S-116836

The FIP1-like-1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRα) fusion oncogene is the driver factor in a subset of patients with hypereosinophilic syndrome (HES)/chronic eosinophilic leukemia (CEL). Most FIP1L1-PDGFRα-positive patients respond well to the tyrosine kinase inhibitor (TKI) imatinib. Resistance to imatinib in HES/CEL has been described mainly due to the T674I mutation in FIP1L1-PDGFRα, which is homologous to the imatinib-resistant T315I mutation in BCR-ABL. Development of novel TKIs is imperative to overcome resistance to imatinib. We synthesized S116836, a novel TKI. In this study, we evaluated the antitumor activity of S116836 in FIP1L1-PDGFRα-expressing cells. The results showed that S116836 potently inhibited PDGFRα and its downstream signaling molecules such as STAT3, AKT, and Erk1/2. S116836 effectively inhibited the growth of the WT and T674I FIP1L1-PDGFRα-expressing neoplastic cells in vitro and in nude mouse xenografts. Moreover, S116836 induced intrinsic pathway of apoptosis as well as the death receptor pathway, coincided with up-regulation of the proapoptotic BH3-only protein Bim-EL through the Erk1/2 pathway. In conclusion, S116836 is active against WT and T674I FIP1L1-PDGFRα-expressing cells, and may be a prospective agent for the treatment of HES/CEL.

Limited treatment options are available for chronic myelogenous leukemia (CML) patients who develop imatinib mesylate (IM) resistance. Here we proposed a novel combination regimen, a co-administration of S116836, a novel small molecule multi-targeted tyrosine kinase inhibitor that was synthesized by rational design, and histone deacetylases inhibitor (HDACi) suberoylanilide hydroxamic acid (SAHA), to overcome IM resistance in CML. S116836 at low concentrations used in the present study mildly downregulates auto-tyrosine phosphorylation of Bcr-Abl. SAHA, an FDA-approved HDACi drug, at 1 μM has modest anti-tumor activity in treating CML. However, we found a synergistic interaction between SAHA and S116836 in Bcr-Abl-positive CML cells that were sensitive or resistant to IM. Exposure of KBM5 and KBM5-T315I cells to minimal or non-toxic concentrations of SAHA and S116836 synergistically reduced cell viability and induced cell death. Co-treatment with SAHA and S116838 repressed the expressions of anti-apoptosis proteins, such as Mcl-1 and XIAP, but promoted Bim expression and mitochondrial damage. Of importance, treatment with both drugs significantly reduced cell viability of primary human CML cells, as compared with either agent alone. Taken together, our findings suggest that SAHA exerts synergistically with S116836 at a non-toxic concentration to promote apoptosis in the CML, including those resistant to imatinib or dasatinib.