Carboplatin/taxane-induced gastrointestinal toxicity: a pharmacogenomics study on the SCOTROC1 trial.

Carboplatin/taxane combination is first-line therapy for ovarian cancer. However, patients can encounter treatment delays, impaired quality of life, even death because of chemotherapy-induced gastrointestinal (GI) toxicity. A candidate gene study was conducted to assess potential association of genetic variants with GI toxicity in 808 patients who received carboplatin/taxane in the Scottish Randomized Trial in Ovarian Cancer 1 (SCOTROC1). Patients were randomized into discovery and validation cohorts consisting of 404 patients each. Clinical covariates and genetic variants associated with grade III/IV GI toxicity in discovery cohort were evaluated in replication cohort. Chemotherapy-induced GI toxicity was significantly associated with seven single-nucleotide polymorphisms in the ATP7B, GSR, VEGFA and SCN10A genes. Patients with risk genotypes were at 1.53 to 18.01 higher odds to develop carboplatin/taxane-induced GI toxicity (P<0.01). Variants in the VEGF gene were marginally associated with survival time. Our data provide potential targets for modulation/inhibition of GI toxicity in ovarian cancer patients.

Mutations in isocitrate dehydrogenase 1 and 2 occur frequently in intrahepatic cholangiocarcinomas and share hypermethylation targets with glioblastomas.

Mutations in the genes encoding isocitrate dehydrogenase, IDH1 and IDH2, have been reported in gliomas, myeloid leukemias, chondrosarcomas and thyroid cancer. We discovered IDH1 and IDH2 mutations in 34 of 326 (10%) intrahepatic cholangiocarcinomas. Tumor with mutations in IDH1 or IDH2 had lower 5-hydroxymethylcytosine and higher 5-methylcytosine levels, as well as increased dimethylation of histone H3 lysine 79 (H3K79). Mutations in IDH1 or IDH2 were associated with longer overall survival (P=0.028) and were independently associated with a longer time to tumor recurrence after intrahepatic cholangiocarcinoma resection in multivariate analysis (P=0.021). IDH1 and IDH2 mutations were significantly associated with increased levels of p53 in intrahepatic cholangiocarcinomas, but no mutations in the p53 gene were found, suggesting that mutations in IDH1 and IDH2 may cause a stress that leads to p53 activation. We identified 2309 genes that were significantly hypermethylated in 19 cholangiocarcinomas with mutations in IDH1 or IDH2, compared with cholangiocarcinomas without these mutations. Hypermethylated CpG sites were significantly enriched in CpG shores and upstream of transcription start sites, suggesting a global regulation of transcriptional potential. Half of the hypermethylated genes overlapped with DNA hypermethylation in IDH1-mutant gliobastomas, suggesting the existence of a common set of genes whose expression may be affected by mutations in IDH1 or IDH2 in different types of tumors.

Methylenetetrahydrofolate reductase genetic polymorphisms and toxicity to 5-FU-based chemoradiation in rectal cancer.

BACKGROUND: There is a large degree of variation in tumour response and host toxicities associated with neoadjuvant chemoradiation for rectal cancer patients. We performed a complimentary pharmacogenetic study to investigate germline polymorphisms of genes involved in 5-fluorouracil (5-FU) and irinotecan pathways and their potential association with clinical outcomes and toxicities from neoadjuvant chemoradiation in patients with rectal cancer treated in a prospective genotype-directed study. METHODS: The germline DNA of 131 patients was genotyped for 10 variants in TYMS, MTHFR, DPYD, UGT1A1, ABCC1 and SLCO1B1 genes. Ninety-six patients were treated with 5-FU/radiotherapy (RT) and 35 received 5-FU/RT/irinotecan. Relationships between genetic variants and adverse events, tumour response, overall and disease-free survivals were assessed. RESULTS: MTHFR 1298A>C and MTHFR diplotypes (for 677C>T and 1298A>C) were associated with chemoradiation-related toxicity when 5-FU was used alone. MTHFR haplotypes (677C-1298C) and diplotypes (CA-TA and TA-TA) showed, respectively, a protective and a negative effect on the incidence of severe diarrhoea or mucositis. No association was observed between genetic markers and drug response. CONCLUSION: MTHFR polymorphisms can potentially predict toxicity in patients treated with 5-FU as a single chemotherapeutic drug.

Imatinib disposition and ABCB1 (MDR1, P-glycoprotein) genotype.

