New Poly(ADP-ribose) Polymerase-1 Inhibitors with Antioxidant Activity Based on 4-Carboxamidobenzimidazole-2-ylpyrroline and -tetrahydropyridine Nitroxides and Their Precursors

Detection of Natural Inhibitors against Human Liver Cancer Cell Lines through QSAR, Molecular Docking and ADMET Studies

BACKGROUND

Liver cancer is ranked as the fifth most prevalent and third most lethal cancer worldwide. The incidence rates of this cancer are on the rise, and only limited treatment options are available.

METHODS

To identify and optimize the inhibitors of liver cancer cell-lines, a QSAR model was developed by using multiple linear regression methods. The robustness of the model was validated through statistical methods and wet-lab experiments.

RESULTS

The developed QSAR models yielded high activity descriptor relationship accuracy of 91%, referred to by regression coefficient (r²= 0.91), and a high activity prediction accuracy of 89%. The external predicted (pred_r²) ability of the model was found to be 90%.

CONCLUSION

The QSAR study indicates that chemical descriptors such as to measure of electronegative atom count (Epsilon3), atom type count descriptors (MMFF_10), number of a carbon atom connected with four single bonds (SssssCE- index), molecular weight and, number of oxygen atom connected with two aromatic bonds (SaaOE-index) are significantly correlated with anticancer activity. The model, which was validated statistically and through wet-lab experiments, was further used in the virtual screening of potential inhibitors against the liver cancer cell line WRL68. ADMET risk screening, synthetic accessibility, and Lipinski's rule of five are used to filter false positive hits. AfterwardS, to achieve a set of aligned ligand poses and rank the predicted active compounds, docking studies were carried out. The studied compounds and their metabolites were also analyzed for different pharmacokinetics parameters. Finally, a series of compounds was proposed as anticancer agents.

Structure-Based Pharmacophore Modeling, Virtual Screening, Molecular Docking and Biological Evaluation for Identification of Potential Poly (ADP-Ribose) Polymerase-1 (PARP-1) Inhibitors

Poly (ADP-ribose) polymerase-1 (PARP-1) plays critical roles in many biological processes and is considered as a potential target for anticancer therapy. Although some PARP-1 inhibitors have been reported, their clinical application in cancer therapy is limited by some shortcomings such as weak affinity, low selectivity and adverse side effects. To identify highly potent and selective PARP-1 inhibitors, an integrated protocol that combines pharmacophore mapping, virtual screening and molecular docking was constructed. It was then used as a screening query to identify potent leads with unknown scaffolds from an in-house database. Finally, four retrieved compounds were selected for biological evaluation. Biological testing indicated that the four compounds showed strong inhibitory activities on the PARP-1 (IC50 < 0.2 μM). MTT assay confirmed that compounds 1-4 inhibited the growth of human lung cancer A549 cells in a dose-dependent manner. The obtained compounds from this study may be potential leads for PARP-1 inhibition in the treatment of cancer.

Novel multitarget-directed tacrine derivatives as potential candidates for the treatment of Alzheimer's disease

Alzheimer’s disease (AD) is a neurodegenerative disorder, which is complex and progressive; it has not only threatened the health of elderly people, but also burdened the whole social medical and health system. The available therapy for AD is limited and the efficacy remains unsatisfactory. In view of the prevalence and expected increase in the incidence of AD, the design and development of efficacious and safe anti-AD agents has become a hotspot in the field of pharmaceutical research. Due to the multifactorial etiology of AD, the multitarget-directed ligands (MTDLs) approach is promising in search for new drugs for AD. Tacrine, which is the first acetylcholinesterase (AChE) inhibitor, has been selected as the ideal active fragment because of its simple structure, clear activity, and its superiority in the structural modification, thus it could be introduced into the overall molecular skeletons of the multi-target-directed anti-AD agents. In this review, we have summarized the recent advances (2012 to the present) in the chemical modification of tacrine, which could provide the reference for the further study of novel multi-target-directed tacrine derivatives to treat AD.

Recent progress on the discovery of antiamoebic agents

A large number of protozoans infect humans but Entamoeba histolytica is the only organism responsible for causing amoebiasis, a deadly disease after malaria. Numerous heterocycle-based antiamoebic agents have been previously synthesized as E. histolytica inhibitors and while some of these agents have shown moderate activity, the search for a novel and ideal antiamoebic compound is still ongoing. In this digest Letter, we present the latest data on antiamoebic agents from 2011 to 2016 based on the different classes of heterocyclic agents.

The synthesis of sterically hindered amines by a direct reductive amination of ketones

An atom-economical methodology for the synthesis of sterically hindered tertiary amines was developed, which is based on a complementary Rh- and Ru-catalyzed direct reductive amination of ketones with primary and secondary amines using carbon monoxide as a deoxygenating agent.

