Asterand PhaseZERO - a solution for Drug Development

Human in vitro testing: an introduction to PhaseZERO^TM
PhaseZERO^TM was established to address what was perceived to be a serious problem for the pharmaceutical industry, namely its staggeringly poor performance in translating good ideas into safe effective medicines. This is no reflection on the quality of the scientists involved, but of the tools available to identify and validate new therapeutic approaches with any certainty. Although the target for such new medicines is man, the methods employed to identify and validate have historically been almost entirely non-human, and their predictivity for man consequently unreliable. PhaseZERO^TM comprises an extensive range of highly developed technologies based on the use of human isolated tissues that may be applied to drug discovery and development issues. These capabilities include identification of the distribution, regulation and function of drug targets both at tissue and cellular levels, and information on the disposition, actions and metabolism of compounds of interest. While PhaseZERO^TM comprises many established assays, it is more flexible than that, offering a way of helping drug discovery and development scientists provide a human perspective to their programmes. And with Asterand’s expertise and human tissue supply network, its access to post mortem and surgical samples of appropriately consented human tissues means that the provision of these services as a reliable and timely component of the industry’s drug research and development programmes is now a reality.

While few are likely to argue with the principle of the introduction of more human-based information into the discovery/development process, it is important to understand at what stages such human focus can contribute, and what benefit it offers. First, considering where it can be introduced; although PhaseZERO^TM can contribute little to the identification of novel drug targets, it can contribute to virtually all subsequent stages in the discovery/development process, as illustrated in Fig.1. The second issue of exactly what PhaseZERO^TM has to offer requires fuller explanation.

Figure 1. Diagramatic representation of the points in the discovery/development process at which PhaseZERO can be introduced.

Picking the best clinical candidates
There are two key aspects of a new compound’s profile that must be satisfied before it can be submitted to clinical evaluation, efficacy and safety. PhaseZERO^TM exists to provide information on both. Evidence of potential clinical effectiveness is the primary determinant for a drug company when deciding whether to take its new chemical entity (NCE) into the clinic. No company is going to commit the huge resources required to evaluate something that they feel is unlikely to work. Interestingly, for the regulatory authorities whom they have to convince, potential efficacy is largely taken as a given. What these gatekeepers are far more interested in is safety. The FDA, the EMEA and the Koseisho would be relatively unconcerned about the failure of a new treatment for diabetes or Alzheimer’s to achieve its desired end points, but what does exercise them greatly is the appearance of side effects or toxicity in the volunteer or patient population. So between them, these two decision makers, the drug company and the regulators, need as much comfort as possible before a clinical trial can begin. It is generating this confidence that is responsible for much of the cost and much of the lost time in drug development programmes.

And of course, getting the drug into the clinic is only a start - the majority of new drugs that enter the clinical stage of development fail to become medicines. The reasons for this are many, including inadequate efficacy, poor ADME profiles, unacceptable side effects and frank toxicity as the main contributors, all risks that may be reduced by appropriate PhaseZERO^TM testing early in a drug’s development.

Putting disease models in their place
At present, much pre-clinical efficacy and safety testing relies on the use of experimental animals, and to one degree or another, this situation is likely to persist.
However, it is essential to know how fit for purpose are the animal species selected and the test methods applied. If these are wrong, the compound will likely fail, or a promising new possibility may never see the light of day, so anything that can be done to provide confidence in their value should be done. Thus the introduction of human in vitro data to validate (or otherwise) animal disease models and other animal-based test methods will enable a more informed choice of test model/method, and is likely to greatly enhance the quality of decision making. In many cases however, it may prove that for establishing proof of concept for efficacy, there is no useful animal model. A good example is cystic fibrosis (CF), a disease that in its severest form is invariably fatal, results from the presence of a mutant form of the gene encoding the epithelial ion transporter, CFTR. While CF affects epithelial cells throughout the body, many of its effects can be treated, but it is the effects on the lung that are usually the cause of death. CF appears to be a uniquely human disorder, and attempts to develop a useful animal model have failed. Indeed, even CFTR knock-out mice fail to display the broncho-pulmonary symptoms that are characteristic of human CF.

It would be a mistake to consider that only in vivo data have any real relevance in clinical go/no go decisions, and in cases such as CF, where there is little point in utilising animal models, efforts would be better directed towards PhaseZERO^TM studies on human lung epithelial cells in vitro. The results of such studies would provide a much sounder basis for the decision as to whether or not a clinical study is warranted. Of course the absence of a useful disease model in which to demonstrate efficacy does not influence the need to undertake the ADME and safety studies that will be necessary to satisfy the regulatory authorities that a test drug may be accepted into clinical testing, but again, the species used should be chosen as far as possible with attention to their relevance.

