Flavonoid derivatives as selective ABCC1 modulators: Synthesis and functional characterization

A series of chromones, bearing substituted amino groups or N-substituted carboxamide moieties in position 2, was synthesized and characterized in cellular assays for modulation of the ABC transporters ABCC1 (MDCKII-MRP1 cells), ABCB1 (Kb-V1 cells) and ABCG2 (MCF-7/Topo cells). The most potent ABCC1 modulators identified among these flavonoid-type compounds were comparable to the reference compound reversan regarding potency, but superior in terms of selectivity concerning ABCB1 and ABCG2 (2-[4-(Benzo[c][1,2,5]oxadiazol-5-ylmethyl)piperazin-1-yl]-5,7-dimethoxy-4H-chromen-4-one (51): ABCC1, IC50 11.3 μM; inactive at ABCB1 and ABCG2). Compound 51 was as effective as reversan in reverting ABCC1-mediated resistance to cytostatics in MDCKII-MRP1 cells and proved to be stable in mouse plasma and cell culture medium. Modulators, such as compound 51, are of potential value as pharmacological tools for the investigation of the (patho)physiological role of ABCC1.

Intracellular targeted co-delivery of shMDR1 and gefitinib with chitosan nanoparticles for overcoming multidrug resistance

Nowadays, multidrug resistance and side effects of drugs limit the effectiveness of chemotherapies in clinics. P-glycoprotein (P-gp) (MDR1), as a member of the ATP-binding cassette family, acts on transporting drugs into cell plasma across the membrane of cancer cells and leads to the occurrence of multidrug resistance, thus resulting in the failure of chemotherapy in cancer. The main aims of this research were to design a nanodelivery system for accomplishing the effective co-delivery of gene and antitumor drug and overcoming multidrug resistance effect. In this study, shMDR1 and gefitinib-encapsulating chitosan nanoparticles with sustained release, small particle size, and high encapsulation efficiency were prepared. The serum stability, protection from nuclease, and transfection efficiency of gene in vitro were investigated. The effects of co-delivery of shMDR1 and gefitinib in nanoparticles on reversing multidrug resistance were also evaluated by investigating the cytotoxicity, cellular uptake mechanism, and cell apoptosis on established gefitinib-resistant cells. The results demonstrated that chitosan nanoparticles entrapping gefitinib and shMDR1 had the potential to overcome the multidrug resistance and improve cancer treatment efficacy, especially toward resistant cells.

Do drugs have access to the P-glycoprotein drug-binding pocket through gates?

The P-glycoprotein efflux mechanism is being studied since its identification as a leading protagonist in multidrug resistance. Recently, it was suggested that drugs enter the drug-binding pocket (DBP) through gates located between the transmembrane domains. For both a substrate and a modulator, the potential of mean force curves along the reaction coordinate obtained with the WHAM approach were similar, with no activation energy required for crossing the gate. Moreover, drug transit from bulk water into the DBP was characterized as an overall free-energy downhill process.

Do adsorbed drugs onto P-glycoprotein influence its efflux capability?

The membrane biophysical aspects by which multidrug resistance (MDR) relate to the ABC transporter function still remain largely unknown. Notwithstanding the central role that efflux pumps like P-glycoprotein have in MDR onset, experimental studies classified additionally the lipid micro-environment where P-gp is inserted as a determinant for the increased efflux capability demonstrated in MDR cell lines. Recently, a nonlinear model for drug-membrane interactions showed that, upon drug adsorption, long-range mechanical alterations are predicted to affect the P-gp ATPase function at external drug concentrations of ∼10-100 μM. However, our results also show that drug adsorption may also occur at P-gp nucleotide-binding domains where conformational changes drive the efflux cycle. Thus, we assessed the effect of drug adsorption to both protein-water and lipid-water interfaces by means of molecular dynamics simulations. The results show that free energies of adsorption are lower for modulators in both lipid/water and protein/water interfaces. Important differences in drug-protein interactions, protein dynamics and membrane biophysical characteristics were observed between the different classes. Therefore, we hypothesize that drug adsorption to the protein and lipid-water interface accounts for a complex network of events that affect the ability of transporters to efflux drugs.