Bis-pyranobenzoquinones as a new family of reversal agents of the multidrug resistance phenotype mediated by P-glycoprotein in mammalian cells and the protozoan parasite Leishmania.

We have synthesized a set of bis-pyranobenzoquinones through a direct and highly efficient approach based on a double intramolecular domino Knoevenagel hetero Diels-Alder reaction. These bis-pyranobenzoquinone derivatives are compounds whose skeletons have similarities to those of some anticancerous and leishmanicidal drugs. Considering that these drugs are substrates for some members of the ATP-binding cassette (ABC) family of proteins that confers a multidrug resistance (MDR) phenotype, we have carried out the biological evaluation of 20 bis-pyranobenzoquinones as modulators of the MDR phenotype in mammalian cell lines overexpressing P-glycoprotein, MRP1, or BCRP. Moreover, we also tested some of these compounds as potential MDR modulators in a Leishmania tropica line overexpressing a P-glycoprotein-like transporter. Compounds 9 and 10 are, in this work, the most promising reversal agents of MDR in human cancer cell lines, while compounds 4 and 20 showed potent reversal activity of MDR phenotype in the protozoan parasite Leishmania.

Insights into the molecular mechanism of action of Celastraceae sesquiterpenes as specific, non-transported inhibitors of human P-glycoprotein.

Dihydro-beta-agarofuran sesquiterpenes from Celastraceae have been recently shown to bind to human P-glycoprotein (Pgp), functioning as specific, mixed-type inhibitors of its drug transport activity, as well as multidrug resistance (MDR) modulators in vitro. However, nothing is known about whether such compounds are themselves transported by Pgp, or whether they affect Pgp expression as well as its activity, or about the location of their binding site within the protein. We performed transport experiments with a newly synthesized fluorescent sesquiterpene derivative, which retains the anti-Pgp activity of its natural precursor. This probe was poorly transported by Pgp, MRP1, MRP2 and BCRP transporters, compared with classical MDR substrates. Moreover, Pgp did not confer cross-resistance to the most potent dihydro-beta-agarofurans, which did not affect Pgp expression levels in several MDR cell lines. Finally, we observed competitive and non-competitive interactions between one of such dihydro-beta-agarofurans (Mama12) and classical Pgp modulators such as cyclosporin A, verapamil, progesterone, vinblastine and GF120918. These findings suggest that multidrug ABC transporters do not confer resistance to dihydro-beta-agarofurans and could not affect their absorption and biodistribution in the body. Moreover, we mapped their binding site(s) within Pgp, which may prove useful for the rational design of improved modulators based on the structure of dihydro-beta-agarofurans.