Characterization of in vivo activity of flavonoid dimer in modulating p-glycoprotein

Abstract

Drug efflux by permeability-glycoprotein (P-gp) transporter in cancer cells is one of the well studied mechanisms for multidrug resistance (MDR). Modulating P-gp by inhibitors is a legitimate method to reverse MDR. Flavonoid dimers belong to a family of modulators that exhibit modulating effect on P-gp mediated MDR in vitro. Flavonoid dimer 18 is a novel synthetic flavonoid dimer with in vitro P-gp modulating activity of EC50 = 148nM. Here drug metabolism and pharmacokinetics study of flavonoid dimers 18 has been conducted using rodent models. Plasma concentration profile of 18 was obtained by UPLC-MSMS. Limit of detection for 18 was 3.9 ng/mL. Intraperitoneal (IP) administration of 18 was chosen for in vivo efficacy study as it gave a systemic circulation level above EC50 for a longer duration compared to intravenous (IV) administration. Metabolites of 18 were identified by mass spectrometry analysis. Their identities were confirmed with authentic compounds. All three metabolites have better hydrophilic properties. Metabolite M1 (named as 14a) demonstrated P-gp modulating activity in vitro (EC50 = 305nM). M2 (named as FM04) also possessed a better P-gp modulating activity in vitro when compared to parent 18. M3 (named FM327) did not show any P-gp modulating activity. EC50 of FM04 in reversing paclitaxel (PTX) mediated MDR was 70 ± 26nM whereas EC50 of 18 was 148 ± 18 nM. Plasma concentration profile for FM04 was obtained by a validated UPLC-MSMS detection method for pharmacokinetics analysis. The detection limit for FM04 was 8.88ng/mL. FM04 was bio-available via oral (5.26%) and IP (24.34%) administration. Effect of P-gp modulators (18 or FM04) on improving PTX oral bioavailability was investigated. Oral bioavailability of PTX was increased by 7 fold, from 6.7% to 47.12%, when FM04 was co-administered. Oral bioavailability of PTX was increased by 4.13 fold, from 2.66% to 11.01%, when 18 was co-administered. Co-administration of PTX (oral, 80mg/kg) with 18 (oral, 30mg/kg) or FM04 (oral, 45mg/kg) resulted in a significant suppression in a LCC6 breast carcinoma xenograft model. Tumor doubling time was increased from 12 ± 0.6 days (no treatment group) to 35.3 ± 6.4 days (oral PTX 80mg/kg with 18 30mg/kg) or 35.3 ± 1.8 days (oral PTX 80mg/kg with FM04 45mg/kg). To conclude, novel flavonoid compound 18 represent a new class of P-gp modulator. We have studied the pharmacokinetics and investigated the metabolism of 18. Metabolites of 18 were identified. One metabolite FM04 showed higher P-gp modulating activity. We then also demonstrated that co-administration of PTX with 18 or its metabolite FM04 can enhance oral bioavailability of PTX to a level sufficient for suppressing breast carcinoma xenograft growth in vivo. This opens up the possibility of administer PTX via oral route.