CYP2J2∗7 Genotype Predicts Risk of Chemotherapy-Induced Hematologic Toxicity and Reduced Relative Dose Intensity in Ethiopian Breast Cancer Patients

Chemotherapy-induced hematologic toxicity is the primary reasons of dose reductions and/or delays, low relative dose intensity (RDI), and predicts anticancer response. We investigated the incidence and predictors of chemotherapy-induced hematologic toxicities and reduced RDI in Ethiopian breast cancer patients, and implication of pharmacogenetics variations. Breast cancer patients (n = 249) were enrolled prospectively to receive cyclophosphamide based chemotherapy. Hematological toxicity (neutropenia, anemia, and thrombocytopenia) were monitored throughout chemotherapy cycle. The primary and secondary outcomes were incidence of grade 3 or 4 toxicity and reduced RDI, respectively. CYP2B6∗6, CYP3A5∗3, CYP2C9 (∗2,∗3), CYP2C19 (∗2,∗3), CYP2J2∗7, POR∗28, and ABCB1 (rs3842) genotyping were done. Cox proportional hazard and logistic regression were used to estimate risk predictors of toxicity and reduced RDI, respectively. Majority (73.5%) of the patients were < 45 years of age. The incidence of grade 3 or 4 hematological toxicity was 51.0% (95% CI = 44.54–57.46%). Multivariate Cox proportional hazard regression indicated CYP2J2∗7 genotype [Hazard ratio (HR) = 1.82; 95% CI = 1.14–2.90], pretreatment grade 1 leukopenia (HR = 2.75; 95% CI = 1.47–5.15) or grade 1 or 2 neutropenia (HR = 2.75; 95% CI = 1.73–4.35) as significant predictors of hematologic toxicities. The odds of having hematologic toxicities was lower in CYP2C9∗2 or ∗3 carriers (p = 0.024). The prevalence of reduced RDI was 56.6% (95% CI = 50.3–62.9%). Higher risk of reduced RDI was associated with CYP2J2∗7 allele [Adjusted odds ratio (AOR) = 2.79; 95% CI = 1.21–6.46], BMI ≤ 18.4 kg/m2 (AOR = 5.98; 95% CI = 1.36–26.23), baseline grade 1 leukopenia (AOR = 6.09; 95% CI = 1.24–29.98), and baseline neutropenia (AOR = 3.37; 95% CI = 1.41–8.05). The odds of receiving reduced RDI was lower in patients with CYP2B6 ∗6/∗6 genotype (AOR = 0.19; 95% CI = 0.06–0.77). We report high incidence of chemotherapy-induced hematological toxicities causing larger proportion of patients to receive reduced RDI in Ethiopian breast cancer patients. Patients carrying CYP2J2∗7 allele and low baseline blood counts are at a higher risk for chemotherapy-induced hematologic toxicities and receiving reduced RDI, and may require prior support and close follow up during chemotherapy

Pharmacological and molecular investigations on the mechanisms underlying resistance of human leukaemia cells to the antimetabolites methotrexate, 6-mercaptopurine and 6-thioguanine

