What is the similarity and sameness between asthma and COPD, cancer and diabetes and influenza and COVID-19 infection? This question often comes in mind when we hear about a drug for one disease that is going to be used for other diseases. Recently, Remdesivir that were developed for ebola and Marburg virus infection is going to be tried for COVID-19. When Thalidomide was released first it was marketed for anxiety and sleep trouble but now it is the first-line treatment for multiple myeloma. Our body is made up of cells and each cell carries approximately 25000-30000 genes. These genes code for certain proteins and these proteins participate in different functions from metabolism to recognizing a virus to protecting cells from becoming a tumor.
Despite in-depth research in the field of genetics, molecular biology and biochemistry along with others, till now we have not understood a cell completely. The behavior of a cell depends on the interaction between intra and extracellular environments. There are several factors present inside and outside of the cell that can give signals to the cell to behave in certain ways. In the case of certain infection or disease, cells try to survive in which they release certain factors or initiate a particular metabolic or signaling pathways. But when damage in the cell reaches the threshold level it can die or may start to behave abnormally as we see in case of cancer. The function of all cellular factors is finely-tuned and slight changes can cause the disease or any abnormality.
Biomolecules involved in a cellular behavior can be involved in two different diseases. For example, the same cytokine can be present at a high level in both breast cancer and ovarian cancer. The same host’s response proteins can be present in two different types of viral infections. Similarly, a common signaling pathway can be deregulated in asthma and COPD. Now if biomolecules behind two different diseases are overlapping then the same drug could be used in both conditions. For example, anti-inflammatory drugs can be used for arthritis and for viral infection both. Etanercept, an anti-inflammatory drug for arthritis could be used for influenza virus infection. If we see the relation between diabetes and cancer we will find that insulin resistance and hyperglycemia that are one of the common features of diabetes can also cause cell proliferation. Studies show that Metformin a drug for diabetes could be useful for breast cancer treatment. This approach of using a drug for a new disease that was previously worked on a different disease called as drug repurposing or repositioning. Effectiveness of any drug while repurposing may vary from disease to disease and also from patient to patient due to the unique genetic constitution of an individual.
Another aspect of drug repurposing is when outside agent such as viruses shares similar protein components. What if there is the pandemic of the new viruses and we don’t have a new drug for it? If there is any new virus that shares some of its viral components with a previously known virus for which drug is already discovered, one can use this drug for the new virus. There are thousands of chemicals, inhibitors, and drugs that are lying in pharmaceutical laboratories. The process of drug discovery is time-consuming and very costly. In this situation, companies can keep trying these drugs for different diseases after careful screening and understanding of pathogenesis.
One of the advantages of repurposing drug is most of the biological parameters such as toxicity and mechanism of action is already studied. One of the major disadvantages of doing repurposing is the misuse of drugs. We often see how information about certain drugs leads to self-medication that can cause severe side effects. Therefore, one needs to be careful while using these drugs if they are suggested for some new infection or disease. Clear guidelines should be made for using repurposed drugs. At the same time lot of care and evaluation of several biological parameters are required before introducing any old drug for a new disease.