Abstract B60: Sitravatanib enhances immune checkpoint blockade in a de novo esophageal adenocarcinoma model
Authors: Sweeney Ryan W. , Fitzpatrick John T. , Omstead Ashten N. , Zheng Ping , Gorbunova Anastasia , Wagner Patrick L. , Kosovec Juliann E. , Jobe Blair A. , Kelly Ronan J. , Zaidi Ali H. 
Published: December 2022

Abstract
Background: Esophageal adenocarcinoma (EAC) is a leading cause of cancer-related mortality. Sitravatinib is a small molecule spectrum-selective tyrosine kinase inhibitor (TKI) that targets TAM receptors (AXL, MERTK and TYRO3), VEGF, PDGF, and c-Kit. Previously, dual inhibition of TAM and VEGF receptors has shown to successfully modulate the tumor immune microenvironment towards a less immunosuppressive state, by depletion of MDSCs and repolarization of TAMs towards a proinflammatory M1 phenotype. In clinical trials, TKIs have shown to improve patient outcomes, alone or in combination with immune checkpoint inhibitors, in multiple solid tumors. In the present study, the antitumor activity of sitravatinib alone and in combination with PD-1 blockade was investigated in a de novo EAC rat model. Methods: Ninety-six rats underwent an end-to-side esophagojejunostomy to induce gastroesophageal reflux, resulting in EAC carcinogenesis. At 32 weeks post-operatively, tumor bearing animals were randomized to a dose of 10mg/kg of sitravatanib (S) or vehicle control (VC), for a total of three 14 day cycles. A PD-1 inhibitor, AUNP-12 (IO), was administered at a dose of 3mg/kg or placebo, on day 12 of each cycle. At 38 weeks post-operatively animals were euthanized. Safety and efficacy was evaluated by on-treatment mortality, MRI, immunofluorescence and qRT PCR. Results: The S+/-IO groups demonstrated a higher mortality when compared to the control groups (p&lt;0.001). Pre- to post-treatment, mean MRI tumor volume decreased by 32% and 73% in the S-IO and S+IO and increased by 90% and 160% in the VC+IO and VC-IO, respectively (p&lt;0.001). Enhanced CD3+CD8+ T-cell densities were observed in the treatment groups when compared to the control groups (p&lt;0.001). Additionally, a higher CD86/CD206 ratio was observed in the S-IO and S+IO groups than in the control groups (p&lt;0.001), indicating a repolarization from M2 to M1 macrophage phenotype. Gene expression analysis of post treatment samples demonstrated upregulation of pro-inflammatory cytokines TNF-α, IFN-γ, IL-1β, IL-6, IL-12 and downregulation of anti-inflammatory cytokines including TGF-β, IL-4, IL-10, and IL-13 in the treated versus control animals (p&lt;0.05). Pre- to post-treatment qRT-PCR levels demonstrated significant inhibition of pathway genes, AXL, AKT, MERTK and PI3K, in the treated animals (p=&lt;0.001). Moreover, pre-treatment AXL levels were significantly higher in major responders (&gt;80% tumor reduction n=8) compared to the non-responders (&lt;25% tumor reduction/progression n=6), in the merged S +/- IO group (p=0.009). Lastly, increased apoptosis and decreased proliferation were confirmed through Cas-3 and Ki-67, respectively, in both treatment groups (p&lt;0.001). Conclusion: This study establishes a promising combination strategy using the multi-gene TKI sitravatinib to overcome PD-1/PD-L1 resistance and potentiate immune checkpoint inhibition in an EAC model.
Citation Format: Ryan W. Sweeney, John T. Fitzpatrick, Ashten N. Omstead, Ping Zheng, Anastasia Gorbunova, Patrick L. Wagner, Juliann E. Kosovec, Blair A. Jobe, Ronan J. Kelly, Ali H. Zaidi. Sitravatanib enhances immune checkpoint blockade in a de novo esophageal adenocarcinoma model [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy; 2022 Oct 21-24; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2022;10(12 Suppl):Abstract nr B60.