Mechanistic Insights into Proglumide’s Role in Immune Cell Efficacy and Response to Immune Checkpoint Inhibitor Therapy in Hepatocellular Carcinoma

Background: New strategies are needed to improve the response to immune checkpoint inhibitors for the treatment of hepatocellular carcinoma. Methods: Mice bearing HCC tumors were treated with PBS (control), a PD-1 antibody (PD-1Ab), proglumide, or the combination of proglumide and the PD-1Ab. The tumor microenvironment (TME) was evaluated histologically for fibrosis and by immunohistochemistry for immune cells. To investigate the mechanisms involved in T-cell efficiency, mouse spleen cells were isolated and examined for T-cell exhaustion markers and cytokine release. The mouse microbiome was analyzed using whole-genome sequencing before therapy and at the end of the study. Results: The combination of proglumide with a PD-1Ab decreased tumoral fibrosis better than monotherapy, and altered the immune cell signature in the TME by decreasing M2-polarized macrophages and increasing the influx of CD8+ T-cells. Proglumide monotherapy or in combination with the PD-1Ab decreased T-cell exhaustion markers and improved cytokine release. The combination therapy resulted in changes to the microbiome, including increased beneficial bacteria and genera known to enhance the efficacy of ICIs. Conclusions: Co-administration of proglumide with ICIs resulted in remodeling of the TME, changing a “cold” tumor to a “hot” immune-responsive tumor, activating T-cells, and altering the host microbiome to a population of bacteria that are beneficial.