Therapeutic and drug resistance mechanisms of quizartinib and omacetaxine mepasuccinate (QUIZOM) in FLT3-ITD acute myeloid leukemia

Abstract

FLT3-ITD is one of the most common genetic mutations in acute myeloid leukemia (AML) and is associated with inferior prognosis. Despite the approval of various FLT3 inhibitors by the FDA, clinical responses have not been seen at a high rate and are often transient, with a high relapse risk unless timely hematopoietic stem cell transplantation (HSCT) is arranged. Therefore, there is an unmet need for novel therapeutics with superior efficacy and tolerability.

In this study, we comprehensively examined the vulnerabilities of FLT3-ITD AML cell lines and identified translational pathways as being more critical for their survival. Based on this finding, we proposed and examined a novel combination therapy with Quizartinib and Omacetaxine Mepesuccinate (QUIZOM) in FLT3-ITD AML. QUIZOM demonstrated strong anti-leukemic effect in both in-vitro studies of FLT3-ITD AML cell lines and in-vivo studies of xenotransplantation model. Transcriptome analysis revealed the disruption of HSP70 chaperone family and the proteostasis network, which was corroborated by increased protein aggregates formation in vitro. In the follow-up study, a previously undescribed axis of HSP70 inhibition leading to protein aggregates, ROS production, DNA damage, and apoptosis was identified, accompanied by cGAS-STING activation and heightened inflammatory response.

The clinical efficacy of QUIZOM was investigated in a phase 2 open-labeled single-arm clinical trial containing 35 relapse or refractory (R/R) and 5 newly diagnosed FLT3-ITD AML patients. QUIZOM treatment led to a high composite remission rate of 82.5% and a median overall survival of 12.9 months (range 1.8-69.2 months). Single cell RNA sequencing was conducted on serial samples collected from clinical trial. In addition to the regulation of AML cell-intrinsic pathways, a pattern of immune activation was also observed. Further analysis consolidated this finding by revealing increased activity of the transcription factors T-bet and EOMES, an expansion of terminally differentiated effector memory CD8-T cells, and a reduction in exhausted CD8-T cells in responders after QUIZOM treatment. Additionally, we identified a sub-population of FLT3-ITD mutated HSC-MPP cells that exhibited high leukemic stem cell signatures and negatively correlated with treatment response, characterized by high JUN expression. Simultaneous inhibition of c-Jun re-sensitized the resistant populations to QUIZOM in primary AML samples.

In conclusion, QUIZOM demonstrated a promising anti-leukemic effect in FLT3-ITD AML by targeting the proteostasis network, which induced both AML-intrinsic apoptosis pathway and activation of immune compartments.