Cell experiment:

Cells (EMT6 AR1.0 8×102/well; A2780 5×103/well; 2780AD 6×103/well) are seeded into 96-well plates. After ~4 h, varying concentrations of Tariquidar are added, and cells are incubated for an additional 4 days (EMT6 AR1.0) or 6 days (2780AD) before quantification of cell growth and calculation of IC10 values (concentration resulting in 10% inhibition of cell growth)[2].

Animal experiment:

Mice[2] MC26 tumor slurry is implanted s.c. in BALB/c mice (day 0). The animals are then randomized, 24 h later, into groups of 15-18 and treated once with various regimens. Tariquidar methanesulfonate or vehicle is administered either i.v. via a lateral tail vein or p.o. with Doxorubicin (5 mg/kg) or vehicle i.v. The modulator is administered either i.v. at 2-4 mg/kg (10 mL/kg) at the same time as Doxorubicin or p.o. at 2-8 mg/kg (10 mL/kg) 1 h before the Cytotoxic drug. GG918 is administered p.o. 1 h before doxorubicin. All of the animals are weighed twice weekly. The animals are killed by cervical dislocation on day 14, and the tumors are excised and weighed. The data are analyzed by Student’s t test. Rat[2] Male CD rats (3 animals per time point) are dosed i.v. with paclitaxel alone [15 min infusion at 10 mg/kg in Tween 80:ethanol:5% dextrose (5:10:85% v/v/v)] or in combination with Tariquidar methanesulfonate (10 mg/kg). Tariquidar methanesulfonate is administered as a bolus (i.v.) dose 15 min before infusion of Paclitaxel. Blood samples are collected by cardiac puncture using heparinized syringes at various times between 0.083 and 48 h and are centrifuged to prepare plasma, which is stored at –20℃ until analysis. Paclitaxel concentration in plasma samples is measured by a LC-MS/MS assay.

Tariquidar methanesulfonate, hydrate is a potent inhibitor of P-glycoprotein (Pgp), a 170-kDa transmembrane protein acting as a drug efflux pump to actively transport structurally unrelated compounds out of cell, which noncompetitively inhibits the basal the activity of ATPase associated with Pgp.
Tariquidar contains a tertiary amine, dimethoxyphenyl group and amide group in its chemical structure, which contribute to its inhibition against Pgp. Results of in vitro assays of three different models have shown that Tariquidar inhibits Pgp with 50% inhibition concentration IC50 values ranging from 15 to 223 nM. However, the inhibition by tariquidar is Pgp-specific and attenuated in tumor cell lines, where multidrug resistance is mediated by multidrug resistance-associated protein.
References:
1.Fox E, Bates SE. Tariquidar (XR9576): a P-glycoprotein drug efflux pump inhibitor. Expert Rev Anticancer Ther. 2007 Apr;7(4):447-59.
2.Bankstahl JP, Bankstahl M, Römermann K, Wanek T, Stanek J, Windhorst AD, Fedrowitz M, Erker T, Müller M, Löscher W, Langer O, Kuntner C. Tariquidar and elacridar are dose-dependently transported by P-glycoprotein and Bcrp at the blood-brain barrier: a small-animal positron emission tomography and in vitro study. Drug Metab Dispos. 2013 Apr;41(4):754-62. doi: 10.1124/dmd.112.049148. Epub 2013 Jan 10.