Anticancer effect of pan-PI3K inhibitor on multiple myeloma cells: Shedding new light on the mechanisms involved in BKM120 resistance.

The correlation between the Phosphoinositide 3-kinase (PI3K) axis and crucial mechanisms involved in the maintenance of the neoplastic nature of multiple myeloma (MM) has recently evolved a general agreement that PI3K inhibition-based therapies could construct an exciting perspective for the future treatment strategies. Our results outlined that abrogation of PI3K using pan-PI3K inhibitor BKM120 decreased survival of MM cells through induction of a caspase-3-dependent apoptosis coupled with SIRT1-mediated G2/M arrest in both KMM-1 and RPMI 8226 cell lines; however, the cell responses to the inhibitor was quite different, introducing wild-type PTEN-expressing RPMI 8226 as less sensitive cells. By investigating the sensitivity extent of a panel of hematological cell lines to BKM120, we found no significant association with respect to PTEN status. As far as we are aware, the results of the present study propose for the first time that the inhibitory effect of BKM120 was overshadowed, at least partially, through over-expression of either c-Myc or nuclear factor (NF)-κB in less sensitive MM cells. While there was no significant effect of the inhibitor on the expression of c-Myc in RPMI 8226, we found an enhanced cytotoxic effect when BKM120 was used in combination with a small molecule inhibitor of c-Myc. Noteworthy, the results of the synergistic experiments also revealed that BKM120 could produce a synergistic anti-cancer effect with carfilzomib (CFZ) and provided an enhanced therapeutic efficacy in MM cells, highlighting that PI3K inhibition might be a befitting approach in MM both in mono and combined therapy.