Melanoma progression is reduced by the ciliated protozoan toxin climacostol: results from in vitro and in vivo studies

Melanoma progression is reduced by the ciliated protozoan toxin climacostol: results from in vitro and in vivo studies Authorship: Federico Buonanno1, Cristiana Perrotta2, Laura Guerra3, Simona Picchietti3, Anna Maria Fausto3, Enrico Marcantoni4, Simone Giorgi4, Claudio Ortenzi1, Davide Cervia2,3 1Laboratory of Protistology and Biology Education, University of Macerata, 62100 Macerata, Italy 2 Department of Biomedical and Clinical Sciences “Luigi Sacco” (DIBIC), Università di Milano, via G.B. Grassi 74, 20157 Milano, Italy 3 Department for Innovation in Biological, Agro-food and Forest systems (DIBAF), Università della Tuscia, via S. Camillo de Lellis snc, 01100 Viterbo, Italy 4School of Sciences and Technologies, Section of Chemistry, University of Camerino, 62032 Camerino, Macerata, Italy Text: Melanoma diagnoses have risen sharply over past decades, and despite new lines of therapy have been introduced the need for additional drugs is urgent. Previous findings from our group demonstrated that climacostol, an alkyl resorcinol produced by the ciliated protozoan Climacostomum virens, decreases the viability of five different mammalian cancer cell lines, while it was devoid of effects on endothelial cells. In order to expand these data and due to the availability of the synthetic toxin, we have further analysed different tumoral and non-tumoral cell lines, observing that viability of human and rodent tumoral cells was negatively affected by climacostol with higher potency when compared to non-tumoral cells. We then focused on the B16-F10 mouse melanoma cells, where climacostol caused a concentration-dependent reduction of viability with an EC50 of 6.3 μg/ml, and an Emax of 30 μg/ml. Flow cytometry analyses indicated that cell proliferation was effectively inhibited by climacostol, with a significant increase of apoptotic cells.The data collected prompted us to investigate the effects of climacostol on in vivo melanoma progression using a B16-F10 allograft transplantation tumor model. The results indicate that climacostol decreased tumour weight and increased the content of apoptotic cells, suggesting that the toxin may be considered for the design of cytotoxic and pro-apoptotic new drugs for melanoma therapy.