PO-154 Gene expression profile in tumour cells exposed in vitro to photodynamic therapy with a novel porphyrinic compound

Introduction Photodynamic therapy (PDT) has emerged as efficient and reasonably safe targeted therapeutic strategy in solid tumours. Briefly, a non-toxic photosensitizer is injected and then is activated at tumor-site only by exposure to tissue-penetrating red light. Cytotoxic singlet oxygen is formed, hence triggering massive death of tumour cells. Material and methods A new porphyrinic compound (P2.2), previously described by us (Boscencu 2017) in Molecules 22.11:1815), was used as photosensitizer in U-87 MG human glioblastoma cells and HT-29 human colon carcinoma cells. A good concentration-dependent uptake of the fluorescent P2.2 compound by the investigated cells was demonstrated by flow cytometry. Cells loaded with 10 µM P2.2 were subjected to in vitro PDT using the MODULIGHT 6600 equipment at fluences of 5 to 10 J/cm 2 . For mechanistic studies, cells were investigated at 3–6 hours post-PDT regarding viability, morphology and gene expression. The gene expression profile was assessed by pathway-focused PCR array (Stress and Toxicity Pathway Finder, QIAGEN), addressing 84 genes critically involved in oxidative, osmotic, hypoxic and inflammatory stress, in cell death by apoptosis, necrosis and autophagy, in DNA damage and heat shock proteins/unfolded protein response. Results and discussions Viability tests indicated that cell death arise within 6 hours post-PDT, but massive cell death occurs more than 48 hours post-PDT. The singlet oxygen burst triggered an early activation of some protective mechanisms against oxidative stress (full signature of the cytoprotective NRF2), hypoxia (SERPINE1) and osmotic stress (HSPA4L). Apoptosis (TNFα mediated), necrosis, autophagy and DNA damage (DDIT3) responses were highlighted. Interestingly, a complex inflammatory network was triggered by PDT (CXCL8, TNF, IL1), possibly associated to oxidative stress through NF-kB. These protective responses could be responsible for the delayed massive death of cells subjected to PDT. Conclusion In response to PDT, glioblastoma and colon carcinoma cells developed in vitro various protective mechanisms against a complex web of stressors. Genes overexpressed in response to PDT might be candidates for co-therapies aiming to increase PDT efficacity. It seems reasonable that inhibition of endogenous NRF2-mediated antioxidant mechanisms could be an option for improving oxidative stress-mediated PDT. Acknowledgement Work was supported by the M-ERA.NET Grant 52/2016 (NANOTHER)