Reversal of P-glycoprotein-mediated multidrug resistance using synthetic, potent and non-toxic galloylated catechins derivatives

Abstract

P-glycoprotein (P-gp) was one of well-known drug-resistance transporters. It was a highly efficient efflux pump with broad substrate specificity, including approximately a third of all anticancer drugs. P-gp expression in cancers can therefore confer cross-resistance to anthracyclines, vinca alkaloids, taxanes, epipodophyllotoxins, mitoxantrone and dactinomycin. Three generations of P-gp modulators were developed to overcome the resistance induced by P-gp, but they all failed to get into clinical application. Natural products were promising to be developed to the next generation of P-gp modulators. Epigallocatechin gallate (EGCG) was one of the well-known galloylated catechins in green tea with various biological activities. It also showed moderate P-gp modulation activity. To improve the P-gp modulation activity of EGCG, a series of compounds were synthesized with modifications including methoxy substitutions in the benzene rings and a long and rigid linker between benzene rings. Compounds, 23, 51, FX3 and WBC5 were the four most potent compounds among all the derivatives. Compared to EGCG (EC50 > 1000 nM), these four derivatives were significantly more potent (EC50 = 37.0 to 385.0 nM) in three different cell lines (LCC6MDR, P388ADR and K562/P-gp). Mechanistically, they can enhance intracellular accumulation of both paclitaxel (PTX) and doxorubicin (DOX) in these cell lines by inhibiting the P-gp-mediated DOX efflux. Pharmacokinetics studies of the four derivatives indicated their bioavailability was high, ranging from 62.88 to 81.81% when they were administrated by i.p. injection. The plasma level of 51, FX3 and WBC5, when administrated by i.p. injection (30 mg/kg), dropped below their corresponding in vitro EC50 value until 1080 minutes post administration. In addition, co-administration of FX3 and PTX suggesting no significant drug-drug interaction in plasma level. Therefore, FX3 was selected for further characterization for its in vivo efficacy. FX3 was co-administered with either PTX or DOX in three in vivo efficacy models of drug resistance including LCC6MDR xenografted solid tumor, and two leukemia models including the mouse P388ADR (i.p. inoculated) and human K562/Pgp (i.v. inoculated). In LCC6MDR xenografted model, combination treatment of FX3 and PTX significantly reduced tumor volume by 27.4% (p < 0.001) and decreased tumor weight by 34% (p < 0.01), when compared to PTX. Intratumor level of PTX was also increased by co-administration of FX3 after 60 to 300 minutes post PTX administration. In P388ADR and K562/P-gp leukemia model, combination treatment of FX3 and DOX could significantly prolong the median survival time by 30.3 (p < 0.001) and 15.6% (p < 0.01), respectively, compared to DOX alone treatment. In P388ADR leukemia model, co-treatment of DOX with FX3 resulted in a lower toxicity and longer median survival time than DOX with GF120918, which was a well-known P-gp modulator. These results suggested that FX3 can reverse P-gp induced MDR in different animal models. In summary, P-gp modulating activity of galloylated catechins derivatives was significantly improved compared with that of EGCG. FX3 can reverse MDR by modulating P-gp both in vitro and in vivo without significant toxicity issue.