Higher Frequency of Glutathione S-Transferase Deletions in Black Children With Acute Lymphoblastic Leukemia

Glutathione S-transferase M1 and T1 null genotype frequency in chronic myeloid leukaemia

Polymorphisms associated with genes coding for glutathione S-transferase enzymes are known to influence metabolism of different carcinogens and have been associated with incidence of various types of cancer. We have determined the GST M1 and GST T1 'null' genotype frequency in 81 patients with chronic myeloid leukaemia (CML) and 123 racially and geographically matched control individuals by multiplex polymerase chain reaction (PCR). GST M1 null genotype frequencies in CML and controls were 28.4% and 27.7%, respectively. GST T1 null genotype frequencies in CML and controls were 19.8% and 7.3%, respectively. The GST T1 null genotype frequency in CML patients is significantly different from that in controls (odds ratio (OR) 3.12, 95% confidence interval (CI) 1.3-7.45, P=0.008).

Predicting drug response and toxicity based on gene polymorphisms

The sequencing of the human genome has allowed the identification of thousands of gene polymorphisms, most often single nucleotide polymorphims (SNP), which may play an important role in the expression level and activity of the corresponding proteins. When these polymorphisms occur at the level of drug metabolising enzymes or transporters, the disposition of the drug may be altered and, consequently, its efficacy may be compromised or its toxicity enhanced. Polymorphisms can also occur at the level of proteins directly involved in drug action, either when the protein is the target of the drug or when the protein is involved in the repair of drug-induced lesions. There again, these polymorphisms may lead to alterations in drug efficacy and/or toxicity. The identification of functional polymorphisms in patients undergoing chemotherapy may help the clinician prescribe the optimal drug combination or schedule and predict with more accuracy the response to these prescriptions. We have recorded in this review the polymorphisms that have been identified up till now in genes involved in anticancer drug activity. Some of them appear especially important in predicting drug toxicity and should be determined in routine before drug administration; this is the case of the most common variations of thiopurine methyltransferase for 6-mercaptopurine and of dihydropyrimidine dehydrogenase for fluorouracil. Other appear determinant for drug response, such as the common SNPs found in glutathione S-transferase P1 or xereoderma pigmentosum group D enzyme for the activity of oxaliplatin. However, confusion factors may exist between the role of gene polymorphisms in cancer risk or overall prognosis and their role in drug response.

Arsenic trioxide inhibits nuclear receptor function via SEK1/JNK-mediated RXRalpha phosphorylation

We have previously published that 2 proven treatments for acute promyelocytic leukemia, As2O3 and retinoic acid, can be antagonistic in vitro. We now report that As2O3 inhibits ligand-induced transcription of the retinoic acid receptor, as well as other nuclear receptors that heterodimerize with the retinoid X receptor alpha (RXRalpha). As2O3 did not inhibit transactivation of the estrogen receptor or the glucocorticoid receptor, which do not heterodimerize with RXRalpha. We further show that As2O3 inhibits expression of several target genes of RXRalpha partners. Phosphorylation of RXRalpha has been reported to inhibit nuclear receptor signaling, and we show by in vivo labeling and phosphoamino acid detection that As2O3 phosphorylated RXRalpha in the N-terminal ABC region exclusively on serine residues. Consistent with our previous data implying a role for JNK in As2O3-induced apoptosis, we show that pharmacologic or genetic inhibition of JNK activation decreased As2O3-induced RXRalpha phosphorylation and blocked the effects of As2O3 on RXRalpha-mediated transcription. A mutational analysis indicated that phosphorylation of a specific serine residue, S32, was primarily responsible for inhibition of RXRalpha-mediated transcription. These data may provide some insight into the rational development of chemotherapeutic combinations involving As2O3 as well as into molecular mechanisms of arsenic-induced carcinogenesis resulting from environmental exposure.

Arsenic in cancer therapy

Arsenic, a natural substance that has been used as a drug for over 2000 years, has been revived because of its remarkable therapeutic efficacy in patients with acute promyelocytic leukemia (APL). Arsenic exerts a dose-dependent dual effect: it causes differentiation at low concentrations and apoptosis at relatively high concentrations. Specific degradation of the leukemogenic PML-RARalpha fusion protein induced by arsenic leads to the differentiation of leukemia cells. The arsenic-induced apoptosis occurs through direct effects on mitochondria, causing the release of apoptotic proteins into the cytosol and the activation of caspases. Preliminary in vitro studies have also extended the potential anti-cancer effect of arsenic to non-APL leukemias, lymphoid malignancies and other cancers. In vitro and in vivo studies demonstrate that arsenic exerts a broad spectrum of anti-cancer effects by induction of apoptosis, inhibition of cell proliferation, anti-angiogenesis and possible immunomodulation. Phase I and II clinical trials are underway to evaluate the feasibility, safety and potential effect of arsenic in various cancer types.

A comparison of glutathione S-transferase mutant frequencies in healthy Han and Uygur Chinese

OBJECTIVE

This study was to compare the frequencies of genetic polymorphisms of GSTM1, GSTT1, and GSTP1 in Uygur Chinese with those in Han Chinese.

METHODS

GSTM1 and GSTT1 polymorphisms were analyzed by a PCR-Multiplex procedure, whereas GSTP1 polymorphism was analyzed by PCR-RFLP.

RESULTS

The frequency of GSTM1 null genotype in Han Chinese (56.1%) was similar to that in Uygur Chinese (53.2%) (P = 0.592), whilst the frequency of GSTT1 null genotype in Han Chinese (50.0%) was significantly (P < 0.05) higher than that of Uygur Chinese (26.6%). GSTP1 had a genotype distribution of 60.7% I/I, 35.2% I/V and 4.1% V/V in Han Chinese, and 51.3% I/I, 40.2% I/V and 8.4% V/V in Uygur Chinese.

CONCLUSION

There is marked ethnic difference in the mutant frequencies of GSTT1 and GSTP1, but not GSTM1, between Uygur and Han Chinese.

Rapid determination of common mutations in glutathione S-transferase gene by PCR-based methods in healthy Chinese

BACKGROUND

The glutathione S-transferase (GST) superfamily comprises multiple isozymes with compelling evidence of functional polymorphisms in various ethnic groups. All these mutations, in particular those in class mu, pi and theta GST, are likely to contribute to interindividual differences in responses to xenobiotics including response to chemotherapy and associated with altered disease. The frequency of common GST mutations in Uygur Chinese is unknown. We investigated the common mutations of GSTM1, GSTT1, and GSTP1 in Uygur (N=154) Chinese and compare with Han Chinese (N=196).

METHOD

GSTM1 and GSTT1 polymorphisms were analyzed by multiplexed PCR, and GSTP1 polymorphism was detected by PCR-based restriction fragment length polymorphism (RFLP) analysis.

