In vitro study | Tariquidar binds to P-gp with high affinity with a B max of 275 pmol/mg. Tariquidar interacts non-competitively with the P-gp substrates Vinblastine and Paclitaxel. Tariquidar acts on CHrB30 cells to increase the steady-state accumulation of these cytotoxins to the levels observed in non-P-gp expressing AuxB1 cells, with an EC50 of 487 nM. Tariquidar can inhibit P-gp Vanadate-sensitive ATPase activity by 60-70% with an effective IC50 value of 43 nM. Tariquidar at high concentrations can inhibit other resistance mechanisms. 1 M Tariquidar in vitro, can abrogate ABCG2(BCRP) mediated Camptothecins resistance. Tariquidar enhances the cytotoxicity of several drugs, including Doxorubicin, Paclitaxel, Etoposide, and Vincristine. Treatment of an intrinsically resistant mouse colon cancer cell line, MC26,Doxorubicin had a 5-fold lower IC50 value than 0.1 μm Tariquidar (36 vs 7 nM). Treatment of acquired chemotherapy-resistant mouse breast cancer, human small cell lung cancer, and human ovarian cancer cell lines (EMT6/AR1.0, H69/LX4, and 2780 AD), the IC50 values of Doxorubicin are 22-150 times lower than those of 0.1 μm Tariquidar. After removal of Tariquidar from the culture system, the inhibitory effect of P-gp lasted for 23 H. Tariquidar restored the cytotoxicity of Doxorubicin and Vinblastine in a multicellular tumor spheroid model derived from the MCF7WT breast cancer cell line. |