Pharmacokinetics and metabolite identification study of flavonoid dimer FD18: A potent P-glycoprotein modulator in reversing cancer drug resistance

Overexpression of P-glycoprotein (P-gp) is one of the leading causes of multidrug resistance in chemotherapy. P-gp reduces the intracellular drug concentration below their respective therapeutic level. To reverse P-gp mediated drug resistance, we recently reported that synthetic flavonoid dimer is a new class of potent P-gp modulator. One of the flavonoid dimmers, FD18, has an effective concentration (EC50) of around 140nM in reversing paclitaxel (PTX) resistance. FD18 can also reverse P-gp-mediated PTX resistance in human breast cancer xenograft model in vivo. Here, we report the PK profile and metabolite identification of FD18; and subsequently in vitro and in vivo P-gp modulating evaluation of FD18 metabolites. PK study of FD18 was conducted in SD rat. Metabolism of FD18 was evaluated in rat and human liver microsome assay in vitro and SD rat in vivo. Metabolite identification of FD18 was done by UPLC-MSMS QTOF and authenticated using pure, synthetic compounds. P-gp modulating activities of the metabolites were evaluated with various anticancer drugs on LCC6MDR cells in vitro and subsequently in breast cancer xenograft model in vivo. IV administration of FD18 resulted in a first order kinetics and a non-linear plasma PK profile. IP administration of 45 mg/kg FD18 resulted in a mean residence time (MRT) of approximately 600 minutes. Three major metabolites of FD18 (M1, M2 and M3) were identified in vitro and in vivo. Metabolites identifies were authenticated using pure, synthetic compounds. The P-gp modulating activities of M1, M2 and M3 (in reversing PTX resistance) was determined to be 305±nM, 70±nM and no activity, respectively. Hydrochloride salt of synthetic M2 demonstrated in vivo efficacy in reversing PTX resistance in breast cancer xenograt model. P-gp-overexpressing xenograft was treated with 12 injections of M2 (28 mg/kg, IP) and PTX (12 mg/kg, IV) every other day (q1d x 12). On day 30, tumor size of animals treated with M2 and PTX was 773±114 mm3 (n=8) while animals in the solvent control group was 1759±455 mm3 (n=6). Tumor size of animals treated with PTX (12 mg/kg, IV) alone was 1208±66 mm3 (n=6). Flavonoid dimer is a new class of safe and potent P-gp modulators. The proposed metabolism pathway of FD18 is via N-dealkylation and oxidative deamination. M2 is a metabolite of FD18 with potent in vitro and in vivo P-gp modulating activity.