Sitravatinib combined with PD-1 blockade enhances cytotoxic T-cell infiltration by M2 to M1 tumor macrophage repolarization in esophageal adenocarcinoma

Esophageal adenocarcinoma (EAC) is a leading cause of cancer-related mortality. Sitravatinib is a novel multi-gene tyrosine kinase inhibitor (TKI) that targets tumor-associated macrophage (TAM) receptors, VEGF, PDGF and c-Kit. Currently, sitravatinib is actively being studied in clinical trials across solid tumors and other TKIs have shown efficacy in combination with immune checkpoint inhibitors (ICI) in cancer models. In this study, we investigated the anti-tumor activity of sitravatinib alone and in combination with PD-1 blockade in an EAC rat model. Treatment response was evaluated by mortality, pre- and post-treatment MRI, gene expression, immunofluorescence and immunohistochemistry. Our results demonstrated adequate safety and significant tumor shrinkage in animals treated with sitravatinib, and more profoundly, sitravatinib and PD-1 inhibitor, AUNP-12 (P < 0.01). Suppression of TAM receptors resulted in increased gene expression of pro-inflammatory cytokines and decreased expression of anti-inflammatory cytokines, enhanced infiltration of CD8+ T cells, and M2 to M1 macrophage phenotype repolarization in the tumor microenvironment of treated animals (P < 0.01). Moreover, endpoint immunohistochemistry staining corroborated the anti-tumor activity by downregulation of Ki67 and upregulation of Caspase-3 in the treated animals. Additionally, pretreatment gene expression of TAM receptors and PD-L1 were significantly higher in major responders compared with the non-responders, in animals that received sitravatinib and AUNP-12 (P < 0.02), confirming that TAM suppression enhances the efficacy of PD-1 blockade. In conclusion, this study proposes a promising immunomodulatory strategy using a multi-gene TKI to overcome developed resistance to an ICI in EAC, establishing rationale for future clinical development.