Carrier-Free Immunotherapeutic Nano-Booster with Dual Synergistic Effects Based on Glutaminase Inhibition Combined with Photodynamic Therapy

The immunotherapeutic effect elicited by photodynamic therapy (PDT) is attenuated by tumor defense mechanisms associated with glutamine metabolism, including the metabolic regulation of redox homeostasis and the limitation of the immunosuppressive tumor microenvironment (ITM). Herein, a carrier-free immunotherapeutic nanobooster C9SN with dual synergistic effects was constructed by the self-assembly of glutaminase (GLS) inhibitor compound 968 (C968) and photosensitizer Chlorin e6. C968-mediated GSH deprivation through inhibiting glutamine metabolism prevented PDT-generated reactive oxygen species from being annihilated by GSH, amplifying intracellular oxidative stress, which caused severe cell death and also enhanced the immunogenic cell death (ICD) effect. In addition, genome-wide analysis was carried out using RNA-sequencing to evaluate the changes in cell transcriptome induced by amplifying oxidative stress. Thereafter, neoantigens generated by the enhanced ICD effect promoted the maturation of dendritic cells, thereby recruiting and activating cytotoxic T lymphocytes (CTLs). Meanwhile, C9SN remodeled the ITM by blocking glutamine metabolism to polarize M2-type tumor-associated macrophages (TAMs) into M1-type TAMs, which further recruited and activated the CTLs. Ultimately, this immunotherapeutic nanobooster suppressed primary and distant tumors. This "kill two birds with one stone" strategy would shed light on enhancing tumor immunogenicity and alleviating tumor immunosuppression to improve the immunotherapeutic effect of PDT.