Synthesis,in silico and in vitro studies of new 1,4-dihydropiridine derivatives for antitumor and P-glycoprotein inhibitory activity

P-glycoprotein (P-gp) is one of the cell membrane pumps which mediate the efflux of molecules such as anticancer drugs to the extracellular matrix of tumor cells. P_gp is a member of the ATP-binding cassette (ABC) transporter family that is implicated in cancer multidrug resistance (MDR). Since MDR is a contributor to cancer chemotherapy failure, modulation of efflux pumps is a viable therapeutic strategy. In this study, new synthetic 1,4 dihydropiridine (DHP) derivatives containing thiophenyl substitution were tested as inhibitors of P-gp. Efflux assay was conducted to evaluate the intracellular accumulation of Rhodamine123 (Rh123) as a pump substrate. MTT assay, cell cycle analysis and in silico methods were also examined. Flow cytometric analysis revealed that synthetic DHP derivatives (15 µM) increased intracellular concentration of the substrate by 2–3 folds compared with verapamil as a standard P-gp inhibitor. MTT assay on EPG85-257P and its drug-resistant EPG85-257RDB cell line revealed antitumor effects (30–45%) for new DHP derivatives at 15 µM following 72 h incubation. However, MTT test on normal cell line showed negligible toxic effects. Finally combination of synthetic derivatives with doxorubicin showed that these compounds decrease IC50 of doxorubicin in resistant cell lines from 9 to 1.5 µM. Sub-G1 peak-related apoptotic cells showed a stronger effect of synthetic compounds at 5 µM compared with verapamil. Molecular dynamic results showed a high binding affinity between DHP derivative and protein at drug binding site. Findings of these biological tests indicated the antitumor activity and P-gp inhibitory effects of new 1,4-DHP derivatives.     

3,5-dibenzoyl-1,4-dihydropyridines: synthesis and MDR reversal in tumor cells

Fifteen 4-phenyl-3,5-dibenzoyl-1,4-dihydropyridines (BzDHPs) (1-15) substituted at the 4-phenyl ring were synthesized and compared to their cytotoxic activity and multidrug resistance (MDR)-reversing activity in in vitro assay systems. Among them, 2-CF3 (5) (IC50=8.7 microM), 2-Cl (11) (IC50=7.0 microM) and 3-Cl (12) (IC50=7.0 microM) derivatives showed the highest cytotoxic activity against human oral squamous carcinoma (HSC-2) cells. The activity of P-glycoprotein (Pgp) response for MDR in tumor cells was reduced by some of derivatives (3, 4, 8, 12), verapamil (VP) and nifedipine (NP). These data suggest that 3,5-dibenzoyl-4-(3-chlorophenyl)-1,4-dihydro-2,6-dimethylpyridine (12) can be recommended as a new drug candidate for MDR cancer treatment.     

Molecular docking studies and in vitro screening of new dihydropyridine derivatives as human MRP1 inhibitors

The overexpression of multidrug resistance protein 1 (MRP1) by tumor cells results in multidrug resistance (MDR) to structurally unrelated anticancer drugs. Circumvention of MDR by combination of chemosensitizers with antitumor compounds is a new field of investigation in cancer chemotherapy. Much effort has been put-in recently to identify the modulators/inhibitors of MRP1 to overcome the MDR. 1,4-Dihydropyridine (DHP) derivatives are indicated to be a new class of MRP1 inhibitors in cancer treatment. Molecular docking studies were carried out on 48 newly synthesized DHP derivatives with the crystal structure of MRP1 to gain some structural insights on the binding mode and possible interactions with the active site of MRP1 (NBD1). The 10 top-ranked molecules were selectively evaluated, experimentally for their MRP1 inhibitory effect using the insect cell membrane MRP1 ATPase assay. The inhibitory capacity (IC(50) concentrations) of the test compounds was compared with the reported IC(50)- or the K(i)-concentrations for benzbromarone, a standard MRP1 inhibitor. Amongst the compounds tested, compounds IA(1) and IIA(5) were found to exhibit a potent MRP1 inhibitory action with IC(50) values of 20±4 and 14±2 μM (mean±SD), respectively as compared to benzbromarone (IC(50)=4 μM). The compound IIA(5), in particular was found to be more potent than IA(1) in accordance with the docking results. These new DHP derivatives possess promising characteristics for their development as MDR reversal agents.     

