Photodynamic Priming Improves the Anti-Migratory Activity of Prostaglandin E Receptor 4 Antagonist in Cancer Cells In Vitro

SIMPLE SUMMARY: Photodynamic priming is an emerging strategy that leverages subtherapeutic photochemistry for therapeutic benefits, often used as part of combination regimens. Our study aimed to couple photodynamically priming with antagonism of the prostaglandin E receptor 4, a therapeutic target linked to cancer-associated migration, invasion, angiogenesis, and immune evasion. Photodynamic priming and antagonism of the prostaglandin E receptor 4 independently attenuated OVCAR-5 ovarian cancer cell migration in a gap closure model, though their combination induced the most significant reductions. More potent combination effects were revealed when invasiveness was characterized using a transwell invasion model with CAOV3 ovarian cancer cells. Immunoblotting identified the epithelial growth factor receptor, cAMP-response element binding protein, and extracellular signal-regulated kinase 1/2 as potential mediators of these combinational effects. This work provides new evidence of a novel and clinically relevant combination strategy to address metastatic behavior, a major challenge in the treatment of cancer. ABSTRACT: The combination of photodynamic agents and biological inhibitors is rapidly gaining attention for its promise and approval in treating advanced cancer. The activity of photodynamic treatment is mainly governed by the formation of reactive oxygen species upon light activation of photosensitizers. Exposure to reactive oxygen species above a threshold dose can induce cellular damage and cancer cell death, while the surviving cancer cells are “photodynamically primed”, or sensitized, to respond better to other drugs and biological treatments. Here, we report a new combination regimen of photodynamic priming (PDP) and prostaglandin E(2) receptor 4 (EP4) inhibition that reduces the migration and invasion of two human ovarian cancer cell lines (OVCAR-5 and CAOV3) in vitro. PDP is achieved by red light activation of the FDA-approved photosensitizer, benzoporphyrin derivative (BPD), or a chemical conjugate composed of the BPD linked to cetuximab, an anti-epithelial growth factor receptor (EGFR) antibody. Immunoblotting data identify co-inhibition of EGFR, cAMP-response element binding protein (CREB), and extracellular signal-regulated kinase 1/2 (ERK1/2) as key in the signaling cascades modulated by the combination of EGFR-targeted PDP and EP4 inhibition. This study provides valuable insights into the development of a molecular-targeted photochemical strategy to improve the anti-metastatic effects of EP4 receptor antagonists.