P659: BUPARLISIB A PROMISING THERAPEUTIC APPROACH IN CHRONIC MYELOID LEUKEMIA RESISTANT TO IMATINIB

Background: Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of the BCR-ABL oncoprotein, which has deregulated tyrosine kinase activity. Despite a high response rate to tyrosine kinase inhibitors, such as imatinib (IMA), some patients develop resistance to treatment. Several mechanisms are involved in IMA resistance and alternative signaling pathways are activated by the BCR-ABL oncoprotein, including the PI3K/AKT/mTOR pathway, increasing cell survival and resistance to apoptosis. Thus, the identification of new therapeutic targets that enable new alternatives to the treatment of CML-resistant patients is extremely important. Aims: Thus, this work aimed to evaluate the therapeutic potential of Buparlisib (BKM 120), a PI3K inhibitor, in in vitro models of CML sensitive and resistant to IMA. Methods: The study was carried out in an IMA-sensitive CML cell line, K-562 cells, and two IMA-resistant cell lines, the K-562 RC and K-562 RD cells. Cell lines were incubated in the absence and presence of Buparlisib in a single dose and in a daily fractionated administration. Additionally, the combined effect of PI3K inhibitor with Imatinib was also evaluated in the three models. The metabolic activity was evaluated by the resazurin assay. Cell death was evaluated by flow cytometry (FC) using annexin V and 7-AAD staining and by cell morphology using light microscopy (Giemsa staining). The cell cycle was analyzed by FC using propidium iodide (PI)/RNase. The results were statistically analyzed and were considered significant when p<0.05. Results: The results showed that BKM-120 (Buparlisib) reduced metabolic activity in a time- and dose-dependent manner, with IC50 after 72h of 1.1μM in K-562 cells, 1.2μM in K-562 RC cells, and 1.0μM in K-562 RD cells. Fractionated administration of BKM-120 was shown to be beneficial compared to a single administration, but only in resistant lines. The combination of BKM-120 and IMA induced a synergistic effect in all three cell lines but was more pronounced in the resistant models. BKM-120 induced a cytotoxic effect through the activation of apoptosis and showed a cytostatic effect by blocking the cell cycle in the G2/M phase. Apoptotic cell death was confirmed by morphological analysis, with the observation of bleebling and cellular contraction in cells after BKM-120 exposure. Summary/Conclusion In conclusion, our results suggest that buparlisib could be a new therapeutic strategy in the treatment of CML, with the most promising results in the case of resistance to IMA. Keywords: PI3K, Targeted therapy, Chronic myeloid leukemia, Drug resistance