Reversal of P-glycoprotein-mediated multidrug resistance by doxorubicin and quinine co-loaded liposomes in tumor cells

Multidrug resistance (MDR) is a major obstacle to successful clinical cancer chemotherapy. Currently, there is still unsatisfactory demand for innovative strategies as well as effective and safe reversing agent to overcome MDR. In this study, we developed a novel nanoformulation, in which doxorubicin hydrochloride (DOX) and quinine hydrochloride (QN) were simultaneously loaded into liposomes by a pH-gradient method for overcoming MDR and enhancing cytotoxicity in a doxorubicin-resistant human breast cancer cell line (MCF-7/ADR). The various factors were investigated to optimize the formulation and manufacturing conditions of DOX and QN co-loaded liposomes (DQLs). The DQL showed uniform size distribution and high encapsulation efficiency (over 90%) for both the drugs. Furthermore, DQLs significantly displayed high intracellular accumulation and potential of MDR reversal capability in MCF-7/ADR cells through the cooperation of DOX with QN, in which QN played the role as a MDR reversing agent. The IC₅₀ of DQL0.5:1 with the DOX/QN/SPC weight ratio of 0.5:1:50 was 1.80?±?0.03?μg/mL, which was 14.23 times lower than that of free DOX in MCF-7/ADR cells. And the apoptotic percentage induced by DQL0.5:1 was also increased to 62.2%. These findings suggest that DQLs have great potential for effective treatment of MDR cancer.     

Cytotoxicity of new polyfluorinated 1,4-naphtoquinones with diverse substituents in the quinone moiety

Fluorinated derivatives of 1,4-naphthoquinones are highly potent inhibitors of Cdc25A and Cdc25B phosphatases and growth of tumor cells. Eight new derivatives of polyfluoro-1,4-naphthoquinone were synthesized and their cytotoxicity in human myeloma, human mammary adenocarcinoma, mouse fibroblasts and primary mouse fibroblast cells as well as their mutagenic and antioxidant properties in a Salmonella tester strain were studied. The efficiency of suppressing the growth of two lines of tumor cells decreased in the order: 2-(2-hydroxy-ethylamino)-3,5,6,7,8-pentafluoro-1,4-naphthoquinone (1), 2,3-dimethoxy-5,6,7,8-tetrafluoro-1,4-naphthoquinone (2), 2-[2-hydroxyethyl(methyl)amino]-3,5,6,7,8-pentafluoro-1,4-naphthoquinone (3), 2-morpholino-3,5,6,7,8-pentafluoro-1,4-naphthoquinone (4), 2-[bis-(2-hydroxyethyl)amino]-3,5,6,7,8-pentafluoro-1,4-naphthoquinone (5), 2-[(2-hydroxy)ethylsulfanyl)]-5,6,7,8-tetrafluoro-1,4-naphthoquinone (6), 2-methoxy-3,5,6,7,8-pentafluoro-1,4-naphthoquinone (7), and 1,4-dioxo-3-(1-pyridinio)-1,4-dihydro-5,6,7,8-tetrafluoronaphthalene-2-olate (8). Taking into account these data together with the better cytotoxic effect against cancer cells as compared with normal mammalian cells, protecting of bacterial cells from spontaneous and H₂O₂-dependent mutagenesis, and lower general toxicity of the compounds towards different cells, one can propose that compounds 3-5 may be considered as useful potential inhibitors of growth of tumor cells.     

