**1.3 Opportunities for drug repositioning comes from path of drug discovery and development**

The process of new drug designing and development involve many steps as mentioned in **Figure 1**. It may happen that Drug is serendipitously screened and found positive result for another disease. Gills et al. tested few anti-HIV drugs against many cancer cell lines using cytotoxicity assays. He found that nelfinavir has potent broad-spectrum antitumor activity [9]. Repurposing can also possible if new role discovered for an existing target. In case of metformin, the similar pathway of is found to be important in two different diseases like diabetes and cancer. It has been observed that unexpected side effects found during and after clinical trials show lead for drug repurposing like thalidomide for certain cancer.
