Breast cancer is known to cause metastatic lesions in the bone, which can lead to skeletal-related events. Currently,
radiation therapy and surgery are the treatment of choice, but the success rate varies and additional adjuncts are desirable.
Photodynamic therapy (
PDT) has been applied successfully as a non-radiative treatment for numerous
cancers. Earlier work has shown that the athymic rat model is suitable to investigate the effect of
PDT on bone
metastasis and
benzoporphyrin-derivative monoacid ring A (
BPD-MA;
verteporfin) has been shown to be a selective
photosensitizer. The aim of this study was to define the therapeutic window of
photosensitizer with regard to
drug and light dose. Human
breast carcinoma cells (MT-1)-stable transfected with the
luciferase gene-were injected intra-cardiacally into athymic rats. At 14 days, the largest vertebral lesion by bioluminescence imaging was targeted for single treatment
PDT. A
drug escalating-de-escalating scheme was used (starting
drug dose and light energy of 0.2 mg/kg and 50 J, respectively). Outcomes included 48 h post-treatment bioluminescence of remaining viable tumour, histomorphometric assessment of tumour burden, and neurologic evaluation. The region of effect by bioluminescence and histology increased with increasing
drug dose and light energy. A safe and effective
drug-light dose combination in this model appears to be 0.5 mg/kg
BPD-MA and applied light energy of less than 50 J for the thoracic spine and 1.0 mg/kg and 75 J for the lumbar spine. For translation to clinical use, it is an advantage that
BPD-MA (
verteporfin), a second-generation
photosensitizer, is already approved to treat
age-related macular degeneration. Overall,
PDT represents an exciting potential new minimally-invasive local, safe and effective
therapy in the management of patients with spinal
metastases.