RESULTS

GSTM1 null genotype was found in 53.2% Uygur Chinese, which was close to that in Han Chinese (56.1%) (P=0.592). A significantly lower frequency (P<0.05) of GSTT1 null genotype in Uygur Chinese (26.6%) was observed compared with Han Chinese (50.0%). Uygur Chinese exhibited a GSTP1 genotype distribution of 51.3% I/I, 40.2% I/V and 8.4% V/V, which was different from that in Han Chinese (60.7% I/I, 35.2% I/V and 4.1% V/V).

CONCLUSIONS

There is marked ethnic difference in the frequency of common GSTT1 and GSTP1 mutation, but not GSTM1 mutation, between Uygur and Han Chinese.

The MTHFR C677T and A1298C polymorphisms and susceptibility to childhood acute lymphoblastic leukemia in Portugal

Methylenetetrahydrofolate reductase (MTHFR) is an essential enzyme in folate metabolism and in DNA methylation and synthesis. The role of two common polymorphisms at the MTHFR gene, C677T and A1298C, in the etiology of childhood or adult acute lymphoblastic leukemia (ALL) has been previously investigated. Although a protective effect of MTHFR*677T against ALL was systematically reported, the magnitude of the effect appeared to be influenced by population-specific gene-environmental interactions. The evidence of the role of MTHFR*1298C in ALL susceptibility was less consistent, emphasizing the need for enlarging molecular epidemiologic studies to independent trials from different populations. The authors analyzed in North Portugal the association between variations at the two MTHFR positions and risk of ALL by comparing genotypes and gene frequencies in 103 affected children with those in 111 healthy controls. None of the variations was found to significantly affect the risk of developing childhood ALL in North Portugal, and this finding per se is of relevance in further studies aimed at assessing the etiology of the pathology in this specific population. Despite the absence of statistical significance, these data revealed that the frequency of MTHFR*677T was lower in patients than in controls, a result that is congruent with other reports and with the functional model usually invoked to explain its ALL protective effect. Concerning MTHFR1298*C, this study failed to corroborate previous findings of decreased risk of ALL in the presence of the variant.

Polymorphisms of drug-metabolizing enzymes and risk of childhood acute lymphoblastic leukemia

The involvement of phase I and II enzymes is well documented in the metabolism of a wide range of drugs and xenobiotics. Single-nucleotide polymorphisms (SNPs) of these enzymes are also known to alter their protein expression and function. Moreover, genetic susceptibility and environmental exposure have been proposed to be an etiology of cancer. We hypothesized that polymorphisms of these enzymes might affect the risk of childhood acute lymphoblastic leukemia (ALL). CYP 1A1, CYP 3A4*1B, CYP 3A5*3, CYP 3A5*6, GSTM1, and GSTT1 polymorphisms were genotyped by using PCR-RFLP in 107 children with ALL and 320 healthy controls. Allele and genotype frequencies of each of the SNPs were compared between two groups. It was found that the allele frequencies of CYP 1A1*1, *2A, *2B, and *4 were not different between cases and controls. CYP 3A4*1B allele frequency was only 0.8% and 0.9% in ALL and controls, respectively. CYP 3A5*1/*1, *1/*3, and *3/*3 genotype frequencies showed no statistically significant difference between patients and controls. CYP 3A5*6 was not detected in our population. The GSTM1 null genotype was significantly increased in children with ALL (OR 1.7; 95% CI, 1.0, 2.7). In contrast, the GSTT1 null genotype did not show this effect. Our data thus demonstrate that the GSTM1 null genotype might increase the risk of childhood ALL in a Thai population.

Glutathione s-transferase polymorphisms (GSTM1, GSTP1 and GSTT1) and the risk of acute leukaemia: a systematic review and meta-analysis

Glutathione s-transferase (GST) polymorphisms (GSTM1, GSTP1 and GSTT1) have been considered as risk factors for developing acute leukaemia in a number of studies; however the overall results of such studies are inconsistent. To investigate a putative association of GST polymorphisms with the risk of acute leukaemia, we performed a systematic review and meta-analysis of 30 published case-control studies. To take into account the possibility of heterogeneity across the studies, a statistical test was performed. The pooled odds ratios (ORs) were assessed using both a fixed-effects and a random-effects model. The pooled OR of acute leukaemia risks associated with GSTM1 null genotype, GSTP1 Val105 allele and GSTT1 null genotype were 1.22 (95% confidence interval (CI) 1.07-1.38), 1.07 (95% CI 1.00-1.13) and 1.19 (95% CI 1.00-1.41), respectively. Significantly increased risk of acute lymphoblastic leukaemia associated with GSTM1 and GSTT1 null genotypes was observed. Their pooled ORs were 1.24 (95% CI 1.17-1.31) and 1.30 (95% CI 1.06-1.60), respectively. We also found substantial evidence of heterogeneity between the studies. Our results suggest that GSTM1 and GSTT1, but not GSTP1 polymorphisms, appear to be associated with a modest increase in the risk of acute lymphoblastic leukaemia. It is conceivable that GSTM1 and GSTT1 null genotypes may thus play a role in leukemogenesis. A review of the 30 case-control studies indicates that greater attention should be paid to the design of future studies.

Pharmacogenetics of outcome in children with acute lymphoblastic leukemia

Acquired genetic characteristics of acute lymphoblastic leukemia (ALL) cells are used to individualize therapy, whereas germ line genetic characteristics generally are not. We determined whether ALL outcome was related to 16 genetic polymorphisms affecting the pharmacodynamics of antileukemic agents. Of 246 children, 116 were treated on the lower-risk (LR) and 130 on the higher-risk (HR) arms of a St Jude protocol. Patients in the HR group with the glutathione S-transferase (GSTM1) non-null genotype had greater risk of hematologic relapse (P = .03), which was further increased by the thymidylate synthetase (TYMS) 3/3 genotype (P = .03). These genotypes remained predictive in multivariate analyses (P < .001 and .003, respectively). No genotypes were predictive in the LR arm. Expression of these 2 genes in ALL blasts was lower in those with low-activity genotypes. For central nervous system relapse, among the HR group, the vitamin D receptor start site (P = .02) and intron 8 genotypes (P = .04) predisposed, whereas for LR patients the TYMS 3/3 genotype predisposed (P = .04). The GSTM1 non-null and TYMS 3/3 genotypes are plausibly linked to drug resistance. Polymorphisms interact to influence antileukemic outcome and represent determinants of response that can be used to optimize therapy.

