Control of distant tumors following local metronomic PDT

Abstract

Metronomic PDT (mPDT) obtains selective apoptosis of malignant tumor by delivering light at low intensity (<1.5mW/cm2) and extended period (a few days). As working with weak light, mPDT is expected as a novel therapy for malignant disease in deeply located organs by using implantable optical devices. However, few data indicated the effectiveness of mPDT.To investigate anti-cancer effects of mPDT, we used a mouse cancer model bearing two homologous intradermal tumors on their back. Following administration of photosensitizer, illuminating one tumor with an optical device resulted in significant growth suppression on both light-irradiated and non-irradiated tumors in one animal, and longer irradiation time induced stronger anti-tumor effects on both tumors. These results showed that mPDT leads to suppression of tumor growth in not onlylocal tumor but also distant disease, suggesting the activation of systemic anti-tumor immune response. This modality has a potential in the systemic treatment of advanced cancers.