3'-O, 4'-O-aromatic acyl substituted 7,8-pyranocoumarins: a new class of P-glycoprotein modulators

P-glycoprotein (Pgp) overexpression in tumour cells leads to multidrug resistance (MDR) and causes failure in cancer chemotherapy. We have previously identified (±)-praeruptorin A (PA) as a potential lead compound for Pgp modulators. In this study we investigated the MDR-reversing activities of PA derivatives.

Series 7,8-pyranocoumarins with various C-3' and C-4' side chains had been semi-synthesized and their MDR-reversing activity was investigated in Pgp-overexpressing MDR tumour cell line HepG2/Dox and in a KB V1 xenograft animal model.

All 7,8-pyranocoumarins exhibited equal or higher activity in modulating Pgp. DCK (12), DMDCK (15), 16, 21, 23 and 24 at 4 µm achieved 91%∼99% decrease in IC50 value (concentration inhibiting cell growth by 50%) of anticancer agents vinblastine, doxorubicin, puromycin and paclitaxel, and were more active than others. DMDCK also remarkably enhanced the growth inhibitory effect of paclitaxel on KB V1 xenografts (P < 0.05), showing a potency required for clinical usage. Mechanistic studies suggested that these 7,8-pyranocoumarins might reverse Pgp-MDR through directly binding to substrate binding site(s) or allosteric site(s) on Pgp therefore impairing Pgp-mediated drug transport.

Results from the study suggested that 3'-O, 4'-O-aromatic acyl substituted 7,8-pyranocoumarins could serve as a new class of Pgp modulator. Acyls play an important role in maintaining and enhancing the Pgp-modulating ability of pyranocoumarins. 3,4-Dimethoxyl substituted aromatic acyls, bearing a methoxy that might interact with Pgp as hydrogen bond accepter, were shown to be the most potent for reversing MDR.