When differences in antiproliferative potencies occur, they are not due to multidrug-resistance by the described moderate expression of MDR1 or MDR3 proteins in HT-29 colon carcinoma cell line [48,53,57], as only a handful of compounds experienced a potency increase in the presence of the Ppg/MDR1 inhibitor, verapamil [58]. The gene discussed is ABCB4; the disease is colon carcinoma.