Effects of New 4-Aryl-1,4-Dihydropyridines and 4-Arylpyridines on Drug Efflux Mediated by Multidrug Resistance-Associated Protein 1

Unsymmetric dihydropyridines bearing 2-pyridyl methyl carboxylate as modulators of P-glycoprotein; synthesis and biological evaluation in resistant and non-resistant cancer cells

Multi-drug resistance (MDR) in cancer cells is often associated with overexpression of P-glycoprotein (P-gp or ABCB1 or MDR1); therefore, modulators of this transporter might be helpful in overcoming MDR. In this study, 16 novel unsymmetrical dihydropyridine (DHP) derivatives bearing 2-pyridyl methyl carboxylate at C3 and a nitroimidazole or nitrophenyl ring at C4 positions of the DHP ring were synthesized. Their cytotoxicity was tested against four human cancer cells by MTT assay. The reversal capacity of MDR was examined in P-gp overexpressing cells (MES-SA/DX5) by measuring the alteration of doxorubicin’s IC50 and performing flow cytometric determination of intracellular rhodamine 123 accumulation. The calcium channel blocking (CCB) activity, as a side effect of DHPs, was tested on the ileum of a guinea pig. Molecular docking was performed to explain the binding mode of compounds. Two derivatives, 4a and 4c, containing 4-nitrophenyl at C4 and possessing methyl (4a) and iso-propyl (4c) carboxylates at the C5 position of DHP core demonstrated superior cytotoxic and MDR reversal activities and lower CCB effect. Docking analysis confirmed the importance of the 4-nitrophenyl ring for P-gp inhibitory activity. Some of the synthesized DHP derivatives with considerable MDR reversal capacity could be promising compounds for further discovery of useful agents for management of drug resistant cancer.

Microwave irradiation: a green approach for the synthesis of functionalizedN-methyl-1,4-dihydropyridines

An eco-friendly and cost-effective, microwave-assisted green approach has been developed for the synthesis of diverse functionalized N-methyl-1,4-dihydropyridines (1,4-DHPs). This pseudo three-component reaction was carried out between two equivalents of (E)-N-methyl-1-(methylthio)-2-nitroethenamine (NMSM) and one equivalent of aromatic aldehydes under microwave irradiation at 100 °C without catalyst and solvent. Short reaction times, avoidance of toxic solvents or expensive, metallic and corrosive catalysts and no need for column chromatographic purification are among the valuable features of the presented method. Moreover, the “greenness” of the method was evaluated within the ambits of the defined green metrics such as atom economy, carbon efficiency, E-factor, reaction mass efficiency, overall efficiency, process mass intensity and solvent intensity and the method exhibited a good to excellent score.

Microwave-assisted green synthesis of N-methyl-1,4-dihydropyridines under eco-friendly conditions.

4-isoxazolyl-1,4-dihydropyridines: a tale of two scaffolds

The association of the isoxazole and dihydropyridine (DHP) ring systems fused at the 4'-isoxazolyl- to the 4-position of the DHP has produced a combination scaffold, the isoxazolyl-DHPs (IDHPs) with unique conformational characteristics. The IDHPs are useful in probing biological activity, as exemplified by our efforts in the fields of voltage gated calcium channel (VGCC) antagonists and inhibitors of the multi-drug resistance (MDR) transporter. A strategically placed methyl group produced a signifcant change at the VGCC, with (R)-(+)-1-phenyl-prop-2-yl (3.7 nM) > phenethyl (22.9 nM) > (S)-(-)-1-phenyl-prop-2-yl (210 nM), a eudismic ratio of 56.7. Branching at the C-5 of the isoxazole produced a 25% increase in MDR binding, and replacing the DHP C-3 ester with a functionalized amide also gave a dramatic increase in binding affinity. Opportunities for combined scaffolds - including examples containing IDHPs - are waiting to be discovered: because new biology is driven by new chemistry.

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.

