Cytochrome P450 2B6*5 Increases Relapse after Cyclophosphamide-Containing Conditioning and Autologous Transplantation for Lymphoma.

Cyclophosphamide (Cy) is a prodrug that depends on bioactivation by hepatic cytochrome P450 (CYP) enzymes for its cytotoxicity. We evaluated the influence of single nucleotide polymorphisms (SNPs) of CYP enzymes on the efficacy of autologous hematopoietic cell transplantation (HCT) for lymphoma. SNPs of 22 genes were analyzed in 93 patients with Hodgkin (n = 52) and non-Hodgkin lymphoma (n = 41) treated with high-dose Cy followed by autologous HCT between 2004 and 2012. Preparative regimens contained Cy (120 mg/kg) combined with carmustine/etoposide (n = 61) or Cy (6000 mg/m(2)) with total body irradiation (n = 32). Lack of complete remission as measured by pretransplant positron emission tomography was the sole clinical factor associated with increased risk of relapse (HR, 2.1). In genomic analysis, we identified a single SNP (rs3211371) in exon 9 (C > T) of the CYP2B6 gene (allele designation 2B6*5) that significantly impacted patient outcomes. After adjusting for disease status and conditioning regimen, patients with the CYP2B6*1/*5 genotype had a higher 2-year relapse rate (HR, 3.3; 95% CI, 1.6 to 6.5; P = .041) and decreased overall survival (HR, 13.5; 95% CI, 3.5 to 51.9; P = .008) than patients with the wild-type allele. Two-year progression-free survival for patients with 2 hypofunctional CYP2B6 variant genotypes (*5 and *6) was only 11% (95% CI, 1% to 39%) compared with 67% (95% CI, 55% to 77%) for patients with the wild-type CYP2B6*1 allele in exon 9. Our results suggest that CYP2B6 SNPs influence the efficacy of high-dose Cy and significantly reduce the success of autologous HCT for lymphoma patients with the CYP2B6*5 variant.

Genetic variation in platinating agent and taxane pathway genes as predictors of outcome and toxicity in advanced non-small-cell lung cancer.

AIM: Lung carcinoma is the most common malignancy and the leading cause of cancer deaths worldwide. Although clinical factors including age, performance status and stage influence the likelihood of benefit from and tolerability of chemotherapy, the genetic profile of individual patients may be an independent predictor of response and toxicity. The present study aimed to identify pharmacogenetic markers associated with clinical response and toxicity in patients with advanced non-small cell lung cancer (NSCLC) treated primarily with carboplatin and paclitaxel. MATERIALS & METHODS: Genomic DNA samples from 90 adult male patients diagnosed with stage IIIB/IV NSCLC were genotyped for SNPs in candidate genes of relevance to platinating agents and paclitaxel and analyzed for association with survival and toxicities in univariate and multivariate models. RESULTS: After adjusting for performance status and stage, SNPs in the drug transporters ABCB1 and ABCC1, as well as within NQO1 were associated with progression-free survival. With respect to hematological and nonhematological toxicities, SNPs in drug transporters (ABCB1 and ABCG2) were associated with thrombocytopenia, nausea and neutropenia, whereas SNPs in the DNA repair pathway genes ERCC4 and XPC were significantly associated with neutropenia and sensory neuropathy, respectively. CONCLUSION: Our study evaluated and identified SNPs in key candidate genes in platinating agent and taxane pathways associated with outcome and toxicity in advanced NSCLC. If validated in large prospective studies, these findings might provide opportunities to personalize therapeutic strategies.

Nonsense mediated decay downregulates conserved alternatively spliced ABCC4 transcripts bearing nonsense codons.

Drug transporters are an important part of the defense of cells against cytotoxic agents. One major group of transporters is known as multidrug resistance associated proteins (MRP; ABCC gene family). The MRPs belong to the ATP binding cassette transporter superfamily. One family member, ABCC4 (also known as MRP4) functions as a cellular efflux pump for anti-HIV drugs, such as 9-(2-phoshoenylmethoxyethyl) adenine and azido-thymidine-monophosphate, an antiviral nucleotide, ganciclovir-monophosphate, and anti-cancer agents such as thiopurines. We isolated a ABCC4 cDNA encoding a non-functional protein, owing to an insertion, and subsequently determined the ABCC4 gene structure. This analysis revealed that the insertion was attributed to two additional exons that would be predicted to produce premature termination codons (PTC) in ABCC4. The highly similar mouse Abcc4 gene also contained these exons, which were remarkable because their size and sequence identity were much higher than the overall similarity between these genes. Further, a comparison of human, monkey and rodent ABCC4 genes revealed that these same PTC-producing exons were also highly conserved in evolution. As all the ABCC4 mRNA containing these PTC exons might produce nonsense mRNA, we further tested the hypothesis that these mRNAs were targets of nonsense-mediated mRNA decay (NMD). Protein synthesis inhibition selectively stabilized PTC containing ABCC4 transcripts in human, monkey and rodent cell lines. Moreover, the amount of PTC-containing ABCC4 transcripts was critically dependent upon protein synthesis, as removal of the inhibitor dramatically decreased expression, which correlated with the resumption of protein synthesis. These are the first studies to indicate that the highly conserved PTC exons of the ABCC4 gene may dictate its expression.