The dissemination of tumor metastasis in the peritoneal cavity, also called peritoneal metastasis (PM) or carcinomatosis, represents a late stage of gastrointestinal and gynecological cancer with very poor prognosis, even when cytoreductive surgery is effective, due to residual microscopic disease. Photodynamic therapy (PDT) in the management of peritoneal metastasis has been clinically limited by the low tumor selectivity of photosensitizers (PS) and important adverse effects. Here, we propose extracellular nanovesicles (EVs) derived from mesenchymal stem/stromal cells (MSCs) as the fourth generation of immune active PS vectors that are able to target peritoneal metastasis with superior selectivity, potentiate PDT cytotoxicity at the tumor site without affecting healthy tissues, modulate the tumor microenvironment of immunocompetent colorectal and ovarian carcinomatosis models, and promote an antitumor immune response. A pioneering strategy was developed for high yield, large-scale production of MSC-EVs encapsulating the drug meta(tetrahydroxyphenyl)chlorin (mTHPC) (EVs-mTHPC) that is compatible with requirements of clinical translation and also preserves the topology and integrity of naturally produced EVs. Intraperitoneal injection of EVs-mTHPC showed an impressive enhancement of tumoral selectivity in comparison to the free drug and to the liposomal formulation Foslip (mean ratio of PS in tumors/organs of 40 for EVs-mTHPC versus 1.5 for the free PS and 5.5 for Foslip). PDT mediated by EVs-mTHPC permitted an important tumoral necrosis (55% of necrotic tumoral nodules versus 18% for Foslip (p < 0.0001)) and promoted antitumor immune cell infiltration, mainly proinflammatory M1-like CD80+ and CD8+ T cell effector. Intratumor proliferation was significantly decreased after PDT with EVs-mTHPC. Overall EVs vectorization of mTHPC afforded important tumoral selectivity while overcoming the PDT toxicity of the free drug and prolonged mice survival in the colorectal carcinomatosis model. MSC-EVs produced by our scalable manufacturing method appears like the clinically relevant fourth-generation PDT vehicle to overcome current limitations of PDT in the treatment of peritoneal metastasis and promote a hot tumor immune environment in PM.
Keywords: antitumor immune response; carcinomatosis; extracellular vesicles; liposome; metastasis; photodynamic therapy; vectorization.