Design,synthesis, and cytotoxic activity of novel 7-substituted camptothecin derivatives incorporating piperazinyl-sulfonylamidine moieties

In our continuing search for camptothecin (CPT)-derived antitumor drugs, novel 7-substituted CPT derivatives incorporating piperazinyl-sulfonylamidine moieties were designed, synthesized and evaluated for cytotoxicity against five tumor cell lines (A-549, MDA-MB-231, MCF-7, KB, and KB-VIN). All of the derivatives showed promising in vitro cytotoxic activity against the tested tumor cell lines, and were more potent than irinotecan. Remarkably, most of the compounds exhibited comparable cytotoxicity against the multidrug-resistant (MDR) KB-VIN and parental KB tumor cell lines, while irinotecan lost activity completely against KB-VIN. Especially, compounds 13r and 13p (IC₅₀ 0.38 and 0.85 μM, respectively) displayed the greatest cytotoxicity against the MDR KB-VIN cell line and merit further development into preclinical and clinical drug candidates for treating cancer, including MDR phenotype.     

2DG enhances the susceptibility of breast cancer cells to doxorubicin

2DG causes cytotoxicity in cancer cells by disrupting thiol metabolism while Doxorubicin (DOX) induces cytotoxicity in tumor cells by generating reactive oxygen species (ROS). Here we examined the combined cytotoxic action of 2DG and DOX in rapidly dividing T47D breast cancer cells vs. slowly growing MCF-7 breast cancer cells. T47D cells exposed to the combination of 2DG/DOX significantly decreased cell survival compared to controls, while 2DG/DOX had no effect on MCF-7 cells. 2DG/DOX also disrupted the oxidant status of T47D treated cells, decreased intracellular total glutathione and increased glutathione disulfide (%GSSG) compared to MCF-7 cells. Lipid peroxidation increased in T47D cells treated with 2DG and/or DOX, but not in MCF-7 cells. T47D cells were significantly protected by NAC, indicating that the combined treatment exerts its action by increasing ROS production and disrupting antioxidant stores. When we inhibited glutathione synthesis with BSO, T47D cells became more sensitive to 2DG/DOX-induced cytotoxicity, but NAC significantly reversed this cytotoxic effect. Finally, 2DG/DOX, and BSO significantly increased the %GSSG in T47D cells, an effect which was also reversed by NAC. Our results suggest that exposure of rapidly dividing breast cancer cells to 2DG/DOX enhances cytotoxicity via oxidative stress and via disruptions to thiol metabolism.     

Redox-responsive nanoparticles from the single disulfide bond-bridged block copolymer as drug carriers for overcoming multidrug resistance in cancer cells

Multidrug resistance (MDR) is a major impediment to the success of cancer chemotherapy. The intracellular accumulation of drug and the intracellular release of drug molecules from the carrier could be the most important barriers for nanoscale carriers in overcoming MDR. We demonstrated that the redox-responsive micellar nanodrug carrier assembled from the single disulfide bond-bridged block polymer of poly(ε-caprolactone) and poly(ethyl ethylene phosphate) (PCL-SS-PEEP) achieved more drug accumulation and retention in MDR cancer cells. Such drug carrier rapidly released the incorporated doxorubicin (DOX) in response to the intracellular reductive environment. It therefore significantly enhanced the cytotoxicity of DOX to MDR cancer cells. It was demonstrated that nanoparticular drug carrier with either poly(ethylene glycol) or poly(ethyl ethylene phosphate) (PEEP) shell increased the influx but decreased the efflux of DOX by the multidrug resistant MCF-7/ADR breast cancer cells, in comparison with the direct incubation of MCF-7/ADR cells with DOX, which led to high cellular retention of DOX. Nevertheless, nanoparticles bearing PEEP shell exhibited higher affinity to the cancer cells. The shell detachment of the PCL-SS-PEEP nanoparticles caused by the reduction of intracellular glutathione significantly accelerated the drug release in MCF-7/ADR cells, demonstrated by the flow cytometric analyses, which was beneficial to the entry of DOX into the nuclei of MCF-7/ADR cells. It therefore enhanced the efficiency in overcoming MDR of cancer cells, which renders the redox-responsive nanoparticles promising in cancer therapy.     

