La 17-AAG, un potente inibitore dell’Hsp90, induce effetti antiproliferativi e proapoptotici nella linea cellulare D22 di osteosarcoma canino.

Osteosarcoma (OSA) is an aggressive neoplasia and the most common primary bone tumor of children and dog, highlyresistant to chemotherapy. Recently, heat shock protein 90 (Hsp90), an ubiquitous molecular chaperone promoting theconformational maturation and stabilization of numerous client proteins, molecules which play important roles intumoral progression, has been recognized as a potential target for therapy in cancer. Hsp90 inhibition has been shownto promote increased degradation of client proteins such as mutant p53. The first class of Hsp90 inhibitors was basedon geldanamycin and its semi-synthetic derivates, such as 17-allylamino-17-demethoxygeldanamycin (17AAG),which has been successfully used in clinical trials against different human tumours.Canine OSA cell line D22 was treated with different concentrations of 17-AAG (0.025, 0.05, 0.1, 0.25, 0.5, 1 μM) andapoptosis was evaluated by immunofluorescence for active caspase 3 and flow cytometry. Ultrastructural analysis wasperformed after epoxy resin embedding.17-AAG treatment promoted strong induction of apoptosis in a time- and dose-dependent manner. Trasmissionelectron microscopy revealed in 17-AAG-treated cells an increased pleomorphism, lamellipodia modifications, surfacebubbles and blisters, cytoplasmic vacuolation, increased RER, mitochondrial degeneration, high number of ribosomesand lysosomes. Morphological signs of autophagy first appeared after 12 hrs at low doses of 17-AAG (0.025-0.05μM), while apoptosis and necrosis were positively correlated with time and dose. Noteworthy is the identification ofthe so-called mitophagy or mitochondrial autophagy (mitochondria-RER association, isolation membrane formation,autophagosomes).The present, in vitro data strongly suggest that Hsp90 inhibition may represent an useful target in the therapy ofosteosarcoma.[...]