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

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

Congreso; Photodynamic Therapy & Photodiagnosis Update 2020 E-congress; 2020

Committee of the Conference Photodynamic Therapy and Photodiagnosis ? Update 2020

and lichens. PTN probed to be a suitable photosensitizer with promising applications in bacterialphotoinactivation [1]. In previous in vitro assays, we demonstrated that PTN is accumulated in the cytoplasmof tumour cells, induces cell death, and impairs cell migration when irradiated with blue light [2]. Theobjective of the present work was to evaluate in vivo the photoactivity of PTN in a subcutaneous tumourmodel 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 wasdetermined 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) inthe skin overlying the tumour, and after 3 h the mice were anaesthetized, and the tumours were irradiated witha blue light of 12.74 J/cm2 (Sica, 15 W). PDT-PTN was applied twice with an interval of one day betweentreatments. 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, andthe 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 thiscorrelates well with the histological damage observed in the tumors treated with PDT-PTN. In addition, thetumour growth was significantly decreased on the third and fourth day after starting the PDT-PTN treatment(p<0.05 control vs PDT-PTN, two-way ANOVA, followed by Sidak´s multiple comparisons test).Therefore, the results of this work encourage the potential use of this anthraquinone as a photosensitizer usingvisible light supporting the recommendations of the World Health Organization to revalue phytomedicine andconsider the healing properties of the country´s flora. We project further studies on the use of PDT-PTN onskin superficial conditions as actinic keratosis or basal cell carcinomas.