Acute myeloid leukaemia in children

EPHX1 rs1051740 T>C (Tyr113His) is strongly associated with acute myeloid leukemia and KMT2A rearrangements in early age

Experimental and epidemiological data have shown that acute myeloid leukemia in early-age (i-AML) originates prenatally. The risk association between transplacental exposure to benzene metabolites and i-AML might be influenced by genetic susceptibility. In this study, we investigated the relationship between genetic polymorphisms in CYP2E1, EPHX1, MPO, NQO1, GSTM1 and GSTT1 genes, and i-AML risk. The study included 101 i-AMLs and 416 healthy controls. Genomic DNA from study subjects was purified from bone marrow or peripheral blood aspirates and genotyped for genetic polymorphisms by real-time PCR allelic discrimination, Sanger sequencing and multiplex PCR. Crude and adjusted odds ratios (OR, _adjOR, respectively) with 95% confidence intervals (95% CI) were assessed using unconditional logistic regression to estimate the magnitude of risk associations. EPHX1 rs1051740 T>C was associated with i-AML risk under the co-dominant (_adjOR 3.04, P = 0.003) and recessive (_adjOR 2.99, P = 0.002) models. In stratified analysis, EPHX1 rs1051740 was associated with increased risk for i-AML with KMT2A rearrangement (_adjOR 3.06, P = 0.045), i-AML with megakaryocytic differentiation (_adjOR 5.10, P = 0.008), and i-AML with type I mutation (_adjOR 2.02, P = 0.037). EPHX1 rs1051740-rs2234922 C-G haplotype was also associated with increased risk for i-AML (_adjOR 2.55, P = 0.043), and for i-AML with KMT2A rearrangement (_adjOR 3.23, P = 0.034). Since EPHX1 enzyme is essential in cellular defense against epoxides, the diminished enzymatic activity conferred by the variant allele C could explain the risk associations found for i-AML. In conclusion, EPHX1 rs1051740 plays an important role in i-AML's genetic susceptibility by modulating the carcinogenic effects of epoxide exposures in the bone marrow.

Treatment of Common Childhood Malignancies

Malignancy is the fourth leading cause of death in persons aged 1 to 19 years. The success of the pediatric oncology cooperative group clinical trials has allowed a systematic approach to the treatment of relatively rare malignancies. Each trial builds on previous results in terms of both survival and toxicity. This article will discuss the current treatment regimens for several of the more common pediatric malignancies and their long-term complications developed through this process.

Thiopurine Prodrugs Mediate Immunosuppressive Effects by Interfering with Rac1 Protein Function

6-Thiopurine (6-TP) prodrugs include 6-thioguanine and azathioprine. Both are widely used to treat autoimmune disorders and certain cancers. This study showed that a 6-thioguanosine triphosphate (6-TGTP), converted in T-cells from 6-TP, targets Rac1 to form a disulfide adduct between 6-TGTP and the redox-sensitive GXXXXGK(S/T)C motif of Rac1. This study also showed that, despite the conservation of the catalytic activity of RhoGAP (Rho-specific GAP) on the 6-TGTP-Rac1 adduct to produce the biologically inactive 6-thioguanosine diphosphate (6-TGDP)-Rac1 adduct, RhoGEF (Rho-specific GEF) cannot exchange the 6-TGDP adducted on Rac1 with free guanine nucleotide. The biologically inactive 6-TGDP-Rac1 adduct accumulates in cells because of the ongoing combined actions of RhoGEF and RhoGAP. Because other Rho GTPases, such as RhoA and Cdc42, also possess the GXXXXGK(S/T)C motif, the proposed mechanism for the inactivation of Rac1 also applies to RhoA and Cdc42. However, previous studies have shown that CD3/CD28-stimulated T-cells contain more activated Rac1 than other Rho GTPases such as RhoA and Cdc42. Accordingly, Rac1 is the main target of 6-TP in activated T-cells. This explains the T-cell-specific Rac1-targeting therapeutic action of 6-TP that suppresses the immune response. This proposed mechanism for the action of 6-TP on Rac1 performs a critical role in demonstrating the capability to design a Rac1-targeting chemotherapeutic agent(s) for autoimmune disorders. Nevertheless, the results also suggest that the targeting action of other Rho GTPases in other organ cells, such as RhoA in vascular cells, may be linked to cytotoxicities because RhoA plays a key role in vasculature functions.

