Current Topics in Medicinal Chemistry - Volume 16, Issue 19, 2016

Computational drug repositioning is popular in academia and pharmaceutical industry globally. The repositioning hypotheses, generated using a variety of computational methods, can be quickly tested experimentally. Several success stories have emerged in the past decade or so. Newer concepts and methods such as drug profile matching are being tried to address the limitations of current computational repositioning methods. The trend is shifting from earlier small-scale to large-scale or global-scale repositioning applications. Other related approaches such as prediction of molecular targets for novel molecules, prediction of side-effect profiles of new molecular entities (NMEs), etc., are applied routinely. The current article focuses on state-of-the-art of computational drug repositioning field with the help of relevant examples and case studies. This ‘lateral’ approach has significant potential to bring down the time and cost of the awfully expensive drug discovery research and clinical development. The persistence and perseverance in the successful application of these methods is likely to be paid off in near future.

Although bioactivation is a well-documented process and the role of active metabolites in the drug discovery field has long been recognized, drug metabolites are usually ignored in virtual screening campaigns oriented to drug repositioning. The present article discusses different issues related to overlooking of the active metabolites in virtual screening campaigns, including an overview of the essential aspects of drug biotransformation and a summary of computational approaches that can provide solutions to those issues. Some valuable computational resources connected with this topic are also overviewed.

Have you a compound in your lab, which was not successful against the designed target, or a drug that is no more attractive? The drug repurposing represents the right way to reconsider them. It can be defined as the modern and rationale approach of the traditional methods adopted in drug discovery, based on the knowledge, insight and luck, alias known as serendipity. This repurposing approach can be applied both in silico and in wet. In this review we report the molecular modeling facilities that can be of huge support in the repurposing of drugs and/or unsuccessful lead compounds. In the last decades, different methods were proposed to help the scientists in drug design and in drug repurposing. The steps strongly depend on the approach applied. It could be a ligand or a structure based method, correlated to the use of specific means. These processes, starting from a compound with potential therapeutic properties and a sizeable number of toxicity passed tests, can successfully speed up the very slow development of a molecule from bench to market. Herein, we discuss the facilities available to date, classifying them by methods and types. We have reported a series of databases, ligand and structure stand-alone software, and of web-based tools, which are free accessible to scientific community. This review does not claim to be exhaustive, but can be of interest to help in drug repurposing through in silico methods, as a valuable tool for the medicinal chemistry community.

As commented by the Nobelist James Black that “The most fruitful basis of the discovery of a new drug is to start with an old drug”, drug repurposing represents an attractive drug discovery strategy. Despite the success of several repurposed drugs on the market, the ultimate therapeutic potential of a large number of non-cancer drugs is hindered during their repositioning due to various issues including the limited efficacy and intellectual property. With the increasing knowledge about the pharmacological properties and newly identified targets, the scaffolds of the old drugs emerge as a great treasure-trove towards new cancer drug discovery. In this review, we summarize the recent advances in the development of novel small molecules for cancer therapy by scaffold repurposing with highlighted examples. The relevant strategies, advantages, challenges and future research directions associated with this approach are also discussed.

The existence of unresponsive tumors and the appearance of resistant tumors during the course of treatments both justify that we increase urgently the panel of pharmacological molecules able to fight cancer. An interesting strategy is drug reprofiling (also known as drug repositioning, drug repurposing or drug retasking) that consists of identifying and developing new uses for existing drugs. This review illustrates drug reprofiling with troglitazone (TGZ), a synthetic PPARγ agonist initially used for the treatment of type II diabetes. The fact that TGZ also displays anticancer effects is known since the end of the nineties but its development as an anticancer agent was slowed down due to hepatotoxic side effects. Part of the knowledge available for TGZ, mainly the molecular basis for PPARγ activation, its metabolization pathways and the side effects on hepatocytes, were taken into account to elaborate new molecules. Key findings were that unsaturated TGZ derivatives, when compared to TGZ, do not activate PPARγ, exhibit a higher efficiency on cancer cells and a lower toxicity towards hepatocytes. However, a weakness is that the mechanisms involved in the anticancer effects are still not completely understood and that the efficiency of such derivatives has not yet been completely studied in vivo. Data about this point should become available very soon from animal models and this will be a prerequisite to initiate clinical trials with these potential new anticancer drugs developed from a drug repurposing strategy.

