T. R. Santhosh Kumar

Induction of Apoptosis by Curcumin and Its Implications for Cancer Therapy

Curcumin (diferuloyl methane), the yellow pigment in turmeric (Curcuma longa), is a potent chemopreventive agent that inhibits proliferation of cancer cells by arresting them at various phases of the cell cycle depending upon the cell type. Curcumin-induced apoptosis mainly involves the mitochondria-mediated pathway in various cancer cells of different tissues of origin. In some cell types like thymocytes, curcumin induces apoptosis-like changes whereas in many other normal and primary cells curcumin is either inactive or inhibits proliferation, but does not appear to induce apoptosis. These together with reports that curcumin protects cells against apoptosis induced by other agents, underscore the need for further understanding of the multiple mechanisms of cell death unleashed by curcumin. Tumor cells often evade apoptosis by expressing several antiapoptotic proteins, down-regulation and mutation of proapoptotic genes and alterations in signaling pathways that give them survival advantage and thereby allow them to resist therapy-induced apoptosis. Many researchers including ourselves, have demonstrated the involvement of several pro and antiapoptotic molecules in curcumin-induced apoptosis, and ways to sensitize chemoresistant cancer cells to curcumin treatment. This review describes the mechanisms of curcumin-induced apoptosis currently known, and suggests several potential strategies that include down-regulation of antiapoptotic proteins by antisense oligonucleotides, use of proapoptotic peptides and combination therapy, and other novel approaches against chemoresistant tumors. Several factors including pharmacological safety, scope for improvement of structure and function of curcumin and its ability to attack multiple targets are in favor of curcumin being developed as a drug for prevention and therapy of various cancers.

Human colon cancer cells differ in their sensitivity to curcumin-induced apoptosis and heat shock protects them by inhibiting the release of apoptosis-inducing factor and caspases

Mild heat treatment induced the expression of heat shock protein‐70 (hsp70), hsp90 and hsp27 in two human colon cancer cell lines, one derived from primary tumor, SW480, and the other derived from the secondary lymph node tissue, SW620, of the same patient. SW620 cells appear to be more sensitive to curcumin‐induced apoptosis. Heat shock protects both the human colon cancer cells from curcumin‐induced apoptosis. Heat shock prevented, at least in part, the release of apoptosis inducing factor from mitochondria induced by curcumin although the release of second mitochondria derived activator of caspase and cytochrome c was unaffected in both the cells. Moreover, heat shock reduced curcumin‐induced activation of caspases 9 and 3 but not 8.

Side Population Cells as Prototype of Chemoresistant, Tumor-Initiating Cells

Classically, isolation of CSCs from tumors exploits the detection of cell surface markers associated with normal stem cells. Invariable expression of these cell surface markers in almost all proliferating tumor cells that albeit impart specific functionality, the universality, and clinical credibility of CSC phenotype based on markers is still dubious. Side Population (SP) cells, as defined by Hoechst dye exclusion in flow cytometry, have been identified in many solid tumors and cell lines and the SP phenotype can be considered as an enriched source of stem cells as well as an alternative source for the isolation of cancer stem cells especially when molecular markers for stem cells are unknown. SP cells may be responsible for the maintenance and propagation of tumors and the proportion of SP cells may be a predictor of patient outcome. Several of these markers used in cell sorting have emerged as prognostic markers of disease progression though it is seen that the development of new CSC-targeted strategies is often hindered by poor understanding of their regulatory networks and functions. This review intends to appraise the experimental progress towards enhanced isolation and drug screening based on property of acquired chemoresistance of cancer stem cells.

