Repurposing drugs in your medicine cabinet: untapped opportunities for cancer therapy?

Abstract

Many forms of cancer lack efficacious treatments, despite continuing advances in our understanding of molecular biology, and the development of precisely targeted agents that exploit relevant drivers and pathways of malignancy. To date the effectiveness of most tumor cell-focused molecularly targeted agents, in terms of event free and overall survival appears to be modest [1]. What is more, these new drugs come with a high price tag as companies seek to recoup development costs and to generate a return on investment (in part a consequence of a high attrition rate in oncological drug development, high regulatory burdens and expensive clinical trial costs) [2]. In the developing economies of the world, where cancer incidence is rising, the problems of unmet patient need is exacerbated by these high costs, putting many cancer treatments out of reach of patients and imposing strains on local health systems [3]. An alternative approach to seeking new drug treatments for cancer is not to start with molecular targets in mind, but to assess those drugs – approved for any indication – in our existing armamentarium which show some evidence of anticancer activity. This is the field of drug repurposing in oncology and there is now an increasing interest in the use of non-cancer drugs as anticancer therapeutics. There are two main advantages of repurposing. Firstly, by starting with well-known and well-characterized drugs we can draw on existing and detailed knowledge of pharmacodynamics, pharmacokinetics, bioavailability, toxicities, established protocols and dosing. This body of knowledge is far in excess of what can be gained in early phase clinical trials of new agents, particularly for first in class drugs. This is not to say that repurposed drugs do not need Phase I trials, since they may be used for cancer in schedules and combinations that differ from their accepted use, but it does represent a considerable short-circuiting of the preclinical phase of the drug d evelopment life cycle [4]. Secondly, many of the candidate drugs for repurposing are available at low cost; indeed many are available as generics. This is in stark contrast to the very high costs associated with the newest agents emerging from current pharmaceutical pipelines.