Evaluation of the mammalian target of rapamycin pathway and the effect of rapamycin on target expression and cellular proliferation in osteosarcoma cells from dogs.
OBJECTIVE
To investigate activation of the mammalian target of rapamycin (mTOR) pathway and the antitumor effect of rapamycin in canine osteosarcoma cells.


METHODS
3 established primary canine osteosarcoma cell lines generated from naturally developing tumors.


METHODS
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
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.
Gordon
Ira K
IK
Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Ye
Fang
F
Kent
Michael S
MS
D000818:Animals; D000970:Antineoplastic Agents / Q000627:therapeutic use; D002455:Cell Division / Q000187:drug effects; D004283:Dog Diseases / Q000188:drug therapy / Q000378:metabolism*; D004285:Dogs; D007166:Immunosuppressive Agents / Q000627:therapeutic use; D012516:Osteosarcoma / Q000188:drug therapy / Q000473:pathology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism; D020123:Sirolimus / Q000627:therapeutic use*; D058570:TOR Serine-Threonine Kinases
D000970:Antineoplastic Agents; D007166:Immunosuppressive Agents; D010750:Phosphoproteins; D011494:Protein Kinases; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus