An information-theoretic analysis of genetics, gender and age in cancer patients

Germline genetics, gender and hormonal-signaling pathways are all well described modifiers of cancer risk and progression. Although an improved understanding of how germline genetic variants interact with other cancer risk factors may allow better prevention and treatment of human cancer, measuring and quantifying these interactions is challenging. In other areas of research, Information Theory has been used to quantitatively describe similar multivariate interactions. We implemented a novel information-theoretic analysis to measure the joint effect of a high frequency germline genetic variant of the p53 tumor suppressor pathway (MDM2 SNP309 T/G) and gender on clinical cancer phenotypes. This analysis quantitatively describes synergistic interactions among gender, the MDM2 SNP309 locus, and the age of onset of tumorigenesis in p53 mutation carriers. These results offer a molecular and genetic basis for the observed sexual dimorphism of cancer risk in p53 mutation carriers and a model is proposed that suggests a novel cancer prevention strategy for p53 mutation carriers.     

Mechanistic understanding of β-cryptoxanthin and lycopene in cancer prevention in animal models

To better understand the potential function of carotenoids in the chemoprevention of cancers, mechanistic understanding of carotenoid action on genetic and epigenetic signaling pathways is critically needed for human studies. The use of appropriate animal models is the most justifiable approach to resolve mechanistic issues regarding protective effects of carotenoids at specific organs and tissue sites. While the initial impetus for studying the benefits of carotenoids in cancer prevention was their antioxidant capacity and pro-vitamin A activity, significant advances have been made in the understanding of the action of carotenoids with regards to other mechanisms. This review will focus on two common carotenoids, provitamin A carotenoid β-cryptoxanthin and non-provitamin A carotenoid lycopene, as promising chemopreventive agents or chemotherapeutic compounds against cancer development and progression. We reviewed animal studies demonstrating that β-cryptoxanthin and lycopene effectively prevent the development or progression of various cancers and the potential mechanisms involved. We highlight recent research that the biological functions of β-cryptoxanthin and lycopene are mediated, partially via their oxidative metabolites, through their effects on key molecular targeting events, such as NF-κB signaling pathway, RAR/PPARs signaling, SIRT1 signaling pathway, and p53 tumor suppressor pathways. The molecular targets by β-cryptoxanthin and lycopene, offer new opportunities to further our understanding of common and distinct mechanisms that involve carotenoids in cancer prevention.This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.     

Resveratrol- induced apoptosis is mediated by p53-dependent pathway in Hep G2 cells

Resveratrol, a phytoalexin found in many plants, has been reported to possess a wide range of pharmacological properties and is one of the promising chemopreventive agents for cancer. Here, we examined the antiproliferation effect of resveratrol in two human liver cancer cell lines, Hep G2 and Hep 3B. Our results showed that resveratrol inhibited cell growth in p53-positive Hep G2 cells only. This anticancer effect was a result of cellular apoptotic death induced by resveratrol via the p53-dependent pathway. Here we demonstrated that the resveratrol-treated cells were arrested in G1 phase and were associated with the increase of p21 expression. In addition, we also illustrated that the resveratrol-treated cells had enhanced Bax expression but they were not involved in Fas/APO-1 apoptotic signal pathway. In contrast, the p53-negative Hep 3B cells treated with resveratrol did not show the antiproliferation effect neither did they show significant changes in p21 nor Fas/APO-1 levels. In summary, our study demonstrated that the resveratrol effectively inhibited cell growth and induced programmed cell death in Hepatoma cells on a molecular basis. Furthermore, these results implied that resveratrol might also be a new potent chemopreventive drug candidate for liver cancer as it played an important role to trigger p53-mediated molecules involved in the mechanism of p53-dependent apoptotic signal pathway.     

PRIMA-1 induces apoptosis by inhibiting JNK signaling but promoting the activation of Bax

