Anticancer agent 191 (Compound 2) is a derivative of probenecid. As a cancer cell efflux inhibitor, Anticancer agent 191 is designed to inhibit P-glycoprotein ( P-gp ), breast cancer resistance protein ( BCRP ), and/or multiple multidrug resistance proteins (MRPs). Anticancer agent 191 increases the accumulation of vinblastine in cancer cells, which is used for cancer research.