Reduced tumor burden through increased oxidative stress in lung adenocarcinoma cells of PARP-1 and PARP-2 knockout mice

Lung cancer (LC) is currently a major leading cause of cancer deaths worldwide. Poly(ADP-ribose) polymerases (PARP)-1 and -2 play important roles in DNA repair and other cell functions. Oxidative stress triggers autophagy and apoptosis. PARP inhibitors are currently used as anticancer strategies including LC. We hypothesized that inhibition of either PARP-1 or -2 expressions in the host animals influences tumor burden through several biological mechanisms, mainly redox imbalance (enhanced oxidative stress and/or decreased antioxidants, and cell regulators) in wild type (WT) lung adenocarcinoma cells. Compared to WT control tumors, in those of Parp-1(-/-) and Parp-2(-/-) mice: 1) tumor burden, as measured by weight, and cell proliferation rates were decreased, 2) oxidative stress levels were greater, whereas those of the major antioxidant enzymes were lower especially catalase, 3) tumor apoptosis and autophagy levels were significantly increased, and 4) miR-223 and nuclear factor of activated T-cells (NFAT)c-2 expression was decreased (the latter only in Parp-1(-/-) mice). Furthermore, whole body weight gain at the end of the study period also improved in Parp-1(-/-) and Parp-2(-/-) mice compared to WT animals. We conclude that PARP-1 and -2 genetic deletions in the host mice induced a significant reduction in tumor burden most likely through alterations in redox balance (downregulation of antioxidants, NFATc-2 and miR223, and increased oxidative stress), which in turn led to increased apoptosis and autophagy. Furthermore, tumor progression was also reduced probably as a result of cell cycle arrest induced by PARP-1 and -2 inhibition in the host mice. These results highlight the relevance of the host status in tumor biology, at least in this experimental model of lung adenocarcinoma in mice. Future research will shed light on the effects of selective pharmacological inhibitors of PARP-1 and PARP-1 in the host and tumor burden, which could eventually be applied in actual clinical settings.

Synthesis, crystal structure, and DNA-binding studies of different coordinate binuclear silver(i) complexes with benzimidazole open-chain ether ligands

Three new binuclear silver(i) complexes with bis-benzimidazole ligands have been developed and they bind to CT-DNA in an intercalation mode.

The synthesis and activities of novel mononuclear or dinuclear cyclen complexes bearing azole pendants as antibacterial and antifungal agents

A series of novel compounds containing 1,4,7,10-tetraazacyclododecane and azoles were synthesized and characterized by (1)H NMR, MS and elemental analysis. Bioactive assay manifested that some target compounds, such as 11a, 11b and 11d, displayed good and broad spectrum antimicrobial activities with relative low MIC values against most of tested strains. These dinuclear complexes gave comparable or even better antimicrobial efficiencies than the reference drugs Fluconazole and Chloromycin. The result showed that the metal ions were the key factors to enhance the antimicrobial activities for mononuclear or dinuclear complexed in varying degrees. The interaction evaluation of compound 11b with bovine serum albumin (BSA) as an example was tested by fluorescence method. The thermodynamic parameters indicated that the hydrogen bonds and van der waals forces played the major roles in the strong association between dinuclear compound and BSA. The CCK-8 tests also confirmed the safeties of these dinuclear compounds in vitro.

PARP inhibitor attenuated colony formation can be restored by MAP kinase inhibitors in different irradiated cancer cell lines

Abstract Purpose: Sensitizing cancer cells to irradiation is a major challenge in clinical oncology. We aimed to define the signal transduction pathways involved in poly(ADP-ribose) polymerase (PARP) inhibitor-induced radiosensitization in various mammalian cancer lines.

MATERIALS AND METHODS

Clonogenic survival assays and Western blot examinations were performed following telecobalt irradiation of cancer cells in the presence or absence of various combinations of PARP- and selective mitogen-activated protein kinase (MAPK) inhibitors.

RESULTS

HO3089 resulted in significant cytotoxicity when combined with irradiation. In human U251 glioblastoma and A549 lung cancer cell lines, Erk1/2 and JNK/SAPK were found to mediate this effect of HO3089 since inhibitors of these kinases ameliorated it. In murine 4T1 breast cancer cell line, p38 MAPK rather than Erk1/2 or JNK/SAPK was identified as the main mediator of HO3089's radiosensitizing effect. Besides the aforementioned changes in kinase signaling, we detected increased p53, unchanged Bax and decreased Bcl-2 expression in the A549 cell line.

CONCLUSIONS

HO3089 sensitizes cancer cells to photon irradiation via proapoptotic processes where p53 plays a crucial role. Activation of MAPK pathways is regarded the consequence of irradiation-induced DNA damage, thus their inhibition can counteract the radiosenzitizing effect of the PARP inhibitor.

