The multiple colorectal adenoma phenotype and MYH, a base excision repair gene.

We summarize the genetic and clinical features of the colorectal adenomas and cancers that occur in MYH-associated polyposis (MAP). MAP results from biallelic germline mutations in the base excision repair gene, mutY homologue (MYH). MAP has a phenotype that is often indistinguishable from classical or attenuated familial adenomatous polyposis (FAP), but the former is inherited as a recessive condition, whereas the latter is a dominantly inherited disease caused by germline mutations of the APC gene. MYH mutations seem to act by increasing the frequency of somatic APC mutations. MAP tumors may then progress to cancer along a distinct genetic pathway. MAP occurs in several different ethnic groups, the mutation spectrum appearing to differ among groups. It remains unknown, however, as to why carriers of MYH mutations specifically develop tumors of the gastrointestinal tract. In general, carriers of biallelic MYH mutations should be treated and followed up as for FAP patients with a similar phenotype. Relatives of MAP patients should be counseled as for any other recessive condition, although it remains possible that carriers of single mutations are at a modestly increased risk of colorectal cancer.     

AML1-ETO rapidly induces acute myeloblastic leukemia in cooperation with the Wilms tumor gene, WT1

AML1-ETO, a chimeric gene frequently detected in acute myelogenous leukemia (AML), inhibits the differentiation of myeloid progenitors by suppressing genes associated with myeloid differentiation and increases the replating ability of clonogenic myeloid progenitors. However, AML1-ETO alone cannot induce AML and thus additional genetic events are required for the onset of AML. The Wilms tumor gene (WT1), which has been identified as the gene responsible for Wilms tumor, is expressed at high levels in almost all human leukemias. In this study, we have generated transgenic mice (WT1-Tg) that overexpress WT1 in hematopoietic cells to investigate the effects of WT1 on AML1-ETO-associated leukemogenesis. AML1-ETO-transduced bone marrow (BM) cells from WT1-Tg mice exhibited inhibition of myeloid differentiation at more immature stages and higher in vitro colony-forming ability compared with AML1-ETO-transduced BM cells from wild-type mice. Most importantly, all of the mice that received a transplant of AML1-ETO-transduced BM cells from the WT1-Tg mice rapidly developed AML. These results demonstrate that AML1-ETO may exert its leukemogenic function in cooperation with the expression of WT1.     

Polymorphisms in human homeobox HLX1 and DNA repair RAD51 genes increase the risk of therapy-related acute myeloid leukemia

Studies of radiation-induced acute myeloid leukemia (AML) in mice suggest that the number of target stem cells is a risk factor, and the HLX1 homeobox gene, which is important for hematopoietic development, is a candidate gene. The distribution of the C/T-3' untranslated region (UTR) polymorphism in HLX1 in patients with AML and therapy-related AML (t-AML) compared with controls was therefore determined. The presence of the variant HLX1 allele significantly increases the risk of t-AML (OR = 3.36, 95% CI, 1.65-6.84). The DNA repair gene RAD51 (135G/C-5' UTR) polymorphism also increases t-AML risk, and when combined analysis was performed on both RAD51 and HLX1 variant alleles, a synergistic 9.5-fold increase (95% CI, 2.22-40.64) in the risk of t-AML was observed. We suggest that the HLX1 polymorphism has an effect on stem cell numbers, whereas an increased DNA repair capacity (RAD51) will suppress apoptosis, a genetic interaction that may increase the number of genomes at risk during cancer therapy.     

Implications of somatic mutations in the AML1 gene in radiation-associated and therapy-related myelodysplastic syndrome/acute myeloid leukemia

