Drug repurposing (also known as drug repositioning) is a strategy for discovering new uses for approved and investigational drugs that are beyond the scope of the original medical indication. This approach offers several advantages over developing a novel drug for a given indication. Various data-driven and experimental approaches have been recommended for the identification of drug candidates that can be repurposed. However, there are some major regulatory as well as technological challenges that need to be addressed.
Advantages of repurposing drugs
Notably, the drug repurposing approach benefits from the fact that approved medicines and several discarded compounds have already been tested in humans and comprehensive information is available on their pharmacology, dose, possible toxicity and formulation. Drug repurposing has numerous advantages over conventional drug discovery approaches, including:
- Considerably cuts research and development (R&D) costs.
- Reduces the drug development timeline, as various existing compounds have already demonstrated safety in humans, it does not require Phase 1 clinical trials.
- Potential for reuse despite evidence of adverse effects and failed efficacy in some indications.
Popular approaches for repurposing drugs
Drug repurposing has now become a significant part of the pharmaceutical industry. There are several drugs that have been – or are currently being repurposed – for novel indications. Repurposing can occur at various stages of the drug development and approval process. Below we list some popular drug repurposing approaches.
Repurposing oncology drugs
The drug repositioning/recycling approach has actively and effectively been adopted by drug discovery researchers and the pharmaceutical industry, especially within the oncology space. Oncology drugs are originally developed for a particular cancer. However, they can then be clinically investigated in other similar tumor types, producing versatile drugs.
Cancer appears appropriate for repurposing drugs as a single mechanism or biomarker is frequently linked to a broad range of tumor types. One prominent cancer immunotherapy is Merck’s Keytruda® (pembrolizumab) which was first approved for advanced melanoma. Today, it is approved for 14 cancer types, including lung cancer and lymphoma. The company is constantly evaluating Keytruda for more cancers, such as triple-negative breast cancer. Notably, Keytruda is a programmed cell death-1 (PD-1) inhibitor that acts by blocking the PD-1 receptor and its interaction with ligands which helps to activate a T-cell mediated immune response against tumor cells. Due to its similar PD-1-based mechanism of action (MOA), Bristol-Myers Squibb’s (BMS) Opdivo® (nivolumab) is currently approved for 10 cancer types and the company is continuing to investigate the drug’s efficacy for other indications.
Novartis’ drug Arzerra (ofatumumab), a monoclonal antibody that targets the CD20 protein, was initially developed to treat chronic lymphocytic leukemia (CLL). However, clinical studies are currently underway to determine its effectiveness as a treatment for adult patients with relapsing forms of multiple sclerosis (MS).
Repositioning drugs across therapeutic areas
Apart from repositioning drugs within a particular disease area, the pharmaceutical industry is also evaluating whether drugs approved for one indication have the potential to benefit patients in an entirely different therapeutic area. Non-oncology drugs, for example, are often repurposed to treat various cancers. For instance, experiments have shown that clarithromycin is effective in H. pylori-associated cancers such as mucosa‐associated lymphoid tissue (MALT) lymphoma. Furthermore, studies have proven its efficacy in other cancer types, including multiple myeloma and chronic myeloid leukemia (CML). The main mechanisms by which clarithromycin exhibits anti-cancer properties are prolonged reduction in pro-inflammatory cytokines, anti-angiogenesis and inhibition of autophagy. This antibiotic’s efficacy in cancer is improved when it is combined with existing cancer drugs targeting other aspects of tumor activity.
Aspirin: The versatile drug
Aspirin (acetylsalicylic acid) is a powerful drug that is not only being evaluated in the oncology field, but also in cardiac-related indications such as myocardial infarction. Studies show that low doses of the drug reduce the risk of developing a broad range of cancer types, including colorectal and pancreatic cancers.
Repositioning drugs for rare diseases
It is common knowledge that there are only a few therapeutic options for rare diseases – those that affect only a small percentage of the overall population. After the discovery of its immunosuppressive properties linked to its inhibition of the mTOR protein kinase, Pfizer’s Rapamune® (sirolimus) was approved to prevent organ transplant rejection. It also became the first drug approved for lymphangioleiomyomatosis (LAM), a rare genetic lung disease.
Repurposing drugs to treat COVID-19
Drugs are also being repurposed as a treatment strategy against COVID-19 – the disease caused by SARS-CoV-2. Several drugs are being evaluated including AbbVie’s Kaletra® (lopinavir/ritonavir), and Ascletis Pharma’s Ganovo® (danoprevir) plus ritonavir and other combinations. Furthermore, Gilead Pharmeceuticals’ Veklury® (remdesivir) has been approved by the US Food and Drug Administration (FDA) as a treatment for COVID-19.
Due to soaring drug prices and the slow pace of drug discovery and development, repurposing existing drugs to treat diseases other than their originally approved indication is becoming an increasingly attractive proposition. Such drugs will likely soon capture a significant portion of the pharmaceutical industry.