Abstract LB090: Targeting GCN2 kinase-driven stress response inactivation to restore immunity in AML Cancers (2022)

Abstract Introduction/Purpose: The most common leukemia in adults is Acute myeloid leukemia (AML) and the 5-year overall survival (OS) in all AML patients is approximately 24%. The highest of AML deaths in the US alone is among older patients at ages ≥ 65 emphasizing the need for better therapeutics. The older patients have more limited curative options available due to their inability to tolerate aggressive chemotherapy. Identifying ways to boost immunotherapy responses could change the paradigm of AML, a disease still difficult to treat despite several approved targeted immunotherapeutic. The development of effective small molecules would be significant since small molecules not only target immunosuppressive mechanisms like mAbs but can stimulate intracellular pathways where antibodies are unable to permeate. In addition, small molecules can provide optimal pharmacokinetics and pharmacodynamics for oral administration, amenable clinical dosing, and can induce relatively acute antitumor efficacy to avoid systemic immunogenicity, thus providing a superior therapeutic potential. The highly proliferative nature of tumor cells, along with infiltration of myeloid cells into the AML leads to depletion of nutrients such as functional/natural amino acids. A key meditator of this nutrient stress pathway, the cytoplasmic GCN2 (EIF2AK4) kinase, switches on reduction of amino acids, and this activity results in T-cell inactivation, T-cell death, regulatory T-cell expansion, and the potentiation of myeloid-derived suppressor cells (MDSCs). We have discovered a series of novel small molecule immunotherapeutic agents (HCI-1046) that reversibly bind to GCN2 kinase, competitively block the ATP site, and elicit responses in AML patient samples and cell lines. Experimental Procedures: GCN2 cell-free kinase binding, EIF2α family selectivity, pGCN2 inhibition assays were performed and confirmed its on-target efficacy and potency of lead inhibitor HCI-1046. Additional experiments were conducted including CellTiterGlo, IncuCyte Live Cell Imaging, FACS Flow Cytometry, Cytotoxicity, Western Blot, ELISpot, and ELISA assays. Results and Summary: GCN2 cell-free kinase binding, kinome selectivity, pGCN2, pEIF2α, ATF4 inhibition data confirmed on-target activities of our lead GCN2 inhibitor HCI-1046. HCI-1046 demonstrated potent activity, with an IC50 of 36 nM in inhibiting GCN2 kinase, and exhibited cellular efficacy with an IC50 of 0.1 to 0.5 μM range. Our preliminary results support the hypothesis that the inhibition of GCN2 reinstates anti-tumor immunity and blocks tumor progression in the AML cancer model in vivo. Our in vivo PK studies on HCI-1046 in rodent species showed excellent PK properties with 55% oral bioavailability, low clearance, and &amp;gt;5.0-hour half-life. Thus, HCI-1046 is nominated as a pre-clinical agent. Additional data regarding the evaluation of the effects of HCI-1046 on the MDSC-suppressive function on T-cells using ELISpot, ELISA assays in AML patient samples, and other mouse model efficacy studies results will be discussed. Citation Format: Zhaoliang Li, Kyle Medley, Dongqing Yan, Kimberly Coffman, Tony Pomicter, David Lum, David J. Bearss, Hariprasad Vankayalapati. Targeting GCN2 kinase-driven stress response inactivation to restore immunity in AML Cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB090.