The goal of this thesis has been to elucidate the mechanisms underlying resistance to methotrexate (MTX), 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG), the antimetabolites widely used in treatment of childhood leukemia, as well as to determine the influence of 7-hydroxymethotrexate (7-OHMTX), the major metabolite of MTX, on the therapeutic action of MTX. Resistant sublines of leukemic cell lines were developed by long-term exposure to stepwise increasing concentrations of these different agents. The mechanism underlying resistance to MTX in cells exposed to this drug was a pronounced reduction (> 10-fold) in reduced folate carrier (RFC) mediated uptake of MTX. In CCRF-CEM cells, this reduction was associated with transcriptional silencing of the RFC gene, due to attenuated or even abolished binding of various transcription factors to their cis-acting elements, including the CRE, E-box, AP1, Mzf-1 and GC-box. In contrast, resistance to 7-OHMTX was due solely to a dramatic decrement (> 95%) in folylpolyglutamate synthetase activity, which also conferred a greater than 100-fold increase in resistance to short-term exposure to MTX. The levels of mRNA species originating from approximately 17000 genes present in MTX- and 7-OHMTX-resistant MOLT4 cells were compared. In the MTX-resistant subline, the levels of mRNA encoding proteins involved in DNA and RNA metabolism and in transport were altered most; whereas in the 7-OHMTX-resistant cells, mRNA species associated with metabolism and cell proliferation were affected more profoundly. In these 7-OHMTX-resistant cells, the 10-fold reduction in the level of the mRNA for adenosine deaminase (the major enzyme of purine catabolism), complete absence of mRNA for cystathionine â synthase, the 3-fold higher level of the mRNA for methylene tetrahydrofolate reductase (involved in methyl-tetrahydrofolate biosynthesis) and the 2-fold elevation in the level of the mRNA for glycinamide ribonucleotide formyltransferase (involved in purine biosyntheses), all revealed a pattern of preservation of pools of intracellular folates and of nucleotide biosynthesis. Neither of the known mechanisms of resistance to thiopurines (i.e., alterations in the activity of hypoxanthine guanine phosphoribosyl transferase or of thiopurine methyltransferase enzymes) was found to occur in 6-MP- or 6-TG-resistant cells. Instead, the primary mechanism of resistance was a pronounced reduction in cellular uptake of 6-MP. Selective down-regulation of the levels of mRNAs encoding two nucleoside transporters, the concentrative nucleoside transporter 3 (CNT3) and equilibrative nucleoside transporter 2 (ENT2), was detected in both resistant sublines. Moreover, silencing of the CNT3 and ENT2 genes by small interfering RNA attenuated both the transport and cytocidal effect of 6-MP. Both of the thiopurine-resistant cell sublines exhibited a collateral enhancement in sensitivity to the cytotoxicity of methylmercaptopurine riboside (meMPR), an intra-cellular metabolite of 6-MP that is known to be a potent inhibitor of de novo purine biosynthesis. Transport of meMPR into these cells remained intact. These findings, together with the reduced rate of de novo purine biosynthesis and low levels of ribonucleoside triphosphates in these cells, can easily explain their enhanced sensitivity to meMPR. An additional investigation revealed that transfection of wild-type cells with small interference RNA molecules targeting the gene encoding the first member of the family of equilibrative nucleoside transporters (ENT1) reduced the initial rate of meMPR uptake. In summary, our present findings clearly demonstrate the major involvement of defective transport in the development of resistance to MTX, 6-MP and 6-TG. Long-term exposure of leukemic cells to 7-OHMTX can impair the clinical efficacy of MTX. The disparate patterns of gene expression exhibited by MTX- and 7-OHMTX-resistant cells further confirms that these agents act in different ways. These results may help to improve individualization of MTX treatment on the basis of plasma levels of 7-OHMTX. The collateral enhancement in the sensitivity of thiopurine-resistant cells to the cytotoxicity of meMPR suggests that administration of meMPR or its analogues to patients with ALL experiencing relapse or resistance might be beneficial

Vitamin D Status and Association of <i>VDR</i> Genetic Polymorphism to Risk of Breast Cancer in Ethiopia

Emerging evidence associates vitamin D deficiency and vitamin D receptor (VDR) genetic variations with risk for breast cancer. This study investigated the prevalence of vitamin D deficiency and its association with tumor characteristics and the implications of VDR genetic variations for risk of breast cancer in Ethiopia. This unmatched case&#8315;control study involved 392 female breast cancer patients and 193 controls. The plasma 25-hydroxyvitamin D (25(OH)D3) level was quantified in chemotherapy-na&#239;ve (N = 112) and tamoxifen-treated patients (N = 89). Genotyping for the VDR common variant alleles rs7975232 (ApaI), rs2228570 (FokI), and rs731236 (TaqI) was done. Eighty-six percent of the patients were vitamin D deficient (&lt;50 nmol/L). Chemotherapy-na&#239;ve breast cancer patients had a higher prevalence of vitamin D deficiency (91.9% vs. 78.3%) compared to the tamoxifen-treated group (p &lt; 0.001). The prevalence of severe vitamin D deficiency (&lt;25 nmol/L) was significantly higher in chemotherapy-na&#239;ve (41.1%) than tamoxifen-treated (11.2%) patients. Vitamin D deficiency was not significantly associated with tumor characteristics or VDR genotype. The rs2228570 GG genotype was associated with increased risk of breast cancer (OR = 1.44, 95% confidence interval = 1.01&#8722;2.06). Our result indicates that rs2228570 might be a moderate risk factor for breast cancer development in the Ethiopian population. The high prevalence of severe vitamin D deficiency in treatment-na&#239;ve breast cancer patients indicates the need for nutritional supplementation of vitamin D at the time of chemotherapy initiation

Therapeutic drug monitoring in oncology: International Association of Therapeutic Drug Monitoring and Clinical Toxicology consensus guidelines for imatinib therapy

Although therapeutic drug monitoring (TDM) is an important tool in guiding drug dosing for other areas of medicine including infectious diseases, cardiology, psychiatry and transplant medicine, it has not gained wide acceptance in oncology. For imatinib and other tyrosine kinase inhibitors, a flat dosing approach is utilised for management of oral chemotherapy. There are many published studies examining the correlation of blood concentrations with clinical effects of imatinib. The International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT) determined that there was a need to examine the published literature regarding utility of TDM in imatinib therapy and to develop consensus guidelines for TDM based on the available data. This article summarises the scientific evidence regarding TDM of imatinib, as well as the consensus guidelines developed by the IATDMCT