FLT3 overexpression

Our systematic alternative splicing analysis uncovered several subtype-specific splicing events and identifiednovel splice variants associated with pediatric ALL. A novel exon skipping alternative splicing event of the FLT3gene enabled us to provide the first validated evidence of FLT3 overexpression in iAMP21-positive B-ALL. Thisfinding may provide a rationale for using FLT3 overexpression as a novel biomarker and for applying FLT3inhibitors or FLT3 specific CAR T-cells in the clinical management of respective patients with high-risk iAMP21-positive B-ALL.

High expression of FLT3 in the TME was associated with immune cell infiltration (especially of NK cells and DCs), increased expression of T-cell exhaustion markers and expression of effector genes of the cGAS-STING pathway, which may consequently increase susceptibility to immunotherapy and radiotherapy. High FLT3 expression correlated with prolonged DFS in the LUSC and LUAD cohorts.

Our results suggest that specific ALL subgroups may also benefit from a deeper understanding of the biology of FLT3 alterations and their clinical implications.

High-resolution genome-wide evaluation not reliant on cell culture substantially expands the scope of detectable variants, for many of which determining the biologic and clinical implications will require larger scale prospective study. Importantly, application of OGM in the clinical setting is likely to result in clinically meaningful disease reclassification and restratification of risk, and in some cases may permit patients access to previously inaccessible targeted therapies (as in the instance of cytogenetically cryptic tyrosine kinase gene fusions).

Over-expression of FLT3 may influence the course of AML by promoting the proliferation of leukemia cells and inhibiting their apoptosis, which in turn may affect the prognosis of patients and serve as a negative prognostic factor for AML.

We tested CTS2016 as a single agent or in combination with either venetoclax, a Bcl-2 inhibitor, or azacitidine, a hypomethylating agent (HMA) and an epigenetic modulation drug, in a series of in vitro and in vivo studies using various AML models. CTS2016 resulted in a potent growth inhibitory effect with strong induction of cell death in a spectrum of AML cell lines carrying FLT3 mutations (FLT3-ITD and/or FLT3-TKD). CTS2016 orally administered once daily, demonstrated potent and dose-dependent antitumor responses in a variety of AML xenograft mouse models. These data demonstrate that CTS2016 could be a promising therapy for treating patients diagnosed with AML and MDS harboring FLT3 mutations and solid tumors such as NSCLC and TNBC with high-expression of AXL. More proof-of-concept data would come from the ongoing clinical trial.

We also observed potent in vivo inhibition of leukemia proliferation in xenograft models of both FLT3-mutant AML and KMT2A-rearranged ALL, including a post-tisagenlecleucel ALL-to-AML lineage switch patient-derived xenograft model pairing. We further demonstrate significant in vitro and in vivo activity of bispecific CD19xFLT3CART against KMT2A-rearranged ALL and posit that this additional approach might also diminish potential antigen escape in these high-risk leukemias. Our preclinical data credential FLT3CART as a highly effective immunotherapeutic strategy for both FLT3-mutant AML and KMT2A-R ALL that is poised for further investigation and clinical translation.

HM43239 inhibited FcγR-induced SYK and JAK/STAT5 activation in KG-1a (FLT3-WT) cells that upregulate RAS signaling which is a mechanism of acquired resistance to gilteritinib. Its ability to also inhibit SYK and, by reducing the activity of these upstream kinases, to also impair the activity of EKR1/2 and JAK/STAT5 that participate in rescue pathways, makes this a particularly interesting molecule with the potential of offsetting the development of resistance that is common with other FLT3 inhibitors. A Phase 1/2 trial of HM43239 in patients with AML is open and accruing patients (NCT03850574).

Furthermore, 2-ME + AA suppressed CML xenograft growth in mice. Collectively, 2-ME + AA promoted miR-223 expression and suppressed FLT3 and the PI3K/AKT pathway, thereby facilitating the apoptosis of CML cells and inhibiting CML xenograft growth in mice.

However, sensitivity to Erlotinib was correlated with high expression of PF4 and PPBP. In summary, FLT3, PF4, CD163, MRC1, CSF2RB, PPBP may be potential biomarkers and potential sensitive small-molecule drugs were correlated with overexpression of the biomarkers in AML.

No abstract available

In summary, we show that expression of immunotargets in pediatric AML differs from known expression profiles in adult AML. We identify CLEC12A/CD33 as preferential generic combinatorial immunotargets in pediatric AML and CD33/FLT3 as immunotargets specific for KMT2A mutated infant AML.