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 acute myeloid leukemia (AML). Nonclinical studies show that TUS targets key prosurvival kinases with IC50 values in the low nmol/L range, including SYK, wild-type (WT) and mutant forms of FLT3, mutant but not WT 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 (VEN) or 5-azacytidine. In vitro, TUS demonstrated potent killing of AML lines [concentration needed to reduce the growth of treated cells to half that of untreated cells (GI50) = 1.3–5.2 nmol/L] and Ba/F3 cells expressing WT (GI50 = 9.1 nmol/L) or various mutant forms of FLT3 (GI50 = 2.5–56 nmol/L). In AML lines, the multikinase 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 VEN (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 VEN, yet the TUS/VEN combination exhibited synergy in the 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.

This article reports preclinical development of TUS, an oral kinase inhibitor currently in clinical development for treatment of AML. The article covers the studies of TUS activities on cellular targets and the nonclinical studies that supported the advancement of TUS to a phase I/II trial of TUS/VEN in refractory AML and a phase I/II trial of TUS/VEN/5-azacytidine in newly diagnosed patients with AML (NCT03850574).