Tariquidar (XR9576)(Kd=5.1 nM) is a specific and effective non-competitive inhibitor of P-glycoprotein. It can reverse drug resistance in MDR cell Lines.

P-gp:5.1 nM(Kd)

Tariquidar 对P-gp具有高亲和力，Bmax值为275 pmol/mg。它与P-gp底物vinblastine和paclitaxel表现出非竞争性相互作用。Tariquidar能够将这些细胞毒药物在CHr<>/supB30细胞中的稳态积累量提高至非P-gp表达的AuxB1细胞观察到的水平，EC50值为487 nM。Tariquidar还能够通过60-70%抑制P-gp的钒酸盐敏感性ATPase活性，具有强大的IC50值43 nM。[1] 在较高浓度时，Tariquidar可能还能抑制其他抗性机制。1 μM Tariquidar能够体外消除ABCG2 (BCRP)介导的对camptothecins的抗性。[2] Tariquidar增强了包括doxorubicin、paclitaxel、etoposide和vincristine在内的多种药物的细胞毒性；在25-80 nM Tariquidar存在时，抗性完全逆转。在具有先天化疗抗性的MC26鼠结肠癌细胞系中，加入0.1 μM Tariquidar后doxorubicin的IC50降低了五倍(36对7 nM)。在获得化疗药物抗性的鼠乳腺癌、人小细胞肺癌和人卵巢癌细胞系(EMT6/AR1.0, H69/LX4和2780 AD)中，加入0.1 μM Tariquidar后体外doxorubicin IC50降低了22-150倍。在移除Tariquidar后，对P-gp的抑制作用可持续23小时。[3] 在由MCF7WT乳腺癌细胞系衍生的国家癌症研究所(NCI)/ADRRES多细胞肿瘤球模型中，Tariquidar恢复了doxorubicin和vinblastine的细胞毒性。[4]

Tariquidar（2-8 mg/kg p.o.）被发现显著增强了多柔比星（5 mg/kg，i.v.）对MC26小鼠结肠癌体内的抗肿瘤活性。在人类癌症异种移植物中，XR9576（6-12 mg/kg p.o.）的共同给药完全恢复了紫杉醇、依托泊苷和长春新碱对两种高度耐药性MDR人类肿瘤异种移植物（2780AD，H69/LX4）裸鼠的抗肿瘤活性。[3]

Steady-state drug accumulation assay: AuxB1 and CHrB30 cells are grown to confluency in 12-well (24 mm) tissue culture dishes and the steady-state accumulation of [3H]-vinblastine is measured. Accumulation is initiated by the addition of 0.1 μ Ci [3H]-vinblastine and unlabelled vinblastine to a final concentration of 100 nM . The accumulation of [3H]-paclitaxel is measured using 0.1 μ Ci [3H]-paclitaxel and unlabelled drug to a final concentration of 1 μM . Cells are incubated in a reaction volume of 1 mL for 60 min at 37 ℃ under 5% CO2 in order to reach steady-state. The effect of the modulators XR9576 on [3H]-ligand accumulation is investigated in the concentration range 10-9 - 10-6 M. Modulators are added from a DMSO stock giving a final solvent concentration of 0.2 % (v/v). Following cell harvesting, accumulated drug is measured by liquid scintillation counting and normalized for cell protein content. Plots of amount accumulated as a function of modulator concentration are fitted with the general dose-response equation: Y={(a-b)/(1+(X/c)d)}+b Where: Y=response; a=initial response; b=final response; c=EC50 concentration; d=slope value; X=drug concentration.

Cells are seeded into 96-well plates at 800/well, in 100 μL of medium and incubated for 4 h at 37 ℃. Varying concentrations of modulator or solvent control (50 μL/well) are subsequently added and incubated for an additional 1 h before the addition of the cytotoxic drug. The cytotoxic drug (50 μL) is added to give a range of final concentrations in quadruplicate wells. After incubation for an additional 4 days, cell proliferation of adherent cells is assessed using the sulforhodamine B assay.(Only for Reference)