Somatically acquired point mutations of AML1/RUNX1 gene have been recently identified in rare cases of acute myeloid leukemia (AML) and myelodysplastic syndrome (MDS). Moreover, germ line mutations of AML1 were found in an autosomal dominant disease, familial platelet disorder with predisposition to AML (FPD/AML), suggesting that AML1 mutants, as well as AML1 chimeras, contribute to the transformation of hematopoietic progenitors. In this report, we showed that AML1 point mutations were found in 6 (46%) of 13 MDS patients among atomic bomb (A-bomb) survivors in Hiroshima. Unlike acute or chronic leukemia patients among A-bomb survivors, MDS patients exposed relatively low-dose radiation and developed the disease after a long latency period. AML1 mutations also were found in 5 (38%) of 13 therapy-related AML/MDS patients who were treated with alkylating agents with or without local radiation therapy. In contrast, frequency of AML1 mutation in sporadic MDS patients was 2.7% (2 of 74). Among AML1 mutations identified in this study, truncated-type mutants lost DNA binding potential and trans-activation activity. All missense mutations with one exception (Gly42Arg) lacked DNA binding ability and down-regulated the trans-activation potential of wild-type AML1 in a dominant-negative fashion. The Gly42Arg mutation that was shared by 2 patients bound DNA even more avidly than wild-type AML1 and enhanced the trans-activation potential of normal AML1. These results suggest that AML1 point mutations are related to low-dose radiation or alkylating agents and play a role distinct from that of leukemogenic chimeras as a result of chromosomal translocations caused by sublethal radiation or topoisomerase II inhibitors.     

The heritable nature of clonal characteristics in acute myeloblastic leukemia

Marked patient-to-patient variation is observed when blood or marrow from AML patients is examined using colony methods in culture. Concentrations of the progenitors of colonies change with time during the course of the disease. We asked whether blast progenitor properties were more stable. We measured blast cell self-renewal and drug sensitivity (adriamycin and cytosine arabinoside) repeatedly in the courses of seven AML patients. These properties were found to be stable or slowly evolving. We conclude that capacity for renewal and sensitivities to certain chemotherapeutic drugs are heritable characteristics in leukemic clones.     

Treatment of acute myeloblastic leukemia in adults. The GOELAM experience

The GOELAM group conducted 2 consecutive trials on the treatment of de novo acute myeloblastic leukemia (AML) in adults. In the GOELAM1 protocol 786 patients aged 15–65 were randomized between two induction treatments (ARA-C 200 mg/m²/day for 7 days plus either Idarubicin 8 mg/m²/day for 5 days or Rubidazone 200 mg/m²/day for 4 days). Out of 731 evaluable patients, 521 (71%) achieved complete remission (CR) without significant difference between the 2 anthracyclines. For patients aged 51–65, the CR rate was significantly higher with Idarubicin (75%) than with Rubidazone (61%) (p=0,03). In this group of patients the post-remission therapy consisted in only one course of high dose ARA-C plus m-Amsa and the 6 year disease free survival (DFS) was 24% (intention to treat analysis). For patients aged 15–50 years, the post remission therapy was either allogeneic bone marrow transplantation (BMT) (patients up to 40 years of age with an HLA identical sibling) or a first course of intensive consolidation chemotherapy (ICC) followed by a randomization between autologous unpurged bone marrow transplantation (ABMT) and a second course of ICC. There was no significant difference in the 4 year DFS between allogeneic BMT (42%) and the other types of intensive post remission-therapy (40%). The 4 year DFS was 42% for ABMT and 38% for ICC (p=0.46) (intention to treat analysis). However the median duration of thrombocytopenia was much longer after ABMT (109.5 days versus 18.5 days p=0.0001). The GOELAM SA3 randomized placebo-controlled protocol tested the impact of GM-CSF given during and after induction treatment for elderly patients (55–75 years). In this study, 232 evaluable patients received induction chemotherapy (Idarubicin 8 mg/m²/day for 5 days plus ARA-C 100 mg/m²/day for 7 days) plus placebo or GM-CSF 5μg/kg/day from day 1 until the end of neutropenia. The CR rate was 61.5%. The median duration of neutropenia was shorter in the GM-CSF arm (22 days versus 27 days p=0.0001). There was no overall significant advantage for the GM-CSF arm, in terms of CR rate and survival. However for patients age 55–64 the 2 year DFS was significantly higher in the GM-CSF arm (43% vs 17% p=0.0013).     

