Impact of Novel MDR Modulators on Human Cancer Cells: Reversal Activities and Induction Studies

Crystal structure of diethyl 6,12-dimethyl-3,9-di-p-tolyl-3,9-diazapentacyclo[6.4.0.02,7.04,11.05,10]dodecane-1,5-dicarboxylate, C32H38N2O4

C15H14N2O, triclinic, P 1 ‾ $P‾{1}$ (no. 2), a = 6.983(5) Å, b = 8.472(6) Å, c = 12.113(7) Å, β = 73.45°, V = 679.29(8) Å3, Z = 1, R gt (F) = 0.0566, wR ref (F 2) = 0.1875, T = 296 K.

The crystal structure of 3,10-bis(4-methoxyphenyl)-6,12-dibenzyl-2,9-acetyl-6,12-diazapentacyclo[6.3.1.02,7.04,11.05,9]dodecane – acetone (1/1), C45H48N2O5

C45H48N2O5, monoclinic, P21/c (no. 14), a = 21.3971(8) Å, b = 15.2249(6) Å, c = 11.2610(5) Å, β = 92.125(4)°, V = 3666.0(3) Å3, Z = 4, R gt(F) = 0.0519, wR ref(F 2) = 0.1308, T = 128.15 K.

MDR1 and cytochrome P450 gene-expression profiles as markers of chemosensitivity in human chronic myelogenous leukemia cells treated with cisplatin and Ru(III) metallocomplexes

Leukemia is a major type of cancer affecting a significant segment of the population, and especially children. In fact, leukemia is the most frequent childhood cancer, with 26 % of all cases, and 20 % mortality. The multidrug resistance phenotype (MDR) is considered one of the major causes of failure in cancer chemotherapy. The present study aimed to investigate the relationship between the expression of MDR1 and CYP450 genes in human chronic myelogenous leukemia cells (K-562) treated with cisplatin (cisPt) and two ruthenium-based coordinated complexes [cisCRu(III) and cisDRu(III)]. The tested compounds induced apoptosis in K-562 tumor cells as evidenced by caspase 3 activation. Results also revealed that the amplification of P-gp gene is greater in K-562 cells exposed to cisPt and cisCRu(III) than cisDRu(III). Taken together, all these results strongly demonstrate that MDR-1 overexpression in K-562 cells could be associated to a MDR phenotype, and moreover, it is also contributing to the platinum and structurally related compound, resistance in these cells.

Novel non-substrate modulators of the transmembrane efflux pump P-glycoprotein (ABCB1)

Novel non-substrate modulators of the transmembrane efflux pump P-gp have been profiled as nontoxic and mdr reversing agents.

Mechanisms of P-gp inhibition and effects on membrane fluidity of a new rifampicin derivative, 1,8-dibenzoyl-rifampicin

PURPOSE

To assess P-glycoprotein (P-gp)-modulation ability and the mechanisms of P-gp inhibition mediated by a new synthetic rifampicin derivative, 1,8-dibenzoyl-rifampicin (DiBenzRif), in an in vitro model of the blood-brain barrier (BBB), RBE4 cells, and in membrane mimetic models (liposomes).

METHODS

P-gp expression (western blot) and activity [rhodamine 123 accumulation studies] were assessed until 72h of exposure to DiBenzRif. The effects on intracellular ATP levels and on P-gp ATPase activity were studied using luciferin-luciferase bioluminescence assay. Membrane fluidity changes were tracked by steady-state anisotropy measurements. Non-P-gp-related rhodamine 123 accumulation was evaluated using liposomes prepared with the main lipids present in RBE4 cell membranes.

RESULTS

A significant increase in intracellular rhodamine 123 content was observed in DiBenzRif-treated cells at all tested time-points. This effect was associated with a significant reduction in ATP intracellular levels, the inhibition of P-gp ATPase activity and a significant increase in membrane fluidity. DiBenzRif also favoured rhodamine 123 accumulation in a liposomal model of RBE4 cells, suggesting that it may be useful in increasing intracellular levels of substances that passively diffuse into the cells.

CONCLUSION

DiBenzRif-induced inhibitory effect on P-gp increases xenobiotic accumulation in BBB cells, which may contribute to the development of therapeutic adjuvants to enhance brain penetration of drugs.

Fluorescent substrates for flow cytometric evaluation of efflux inhibition in ABCB1, ABCC1, and ABCG2 transporters

ATP binding cassette (ABC) transmembrane efflux pumps such as P-glycoprotein (ABCB1), multidrug resistance protein 1 (ABCC1), and breast cancer resistance protein (ABCG2) play an important role in anticancer drug resistance. A large number of structurally and functionally diverse compounds act as substrates or modulators of these pumps. In vitro assessment of the affinity of drug candidates for multidrug resistance proteins is central to predict in vivo pharmacokinetics and drug-drug interactions. The objective of this study was to identify and characterize new substrates for these transporters. As part of a collaborative project with Life Technologies, 102 fluorescent probes were investigated in a flow cytometric screen of ABC transporters. The primary screen compared substrate efflux activity in parental cell lines with their corresponding highly expressing resistant counterparts. The fluorescent compound library included a range of excitation/emission profiles and required dual laser excitation as well as multiple fluorescence detection channels. A total of 31 substrates with active efflux in one or more pumps and practical fluorescence response ranges were identified and tested for interaction with eight known inhibitors. This screening approach provides an efficient tool for identification and characterization of new fluorescent substrates for ABCB1, ABCC1, and ABCG2.

Dihydropyridines and multidrug resistance: previous attempts, present state, and future trends

Multidrug resistance is defined as the resistance of a tumor cell to the cytotoxic action of divergent drugs used in chemotherapy. Dihydropyridines are a class of calcium channel antagonists that were discovered to have a multidrug resistance reversing effect and prompted investigations resulting in the synthesis of hundreds of new derivatives. Most of the investigators tried to achieve two goals: a decrease in Ca²(+) channel-blocking activity and an increase in the multidrug resistance reversing effect. Most of the synthesized compounds failed in the later stages of studies especially in clinical trials because of pharmacokinetic or pharmacodynamic limitations. Therefore, it will be necessary to include new methods, such as combinatorial synthesis, and, more importantly, to apply computational methods based on global structure-activity relationship models that consider all problems. Moreover, some compounds should be synthesized that are effective on several multidrug resistance targets.

Efflux pump inhibitors: a strategy to combat P-glycoprotein and the NorA multidrug resistance pump

Multidrug resistance (MDR) is the cause of an ever-increasing number of problems in the treatment of cancers and bacterial infections. The active efflux of drugs contributes significantly to this phenomenon. This minireview summarizes recent advances in combating MDR, with particular emphasis on natural and synthetic efflux pump inhibitors of P-glycoprotein in resistant tumor cells and of the NorA MDR pump in Staphylococcus aureus.

Dihydropyridines: evaluation of their current and future pharmacological applications

The 1,4-dihydropyridines (DHPs), a class of drugs, possess a wide variety of biological and pharmacological actions, have represented one of the most important groups of calcium-channel-modulating agents and have experienced widespread use in the treatment of cardiovascular disease. Moreover, it has been demonstrated that DHPs could prove to be highly important as multidrug-resistance-reversing agents in cancer chemotherapy. Recent reports suggest that this class also has other notable activities, particularly as antimycobacterial and anticonvulsant agents. Finally, it might be possible for the DHP motif to serve as a scaffold for other pharmacological applications.