Current Topics in Medicinal Chemistry - Volume 16, Issue 22, 2016

Telomeres are the terminal part of the chromosome containing a long repetitive and noncodifying sequence that has as function protecting the chromosomes. In normal cells, telomeres lost part of such repetitive sequence in each mitosis, until telomeres reach a critical point, triggering at that time senescence and cell death. However, in most of tumor cells in each cell division a part of the telomere is lost, however the appearance of an enzyme called telomerase synthetize the segment that just has been lost, therefore conferring to tumor cells the immortality hallmark. Telomerase is significantly overexpressed in 80–95% of all malignant tumors, being present at low levels in few normal cells, mostly stem cells. Due to these characteristics, telomerase has become an attractive target for new and more effective anticancer agents. The capability of inhibiting telomerase in tumor cells should lead to telomere shortening, senescence and apoptosis. In this work, we analyze the different strategies for telomerase inhibition, either in development, preclinical or clinical stages taking into account their strong points and their caveats. We covered strategies such as nucleosides analogs, oligonucleotides, small molecule inhibitors, G-quadruplex stabilizers, immunotherapy, gene therapy, molecules that affect the telomere/ telomerase associated proteins, agents from microbial sources, among others, providing a balanced evaluation of the status of the inhibitors of this powerful target together with an analysis of the challenges ahead.

Histone deacetylases (HDACs) regulate gene expression by modulating chromatin architecture via histone hypoacetylation. They play a key role in regulating cellular processes including cell cycle arrest and apoptosis. Hyperactivity of HDACs plays a key role in tumour onset and progression making these enzymes as striking targets for anticancer drugs and therapy. Certain cancers are associated with upregulation of specific class II HDAC isoform rather than multiple ones. Therapeutic intervention using small-molecules namely histone deacetylase inhibitors (HDACi), often targets many isoforms unselectively (pan-HDACi) due to structural identity culminating in debilitating off-target effects and reduced in vivo potency. This emphasizes the escalating need for developing isoform-selective inhibitors against the defined class of HDACs. Despite the safe and elevated therapeutic benefit, the design of such inhibitors has been challenging. The present article provides intricate details about the role of class II HDAC isoforms in fuelling distinct cancers and the current challenges with the use of pan-HDAC inhibitors in anticancer therapy. The article also highlights the diverse synthetic and in silico approaches taken by scientific community towards the designing of isoform-selective inhibitors against class II HDAC isoforms. The strategies discussed in this review will provide further impetus to the ongoing research regarding the designing of isoform-selective inhibitors for safe and effective anticancer therapy which is today’s need.

Background: Aberrant signal transducer and activator of transcription 3 (STAT-3) molecular signaling elicit hepatocellular carcinoma (HCC) in humans. Therefore, targeting STAT-3 is considered as an attractive option towards suppression of HCC in humans. Objective: Our objective is to identify a potential small molecule inhibitor that can specifically target STAT-3 and suppress HCC. Methods: In this study, we analyze a group of sesquiterpene lactone (STL) candidates that has been recently reported in preclinical trials against cancer by a unified computational and experimental approach. Results: Our virtual analysis of the STL candidates revealed Artesunate (ATS) as the best potential inhibitor of STAT-3 with comparable potency to specific inhibitor S3I-201. We also observed that ATS inhibited IL-6 driven STAT-3-DNA binding activity with comparable potency to S3I-201 in a cell free system. Furthermore ATS was observed to interfere with STAT-3 dimerization and suppression of both constitutive and IL-6 inducible STAT-3 in vitro. Nevertheless, we also observed that ATS modulated STAT-3 dependent targets (procaspase-3, Bcl-xl and survivin) favoring occurrence of apoptosis in vitro. Overall, the putative inhibition of STAT-3 by ATS suggested its capacity to interfere with STAT-3 dimerization by binding to the SH2 domain of STAT-3 monomer. It resulted in suppression of STAT-3 and also favored promotion of in vitro cells towards apoptosis. Consequently, ATS also exhibited selective cytotoxicity of cancer cells over normal cells in vitro. Conclusion: All the above observations substantiated by unified computational and in vitro experimental approaches suggested its potential role as a therapeutic anti-cancer agent against HCC.

Nitroxyl (HNO), the one electron reduced form of nitric oxide (NO), shows a very distinct chemistry and biology from that of NO. Chemical profile is characterized by reactions with thiols and thiol proteins such as aldehyde dehydrogenase, glyceraldehyde 3-phosphate dehydrogenase, caspases among others. Biological profile of HNO includes cardioprotective actions especially in cases of heart failure. This short review focuses on the cytotoxic properties for HNO. Nitroxyl was found to be toxic to several cancer cell lines including lung and breast cancers. Critical thiols that control cancer cellular functions might be the target for HNO activity. The anti-tumor actions of HNO donating aspirin is also summarized.

