Hyperthermic potentiation of photodynamic therapy employing Photofrin I and II: comparison of results using three animal tumor models

Hyperthermia induced by a microwave source (2,450 MHz) was used alone and in combination with photodynamic therapy (PDT) to treat the SMT-F, EMT-6, and RIF animal tumors in vivo. PDT was administered using either Photofrin I or II as the photosensitizer and an argon-pumped tunable dye laser (630 nm) as the light source. Greater than additive increases in long-term tumor control were achieved when hyperthermia was given immediately post-PDT in the SMT-F and RIF tumor systems. Only additive (or independent) increases in tumor control were achieved when hyperthermia was given immediately before PDT in all these tumor systems and when heat was applied post-PDT using the EMT-6 tumor. In a series of experiments using the SMT-F tumor, it was observed that decreases in PDT drug or light doses could be offset (in terms of tumor control) by the addition of a subsequent heat treatment. This result, along with others presented, indicates the clinical potential of PDT and hyperthermia as adjuvant cancer modalities.