Haematologica 2004;89: supplement no. 6 - Supplements ...

VIII Congress of the Italian Society of Experimental Hematology, Pavia, September 14-16, 200447mutant c-kit, but has no effect on RT mutant kit.Here, we report on six patients that met the majorclassification criteria for SMCD, that were symptomaticand that had the diagnosis of SMCD based onbiopsy-proven and histological and immunohistochemistryevidence of Systemic Mastocytosis. Weconsidered two patients as aggressive systemic mastocytosis(ASM), and three of them as indolent sporadicmastocytosis (ISM); one of the patients couldbe considered SM with an associated clonal hematologicnon-mast cell lineage disease (AHNMD) classifiedas SM-NHL. Five of them were male and onefemale. Tryptase serum levels were elevated in all ofthem (>190mg/L). Two patients has both absoluteand perceptually elevated eosinophils in their peripheralblood (45% and 19%, respectively). xWe treatedfour of them with Imatinib therapy (400 mg/die)for a median period of 3 months (range 1,5-5months). Before therapy, mastocyte cells from all ofthem were found positive for A816 mutant of c-Kitand negative for the presence of FIP1L1-PDGFRα,PDGFRβ-ETV6 and FGR1-BCR fusion transcripts,occasionally associated with SMCD with eosinophilia.One patient, with elevated count of eosinophils inperipheral blood, showed an initial response to Imatinib,but lost it after 1 month from the beginning oftreatment. Another patient had a decrease of themastocyte bone marrow infiltration. The remainingtwo patients were non-responsive. Our observationsconfirm the in vitro data showing that Imatinibtreatment is ineffective for SM characterized by ESTc-kit mutations, also if associated with hypereosinophilia.Funding: COFIN 2003, by FIRB 2001, by the Universityof Bologna (60% grants), by the Italian Associationfor Cancer Research (A. I. R. C. ), by the ItalianNational Research Council (C. N. R), and bygrants from the Campania Region, Fondazione delMonte di Bologna e Ravenna and A. I. L.CO-45THE ROLE OF CDK2-CDC25A-CDK2 AXIS IN THE RESISTANCETO STI571 (IMATINIB) OF CLONAL MYELOID PROGENITORSTRANSDUCING THE P210 BCR-ABL FUSION GENEMancini M, Pavan S, Saponaro M, Calabrò A,Brusa G, Santucci MAIstituto di Ematologia e Oncologia Medica "Lorenzoe Ariosto Seràgnoli", Università di Bologna, ItalyUnrestrained progression throughout cell cycle,mostly resulting from the abrogation of G1/S checkpoint,has a key role in the pathogenesis and progressionof Chronic Myeloid Leukemia (CML). It permits,in fact, the illegitimate enlargement of clonalhematopoiesis over its normal counterpart and causesthe genomic instability that drives further evolutiontowards the fully transformed phenotype ofblast crisis. It is conditional upon the constitutivetyrosine kinase of p210 bcr-abl fusion protein thatthrough interactions with a complex network,including signal transcription factors, adaptor proteins,cytoskeletal components and proteins involvedin the DNA repair process, continuously transducesthe mitogenic signal and deleteriously impacts thefidelity of replicated DNA. Accordigly, the tyrosinekinase inhibitor STI571 (Imatinib) is considered, sofar, the first-choice drug in the management of CML.In our previous studies we provided evidence for a ofa role of Cdk2 in bcr-abl-rearranged myeloid progenitorescape from STI571 effects on p210 tyrosinekinase (Mazzacurati et al. , The Hematology Journal5,168-177, 2004). The aim of our present study wasto investigate whether the Chk2-Cdc25A-axis, apathway alternative to p53 in the control of Cdk2activity, may drive CML progenitor clonal evolutiontowards STI571 unresponsiveness. In p210 bcr-abltransduced32D cell clones the resistance toSTI571was, indeed, associated with a significantenhnacement of Cdk2 phosphorylation and activityresulting, in turn, from Cdc25A overexpression, thatis expected to catalyze more efficiently the removalof Cdk2 phosphorylation at Thr14 and Tyr15, andWee1 downmodulation, that would preclude theCdk2 inhibitory phosphorylation at Tyr15.BothCdc25A overexpression and Wee1 downmodulationoccurred independently from p210 bcr-abl amplificationand proceeded from two autonomous pathwys:the dowmodulation and inactivation of Chk2(whose phosphoryaltion addresses Cdc25A towardsthe ubiquitin-dependent/proteasome-mediated degradation)and the upregulation of c-Myc (that is atranscriptional regulator of Cdc25A). In conclusion,our results suggest that Cdk2 may be considered asan additional target in the treatment of CML andChk2-Cdc25A levels as predictors of bcr-ablrearrangedmyeloid progenitor response to STI571.Funding: The study was supported by Università diBologna (ex60% and Progetti Pluriennali), CarisboFoundation, Forlì-CesenaAIL and CIB. GB is therecipient of a grant entitled to Mrs. Lalla Seràgnoli.CO-46SODIUM VALPROATE ENHANCES IMATINIB INDUCEDAPOPTOSIS AND GROWTH ARREST IN BCR-ABL CELL LINESMorotti A, Cilloni D, Pautasso M, Baraban D, MessaF, Arruga F, De Filippi I, Messa E, Carturan S,Rege-cambrin G, Pilatrino C, Guerrasio A,Gottardi E, Saglio GDept. of Clinical and Biological Sciences, Universityof Turin, Italyhaematologica vol. 89[suppl. n. 6]:september 2004