Preclinical evaluation of a novel SHIP1 phosphatase activator for inhibition of PI3K signaling in malignant B-cells.

Purpose. Phosphatidylinositol-3 kinase (PI3K) signaling is a common feature of B-cell neoplasms, including chronic lymphocytic leukemia (CLL) and diffuse large B-cell lymphoma (DLBCL), and PI3K inhibitors have been introduced into the clinic. However, there remains a clear need to develop new strategies to target PI3K signaling. PI3K activity is countered by Src homology domain 2-containing inositol-59-phosphatase1 (SHIP1) and, here, we have characterized the activity of a novel SHIP1 activator, AQX-435, in pre-clinical models of B-cell malignancies. Experimental design. In vitro activity of AQX-435 was evaluated using primary CLLcellsand DLBCL-derived cell lines. In vivo activity of AQX-435, alone or in combination with the BTK inhibitor ibrutinib, was assessed using DLBCL cell line and patient-derived xenograft models. Results. Pharmacological activation of SHIP1 using AQX-435 was sufficient to inhibit anti-IgM-induced PI3K-mediated signaling, including induction of AKT phosphorylation and MYC expression, without effects on upstream SYK phosphorylation. AQX-435 also co-operated with the BTK inhibitor ibrutinib to enhance inhibition of anti-IgM-induced AKT phosphorylation. AQX-435 induced caspase-dependent apoptosis of CLL cells preferentially as compared to normal B cells, and overcame in vitro survival promoting effects of microenvironmental stimuli. Finally, AQX-435 reduced AKT phosphorylation and growth of DLBCL in vivo,and co-operated with ibrutinib for tumor growth inhibition. Conclusions. Our results using AQX-435 demonstrate that SHIP1 activation may be an effective novel therapeutic strategy for treatment of B-cell neoplasms, alone or in combination with ibrutinib.