Glutathione S-transferase polymorphisms and susceptibility to neuroblastoma

There is evidence to suggest that polymorphic variations in the glutathione S-transferase (GSTs) are associated with cancer susceptibility. The GST supergene family includes several genes with well characterized polymorphisms. Approximately 50% of the Caucasian population is homozygous for deletions in GSTM1 and approximately 20% are homozygous for deletions in GSTT1. Deletions lead to an absence of the protein, thus resulting in conjugation deficiency of mutagenic electrophiles to glutathione. The GSTP1 gene displays a polymorphism at codon 105 resulting in an Ile to Val substitution, which alters the enzymatic activity of the protein, and this has been suggested as a putative high-risk genotype in various cancers. In the present study, we investigated the relationship between GSTs polymorphism and the susceptibility to neuroblastoma, comparing GSTs genotypes of 256 children with neuroblastoma with those of 392 normal control subjects. No significant differences of allele frequencies were found between patients and controls. Within the neuroblastoma group, we further investigated whether any particular GSTs genotype was correlated with clinical and biological characteristics at diagnosis, but no association was detected. Our data do not support an important effect of GSTs genotype on neuroblastoma susceptibility.

Acute promyelocytic leukemia: recent advances in therapy and molecular basis of response to arsenic therapies

PURPOSE OF REVIEW

While arsenic has long been known as a poison and environmental carcinogen, its dramatic effect in the treatment of acute promyelocytic leukemia (APL) has made its mechanism of action a topic of intense interest. This paper reviews recent findings that reveal why a traditional poison has become a magical potion for a major type of APL, which is characterized by a balanced chromosomal translocation t(15;17).

RECENT FINDINGS

Daily IV infusion of arsenic trioxide (As2O3; ATO) for 30 to 40 days can lead to complete remission in about 85% of patients with newly diagnosed or relapsed APL. Oral preparations of ATO and tetra-arsenic tetra-sulfide (As4S4) seem to be as effective as parenteral ATO, with similar toxicity profiles. The combination of all-trans retinoic acid and ATO in patients with newly diagnosed APL has yielded more durable remission than monotherapy. The mechanism of arsenic cytotoxicity is thought to involve posttranslational modification followed by degradation of the PML-retinoic acid receptor-alpha (PML-RARalpha) fusion protein; targeting of PML to nuclear bodies with restoration of its physiologic functions; and production of reactive oxygen species (ROS) by NADPH oxidase in leukemic cells or collapse of the mitochondrial transmembrane potential. The understanding of arsenic cytotoxicity has stimulated modifications that promise to improve efficacy, such as interfering with ROS scavenging or boosting of ROS production to enhance the cytotoxicity, and adding cAMP or interferons to ATO regimens.

SUMMARY

Recent advances in the clinical use of arsenic, the mechanism of arsenic-mediated cytotoxicity, and modulations of ATO to increase its efficacy and expand its clinical spectrum are reviewed.

Retinoic acid and arsenic for treating acute promyelocytic leukemia

What were the critical steps in the development of ATRA and arsenic as treatments for APL? Researchers in Shanghai tell the story and look to the future

Pharmacogenetics of acute lymphoblastic leukemia

PURPOSE OF REVIEW

The outcome in children with acute lymphoblastic leukemia has improved significantly over the past four decades. Current therapy results in event-free survival exceeding 80% for most patients. The development of risk-adapted therapy based on characteristics of the child (age), leukemia (leukocyte count, acquired genetic characteristics) and early response to therapy allows dose intensification for children with higher-risk disease. Much less attention has been given to the role of host variability (pharmacogenetic polymorphism) in determining outcome. This review discusses literature reports in this area and describes some of the challenges facing the field as it moves forward.

RECENT FINDINGS

Polymorphisms in many different metabolic pathways have been demonstrated in single gene studies to influence the outcome of acute lymphoblastic leukemia. Challenges arise in establishing the generalizability of observations and interpreting complex gene-gene interactions in multigene pathways. Recent studies also illustrate the importance of correlation of clinical associations with biological mechanisms.

SUMMARY

Despite significant progress in the treatment of childhood acute lymphoblastic leukemia, therapy is still unsuccessful in 20% of patients. Further knowledge of and insight into the role of host genetic polymorphisms will improve the results by integrating pharmacodynamic and pharmacogenomic studies in individualizing therapy for children with acute lymphoblastic leukemia.

Polymorphism within the glutathione S-transferase P1 gene is associated with increased susceptibility to childhood malignant diseases

BACKGROUND

Glutathione S-transferases (GSTs) are involved in the metabolism of carcinogens and anticancer drugs. Functional polymorphisms exist in at least three genes that code for the GSTs, such as the GSTM1 and GSTT1 gene deletions or the A-G transition within the GSTP1 gene, which represents distinct GSTP1a and GSTP1b alleles. In the present case-control study, we aimed at estimation of the relationship between the GSTM1, GSTT1, and GSTP1 genotypes and the susceptibility to various types of childhood malignancies and the early relapses of diseases.

PROCEDURE

Using the polymerase chain reaction on the DNA extracted from peripheral blood leukocytes, we identified the GSTM1, GSTT1, and GSTP1 genotypes in 234 children at the initial stage of a childhood malignancy as well as in 460 age-and sex-matched healthy subjects who served as controls. The follow-up period for the effects of the anticancer therapy ranged from 11 to 43 months.

RESULTS

Compared to the controls, a significant increase in the frequency of the GSTP1b/GSTP1b genotype (odds ratio (OR) 5.7; 95% confidence limit (CL) from 2.4 to 13.8; Pearsons Chi-square P = 0.0001) was detected in the children with neoplasms. The GSTM1 and GSTT1 genotypes did not show any correlation with the risk of the de novo diagnosed neoplasms. During the observation, 62 children (26%) were found to be present with a local or disseminated recurrence of the diseases. The analysis indicated a trend in increasing risk of relapse for carriers of the GSTP1a allele (OR = 3.29; 95% CL from 0.73 to 14.67 P = 0.03).

CONCLUSIONS

Our results support the hypothesis that GST genotype affects etiology and outcome of a variety of childhood malignancies.

Genetic polymorphism of CYP1A1, CYP2D6, GSTM1 and GSTT1 and susceptibility to acute lymphoblastic leukaemia in Indian children

BACKGROUND

Biotransformation plays a crucial role in carcinogen activity and many genetic polymorphisms in xenobiotic metabolising enzymes have been associated with an increased risk of cancer. Such polymorphisms can lead to considerable variation in the activities of these enzymes, which are crucial in carcinogen and drug metabolism. These variations could play a role in the risk of developing paediatric acute lymphoblastic leukaemia (ALL) by their varying action on environmental carcinogens.

PROCEDURE

The present study looked for two polymorphisms (m1 and m2) in the CYP1A1, CYP2D6*4 genes and deletions of the glutathione S-transferases (GSTM1 and GSTT1) in 118 paediatric ALL patients and 118 age matched control children. The polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) were used to study gene polymorphisms.

RESULTS

In children with ALL, CYP1A1 m1 polymorphism was evident in 42.4% of subjects and CYP1A1 m2 in 37.3%. These were significantly different from the results obtained for control children (20.3% for CYP1A1 m1 and 19.5% for m2). Subjects with CYP1A1 m1 homozygous variant had a sixfold risk and CYP1A1 m2 a fourfold risk. In contrast, CYP2D6*4 was more prevalent in the controls than in the cases. Subjects with GSTM1 deletions had increased risk of ALL (OR = 2.1, P = 0.009). The odds ratios for both CYP1A1 m1 and m2 homozygous polymorphisms being associated with childhood ALL was 5.67 (95% CI = 2.11-15.27). The odds ratios for both GSTM1 and GSTT1 deletions being associated with ALL was 2.78 (95% CI = 0.67-11.56).

CONCLUSIONS

These results suggest that genetic polymorphisms of xenobiotic metabolising enzymes appear to influence susceptibility to childhood ALL.

Predictive values of traditional animal bioassay studies for human perinatal carcinogenesis risk determination

The many physiological, biochemical, and structure differences between rodents and humans, especially with regard to gestation and fetal development, invite questions as to the utility of rodent models for the prediction of risk of perinatal carcinogenesis in humans and for extrapolation of mechanistic studies. Here, the relevance of basic generalities, derived from rodent perinatal studies, to human contexts is considered. The cross-species usefulness of these generalities was upheld by the example of carcinogen activation and detoxification as determining factors. These have been established in rodent studies and recently indicted in humans by investigations of genetic polymorphisms in cytochromes P450, N-acetyltransferase, myeloperoxidase, quinone reductase, and glutathione S-transferase. Also, published data have been analyzed comparatively for diethylstilbestrol and irradiation, the two known human transplacental carcinogenic agents. At similar doses to those experienced by humans, both diethylstilbestrol and X- and gamma-irradiation in rodents and dogs yielded increased tumors at rates similar to those for humans. In rodents, there was a clearly negative relationship between total diethylstilbestrol dose and tumors per dose unit, and a similar pattern was suggested for radiation. Diethylstilbestrol had transgenerational effects that did not diminish over three generations. Overall, this analysis of the published literature indicates that there are basic qualitative and quantitative similarities in the responsiveness of human and rodent fetuses to carcinogens, and that dose effects may be complex and in need of further investigation.

All-trans retinoic acid/As2O3 combination yields a high quality remission and survival in newly diagnosed acute promyelocytic leukemia

Both all-trans retinoic acid (ATRA) and arsenic trioxide (As(2)O(3)) have proven to be very effective in obtaining high clinical complete remission (CR) rates in acute promyelocytic leukemia (APL), but they had not been used jointly in an integrated treatment protocol for remission induction or maintenance among newly diagnosed APL patients. In this study, 61 newly diagnosed APL subjects were randomized into three treatment groups, namely by ATRA, As(2)O(3), and the combination of the two drugs. CR was determined by hematological analysis, tumor burden was examined with real-time quantitative RT-PCR of the PML-RAR alpha (promyelocytic leukemia-retinoic acid receptor alpha) fusion transcripts, and side effects were evaluated by means of clinical examinations. Mechanisms possibly involved were also investigated with cellular and molecular biology methods. Although CR rates in three groups were all high (> or =90%), the time to achieve CR differed significantly, with that of the combination group being the shortest one. Earlier recovery of platelet count was also found in this group. The disease burden as reflected by fold change of PML-RAR alpha transcripts at CR decreased more significantly in combined therapy as compared with ATRA or As(2)O(3) mono-therapy (P < 0.01). This difference persisted after consolidation (P < 0.05). Importantly, all 20 cases in the combination group remained in CR whereas 7 of 37 cases treated with mono-therapy relapsed (P < 0.05) after a follow-up of 8-30 months (median: 18 months). Synergism of ATRA and As(2)O(3) on apoptosis and degradation of PML-RAR alpha oncoprotein might provide a plausible explanation for superior efficacy of combination therapy in clinic. In conclusion, the ATRA/As(2)O(3) combination for remission/maintenance therapy of APL brings much better results than either of the two drugs used alone in terms of the quality of CR and the status of the disease-free survival.

Pharmacogenetic determinants of outcome in acute lymphoblastic leukaemia

Present day paediatric co-operative group acute lymphoblastic leukaemia (ALL) protocols cure approximately 80% of patients, a result achieved largely through the use of risk-stratified therapies that employ multiple chemotherapy agents. These risk-based therapies utilize host and leukaemia traits to select the most appropriate therapy. However, these risk-stratified approaches predict therapy response imperfectly and an important fraction of patients experience relapse or therapy-related toxicity. Pharmacogenetics, the study of genetic variations in drug-processing genes and individual responses to drugs, may enable the improved identification of patients at higher risk for either disease relapse or chemotherapy-associated side effects. While the impact of genetic variation in the thiopurine-S-methyltransferase gene on ALL treatment outcome and toxicity has been extensively studied, the role of other polymorphisms remains less well known. This review summarizes current research on the impact of genetic variation in drug-processing genes in paediatric ALL and reviews important methodological and statistical issues presently challenging the field of pharmacogenetics.

Genetic polymorphisms and susceptibility to childhood acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is the most common form of pediatric cancer. Although exposure to environmental agents appears to predispose individuals to this disease, little attention has been paid to the role of genetic susceptibility to environmental exposures in the etiology of childhood ALL. The enzymes GSTM1, GSTT1, GSTP1, CYP1A1, and CYP2E1 are involved in the bioactivation and detoxification of a variety of xenobiotics present in food, organic solvents, tobacco smoke, drugs, alcoholic drinks, pesticides, and environmental pollutants. Polymorphisms in the genes coding for these enzymes have been associated with increased susceptibility to different cancers, including hematologic malignancies. To investigate whether these polymorphisms represent risk-modifying factors for childhood ALL, a study was conducted involving 113 Brazilian patients of childhood ALL and 221 controls with similar ethnic backgrounds. The data revealed that carriers of the rare GSTP1 Val allele were at higher risk of ALL (odds ratio [OR] = 2.7; 95% confidence interval [CI] = 1.1-6.8; P = 0.04). No difference was found in the prevalence of the GSTM1 and GSTT1 null genotypes between ALL patients and the controls, and no association was found between CYP1A1*2 and CYP2E1*3 variants and ALL. However, when the mutant CYP1A1 and CYP2E1 alleles were considered together with the GSTM1 and GSTP1 risk-elevating genotypes, the risk of ALL was increased further (OR = 10.3; 95% CI = 1.0-111.8; P = 0.05), suggesting a combined effect. These results imply that genetic variants of xenobiotic metabolizing genes influence the risk of developing childhood ALL.

