Harnessing Drug Repurposing for Exploration of New Diseases: An Insight to Strategies and Case Studies

Drug Repurposing in the Chemotherapy of Infectious Diseases

Repurposing is a universal mechanism for innovation, from the evolution of feathers to the invention of Velcro tape. Repurposing is particularly attractive for drug development, given that it costs more than a billion dollars and takes longer than ten years to make a new drug from scratch. The COVID-19 pandemic has triggered a large number of drug repurposing activities. At the same time, it has highlighted potential pitfalls, in particular when concessions are made to the target product profile. Here, we discuss the pros and cons of drug repurposing for infectious diseases and analyze different ways of repurposing. We distinguish between opportunistic and rational approaches, i.e., just saving time and money by screening compounds that are already approved versus repurposing based on a particular target that is common to different pathogens. The latter can be further distinguished into divergent and convergent: points of attack that are divergent share common ancestry (e.g., prokaryotic targets in the apicoplast of malaria parasites), whereas those that are convergent arise from a shared lifestyle (e.g., the susceptibility of bacteria, parasites, and tumor cells to antifolates due to their high rate of DNA synthesis). We illustrate how such different scenarios can be capitalized on by using examples of drugs that have been repurposed to, from, or within the field of anti-infective chemotherapy.

Emerging drug design strategies in anti-influenza drug discovery

Influenza is an acute respiratory infection caused by influenza viruses (IFV), According to the World Health Organization (WHO), seasonal IFV epidemics result in approximately 3-5 million cases of severe illness, leading to about half a million deaths worldwide, along with severe economic losses and social burdens. Unfortunately, frequent mutations in IFV lead to a certain lag in vaccine development as well as resistance to existing antiviral drugs. Therefore, it is of great importance to develop anti-IFV drugs with high efficiency against wild-type and resistant strains, needed in the fight against current and future outbreaks caused by different IFV strains. In this review, we summarize general strategies used for the discovery and development of antiviral agents targeting multiple IFV strains (including those resistant to available drugs). Structure-based drug design, mechanism-based drug design, multivalent interaction-based drug design and drug repurposing are amongst the most relevant strategies that provide a framework for the development of antiviral drugs targeting IFV.

Drug repurposing for cancer therapy in the era of precision medicine

Drug repurposing refers to the identification of clinically approved drugs, with the known safety profiles and defined pharmacokinetic properties, to new indications. Despite the advances in oncology research, cancers are still associated with the most unmet medical needs. Drug repurposing has emerged as a useful approach for the search for effective and durable cancer treatment. It may also represent a promising strategy to facilitate precision cancer treatment and to overcome drug resistance. The repurposing of non-cancer drugs for precision oncology effectively extends the inventory of actionable molecular targets and thus increases the number of patients who may benefit from precision cancer treatment. In cancer types where genetic heterogeneity is so high that it is not feasible to identify strong repurposed drug candidates for standard treatment, the precision oncology approach offers individual patients access to novel treatment options. For repurposed candidates with low potency, a combination of multiple repurposed drugs may produce a synergistic therapeutic effect. Precautions should be taken when combining repurposed drugs with anticancer agents to avoid detrimental drug-drug interactions and unwanted side effects. New multifactorial data analysis and artificial intelligence methods are needed to untangle the complex association of molecular signatures influencing specific cancer subtypes to facilitate drug repurposing in precision oncology.

Dual targeting of 3CLpro and PLpro of SARS-CoV-2: A novel structure-based design approach to treat COVID-19

With the rapid growth of the COVID-19 (coronavirus disease 2019) pandemic across the globe, therapeutic attention must be directed to fight the novel severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2). However, developing new antiviral drugs and vaccines is time-consuming, so one of the best solutions to tackle this virus at present is to repurpose ready-to-use drugs. This paper proposes the repurposing of the Food and Drug Administration (FDA)-approved, purchasable, and naturally occurring drugs for preventive and therapeutic use. We propose to design a dual-inhibitor for the SARS-CoV-2 cysteine proteases-3 Chemotrypsin-like protease or main protease (3CLpro or Mpro) and Papain-like protease (PLpro) responsible for processing the translated polyprotein chain from the viral RNA yielding functional viral proteins. For virtual screening, an unbiased blind docking was performed from which the top nine dual-targeting inhibitors for 3CLpro and PLpro were selected. The nine repurposed drugs, block the catalytic dyad (His41 and Cys145) of 3CLpro as well as the catalytic triad (Cys111, His272, and Asp286) of PLpro. Repurposing known drugs will not only pave the way for rapid in-vitro and in-vivo studies to battle the SARS-CoV-2 but will also expedite the quest for a potent anti-coronaviral drug.