Preeti Roy

Resveratrol induces apoptosis involving mitochondrial pathways in mouse skin tumorigenesis

Resveratrol, a plant constituent enriched in the skin of grapes, is one of the most promising agents for chemoprevention. In the present study, resveratrol-induced apoptosis in 7, 12-dimethylbenz[a]anthracene (DMBA)-initiated and 12-O-tetradecanoylphorbol-13-acetate (TPA) promoted, mouse skin tumors. The chemopreventive effects of resveratrol in terms of delayed onset of tumorigenesis, cumulative number of tumors and average number of tumors/mouse were recorded. Resveratrol treatment resulted in regression of tumors (28%) after withdrawal of the TPA treatment. Induction of apoptosis by resveratrol in DMBA-TPA induced skin tumors was recorded by the appearance of a sub-G1 fraction (30%) using flow cytometry and an increase in the number of apoptotic cells by terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay. Western blot analysis combined with multivariable flow cytometry, showed that resveratrol application induces the expression of the p53 and pro-apoptotic Bax, with concomitant decrease in anti-apoptotic protein Bcl-2. Alteration in Bax/Bcl2 ratio by resveratrol treatment resulted in apoptosis, which was associated with the release of cytochrome c and induction of apoptotic protease-activating factor-1(APAF-1). Further, this effect was found to result in cleaved fragments of caspase-9,-3, and poly (ADP-ribose) polymerase (PARP). These findings demonstrate for the first time that resveratrol induces apoptosis through activation of p53 activity in mouse skin tumors, thereupon suggesting its chemopreventive activity, through the modulation of proteins involved in mitochondrial pathway of apoptosis.

Resveratrol and Black Tea Polyphenol Combination Synergistically Suppress Mouse Skin Tumors Growth by Inhibition of Activated MAPKs and p53

Cancer chemoprevention by natural dietary agents has received considerable importance because of their cost-effectiveness and wide safety margin. However, single agent intervention has failed to bring the expected outcome in clinical trials; therefore, combinations of chemopreventive agents are gaining increasing popularity. The present study aims to evaluate the combinatorial chemopreventive effects of resveratrol and black tea polyphenol (BTP) in suppressing two-stage mouse skin carcinogenesis induced by DMBA and TPA. Resveratrol/BTP alone treatment decreased tumor incidence by ∼67% and ∼75%, while combination of both at low doses synergistically decreased tumor incidence even more significantly by ∼89% (p<0.01). This combination also significantly regressed tumor volume and number (p<0.01). Mechanistic studies revealed that this combinatorial inhibition was associated with decreased expression of phosphorylated mitogen-activated protein kinase family proteins: extracellular signal-regulated kinase 1/2, c-Jun N-terminal kinase 1/2, p38 and increased in total p53 and phospho p53 (Ser 15) in skin tissue/tumor. Treatment with combinations of resveratrol and BTP also decreased expression of proliferating cell nuclear antigen in mouse skin tissues/tumors than their solitary treatments as determined by immunohistochemistry. In addition, histological and cell death analysis also confirmed that resveratrol and BTP treatment together inhibits cellular proliferation and markedly induces apoptosis. Taken together, our results for the first time lucidly illustrate that resveratrol and BTP in combination impart better suppressive activity than either of these agents alone and accentuate that development of novel combination therapies/chemoprevention using dietary agents will be more beneficial against cancer. This promising combination should be examined in therapeutic trials of skin and possibly other cancers.

Induction of apoptosis by lupeol in human epidermoid carcinoma A431 cells through regulation of mitochondrial, Akt/PKB and NFκB signaling pathways

The rising incidence of Skin cancer in humans makes it equivalent to other malignancies of other organs Therefore, it is necessary to intensify our efforts for better understanding and development of novel treatment and preventive approaches for skin cancer. Fruits and other plant derived products have gained considerable attention as they can reduce the risk of several cancer types. Lupeol, a triterpene, present in many fruits and medicinal plants, has been shown to possess many pharmacological properties including anti-cancer effect in both in vitro and in vivo assay systems. In the present study, apoptosis inducing effects of lupeol were studied in human epidermoid carcinoma A431cells. Cell cycle analysis showed that lupeol treatment induces apoptosis (14-37%) in a dose dependent manner as evident by an increased sub G1 cell poulation. The RT-PCR and western blot analysis showed that lupeol- induced apoptosis was associated with Caspase dependent mitochondrial cell death pathway through activation of Bax, Capases, Apaf1, decrease in Bcl-2 expression and subsequent cleavage of PARP. Lupeol treatment also inhibited Akt/PKB signaling pathway by inhibition of Bad (Ser136) phosphorylation and 14-3-3 expression. In addition, lupeol treatment inhibited cell survival by inactivation of NF-κB through up-regulation of its inhibitor IκBα. The Caspase mediated apoptosis was noticed by decrease in lupeol induced apoptosis by Caspase inhibitors as well as increase in reactive oxygen species generation and loss of mitochondrial membrane potential. These results suggest that lupeol could be an effective anti-cancer agent and merits further investigation.

