Preclinical development of tuspetinib for the treatment of acute myeloid leukemia.

Tuspetinib (TUS) is a well-tolerated, once daily, oral kinase inhibitor in clinical development for treatment of AML. Nonclinical studies show that TUS targets key pro-survival kinases with IC50 values in the low nM range, including SYK, wildtype and mutant forms of FLT3, mutant but not wildtype forms of KIT, RSK2 and TAK1-TAB1 kinases, and indirectly suppresses expression of MCL1. Oral TUS markedly extended survival in subcutaneously and orthotopically inoculated xenograft models of FLT3 mutant human AML, was well tolerated, and delivered enhanced activity when combined with venetoclax or 5-azacytidine. In vitro, TUS demonstrated potent killing of AML lines (GI50 = 1.3 to 5.2 nM) and Ba/F3 cells expressing wildtype (GI50 = 9.1 nM) or various mutant forms of FLT3 (GI50 = 2.5 - 56 nM). In AML lines, the multi-kinase targeting capacity of TUS suppressed phosphorylation of SYK, FLT3, STAT5, MEK, ERK, AKT, mTOR, 4E-BP1 and S6K kinases. Cells selected for stable acquired resistance to TUS exhibited increased BAX and hypersensitivity to venetoclax (1900-fold), navitoclax and MCL1 inhibitors. MV-4-11 FLT3-ITD clones expressing NRASG12D revealed that high-level expression of NRASG12D generated modest resistance to TUS and greater resistance to venetoclax (VEN), yet the TUS/VEN combination exhibited synergy in NRASG12D AML model. Favorable preclinical safety and pharmacology properties, the efficacy of the TUS/VEN combination in a murine model, and the synthetic lethal vulnerability to VEN that accompanies TUS resistance provide the basis for exploration of the TUS/VEN combination in patients with relapsed or refractory AML.