The carotenoid fucoxanthin can sensitize multidrug resistant cancer cells to doxorubicin via induction of apoptosis,inhibition of multidrug resistance proteins and metabolic enzymes

BackgroundMultidrug resistance (MDR) causes failure of doxorubicin therapy of cancer cells, which develops after or during doxorubicin treatment resulting in cross-resistance to structurally and functionally-unrelated other anticancer drugs. MDR is multifactorial phenomenon associated with overexpression of ATP-binding cassette (ABC) transporters, metabolic enzymes, impairment of apoptosis, and alteration of cell cycle checkpoints. The cancer-prevention of the dietary carotenoid; fucoxanthin (FUC) has been extensively explored. Nevertheless, the underlying mechanism of its action is not full elucidated.Hypothesis/PurposeInvestigation of the underlying mechanism of MDR reversal by the dietary carotenoid fucoxanthin (FUC) and its ability to enhance the doxorubicin (DOX) cytotoxicity in resistant breast (MCF-7/ADR), hepatic (HepG-2/ADR), and ovarian (SKOV-3/ADR) cell lines.MethodsThe synergistic interaction of FUC and DOX was evaluated using several techniques, viz.; MTT assay, ABC transporter function assays using FACS and fluorimetry, enzyme activity via spectroscopy and luminescence assays, and apoptosis assay using FACS, and gene expression using RTPCR.ResultsFUC (20 µM) synergistically enhanced the cytotoxicity of DOX and significantly reduced the dose of DOX (FR) in DOX resistant cells (MCF-7/ADR), hepatic (HepG-2/ADR), and ovarian (SKOV-3/ADR) to 8.42-(CI= 0.25), 6.28-(CI= 0.32), and 4.56-fold (CI=0.37) (P<0.001). FUC significantly increased the accumulation of DOX more than verapamil in resistant cells by 2.70, 2.67, and 3.95-fold of untreated cells (p<0.001), respectively. A FUC and DOX combination significantly increased the Rho123 accumulation higher than individual drugs by 2.36-, 2.38-, 1.89-fold verapamil effects in tested cells (p<0.001), respectively. The combination of the FUC and DOX decreased ABCC1, ABCG2, and ABCB1 expression. The FUC and DOX combination increased the levels and activity of caspases (CASP3, CASP8) and p53, while decreased the levels and activity of CYP3A4, GST, and PXR in resistant cancer cells. The combination induced early/late apoptosis to 91.9/5.4% compared with 0.0/0.7% of untreated control.ConclusionOur data suggests a new dietary and therapeutic approach of combining the FUC with DOX to overcome multidrug resistance in cancer cells. However, animal experiments should be conducted to confirm the findings before applying the results into clinical trials.     

Altered Expression of Proliferation-Inducing and Proliferation-Inhibiting Genes Might Contribute to Acquired Doxorubicin Resistance in Breast Cancer Cells

This study was designed to investigate the molecular changes that may develop during exposure of breast cancer cells to anticancer agents and that may lead to acquired resistance. We used two breast cancer cell lines, a parental (MCF7/WT) and a doxorubicin-resistant (MCF7/DOX) one. Cell survival, cell cycle distribution and RT-PCR expression level of genes involved in DNA damage response, MDR1, GST and TOPOIIα were measured. MCF7/DOX cells were five-fold more resistant to doxorubicin (DOX) than the MCF7/WT cells. DOX treatment causes arrest of MCF7/DOX cells in G1 and G2 phases of cell cycle whereas MCF7/WT cells were arrested in S-phase. The molecular changes in both cell lines due to DOX treatment could be classified into: (1) the basal level of p53, p21, BRCA1, GST and TOPOIIα mRNA was higher in MCF7/DOX than MCF7/WT. During DOX treatment, the expression level of these genes decreased in both cell lines but the rate of down-regulation was faster in MCF7/WT than MCF7/DOX cells. (2) The expression level of MDR1 was the same in both cell lines but 48 and 72 h of drug treatment, MDR1 disappeared in MCF7/WT but still expressed in MCF7/DOX. (3) There was no change in the expression level of BAX, FAS and BRCA2 in both cell lines. Conclusively, after validation in clinical samples, overexpression of genes like BRCA1, p53, p21, GST, MDR1 and TOPOIIα could be used as a prognostic biomarker for detection of acquired resistance in breast cancer and as therapeutic targets for the improvement of breast cancer treatment strategies.     

Synthesis and photochemical transformation of 3β,21-dihydroxypregna-5,7-dien-20-one to novel secosteroids that show anti-melanoma activity

We have synthesized 3β,21-dihydroxypregna-5,7-dien-20-one (21(OH) 7DHP) and used UVB radiation to induce its photoconversion to analogues of vitamin D (pD), lumisterol (pL) and tachysterol (pT). The number and character of the products and the dynamics of the process were dependent on the UVB dose. The main products: pD and pT compounds were characterized by UV absorption, MS and NMR spectroscopy after RP-HPLC chromatography. In addition, formation of multiple oxidized derivatives of the primary products was detected and one of these derivatives was characterized as oxidized 21-hydroxyisotachysterol compound (21(OH)oxy-piT). These newly synthesized compounds inhibited growth of human melanoma cells in a dose dependent manner, with greater or equal potency to calcitriol. 3β,21-Dihydroxy-9β,10α-pregna-5,7-dien-20-one (21(OH)pL) and 21(OH)oxy-piT had higher potency against pigmented melanoma cells, while the EC(50) for compounds 21(OH)7DHP and (5Z,7E)-3β,21-dihydroxy-9,10-secopregna-5,7,10(19)-trien-20-one (21(OH)pD) were similar in both pigmented and non-pigmented cells. Moreover, 21(OH)7DHP and its derivatives inhibited proliferation of human epidermal HaCaT keratinocytes, albeit at a lower activity compared to melanoma cells. Importantly, 21(OH)7DHP derivatives strongly inhibited the colony formation of human melanoma cells with 21(OH)pD being the most potent. The potential mechanism of action of newly synthesized compounds was similar to that mediated by 1,25(OH)(2)D(3) and involved ligand-induced translocation of vitamin D receptor into the nucleus. In summary, we have characterized for the first time products of UVB-induced conversion of 21(OH)7DHP and documented that these compounds have selective, inhibitory effects on melanoma cells.     

Synthesis and protective effects of coumarin derivatives against oxidative stress induced by doxorubicin

The use of doxorubicin (DOX) in the treatment of solid tumors is limited by cardiotoxicity essentially due to oxidative stress generation. The aim of this study was to identify coumarin derivatives displaying a protective antioxidant activity without affecting DOX antitumoral efficiency. A set of eighteen coumarinic derivatives was synthesized. Their antioxidant power was evaluated in vitro with the FRAP (ferric reducing ability of plasma) method and in human breast adenocarcinoma MCF7 cells using H(2)DCFDA (2',7'-dichlorodihydrofluorescein diacetate) in a cytometric analysis. 4-Methyl-7,8-dihydroxycoumarin was found to exhibit an important antioxidant strength, a low cytotoxicity, and could decrease ROS (reactive oxygen species) production generated by DOX treatment without affecting DOX cytotoxicity in MCF7 cells.     

Sensitization of multidrug-resistant malignant cells by liposomes co-encapsulating doxorubicin and chloroquine through autophagic inhibition

Adenosine triphosphate (ATP)-binding cassette (ABC) transporters play a key role in the development of multidrug resistance (MDR) in cancer cells. P-glycoprotein (P-gp) and multidrug resistance-associated protein 1 (MRP1) are important proteins in this superfamily which are widely expressed on the membranes of multidrug resistance (MDR) cancer cells. Besides, upregulation of cellular autophagic responses is considered a contributing factor for MDR in cancer cells. We designed a liposome system co-encapsulating a chemotherapeutic drug (doxorubicin hydrochloride, DOX) and a typical autophagy inhibitior (chloroquine phosphate, CQ) at a weight ratio of 1:2 and investigated its drug resistance reversal mechanism. MTT assay showed that the IC₅₀ of DOX/CQ co-encapsulated liposome in DOX-resistant human breast cancer cells (MCF7/ADR) was 4.7?±?0.2?μM, 5.7-fold less than that of free DOX (26.9?±?1.9 μM), whereas it was 19.5-fold in doxorubicin-resistant human acute myelocytic leukemia cancer cells (HL60/ADR) (DOX/CQ co-encapsulated liposome 1.2?±?0.1?μM, free DOX 23.4?±?2.8?μM). The cellular uptake of DOX increased upon addition of free CQ, indicating that CQ may interact with P-gp and MRP1; however, the expressions of P-gp and MRP1 remained unchanged. In contrast, the expression of the autophagy-related protein LC3-II increased remarkably. Therefore, the mechanism of MDR reversal may be closely related to autophagic inhibition. Evaluation of anti-tumor activity was achieved in an MCF-7/ADR multicellular tumor spheroid model and transgenic zebrafish model. DOX/CQ co-encapsulated liposome exerted a better anti-tumor effect in both models than that of liposomal DOX or DOX alone. These findings suggest that encapsulating CQ with DOX in liposomes significantly improves the sensitivity of DOX in DOX-resistant cancer cells.     

In vitro activities of native and designed peptide antibiotics against drug sensitive and resistant tumor cell lines

In order to develop peptide agents with reduced length and enhanced tumoricidal activity, we have designed gaegurin 6 (GGN6) derivatives through deletions and/or substitutions of amino acids. The deletion of hydrophobic amino terminal region completely abolished antitumor activity whereas the deletion of carboxy terminal region had little influence on antitumor activity. Antitumor activity of the PTP peptides did not correlate with antibacterial activity. PTP7, the most potent derivative, was found to have comparable antitumor activity to GGN6 in spite of reduced number of amino acids which is about half the size of gaegurin 6; furthermore, it showed little cytotoxicity on PBMCs and RBCs. GGN6 and PTP7 also showed equivalent cytotoxicity against drug sensitive (MCF-7) and multidrug-resistant cell lines (MCF-7/DOX). Plasma membrane blebbing and DNA fragmentation of peptide-treated tumor cells indicated that the peptides could induce apoptosis in tumor cells. These results suggest that GGN6 and its derivatives can be developed as new anticancer agents and may provide a new strategy for overcoming MDR which is a major problem in cancer therapy.     

Synthesis and evaluation of furoxan-based nitric oxide-releasing derivatives of tetrahydroisoquinoline as anticancer and multidrug resistance reversal agents

Multidrug resistance in tumor cells poses a major obstacle to efficient chemotherapy. Several types of agents have been recognized as multidrug resistance inhibitors, among which the tetrahydroisoquinolines is the most studied. In current study 16 furoxan-based nitric oxide-releasing derivatives of tetrahydroisoquinoline were synthesized. Their cytotoxic activities and effects in reversing multidrug resistance have been evaluated. The results revealed that these compounds had moderate cytotoxic effects. Compounds 7a-f, 7h, and 7l showed higher cytotoxicities than the rest, but lower than adriamycin on K562 cell line. Compounds 7d, 7f, and 7l exhibited potent MDR reversal activities on K562/A02 cell line. The accumulation assay indicated that compounds 7d, 7f, and 7l significantly increased the intracellular accumulation of rhodamine123 in K562/A02 cells. Furthermore, these three compounds produced high concentrations of NO in K562/A02 cells. Potentially, the high concentrations of NO produced by NO donor moieties will lead to an increased cytotoxicity to K562/A02 cells. Our results suggested that compounds 7d, 7f, and 7l had anticancer effects, as well as multidrug resistance reversal effects.     

