Combination therapies to enhance efficacy of immune checkpoint inhibitors in hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) is a lethal disease with few treatment options. Immune checkpoint inhibitors (ICIs) emerge as promising therapeutic approach in multiple cancer types, including HCC. While ICIs improve the response rate of cancer patients significantly, a lot of the patients are still unresponsive to ICIs. This is mainly due to a compromised cancer immunity cycle, leading to insufficient anti-tumor immune responses. Two major reasons behind a failed cancer immunity cycle are [1] insufficient antigen presentation and [2] hypoxia-induced immunosuppressive tumor microenvironment (TME). Therefore, we explored different approaches targeting them to enhance ICIs efficacy: [1] induction of immunogenic cell death to enhance antigen presentation and [2] blocking the signaling of immunosuppressive metabolite in hypoxic TME. We first explored ferroptosis induction as a way to increase antigen availability and presentation to enhance ICIs. Ferroptosis is a form of immunogenic cell death (ICD) that elicit immune responses. We showed that HCC cells relied on ferroptosis suppressor protein 1 (FSP1) to protect themselves from ferroptosis. The induction of ferroptosis by targeting FSP1 genetically and pharmaceutically induce tumor cell death and suppressed HCC growth. More importantly, single cell RNA sequencing analysis showed that FSP1 inhibition promoted the recruitment of antigen presenting cells to tumor site and enhanced anti-tumor immune responses in HCC tumor. We demonstrated that FSP1 inhibitor worked synergistically with ICIs. We next investigated counteracting the immunosuppressive effect of hypoxia-induced adenosine accumulation in TME. We identified the dual role of hypoxia in establishing an immunosuppressive TME by promoting extracellular adenosine accumulation. Hypoxia suppressed adenosine kinase (ADK) while induced equilibrative nucleoside transporter 4 (ENT4). ADK inhibition led to intracellular accumulation of adenosine while ENT4 upregulation promoted the efflux of adenosine to the interstitial space, resulting in extracellular adenosine accumulation. We showed that manipulation of ADK and ENT4 augmented extracellular adenosine level and mediated immunosuppressive effects. Blockade of adenosine receptor antagonists significantly enhance efficacy of ICIs. Together, our studies revealed two potential therapeutic strategies to restore cancer immunity cycle and promote anti-tumor immune responses. They both work in synergy with ICIs, offering promising combination treatment options to enhance efficacy of ICIs.