Research over the years has gradually and sequentially highlighted contributory role of hypothalamic- based kisspeptin-signaling axis as a major positive modulator of the neuroendocrinological reproductive axis in mammals. However, a series of landmark studies provided convincing evidence of role of this signaling in regulation of cancer development and progression. It is becoming progressively more understandable that loss or reduction of KISS1 expression in different human cancers correlates inversely with progression of tumor, metastasizing potential and survival. In this review we have attempted to provide an overview highlight of the most recent updates addressing metastasis- suppressing role of KISS1. We also summarize interplay of microRNA and KISS1 in cancer. The miRNA regulation of different genes is a rapidly expanding area of research however, the community lacks a deep understanding of miRNA regulation of KISS1. Recently, emerging laboratory findings have shown that KISS1 is transcriptionally controlled by TCF21 that is in turn regulated by miR-21. Therefore, there is an urgent need for further study of how miRNA directly or indirectly influences KISS1 at the posttranscriptional level. There is also a lack of evidence regarding natural agents that mediate upregulation or downregulation of KISS1. Increasing the knowledge of the KISS1/KISS1R signaling axis will be helpful in achieving personalized medicine.

Cancer is a multifaceted and genomically complex disease. Rapidly accumulating preclinical and clinical studies are emphasizing on wide ranging molecular mechanisms that underpin cancer development, progression and metastasis. Intratumor heterogeneity, loss of apoptosis, rapidly developing resistance against molecular therapeutics and off-target effects are some of the deeply studied resistance mechanisms. Data obtained through high-throughput technologies has considerably enhanced our understanding of the intracellular signaling cascades frequently dysregulated spatio-temporally. There is an ever-expanding list of synthetic and natural agents reported to activate tumor suppressor genes and inhibit oncogenes in cancer cells. Markedly reduced tumor growth has also been documented in xenografted mice administered with phytochemicals. Oleuropein is a bioactive ingredient isolated from various sources and there is evidence of complete regression of tumors in 9- 12 days in mice orally administered with Oleuropein. In this review we summarize recent developments in use of Oleuropein as an anticancer agent. Extraction and isolation of Oleuropein and how it modulates intracellular signaling network to induce apoptosis in cancer cells. Human epidermal growth factor receptor 2 (HER2) frequently overexpressed in breast cancer cells is inhibited by Oleuropein. Interestingly, trastuzumab efficacy was notably enhanced in Oleuropein treated breast cancer cells. There is still insufficient information related to Oleuropein mediated microRNA regulation in cancer cells. We still do not have information about regulation of different signaling cascades by Oleuropein which are deregulated in cancer. Future studies must converge on a deeper analysis of target molecular network of Oleuropein and its efficacy as a tumor growth inhibitor in xenografted mice.

A major impediment for cancer chemotherapy is the development of multidrug-resistance (MDR). Continuous use of chemotherapeutic drugs during cancer therapy induces the expression of PGlycoprotein (P-gp, MDR1), an ATP dependant transporter, which in turn reduces the intracellular accumulation of chemotherapeutic drugs leading to MDR. Extensive research over the years has identified several potential P-gp inhibitors, both synthetic as well as natural origin, to overcome the MDR during cancer chemotherapy. In this review, we discuss the cellular pathways involved and transcription factors regulating the expression of P-gp. A number of phytochemicals are reported to inhibit P-gp activity and MDR1 expression; the structure-activity relationship (SAR) among the phytochemicals for P-gp inhibition and the effect of these phytochemicals on cellular signaling pathways regulating P-gp expression are discussed in detail. Moreover, structural biology and mutagenesis studies on P-gp along with docking studies throw light on the structural requirements for P-gp inhibition. Insight provided in the review about the phytochemicals molecular mechanism and SAR could catalyze the design of potent P-gp inhibitors in the future and could help to overcome MDR in cancer chemotherapy.

In the present study an efficient strategy for the synthesis of thiazole and thiadiazole derivatives was developed and clubbed together both of the substituted nucleus to form the analogues of combretastatin A-4 (tubulin polymerization inhibitors.). Synthesis was started by the reaction of substituted benzoic acid with thionyl chloride followed by the reaction with hydrazine, p-chloro benzaldehyde and thioglycolic acid to form substituted thiazole derivatives. On the other side hydrazides were reacted with ammonium thiocyanate and strong acid to form substituted thiadiazole compounds. Finally thiazole and thiadiazole compounds were clubbed with the help of dioxan and triethylamine. All novel derivatives (TH01-TH40) were screened for their cytotoxicity activity using MTT assay against three cancer cell lines viz. A-549 (lung carcinoma), HT-29 (colon carcinoma), HeLa (cervix carcinoma). Compounds TH08 exhibited highest activity, due to the presence of trimethoxy substitution on phenyl ring. In QSAR study these results were correlated with physicochemical parameters and the correlation of XlogP, kaapa2, Quadrupole1 with cytotoxic activity on A-549 (lung carcinoma) was found highest (r²: 0.941; F: 99.103; Se: 0.0006). In docking study binding of active molecule (TH08) was found very well with α, β tubulin (PDB: 1SA0) protein.