Synthesis and Cytotoxicity Evaluation of Panaxadiol Derivatives

In this study, 13 panaxadiol (PD) derivatives were synthesized via reactions with aromatic compounds and amino acids. Following this, the cytotoxicity of these compounds was evaluated against four cancer cell lines (human hepatoma cells HepG‐2, human lung cancer cells A549, human breast cancer cells MCF‐7, and human colon cancer cells HCT‐116) and one normal cell lines (human gastric epithelial cells GES‐1). The results showed that the panaxadiol derivatives 3 , 12 , and 13 showed significant inhibition of cellular proliferation against cancer cells compared with PD, and the panaxadiol derivative 12 had the lowest IC₅₀ value for A549 (IC₅₀=18.91±1.03 μm ). For MCF‐7 cells, most compounds exhibited good inhibition of cellular proliferation, and the panaxadiol derivative 13 showed the strongest inhibitory effect (IC₅₀=8.62±0.23 μm ), which significantly increased the cytotoxicity of PD and was stronger than the positive control (mitomycin). For normal cells, all compounds exhibited low or no toxic effects; thus, these derivatives can be used to develop novel antiproliferative agents.     

Multidrug-resistant cancer cell susceptibility to cytotoxic quassinoids, and cancer chemopreventive effects of quassinoids and canthin alkaloids

Twenty-three quassinoids (1-23), which were isolated previously from Simaroubaceous plants, were evaluated for cytotoxicity against three multidrug-resistant cancer cell lines, KB-VIN, KB-7d, and KB-CPT. Nine compounds (2-7 and 9-11) showed significant cytotoxicity in all three cell lines. Compounds 1, 12-14, 17, and 20 demonstrated significant activity against the KB-7d and KB-CPT cell lines, and compounds 18, 19, and 23 revealed notable activity only against KB-7d cells. Structure-activity relationships were drawn based on these data. In addition, six quassinoid derivatives (24-29) and four canthin alkaloids (30-33), which were isolated from Brucea antidysenterica, were examined for their inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate (TPA) induced Epstein-Barr virus early antigen (EBV-EA) activation as cancer chemopreventive agents. All of these compounds demonstrated significant inhibitory effects against EBV-EA activation.     

Design,semisynthesis and potent cytotoxic activity of novel 10-fluorocamptothecin derivatives

Fluorination is a well-known strategy for improving the bioavailability of bioactive molecules in the lead optimization phase of drug discovery projects. In an attempt to improve the antitumor activity of camptothecins (CPTs), novel 10-fluoro-CPT derivatives were designed, synthesized and evaluated for cytotoxicity against five human cancer cell lines (A-549, MDA-MB-231, KB, KB-VIN and MCF-7). All of the derivatives showed more potent in vitro cytotoxic activity than the clinical CPT-derived drug irinotecan against the tumor cell lines tested, and most of them showed comparable or superior potency to topotecan. Remarkably, compounds 16b (IC₅₀, 67.0 nM) and 19b (IC₅₀, 99.2 nM) displayed the highest cytotoxicity against the multidrug-resistant (MDR) KB-VIN cell line and merit further development as preclinical drug candidates for treating cancer, including MDR phenotype. Our study suggested that incorporation of a fluorine atom into position 10 of CPT is an effective method for discovering new potent CPT derivatives.     

Novel 1,4-dihydropyridine induces apoptosis in human cancer cells through overexpression of Sirtuin1