Inhibition of cell proliferation and the action mechanisms of arsenic trioxide (As2O3) on human breast cancer cells

Arsenic trioxide (As(2)O(3)) is one of the arsenic compounds found in nature. As(2)O(3) has recently been used to treat patients suffering from retinoic acid receptor (AML). It is of clinical interest to investigate whether As(2)O(3) is also effective in treating solid tumors. Here, we report that As(2)O(3) exhibited inhibitory effects on the proliferation of human breast cancer MCF-7 cells in a dose- and time-dependent manner. The 50% inhibitory concentration (IC(50)) of As(2)O(3) in inhibiting proliferation of MCF-7 cells were 8, 1.8, and 1.2 microM upon 1-, 2-, and 3-day treatment, respectively. In elucidating the underlying action mechanisms, the results of experiments concerning DNA fragmentation and externalization indicated that As(2)O(3) exerted its action on MCF-7 cells via apoptosis, whereas the result of flow cytometry also indicated that As(2)O(3) could induce mitochondrial mediated cell-cycle arrest at G(1) phase. Further studies by Western blot analysis indicated that As(2)O(3) regulated apoptosis and the expression of cell-cycle-related proteins as it upregulated p53 protein level and downregulated bcl-2 protein level. Results in present study indicated that As(2)O(3) might also be a good candidate for treating breast cancer.

Ontogenic differences in human liver 4-hydroxynonenal detoxification are associated with in vitro injury to fetal hematopoietic stem cells

4-hydroxynonenal (4HNE) is a highly mutagenic and cytotoxic alpha,beta-unsaturated aldehyde that can be produced in utero during transplacental exposure to prooxidant compounds. Cellular protection against 4HNE injury is provided by alcohol dehydrogenases (ADH), aldehyde reductases (ALRD), aldehyde dehydrogenases (ALDH), and glutathione S-transferases (GST). In the present study, we examined the comparative detoxification of 4HNE by aldehyde-metabolizing enzymes in a panel of adult and second-trimester prenatal liver tissues and report the toxicological ramifications of ontogenic 4HNE detoxification in vitro. The initial rates of 4HNE oxidation and reduction were two- to fivefold lower in prenatal liver subcellular fractions as compared to adult liver, and the rates of GST conjugation of 4HNE were not detectable in either prenatal or adult cytosolic fractions. GSH-affinity purification of hepatic cytosol yielded detectable and roughly equivalent rates of GST-4HNE conjugation for the two age groups. Consistent with the inefficient oxidative and reductive metabolism of 4HNE in prenatal liver, cytosolic fractions prepared from prenatal liver exhibited a decreased ability to protect against 4HNE-protein adduct formation relative to adults. Prenatal liver hematopoietic stem cells (HSC), which constitute a significant percentage of prenatal liver cell populations, exhibited ALDH activities toward 4HNE, but little reductive or conjugative capacity toward 4HNE through ALRD, ADH, and GST. Cultured HSC exposed to 5 microM 4HNE exhibited a loss in viability and readily formed one or more high molecular weight 4HNE-protein adduct(s). Collectively, our results indicate that second trimester prenatal liver has a lower ability to detoxify 4HNE relative to adults, and that the inefficient detoxification of 4HNE underlies an increased susceptibility to 4HNE injury in sensitive prenatal hepatic cell targets.

Characterization of MTHFR, GSTM1, GSTT1, GSTP1, and CYP1A1 genotypes in childhood acute leukemia

The role of methylenetetrahydrofolate reductase (MTHFR C677T), glutathione S-transferases (GSTM1 and GSTT1 null, GSTP1 Ile105Val), and cytochromes p450 (CYP1A1*2A) genotypes in the etiology of childhood leukemia was simultaneously investigated. 144 Turkish children with acute lymphoblastic leukemia (ALL) and 33 with acute nonlymphoblastic leukemia (ANLL) were studied and compared with 185 healthy pediatric controls. The frequency of MTHFR genotype was insignificantly higher in ALL (7.7%) and ANLL (6.3%) than in controls (4.4%). Equal distribution of the GSTM1 null genotype was detected between ALL patients and controls (55%), while its incidence was slightly higher in ANLL patients (61.3%). Although GSTT1 null genotype was insignificantly lower in ALL patients (20.9%) than controls (22.7%), it was significantly underrepresented in ANLL patients (6.5%) (P = 0.05, OR 0.24, 95% CI 0.05-1.03). The homozygous frequency of GSTP1 genotype did not differ significantly between groups of ALL (3.7%), ANLL patients (9.1%) and controls (4.9%). Homozygous CYP1A1*2A genotype was underrepresented in ALL patients (1%) as compared to control (4.8%) but the differences did not reach to statistical significance (OR 0.21; 95% CI 0.03-1.72). Homozygosity for this genotype was not detected in ANLL patients. No particular association was noted between different combinations of combined genotypes and risk of development of childhood ALL and ANLL. These results suggested that there are no significant associations between the studied genotypes and the risk of developing either form of acute leukemia except GSTT1 null and homozygosity for CYP1A1 genotypes that may play protective roles in the development of ANLL in Turkish children.

Update in childhood acute myeloid leukemia: recent developments in the molecular basis of disease and novel therapies

Childhood acute myeloid leukemia is a heterogeneous group of disorders that remains challenging to treat. There are multiple common genetic alterations in childhood acute myeloid leukemia. These include chromosomal translocations affecting RUNX1-CBFbeta, RARalpha, and MLL. There are known activating mutations in the genes for the receptor tyrosine kinases FLT3, KIT, and FMS. As these abnormalities are better understood, they are providing important insights into the pathogenesis of disease as well as information about prognosis. Although intensive chemotherapy remains the mainstay of acute myeloid leukemia therapy, long-term cure rates with chemotherapy alone remain approximately 50%, creating an urgent need for better therapies. Multiple avenues are being explored in the design of new treatments for pediatric acute myeloid leukemia. Targeted therapies include targeted antibody therapy; inhibitors of FLT3, KIT, and farnesyltransferase; diphtheria toxin conjugated to the granulocyte-macrophage colony-stimulating factor; and antisense oligonucleotides. Another area of interest is chromatin remodeling and differentiation therapy, including agents such as all- retinoic acid, arsenic trioxide, and inhibitors of DNA methylation and histone deacetylation. There are also ongoing trials of antiangiogenesis agents. Another avenue for novel therapies is immunotherapy with agents such as interleukin-2 and tumor vaccines. This article reviews recent advances in understanding of the molecular basis for childhood acute myeloid leukemia and the design of novel therapies for the treatment of childhood acute myeloid leukemia.

