- opment, testing scheme or pharmaceutical quality covered. Finding their prospective ligands is a mat- control. In 2004, FDA launched the Critical Path ter of formidable complexity. Chemical space, Initiative as national strategy for development, eval- accommodating all possible structures may be infi- uation and manufacturing not only human drugs but nite, but even its fraction containing only small mol- also foods and cosmetics with intention to turn more ecules up to 500 Da molecular weight sums up to at research into new tools and methodologies which least 1060 compounds, unmanageable as a reservoir could improve all FDA regulated products (26). of structural diversity by any means, except virtual This initiative has received appropriate funding Preclinical Drug Development 585 from the US Congress, making hopes for accelerat- 15. Fagerholm U.: Pharm. Res., 25, 625 (2008). ed drug development technologies realistic and set- 16. Lappin G., Garner R.C.: Int. J. Pharm. Med., 20, ting an example for ICH actions. 159 (2006). 17. Stevens J.L., Baker T.K.: Drug Disc. Today 14, REFERENCES 162 (2009). 18. Merlot C.: Drug Disc. Today 15, 16 (2010). 1. Balaram P.: Curr. 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