Maja Krajinovic

Multidrug resistance gene (MDR1) polymorphisms are associated with major molecular responses to standard-dose imatinib in chronic myeloid leukemia.

Despite the excellent efficacy of imatinib in chronic myeloid leukemia (CML), the response in patients is heterogeneous, which may in part be caused by pharmacogenetic variability. Imatinib has been reported to be a substrate of the P-glycoprotein pump. In the current study, we focused on the ABCB1 (MDR1) genotype. We analyzed the 3 most relevant single nucleotide polymorphisms of MDR1 in 90 CML patients treated with imatinib. Among the patients homozygous for allele 1236T, 85% achieved a major molecular response versus 47.7% for the other genotypes (P = .003). For the 2677G>T/A polymorphism, the presence of G allele was associated with worse response (77.8%, TT/TA; vs 47.1%, GG/GA/GT; P = .018). Patients with 1236TT genotype had higher imatinib concentrations. One of the haplotypes (1236C-2677G-3435C) was statistically linked to less frequent major molecular response (70% vs 44.6%; P = .021). Hence, we demonstrated the usefulness of these single nucleotide polymorphisms in the identification of CML who may or may not respond optimally to imatinib.

Risk of childhood leukemia associated with exposure to pesticides and with gene polymorphisms.

We conducted a population-based case-control study of childhood acute lymphoblastic leukemia (ALL) to evaluate the risk posed by reported exposure to pesticides used in and around the home. We compared 491 cases 0-9 years of age to as many controls. We also conducted a case-only study on a subsample of 123 cases to evaluate gene-environment interaction between child genotype and maternal exposure during pregnancy as well as child exposure after birth. We used the polymerase chain reaction (PCR) approach to analyze polymorphisms in CYP1A1, CYP2D6, GSTT1, and GSTM1 genes, which encode enzymes involved in carcinogen metabolism. Indoor use of some insecticides by the owners and pesticide use in the garden and on interior plants, in particular frequent prenatal use, was associated with increased risks up to severalfold in magnitude. Interaction odds ratios were increased among carriers of the CYP1A1m1 and CYP1a1m2 mutations when mother during pregnancy or the child had been exposed to certain indoor insecticides. No such effects were observed in the presence of other tested polymorphisms.

Variation in CDKN2A at 9p21.3 influences childhood acute lymphoblastic leukemia risk

Using data from a genome-wide association study of 907 individuals with childhood acute lymphoblastic leukemia (cases) and 2,398 controls and with validation in samples totaling 2,386 cases and 2,419 controls, we have shown that common variation at 9p21.3 (rs3731217, intron 1 of CDKN2A) influences acute lymphoblastic leukemia risk (odds ratio = 0.71, P = 3.01 × 10−11), irrespective of cell lineage.

Role of polymorphisms in MTHFR and MTHFD1 genes in the outcome of childhood acute lymphoblastic leukemia

ABSTRACTThe central role of 5,10-methylenetetrahydrofolate reductase (MTHFR) and methylenetetrahydrofolate dehydrogenase (MTHFD1) in folate metabolism renders polymorphisms in genes encoding these enzymes potential modulators of therapeutic response to antifolate chemotherapeutics. The analysis of 201 children treated with methotrexate for childhood acute lymphoblastic leukemia (ALL) showed that patients with either the MTHFR T677A1298 haplotype or MTHFD1 A1958 variant had a lower probability of event-free survival (EFS) in univariate analysis (hazard ratio (HR)=2.2, 95% confidence interval (CI), 1.0–4.7 and 2.8, 95% CI, 1.1–7.3, respectively). Multivariate analysis supported only the role of the MTHFR variant (HR=2.2, 95% CI, 0.9–5.6). However, the association of both genes with ALL outcome appears to be more obvious in the presence of another event-predisposing variant belonging to the same path of drug action. The combined effect of a thymidylate synthase (TS) triple repeat associated with increased TS levels, with either the MTHFR T677A1298 haplotype or MTHFD1 A1958 allele, resulted in a highly significant reduction of EFS (multivariate HR=9.0, 95% CI, 1.9–42.8 and 8.9, 95% CI, 1.8–44.6, respectively). These results reveal the role of gene–gene interactions within a folate pathway, and how they can correlate with relapse probabilities in ALL patients.