The p53 protein plays a major role in the maintenance of genome stability in mammalian cells. Mutations of p53 occur in over 40% of breast cancers and are indicative of tumor resistance to chemotherapeutic agents. Recently, there has been a high degree of interest in pharmacological approaches for restoring the normal function to mutant p53. The low molecular weight compound p53 reactivation and induction of massive apoptosis (PRIMA-1) was shown to induce cytotoxic effects and apoptosis in human tumor cells with mutant p53. Here, we studied the molecular mechanisms of PRIMA-1-induced apoptosis in human breast cancer cells with p53 mutations such as MDA-231 and GI-101A as compared to MCF-7 cells. We show that PRIMA-1 selectively induces apoptosis in human breast cancer cells MDA-231 and GI-101A compared to the MCF-7. This effect was paralleled by an increase in total p53 level in the nucleus and the induction of its phosphorylation at Ser-15 site. Using the chromatin immunoprecipitation (ChIP) assays, we show that PRIMA-1 restored p53 DNA binding activity to the promoters of the proapoptotic genes such as Bax and PUMA, but inhibited the binding activity to the promoters of the MAP4K4 gene. Knockdown of p53 protein in breast cancer cells using siRNA followed by PRIMA-1 treatment resulted in decline of Bax and PUMA proteins expression. Cell incubation with either PRIMA-1 or SP600125 (c-Jun NH2-terminal kinase inhibitor) resulted in the abrogation of adriamycin-induced c-Jun NH2-terminal kinase (JNK) activation, whereas Bax activation was not inhibited. We conclude that both Bax and PUMA but not JNK signaling are involved in PRIMA-1-induced apoptosis in breast cancer cells with p53 mutation.     

Targeting signal transduction pathways by chemopreventive agents

Cancer is a dynamic process that involves many complex factors, which may explain why a "magic bullet" cure for cancer has not been found. Death rates are still rising for many types of cancers, which possibly contributes to the increased interest in chemoprevention as an alternative approach to the control of cancer. This strategy for cancer control is based on the presumption that because cancer develops through a multi-step process, each step may be a prospective target for reversing or suppressing the process. Thus, the design and development of chemopreventive agents that act on specific and/or multiple molecular and cellular targets is gaining support as a rational approach to control cancer. Nutritional or dietary factors have attracted a great deal of interest because of their perceived ability to act as highly effective chemopreventive agents. They are professed as being generally safe and may have efficacy as chemopreventive agents by preventing or reversing premalignant lesions and/or reducing second primary tumor incidence. Many of these dietary compounds appear to act on multiple target signaling pathways. Some of the most interesting and well documented are resveratrol and components of tea, including EGCG, theaflavins and caffeine. This review will focus on recent work regarding three well-accepted cellular/molecular mechanisms that may at least partially explain the effectiveness of selected food factors, including those indicated above, as chemopreventive anti-promotion agents. These food compounds may act by: (1) inducing apoptosis in cancer cells; (2) inhibiting neoplastic transformation through the inhibition of AP-1 and/or NF-kappaB activation; and/or (3) suppressing COX-2 overexpression in cancer cells.     

Germline BRCA1 mutations predispose to pancreatic adenocarcinoma

Although the association of germline BRCA2 mutations with pancreatic adenocarcinoma is well established, the role of BRCA1 mutations is less clear. We hypothesized that the loss of heterozygosity at the BRCA1 locus occurs in pancreatic cancers of germline BRCA1 mutation carriers, acting as a “second-hit” event contributing to pancreatic tumorigenesis. Seven germline BRCA1 mutation carriers with pancreatic adenocarcinoma and nine patients with sporadic pancreatic cancer were identified from clinic- and population-based registries. DNA was extracted from paraffin-embedded tumor and nontumor samples. Three polymorphic microsatellite markers for the BRCA1 gene, and an internal control marker on chromosome 16p, were selected to test for the loss of heterozygosity. Tumor DNA demonstrating loss of heterozygosity in BRCA1 mutation carriers was sequenced to identify the retained allele. The loss of heterozygosity rate for the control marker was 20%, an expected baseline frequency. Loss of heterozygosity at the BRCA1 locus was 5/7 (71%) in BRCA1 mutation carriers; tumor DNA was available for sequencing in 4/5 cases, and three demonstrated loss of the wild-type allele. Only 1/9 (11%) sporadic cases demonstrated loss of heterozygosity at the BRCA1 locus. Loss of heterozygosity occurs frequently in pancreatic cancers of germline BRCA1 mutation carriers, with loss of the wild-type allele, and infrequently in sporadic cancer cases. Therefore, BRCA1 germline mutations likely predispose to the development of pancreatic cancer, and individuals with these mutations may be considered for pancreatic cancer-screening programs.     

