Abstract 100: Novel selective PI3Kγ inhibitor AZD3458 promotes anti-tumor immune responses and reverts resistance to immunotherapy in checkpoint blockade refractory preclinical models

The PI3Kγ isoform is a key regulator of immune cell proliferation, survival, migration and activation. PI3Kγ inhibitors have the potential to treat a variety of diseases including respiratory, inflammatory, metabolic disorders and cancer. In the context of cancer PI3Kγ inhibition re-polarizes macrophages to an immuno-stimulatory phenotype activating a T-cell mediated tumor immune response. Selective PI3Kγ inhibitors have potential as monotherapy and in combination with checkpoint inhibition to overcome resistance and to enhance efficacy of checkpoint inhibitors. AZD3458 is a highly selective PI3Kγ clinical candidate kinase inhibitor with a cellular IC50 of 8nM with a 100-fold selectivity over PI3Kδ. In vitro, AZD3458 inhibits pAKTS308/S473 in human macrophages and mouse CD11b activation at 32nM and 30nM free IC50, respectively. At these concentrations AZD3458 reverses macrophage polarization increasing IL12/IL-10 ratio and does not impact T cell proliferation and function analysed by gene expression profiling, cytokine quantification and flow cytometry. Oral administration of AZD3458 (20mg/Kg BID) remodeled the tumor microenvironment in 4T1 orthotopic breast tumor model. AZD3458 decreased tumor associated macrophages by 20% compared to vehicle and reduced overall protein expression of immunosuppressive markers CD206 and PD-L1 measured by flow cytometry. In addition, AZD3458 reduced MDSC/neutrophil activation and promoted cytotoxic T-cell activation in vivo, measured by GzmB and Perforin mRNA and protein expression. Consistent to the observed tumor remodeling, combination with checkpoint inhibitors α-PD-1 or α-PD-L1 antibodies (10mg/kg 3x week) had greater anti-tumor effects than checkpoint inhibitor alone in 4T1, LLC, CT-26 and MC-38 mouse syngeneic models. These data demonstrate that AZD3458 can reverse myeloid suppressive tumor microenvironment and revert tumor resistance to immunotherapy in myeloid-enriched immunosuppressive tumor types. Citation Format: Larissa S. Carnevalli, Danielle Carrol, Michele Moschetta, Pablo Morentin Gutierrez, Cristina Gardelli, Molly A. Taylor, Antonio Montoya, Adina Hughes, Matthew King, Teresa Klinowska, Simon T. Barry. Novel selective PI3Kγ inhibitor AZD3458 promotes anti-tumor immune responses and reverts resistance to immunotherapy in checkpoint blockade refractory preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 100.