Pediatric acute lymphoblastic leukemia

The outcome for children with acute lymphoblastic leukemia (ALL) has improved dramatically with current therapy resulting in an event free survival exceeding 75% for most patients. However significant challenges remain including developing better methods to predict which patients can be cured with less toxic treatment and which ones will benefit from augmented therapy. In addition, 25% of patients fail therapy and novel treatments that are focused on undermining specifically the leukemic process are needed urgently. In Section I, Dr. Carroll reviews current approaches to risk classification and proposes a system that incorporates well-established clinical parameters, genetic lesions of the blast as well as early response parameters. He then provides an overview of emerging technologies in genomics and proteomics and how they might lead to more rational, biologically based classification systems. In Section II, Drs. Mary Relling and Stella Davies describe emerging findings that relate to host features that influence outcome, the role of inherited germline variation. They highlight technical breakthroughs in assessing germline differences among patients. Polymorphisms of drug metabolizing genes have been shown to influence toxicity and the best example is the gene thiopurine methyltransferase (TPMT) a key enzyme in the metabolism of 6-mercaptopurine. Polymorphisms are associated with decreased activity that is also associated with increased toxicity. The role of polymorphisms in other genes whose products play an important role in drug metabolism as well as cytokine genes are discussed. In Sections III and IV, Drs. James Downing and Cheryl Willman review their findings using gene expression profiling to classify ALL. Both authors outline challenges in applying this methodology to analysis of clinical samples. Dr. Willman describes her laboratory's examination of infant leukemia and precursor B-ALL where unsupervised approaches have led to the identification of inherent biologic groups not predicted by conventional morphologic, immunophenotypic and cytogenetic variables. Dr. Downing describes his results from a pediatric ALL expression database using over 327 diagnostic samples, with 80% of the dataset consisting of samples from patients treated on a single institutional protocol. Seven distinct leukemia subtypes were identified representing known leukemia subtypes including: BCR-ABL, E2A-PBX1, TEL-AML1, rearrangements in the MLL gene, hyperdiploid karyotype (i.e., > 50 chromosomes), and T-ALL as well as a new leukemia subtype. A subset of genes have been identified whose expression appears to be predictive of outcome but independent verification is needed before this type of analysis can be integrated into treatment assignment. Chemotherapeutic agents kill cancer cells by activating apoptosis, or programmed cell death. In Section V, Dr. John Reed describes major apoptotic pathways and the specific role of key proteins in this response. The expression level of some of these proteins, such as BCL2, BAX, and caspase 3, has been shown to be predictive of ultimate outcome in hematopoietic tumors. New therapeutic approaches that modulate the apoptotic pathway are now available and Dr. Reed highlights those that may be applicable to the treatment of childhood ALL.

Metabolic enzyme polymorphisms and susceptibility to acute leukemia in adults

Genetic approaches to understanding the etiology of the acute leukemias are beginning to deliver meaningful insights. Polymorphic variants in xenobiotic metabolizer loci were a natural starting point to study the relevance of these changes. The finding that glutathione S-transferase (GST) T1 null variants increase leukemia risk has implicated oxidative stress in hematopoietic stem cells as an important etiological factor in acute myeloid leukemia (AML). The importance of these enzyme systems in handling specific substrates has also been confirmed by the finding of an increased risk of therapy-related leukemia in individuals with underactive variants of GSTP1 who have been exposed to a chemotherapeutic agent metabolized by this enzyme. Benzene is a well-recognized leukemogen, and genetic variants in its metabolic pathway can modulate the risk of leukemia following exposure. In particular, underactive variants of the NAD(P)H:quinone oxidoreductase 1 gene (NQO1) seem to increase the risk of AML. Other enzymes within the pathway are proving more difficult to study because of the absence of variants that significantly affect the biological activity of the enzyme under study. No effect of the myeloperoxidase (MPO) gene variants in altering the risk of AML has been seen in our studies. Another pathway recently shown to be important in determining leukemia risk is folic acid metabolism, particularly important in predisposition to acute lymphocytic leukemia (ALL). Polymorphic variants of the methylenetetrahydrofolate reductase gene (MTHFR) which impair its activity have been shown to be associated with a protective effect. This is thought to be due to an increased availability of nucleotide precursors for incorporation into DNA. This finding implicates misincorporation of uracil into DNA as an important mechanism of leukemic change in lymphoid precursors. Future studies will extend these observations but will require biological material collected from large well-controlled epidemiological studies. The technological challenges imposed by the high throughput of samples required by these studies are currently being addressed.

Polymorphisms of drug metabolizing enzymes and markers of genotoxicity to identify patients with Hodgkin's lymphoma at risk of treatment-related complications

Survivors of childhood Hodgkin's lymphoma (HL) have an increased risk of developing treatment-related complications, especially second malignant neoplasms, as a result of treatment regimens incorporating chemotherapy and radiation therapy. Second cancers include leukemias that generally occur in the first two decades after therapy, and adult-type solid tumors that generally exhibit continued increasing incidence throughout subsequent follow-up. Identified clinical risk factors for second cancers include age at the time of treatment and intensity and type of therapy, with particularly strong associations between the use of radiotherapy and subsequent breast cancer, and alkylator chemotherapy dose-intensity and risk of secondary leukemia. However, second cancers affect a minority of patients, and there is probably great variability in individual susceptibility for this complication. Common genetic polymorphisms in drug-metabolizing enzymes that result in impaired detoxification of chemotherapy or inefficient repair of drug- or radiation-induced genetic damage may lead to increased risk of a second cancer. Studies of the potential role of polymorphisms in the genes encoding the glutathione S-transferases, cytochrome P450 3A4, NAD(P)H:quinone oxidoreductase and myeloperoxidase in the etiology of treatment-related complications are reviewed. Biological markers of drug- and radiation-induced genetic damage may also identify patients at higher risk of immediate and delayed side effects of therapy. The Children's Oncology Group (COG) is examining the roles of polymorphisms in drug metabolizing enzymes and biological markers of genotoxicity in predicting the treatment-related outcomes of patients with HL. These investigations may ultimately allow the use of pharmacogenetically guided therapy to improve the outcome of HL therapy and reduce the risk of therapy-related complications, especially secondary malignancies.

Genetic predisposition and screening in pediatric cancer

Pediatricians are often the health care providers who first detect the signs and symptoms of childhood cancer. Although pediatric malignancies are rare diseases, early diagnosis is an important factor leading to high cure rates of many types of cancers including retinoblastomara, Wilms' tumor, hepatoblastoma, rhabdomyosarcoma. thyroid carcinoma, and other solid tumors. A number of familial cancer syndromes present with childhood cancers that can be recognized or diagnosed by pediatricians. The genetic origins of several syndromes have been elucidated. Genetic testing is not yet available for all of these inherited cancers. A frequently updated list of genetic tests is available at www.genetests.org. The ordering and interpreting of genetic tests, however, is often best done by trained genetic counselors. The pediatrician will play a vital on-going role in following the at-risk child. In many of syndromes discussed, the cost effectiveness of the tests as well as that of any potential intervention needs further study. The role of the subtle genetic polymorphisms in pediatric tumorigenesis. many more of which will undoubtedly be described in the coming years, has not yet been translated into defined needs for interventions. Perhaps in the future it will be possible to understand the additive effect of multiple genetic polymorphisms and to determine genetic profiles of high cancer risk. Until suitable interventions are established, however, the study of genetic variability and cancer will await practical significance. Undoubtedly other major important cancer genes are yet to be discovered and characterized. An additional challenge is the counseling and management of children and adults who have a strong family history of cancer yet who do not have a recognizable syndrome. The role of the primary pediatrician is to recognize the major cancer genetic syndromes, to make appropriate referrals for genetic counseling and testing when indicated, and to ensure that adequate screening tests are being done.