Rutin and quercetin enhance glucose uptake in L6 myotubes under oxidative stress induced by tertiary butyl hydrogen peroxide

Scientific evidence suggests a strong link between the oxidative stress-induced pathways and onset of diabetes and its complications. The present study evaluates the antidiabetic potential of the flavonoids, rutin and its metabolite quercetin under oxidative stress induced by tertiary butyl hydrogen peroxide (TBHP). Our results demonstrate that reactive oxygen species generated by TBHP decreased markedly in the L6 cells on preincubation with flavonoids in a dose-dependent manner and remarkably retrieved the glutathione level which was drastically decreased on oxidative challenge. These flavonoids were also found to prevent lipid peroxidation in L6 myoblast. Flavonoids increased glucose following chronic and acute pretreatment in the presence of oxidative stress. Increased glucose uptake in L6 myotubes was attributed to GLUT 4 translocation, the most downstream factor in the insulin signalling cascade, which increased two to threefold on chronic pretreatment of quercetin (10 μM) and rutin (100 μM).

New plant sources of the anti-cancer alkaloid, camptothecine from the Icacinaceae taxa, India

In this study, the production of camptothecine and its derivatives, in thirteen species of the family Icacinaceae, namely, Apodytes dimidiata, Codiocarpus andamanicus, Gomphandra comosa, Gomphandra coriacea, Gomphandra polymorpha, Gomphandra tetrandra, Iodes cirrhosa, Iodes hookeriana, Miquelia dentata, Miquelia kleinii, Natsiatum herpeticum, Pyrenacantha volubilis and Sarcostigma kleinii is reported. Seeds of M. dentata were found to produce the highest content of camptothecine (1.0-1.4% by dry weight of seeds). Full scan LC-MS and ESI-MS/MS analysis of M. dentata revealed, besides camptothecine, a number of other derivatives, namely, 10-hydroxycamptothecine, 9-methoxycamptothecine, 20-deoxycamptothecine. Crude extract preparations of the seeds of M. dentata were effective against a breast cancer cell line (IC50=3.82 μg/ml for MDA MB273 cell lines) and two ovarian cancer cell lines (IC50=2.8 μg/ml for NCI/ADR-RES and 4.5 μg/ml for SKOV). These results are the first reports of camptothecine and its derivatives in these species and offer rich alternative plant sources for the anticancer compound, camptothecine.

Multiple drug resistant, tumorigenic stem-like cells in oral cancer.

An in vitro cell line model was established to exemplify tumor stem cell concept in oral cancer. We were able to identify CD147 expressing fractions in SCC172 OSCC cell line with differing Hoechst dye efflux activity and DNA content. In vivo tumorigenic assay revealed three fractions enriched with stem-like cells capable of undergoing mesenchymal transition and a non-tumorigenic fraction. The regeneration potential and transition of one fraction to other imitated the phenotypic switch and functional disparities evidenced during oral tumor progression. Knowledge of these additional stem-like subsets will improve understanding of stem cell based oral epithelial tumor progression from normal to malignant lesions.

Effect of Apoptosis-Inducing Antitumor Agents on Endocardial Endothelial Cells

Chemotherapy is one of the common treatment modalities for cancer. Some of the antineoplastic drugs have, however, been found to be toxic for vascular endothelium, resulting in complications such as endothelial dysfunction, thromboembolism, heart failure, and cardiomyopathy. In this study, we investigated the cytotoxic effect of widely used antitumor agents doxorubicin, camptothecin, and thapsigargin on primary and immortalized porcine endocardial endothelial cells and compared with the effects of these agents on human umbilical vein endothelial cells, human aortic endothelial cells, and EA.hy926 cells. Our study revealed that endocardial endothelial cells are relatively resistant to apoptosis induced by these drugs. Interestingly, our study indicates that response to antitumor agents greatly differs depending on the site of origin of endothelial cells. Doxorubicin, camptothecin, and thapsigargin induce mitochondrial-dependent cell death following loss of mitochondrial membrane potential (MMP) in vascular endothelial cells, with subsequent increase in sub-G0 population. In endocardial endothelial cells, there was no MMP loss; and only cell cycle arrest either at G1 or S phases was observed when the cells were treated with doxorubicin, camptothecin, and thapsigargin.