1,4-Dihydropyridines (1,4-DHPs) are important as a class of heterocyclic compounds that exhibit wide range of biological actions. Many of its derivatives are already characterized as medicinally important drugs and used worldwide. In this study, we have screened some novel Hantzsch 1,4-DHP compounds using both in silico (QSAR and Pharmacophore) and in vitro (cytotoxic screening). 1,4-DHP showed selective cytotoxicity against five human cancerous cell lines; A375, A549, HeLa, HepG2 and SH-SY5Y but limited effect towards normal skin keratinocyte (HaCaT), lung fibroblast (WL-38) and healthy peripheral blood mononuclear cells. In A375 and HepG2 cells, one of the 1,4-DHP derivative (DHP-8) was found to inhibit cell proliferation, and simultaneously increased the apoptotic population as well as mitochondrial membrane depolarization. Furthermore, the mitochondrial signal was triggered with the activation of cleaved Caspase9, Caspase3 and PARP. The treatment with DHP-8 also increased the expression level of SIRT1, subsequently decreasing the level of pAKT^ser473 and survivin. Reduced pAKT^ser473 expression led to decrease the phosphorylated inactive form of GSK3β^ser9 and as a result, proteasomal degradation of Mcl-1 occurred in both the cell lines. Here, we suggest that the apoptotic effect of DHP-8 in A375 and HepG2 cells was mediated by AKT and survivin pathways through SIRT1 activation. The involvement of DHP-8 in SIRT1 activation was further verified by co-treatment of nicotinamide with DHP-8 in both A375 and HepG2 cells. Overall, this study emphasizes the possible potential and therapeutic role of DHP-8 in skin and liver cancer.     

Synthesis and chemical characterization of 2-methoxy-N(10)-substituted acridones needed to reverse vinblastine resistance in multidrug resistant (MDR) cancer cells

In an attempt to find clinically useful modulators of multidrug resistance (MDR), a series of 19 N(10)-substituted-2-methoxyacridone analogues has been synthesized. 2-Methoxyacridone and its derivatives (1-19) were synthesized. Compound 1 was prepared by the Ullmann condensation of o-chlorobenzoic acid and p-anisidine followed by cyclization using polyphosphoric acid. This compound undergoes N-alkylation in the presence of phase transfer catalyst (PTC). Stirring of 2-methoxy acridone with 1-bromo-3-chloropropane or 1-bromo-4-chlorobutane in a two-phase system consisting of organic phase (tetrahydrofuran) and 6N potassium hydroxide in the presence of tetrabutylammonium bromide leads to the formation of compounds 2 and 11 in good yield. N-(omega-Chloroalkyl) analogues were found to undergo iodide catalyzed nucleophilic substitution reaction with various secondary amines. Products were characterized by UV, IR, 1H and 13C NMR, mass-spectral data and elemental analysis. The lipophilicity expressed in log(10) P and pK(a) of compounds have been determined. All compounds were examined for their ability to increase the uptake of vinblastine (VLB) in MDR KBCh(R)-8-5 cells and the results showed that the compounds 7, 10, 12, and 15-19 at 100 microM caused a 1.05- to 1.7-fold greater accumulation of vinblastine than did a similar concentration of the standard modulator, verapamil (VRP). However, the effects on VLB uptake were specific because these derivatives had little effect in the parental drug sensitive line KB-3-1. Steady state accumulation of VLB, a substrate for P-glycoprotein (P-gp) mediated efflux, was studied in the MDR cell line KBCh(R)-8-5 in the presence and absence of novel MDR modulators. Results of the efflux experiment showed that VRP and each of the modulators (1-19) significantly inhibited the efflux of VLB, suggesting that they may be competitors for P-gp. From among the compounds examined, 14 except 1, 2, 4, 8, and 11, exhibited greater efflux inhibiting activity than VRP. All the 19 compounds effectively compete with [(3)H] azidopine for binding to P-gp, pointed out this transport membrane protein as their likely site of action. Cytotoxicity has been determined and the IC(50) values lie in the range 8.00-18.50 microM for propyl and 4-15 microM for butyl derivatives against KBCh(R)-8-5 cells suggesting that the antiproliferative activity increases as chain length increases from 3 to 4 carbons at N(10)-position. Compounds at IC(10) were evaluated for their efficacy to modulate the cytotoxicity of VLB in KBCh(R)-8-5 cells and found that the modulators enhanced the cytotoxicity of VLB by 5- to 35-fold. Modulators 12, 14-16, and 19 like VRP, were able to completely reverse the 24-fold resistance of KBCh(R)-8-5 cells to VLB. Examination of the relationship between lipophilicity and antagonism of MDR showed a reasonable correlation suggesting that hydrophobicity is one of the determinants of potency for anti-MDR activity of 2-methoxyacridones.