In Vitro And In Vivo Anti-Leukemic Effects Of Cladoloside C-2 Are Mediated By Activation Of Fas/Ceramide Synthase 6/P38 Kinase/C-Jun Nh2-Terminal Kinase/Caspase-8

We previously demonstrated that the quinovose-containing hexaoside stichoposide C (STC) is a more potent anti-leukemic agent than the glucose-containing stichoposide D (STD), and that these substances have different molecular mechanisms of action. In the present study, we investigated the novel marine triterpene glycoside cladoloside C-2 from Cladolabes schmeltzii, which has the same carbohydrate moiety as STC. We assessed whether cladoloside C-2 could induce apoptosis in K562 and HL-60 cells. We also evaluated whether it showed antitumor action in mouse leukemia xenograft models, and its molecular mechanisms of action. We investigated the molecular mechanism behind cladoloside C-2-induced apoptosis of human leukemia cells, and examined the antitumor effect of cladoloside C-2 in a HL-60 and K562 leukemia xenograft model.Cladoloside C-2 dose-and time-dependently induced apoptosis in the analyzed cells, and led to the activation of Fas/ceramide synthase 6 (CerS6)/p38 kinase/JNK/caspase-8. This cladoloside C-2-induced apoptosis was partially blocked by specific inhibition by Fas, CerS6, and p38 siRNA transfection, and by specific inhibition of JNK by SP600125 or dominant negative-JNK transfection. Cladoloside C-2 exerted antitumor activity through the activation of Fas/CerS6/p38 kinase/JNK/caspase-8 without showing any toxicity in xenograft mouse models. The antitumor effect of cladoloside C-2 was reversed in CerS6 shRNA-silenced xenograft models. Our results suggest that cladoloside C-2 has in vitro and in vivo anti-leukemic effects due to the activation of Fas/CerS6/p38 kinase/JNK/caspase-8 in lipid rafts. These findings support the therapeutic relevance of cladoloside C-2 in the treatment of human leukemia.