Determination of DNA topoisomerase II in newly diagnosed childhood acute lymphoblastic leukemia by immunocytochemistry and RT-PCR

High levels of topoisomerase IIalpha protein expression in diffuse large B-cell lymphoma are associated with high proliferation, germinal center immunophenotype, and response to treatment

Gene copy number and protein expression of topoisomerase IIalpha were correlated to benefit from anthracyclines in various tumors. A retrospective series of 69 patients with DLBCL managed with CHOP chemotherapy were studied for immunohistochemical TopoIIalpha expression and numerical gene abnormalities by fluorescent in situ hybridization (FISH). The results were analyzed in relation to the expression of cell cycle proteins (Ki67, p53, HDM2, p21, p14, pRb, p16, and cyclins A, B1, D1, D2, D3, and E) and BCL6/CD10/MUM1/CD138 B-cell differentiation immunophenotype and outcome. High levels of TopoIIalpha protein were found in 91% of DLBCL cases. No evidence of TopoIIalpha gene amplification or deletion was found. The TopoIIalpha expression showed significant positive correlations with the proliferation index Ki67 (p = 0.002), cell cycle proteins pRb and cyclin D2 (p = 0.018 and p = 0.028, respectively), and the germinal center proteins bcl6 and CD10 (p = 0.010 and p < 0.0001, respectively). TopoIIalpha expression was significantly higher in germinal center B-cell like (GCB) DLBCL than in non-germinal center B-cell like (non-GCB) DLBCL (p = 0.048). TopoIIalpha protein was significantly associated with response to chemotherapy (chi(2), p = 0.024), but not with relapse-free or overall survival (p = 0.5). On multivariate analysis, only stage of disease retained independent prognostic significance (HR 0.33 for early stage, p = 0.008). Although TopoIIa gene copy number abnormalities were not found in DLBCL, high levels of protein expression are associated with GCB-cell differentiation immunophenotype, high proliferation, and response to treatment.

Modification of topoisomerase genes copy number in newly diagnosed childhood acute lymphoblastic leukemia

Topoisomerase genes were analyzed at both DNA and RNA levels in 25 cases of newly diagnosed childhood acute lymphoblastic leukemia (ALL). The results of molecular analysis were compared to risk group classification of children in order to identify molecular characteristics associated with response to therapy. At diagnosis, allelic imbalance at topo-isomerase IIalpha (TOP2A) gene locus was found in 75% of informative cases whereas topoisomerase I and IIbeta gene loci are altered in none or only one case, respectively. By semi-quantitative Polymerase chain reaction, we found a 2.5 to 8-fold TOP2A gene amplification in 72% of the children, which was correlated to gene overexpression in every case. These results show that TOP2A gene amplification is a frequent event in ALL at diagnosis. Interestingly, we also identified a small population of children that do not present TOP2A gene amplification or gene overexpression and who are significantly associated with very high risk classified patients showing glucocorticoid resistance. In conclusion, characterization of TOP2A gene status in childhood ALL at diagnosis provides useful complementary information for risk assessment.

Incidence and prognostic significance of MDM2 oncoprotein overexpression in relapsed childhood acute lymphoblastic leukemia

MDM2 overexpression by pediatric ALL cells at initial diagnosis has been linked to poor response to therapy. In the present study, we evaluated the incidence of MDM2 overexpression by ALL cells from pediatric patients at first relapse and compared MDM2 protein levels with in vitro response to adriamycin and with duration of initial complete remission (CR1). Since an important role of MDM2 in enhancing cell proliferation and survival appears to be inhibition of p53 activity, we also evaluated the status of p53 in these patients' leukemic cells. MDM2 protein levels were determined by Western blot analysis of leukemic bone marrow cells obtained from 42 patients with B cell precursor (BCP) ALL who relapsed during or following therapy on standard POG ALL protocols. Twelve of 42 (29%) cases have MDM2 levels >/=10-fold higher than those detected in normal bone marrow mononuclear (NMMC) cells, which express relatively low levels of protein. Thirty cases (71%) expressed MDM2 at levels <10-fold those in NMMC, including 24 MDM2-negative cases (57%). P53 mutations were detected by single-strand conformation polymorphism analysis in two cases. Overexpression of MDM2 (>/=10-fold) was significantly correlated with adriamycin resistance and decreased duration of CR1. Eight of 12 (75%) overexpressers showed high levels of in vitro resistance to adriamycin, compared to four of 30 (13%) non-overexpressers (P < 0.005). The median CR1 for MDM2 overexpressers was 20.5 months (range: 3-75 months) compared to 41 months (range: 8-98 months) for non-overexpressers (P < 0.01). Four of 42 patients failed to achieve CR following re-induction: leukemic cells from three of these patients either overexpressed MDM2 or contained a mutant p53. These results indicate that overexpression of MDM2 plays a significant role in refractory pediatric ALL and is associated with early relapse, adriamycin resistance, and failure to respond to re-induction therapy. Leukemia (2000) 14, 61-67.

Topoisomerase II and the response to antileukemic therapy

A number of recent studies have investigated the expression of topoisomerase II in clinical leukemia specimens. Here we outline the rationale for these studies, identify potential pitfalls, summarize recent results, and discuss unanswered questions in this area.

Messenger RNA expression of resistance factors and their correlation to the proliferative activity in childhood acute lymphoblastic leukemia

In this report we analyzed the mRNA expression of the resistance-related enzymes DNA topoisomerase II (Topo II), thymidylate synthase (TS), glutathione S-transferase-pi (GST-pi) and glutathione peroxidase (GP) in childhood acute lymphoblastic leukemia (ALL) and their correlation to the proliferative activity, determined by Ki-67. RNA of blast cells from 54 children with untreated ALL were examined by dot blot hybridization. We found a significant positive correlation between Topo II and TS and cell proliferation. No significant correlation was detected between the mRNA expression of the glutathione-dependent enzymes GST-pi or GP and Ki-67. The results were substantiated by a semiquantitative RT-PCR-assay and by immunocytochemistry.