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

Screening Techniques for Drug Discovery in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by progressive and irreversible impairment of memory and other cognitive functions of the aging brain. Pathways such as amyloid beta neurotoxicity, tau pathogenesis and neuroinflammatory have been used to understand AD, despite not knowing the definite molecular mechanism which causes this progressive disease. This review attempts to summarize the small molecules that target these pathways using various techniques involving high-throughput screening, molecular modeling, custom bioassays, and spectroscopic detection tools. Novel and evolving screening methods developed to advance drug discovery initiatives in AD research are also highlighted.

Discovery of new symmetrical and asymmetrical nitrile-containing 1,4-dihydropyridine derivatives as dual kinases and P-glycoprotein inhibitors: synthesis, in vitro assays, and in silico studies

Two new series of symmetric (1a-h) and asymmetric (2a-l) 1,4-DHP derivatives were designed, synthesised, and evaluated as anticancer agents. In vitro anticancer screening of target compounds via National cancer institute “NCI” revealed that analogues 1g, 2e, and 2l demonstrated antiproliferative action with mean growth inhibition percentage “GI%” = 41, 28, and 64, respectively. The reversal doxorubicin (DOX) effects of compounds 1g, 2e, and 2l were examined and illustrated better cytotoxic activity with IC₅₀ =1.12, 3.64, and 3.57 µM, respectively. The most active anticancer analogues, 1g, 2e, and 2l, were inspected for their putative mechanism of action by estimating their epidermal growth factor receptor (EGFR), human epidermal growth factor receptor 2 (HER-2), and Bruton’s tyrosine kinase (BTK) inhibitory activities. Furthermore, the antimicrobial activity of target compounds was assessed against six different pathogens, followed by determining the minimum inhibitory concentration “MIC” values for the most active analogues. Molecular docking study was achieved to understand mode of interactions between selected inhibitors and different biological targets.

Design, Synthesis, Molecular Docking Study and Anti-Hepatocellular Carcinoma Evaluation of New Bis-Triazolothiadiazines

OBJECTIVE

The reaction of bis(4-amino-4H-1,2,4-triazole-3-thiol) with hydrazonoyl halides and α-halo-ketones gave a new series of bis-1,2,4-triazolo[3,4-b]thiadiazine derivatives.

METHODS

The structure of the new products was established on the basis of their elemental and spectral data (mass, 1H NMR, 13C NMR and IR) and an alternate method.

RESULTS

Several of the synthesized products were subjected to in vitro anticancer screening against human hepatocellular carcinoma (HepG-2) and the results showed that compounds 16, 14 and 12 have promising activities (IC50 value of 24.8±9.1, 28.3±0.5, and 31±2.9μM, respectively) compared with Harmine reference drug (IC50 value of 22.4±1.11 μM).

CONCLUSION

Moreover, molecular docking studies were performed to analyze the binding modes of the discovered hits into the active site of DYRK1A using iGEMDOCK.

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.

A High-Throughput Flow Cytometry Assay for Identification of Inhibitors of 3',5'-Cyclic Adenosine Monophosphate Efflux

Assays to identify small molecule inhibitors of cell transporters have long been used to develop potential therapies for reversing drug resistance in cancer cells. In flow cytometry, these approaches rely on the use of fluorescent substrates of transporters. Compounds which prevent the loss of cell fluorescence have typically been pursued as inhibitors of specific transporters, but further drug development has been largely unsuccessful. One possible reason for this low success rate could be a substantial overlap in substrate specificities and functions between transporters of different families. Additionally, the fluorescent substrates are often synthetic dyes that exhibit promiscuity among transporters as well. Here, we describe an assay in which a fluorescent analog of a natural metabolite, 3',5'-cyclic adenosine monophosphate (F-cAMP), is actively effluxed by malignant leukemia cells. The F-cAMP is loaded into the cell cytoplasm using a procedure based on the osmotic lysis of pinocytic vesicles. The flow cytometric analysis of the fluorescence retained in F-cAMP-loaded cells incubated with various compounds can subsequently identify inhibitors of cyclic AMP efflux (ICE).

Dimeric isoxazolyl-1,4-dihydropyridines have enhanced binding at the multi-drug resistance transporter

A series of dimeric isoxazolyl-1,4-dihydropyridines (IDHPs) were prepared by click chemistry and examined for their ability to bind the multi-drug resistance transporter (MDR-1), a member of the ATP-binding cassette superfamily (ABC). Eight compounds in the present study exhibited single digit micromolar binding to this efflux transporter. One monomeric IDHP m-Br-1c, possessed submicromolar binding of 510nM at MDR-1. Three of the dimeric IDHPs possessed <1.5µM activity, and 4b and 4c were observed to have superior binding selectivity compared to their corresponding monomers verses the voltage gated calcium channel (VGCC). The dimer with the best combination of activity and selectivity for MDR-1 was analog 4c containing an m-Br phenyl moiety in the 3-position of the isoxazole, and a tether with five ethyleneoxy units, referred to herein as Isoxaquidar. Two important controls, mono-triazole 5 and pyridine 6, also were examined, indicating that the triazole - incorporated as part of the click assembly as a spacer - contributes to MDR-1 binding. Compounds were also assayed at the allosteric site of the mGluR5 receptor, as a GPCR 7TM control, indicating that the p-Br IDHPs 4d, 4e and 4f with tethers of from n=2 to 5 ethylenedioxy units, had sub-micromolar affinities with 4d being the most efficacious at 193nM at mGluR5. The results are interpreted using a docking study using a human ABC as our current working hypothesis, and suggest that the distinct SARs emerging for these three divergent classes of biomolecular targets may be tunable, and amenable to the development of further selectivity.