Photodynamic Therapy with Indocyanine Green Injection and Near-Infrared Light Irradiation Has Phototoxic Effects and Delays Paralysis in Spinal Metastasis

Abstract

The purpose of this study was to investigate the phototoxic effects of photodynamic therapy (PDT) with indocyanine green (ICG) and near-infrared light irradiation on rat mammary adenocarcinoma cells, and its therapeutic efficacy in a rat model of spinal metastasis. Although PDT has been successfully used as a non-radiation treatment for many malignancies, it has not yet been clinically applied for treating spinal metastasis. For the phototoxicity study, CRL-1666 cells were treated with PDT and cell viability was measured by WST-1 assay. For the efficacy study, 26 female Fischer 344 rats with spinal metastasis in the L6 vertebra were divided into three treatment groups: PDT with local injection of ICG (9 rats), PDT with systemic injection of ICG (10 rats), and no treatment or control (7 rats). Both the PDT groups received near-infrared light irradiation with a total energy of 10 J (1 W for 10 sec). The light was delivered directly through a single silica probe which was set on the left side of the L6 vertebral body. Hindlimb motor function was monitored according to the Basso-Beattie-Bresnahan (BBB) scale. Further, the observation periods were calculated to determine the survival time. The PDT exerted immediate and persistent phototoxic effects. Furthermore, the PDT with local injection of ICG as well as systemic injection of ICG delayed the deterioration of paralysis and prolonged the observation period. PDT with ICG injection and near-infrared light irradiation could be an effective local adjuvant treatment for spinal metastasis.