Tumor-selective near-infrared photodynamic therapy with novel indocyanine green-loaded nanocarrier delays paralysis in rats with spinal metastasis

SummaryBackgroundAlthough recent advances in surgery have improved the quality of life of patients with spinal metastasis, local recurrence is still relatively common. Therefore, there is an urgent need for new surgical treatment options for metastatic spinal cancer. We previously described a novel nanocarrier loaded with indocyanine green (ICG), ICG-lactosome which exhibits tumor selectivity and is a potential near-infrared (NIR) fluorescence imaging agent for the diagnosis of spinal metastasis. The purpose of this study was to investigate the therapeutic effects of tumor-selective photodynamic therapy (PDT) with ICG-lactosome and NIR light irradiation in a rat model of spinal metastasis.MethodsTwenty-one Fischer 344 rats each with a single spinal metastasis in the L6 vertebral body were divided into 3 treatment groups: PDT with a low-concentration ICG-lactosome injection (6 rats), PDT with high-concentration ICG-lactosome injection (7 rats), and a group without ICG-lactosome injection (8 rats). All the animals received local NIR light irradiation with a total energy of 5 J (0.5 W for 10 s).ResultsBoth the PDT groups injected with ICG-lactosome showed delayed deterioration of hind-limb paralysis compared with the group without ICG-lactosome.ConclusionThis modified PDT procedure could be an effective local treatment for spinal metastasis.