Near-infrared Theranostic Photoimmunotherapy (PIT): Repeated Exposure of Light Enhances the Effect of Immunoconjugate

Armed antibody-based targeted molecular therapies offer the possibility of effective tumor control with a minimum of side effects. Photoimmunotherapy (PIT) employs a monoclonal antibody-photo-toxic phthalocyanine dye, IR700 conjugate, that is activated by focal near-infrared (NIR) light irradiation after antibody binding to the targeted tumor cell surface leading to rapid necrotic cell death. Therapy by single NIR light irradiation was effective without significant side effects; however, recurrences were seen in most treated mice probably because of inhomogeneous distribution of panitumumab-IR700 immunoconjugate in the tumor, leading to ineffective PIT. We describe here an optimized regimen of effective PIT method for the same HER1-overexpressing tumor model (A431) with fractionated administration of panitumumab-IR700 conjugate followed by systematic repeated NIR light irradiation to the tumor based on timing of antibody redistribution into the remnant tumor under the guidance of IR700 fluorescence signal. Eighty percent of the A431 tumors were eradicated with repeated PIT without apparent side effects and survived tumor-free for more than 120 days even after stopping therapy at day 30. Therapeutic effects were monitored using IR700 fluorescent signal. PIT is a promising highly selective and clinically feasible theranostic method for treatment of mAb-binding tumors with minimal off-target effects.