XR9576 is primarily known for its role as a potent inhibitor of P-glycoprotein, a protein that contributes to multidrug resistance in cancer cells. By blocking this protein, it enhances the effectiveness of chemotherapy drugs, allowing them to remain active within cancer cells for longer periods. This makes it a valuable adjunct in cancer treatment, particularly for tumors that have developed resistance to multiple drugs. Its application is mainly in research settings, where it is used to study mechanisms of drug resistance and to improve the efficacy of existing cancer therapies. Additionally, it has potential in clinical trials aimed at overcoming resistance in various cancers, offering hope for more effective treatment strategies.