| BackgroundAcute lymphoblastic leukemia(ALL)is one of the common hematological malignancies.In recent years,with the gradual maturity of the stratified treatment system and the use of new drugs,the treatment effect of ALL patients has been significantly improved.However,the overall survival rate of adult ALL patients is still significantly lower than that of children,and a considerable number of ALL patients still face refractory and recurrent situations.Glutathione-S-transferase(GSTs)is a common metabolic enzyme in the human body and is involved in the detoxification of carcinogens.GSTM1 is one of the important members of the GST family.Some studies found that the polymorphism and methylation of GSTM1 gene are related to the occurrence and prognosis of cancers.The relationship between GSTM1 gene polymorphism and methylation with the occurrence and prognosis of ALL is not yet clear.This study intends to explore the value of GSTM1 gene polymorphism and methylation in the prognosis of ALL by detecting the expression and the methylation level of GSTM1 gene in ALL patients,in order to find a new therapeutic target for ALL.Material and MethodsEntirely,66 newly diagnosed ALL patients between January 2013 and January 2017 were enrolled in our study,there are 18 children and 48 adults,who were confirmed through bone marrow morphology,immunology,cytogenetics,molecular biology examination in Nanfang hospital or Fujian provincial hospital.All patients received induction,chemotherapy,hematopoietic stem cell transplantation,maintenance and other treatments according to the China ALL guidelines.The bone marrow specimens of all patients were collected before treatment,and extracted to DNA,for detecting the GSTM1 gene polymorphism by PCR technology,and analyzing the GSTM1 gene methylation level by the MassARRAY platform.The polymorphism and methylation level of the GSTM1 gene in ALL patients were compared between groups such as different gender,age,white blood cell,lactate dehydrogenase,immunotype,genetic subtype,with t-test,rank-sum test,one-way analysis of variance and other statistical methods.All the clinical characteristics,immunotypes,genetic subtypes and methylation at different sites of the GSTM1 gene were included as independent variables into the Cox model.Results1.Children ALL patients were significantly different from adult ALL patients in molecular biology and epigenetics.The proportion of TEL-AML1 gene mutations was higher in children ALL patients than adult ALL patients(38.9%vs.8.3%),and the proportion of Ph-positive subtype was lower in children ALL patients(11.1%vs.39.6%),p<0.05.The methylation level of GSTM1 gene CpG different sites in children ALL patients were lower than adult ALL patients(CpG-40 0.21 vs.0.36,CpG-106 0.11 vs.0.19,CpG-234 0.28 vs.0.43,p<0.05).Compared to adult ALL patients,children ALL patients had a better response to corticosteroids induction therapy(55.6%vs.22.9%,p=0.047),a lower recurrence rate(16.7%vs.45.9%),and a better survival time(median OS 48.2m vs.20.1m,p<0.05),showing better clinical efficacy and prognosis.2.GSTM1 gene polymorphism was detected in 66 ALL patients,35 cases of GSTM1*0 type(null genotype)and 31 cases of GSTM1 type were found.There were no significant differences between this two GSTM1 genotype groups in gender,age,clinical characteristics,immunotype,gene mutation,cytogenetics subtype,recurrence rate and survival time.3.Methylation levels were obtained for 30 CpG sites of GSTM1 gene in ALL patients.After comparisons,8 sites(40,47,106:119,125:132:137,234,251,357,474)were adopted in further explorations.ALL patients with central nervous system(CNS)invasion had lower methylation levels at the two sites than those patients without CNS invasion(CpG-40 0.25 vs.0.34,CpG-106 0.06 vs.0.18,p<0.05).In ALL patients with MLL rearrangement,the methylation levels were significantly higher than those without MLL rearrangement at three sites(CpG-125 0.82 vs.0.34,CpG-234 0.83 vs.0.38,CpG-251 0.94 vs.0.66,p<0.05).Multivariate analysis of the Cox model showed that the risk of recurrence in ALL patients increased with age(HR 1.7,95%CI:1.3-2.22,p<0.05),and patients with hepatomegaly before treatment had a low risk of recurrence(HR 0.42,95%CI:0.2-0.88,p<0.05).GSTM1 gene methylation has nothing to do with the risk of recurrence.Multivariate analysis of the Cox model showed that hypermethylation at 40,106,and 234 sites of the GSTM1 gene,older age,none-hepatomegaly,and poor corticosteroids-induced response were all survival risk factors of ALL patients.Among them,older age and hypermethylation at 40 site of GSTM1 gene are independent risk factors that affect the survival of ALL patients,(HR 1.66,95%CI:1.23-2.24,HR 1.18,95%CI:1.02-1.37,p<0.05).The median OS of ALL patients with a methylation value higher than 0.675 at the 40 site of GSTM1 gene was shorter than that of patients with a methylation value lower than 0.675(200d vs.830d,p<0.05).ConclusionsThere is no clear correlation between GSTM1 gene polymorphism and the prognosis of ALL patients.GSTM1 gene hypermethylation is another independent risk factor that affects the survival of ALL patients in addition to age.The sample size needs to be expanded in the future to further verify the value of methylation at different sites of the GSTM1 gene in the prognostic stratification of ALL. |
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