Effect of photodynamic therapy using the natural photosensitiser parietin on superficial mouse tumours

MUGAS L, CALVO G, MARIONI J, CÉSPEDES M, SÁENZ D, DI VENOSA G, NUÑEZ MONTOYA S, CASAS A.

virtual

Congreso; Update PDT PDD 2020; 2020

Parietin (PTN: 1,8-dihydroxy-3-methoxy-6-methylanthraquinone), is an anthraquinone found in some plants and lichens. PTN probed to be a suitable photosensitizer with promising applications in bacterial photoinactivation [1]. In previous in vitro assays, we demonstrated that PTN is accumulated in the cytoplasm of tumour cells, induces cell death, and impairs cell migration when irradiated with blue light [2]. The objective of the present work was to evaluate in vivo the photoactivity of PTN in a subcutaneous tumour model and infer its potential use in Photodynamic Therapy (PDT) of cancer. PTN was isolated from the lichen Teoloschistes nodulifer (Nyl.) Hillman (Teloschistaceae), and its purity was determined by HPLC. BALB/c mice were subcutaneously inoculated with mammary adenocarcinoma cells (LM2), and after one week, we selected the animals that presented subcutaneous tumours with uniform size (less than 1 cm diameter). PDT-PTN consisted on topical application of a PTN solution in DMSO (46 mM) in the skin overlying the tumour, and after 3 h the mice were anaesthetized, and the tumours were irradiated with a blue light of 12.74 J/cm2 (Sica, 15 W). PDT-PTN was applied twice with an interval of one day between treatments. The penetration of PTN into the tumors was evaluated by fluorescence microscopy. After PDTPTN, tumour damage was evaluated by histological analysis of sections stained with hematoxylin-eosin, and the effect on tumour growth was analyzed by measuring the tumour with a caliper. The results showed that PTN penetrates the inner layers of the tumour (approximately 5 mm), and this correlates well with the histological damage observed in the tumors treated with PDT-PTN. In addition, the tumour growth was significantly decreased on the third and fourth day after starting the PDT-PTN treatment (p