Development of new drugs is a time-consuming, hugely expensive and an uncertain endeavor. The pharmaceutical industry is looking for cost-effective alternatives with reduced risks of drug failure. Validated target machinery along with established inhibitors indicates usefulness in drug design, discovery and further development. Folate metabolism, found in both prokaryotes and eukaryotes, represents an essential druggable target for chemotherapy. Numerous enzymes in the cell replication cycle use folate either as a cofactor or as a substrate. DHFR, an enzyme of the folate biosynthesis pathway is an established chemotherapeutic target, initially explored for anti-cancer drug discovery. Diaminopteridines e.g. methotrexate and aminopterin, primarily used as anti-cancer agents, are folic acid analogues, first reported in late 1940’s, used to produce temporary remission of acute leukaemia in children. However, due to the toxicity of these drugs, they could not be used for other therapeutic implications such as in the treatment of infectious diseases. Development of newer diaminopteridine derivatives has helped in repositioning their therapeutic usefulness. These analogues have now been proven as anti-parasitic, immuno-suppressants, anti-bacterial agents, to enlist a few therapeutic applications. Likewise, diaminopyrimidine, diaminoquinazoline and diaminodihydrotriazines are being explored for structural modifications by which they can be repurposed from their originally developed medicinal applicability and exploited for various other infectious disease conditions. In this review, we encompass the study of DHFR inhibitors potentially to be repurposed for different infectious disease case scenario and also highlight the novel anti-infective drug discovery benefits therein.

Although tremendous effort has been made over the past century to treat cancer effectively, the pace of drug development is far behind the increasing rate of cancer incidence and mortality. There are two major hurdles in anticancer drug development: dose-limiting toxic side effects that reduce either drug effectiveness or the quality of life of patients and complicated drug development processes that are costly and time consuming. Drug repositioning has recently gained increasing attention among cancer researchers as this approach utilizes existing drugs and is significantly cost- and time-effective. Existing drugs, particularly non-cancer drugs, have favorable safety profiles in humans and serve as an ever-increasing source for new anticancer drug discovery. Here we review the recent examples of drug repositioning of existing non-cancer drugs for preclinical and clinical introductions of cancer therapy.

Increased investments and development of new technologies in drug discovery have barely improved the outcome of medicinal entities in the drug discovery market from a long time. Minimal success rates of drug approvals, poor safety profiles, and long development processes are some of many hurdles encountered in the drug discovery field. Therefore, drug repurposing can provide an alternative approach to meet the demands of the new, potent and safe anti-cancer agents in terms of both economic cost and time efficiency. The common molecular pathways of different diseases and secondary indications of most of the approved drugs, and advances in genomics, informatics and biology, as well as the availability of approved or safe drug libraries can certainly provide an improved and efficient way of screening safer drugs for new indications. Promising results of drug repurposing in different therapeutic areas have encouraged the scientific community to discover new drugs for different diseases using this methodology. Herein, we provide a general overview of structurally and functionally diverse approved drugs that have been repurposed as anti-cancer drugs.

Development of agents for cancer prevention has been particularly challenging for two main reasons. One is the inherent difficulty in identifying targets for the heterogeneous group of processes that lead to invasive cancer arising at different target organ sites, while the other is the need for safe, tolerable interventions that can be given for lengthy periods of time. The rapidly increasing understanding of the molecular pathogenesis of cancer is providing new opportunities for early intervention, prior to the development of invasive disease. Furthermore, there is an ever-increasing number of approved drugs with many different mechanisms of action. The appeal of using drugs with well described mechanisms of action and safety profiles has led to renewed interest in repurposing such agents for cancer prevention. Here we review the rationale and evidence of effectiveness of three agents that are the current focus of much interest in the field of cancer prevention - aspirin, metformin, and pioglitazone.