Insight into the 6-thiopurine-mediated termination of the invasive motility of tumor cells derived from inflammatory breast cancer

Our study showed that a combination of 6-thiopurine (6-TP) drugs and a redox agent effectively inhibits the motility of SUM cells derived from human inflammatory breast cancer (IBC) cells and RhoC-overexpressed mammary epithelium cells. This 6-TP-mediated inhibition of cell motility occurs because the treated 6-TPs target and inactivate RhoC. A molecular mechanism for inactivation by the 6-TP-mediated RhoC is proposed by which treated TPs are converted in cells into 6-thioguanosine phosphate (6-TGNP). This 6-TGNP in turn reacts with the Cys(20) side chain of the redox-sensitive GXXXCGK(S/T)C motif of RhoC to produce a 6-TGNP-RhoC disulfide adduct. A redox agent synergistically enhances the formation process of this disulfide. The adduct that is formed impedes RhoC guanine nucleotide exchange, which populates an inactive RhoC. Our results suggest that 6-TGNP can also react with the redox-sensitive GXXXCGK(S/T)C and GXXXXGK(S/T)C motif of RhoA and Rac, respectively, to produce a 6-TGNP-RhoA and 6-TGNP-Rac disulfide adduct. However, given that RhoC has been shown to be overexpressed in ∼90% of IBC lesions, the populated RhoC but not other Rho proteins is likely to be a primary target for 6-TPs and a redox agent to terminate the metastasis of IBC.

A review of the potential association between childhood leukemia and benzene

Chronic exposure to high concentrations of benzene is an established cause of acute myeloid leukemia (AML) in occupationally exposed workers. Based on this association, it is not unreasonable to assume that children could also get AML if they were exposed to comparable levels of benzene. Fortunately, reports of such exposures and subsequent AML development in children are non-existent. However, the question of whether children can develop leukemia at far lower, environmental levels of benzene remains. The existing scientific evidence relevant to this question will be addressed in this review. While positive findings have been reported, the collective literature does not indicate that exposure to environmental levels of benzene is related to an increased risk of childhood leukemia. Our understanding of this important issue would be strengthened by additional studies that accurately characterize exposures as well as differentiate between the various forms of leukemias observed in children.

Improved outcome in childhood acute myeloid leukemia in Singapore with the MRC AML 10 protocol

BACKGROUND

The introduction of the United Kingdom Medical Research Council's 10th AML trial (MRC AML 10) protocol incorporating high-dose anthracycline therapy has improved outcome of children with acute myeloid leukemia (AML). In this study, we review the results of childhood AML therapy in a Singapore university hospital over the last 17 years emphasizing toxicity and outcome.

PROCEDURE

Retrospective analysis revealed 34 children with AML between 1988 and 2003. Prior to September 1996, therapy consisted of: POG-8498 (n = 10), others (n = 9). From September 1996, all but one of 15 children received MRC AML 10 treatment.

RESULTS

At the time of analysis, 17 had died from disease, and 17 patients were alive among whom 2 had relapsed. MRC AML 10-treated patients (n = 14) had significantly better 3-year overall, event-free, and disease-free survival (74% vs. 35%, 77% vs. 20%, 83% vs. 31%; P = 0.019, P = 0.002, and P = 0.010, respectively) and were likelier to achieve complete remission (CR) than non-MRC AML 10 patients (P = 0.102). Among patients who achieved CR, MRC AML 10-treated patients were significantly more likely to achieve CR after only one cycle of chemotherapy (P = 0.016). Hematologic toxicity was similar among the different regimens (P = 0.9).

CONCLUSIONS

These findings suggest that MRC AML 10 treatment results in significantly superior survival, without excess toxicity. Future studies should attempt to elucidate the relative importance of individual MRC AML 10 components and reduce the high cumulative anthracycline dose without compromising outcome.

Benzene and the hemopoietic stem cell

The emerging understanding of the biology of the hemopoietic stem cell is beginning to shed light on the mechanisms by which benzene gives rise to acute myeloid leukaemia. These mechanisms are complex, affecting not only the DNA, but also the complex intercellular interactions present in the bone marrow microenvironment. The toxic effects of benzene are mediated within the bone marrow and we are beginning to understand the contributions of inter-individual variation in xenobiotic metabolisms and DNA repair to the definition of risk following exposure to benzene in the environment. This process is likely to be accelerated by recent advances in high throughput genotyping. Until now, research has focussed directly on mutation and chromosomal translocations, but we are beginning to understand more how environmental exposures can modify chromatin structure giving rise to heritable changes not affecting DNA. These epigenetic studies are likely to give important further insights into the mode of action of benzene as are studies of its effect on the immune system.