Advances and Challenges in Quizartinib-Based FLT3 Inhibition for Acute Myeloid Leukemia: Mechanisms of Resistance and Prospective Combination Therapies.

FLT3 mutations are among the most common genetic alterations in acute myeloid leukemia (AML) and are associated with poor prognosis. Significant advancements have been made in developing FLT3 inhibitors (FLT3Is), such as quizartinib, which have improved treatment outcomes in both newly diagnosed and relapsed/refractory AML. Resistance to FLT3Is remains a major clinical challenge, driven by diverse mechanisms including FLT3 point mutations, cellular escape pathways, and the influence of the bone marrow microenvironment. Sustained STAT5 phosphorylation, AXL upregulation, and CXCR4 signaling have been identified as key factors in FLT3I resistance. Additionally, metabolic adaptations have been shown to support the survival of FLT3I-resistant cells. Ongoing clinical trials are investigating various combination regimens, including quizartinib with chemotherapy, Bcl-2 inhibitors, hypomethylating agents, and immune-modulatory drugs, with promising preliminary results. The European LeukemiaNet 2022 guidelines recommend incorporating FLT3Is into treatment regimens; however, questions remain regarding the best timing for the administration of each FLT3I. Additional studies are required to determine the optimal FLT3I-based combinations, reduce resistance emergence, and improve outcomes. This review highlights the current state of FLT3I therapy, ongoing challenges with resistance, and future directions in optimizing treatment for FLT3-mutated AML, focusing on quizartinib.