Due to the increasing costs and time consuming for new drug discovery, a large number of pharmaceutical firms have chosen to modify the existing drug molecules for repositioning candidates with new or improved properties, especially those with severe adverse effects, thereby accelerating the drug discovery process. Such strategy has witnessed its success with several examples reported. As the first identified histone lysine specific demethylase, lysine specific demethylase 1 (LSD1) is classified as a member of monoamine oxidase (MAO) superfamily, and specifically removes mono- and dimethylated histone 3 lysine 4 (H3K4) and H3 lysine 9 (H3K9). It has been reported that LSD1 and its downstream targets are involved in cancer cell growth and metastasis. Meanwhile, it is overexpressed in a variety of tumor cells. Inactivating LSD1 specifically inhibits tumor progression and metastasis. Hence, LSD1 inhibition may represent a new and promising direction in anti-cancer drug discovery. Based on the structure and cofactor of LSD1, some clinical applied MAO inhibitors have been identified as LSD1 inactivators. Among them, tranylcypromine presented the most potency against LSD1 and its derivatives were further developed by medicinal chemists in order to develop potent and selective LSD1 inhibitors. Currently, a number of tranylcypromine based LSD1 inhibitors have been developed and two of them, ORY-1001 and GSK2879552, are in clinical trials for cancer treatment. This review highlights recent advances in the repurposing of tranylcypromine and its derivatives as irreversible LSD1 inhibitors for cancer treatment, which are conventionally used for the treatment of depression.

Cardiometabolic disorder (CMD) is a cluster of diseases, including cardiovascular diseases (CVDs), metabolic syndrome (MS) and diabetes mellitus (DM). Cardiometabolic disorders (CMDs) remain the principal cause of death in both developed and developing countries, accounting for nearly 32% of all deaths worldwide per year. In addition, dyslipidemia, angina, arrhythmia, cardiac failure, myocardial infarction (MI), and diabetes mellitus represent the leading killer with an estimated 19 million people died from CMDs in 2012. By 2030 more than 23 million people will die annually from CVDs. Existing drugs are not efficient enough to reduce the disease burden as well as mortality. Therefore, there is an urgent demand for new drugs in this area to reduce the mortality and control the associated disability. Nonetheless, new drug discovery (NDD) in CMDs has become more challenging for last couple of decades due to increased expenses and decreased success rate. In such a scenario, drug repositioning in the CMDs appears promising for introducing existing drugs for new therapeutic indication. Repositioning is quite an old strategy dating back to 1960s and mainly followed by serendipitous observations during clinical use of drugs. A major advantage of repositioning is that the safety profile of the drug is well established thus reducing the chances of failure due to adverse toxic effects. In addition, repositioning requires less time and investment than NDD. Considering these facts, pharmaceutical companies are now becoming increasingly interested in drug repositioning. In this follow-up, we have talked about the concept of repositioning with important examples of repositioned drugs in cardiometabolic disorder.

Neglected tropical diseases represent a major sanitary problem and a huge economic burden to endemic countries, and are currently expanding to non-endemic countries owing to migration currents. Though long abandoned in the past, recent research on novel therapeutics has already started to show results. Drug repositioning is one of the prominent, more successful strategies to approach the development of new treatments for these diseases. Here we present an overview on the limitations of the current available medications to treat African trypanosomiasis, Chagas disease and Leishmaniasis, along with a review on drug candidates presently undergoing clinical trials and drug candidates identified through drug repositioning initiatives.

Autoimmune diseases are characterized by the production of autoantibodies directed against specific organs of own organism. Additional common traits of autoimmune diseases are chronic inflammation due to generation of inflammatory mediators, and disorders of redox processes. The pathogenesis of autoimmune diseases is still unknown. Treatment is based only on relieving the symptoms and improving the quality of patients lives. Metformin, which is used in treatment of type 2 diabetes, has properties which are desirable for autoimmune disease therapy, including anti-inflammatory and antioxidant effects, and the ability to regenerate the endothelium.