Pleiotropic Role of Dietary Phytochemicals in Cancer: Emerging Perspectives for Combinational Therapy

Cancer is considered a complicated health issue worldwide. The mean cancer survival through standard therapeutic strategies has not been significantly improved over the past few decades. Hence, alternate remedies are needed to treat or prevent this dreadful disease being explored. Currently, it has been recognized that repeated treatment with chemotherapeutic agents has been largely ineffective due to multidrug resistance and further conventional treatment possesses limited drug accessibility to cancerous tissues, which in turn necessitates a higher dose resulting in increased cytotoxicity. Drug combinations have been practiced to address the problems associated with conventional single drug treatment. Recently, natural dietary agents have attracted much attention in cancer therapy because of their synergistic effects with anticancer drugs against different types of cancer. Natural phytochemicals may execute their anticancer activity through targeting diverse cancer cell signaling pathways, promoting cell cycle arrest and apoptosis, regulating antioxidant status and detoxification. This review focuses mainly on the anticancer efficacy of dietary phytochemicals in combination with standard therapeutic drugs reported from various in vitro and in vivo experimental studies apart from clinical trials. This review adds knowledge to the field of intervention studies using combinational modalities that opens a new window for cancer treatment/chemoprevention.

Effect of diallyl disulfide on insulin-like growth factor signaling molecules involved in cell survival and proliferation of human prostate cancer cells in vitro and in silico approach through docking analysis

PURPOSE

Diallyl Disulfide (DADS) is one of the major components of garlic, which inhibits the proliferation of various cancer cells. Our previous studies showed that DADS inhibits cell growth and induces apoptosis on prostate cancer cells. Insulin like growth factor signaling pathway plays a significant role on prostate cancer cell growth and survival and it's over expression also identified in human prostate cancers. The molecular mechanism of IGF mediated PI3K/Akt signaling remains to be elucidated. The present study was designed to evaluate the effects of diallyl disulfide on IGF signaling in androgen independent prostate cancer cells (PC-3).

METHODS

DADS (10-50 μM) caused dose-dependent inhibition of PC-3 cells, were analyzed by MTT, IC50 value of PC-3 cells was 40 μM for 24h. Interestingly, DADS also altered the mRNA and protein expressions of IGF signaling and apoptotic molecules which were confirmed by semi quantitative PCR and western blot method. Further the docking study of DADS with IGF receptor was carried out by Ligand Fit of Discovery studio. Accord Excel Package was used for the prediction of ADME properties of the compound.

RESULTS

The results suggests that DADS decreases the survival rate of androgen independent prostate cancer cells by modulating the expression of IGF system, which leads to inhibition of phosphorylation of Akt, thereby inhibits cell cycle progression and survival by lowering the expression of cyclin D1, NFkB and anti-apoptotic Bcl-2 molecule and increasing the level of pro-apoptotic (Bad and Bax) signaling molecules which leads to apoptosis.

CONCLUSION

The present investigation showed downregulation of Akt and a concomitant increase in apoptosis in DADS treated prostate cancer cells. Since inhibition of this Akt pathway by DADS leads to inhibition in cancer cell progression, it is highly suggested that DADS has the potential use as a therapy for prostate cancer.

Protective effect of zinc on N-methyl-N-nitrosourea and testosterone-induced prostatic intraepithelial neoplasia in the dorsolateral prostate of Sprague Dawley rats

Previous studies have suggested that zinc exerts anticarcinogenic and antiproliferative effects against prostate cancer both in vitro and in rat ventral prostate. Zinc accumulation diminishes early in the course of prostate malignancy and it inhibits the growth of several carcinoma cells through induction of cell cycle arrest and apoptosis. In this study, we have investigated the influence of zinc on N-methyl-N-nitrosourea (MNU) and testosterone (T)-induced prostatic intraepithelial neoplasia in the dorsolateral prostate of Sprague Dawley (SD) rats. The results indicate that zinc plays an important role in prostate carcinogenesis. Increased tumor incidence was accompanied by a decrease in prostatic acid phosphatase activity, citrate, zinc, glutathione-S-transferase, reduced glutathione, p53, B-cell lymphoma protein (Bcl-2)-associated X protein and caspase-3 levels in MNU + T-treated rats. On the contrary, significantly increased phase I drug metabolizing enzyme activities, lipid peroxide, hydrogen peroxide, proliferating cell nuclear antigen, Bcl-2 and Bcl-X(L) protein levels were observed in the dorsolateral prostate of MNU + T-treated rats. Simultaneous zinc supplementation significantly reversed these effects in MNU + T-treated rats. Signs of dysplasia, a characteristic of prostatic intraepithelial neoplasia, were evident in the dorsolateral prostatic tissue sections by MNU + T administration. However, zinc supplementation has reversed these effects in the dorsolateral prostatic histoarchitecture. These results suggest that zinc may act as an essential trace element against MNU and testosterone-induced prostatic preneoplastic progression in SD rats.

