HB023: A glutamine antagonist prodrug boosting antitumor lmmunity via PD-L1 suppression and mitochondrial membrane remodeling

Introduction Glutamine is a key nutrient that supports tumor cell metabolism, biosynthesis, and proliferation. It also shapes the tumor microenvironment and modulates cell death pathways. Glutamine antagonists have emerged as effective therapeutic agents by both disrupting tumor energy metabolism and enhancing antitumor immune responses. However, recent evidence reveals a paradoxical effect: glutamine deprivation can induce PD-L1 expression on tumor cells, facilitating immune escape and reducing the efficacy of immunotherapies. Objectives This study aims to overcome the immune evasion triggered by glutamine deprivation by developing a dual-functional therapeutic strategy that enhances metabolic stress while simultaneously inhibiting PD-L1 expression. The ultimate goal is to strengthen antitumor immunity and improve therapeutic outcomes. Methods We designed and synthesized a novel prodrug, HB023, by covalently linking a glutamine metabolism inhibitor with JQ1, a well-characterized PD-L1 inhibitor. We evaluated the effects of HB023 on tumor cell pyroptosis, energy metabolism, PD-L1 expression, T cell-mediated cytotoxicity, and macrophage polarization using a combination of in vitro cell-based assays and in vivo tumor models. Results HB023 significantly enhanced glutamine starvation in tumor cells, leading to increased pyroptosis and restricted energy supply. It effectively downregulated PD-L1 expression, which restored T cell cytotoxic activity. Additionally, HB023 induced mitochondrial membrane remodeling in macrophages, promoting M1 polarization and thereby enhancing innate immune responses. These mechanisms cooperatively activated both adaptive and innate antitumor immunity, thereby conferring HB023 with superior antitumor efficacy compared with JQ1, JHU083, or their combination. Conclusion HB023 successfully addresses the challenge of glutamine deprivation-induced immune escape by integrating metabolic inhibition with immune checkpoint blockade. This dual-modulatory approach reprograms the tumor immune microenvironment and improves immunotherapeutic efficacy, representing a promising strategy for advancing cancer treatment.