Annihilation of metastatic 4T1 breast tumor micrometastases by vascular targeted photodynamic therapy with immunomodulation

Background: The combination of therapeutic modalities constitutes a promising avenue for controlling primary tumor growth and eradicating metastases. Vascular-targeted photodynamic therapy (VTP) with WST11 is a localized ablation approach relying upon rapid, free radical-mediated destruction of the tumor vasculature that self-propagates into the tumor core. WST11 was recently approved by the European community for prostate cancer treatment. VTP with a metronomic regimen of Gemzar (GEM), an approved immune suppressor cell-attenuating agent, and anti-PD-L1, an immune checkpoint inhibitor, was hypothesized to improve primary tumor control and anti-tumor immunity.

Methods:4T1-Luc mouse mammary pad tumors were subjected to WST11-VTP, alongside intraperitoneal GEM and anti-PD-L1 treatment. Metastases were identified by luciferin bioluminescence. Single-cell RNA sequencing of splenocytes and peripheral blood mononuclear cells was performed using the 10X Genomics.

Results:GEM monotherapy induced tumor growth retardation but no primary tumor or metastasis cure. Anti-PD-L1-treated mice showed rapid and fatal hypersensitivity reactions shortly after the last injection.WST11-VTP alone led to primary tumor ablation in 70% of treated mice, but only 20% were disease-free 90 days post-treatment. WST11-VTP with metronomic GEM, yielded complete cure in 40% of the animals. WST11-VTP combined with GEM and anti-PD-L1 resulted in complete cure in 62% of the treated animals; no signs of hypersensitivity reactions were noted. Single-cell 10X Genomics indicated an increase in CD8, CD4 T cells, B cells, and natural killer cells, alongside a dramatic decrease in granulocyte cell counts intreated animals.

Conclusion: Concomitant WST11-VTP, metronomic Gemzar and anti PD-L1 therapy enables control of disseminated disease through evolution of antitumor immunity, without eliciting immune-related adverse events.