Immediate in vivo target-specific cancer cell death after near infrared photoimmunotherapy

Background: Near infrared (NIR) photoimmunotherapy (PIT) is a new type of cancer treatment based on a monoclonal antibody (mAb)-NIR phthalocyanine dye, (IR700) conjugate. In vitro cancer-specific cell death occurs during NIR light exposure in cells previously incubated with mAb-IR700 conjugates. However, documenting rapid cell death in vivo is more difficult. Methods: A luciferase-transfected breast cancer cell (epidermal growth factor receptor+, MDA-MB-468luc cells) was produced and used for both in vitro and in vivo experiments for monitoring the cell killing effect of PIT. After validation of cytotoxicity with NIR exposure up to 8 J/cm(2) in vitro, we employed an orthotopic breast cancer model of bilateral MDA-MB-468luc tumors in female athymic mice, which subsequently received a panitumumab-IR700 conjugate in vivo. One side was used as a control, while the other was treated with NIR light of dose ranging from 50 to 150 J/cm(2). Bioluminescence imaging (BLI) was performed before and after PIT. Results: Dose-dependent cell killing and regrowth was successfully monitored by the BLI signal in vitro. Although tumor sizes were unchanged, BLI signals decreased by > 95% immediately after PIT in vivo when light intensity was high (> 100 J/cm(2)), however, in mice receiving lower intensity NIR (50 J/cm(2)), tumors recurred with gradually increasing BLI signal. Conclusion: PIT induced massive cell death of targeted tumor cells immediately after exposure of NIR light that was demonstrated with BLI in vivo.