Inhibition of Glutamine Metabolism Suppresses Tumor Progression through Remodeling of the Macrophage Immune Microenvironment

BackgroundTargeting glutamine metabolism has emerged as a promising strategy in cancer therapy. However, several barriers, such as in vivo anti-tumor efficacy, drug toxicity, and safety, remain to be overcome to achieve clinical utility. Prior preclinical in vivo studies had generated encouraging data showing promises of cancer metabolism targeting drugs, although most were performed on immune-deficient murine models. It is being recognized that aside from tumor cells, normal cells such as immune cells in the tumor microenvironment may also utilize glutamine for maintaining physiological functions. To provide an in-depth view of glutamine antagonist (GLNi) treatment on the tumor immune microenvironment, the current study made several unique approaches. MethodFirst, to evaluate GLNi treatment modality that potentially involves immune cells, the study was performed on immunocompetent murine models of gynecological cancers. Second, to enhance safety and reduce potential off-target effects, we developed a GLNi prodrug, JHU083, which is bio-activated restrictively in cancer tissues. Third, to unbiasedly decode the response of single cells in the tumor microenvironment to GLNi treatment, single-cell RNA sequencing (scRNA-seq) was performed on cells prepared from tumors of the JHU083 or vehicle control-treated mice. ResultsIn both immunocompetent murine tumor models, we observed a significant anti-tumor efficacy, resulting in reduced tumor burden and impeded tumor progression. Similarly, in both tumor models, scRNA-seq revealed significantly impeded immunosuppressive M2-like macrophages by JHU083, while the treatment spared pro-inflammatory M1-like tumor macrophages. In many tumor microenvironment (TME) cells, JHU083 downregulated genes regulated by Myc and hypoxia. M2 macrophages greater sensitivity to glutamine antagonism when compared to M1 macrophages or monocytes was further validated on ex vivo cultures of bone marrow-derived macrophages. ConclusionOur findings support a converged mechanism of glutamine metabolism antagonists. JHU083 exerted its anti-tumor efficacy through not only direct targeting of glutamine-addicted cancer cells but also by suppressing glutamine-dependent M2 macrophages, leading to a shift in the M1/M2 macrophage landscape in favor of an immune-stimulatory microenvironment.