Why we should be vigilant: drug cytotoxicity observed with in vitro transporter inhibition studies

From routine in vitro drug-transporter inhibition assays, observed inhibition is typically assumed from direct interaction with the transporter. Other mechanisms that possibly reduce substrate uptake are not frequently fully examined. The objective of this study was to investigate the association of transporter inhibition with drug cytotoxicity. From a pool of drugs that were identified as known ASBT or OCTN2 inhibitors, 21 drugs were selected to screen inhibitory potency of their prototypical substrate and cytotoxicity against three human sodium-dependent solute carrier (SLC) transporters: apical sodium-dependent bile acid transporter (ASBT), organic cation/carnitine transporter (OCTN2), and the excitatory amino acid transporter 4 (EAAT4) in stable cell lines. Twenty drugs showed apparent inhibition in OCTN2-MDCK and ASBT-MDCK. Four dihydropyridine calcium channel blockers were cytotoxic to MDCK cells, and the observed cytotoxicity of three of them accounted for their apparent OCTN2 inhibition, and consequently were classified as non-OCTN2 inhibitors. Meanwhile, since their cytotoxicity only moderately contributed to ASBT inhibition, these three were still considered ASBT inhibitors. Four other drugs showed apparent inhibition in EAAT4-HEK cells, and cytotoxicity of three drugs corresponded with their inhibition of this transporter. Therefore, cytotoxicity significantly affected EAAT4 observations. Results showed the potential of cytotoxicity as a mechanism that can account for apparent in vitro transporter inhibition. Drug cytotoxicity varied in different cell lines, which could increase false positives for pharmacophore development.

Design and synthesis of new symmetrical derivatives of dihydropyridine containing a pyridyl group on the 3, 5-positions and evaluation of their cytotoxic and multidrug resistance reversal activity

Today, chemotherapy is an important part in the treatment of several kinds of cancer; however, the development of drug resistance remains one of the major obstacles in successful chemotherapy. Several types of agents have been recognized as multidrug resistance (MDR) inhibitors, among which the 1,4-dihydropyridines (DHPs) have been investigated the most. P-glycoprotein inhibition has been reported as the main MDR reversal mechanism of DHPs, whilst other mechanisms such as inhibition of topoisomerase II have received less attention. Therefore, in this study new derivatives of DHP have been synthesized. Their cytotoxic activity and their effects in reversing atypical MDR have been evaluated. The results confirmed the appropriate effect of these compounds on atypical MDR. Although it was observed that these compounds had a moderate cytotoxic effect, the cytotoxicity of one compound on the K562 cell line (IC50 = 6.61 μM) was comparable with that of doxorubicin (IC50 = 4.17 μM). Finally, the Ca2+-channel antagonistic activity, an undesired effect for these compounds, was evaluated.

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.

Development of inhibitors of ATP-binding cassette drug transporters: present status and challenges

BACKGROUND

Multi-drug resistance (MDR) of cancer cells is an obstacle to effective chemotherapy of cancer. The ATP-binding cassette (ABC) transporters, including P-glycoprotein (ABCB1), MRP1 (ABCC1) and ABCG2, play an important role in the development of this resistance. An attractive approach to overcoming MDR is the inhibition of the pumping action of these transporters. Several inhibitors/modulators of ABC transporters have been developed, but cytotoxic effects and adverse pharmacokinetics have prohibited their use. The ongoing search for such inhibitors/modulators that can be applied in the clinic has led to three generations of compounds. The most recent inhibitors are more potent and less toxic than first-generation compounds, yet some are still prone to adverse effects, poor solubility and unfavorable changes in the pharmacokinetics of the anticancer drugs.

OBJECTIVE

This review provides an update of the published work on the development of potent modulators to overcome MDR in cancer cells, their present status in clinical studies and suggestions for further improvement to obtain better inhibitors.

METHODS

This review summarizes recent advances in the development of less toxic modulators, including small molecules and natural products. In addition, a brief overview of other novel approaches that can be used to inhibit ABC drug transporters mediating MDR has also been provided.

CONCLUSION

The multifactorial nature of MDR indicates that it may be important to develop modulators that can simultaneously inhibit both the function of the drug transporters and key signaling pathways, which are responsible for development of this phenomenon.

1H and 13C spectral assignment of 4-aryl-1,4,5,6,7,8-hexahydro-2,7,7,5-oxo-quinolines 3-substituted derivatives

The 1H and 13C NMR spectroscopic data for 4-aryl-1,4,5,6,7,8-hexahydro-2,7,7,5-oxo-quinoline 3-substituted derivatives have been fully assigned by the combination of one- and two dimensional experiments (DEPT, HMBC, HMQC, COSY, NOE).