Abstract 251: Disabled gene is involved in CML progression and its expression level at diagnosis can predict major molecular response (MMR) to imatinib therapy

Abstract

Abstract Despite the role of Bcr-Abl in the pathogenesis of Chronic Myeloid Leukemia (CML) is well established, the mechanisms leading to CML progression remain unknown. Using our model of Drosophila melanogaster (Dm) transgenic for human Bcr-Abl we identified Dab1 and Dab2, the homologs of Dm Disabled (Dab), as genes involved in CML progression. In Dm the Dab loss of function induced a worsening of the hBcr-Abl eye phenotype and an even stronger phenotype was obtained using Dab RNAi fly strains. By contrast, Dab gain of function rescued Bcr-Abl phenotype. Dab is an adaptor protein acting downstream of many receptor tyrosine kinases (RTK). One of the human homolog of Dab, Dab1 is a large common fragile site gene involved in neural migration, and the other homolog Dab2 encodes an adaptor protein implicated in RTK signalling, endocytosis, cell adhesion and differentiation. The downregulation of both genes is described in many cancers suggesting their possible role in oncogenesis but their involvement in haematological malignancies has never been described. The aim of the study was to investigate the role of Dab1/2 in CML progression. Dab1 and Dab2 mRNA was analyzed by Real Time PCR in 94 samples from 82 CML patients (34 PB and 60 BM) distributed as follows: 55 patients at diagnosis (19 enrolled in TOPS study), 9 chronic phase (CP), 7 accelerated phase (AP) and 11 blast crisis (BC). 21 healthy donors (10 PB and 11 BM) were analyzed as control. In 18 patients, genes expression was analyzed during remission as well. Protein expression was evaluated by Western Blot (WB) and Immunofluorescence (IF). In addition, K562 cells were transfected with Dab plasmids to evaluate the effects on cell proliferation. We found that in CML patients Dab1/2 expression was significantly decreased both in BM and PB (p<0.002 and p<0.0004) compared to healthy donors. In BC Dab1/2 levels were further decreased whereas during remission the expression was comparable to normal values. Data analysis of patients included in TOPS studies shows that Dab1 values are higher among those achieving MMR by 12 months (median value: 0,017) compared to those without MMR (median value: 0,001); WB and IF confirmed the absence of Dab1/2 proteins in course of active CML samples while it reappeared during remission. Moreover, Dab1 transfection of K562 significantly reduced proliferation (p=0,002). In conclusion, our results show a significant decrease of Dab1/2 expression in BC samples, when compared to CP CML and healthy donors. Among CP CML patients the responders to Tyrosine Kinase Inhibitors (TKI) therapy have been detected to express higher Dab levels than non responders, and these expression levels can predict MMR to Imatinib therapy. In conclusion, this study points to specific gene pathways that might offer new molecular markers for the monitoring of CML and new targets for CML therapy in order to prevent or overcome disease progression. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 251.