Synthesis and functional survey of new Tacrine analogs modified with nitroxides or their precursors

A series of new Tacrine analogs modified with nitroxides or pre-nitroxides on 9-amino group via methylene or piperazine spacers were synthesized; the nitroxide or its precursors were incorporated into the Tacrine scaffold. The new compounds were tested for their hydroxyl radical and peroxyl radical scavenging ability, acetylcholinesterase inhibitor activity and protection against Aβ-induced cytotoxicity. Based on these assays, we conclude that Tacrine analogs connected to five and six-membered nitroxides via piperazine spacers (9b, 9b/HCl and 12) exhibited the best activity, providing direction for further development of additional candidates with dual functionality (anti Alzheimer's and antioxidant).

In silico identification of poly(ADP-ribose)polymerase-1 inhibitors and their chemosensitizing effects against cisplatin-resistant human gastric cancer cells

Poly(ADP-ribose)polymerase-1 (PARP-1) enzyme is involved in the repair of DNA damages made by certain anticancer agents. It is suggested that PARP-1 inhibitors potentiate the cytotoxic effects and circumvent the resistance of DNA-modifying anticancer agents such as cisplatin. In this study, we conducted virtual screening of Korea Chemical Bank database targeting PARP-1 and identified several potent PARP-1 inhibitors with submicromolar IC50 values (77-79 nM). We then examined the chemosensitization of cisplatin by pre-treatment of PARP-1 inhibitors in cisplatin-resistant human gastric cancer cells. Our results show that PARP-1 inhibitors suppress the formation of poly(ADP-ribose) and enhance the cytotoxicity of cisplatin.

5-AIQ inhibits H2O2-induced apoptosis through reactive oxygen species scavenging and Akt/GSK-3β signaling pathway in H9c2 cardiomyocytes

Poly(adenosine 5'-diphosphate ribose) polymerase (PARP) is a nuclear enzyme activated by DNA strand breaks and plays an important role in the tissue injury associated with ischemia and reperfusion. The aim of the present study was to investigate the protective effect of 5-aminoisoquinolinone (5-AIQ), a PARP inhibitor, against oxidative stress-induced apoptosis in H9c2 cardiomyocytes. 5-AIQ pretreatment significantly protected against H2O2-induced cell death, as determined by the XTT assay, cell counting, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay, and Western blot analysis of apoptosis-related proteins such as caspase-3, Bax, and Bcl-2. Upregulation of antioxidant enzymes such as manganese superoxide dismutase and catalase accompanied the protective effect of 5-AIQ on H2O2-induced cell death. Our data also showed that 5-AIQ pretreatment protected H9c2 cells from H2O2-induced apoptosis by triggering activation of Akt and glycogen synthase kinase-3β (GSK-3β), and that the protective effect of 5-AIQ was diminished by the PI3K inhibitor LY294002 at a concentration that effectively abolished 5-AIQ-induced Akt and GSK-3β activation. In addition, inhibiting the Akt/GSK-3β pathway by LY294002 significantly attenuated the 5-AIQ-mediated decrease in cleaved caspase-3 and Bax activation and H9c2 cell apoptosis induction. Taken together, these results demonstrate that 5-AIQ prevents H2O2-induced apoptosis in H9c2 cells by reducing intracellular reactive oxygen species production, regulating apoptosis-related proteins, and activating the Akt/GSK-3β pathway.

The therapeutic journey of benzimidazoles: a review

Presence of benzimidazole nucleus in numerous categories of therapeutic agents such as antimicrobials, antivirals, antiparasites, anticancer, anti-inflammatory, antioxidants, proton pump inhibitors, antihypertensives, anticoagulants, immunomodulators, hormone modulators, CNS stimulants as well as depressants, lipid level modulators, antidiabetics, etc. has made it an indispensable anchor for development of new therapeutic agents. Varied substitutents around the benzimidazole nucleus have provided a wide spectrum of biological activities. Importance of this nucleus in some activities like, Angiotensin I (AT(1)) receptor antagonism and proton-pump inhibition is reviewed separately in literature. Even some very short reviews on biological importance of this nucleus are also known in literature. However, owing to fast development of new drugs possessing benzimidazole nucleus many research reports are generated in short span of time. So, there is a need to couple the latest information with the earlier information to understand the current status of benzimidazole nucleus in medicinal chemistry research. In the present review, various derivatives of benzimidazole with different pharmacological activities are described on the basis of substitution pattern around the nucleus with an aim to help medicinal chemists for developing an SAR on benzimidazole derived compounds for each activity. This discussion will further help in the development of novel benzimidazole compounds.

