Abstract 2419: A multimodel preclinical platform to evaluate photodynamic therapy as a strategy to reduce local recurrence in myxofibrosarcoma and osteosarcoma
Authors: Spadazzi Chiara , Pannella Micaela , Bellotti Chiara , Martella Elisa , Vanni Silvia , De Vita Alessandro , Liverani Chiara , Miserocchi Giacomo , Cocchi Claudia , Calabrese Chiara , Fausti Valentina , Casadei Roberto , Pieri Federica , Guerrieri Ania Naila , Martinelli Giovanni , Varchi Greta , Lucarelli Enrico , Mercatali Laura , Ibrahim Toni 
Published: April 2023

Sarcomas are heterogeneous and rare malignant tumors that develop from connective tissues. Myxofibrosarcoma (MFS) and Osteosarcoma (OS) are the main representative subtypes of Soft tissues and Bone sarcomas. Conventional treatment consists of surgical resection and neo/adjuvant chemotherapy. However, a challenging clinical feature is a high local recurrence rate, calling for the development of novel strategies to eradicate MFS and OS. Fluorescence-guided surgery (FGS), coupled with photodynamic therapy (PDT), enables to detect and eradicate malignant tissues using a light-sensitive photosensitizer (PS). These compounds could be retained by neoplastic cells to a greater extent than by healthy tissue. Thus, when photoactivated, they lead to cancer cell death, minimizing normal tissues toxicity.

The project aims to provide a preclinical proof of concept of FGS and PDT for MFS and OS, allowing us to pave the way for a more effective treatment strategy.

A multimodel preclinical platform of MFS and OS comprising 2D, 3D-collagen based scaffold was developed. A MFS stabilized cell line (IM-MFS-1) and four OS cell lines (Saos-2, U-2 OS, MG-63, 143B) were used. NIH-3T3 fibroblast cell line was used as healthy counterpart. We tested a panel of synthetic PSs: Toluidine Blue, 5-Aminolevulinic Acid hydrochloride (ALA), Methylene Blue, Chlorin e6 (Ce6), Pheophorbide a (Pba) and Al(III) Phthalocyanine Chloride Tetrasulfonic Acid (AlPcS4) that can be photoactivated with light in the 630-660 nm wavelengths’ range. The PSs were ranked on (a) selective uptake by tumor cells, respect to healthy cells and (b) the cytotoxic effect, after photoactivation. PSs cell uptake was evaluated by Countess II FL automated cell counter. Cytotoxicity was evaluated by WST-1 and Presto Blue assays.

For each PS we determined the highest concentration, causing less than 50% dark toxicity in IM-MFS-1, OS cell lines and fibroblast NIH-3T3, seeded in 2D and 3D collagen-based models. Then, we evaluated the cell viability upon light irradiation (λ=630 or 660 nm; 10 mW/cm^2, 5 min). For all PSs, dark toxicity was very low. However, only Ce6 was effectively uptaken by tumor cells (% uptake &gt; 60%) and not by NIH-3T3 cells (% uptake = 27%). Moreover, upon photoactivation, Ce6 induced significantly higher cell death in cancer cells as compared to NIH-3T3 cells, e.g. 1-3% cell viability in tumor cells and 76% cell viability in NIH-3T3.

Results from our multimodel platform highlight PDT as a powerful strategy for the treatment of MFS and OS. Among the screened PSs, Ce6 is the most promising, showing a remarkable selectivity in tumor cells uptake and cytotoxicity. To increase the clinical significance of our approach, we will confirm its efficacy in patient-derived primary cultures; xenograft zebrafish in vivo embryos will be used to evaluate how PDT affects the disease aggressiveness and metastatic potential.

Citation Format: Chiara Spadazzi, Micaela Pannella, Chiara Bellotti, Elisa Martella, Silvia Vanni, Alessandro De Vita, Chiara Liverani, Giacomo Miserocchi, Claudia Cocchi, Chiara Calabrese, Valentina Fausti, Roberto Casadei, Federica Pieri, Ania Naila Guerrieri, Giovanni Martinelli, Greta Varchi, Enrico Lucarelli, Laura Mercatali, Toni Ibrahim. A multimodel preclinical platform to evaluate photodynamic therapy as a strategy to reduce local recurrence in myxofibrosarcoma and osteosarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2419.