Photodynamique therapy relieves tumor vascular anergy and promotes immune cell trafficking in an orthotopic mouse model of malignant pleural mesothelioma

Objective

Malignant pleural mesothelioma (MPM) is a deadly disease with limited treatment options. Recently, dual immune checkpoint inhibition therapy (ICI) showed improved patient survival. However, only a fraction of patients were responsive to immunotherapy. One potential mechanism of MPM resistance to ICIs could be their endothelial anergy that hampers leukocyte trafficking to the tumor bulk. Here, we hypothesized that vascular-targeted low dose photodynamic therapy (L-PDT), treatment of MPM could relieve tumor endothelial anergy and improve immunotherapy efficacy.

Methods

Using an orthotopic syngeneic MPM murine model (AB12 cells injected in the pleura of BALB/c mice), we determined the impact of L-PDT on the endothelial expression of E-Selectin, a key molecule involved in leukocyte diapedesis by immunohistochemistry. Furthermore, to confirm the role of E-selectin, we determined the extravasation of effector T cells (CD8+/CD4+) by immunostaining in L-PDT treated tumors in the presence or absence of an E-selectin blocking antibody. Finally, we assessed tumor growth/survival of our MPM murine model treated with L-PDT alone or combined to ICIs.

Results

L-PDT pre-treatment enhanced MPM endothelial E-Selectin expression in vivo. The latter was associated with increased CD4+ and CD8+ lymphocyte infiltration of MPM following L-PDT which did not occur after E-Selectin blockade. Also, L-PDT pre-treatment of MPM influenced favorably tumor control, mouse survival and the impact of ICIs compared to controls.

Conclusion

L-PDT pre-treatment relieves endothelial anergy in MPM which improves antitumor immunity and response to ICI. This approach could constitute a promising pre-treatment option, in combination with ICIs, for the management of this deadly disease.

Intrapleural hyperthermic chemotherapy induces pro-immunogenic e-selectin expression in the vasculature of malignant pleural mesothelioma

Objective

Malignant pleural mesothelioma (MPM) is a deadly disease with dismal prognosis. Prior studies combining surgery with intrapleural hyperthermic chemotherapy (IPHC) have shown improved survivals in selected patients with MPM. However, the mechanisms by which IPHC acts on MPM and its microenvironment remains unknown. Here we focus on tumor endothelial adhesion molecule expression patterns.

Methods

First, we determined the impact of IPHC on MPM tumor and vascular compartments in vitro using a novel bioincubater for hyperthermic cell culture. The cytotoxicity of normo (37 °C) / hyperthermic (42 °C for 60 minutes) cisplatin/carboplatin therapies were evaluated on four MPM (MSTO211H, H-Meso, AE17 and AB12) and one endothelial (EC-RF24) cell lines at a minimum of 24 hours using a presto-blue assay. Second, we treated endothelial cells with IPHC (60 min, 42 °C at optimized cytotoxic concentrations) and determined its impact on pro-immunogenic adhesion molecule (E-selectin, VE-cadherin, VCAM and Connexin-43) expression at 24 hours by Western blot.

Results

Tumor and endothelial cell viability decreased with increasing doses of both chemotherapeutics but was not affected by hyperthermia (IC50 with or without hyperthermia of each cell line at 24 hours reported in Figure 1A). Interestingly, endothelial cell line IC50 was much higher than that of MPM tumor cells for both chemotherapeutics (Figure 1A). Pro-immunogenic adhesion molecule E-Selectin was increased at 24 hours by IPHC with both chemotherapeutics while VE-Cadherin, VCAM and Connexin-43 were not affected (Figure 1B).

Conclusion

Hyperthermia adds no cytotoxicity to intrapleural chemotherapy. However, IPHC favors pro-immunogenic endothelial E-selectin expression. The latter could help induce patient immunity against their MPM and improve survival. Confirmation of these findings in vivo is mandatory.