Treatment of acute myeloblastic leukemia in adults. The GOELAM experience

The GOELAM group conducted 2 consecutive trials on the treatment of de novo acute myeloblastic leukemia (AML) in adults. In the GOELAM1 protocol 786 patients aged 15–65 were randomized between two induction treatments (ARA-C 200 mg/m²/day for 7 days plus either Idarubicin 8 mg/m²/day for 5 days or Rubidazone 200 mg/m²/day for 4 days). Out of 731 evaluable patients, 521 (71%) achieved complete remission (CR) without significant difference between the 2 anthracyclines. For patients aged 51–65, the CR rate was significantly higher with Idarubicin (75%) than with Rubidazone (61%) (p=0,03). In this group of patients the post-remission therapy consisted in only one course of high dose ARA-C plus m-Amsa and the 6 year disease free survival (DFS) was 24% (intention to treat analysis). For patients aged 15–50 years, the post remission therapy was either allogeneic bone marrow transplantation (BMT) (patients up to 40 years of age with an HLA identical sibling) or a first course of intensive consolidation chemotherapy (ICC) followed by a randomization between autologous unpurged bone marrow transplantation (ABMT) and a second course of ICC. There was no significant difference in the 4 year DFS between allogeneic BMT (42%) and the other types of intensive post remission-therapy (40%). The 4 year DFS was 42% for ABMT and 38% for ICC (p=0.46) (intention to treat analysis). However the median duration of thrombocytopenia was much longer after ABMT (109.5 days versus 18.5 days p=0.0001). The GOELAM SA3 randomized placebo-controlled protocol tested the impact of GM-CSF given during and after induction treatment for elderly patients (55–75 years). In this study, 232 evaluable patients received induction chemotherapy (Idarubicin 8 mg/m²/day for 5 days plus ARA-C 100 mg/m²/day for 7 days) plus placebo or GM-CSF 5g/kg/day from day 1 until the end of neutropenia. The CR rate was 61.5%. The median duration of neutropenia was shorter in the GM-CSF arm (22 days versus 27 days p=0.0001). There was no overall significant advantage for the GM-CSF arm, in terms of CR rate and survival. However for patients age 55–64 the 2 year DFS was significantly higher in the GM-CSF arm (43% vs 17% p=0.0013).This work was supported by a major grant from Programme Hospitalier de Recherche Clinique     

Activation of an N-ras gene in acute myeloblastic leukemia through somatic mutation in the first exon.

A transforming N-ras gene has been cloned from acute myeloblastic leukemia bone marrow cells, in parallel with the N-ras gene derived from fibroblasts of the same patient. N-ras derived from fibroblasts lacked focus-forming activity in NIH/3T3 cells, indicating that gene activation in the leukemia cells must have occurred by a somatic event. Construction of chimeric molecules between the transforming and the normal N-ras genes and subsequent biological and sequence analysis of these constructs revealed that the transforming gene was altered by a point mutation changing amino acid 12 of the N-ras protein from glycine to aspartic acid.     

The proliferation in suspension of the progenitors of the blast cells in acute myeloblastic leukemia

A minority of blast cells in acute myeloblastic leukemia (AML) form colonies in culture in methylcellulose when stimulated by media conditioned by normal leukocytes in the presence of phytohemagglutinin (PHA-LCM). Blast colonies can be replated successfully, either as pooled cells or suspensions from single colonies. However, the plating efficiency declines with repeated passages, and more than four subcultures have not been achieved. In this study, blast populations were cultured in suspension, with fetal calf serum, alpha-minimal essential medium and PHA-LCM. In cells from 17 of 18 patients, exponential growth of clonogenic blast cells was maintained for six to seven days without reculturing. Colonies obtained from progenitors taken from liquid culture and replated in methylcellulose were replated to obtain the secondary plating efficiency (PE2). In 14 cases, this value was maintained or increased. In three instances, PE2 fell following culture in methylcellulose. When cells in suspension were recultured, exponential growth continued. In nine instances, exponential growth was maintained for from seven to 70 days. During this time, PE2 was maintained. Results from experiments using velocity sedimentation separation and analysis of single colonies were consistent with the view that the increase in clonogenic cells in suspension was a manifestation of their self-renewal capacity. The observations also support a model of blast progenitor growth that contains the postulate that these are capable not only of self-renewal but also of determination-like events leading to loss of proliferative capacity.     

