Appraisal of mechanisms of radioprotection and therapeutic approaches of radiation countermeasures.

Radiation countermeasures are radioprotective agents that reduce the harmful effects of ionizing radiation. They have wide range of applications extending from protection of normal tissues of cancer patients during radiotherapy to safeguard people aftermath of radiologic or nuclear accidents. Despite the screening of thousands of natural and synthetic compounds, only few found place in clinic with limited tolerance. Therefore, mechanistic understanding is essential in the development of more suitable and customized radiation countermeasure agents. This review focuses on the mechanisms of radioprotection imparted by these agents. Radioprotectors are diverse and act through widely varying mechanisms that can be classified in 10 categories: 1) scavenging of free radicals; 2) enhancing DNA repair; 3) synchronizing of cells; 4) modulating redox sensitive genes; 5) modulating growth factors and cytokines; 6) inhibiting apoptosis; 7) repurposing of drug; 8) interacting and chelating of radionuclides; and therapeutic methods of tissue regeneration such as 9) gene therapy; and 10) stem cell therapy. The most common mechanism of radioprotection is the scavenging of free radicals whereas, modulation of growth factors, cytokines and redox genes emerge as effective strategies. Gene and stem cell therapies as therapeutic radiation countermeasures are being developed and can be applied in the near future to minimize the side effects of radiation exposure through tissues regenerations. Thus, the management of radiation exposure may require a holistic multi-mechanistic approaches to achieve optimal radiation protection during radiotherapy of cancer patients and in cases of nuclear eventualities.

Genetic Predisposition to Cervical Cancer and the Association With XRCC1 and TGFB1 Polymorphisms.

OBJECTIVE: Cervical carcinoma (CC), a multifactorial cancer, is assumed to have a host genetic predisposition component that modulates its susceptibility in various populations. We investigated the association between CC risk in Saudi women and 6 single-nucleotide polymorphisms (SNPs) in hypothesis-driven candidate genes. METHODS: A total of 545 females were included, comprising 232 CC patients and 313 age-/sex-matched control subjects. Six SNPs (CDKN1A C31A, ATM G1853A, HDM2 T309G, TGFB1 T10C, XRCC1 G399A, and XRCC3 C241T) were genotyped by direct sequencing. RESULTS: Of the 6 SNPs studied, TGFB1 T10C (odds ratio, 0.74; 95% confidence interval, 0.57-0.94) and XRCC1 G399A (odds ratio, 1.45; 95% confidence interval, 1.11-1.90) displayed different frequencies in cancer patients and control subjects and showed statistically significant association in univariate (P = 0.017, P = 0.005, respectively) analysis. The Cochran-Armitage trend test had confirmed the results (P = 0.027 and P = 0.006, respectively), indicating an ordering in the effect of the risk alleles in CC patients. The 2 SNPs, TGFB1 T10C and XRCC1 G399A, showed also degrees of deviation from Hardy-Weinberg equilibrium in cancer patients (P = 0.001 and P = 0.083, respectively) but not in the control subjects. Furthermore, correction for multiple testing using multivariate logistic regression to assess the joint effect of all SNPs has sustained significant statistical association (P = 0.025 and P = 0.009, respectively). CONCLUSIONS: TGFB1 T10C and XRCC1 G399A SNPs were associated with CC risk in univariate and multivariate analysis and displayed allele-dosage effects and coselection in cancer patients. Patients harboring the majority allele TGFB1 T10 (Leu) or the variant allele XRCC1 399A (Gln) have approximately 1.5-fold increased risk to develop CC. Host SNPs genotyping may provide relevant biomarkers for CC risk assessment in personalized preventive medicine.