Protective effect of the poly(ADP-ribose) polymerase inhibitor PJ34 on mitochondrial depolarization-mediated cell death in hepatocellular carcinoma cells involves attenuation of c-Jun N-terminal kinase-2 and protein kinase B/Akt activation

Background

2,4-Dimethoxyphenyl-E-4-arylidene-3-isochromanone (IK11) was previously described to induce apoptotic death of A431 tumor cells. In this report, we investigated the molecular action of IK11 in the HepG2 human hepatocellular carcinoma cell line to increase our knowledge of the role of poly (ADP-ribose)-polymerase (PARP), protein kinase B/Akt and mitogen activated protein kinase (MAPK) activation in the survival and death of tumor cells and to highlight the possible role of PARP-inhibitors in co-treatments with different cytotoxic agents in cancer therapy.

Results

We found that sublethal concentrations of IK11 prevented proliferation, migration and entry of the cells into their G2 phase. At higher concentrations, IK11 induced reactive oxygen species (ROS) production, mitochondrial membrane depolarization, activation of c-Jun N-terminal kinase 2 (JNK2), and substantial loss of HepG2 cells. ROS production appeared marginal in mediating the cytotoxicity of IK11 since N-acetyl cysteine was unable to prevent it. However, the PARP inhibitor PJ34, although not a ROS scavenger, strongly inhibited both IK11-induced ROS production and cell death. JNK2 activation seemed to be a major mediator of the effect of IK11 since inhibition of JNK resulted in a substantial cytoprotection while inhibitors of the other kinases failed to do so. Inhibition of Akt slightly diminished the effect of IK11, while the JNK and Akt inhibitor and ROS scavenger trans-resveratrol completely protected against it.

Conclusions

These results indicate significant involvement of PARP, a marginal role of ROS and a pro-apoptotic role of Akt in this system, and raise attention to a novel mechanism that should be considered when cancer therapy is augmented with PARP-inhibition, namely the cytoprotection by inhibition of JNK2.

Synthesis and study of new paramagnetic resveratrol analogues

New resveratrol analogues containing five- and six-membered nitroxides and isoindoline nitroxides were synthesized. These new compounds were compared to resveratrol based on their ABTS radical scavenging ability as well on their capacity to suppress inflammatory process in macrophages induced by lipopolysaccharides. The ABTS and ROS scavenging activities of new molecules were the same or weaker than that of resveratrol, but some of paramagnetic resveratrol derivatives suppressed nitrite and TNFα production more efficiently than resveratrol. Based on these results the new nitroxide and phenol containing hybrid molecules can be considered as new antioxidant and anti-inflammatory agents.

Synthesis of N-substituted 3,5-bis(arylidene)-4-piperidones with high antitumor and antioxidant activity

A series of 3,5-bis(arylidene)-4-piperidone (DAP) compounds are considered as synthetic analogues of curcumin for anticancer properties. We performed structure-activity relationship studies by synthesizing a number of DAPs N-alkylated or acylated with nitroxides or their amine precursors as potent antioxidant moieties. Both subtituents on arylidene rings and on piperidone nitrogen (five- or six-membered, 2- or 3-substituted or 3,4-disubstituted isoindoline nitroxides) were varied. The anticancer efficacy of the new DAP compounds was tested by measuring their cytotoxicity to cancer cell lines A2780 and MCF-7 and to the H9c2 cell line. The results showed that all DAP compounds induced a significant loss of cell viability in the human cancer cell lines tested; however, only pyrroline appended nitroxides (5c (Selvendiran, K.; Tong, L.; Bratasz, A.; Kuppusamy, L. M.; Ahmed, S.; Ravi, Y.; Trigg, N. J.; Rivera, B. K.; Kálai, T.; Hideg, K.; Kuppusamy, P. Mol. Cancer Ther. 2010, 9, 1169-1179), 5e, 7, 9) showed limited toxicity toward noncancerous cell lines. Computer docking simulations support the biological activity tested. These results suggest that antioxidant-conjugated DAPs will be useful as a safe and effective anticancer agent for cancer therapy.

Induction of mitochondrial destabilization and necrotic cell death by apolar mitochondria-directed SOD mimetics

In this paper, we present evidence, for the first time, that increasing the lipophilicity of mitochondria targeting SOD mimetics reverses their cytoprotective properties, destabilizing the mitochondrial membrane system and promoting cell death. A new mitochondria-directed apolar SOD mimetic, HO-3814, was found to provoke mitochondrial swelling and loss of mitochondrial membrane potential, and these effects were not inhibited by cyclosporine A. HO-3814-induced cell death was predominantly necrotic, caspase-independent, and not affected by mitochondrial permeability transition inhibitors or cyclophilin D-suppression, inhibitors of mitogen-activated protein kinases or Akt, or various antioxidants. In contrast, Bcl-2 overexpression diminished the effects of HO-3814.