EVALUATION OF THE EFFICACY AND ANTITUMOR ACTIVITY OF THE PAN-CLASS I PHOSPHATIDYLINOSITOL 3-KINASE (PI3K) INHIBITOR NVP-BKM120 IN HUMAN T-CELL ACUTE LYMPHOBLASTIC LEUKEMIA (T-ALL)

Introduction. T-ALL is an aggressive malignancy and despite improvements in survival rates prognosis is still poor. A common aberrantly expressed pathway related to T-ALL and converging on anti-apoptotic and pro-survival signals activation is PI3K/Akt and its inhibition is an attractive strategy to improve current treatments. NVP-BKM120 is a highly selective pan-class I PI3K inhibitor which has shown antitumor activity in preclinical and clinical studies in solid cancers. Here we investigated its efficacy in T-ALL. Methods. A panel of T-ALL cell lines with up-regulated PI3K/Akt signaling and primary T-ALL blasts were treated with increasing concentrations of NVP-BKM120 and analyzed at different time points. Results. MTT assays documented a strong reduction of viability in all cell lines tested with a median IC50 lower than 2μM after 48 hours treatment that correlate with apoptosis as documented by Annexin V/PI analysis and activatation of caspases. To asses selective inhibition of PI3K, levels of the pathway components p-Akt(ser473) and p-S6RP(Ser235/236) have been evaluated by western blotting showing a strong decrease in a dose and time dependent manner. Efficacy of NVP-BKM120 was also tested in an ex-vivo model of primary blasts from T-ALL patients with assessed constitutive activation of PI3K/Akt pathway and results were consistent with in vitro studies. Comparison between NVP-BKM120 and PI3K selective inhibitors p110 isoforms provided its stronger effect in terms of viability and pathway inhibition. The drug was also able to synergize with dexamethasone and vincristine both in vitro and ex-vivo. To note, NVP-BKM120 extents pro-apoptotic effects also in Jurkat cells co-cultured with MS-5 stromal cells which mimic bone marrow microenvironment suggesting a potential overcome of its protective effect toward leukemic cells in vivo. Finally cell cycle has been analyzed by flow cytometry revealing a strong accumulation in the G2/M phase while immunofluorescent analysis identified an increased number of mitotic cells with disorganized mitotic spindle compared to control, suggesting an impairment in G2/M regulation and in mechanisms involved in cell cycle progression. Conclusion: NVPBKM120 showed viability reduction and apoptosis induction in T-ALL cells as well as in primary T-ALL blasts due to PI3K pathway inhibition supporting its clinical evaluation in T-ALL.