Role of pharmacogenomics and pharmacodynamics in the treatment of acute lymphoblastic leukaemia

Pharmacodynamic studies have been used to establish the relationships between the administered dosage and the concentration of drugs and metabolites in the blood or tissues and that between these concentrations and pharmacological effects. Polymorphisms in the genes that encode drug-metabolizing enzymes, drug transporters and drug targets can affect a person's response to therapy and may affect the development of de novo or therapy-related leukaemias. The burgeoning field of pharmacogenomics elucidates inherited differences in drug metabolism and treatment response. Increasingly, pharmacodynamic and pharmacogenomic studies are being used to individualize therapy to enhance efficacy and reduce toxicity.

Glutathione S-transferase P1 genetic polymorphisms and susceptibility to childhood acute lymphoblastic leukaemia

Glutathione S-transferase pi (GSTP1) is involved in the metabolism of carcinogens. We assessed the association of GSTP1 genetic polymorphisms and the susceptibility to childhood acute lymphoblastic leukaemia (ALL) by conducting a case-control study on 278 ALL patients and 303 healthy controls, both of French-Canadian origin. The carriers of the GSTP1*B variant (only the Val105 substitution) were found to be associated with an increased risk of ALL [odds ratio (OR) = 1.5, 95% confidence interval (CI) 1.1-2.0], whereas the GSTP1*C variant (both Val105 and Val114) was underrepresented in cases. Thus, genetic variants of GSTP1 that are expressed at the protein level appear to contribute differently to the risk of ALL, probably because of distinct substrate specificities. When combined with other GST genotypes, we found that the combination of GSTP1*B and GSTM1 null genotypes further increased the risk of ALL (OR = 2.1; 95% CI-1.3-3.4). These findings suggest that GSTP1 variants (alone or combined with other GSTs) represent significant genetic determinants of childhood ALL.

Negative prognostic value of glutathione S-transferase (GSTM1 and GSTT1) deletions in adult acute myeloid leukemia

Glutathione S-transferases (GSTs) are enzymes involved in the detoxification of several environmental mutagens, carcinogens, and anticancer drugs. GST polymorphisms resulting in decreased enzymatic activity have been associated with several types of solid tumors. We determined the prognostic significance of the deletion of 2 GST subfamilies genes, M1 and T1, in patients with acute myeloid leukemia (AML). Using polymerase chain reactions, we analyzed the GSTM1 and GSTT1 genotype in 106 patients with AML (median age, 60.5 years; range, 19-76 years). The relevance of GSTM1 and GSTT1 homozygous deletions was studied with respect to patient characteristics, response to therapy, and survival. Homozygous deletions resulting in null genotypes at the GSTM1 and GSTT1 loci were detected in 45 (42%) and 30 (28%) patients, respectively. The double-null genotype was present in 19 patients (18%). GST deletions predicted poor response to chemotherapy (P =.04) and shorter survival (P =.04). The presence of at least one GST deletion proved to be an independent prognostic risk factor for response to induction treatment and overall survival in a multivariate analysis including age and karyotype (P =.02). GST genotyping was of particular prognostic value in the cytogenetically defined intermediate-risk group (P =.003). In conclusion, individuals with GSTM1 or GSTT1 deletions (or deletions of both) may have an enhanced resistance to chemotherapy and a shorter survival.

How acute promyelocytic leukaemia revived arsenic

Despite its many therapeutic qualities, arsenic trioxide has been more commonly remembered as Madame Bovary's poison than as an anticancer drug. The ability of arsenic trioxide to treat acute promyelocytic leukaemia has radically changed this view, providing new insights into the pathogenesis of this malignancy and raising hopes that arsenicals might be useful in treating other cancers.

Association between xenobiotic gene polymorphisms and non-Hodgkin's lymphoma risk

The last four decades have seen a significant increase in the incidence of non-Hodgkin's lymphoma (NHL) as a possible result of increasing environmental carcinogen exposure, particularly pesticides and solvents. Based on the increasing evidence for an association between carcinogen exposure-related cancer risk and xenobiotic gene polymorphisms, we have undertaken a case-control study of xenobiotic gene polymorphisms in individuals with a diagnosis of NHL. Polymorphisms of six xenobiotic genes (CYP1A1, GSTT1, GSTM1, PON1, NAT1, NAT2) were characterized in 169 individuals with NHL and 205 normal controls using polymerase chain reaction-based methods. Polymorphic frequencies were compared using Fisher's exact tests, and odds ratios for NHL risk were calculated. Among the NHL group, the incidence of GSTT1 null and PON1 BB genotypes were significantly increased compared with controls, 34% vs 14%, and 24% vs 11% respectively. Adjusted odds ratios calculated from multivariate analyses demonstrated that GSTT1 null conferred a fourfold increase in NHL risk (OR = 4.27; 95% CI, 2.40-7.61, P < 0.001) and PON1 BB a 2.9-fold increase (OR = 2.92; 95% CI, 1.49-5.72, P = 0.002). Furthermore, GSTT1 null combined with PON1 BB or GSTM1 null conferred an additional risk of NHL. This is the first time that a PON1 gene polymorphism has been shown to be associated with cancer risk. We conclude that the two polymorphisms, GSTT1 null and PON1 BB, are common genetic traits that pose low individual risk but may be important determinants of overall population NHL risk, particularly among groups exposed to NHL-related carcinogens.

