In vitro anti-echinococcal activity of octreotide: Additive effect of metformin linked to autophagy

Cystic echinococcosis (CE) is a worldwide zoonosis caused by the Echinococcus granulosus larval stage. The currently available therapy for this disease is based on benzimidazoles, which are rarely curative and cause several adverse effects. Therefore, new treatment options are needed. Octreotide (Oct) is a somatostatin analogue which exhibits anti-proliferative and anti-secretory effects over several cancer cell lines expressing somatostatin receptors. Here, we assessed the in vitro pharmacological effect of Oct against the E. granulosus larval stage. The drug caused a significant dose-dependent decrease in the viability of both protoscoleces and metacestodes. SEM and TEM analysis showed ultrastructural damage in both larval forms under drug treatment. Based on this, we investigated the possible presence of an Oct binding receptor in the parasite. The putative somatostatin/allatostatin-like receptor (Eg-s/ast) conserves the characteristic topology and signature sequences of the prototype somatostatin receptor common to vertebrates and is expressed in both metacestodes and protoscoleces. Moreover, Oct treated-parasites showed the presence of autophagic structures and a significant increase in transcriptional expression of autophagy key genes such as Eg-atg6, Eg-atg8, Eg-atg12 and Eg-atg16. In addition, by in toto immunolocalization assays, an increase in the punctate pattern and Eg-Atg8 protein expression was detected in Oct-treated metacestodes. Subsequently, the combination of Oct and Met had an additive effect on the viability of both larval forms. Our results provide additional evidence for the participation of PI3K/AKT/TOR/autophagy pathway in the Echinococcus survival and suggest the concomitant use of these drugs as potential therapeutic agents in treating of CE.