PIK3CA promotes hepatic tumor growth through evasion of phagocyte-mediated anti-tumor immunity

Abstract

Both primary and metastatic liver cancers are highly lethal diseases, for which effective treatment options remain limited. The unique hepatic microenvironment provides a niche that enables tumor cells to evade immune surveillance. To identify factors that mediate tumor growth within this immune microenvironment, we performed an in vivo RNAi screen to identify genes whose knockdown reduces liver tumor burden. We performed an in vivo RNAi screen by transplanting CT26 tumor cells into the liver of immunocompetent mice via hemi-spleen injection, aiming to compare gene essentiality in the liver versus in vitro cultured cells. The top hit depleted in vivo, Pik3ca , was validated in multiple syngeneic tumor models. Liver specificity of PIK3CA function was confirmed using an intracardiac injection model. To assess the contribution of T cells and phagocytes to tumor control, we employed TCR knockout mice and clodronate-mediated phagocyte depletion, respectively. Tumor progression and immune cell infiltration were analyzed via bioluminescence imaging and immunohistochemistry. Finally, the therapeutic efficacy of the PIK3CA inhibitor Alpelisib was evaluated in the hemi-spleen injection models of CT26 and Hepa1-6. Loss of Pik3ca in CT26 and Hepa1-6 cells markedly impaired tumor growth in the liver but not in subcutaneous sites or other organs, indicating a liver-specific dependency. Mechanistically, insulin and insulin-like growth factors—both enriched in the liver—activate their respective receptors to stimulate PIK3CA/AKT/mTOR signaling, thereby promoting tumor progression. Phagocyte depletion abrogated the anti-tumor effects of Pik3ca loss, whereas T cell deficiency had no impact, highlighting a phagocyte-mediated mechanism. Moreover, Pik3ca loss promoted F4/80 + macrophage infiltration into tumors. Treatment with the PIK3CA inhibitor Alpelisib recapitulated both the tumor suppression and the enhanced F4/80 + macrophage infiltration phenotypes observed in genetic models, confirming the therapeutic relevance of PIK3CA inhibition for treating hepatic malignancies. We identify PIK3CA as a key regulator of tumor-phagocyte interplay in the liver. Genetic or pharmacological targeting of PIK3CA suppresses liver tumor growth not through a direct, cancer cell-autonomous effect, but rather by activating phagocyte-mediated anti-tumor responses. These findings suggest that therapeutic strategies combining PI3K inhibition with immune modulation may be effective for treating liver malignancies driven by PI3K overactivation.