Arsenic trioxide in the treatment of newly diagnosed acute promyelocytic leukemia: a single center experience

Arsenic trioxide (As(2)O(3)) has been found effective in the treatment in the treatment of acute promyelocytic leukemia (APML). Most studies with As(2)O(3) involve patients with APML who have relapsed following standard therapy. Between January 1998 and July 2000, 14 patients were recruited for an ongoing trial of As(2)O(3) in the treatment of newly diagnosed APML. Arsenic trioxide was administered at a dose of 10 mg/day until complete remission (CR) was achieved. Afterward, a consolidation course and a maintenance schedule consisting of As(2)O(3) as a single agent were administered over 6 months. There were 3 early deaths related to intra-cerebral hemorrhage: two on day 3 and one on day 4. Of the 11 evaluable patients, one died on day 21 secondary to uncontrolled sepsis, while the remaining 10 (91%) have attained CR. The average time to CR was 52.3 days (range: 34-70 days). One patient developed an isolated central nervous system (CNS) relapse and subsequently went into a second CR following therapy with triple intrathecal chemotherapy, cranial irradiation, and an additional 4-week course of systemic As(2)O(3). This patient, as well as the remaining nine, has continued to remain in CR at a median follow up of 15 months (range: 2-33 months). Eight out of 10 patients achieved molecular remission at variable periods during their consolidation and maintenance schedules. One patient developed an ATRA syndrome and was administered daunorubicin (40 mg/day) for 2 days. The side effects with this therapy were minimal and did not require cessation of therapy in any patient. There was no significant hepatic toxicity. In our experience, arsenic trioxide is effective in inducing and maintaining remission in patients with APML with minimal side effects. The optimal regimen and total dose required need to be defined.

Glutathione S-transferase genotypes, genetic susceptibility, and outcome of therapy in childhood acute lymphoblastic leukemia

The glutathione S-transferase (GST) genes are involved in the metabolism of environmental carcinogens and of some classes of chemotherapy drugs. GSTM1 and GSTT1 genotypes are polymorphic in humans, and the phenotypic absence of enzyme activity is caused by a homozygous inherited deletion of the gene. Previous, smaller studies of childhood acute lymphoblastic leukemia (ALL) provided contrasting data on the role of the GST genotype in susceptibility and treatment outcomes. We analyzed GST genotypes in 710 children with ALL treated by the Children's Cancer Group. Frequencies were compared with those of normal controls, and outcomes were analyzed according to genotype. Comparisons of gene frequencies in ALL case and control patients showed similar frequencies (54% vs 53% GSTM1 null in whites, P =.9; 40% versus 32% in blacks, P =.45; 16% versus 15% GSTT1 null in whites, P =.8; 17% versus 28% in blacks, P =.3). ALL was not associated with the GSTM1-null genotype or the double-null genotype in blacks or whites, in contrast to previous reports. Stratification of cases by age at diagnosis, sex, white blood cell count at diagnosis, B or T lineage, or cytogenetics revealed no differences in genotype frequencies. Analysis of treatment outcomes showed no differences in outcome according to GST genotype; in particular, there were no differences in frequencies of relapse at any site. These data, representing a larger series than any reported previously, suggest that GST genotype does not affect etiology or outcome of childhood ALL.

Childhood acute lymphoblastic leukemia

As cure rates in childhood acute lymphoblastic leukemia reach 80%, emphasis is increasingly placed on the accurate identification of drug-resistant cases, the elucidation of the mechanisms involved in drug resistance and the development of new therapeutic strategies targeted toward the pivotal molecular lesions. Pharmacodynamic and pharmacogenomic studies have provided rational criteria for individualizing therapy to enhance efficacy and reduce acute toxicity and late sequelae. Currently, assessment of the early response to treatment by measurement of minimal residual disease (MRD) is the most powerful independent prognostic indicator. MRD is affected by both the drug sensitivity of leukemic cells and the pharmacodynamic and pharmacogenetic properties of the host cells. Rapid advances in biotechnology and bioinformatics should ultimately facilitate the development of molecular diagnostic assays that can be used to optimize antileukemic therapy and elucidate the mechanisms of leukemogenesis. In the interim, prospective clinical trials have provided valuable clues that are further increasing the cure rate of childhood acute lymphoblastic leukemia.

Applications of advances in molecular biology and genomics to clinical cancer care

Genetics technologies, methods, and discoveries are being integrated rapidly into medical and nursing practices in a variety of ways. The purpose of this article is to familiarize nurses with how new genetic technologies and discoveries are being incorporated into various phases of clinical oncology practice. The scope of this article is broad to provide an overview of the of ways in which cancer prevention, surveillance, diagnosis, prognosis, monitoring, treatment, and gene therapy are evolving due to advances in the molecular biology of cancer. We use specific examples to demonstrate the use of genetic information to achieve these objectives and to illustrate principles and strategies that may be applied to a variety of cancers.

Genetic polymorphisms and metabolism of endocrine disruptors in cancer susceptibility

Epidemiological studies have estimated that approximately 80% of all cancers are related to environmental factors. Individual cancer susceptibility can be the result of several host factors, including differences in metabolism, DNA repair, altered expression of tumor suppressor genes and proto-oncogenes, and nutritional status. Xenobiotic metabolism is the principal mechanism for maintaining homeostasis during the body's exposure to xenobiotics. The balance of xenobiotic absorption and elimination rates in metabolism can be important in the prevention of DNA damage by chemical carcinogens. Thus the ability to metabolize and eliminate xenobiotics can be considered one of the body's first protective mechanisms. Variability in individual metabolism has been related to the enzymatic polymorphisms involved in activation and detoxification of chemical carcinogens. This paper is a contemporary literature review on genetic polymorphisms involved in the metabolism of endocrine disruptors potentially related to cancer development.

Abnormalities in hemostasis in acute promyelocytic leukemia

Our understanding of the hemostatic abnormalities in acute promyelocytic leukemia (APL) has undergone remarkable changes over the past three decades. Hemorrhagic complications lead to significant morbidity and mortality in patients with APL. Up to 30% of early deaths are due to hemorrhagic complications. Our concept of the coagulation changes in APL have evolved from a simple belief that the bleeding was due to disseminated intravascular coagulation (DIC) from underlying infection, to a knowledge that the APL cells themselves are responsible for the bleeding. We have observed that apoptotic APL cells have increased generation of thrombin and therefore contribute to the hypercoagulability and DIC. In addition, excessive fibrinolysis has been recognized to play an important role. The advent of a new therapeutic approach with all-trans-retinoic acid has improved overall survival and has greatly shortened the hemorrhagic phase of the disease, but only to produce a new complication, the retinoic acid syndrome. Its pathogenesis and management still remain to be the challenge for the present.

Update on pharmacogenetics in cancer chemotherapy

This review describes how genetic differences among patients may change the therapeutic outcome in cancer chemotherapy. Severe toxicity in genetically predisposed patients is predominantly associated with mutations in drug metabolism enzyme genes, and an update on genetic intolerance to 6-mercaptopurine, 5-fluorouracil, and irinotecan is provided. Moreover, recent findings pointed out that the methylenetetrahydrofolate reductase (MTHFR) C677T mutation might change patient susceptibility to the toxic effects of the cyclophosphamide, methotrexate, 5-fluorouracil (CMF) regimen and raltitrexed. Finally, it is emerging that not only toxicity, but also response to chemotherapy could be influenced by pharmacogenetic determinants, and the clinical relevance of polymorphisms in thymidylate synthase (TS) and glutathione-S-transferase (GST) genes is discussed.