Polymorphism of the thymidylate synthase gene and outcome of acute lymphoblastic leukaemia

Interindividual variability in response to methotrexate could be caused by variable concentrations of thymidylate synthase. We investigated the possible association between a tandem-repeat polymorphism in the thymidylate synthase promoter, of which a triple repeat is associated with increased expression of thymidylate synthase, and outcome of acute lymphoblastic leukaemia in 205 children treated with methotrexate. We obtained DNA samples from buccal epithelial cells, peripheral blood, or bone marrow in remission, and analysed them for the polymorphism by PCR amplification. Individuals who were homozygous for the triple repeat had a poorer outlook than those with other genotypes (odds ratio 4.1, 95% CI 1.9-9.0, p=0.001). Genotyping of thymidylate synthase might make it possible to individualize treatment for patients with acute lymphoblastic leukaemia.

Role of NQO1, MPO and CYP2E1 genetic polymorphisms in the susceptibility to childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer. The genetic factors underlying the susceptibility to this disease remain elusive. The enzymes CYP2E1, MPO and NQO1 are involved in the biotransformation of a variety of xenobiotics present in organic solvents, tobacco smoke, drugs, plastic derivatives and pesticides. They also control the level of the oxidative stress by catalyzing the formation of free radicals or by protecting cells from their deleterious effect. DNA variants in the corresponding genes have been associated with an increased susceptibility to different adult cancers, including hematologic malignancies. To investigate whether they represent risk‐modifying factors in childhood ALL, we conducted a case‐control study involving 174 patients and 337 controls, both of French‐Canadian origin. We found that carriers of the CYP2E1*5 variant were at 2.8‐fold higher risk of ALL (95%CI, 1.2–6.4) and that NQO1 alleles *2 and *3 contributed to the risk of ALL as well (OR = 1.7, 95%CI, 1.2–2.4). No such association was found with MPO alone. However, when the wild‐type MPO allele was considered together with the CYP2E1 and NQO1 risk‐elevating genotypes, the risk of ALL was increased further (OR = 5.4, 95%CI, 1.2–23.4) suggesting a combined effect. We also found a gene‐gene interaction between the GSTM1 null genotype and NQO1 mutant alleles. It is therefore plausible that exposure to xenobiotics metabolized by these enzymes play a role in the etiology of childhood ALL.

Genetic susceptibility to breast cancer in French-Canadians: Role of carcinogen-metabolizing enzymes and gene–environment interactions

Breast cancer is the most frequent malignancy among women. Since genetic factors such as BRCA1 and BRCA2 as well as reproductive history constitute only 30% of the cause, environmental exposure may play a significant role in the development of breast cancer. Likewise, the relevant enzymes involved in the biotransformation of xenobiotics (from tobacco smoke, diet or other environmental sources) might play a role in breast carcinogenesis. Since individuals with modified ability to metabolize these carcinogens could have a different risk for breast cancer, we investigated the role of cytochromes P‐450 (CYP1A1, CYP2D6), glutathione‐S‐transferases (GSTM1, GSTT1, GSTP1) and N‐acetyltransferases (NAT1, NAT2) gene variants in breast carcinogenesis. A case‐control study was conducted on 149 women with breast carcinoma and 207 healthy controls, both of French‐Canadian origin. The CYP1A1*4 allele was found to be a significant risk determinant of breast carcinoma (OR = 3.3, 95% CI 1.1–9.7), particularly among post‐menopausal women (OR = 4.0, 95% CI 1.2–13.8). The frequency of NAT2 rapid acetylators was increased among smokers (OR = 2.6, 95% CI 0.8–8.2), while the NAT1*10 allele conferred a 4‐fold increase in risk among women who consumed well‐done meat (OR = 4.4, 95% CI 1.0–18.9). These data suggest that CYP1A1*4, NAT1 and NAT2 variants are involved in the susceptibility to breast carcinoma by modifying the impact of exogenous and/or endogenous exposures.