The selenium analog of the chemopreventive compound S,S′-(1,4-phenylenebis[1,2-ethanediyl])bisisothiourea is a remarkable inducer of apoptosis and inhibitor of cell growth in human non-small cell lung cancer

Lung cancer continues to be the leading cause of cancer deaths throughout the world and conventional therapy remains largely unsuccessful. Although, chemoprevention is a plausible alternative approach to curb the lung cancer epidemic, clinically there are no effective chemopreventive agents. Thus, development of novel compounds that can target cellular and molecular pathways involved in the multistep carcinogenesis process is urgently needed. Previous studies have suggested that substitution of sulfur by selenium in established cancer chemopreventive agents may result in more effective analogs. Thus in the present study we selected the chemopreventive agent S,S′-(1,4-phenylenebis[1,2-ethanediyl])bisisothiourea (PBIT), also known to inhibit inducible nitric oxide synthase (iNOS), synthesized its selenium analog (Se-PBIT) and compared both compounds in preclinical model systems using non-small cell lung cancer (NSCLC) cell lines (NCI-H460 and A549); NSCLC is the most common histologic type of all lung cancer cases. Se-PBIT was found to be superior to PBIT as an inducer of apoptosis and inhibitor of cell growth. Se-PBIT arrested cell cycles at G1 and G2-M stage in both A549 and H460 cell lines. Although both compounds are weakly but equally effective inhibitors of iNOS protein expression and activity, only Se-PBIT significantly enhanced the levels of p53, p38, p27 and p21 protein expression, reduced levels of phospholipase A2 (PLA2) but had no effect on cyclooxygenase-2 (COX-2) protein levels; such molecular targets are involved in cell growth inhibition, induction of apoptosis and cell cycle regulation. The results indicate that Se-PBIT altered molecular targets that are involved in the development of human lung cancer. Although, the mechanisms that can fully account for these effects remain to be determined, the results are encouraging to further evaluate the chemopreventive efficacy of Se-PBIT against the development of NSCLC in a well-defined animal model.     

Cell cycle checkpoints and their impact on anticancer therapeutic strategies

Cells contain numerous pathways designed to protect them from the genomic instability or toxicity that can result when their DNA is damaged. The p53 tumor suppressor is particularly important for regulating passage through G1 phase of the cell cycle, while other checkpoint regulators are important for arrest in S and G2 phase. Tumor cells often exhibit defects in these checkpoint proteins, which can lead to hypersensitivity; proteins in this class include ataxia-telangiectasia mutatated (ATM), Meiotic recanbination 11 (Mre11), Nijmegen breakage syndrome 1 (Nbs 1), breast cancer susceptibility genes 1 and 2 (BRCA1), and (BRCA2). Consequently, tumors should be assessed for these specific defects, and specific therapy prescribed that has high probability of inducing response. Tumors defective in p53 are frequently considered resistant to apoptosis, yet this defect also provides an opportunity for targeted therapy. When their DNA is damaged, p53-defective tumor cells preferentially arrest in S or G2 phase where they are susceptible to checkpoint inhibitors such as caffeine and UCN-01. These inhibitors preferentially abrogate cell cycle arrest in p53-defective cells, driving them through a lethal mitosis. Wild type p53 can prevent abrogation of arrest by elevating levels of p21(waf1) and decreasing levels of cyclins A and B. During tumorigenesis, tumor cells frequently loose checkpoint controls and this facilitates the development of the tumor. However, these defects also represent an Achilles heel that can be targeted to improve current therapeutic strategies.     

Proliferative inhibition, cell-cycle dysregulation, and induction of apoptosis by ursolic acid in human non-small cell lung cancer A549 cells

Ursolic acid (UA) is a pentacyclic triterpene compound isolated from many types of medicinal plants and is present in human diet. It has been reported to possess a wide range of pharmacological properties, and is one of the most promising chemopreventive agents for cancer. Here, we report that UA inhibits the cell proliferation of human lung cancer cell line A549 and provide a molecular understanding of this effect. The results showed that UA blocked cell cycle progression in the G1 phase that was associated with a marked decrease in the protein expression of cyclin D1, D2, and E and their activating partner cdk2, 4, and 6 with concomitant induction of p21/WAF1. This accumulation of p21/WAF1 might be through a p53-dependent manner. Further, UA treatment also resulted in the triggering of apoptosis as determined by DNA fragmentation assay. This effect was found to correlate with the up-regulation of Fas/APO-1, Fas ligand, and Bax, and down-regulation of NF-kappaB, Bcl-2, and Bcl-XL. Taken together, our study indicated that UA might be a potential chemopreventive agent for lung cancer.