Resveratrol enhances ultraviolet B-induced cell death through nuclear factor-κB pathway in human epidermoid carcinoma A431 cells

Resveratrol has been reported to suppress cancer progression in several in vivo and in vitro models, whereas ultraviolet B (UVB), a major risk for skin cancer, is known to induce cell death in cancerous cells. Here, we investigated whether resveratrol can sensitize A431 human epidermoid carcinoma cells to UVB-induced cell death. We examined the combined effect of UVB (30 mJ/cm(2)) and resveratrol (60 microM) on A431 cells. Exposure of A431 carcinoma cells to UVB radiation or resveratrol can inhibit cell proliferation and induce apoptosis. However, the combination of resveratrol and UVB exposure was associated with increased proliferation inhibition of A431 cells compared with either agent alone. Furthermore, results showed that resveratrol and UVB treatment of A431 cells disrupted the nuclear factor-kappaB (NF-kappaB) pathway by blocking phosphorylation of serine 536 and inactivating NF-kappaB and subsequent degradation of IkappaBalpha, which regulates the expression of survivin. Resveratrol and UVB treatment also decreased the phosphorylation of tyrosine 701 of the important transcription factor signal transducer activator of transcription (STAT1), which in turn inhibited translocation of phospho-STAT1 to the nucleus. Moreover, resveratrol/UVB also inhibited the metastatic protein LIMK1, which reduced the motility of A431 cells. In conclusion, our study demonstrates that the combination of resveratrol and UVB act synergistically against skin cancer cells. Thus, resveratrol is a potential chemotherapeutic agent against skin carcinogenesis.

Induction of apoptosis by tea polyphenols mediated through mitochondrial cell death pathway in mouse skin tumors.

Many naturally occurring phytochemicals have shown cancer chemopreventive potential in a variety of bioassay systems. One such naturally occurring biologically active compound is tea (Camellia sinensis), which is the most consumed beverage in the world after water. The most abundant and active constituents of tea are polyphenols (epigallocatechin gallate and theaflavins). In the present study, cancer chemopreventive properties of both black tea polyphenols (BTP) and green tea polyphenols (GTP) on 7,12- dimethylbenz[a]anthracene (DMBA) induced mouse skin carcinogenesis were studied. BTP and GTP treatment showed delay in onset of tumorigenesis, reduction in cumulative number of tumors and increased tumor free survival. Both BTP and GTP were found to modulate the expression of proteins involved in apoptotic pathway. Tea polyphenols treatment along with DMBA exposure resulted in up-regulation of p53, and proapoptotic protein Bax, whereas enhanced expression of antiapoptotic proteins, Bcl-2 and survivin by DMBA were down-regulated. Further, we showed that tea polyphenols supplementation resulted in release of cytochrome c, caspases activation, and increase in apoptotic protease activating factor and poly (ADP-ribose) polymerase cleavage as mechanism of apoptosis induction. The results also provide strong evidence that BTP is a better chemopreventive agent against skin tumorigenesis as compared to GTP at the tested dose levels. Thus, we can conclude that the polyphenolic constituents present in black tea and green tea induce mitochondrial pathway of apoptosis and hence can be used as a potential chemopreventive agents against skin cancer.

Inhibitory effects of tea polyphenols by targeting cyclooxygenase-2 through regulation of nuclear factor kappa B, Akt and p53 in rat mammary tumors

SummaryBreast cancer has become the second leading cause of cancer-related deaths worldwide. The control of this disease can be achieved through chemoprevention, which refers to the consumption of synthetic or naturally occurring agents to block, reverse, or delay the process of tumor development. Tea (Camellia sinensis), the most widely consumed beverage, has shown promises in the field of cancer chemoprevention. Inhibition of tumorigenesis by green or black tea polyphenols has been demonstrated in various in vitro and in vivo models. Here, we examined the inhibitory effect of green tea polyphenol (GTP) and black tea polyphenol (BTP) on the development of mammary tumors- induced by 7, 12-dimethylbenz (a) anthracene (DMBA) in female, Wistar rats. 13% and 33% of animals developed tumors in GTP and BTP supplemented groups, respectively. Both GTP and BTP are effective in significantly inhibiting the cumulative number of mammary tumors (by ~92% and 77%, respectively) and in reducing their growth. Mechanistically, we investigated the effects of GTP and BTP on the components of cell signaling pathways, connecting biomolecules involved in cancer development. GTP and BTP supplementation as a sole source of drinking solution leads to scavenging of reactive oxygen species (ROS) (by ~72% and 69%, respectively) by inhibiting cyclooxygenase-2 (Cox-2) and inactivation of phosphorylated forms of nuclear factor-kappa B (NF-κB) and Akt. Altogether, the study suggests that both cultivars of tea, i.e. green and black, have anti-tumorigenic potential against DMBA-induced mammary tumorigenesis in Wistar rats. Further studies such as large and long term cohort studies and clinical trials are warranted.