(P 336) IMPROVEMENT OF PHOTODYNAMIC THERAPY IN SARCOMA: IN VITRO VALIDATION ON OSTEOSARCOMA AND MYXOFIBROSARCOMA

Objective: Sarcomas are a family of rare tumors that are generally treated with a combination of treatments, including chemotherapy, radiotherapy, and surgery. Despite the progress made in treatment in the last 20 years, chemoresistance, tumor recurrence, and metastatic progression are still a challenge. To improve patients’ outcomes, innovative therapeutic approaches that specifically target residual cancer cells and spare healthy tissue must be developed. Photodynamic therapy (PDT) is a promising therapy for the localized and specific treatment of different types of cancer. In PDT, light at an appropriate wavelength is used to activate a ROS-generating fluorescent drug, i.e., a photosensitizer (PS), that accumulates in cancer tissue.
The objective of this work is to test 6 PSs on 3D osteosarcoma (OS) and myxofibrosarcoma (MFS) models to select which one can selectively kill tumor cells.

Methods: To this purpose, a representative panel of 4 OS and 2 MFS cell lines, 2 cell lines of normal fibroblast (NIH-3T3) as healthy cell control have been selected. Cells were grown on 3D collagen-based scaffolds before 24 h treatment with one of six synthetic PSs that can be photoactivated in the Far-Red spectrum: 5-aminolevulinic acid (5-ALA), Toluidine Blue (TB), Methylene Blue (MB), Aluminium Phthalocyanine Chloride Tetrasulfonic Acid (AI-FTA), Chlorin e6 (Ce6) and PheophorbideA (PheoA) at a dose previously determined as the highest concentration, which caused less than 50% dark toxicity. At the end of treatment, cells have been photoactivated. Viability of irradiated and not irradiated cells (dark toxicity) was evaluated through the metabolic assay Presto Blue (Life-Technologies) cell PSs internalization was also analyzed.

Results: Photosensitizers were tested over their ability to exert a selective cytotoxic effect on sarcoma cells, i.e., reducing OS cells viability upon photoactivation, while sparing healthy cells.
Among the selected PSs, Ce6 showed a specific cytotoxic effect on all the OS cell lines, with cancer death after irradiation ranging from 50 to 85%, while fibroblasts were unaffected. None of the PSs analyzed selectively targeted MFS cells. The most effective one was PheoA, which reduced the MFS lines survival between 23% and 33% with no dark toxicity. No differences in PSs internalization were found when PheoA internalization was investigated in control and MFS 3D cultures.

Conclusion: Among the 6 PSs screened, we identified the Ce6 as a potential candidate for PDT treatment of OS, as it can selectively kill OS cells and spare normal cells. For the MFS cell, PheoA was the most effective PSs. These promising results require further analysis to be validated.