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The polymorphic human GSTP1 gene locus encodes proteins that differentially metabolize electrophilic substrates, including, many chemotherapeutic agents used in clinical cancer therapy. In this study, we used Escherichia coli XL1-Blue MRF ′ strain, transformed with phagemid expression vectors carrying cDNAs of three GSTP1 alleles, to investigate the cytoprotective abilities of the different GSTP1 alleles against four clinically active anticancer agents, namely, carboplatin, cisplatin, thiotepa, and 4-hydroperoxyifosfamide. Following induction of protein expression with isopropyl-β-d-thiogalactoside, the cells were treated with each drug for 3 h (1 h for 4-hydroperoxyifosfamide). Surviving fractions were determined and used to compute a cytoprotective factor for each allele against each drug. The results showed all the GSTP1 alleles to be cytoprotective, albeit, to different degrees. For cisplatin and carboplatin, the GSTP1*C allele was most protective, with CPs of 5.58 and 3.76, respectively, compared with 1.21 and 1.61 for GSTP1*A and 2.50 and 2.79 for GSTP1*B. In contrast, protection against thiotepa was highest for the GSTP1*A allele, with a cytoprotective factor of 1.56, compared to 1.32 for GSTP1*B and 1.1 for GSTP1*C. For 4-hydroperoxyifosfamide, the CP for GSTP1*B and GSTP1*C was the same, 1.45, compared with 1.18 for GSTP1*A. These data demonstrate significant differences in the ability of the different GSTP1 alleles to protect against the cytotoxicity of electrophilic anticancer agents. The level of protection differs significantly between different GSTP1 alleles, and between different anticancer agents. The optimized prokaryotic system described provides a useful and rapid tool for pharmacogenetic analysis of the effects of genes on drug sensitivity.