Since ancient times, natural products, herbs and spices have been used for preventing several diseases, including cancer. The term chemoprevention was coined in the late 1970s and referred to the prevention of cancer by selective use of phytochemicals or their analogs. The field utilizes experimental carcinogenesis models to examine the efficacy of chemopreventive agents in a stage-specific manner. The concept of using naturally derived chemicals as potential chemopreventive agents has advanced the field dramatically. Throughout the years, a vast number of chemopreventive agents present in natural products have been evaluated using various experimental models. A number of them have progressed to early clinical trials. More recently, the focus has been directed towards molecular targeting of chemopreventive agents to identify mechanism(s) of action of these newly discovered bioactive compounds. Moreover, it has been recognized that single agents may not always be sufficient to provide chemopreventive efficacy, and, therefore, the new concept of combination chemoprevention by multiple agents or by the consumption of "whole foods" has become an increasingly attractive area of study. Novel technologies, such as nanotechnology, along with a better understanding of cancer stem cells, are certain to continue the advancement of the field of cancer chemoprevention in years to come.

Numerous numbers of biologically active agents have been identified for their diverse therapeutic functions. Detailed investigations of phytochemicals for antiviral activities have assumed greater importance in the last few decades. A wide variety of active phytochemicals, including the flavonoids, terpenoids, organosulfur compounds, limonoids, lignans, sulphides, polyphenolics, coumarins, saponins, chlorophyllins, furyl compounds, alkaloids, polyines, thiophenes, proteins and peptides have been found to have therapeutic applications against different genetically and functionally diverse viruses. The antiviral mechanism of these agents may be explained on basis of their antioxidant activities, scavenging capacities, inhibiting DNA, RNA synthesis, inhibition of the viral entry, or inhibiting the viral reproduction etc. Large number candidate substances such as phytochemicals and their synthetic derivatives have been identified by a combination of in vitro and in vivo studies in different biological assays. In this article we have made attempts to extensively review and provide comprehensive description of different phyto-antiviral agents. We have examined the recent developments in the field of plant derived antiviral agents. The major advances in the field of viral interactions in various biological assays have been summarized. In addition sources of origin, major viral studies mechanistic action and phase trials of various phytoantiviral agents have been included in the review.

The identification of differentially regulated apoptotic signals in normal and tumor cells allows the development of cancer cellselective therapies. Increasing evidence shows that the inhibitor of apoptosis (IAP) proteins survivin and XIAP are highly expressed in tumor cells but are absent or have very low levels of expression in normal adult tissues. We found that inhibiting AKT activity with 10 to 100 nM deguelin, a small molecule derived from natural products, markedly reduced the levels of both survivin and XIAP, inducing apoptosis in human breast cancer cells but not in normal cells. It is noteworthy that we detected an elevated level of cleaved poly(ADP-ribose) polymerase, a signature of caspase activation, without a significant increase in caspase activity in deguelin-treated cancer cells. Our results suggest that severe down-regulation of the IAPs by deguelin releases their inhibitory activity over pre-existing active caspases present in cancer cells, inducing apoptosis without the need for further caspase activation. Because normal cells have very low levels of p-AKT, XIAP, survivin, and preexisting caspase activity, deguelin had little effect on those cells. In addition, we found that combining deguelin with chemotherapy drugs enhanced drug-induced apoptosis selectively in human tumor cells, which suggests that deguelin has great potential for chemosensitization and could represent a new therapeutic agent for treatment of breast cancer.The development of mechanisms that give resistance to apoptosis confers both a high survival ability and a low drug sensitivity to human cancer cells (Deveraux and Reed, 1999;Reed, 1999). To develop cancer-specific therapeutic approaches, it is important to identify the molecular targets in the apoptotic pathway that are differentially regulated in normal and tumor cells. It is well known that a balance of pro-and anti-apoptotic factors determines whether a cell survives or undergoes apoptosis (Igney and Krammer, 2002;Yang et al., 2003). In tumor cells, apoptosis can be induced either by activation of molecules upstream of apoptosis signaling or by inhibition of antiapoptotic factors (Mesri et al., 2001;Reed, 2001). A previous study of ours shows that although direct activation of caspase 3 is able to induce apoptosis, normal cells still seem to be more sensitive to caspase 3-induced activation of apoptosis than human tumor cells are (Yang et al., 2003). The presence in cancer cells, but not normal cells, of high levels of antiapoptotic factors, such as the inhibitor of apoptosis (IAP) proteins may confer this insensitivity to apoptosis induction by caspase 3 activation in tumor cells. Members of the IAP family of proteins contain one or more conserved regions termed baculoviral IAP repeat (BIR) N-terminal domains and a C-terminal RING domain (Deveraux and Reed, 1999;Reed, 1999). The BIR domain of these IAP binds to active caspases to block their activity, whereas the RING domain acts as an ubiquitin ligase to facilitate proteasomal degradation of caspases (Listo...

Selenium is an important trace element involved in different physiological functions of human body. Knowledge of selenium in biology of cancer has increased at rapid rate especially during last two decades. Basic research and clinical studies involving animal models and more recently studies in human strongly support the protective role of selenium against various types of cancer. Selenium's role as an essential nutrient is as a result of its unique chemistry enabled by the presence of selenium in selenoproteins. Epidemiological findings have linked inadequate status of selenium to increased risk of cancer. The protective action of selenium is a combination of various mechanisms. Amongst all the diverse mechanism that have been proposed some important ones are (a) Protective role of selenoproteins/selenoenzymes (b) induction of apoptosis (c) immune system effects (d) detoxification of antagonistic metals (e) inactivation of nuclear transcription factor (f) regulation of lipoxygenases (g) effect on advanced cancer condition (h) reduction of oxidative stress (i) induction of Phase II enzymes (j) androgen receptor down regulation (k) inhibition of DNA adduct formation (l) cell cycle arrest. The purpose of this review is to focus the recent development in the field of cancer prevention utilizing selenium. The metabolism of selenium compounds , carcinogenesis studies, epidemiological data, and various proposed chemopreventive mechanisms of selenium compounds along with results of human intervention trials have been discussed.

Cancer chemoprevention refers to the use of pharmacological agents to inhibit, delay or reverse the multi-step process of carcinogenesis. The last two decades in particular have witnessed explosive growth in this emerging field of cancer chemoprevention. Extensive efforts to evaluate possible application of various chemopreventive agents, in individuals at high risk of neoplastic development have been carried out. Epidemiological studies suggest a protective role of several agents in reducing the risk of cancer. The protective action of all these agents is explained as a combination of various proposed mechanisms involving anti-oxidant, anti-inflammatory, immunomodulatory action, apoptosis induction, molecular association with carcinogen, cell cycle arrest, cell differentiation induction, antimicrobial effect, and anti- angiogenesis etc. Large numbers of candidate substances such as phytochemicals and their synthetic derivatives have been identified by a combination of in vitro and in vivo studies in a wide range of biological assays. However, a comprehensive description of these chemopreventive agents has not been extensively reviewed. In this review we discuss cancer chemopreventive agents in relation to their source, efficacy in cancer chemopreventive action in vivo and epidemiological data. The experimental carcinogenesis studies in different biological models, in addition to the contribution from our laboratory are summarized.