Abstract
Photoimmunotherapy (PIT) using the near-infrared-absorbing photosensitizing phthalocyanine dye, IRDye 700DX (IR-700), conjugated with a tumor-targeting antibody such as panitumumab (Pan) has shown efficacy in in vitro studies and several preclinical models in mice with promise for clinical translation. PIT results in rapid necrotic cell death in vitro and tumor shrinkage in vivo. Photochemical studies with the Pan-IR-700 conjugate showed that this agent can support generation of singlet oxygen and also generate reactive oxygen species after exposure to near-infrared (NIR) light. Moreover, in vitro studies using A431 cells, singlet oxygen scavengers abrogated the efficacy of PIT with Pan-IR-700, while oxygen depletion to undetectable levels in the exposure chamber almost completely inhibited the cellular cytotoxicity of PIT. Survival of tumor bearing mice was prolonged in PIT-treated animals but mice whose tumors were made transiently hypoxic prior to PIT had no benefit from the treatment. The results from this study support a central role for molecular oxygen-derived species in cell death caused by PIT.