https://pmc.ncbi.nlm.nih.gov/articles/PMC7404055/ An excerpt:
1. Introduction
"Cancer represents a major public health and economic problem and is a leading cause of death worldwide. For both sexes combined, lung and breast cancer are the most commonly diagnosed cancers (accounting for 11.6 % of the total cases each) and the leading causes of cancer death (18.4% and 6.6% of the total cancer deaths respectively) [1]. Nevertheless, cancers of the digestive system, when combined together, account for more new cases and deaths per year than cancers arising in any other organ [1]. In 2018, among all the cancers of the digestive system, colorectal cancer (CRC) was estimated to have both the highest number of new diagnosed cases and the highest number of deaths followed by stomach and liver cancer [1]. Present day therapy of solid tumors is focused on surgical removal, although this option is usually available only in the earlier stages of cancer development [2]. In later stages, when metastases are detected, chemotherapy is the treatment of choice. Unfortunately, many patients experience chemotherapy resistance, either from the beginning or during the course of treatment, ultimately resulting in therapy failure [3]. These issues create the need for other therapeutic options and force the pursuit of the discovery of new chemicals.
However, the development of new therapeutics has become increasingly difficult for pharmaceutical companies, as the pipeline leading to any drug’s development is extremely protracted, exacting and costly. Nowadays, it takes about 10–15 years to develop a new drug [4], and despite all the effort, the success rate remains very low (around 2 %) [5]. In recent years, the pool of newly discovered and Food and Drug Administration (FDA)-approved drugs has been dwindling [6], mostly due to the increasing cost of clinical trials [7]. From 2004 through 2012, the median total cost for a pharmaceutical clinical trial was estimated to be around 2–3 billion US dollars, although, when adjusted for inflation, the money required for funding would be even higher by now [4]. It has been predicted that for each dollar invested, less than a dollar returns as profit, thereby making the development of new drugs a risky and undesirable process for most companies [8]. Given these drawbacks, new approaches to drug development should be employed in order to make drug research less time-consuming and financially demanding.
One such approach is drug repositioning (also referred to as drug repurposing); that is, the strategy of identifying new uses for approved or investigational drugs that are outside the scope of the original medical indication [9]."