Genetic Susceptibility to Childhood Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer. The origin of this disease can be explained by a combination of genetic susceptibility factors and environmental exposures. For the purpose of our study it can be considered as a complex disease, caused by the “carcinogenic” effect of the environment modified by a series of genes. In population, these genes tend to occur in allelic forms representing functional polymorphisms thus explaining inter-individual variability in cancer susceptibility. The latter can be evaluated more realistically in childhood ALL than in sporadic cancers of the adult because of its relatively short latency period. We asked therefore, the question about the role of genes controlling the efficiency of xenobiotics metabolism in childhood leukemogenesis. Xenobiotics (drugs and carcinogens) are excreted from the body after metabolic conversion by enzymes mediating oxidation activation (Phase I) and conjugation detoxificaton (Phase II). Functional variants of these enzymes, resulting from known DNA polymorphisms in the corresponding genes, were shown to influence the risk to a variety of solid tumours in adults. A case-control study on ALL patients and healthy controls in a French-Canadian population was carried out by examining the loci of Phase I, CYP1A1 and CYP2D6, as well as Phase II enzymes, GSTM1, GSTT1, NAT1 and NAT2. The NAT2 slow-acetylator, CYP1A1*2A and GSTM1 null genotypes were shown to be significant risk determinants of ALL (OR=1.6, 1.8 and 1.8, respectively), whereas, polymorphisms in CYP2D6 and GSTT1 genes did not seem to play an important role in the aetiology of ALL. Interestingly, the risk associated with NAT2 slow-acetylators was most apparent among males homozygous for NAT1* 4 (OR=3.3) whereas girls carrying the CYP1A1* 4 allele were significantly underrepresented in the patient group (OR=0.2). These findings point to a gender-specific effect of DNA variants which, at least in part, may explain why ALL is more prevalent among boys. To assess gene-gene interactions, NAT2 slow-acetylators were considered together with GSTM1 null genotypes and CYP1A1 *2A alleles. The combined presence of two risk-elevating genotypes appeared to confer an increased risk of ALL among the carriers (OR=2.6). This risk was increased further (OR=3.3) when all three genotypes occurred in the same individuals indicating that the combination of susceptibility variants is more predictive of risk then either of them independently. The association of leukemogenesis in children with metabolising gene variants suggests causal relation to environmental exposures.

Parental smoking, CYP1A1 genetic polymorphisms and childhood leukemia (Québec, Canada)

AbstractObjective: To evaluate the effect of parental smoking on childhood acute lymphoblastic leukemia and to determine if it is modified by child genetic polymorphisms. Methods: We carried out a case–control study in Québec, Canada, including 491 incident cases aged 0–9 years and as many healthy controls matched on age and sex. Each parent was interviewed separately with respect to smoking habits during and after pregnancy. In addition, we carried out a case-only substudy with 158 cases classified according to presence or absence of the alleles *2A, *2B, and *4 in the CYP1A1 gene. Results: There were small risk increases with maternal smoking during the later trimesters. Interaction odds ratios were increased (although often not significantly) for the CYP1A1*4 allele at high levels of maternal smoking in the last trimesters and at low level of paternal postnatal smoking, and decreased for the CYP1A1*2B allele. The latter appeared to confer a protective advantage at low levels for maternal prenatal smoking and at high levels for paternal postnatal smoking. Conclusions: Reported smoking habits showed no association with leukemia; risks for genetic polymorphisms lacked precision but indicated that the effect of parental smoking could be modified by variant alleles in the CYP1A1 gene.

Childhood acute lymphoblastic leukemia associated with parental alcohol consumption and polymorphisms of carcinogen-metabolizing genes

Background. Limited information is available on the association of parental consumption of alcohol prior to and during pregnancy with the risk of childhood leukemia, as well as for the potentially modifying role of genetic polymorphisms. Methods. We conducted a population-based, case-control study of 491 incident cases of acute lymphoblastic leukemia age 0–9 years and matched on age and sex to 491 healthy controls. Cases were identified at tertiary care centers in the Province of Québec between 1980 and 1993. Each parent was interviewed separately about alcohol consumption habits. We also used a case-only design with 186 cases to estimate interaction odds ratios between prenatal exposure and child DNA variants in the GSTM1 and CYP2E1 genes. Results. The adjusted odds ratio for any maternal consumption during pregnancy was 0.7 (95% confidence interval = 0.5–0.9). The interaction odds ratios for the GSTM1 null genotype during third pregnancy trimester was 2.4 (95% confidence interval = 1.1–5.4); the interaction odds ratio for CYP2E1 variant G-1295C (or allele *5) during the nursing period was 4.9 (95% confidence interval = 1.5–16.7). Conclusions. The observed association with maternal alcohol consumption during pregnancy could be due to the potential chemopreventive effects of flavonoids found in wine and beer. These possible effects of alcohol may be at least partially genetically determined, although data are preliminary.