Pharmacogenetics of the human glutathione S-transferase P1 gene in the metabolism and therapeutic efficacy of cis-diamminedichloroplatinum

The human GSTP1 gene has been shown, conclusively, to be polymorphic. The three main GSTP1 alleles, GSTP1*A, GSTP1*B, and GSTP1*C, encode proteins which differ in the 3-dimensional structure of their active sites and in their function in phase II metabolism of carcinogens, mutagens, and anticancer agents. Although, it is well established that GSTP1 is over expressed in many human tumors and that the levels of GSTP1 expression correlate directly with tumor resistance to chemotherapy and inversely with patient survival, the significance of the polymorphic GSTP1 gene locus on tumor response to chemotherapy remains unclear. The goal of this project was to define the role and significance of the polymorphic GSTP1 gene locus in GSTP1-based tumor drug resistance and as a determinant of patient response to chemotherapy. The hypothesis to be tested was that the polymorphic GSTP1 gene locus will confer to tumors a differential ability to metabolize cisplatin resulting in a GSTP1 genotype-based sensitivity to cisplatin. The study examined: (a) whether the different GSTP 1 alleles confer different levels of cellular protection against cisplatin-induced cytotoxicity, (b) whether the allelic GSTP1 proteins metabolize cisplatin with different efficiencies, and (c) whether the GSTP1 genotype is a determinant of tumor response to cisplatin therapy. The results demonstrate that the GSTP1 alleles differentially protect tumors against cisplatin-induced apoptosis and clonogenic cell kill in the rank order: GSTP1*C > GSTP1*B > GSTP1*A. The same rank order was observed for the kinetics of GSTP1-catalyzed cisplatin metabolism, both in cell-free and cellular systems, to the rate-limiting monoglutathionyl-platinum metabolite, which was characterized, for the first time, by mass spectral analysis. Finally, this study demonstrates that both GSTP1 genotype and the level of GSTP1 expression significantly contribute to tumor sensitivity to cisplatin treatment. Overall, the results of this project show that the polymorphic GSTP1 gene locus plays a significant role in tumor sensitivity to cisplatin treatment. Furthermore, these studies have contributed to the overall understanding of the significance of the polymorphic GSTP1 gene locus in tumor resistance to cancer chemotherapy and have provided the basis for further investigations into how this can be utilized to optimize and individualize cancer chemotherapy for cancer patients. ^

Hybrid stochastic simulations of intracellular reaction-diffusion systems.

With the observation that stochasticity is important in biological systems, chemical kinetics have begun to receive wider interest. While the use of Monte Carlo discrete event simulations most accurately capture the variability of molecular species, they become computationally costly for complex reaction-diffusion systems with large populations of molecules. On the other hand, continuous time models are computationally efficient but they fail to capture any variability in the molecular species. In this study a hybrid stochastic approach is introduced for simulating reaction-diffusion systems. We developed an adaptive partitioning strategy in which processes with high frequency are simulated with deterministic rate-based equations, and those with low frequency using the exact stochastic algorithm of Gillespie. Therefore the stochastic behavior of cellular pathways is preserved while being able to apply it to large populations of molecules. We describe our method and demonstrate its accuracy and efficiency compared with the Gillespie algorithm for two different systems. First, a model of intracellular viral kinetics with two steady states and second, a compartmental model of the postsynaptic spine head for studying the dynamics of Ca+2 and NMDA receptors.

Mammalian Snm1 participates in cellular responses to genotoxic and mitotic stress

Eukaryotic cells have evolved a complex network of metabolic processes and regulatory systems to help ensure that hereditary information is protected or restored when exposed to genotoxic agents. Two members of the Snm1 protein family have been characterized; scSNM1/PSO2, a yeast gene responsible for repair of DNA interstrand crosslinks, and hARTEMIS, a human gene that is mutated in radiosensitive severe combined immunodeficiency (RS-SCID). Here we report on another member of this protein family, hSNM1, and its response to DNA damage and mitotic stress. We have found that this protein colocalizes and physically associates with 53BP1, a crucial member of the mammalian response to DNA damage. In addition, hSnm1 interacts with several proteins involved in mitosis, and mSNM1 deficiency causes a mitotic checkpoint defect in mouse embryonic fibroblasts. ^