LY-335979 is primarily utilized in research settings to study the mechanisms of multidrug resistance in cancer cells. It functions as a potent inhibitor of P-glycoprotein, a protein that often leads to resistance against various chemotherapeutic agents by pumping drugs out of cancer cells. By blocking this protein, LY-335979 helps enhance the effectiveness of chemotherapy drugs, allowing them to remain inside the cancer cells and exert their cytotoxic effects. This makes it a valuable tool in preclinical studies aimed at developing strategies to overcome drug resistance in cancer treatment. Additionally, it is used in pharmacological experiments to understand the role of P-glycoprotein in drug transport and absorption, contributing to the development of more efficient therapeutic approaches.