Effects of a combined treatment with mTOR inhibitor RAD001 and tamoxifen in vitro on growth and apoptosis of human cancer cells.
OBJECTIVE
Interactions between estrogen receptor signaling and the PI3K/Akt pathway are present in estrogen-dependent cancer cells. Therapeutical inhibition of each of these pathways has been proven to exert antitumoral effects. Inhibition of mammalian target of rapamycin (mTOR), a downstream target of Akt, is able to restore tamoxifen response in tamoxifen-resistant breast cancer cells. Given that Akt and mTOR phosphorylation also is frequently detected in ovarian and endometrial cancer, we intended to find out to what extent mTOR inhibitor RAD001 (everolimus) and tamoxifen add to each other's effects on growth and apoptosis of cancer cell lines derived from these tissues when given concomitantly.


METHODS
OVCAR-3 and SK-OV-3 ovarian cancer cells, HEC-1A endometrial adenocarcinoma cells and MCF-7 breast cancer cells were treated with different concentrations of mTOR inhibitor RAD001 alone or in combination with 4-OH tamoxifen. Relative numbers of viable cells were assessed by means of the resazurin-based Cell Titer Blue assay, cellular apoptosis was examined by measurement of activated caspases 3 and 7 by means of the luminometric Caspase-Glo assay.


RESULTS
Treatment with RAD001 resulted in growth inhibition of all employed cancer cell lines in a dose-dependent manner, and SK-OV-3 ovarian cancer cells proved to be most sensitive to this drug. Moreover, we report the observation of additive, but not synergistical growth inhibitory effects of a combination treatment with RAD001 and 4-OH TAM on SK-OV-3 and OVCAR-3 ovarian cancer cells and MCF-7 breast cancer cells in vitro, whereas no such effect was observed in HEC-1A endometrial adenocarcinoma cells. Combination treatment with both drugs was demonstrated to be superior to single treatment with lower concentrations (0.1 and 1 nM) of RAD001 or standard concentrations of 4-OH TAM. Furthermore, RAD001 increased the apoptotic effect triggered by high 4-OH TAM concentrations in SK-OV-3 ovarian cancer cells.


CONCLUSIONS
Combination treatment with RAD001 and 4-OH TAM in vitro exerts an additive antitumoral effect on ovarian cancer cells and MCF-7 breast cancer cells. The significance of these data in the clinical situation has to be evaluated in further studies.
Treeck
Oliver
O
Department of Obstetrics and Gynecology, University Regensburg, Caritas Hospital St. Josef, Landshuter Strasse 65, 93053 Regensburg, Germany. otreeck@caritasstjosef.de
Wackwitz
Birgit
B
Haus
Ulrike
U
Ortmann
Olaf
O
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D016889:Endometrial Neoplasms / Q000188:drug therapy* / Q000473:pathology; D000068338:Everolimus; D005260:Female; D006801:Humans; D010051:Ovarian Neoplasms / Q000188:drug therapy* / Q000473:pathology; D011494:Protein Kinases / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D020123:Sirolimus / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D013629:Tamoxifen / Q000008:administration & dosage / Q000031:analogs & derivatives
D012333:RNA, Messenger; D013629:Tamoxifen; C016601:afimoxifene; D000068338:Everolimus; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus