ABSTRACT
We recently described the modulatory activities of apigenin homodimers linked by ethylene glycol units in multidrug- resistant breast cancer and leukemic cells overexpressing ABCB1 (P-glycoprotein, P-gp). To further improve the potency of these dimers, a small library of flavonoid homodimers and heterodimers were synthesized, and their in vitro activity in reversing cellular resistance to paclitaxel, along with structure-activity relationships (SAR), were evaluated using a P-gp-expressing human breast cancer cell line. Among these synthesized homodimers, many showed more potent reversing activity than that of the parent compound and verapamil. Two compounds in particular showed promising reversing activity at sub-micromolar concentrations with no cytotoxic effects. Regarding SAR trends, flavonoid dimers with nonpolar and hydrophobic substituents (e.g., methyl and ethyl groups) generally showed more potent resistance-reversing activity than that of dimers with polar and hydrophilic substituents (e.g. hydroxy groups) at the C3, C6, and C7 positions, but not at C5. In terms of substituent steric bulk at C6, it was found that the flavonoid dimer with methyl groups was optimal, with bulkier substituents leading to lower reversing activity. Comparisons of flavonoid heterodimers with the corresponding homodimers revealed that the two binding sites on P-gp for flavonoid moieties are quite similar to each other. Besides paclitaxel, these new compounds also increased drug accumulation and enhanced the cytotoxicity of other cancer drugs such as doxorubicin, vincristine, and vinblastine by decreasing the IC(50) values 4-45-fold.
Subject(s)
ATP Binding Cassette Transporter, Subfamily B, Member 1/chemistry , Dimerization , Drug Resistance, Multiple/drug effects , Flavonoids/chemistry , Flavonoids/pharmacology , ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism , Apigenin/chemistry , Cell Line, Tumor , Cell Survival/drug effects , Flavonoids/chemical synthesis , Humans , Microwaves , Molecular Structure , Paclitaxel/chemical synthesis , Paclitaxel/chemistry , Paclitaxel/pharmacology , Structure-Activity RelationshipABSTRACT
Drug resistance by overexpression of ATP-binding cassette (ABC) transporters is an impediment in the treatment of leishmaniasis. Flavonoids are known to reverse multidrug resistance (MDR) in Leishmania and mammalian cancers by inhibiting ABC transporters. Here, we found that synthetic flavonoid dimers with three (compound 9c) or four (compound 9d) ethylene glycol units exhibited a significantly higher reversing activity than other shorter or longer ethylene glycol-ligated dimers, with approximately 3-fold sensitization of pentamidine and sodium stibogluconate (SSG) resistance in Leishmania, respectively. This modulatory effect was dosage dependent and not observed in apigenin monomers with the linker, suggesting that the modulatory effect is due to its bivalent nature. The mechanism of reversal activity was due to increased intracellular accumulation of pentamidine and total antimony in Leishmania. Compared to other MDR modulators such as verapamil, reserpine, quinine, quinacrine, and quinidine, compounds 9c and 9d were the only agents that can reverse SSG resistance. In terms of reversing pentamidine resistance, 9c and 9d have activities comparable to those of reserpine and quinacrine. Modulators 9c and 9d exhibited reversal activity on pentamidine resistance among LeMDR1(-/-), LeMDR1(+/+), and LeMDR1-overexpressed mutants, suggesting that these modulators are specific to a non-LeMDR1 pentamidine transporter. The LeMDR1 copy number is inversely related to pentamidine resistance, suggesting that it might be involved in importing pentamidine into the mitochondria. In summary, bivalency could be a useful strategy for the development of more potent ABC transporter modulators and flavonoid dimers represent a promising reversal agent for overcoming pentamidine and SSG resistance in parasite Leishmania.
Subject(s)
Antifungal Agents/pharmacology , Antimony Sodium Gluconate/pharmacology , Antiprotozoal Agents/pharmacology , Flavonoids/pharmacology , Leishmania enriettii/drug effects , Pentamidine/pharmacology , ATP Binding Cassette Transporter, Subfamily B, Member 1/genetics , ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism , Animals , Apigenin/pharmacology , Chromatography, High Pressure Liquid , Dose-Response Relationship, Drug , Drug Resistance , Flavonoids/chemistry , Leishmania enriettii/genetics , Mass Spectrometry , Structure-Activity RelationshipABSTRACT
Much effort has been spent on searching for better P-glycoprotein- (P-gp-) based multidrug resistance (MDR) modulators. Our approach was to target the binding sites of P-gp using dimers of dietary flavonoids. A series of apigenin-based flavonoid dimers, linked by poly(ethylene glycol) chains of various lengths, have been synthesized. These flavonoid dimers modulate drug chemosensitivity and retention in breast and leukemic MDR cells with the optimal number of ethylene glycol units equal to 2-4. Compound 9d bearing four ethylene glycol units increased drug accumulation in drug-resistant cells and enhanced cytotoxicity of paclitaxel, doxorubicin, daunomycin, vincristine, and vinblastine in drug-resistant breast cancer and leukemia cells in vitro, resulting in reduction of IC50 by 5-50 times. This compound also stimulated P-gp's ATPase activity by 3.3-fold. Its modulating activity was presumably by binding to the substrate binding sites of P-gp and disrupting drug efflux.