In vitro testing of course has its limitations, and there are many diseases for which efficacy and side effect testing can really only be undertaken in vivo, eg new drugs for psychiatric disorders. In such cases, as with the choice of species for ADME/safety testing, research scientists have a responsibility to establish as far as possible the relevance of the model(s) chosen. A study of the literature evidence as to the similarity of the relevant aspects of the candidate test species to man will provide some clarity. However, more direct inquiries relating to the expression and function of key targets and biochemical pathways in relevant human tissues through application of PhaseZERO^TM may prove to be a powerful additional indicator.

Questioning the use of surrogate species
Surrogate, ie non-human, species are and will continue to be used experimentally as models for man in attempts to develop new medicines, and while they undeniably have their uses, it is essential to understand their limitations, and not to consider them as the whole answer. To illustrate, I will use the mouse, for which there has been considerable enthusiasm as a human surrogate, based ostensibly on the much vaunted genetic similarity between the two species. In truth, this enthusiasm is as much a function of the fact that mice are cheap and easy to use, and that there is a vast range of established models available to the experimenter. A review article from the Lexicon group extolling the virtues of knock-out mice in predicting drug efficacy in man essentially ignored data in the references they cited that did not support their contention. For example, it was clear that such mice provided no evidence whatsoever for the efficacy of beta-agonist bronchodilators in the treatment of asthma, and even suggested that thiazolidinedione anti-diabetes drugs should actually make diabetes worse. In contrast, the potential beneficial effects of both of these classes of drugs can be clearly demonstrated by PhaseZERO^TM studies on human bronchial smooth muscle and pancreatic islets respectively.

An enthusiasm for established, available animal models in the face of evidence of their unsuitability for purpose is commonplace. A good example is the direction taken by the pharma industry at large in developing new treatments for IBS in man, a disorder of human colon in which clinical studies have strongly implicated the involvement of 5-HT (serotonin). On the basis of experimental animal data, the industry has chosen to pursue drugs which act at 5-HT3 and 5-HT4 receptors; two such drugs, Lotronex and Zelmac, having already reached the market. The enthusiasm for this approach seems unaffected not only by the growing evidence of the limited clinical efficacy and use-limiting side effects of these compounds, but also by the clear demonstration that in man, unlike any other experimental animals tested, the excitatory 5-HT receptor in the colon is 5-HT2b. Such failings do not condemn the animal model approaches as a whole, but highlight the potential shortcomings of relying on non-human species to predict for man.

Helping to fail early
Accepting that most NCEs emerging from research programmes are destined to fail, whether through inadequate efficacy, pharmacokinetics, safety or tolerability, it is better to get these failures out of the way as early as possible. While none would recommend regarding failure as a primary driver behind discovery/development programmes, it is a fact of life that must be accepted, and failing early serves to limit the commitment of unnecessary time, effort and money, allowing available resources to be focussed on more worthwhile programmes. The failure of the anti-diabetes drug Rezulin (troglitazone) through the appearance in some patients of liver toxicity was a major blow to Sankyo and Parke-Davis, and presumably one about which they had no prior knowledge. However, in a published PhaseZERO^TM study in which troglitazone and two other compounds of the same class, rosiglitazone and pioglitazone, were tested for hepatotoxicity on human hepatocytes, troglitazone demonstrated a very narrow therapeutic window when comparing the concentrations required to induce frank hepatotoxicity in vitro with the maximum blood concentrations in patients. This narrow window was not observed with the other thiazolidinediones. Early PhaseZERO^TM profiling of troglitazone would have identified a high risk of liver toxicity, and provided a means of identifying a safer compound of comparable efficacy.

Establishing a positive ethical approach to drug testing
Finally, the question of ethics. Experimental animals are not only expensive to breed and to keep, their use is also the source of much public concern. Few would argue with the suggestion that any unnecessary use of experimental animals in drug research should be avoided, and that the use of human tissue alternatives should result in a significant reduction in animal usage. Thus, where the use of human tissue research provides a viable alternative, it would be unreasonable and unethical not to take that course. Such a change in direction will undoubtedly lead to a reduction in animal use, an outcome that will be appreciated both by those responsible for holding the drug development budgets and general public alike. In short, the use of PhaseZERO^TM can provide hugely valuable research information without being an ethical and emotional minefield.

Conclusions
The huge and ever-increasing cost of developing new drugs is no secret, with current estimates of the order of $1B being required to get a new drug to market, and even then, a resulting medicine may not be a commercial success. Also no secret is the industry’s staggering attrition rate, with hundreds of thousands of compounds being tested and abandoned simply to get one to the clinic. Anything that would help pick out the potential winners and losers at an earlier stage is going to impact on these measures of efficiency. PhaseZERO^TM , with its basis of human biology, was developed to provide more insight into the likely success or otherwise of a novel clinical candidate. PhaseZERO^TM will never provide all the answers, and it is unlikely that PhaseZERO^TM can or should ever totally replace whole animal studies, but there is little doubt that its appropriate and systematic use will result in more effective drug discovery and development programmes.

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