The sensitivity to cytosine arabinoside of the blast progenitors of acute myeloblastic leukemia

Two culture methods are available for the study of the blast cells of acute myeloblastic leukemia (AML). One is an assay for clonogenic precursors; it depends on their ability to form blast colonies in culture in the presence of methylcellulose and suitable growth factors. The other assesses the growth of blast cells in suspension culture, where growth is measured by increasing numbers of clonogenic cells. We have compared the two methods as assays for the cytotoxic effects of the chemotherapeutic drug cytosine arabinoside (Ara-C). Marked patient- to-patient variation was found using either method; however, the slopes of the dose-response curves were usually greater when cells were exposed to drug in suspension rather than in methylcellulose. Control experiments showed that the difference could not be explained by drug carry-over from the suspension cultures to the methylcellulose plates when clonogenic cells in the suspensions were assessed. Further, the survival curves for Adriamycin were very similar, regardless of which assay was used. No correlation was found between D10 Ara-C values measured in suspension or in methylcellulose. However, a significant association with outcome was found between D10 Ara-C in suspension and response to treatment with a regimen in which Ara-C was the only chemotherapeutic agent used. No such association was detected when the D10 values obtained with the clonogenic assay were compared with outcome for the same group of 15 patients. Finally, a feasibility experiment was performed in which blast cells were exposed to Ara-C repeatedly during exponential growth over 238 days. A dose-related inhibition of growth was observed; no evidence was seen of emerging drug-resistant cells. Nor did the morphology of the cells change as a result of drug exposure. We conclude that drug sensitivities of AML blast cells in culture are dependent on measurement methods, even when techniques affecting cell proliferation are compared. Measurements of drug sensitivity in culture may best be interpreted when the bases of the assay systems are understood.     

WT1基因在白血病患者中的表达

目的 研究急性白血病（ＡＬ）患者中ＷＴ１基因的表达情况及其与预后的关系。方法 用逆转录－聚合酶链反应（ＲＴ－ＰＣＲ）的方法,研究ＷＴ１基因在１０２例ＡＬ中的表达。结果 ＲＴ－ＰＣＲ检测ＷＴ１基因的敏感性为１０＾－４。ＷＴ１基因在ＡＬ所有亚型中都有表达,初治和复发的ＡＬ中阳性率为６６．７％,而在５年长期生存者中阳性率只有７．７％（４／５２）。随着完全缓解（ＣＲ）时间的延长,ＷＴ１基因阳性率有所下降,     

Efficiency of the DNA repair and polymorphisms of the XRCC1, XRCC3 and XRCC4 DNA repair genes in systemic lupus erythematosus

Impaired DNA repair efficiency in systemic lupus erythematosus (SLE) patients has been reported in some studies, mainly regarding the repair of oxidative damage, but little is known about repair kinetics towards primarily single-stranded DNA breaks. In the present study, we aimed to investigate: (a) the efficiency of SLE peripheral blood leucocytes in repairing DNA damage induced by ionizing radiation and (b) the association of DNA repair gene (XRCC1 Arg399Gln, XRCC3 Thr241Met and XRCC4 Ile401Thr) polymorphisms in SLE patients, considering the whole group, or stratified sub-groups according to clinical and laboratory features. A total of 163 SLE patients and 125 healthy controls were studied. The kinetics of DNA strand break repair was evaluated by the comet assay, and genotyping for DNA repair genes was performed by PCR-RFLP. Compared with controls, SLE leucocytes exhibited decreased efficiency of DNA repair evaluated at 30 min following irradiation. A significant association with DNA repair gene polymorphisms was not observed for the whole group of SLE patients; however, the XRCC1Arg399Gln polymorphism was associated with the presence of anti-dsDNA antibody. The concomitance of two DNA repair polymorphic sites was associated with the presence of neuropsychiatric manifestations and antiphospholipid antibody syndrome. Taken together, these results indicated that SLE leucocytes repair less efficiently the radiation-induced DNA damage, and DNA repair polymorphic sites may predispose to the development of particular clinical and laboratory features.