Objective—To investigate activation of the mammalian target of rapamycin (mTOR) pathway and the antitumor effect of rapamycin in canine osteosarcoma cells.
Sample Population—3 established primary canine osteosarcoma cell lines generated from naturally developing tumors.
Procedures—Expression of total and phosphorylated mTOR and p70S6 kinase was assessed by use of western blot analysis in canine osteosarcoma cells with and without the addition of rapamycin. A clonogenic assay was performed to determine the surviving fraction of osteosarcoma cells at various concentrations of rapamycin.
Results—Total and phosphorylated mTOR and p70S6 kinase expression was evident in all 3 cell lines evaluated, which was indicative of activation of this pathway. Treatment with rapamycin resulted in a time-dependent decrease in phosphorylated mTOR expression and a lack of detectable phosphorylated p70S6 kinase. No detectable change in expression of total mTOR and total p70S6 kinase was identified after rapamycin treatment. The clonogenic assay revealed a significant dose-dependent decrease in the surviving fraction for all 3 cell lines when treated with rapamycin.
Conclusions and Clinical Relevance—These data indicated that mTOR and its downstream product are present and active in canine osteosarcoma cells. The pathway can be inhibited by rapamycin, and treatment of cells with rapamycin decreased the surviving tumor cell fraction. These data support the molecular basis for further investigation into the use of mTOR inhibitors as an antineoplastic approach for dogs with osteosarcoma.
Objective—To investigate the activation of the AKT and mammalian target of rapamycin (mTOR) pathways and assess the inhibitory effects of rapamycin on those pathways in canine malignant melanoma cells.
Sample Population—3 established primary canine melanoma cell lines generated from naturally occurring tumors.
Procedures—Expressions of total and phosphorylated AKT, mTOR, and p70 ribosomal S6 kinase 1 (p70S6K) in canine melanoma cells that were or were not exposed to 10nM rapamycin were assessed via western blot analysis. Clonogenic assays were performed to determine the surviving fraction of melanoma cells after exposure to 0.1, 1, 10, or 100nM rapamycin.
Results—Expressions of total and phosphorylated AKT, mTOR, and p70S6K proteins were detected (ie, the AKT and mTOR pathways were activated) in all 3 cell lines. Rapamycin treatment resulted in decreases in phosphorylated mTOR expression and phosphorylated p70S6K expression but no change in phosphorylated AKT expression. Expression of total AKT, mTOR, and p70S6K persisted after rapamycin treatment. There was a significant dose-dependent decrease in surviving tumor cell fraction for each cell line following treatment with rapamycin.
Conclusions and Clinical Relevance—These data indicated that AKT and mTOR, as well as their downstream product p70S6K, are present and active in canine melanoma cells. Activation of the mTOR pathway can be inhibited by rapamycin; treatment of melanoma cells with rapamycin decreased the surviving tumor cell fraction. Use of mTOR inhibitors as antineoplastic treatments in dogs with melanoma warrants investigation. Furthermore, these data support the use of canine melanoma cells as a molecular model for melanoma in humans.