Abstract 1298: An allosteric SHP2 inhibitor RMC-4550 induces immunogenicity in pancreatic adenocarcinoma (PDA) and enhances the cytotoxicity of CD8+ effector T cells
Authors: Looney Agnieszka , Giri Uma , Zhu Yezi , Somma Alex , Holay Nisha , Soleimani Milad , Gandhi Heta , Capasso Anna , Kowalski Jeanne , Matsui William , Van Berg Carla , Eckhardt S Gail , Triplett Todd , Aung Kyaw Lwin 
Published: June 2022

Abstract
Background: Immunotherapy is ineffective in MSS PDA. Src homology-2 domain-containing protein tyrosine phosphatase (SHP2) mediates multiple immunosuppressive mechanisms in tumor cells and tumor microenvironment (TME). SHP2 plays an important role in oncogenic RAS signaling, the hallmark of PDA, that reduces tumor MHC-I expression and promotes immunotherapy resistance by stabilizing PD-L1. It modulates multiple T cell inhibitory pathways including PD-1 signaling via dephosphorylation of ITIM and ITSM. We hypothesize that SHP2i will increase anti-PDA immunity and help overcome resistance to PD-1 blockade when combined with gemcitabine, an active cytotoxic agent against PDA with pleiotropic immunomodulatory effects on its TME.
Methods: Mouse KPC-luc cells (derived from LSL-KrasG12D/+;LSL-Trp53R172H/+;Pdx-1-Cre GEMM) and human RAS mutant PDA cells were treated in vitro with various concentrations of RMC-4550, a potent and selective allosteric SHP2 inhibitor, to test its cytotoxicity using cell viability assay and measure tumor MHC-I and PD-L1 expression upon IFNy stimulation. Human PBMC were used for T cells in vitro experiments to examine the effect of RMC-4550 on T-cell proliferation inhibition by PD-1 ligand (PD-L1) stimulation. In vivo antitumor activity of RMC-4550 combined with αPD-1 or with αPD-1 and gemcitabine was investigated in a syngeneic KPC-luc subcutaneous model. After treatment, tumors and spleens were harvested, digested to single cell suspensions, and immune infiltrates quantified using flow cytometry.
Results: In vitro, there was no direct cytotoxicity of RMC-4550 on mouse KPC or human PDAC cells and no additive effect to gemcitabine. SHP2i increases IFNy mediated upregulation of MHC-I, and downregulates PD-L1 in both KPC mouse and MiaPaca-2 human PDA cells. In vitro, RMC-4550 reverses the PD-L1-mediated inhibition of T cell proliferation. In vivo, SHP2i with αPD-1 has a combinatorial effect on tumor growth inhibition. Gemcitabine seems to augment this effect. Preliminary data revealed no significant changes in number of immune cells in treatment groups when compared to the control group while an increase in proportion of Granzyme B+ CD8+ T cells and Ki-67+ CD8+ T cells in spleen and a decrease in proportion of PD1+ CD8+ T cells in TME was observed in RMC-4550 plus αPD-1 plus gemcitabine group compared to the control group.
Conclusion: SHP2i RMC-4550 and αPD-1 combination induces significant anti-tumor benefit in an in vivo PDA tumor model, an effect that is enhanced by adding gemcitabine. SHP2i may promote antitumor immunity in part by increasing MHC-I expression and reducing PD-L1 expression in RAS mutant PDA cells. PD-L1 mediated suppression of T cell proliferation was overcome by RMC-4550. In vivo, RMC-4550 may potentiate anti-PD-1 therapy by enhancing cytotoxicity of CD8+ effector T cells.
Citation Format: Agnieszka Looney, Uma Giri, Yezi Zhu, Alex Somma, Nisha Holay, Milad Soleimani, Heta Gandhi, Anna Capasso, Jeanne Kowalski, William Matsui, Carla Van Berg, S Gail Eckhardt, Todd Triplett, Kyaw Lwin Aung. An allosteric SHP2 inhibitor RMC-4550 induces immunogenicity in pancreatic adenocarcinoma (PDA) and enhances the cytotoxicity of CD8+ effector T cells [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 1298.