Association of methylenetetrahydrofolate reductase gene polymorphisms & colorectal cancer in India

Background & objectives: Methylenetetrahydrofolate reductase (MTHFR) is a critical enzyme in folate metabolism and involved in DNA synthesis, DNA repair and DNA methylation. The two common functional polymorphisms of MTHFR, 677C -> T and 1298 A -> C have shown to impact several diseases including cancer. This case-control study was undertaken to analyse the association of the MTHFR gene polymorphisms 677 C -> T and 1298 A -> C and risk of colorectal cancer (CRC).Methods: One hundred patients with a confirmed histopathologic diagnosis of CRC and 86 age and gender matched controls with no history of cancer were taken for this study. DNA was isolated from peripheral blood samples and the genotypes were determined by PCR-RFLP. The risk association was estimated by compounding odds ratio (OR) with 95 per cent confidence interval (CI). Results: Genotype frequency of MTHFR 677 CC, CT and TT were 76.7, 22.1 and 1.16 per cent in controls, and 74,25 and 1.0 per cent among patients. The 'T' allele frequency was 12.21 and 13.5 per cent in controls and patients respectively. The genotype frequency of MTHFR 1298 AA, AC, and CC were 25.6, 58.1 and 16.3 per cent for controls and 22, 70 and 8 per cent for patents respectively. The 'C' allele frequency for 1298 A -> C was 43.0 and 45.3 per cent respectively for controls and patients. The OR for 677 CT was 1.18 (95% CI 0.59-2.32, P = 0.642), OR for 1298 AC was 1.68 (95% CI 0.92-3.08, P = 0.092) and OR for 1298 CC was 0.45(95% CI 0.18-1.12, P = 0.081). The OR for the combined heterozygous state (677 CT and 1298 AC) was 1.18(95% CI 0.52-2.64, P =0.697).Interpretation & conclusion: The frequency of the MTHFR 677 TT genotype is rare as compared to 1298 CC genotype in the population studied. There was no association between 677 C -> T and 1298 A -> C polymorphisms and risk of CRC either individually or in combination. The homozygous state for 1298 A -> C polymorphism appears to slightly lower risk of CRC. This needs to be confirmed with a larger sample size.

Cross Talk between Receptor Guanylyl Cyclase C and c-src Tyrosine Kinase Regulates Colon Cancer Cell Cytostasis

Increased activation of c-src seen in colorectal cancer is an indicator of a poor clinical prognosis, suggesting that identification of downstream effectors of c-src may lead to new avenues of therapy. Guanylyl cyclase C (GC-C) is a receptor for the gastrointestinal hormones guanylin and uroguanylin and the bacterial heat-stable enterotoxin. Though activation of GC-C by its ligands elevates intracellular cyclic GMP (cGMP) levels and inhibits cell proliferation, its persistent expression in colorectal carcinomas and occult metastases makes it a marker for malignancy. We show here that GC-C is a substrate for inhibitory phosphorylation by c-src, resulting in reduced ligand-mediated cGMP production. Consequently, active c-src in colonic cells can overcome GC-C-mediated control of the cell cycle. Furthermore, docking of the c-src SH2 domain to phosphorylated GC-C results in colocalization and further activation of c-src. We therefore propose a novel feed-forward mechanism of activation of c-src that is induced by cross talk between a receptor GC and a tyrosine kinase. Our findings have important implications in understanding the molecular mechanisms involved in the progression and treatment of colorectal cancer.

Counselling and predictive testing for familial adenomatous polyposis in a rural South Indian community

Background—Mutations of the APC gene cause familial adenomatous polyposis (FAP), a hereditary colorectal cancer predisposition syndrome.Aims—To conduct a cost comparison analysis of predictive genetic testing versus conventional clinical screening for individuals at risk of inheriting FAP, using the perspective of a third party payer. Methods—All direct health care costs for both screening strategies were measured according to time and motion, and the expected costs evaluated using a decision analysis model.Results—The baseline analysis predicted that screening a prototype FAP family would cost $4975/£3109 by molecular testingand $8031/£5019 by clinical screening strategy, when family members were monitored with the same frequency of clinical surveillance (every two to three years). Sensitivity analyses revealed that the genetic testing approach is cost saving for key variables including the kindred size, the age of screening onset, and the cost of mutation identification in a proband. However, if the APC mutation carriers were monitored at an increased (annual) frequency, the cost of the genetic screening strategy increased to $7483/ £4677 and was especially sensitive to variability in age of onset of screening, family size, and cost of genetic testing of at risk relatives. Conclusions—In FAP kindreds, a predictive genetic testing strategy costs less than conventional clinical screening, provided that the frequency of surveillance is identical using either strategy. An additional significant benefit is the elimination of unnecessary colonic examinations for those family members found to be noncarriers.

Protamine-Capped Mesoporous Silica Nanoparticles for Biologically Triggered Drug Release

The fabrication of a mesoporous silica nanoparticle (MSN)-protamine hybrid system (MSN-PRM) is reported that selectively releases drugs in the presence of specific enzyme triggers present in the proximity of cancer cells. The enzyme trigger involved is a protease called trypsin, which is overexpressed in certain specific pathological conditions, such as inflammation and cancer. Overexpression of trypsin is known to be associated with invasion, metastasis, and growth in several cancers, such as leukemia, colon cancer, and colorectal cancer. The current system (MSN-PRM) consists of an MSN support in which mesopores are capped with an FDA-approved peptide drug protamine, which effectively blocks the outward diffusion of the drug molecules from the mesopores of the MSNs. On exposure to the enzyme trigger, the protamine cap disintegrates, opening up the molecular gates and releasing the entrapped drug molecules. The system exhibits minimal premature release in the absence of the trigger and selectively releases the encapsulated drugs in the presence of the proteases secreted by colorectal cancer cells. The ability of the MSN-PRM particles to deliver anticancer drugs to colorectal cancer cells has also been demonstrated. The hydrophobic drug is released into cancer cells subsequent to disintegration of the protamine cap, resulting in cell death. Drug-induced cell death in colorectal cancer cells is significantly enhanced when the hydrophobic drug that is known to degrade in aqueous environments is encapsulated in the MSN-PRM system in comparison to the free drug (P < 0.05). The system, which shows good biocompatibility and selective drug release, is a promising platform for cancer specific drug delivery.