Quercetin regulates insulin like growth factor signaling and induces intrinsic and extrinsic pathway mediated apoptosis in androgen independent prostate cancer cells (PC-3)

Progression of prostate cancer is facilitated by growth factors that activate critical signaling cascades thereby promote prostate cancer cell growth, survival, and migration. To investigate the effect of quercetin on insulin-like growth factor signaling and apoptosis in androgen independent prostate cancer cells (PC-3), IGF-IR, PI-3K, p-Akt, Akt, cyclin D1, Bad, cytochrome c, PARP, caspases-9 and 10 protein levels were assessed by western blot analysis. Mitochondrial membrane potency was detected by rhodamine-123 staining. Quercetin induced caspase-3 activity assay was performed for activation of apoptosis. Further, RT-PCR was also performed for Bad, IGF-I, II, IR, and IGFBP-3 mRNA expression. Quercetin significantly increases the proapoptotic mRNA levels of Bad, IGFBP-3 and protein levels of Bad, cytochrome C, cleaved caspase-9, caspase-10, cleaved PARP and caspase-3 activity in PC-3 cells. IGF-IRβ, PI3K, p-Akt, and cyclin D1 protein expression and mRNA levels of IGF-I, II and IGF-IR were decreased significantly. Further, treatment with PI3K inhibitor (LY294002) and quercetin showed decreased p-Akt levels. Apoptosis is confirmed by loss of mitochondrial membrane potential in quercetin treated PC-3 cells. This study suggests that quercetin decreases the survival of androgen independent prostate cancer cells by modulating the expression of insulin-like growth factors (IGF) system components, signaling molecules and induces apoptosis, which could be very useful for the androgen independent prostate cancer treatment.

Effects of diallyl disulfide (DADS) on expression of apoptosis associated proteins in androgen independent human prostate cancer cells (PC-3)

Prostate cancer is a leading cause of death among the aging men. Surgical or radiotherapy is effective when the cancer is confined to the prostate gland but once the cancer spreads beyond the pelvis even chemotherapy and hormonal ablation therapy fails in curing this disease. Our previous studies have shown that diallyl disulfide (DADS) induces cell cycle arrest and also induces apoptosis in PC-3 cells. And now the present study is focused to see whether there is an activation of caspase cascade pathway. Hence, in the present study the apoptotic effect of DADS is studied by Western blot analysis of caspase-3, -9, -10 and Bcl-2, Bad, and Bax protein. The Apoptotic cells were assessed by Hoechst 33342 staining with 25 and 40 microM concentrations of DADS for 24 h. The results have shown that DADS at 25 and 40 microM concentrations has induced the activation of caspases. There is a significant increase in the expression of caspases (3, 9, and 10). The proapoptotic protein Bax has significantly increased at 40 microM of DADS treatment and there is significant increase of Bad protein at both the concentration. Bcl-2 protein has significantly decreased in DADS treated cells. Therefore, the present investigation serves as evidence that DADS may be a therapeutic drug in the treatment of prostate cancer.

Role of alpha-tocopherol on antioxidant status in liver, lung and kidney of PCB exposed male albino rats

Polychlorinated biphenyls (PCB) are widespread, lipophilic environmental pollutants which have been identified as contaminants in almost every component of the global ecosystem including fish, wildlife, and human adipose tissue, breast milk, and serum. Several studies have shown that PCBs can cause oxidative damage to biomolecules, in the form of lipid peroxidation, modulation of antioxidant enzymes, and oxidative stress. In the present study, we have sought to investigate the effects of alpha-tocopherol (vitamin E) on antioxidant status of PCB-induced toxicity in male Wistar rats. The protective effect of alpha-tocopherol (50mg/kg body weight/day) was tested in PCB-induced toxicity in rat liver, lung, and kidney. We report here that the oral supplementation of alpha-tocopherol was found to maintain the cellular redox status by maintaining the activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase accompanied with glutathione and vitamin E levels and down regulation in the levels of lipid peroxides, hydroxyl radical and hydrogen peroxides generation in PCB treated rats. Therefore, our present study demonstrates the PCB-induced deficits in antioxidant enzyme activities and increase in reactive oxygen species and lipid peroxidation levels in liver, kidney, and lung which can be overcome through simultaneous supplementation with alpha-tocopherol.

Effects of Vitamin C and E on PCB (Aroclor 1254) induced oxidative stress, androgen binding protein and lactate in rat Sertoli cells

The effect of Aroclor 1254 and the ameliorative effect of Vitamin C and E on Sertoli cell function were studied in adult male rats. The rats were administered Aroclor 1254 at a dose of 2 mg/kg bw/day intraperitoneally for 30 days. One group of rats received Vitamin C (100 mg/kg bw/day) while the other group received Vitamin E (50 mg/kg bw/day) orally simultaneously with Aroclor 1254 for 30 days. Necropsy was performed at 24 h after the last injection. Sertoli cells were isolated for the estimation of enzymatic antioxidants superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GST), and gamma-glutamyl transpeptidase (gamma-GT). Lipid peroxidation (LPO), hydrogen peroxide and hydroxyl radical were estimated. Sertoli cellular androgen binding protein (ABP) and lactate were also quantified. Whereas body weight, testis weight, relative weight of testis, ABP, lactate and specific activities of SOD, CAT, GPx, GR, GST, gamma-GT were all decreased, the levels of hydrogen peroxide, hydroxyl radical and LPO were significantly increased in the Sertoli cells of Aroclor 1254 treated rats. Simultaneous administration of Vitamin C or E restored these parameters to a normal range. Thus, the present study suggests that Aroclor 1254 exposure induces oxidative stress in rat Sertoli cells and furthermore that simultaneous administration of Vitamin C or E ameliorated these effects.