Zosuquidar Trihydrochloride is primarily used in cancer research and treatment, particularly in the study of multidrug resistance (MDR) in cancer cells. It functions as a potent inhibitor of P-glycoprotein, a protein often overexpressed in cancer cells that pumps chemotherapeutic drugs out of the cells, reducing their effectiveness. By blocking this protein, it enhances the efficacy of anticancer drugs, making them more effective in killing cancer cells. This compound is particularly valuable in experimental settings to understand and overcome drug resistance mechanisms, aiding in the development of more effective cancer therapies. It is also used in preclinical studies to evaluate its potential in combination with other chemotherapeutic agents to improve treatment outcomes.