Preconditioning L6 Muscle Cells with Naringin Ameliorates Oxidative Stress and Increases Glucose Uptake

Enhanced oxidative stress contributes to pathological changes in diabetes and its complications. Thus, strategies to reduce oxidative stress may alleviate these pathogenic processes. Herein, we have investigated Naringin mediated regulation of glutathione (GSH) & intracellular free radical levels and modulation of glucose uptake under oxidative stress in L6 cell lines. The results from the study demonstrated a marked decrease in glutathione with a subsequent increase in free radical levels, which was reversed by the pretreatment of Naringin. We also observed that the increased malondialdehyde level, the marker of lipid peroxidation on induction of oxidative stress was retrieved on Naringin pretreatment. Addition of Naringin (100 μM) showed approximately 40% reduction in protein glycation in vitro. Furthermore, we observed a twofold increase in uptake of fluorescent labeled glucose namely 2-(N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)Amino)-2-Deoxyglucose (2 - NBDG) on Naringin treatment in differentiated L6 myoblast. The increased uptake of 2-NBDG by L6 myotubes may be attributed due to the enhanced translocation of GLUT4. Our results demonstrate that Naringin activate GSH synthesis through a novel antioxidant defense mechanism against excessive Reactive Oxygen Species (ROS) production, contributing to the prevention of oxidative damage in addition to its effect on glycemic control.

Biosynthesized composites of Au-Ag nanoparticles using Trapa peel extract induced ROS-mediated p53 independent apoptosis in cancer cells

Abstract The current study highlights rapid, sustainable, and cost-effective biosynthesis of silver (Ag), gold (Au) nanoparticles (NPs), and bimetallic Au-AgNPs composites using bio-waste extract of Trapa natans. Growth of the NPs was monitored spectrophotometrically and peak was observed at ∼525 nm, ∼450 nm, and ∼495 nm corresponding to Plasmon absorbance of AuNPs, AgNPs, and Au-AgNPs, respectively. Transmission electron microscopy (TEM) revealed the size of AgNPs (∼15 nm), AuNPs (∼25 nm), and Au-AgNPs (∼26–90 nm). Synthesized NPs follow the Gaussian bell curve and its crystalline nature was identified by X-ray diffraction (XRD). Furthermore, Au-AgNPs induced cytotoxicity in various cancer cells (HCT116, MDA-MB-231, and HeLa) effectively at 200 μg/mL. Au-AgNPs-exposed cancer cells exhibited apoptotic features such as nuclear condensation, mitochondrial membrane potential loss, and cleavage of casp-3 and poly (ADP-ribose) polymerase-1 (PARP). Au-AgNPs exposure enhanced reactive oxygen species (ROS) and upon inhibition of ROS, apoptosis was reduced effectively. NPs treatment killed HCT116 WT and p53 knockout cells without any significant difference. Mechanistically, Au-AgNPs derived with Trapa peel extract significantly enhance ROS which trigger p53-independent apoptosis in various cancer cells effectively. Our study explores the use of bio-waste for the green synthesis of NPs, which can be attractive candidates for cancer therapy.

Non-steroidal Estrogen Receptor Isoform Selective Biphenyls

Estrogen receptor (ER) has been a therapeutic target to treat ER‐positive breast cancer, most notably by agents known as selective estrogen receptor modulators (SERMs). However, resistance and severe adverse effects of known drugs gave impetus to the search for newer agents with better therapeutic profile. ERα and ERβ are two isoforms sharing 56% identity and having different physiological functions and expressions in various tissues. Only two residues differ in the active sites of the two isoforms motivating us to design isoform‐selective ligands. Guided by computational docking and molecular dynamics simulations, we have designed, synthesized, and tested, substituted biphenyl‐2,6‐diethanones and their derivatives as potential agents targeting ERα. Four of the molecules synthesized exhibited preferential cytotoxicity in ERα+ cell line (MCF‐7) compared to ERβ+ cell line (MDA‐MB‐231). Molecular dynamics (MD) in combination with molecular mechanics‐generalized Born surface area (MM‐GBSA) methods could account for binding selectivity. Further cotreatment and E‐screen studies with known ER ligands—estradiol (E2) and tamoxifen (Tam)—indicated isoform‐selective anti‐estrogenicity in ERα+ cell line which might be ER‐mediated. ERα siRNA silencing experiments further confirmed the ER selective nature of ligands.