Role of a DT-diaphorase mutation in the response of anal canal carcinoma to radiation, 5-fluorouracil, and mitomycin C

Pharmacogenetics for individualized cancer chemotherapy

The same doses of medication cause considerable heterogeneity in efficacy and toxicity across human populations. Genetic factors are thought to represent important determinants of drug efficacy and toxicity. Pharmacogenetics focuses on the prediction of the response of tumor and normal tissue to standard therapy by genetic profiling and, thereby, to select the most appropriate medication at optimal doses for each individual patient. In the present review, we discuss the relevance of single nucleotide polymorphisms (SNP) in genes, whose gene products act upstream of the actual drug target sites, that is, drug transporters and drug metabolizing phase I and II enzymes, or downstream of them, that is, apoptosis-regulating genes and chemokines. SNPs in relevant genes, which encode for proteins that interact with anticancer drugs, were also considered, that is, enzymes of DNA biosynthesis and metabolism, DNA repair enzymes, and proteins of the mitotic spindle. A significant body of evidence supports the concept of predicting drug efficacy and toxicity by SNP genotyping. As the efficacy of cancer chemotherapy, as well as the drug-related toxicity in normal tissues is multifactorial in nature, sophisticated approaches such as genome-wide linkage analyses and integrate drug pathway profiling may improve the predictive power compared with genotyping of single genes. The implementation of pharmacogenetics into clinical routine diagnostics including genotype-based recommendations for treatment decisions and risk assessment for practitioners represents a challenge for the future.

Pharmacogenomics and stomach cancer

In subgroups of gastric cancer patients, chemotherapy treatments carry a high risk of toxicity without any clear evidence of antitumor activity. Individualization of therapy is required to treat each patient with the optimal drug and dose. Genetic polymorphisms are the hereditary determinants for interindividual variations of drug effect and the genetic approach represents a new tool to design a tailored therapy. This review focuses on the relevance of the host polymorphisms involved in metabolism, cellular transport and interaction with molecular targets of the drugs used in gastric cancer in conventional or innovative chemotherapy regimens. Pharmacogenetic studies based on a single gene or multi-gene approach (pharmacogenomics) are promising to identify gastric cancer patients at risk for adverse toxicity, but larger and controlled studies are needed to justify changes in the chemotherapeutic strategies.

Clinical significance of a NAD(P)H: quinone oxidoreductase 1 polymorphism in patients with disseminated peritoneal cancer receiving intraperitoneal hyperthermic chemotherapy with mitomycin C

Recent data indicate that NAD(P)H: quinone oxidoreductase 1 (NQO1) is important in the activation of mitomycin C. A polymorphism in human NQO1 (609C>T) is associated with diminished NQO1 activity. The purpose of our study was to determine the effect of the 609C>T polymorphism on tumor NQO1 activity and overall survival in patients with disseminated peritoneal cancer receiving intraperitoneal mitomycin C therapy. Patients with disseminated peritoneal cancer of gastrointestinal or other origin were eligible. Following aggressive surgical debulking, patients were administered a 2-h heated (40.5 degrees C) intraperitoneal perfusion with mitomycin C. NQO1 activity was determined in tumor tissue obtained during surgery and patients were genotyped for the NQO1 C609T polymorphism using a polymerase chain reaction-based method. The major response variable monitored during the trial was overall survival. Of the 117 patients genotyped for the NQO1 609C>T polymorphism, 67% were wild-type (WT), 31% were heterozygous (HE), and 2% were homozygous mutant (HM). In tumor tissue, the mean NQO1 activities from WT (n = 14) and HE (n = 5) patients were 794 +/- 603 and 70 +/- 133.1 nmol/min/mg protein respectively (P = 0.006). Significant differences in survival between WT versus HE/HM genotypes were noted in optimally debulked patients (R0/R1) (43.6+ months, median not yet reached versus 23 months respectively, P = 0.037) and in patients with peritoneal carcinomatosis of colonic origin (18.2 versus 11.5 months respectively, P = 0.050). These data indicate that the NQO1 609C>T polymorphism results in significantly reduced tumor NQO1 activity and reduced survival in subsets of patients receiving intraperitoneal hyperthermic mitomycin C therapy.

Assessment of the relationship between genotypic status of a DT-diaphorase point mutation and enzymatic activity

DT-diaphorase, a cytosolic reductase, has been implicated as an activator of chemotherapeutic prodrugs and a detoxifier of certain potentially carcinogenic xenobiotics. A common C to T nucleotide 609 substitution in DT-diaphorase cDNA has been associated with protein instability and reduced catalytic activity. The degree to which the allelic status of the substitution correlates with enzymatic activity was assessed in 45 normal human skin fibroblast strains using a PCR-RFLP assay. Included in this study was the 3437T strain, which is unique in that it is heterozygous for the polymorphism yet contains undetectable enzymatic activity. An allele-specific RT-PCR-RFLP technique attributed this phenomenon to exclusive DT-diaphorase mRNA expression from the variant allele. Overlap in activities was observed between individual strains homozygous for the wild-type allele and heterozygotes, but the former group displayed enzymatic activity that was on average 2-fold higher. Western blot analysis of the two strains in this panel that are homozygous for the variant allele revealed that they express relatively low amounts of DT-diaphorase protein, consistent with the role of the substitution in protein instability. This work confirms that genotypic status is a reliable initial estimate of DT-diaphorase activity.