FLT3-selective PROTAC: Enhanced safety and increased synergy with Venetoclax in FLT3-ITD mutated acute myeloid leukemia

Acute myeloid leukemia (AML) patients carrying Fms-like tyrosine kinase 3-internal tandem duplication (FLT3-ITD) mutations often face a poor prognosis. While some FLT3 inhibitors have been used clinically, challenges such as short efficacy and poor specificity persist. Proteolytic targeting chimera (PROTAC), with its lower ligand affinity requirement for target proteins, offers higher and rapid targeting capability. Gilteritinib, used as the ligand for the target protein, was connected with different E3 ligase ligands to synthesize several series of PROTAC targeting FLT3-ITD. Through screening and structural optimization, the optimal lead compound PROTAC Z29 showed better specificity than Gilteritinib. Z29 induced FLT3 degradation through the proteasome pathway and inhibited tumor growth in subcutaneous xenograft mice. We verified Z29's minimal impact on platelets in a patient-derived xenografts (PDX) model compared to Gilteritinib. The combination of Z29 and Venetoclax showed better anti-tumor effects, lower platelet toxicity, and lower hepatic toxicity in FLT3-ITD+ models. The FLT3-selective PROTAC can mitigate the platelet toxicity of small molecule inhibitors, ensuring safety and efficacy in monotherapy and combination therapy with Venetoclax. It is a promising strategy for FLT3-ITD+ patients, especially those with platelet deficiency or liver damage.