Purpose: The aim of this study was to explore the tumor growth response of the combination photochemical internalization and external-beam radiotherapy. Photochemical internalization is a technology to improve the utilization of therapeutic macromolecules in cancer therapy by photochemical release of endocytosed macromolecules into the cytosol.
Methods and materials: A human sarcoma xenograft TAX-1 was inoculated subcutaneously into nude mice. The photosensitizer AlPcS(2a) and bleomycin were intraperitoneally administrated 48 h and 30 min, respectively, before diode laser light exposure at 670 nm (20 J/cm(2)). Thirty minutes or 7 days after photochemical treatment, the animals were subjected to 4 Gy of ionizing radiation.
Results: Using photochemical internalization of bleomycin as an adjunct to ionizing radiation increased the time to progression for the tumors from 17 to 33 days as compared with that observed with photodynamic therapy combined with ionizing radiation as well as for radiochemotherapy with bleomycin. The side effects observed when photochemical internalization of bleomycin was given shortly before ionizing radiation were eliminated by separating the treatment modalities in time.
Conclusion: Photochemical internalization of bleomycin combined with ionizing radiation increased the time to progression and showed minimal toxicity and may therefore reduce the total radiation dose necessary to obtain local tumor control while avoiding long-term sequelae from radiotherapy.