The aim of this study was to explore the impact of individual variation in drug elimination on imatinib disposition. Twenty-two patients with gastrointestinal stromal tumor or chronic myeloid leukemia initially received imatinib 600 mg daily with dosage subsequently toxicity adjusted. Pharmacokinetic parameters on day 1 and at steady-state were compared with elimination phenotype and single-nucleotide polymorphisms of CYP3A5 and ABCB1. A fivefold variation in estimated imatinib clearance (CL/F) was present on day 1 and mean CL/F had fallen by 26% at steady state. This reduction in imatinib CL/F was associated with ABCB1 genotype, being least apparent in thymidine homozygotes at the 1236T>C, 2677G>T/A and 3435C>T loci. Toxicity-related dose reduction also tended to be less common in these individuals. ABCB1 genotype was associated with steady-state CL/F due to an apparent genotype-specific influence of imatinib on elimination. Further evaluation of ABCB1 genotype and imatinib dosage is warranted.

The effects of cannabinoids on P-glycoprotein transport and expression in multidrug resistant cells.

Cannabis is the most widely used illicit drug in the world. Cannabinoids are used therapeutically by some patients as they have analgesic, anti-emetic and appetite stimulant properties which palliate adverse symptoms. Use of these agents in an oncology setting raises the question of whether they act to modulate the effectiveness of concurrently administered anti-cancer drugs. The transporter, P-glycoprotein (P-gp) confers multiple drug resistance (MDR) by effluxing a diverse array of anti-cancer agents. This study was undertaken to examine the effect of cannabinoids on P-gp. Unlike the known P-gp inhibitor, PSC833, short 1h exposure to three plant-derived cannabinoids, cannabinol (CBN), cannabidiol (CBD) and Delta(9)-tetrahydrocannabinol (THC) and the synthetic cannabinoid receptor agonist, WIN55, 212-2 (WIN) did not inhibit the efflux of the P-gp substrate Rhodamine 123 (Rh123) in either a drug-selected human T lymphoblastoid leukaemia cell line (CEM/VLB(100)) or in a mouse fibroblast MDR1 transfected cell line (77.1). However, in CEM/VLB(100) cells, prolonged 72 h exposure to the cannabinoids, THC and CBD, decreased P-gp expression to a similar extent as the flavonoid, curcumin (turmeric). This correlated with an increase in intracellular accumulation of Rh123 and enhanced sensitivity of the cells to the cytotoxic actions of the P-gp substrate, vinblastine. Taken together, these results provide preliminary evidence that cannabinoids do not exacerbate P-gp mediated MDR. Further, plant-derived cannabinoids are moderately effective in reversing MDR in CEM/VLB(100) cells by decreasing P-gp expression.

The erythromycin breath test for the prediction of drug clearance.

The erythromycin breath test (EBT) is a putative probe of cytochrome P450 (CYP) 3A4 activity in vivo. Therefore, the EBT might prove useful for the individualisation of doses of drugs that have a low therapeutic window (for example the immunosuppressants or cytotoxics) and are metabolised by CYP3A4. However, there is a lack of consensus as to how the EBT should be used to predict total body clearance (CL), and the results so far have been largely disappointing. We argue that the required assumption that individuals produce 5 mmol of CO2/min per m2 at rest is one of the problems with the existing EBT, as the literature suggests significant variability and possible gender differences in this parameter. An examination of the EBT with a simple compartment model suggests that alternative parameters could be more useful in the prediction of CL. In particular, there is theoretical support for the use of the time-point at which breath radioactivity is maximal (tmax) as a correlate for CL. This is in agreement with our recent study of the pharmacokinetics of erythromycin in patients with cancer.

Optimizing the erythromycin breath test for use in cancer patients.

The erythromycin breath test (EBT) is a putative in vivo probe for drug metabolism by cytochrome P450 3A4 (CYP3A4). Because many anticancer drugs are metabolized by this system, we sought to further develop the EBT as a tool for predicting the clearance, in cancer patients, of drugs metabolized by CYP3A4. Sixteen adult patients with incurable cancer were studied. The EBT was performed on day 1 and breath sampled after the i.v. injection of 4 microCi of 14C-erythromycin. The breath 14CO2 flux (CERt) was estimated at 11 time points over 2 h. On day 2, the EBT was repeated midway through a 10-min infusion of 100 mg of erythromycin lactobionate, and the plasma pharmacokinetics of erythromycin were determined. The infusion of 100 mg of erythromycin did not modify the EBT results significantly. The values of the conventional EBT parameter CER20 min obtained on day 1 were comparable for most subjects (0.03-0.06% dose/min), with the exception of an individual receiving the known CYP3A4 inducers dexamethasone and phenytoin who returned a value of 0.14% dose/min. There was no significant correlation between any of the conventional EBT parameters and erythromycin clearance. However, two parameters reflecting early emergence of breath radioactivity (1/TMAX and CER3 min/CERMAX) correlated significantly with erythromycin clearance (P = 0.005 and 0.006, respectively). Novel parameters derived from the EBT are significantly correlated with the clearance of erythromycin even in the presence of confounding factors, such as metastatic liver disease, altered protein binding, and comedication. These parameters may enable dose optimization of cytotoxics metabolized by CYP3A4.