title: Antiangiogenic potential of the Mammalian target of rapamycin inhibitor temsirolimus.
abstract: Mammalian target of rapamycin (mTOR) is increasingly recognized as a master regulator of fundamental cellular functions, whose deregulation may underlie neoplastic transformation and progression. Hence, mTOR has recently emerged as a promising target for therapeutic anticancer interventions in several human tumors, including breast cancer. Here, we investigated the antiangiogenic potential of temsirolimus (also known as CCI-779), a novel mTOR inhibitor currently in clinical development for the treatment of breast cancer and other solid tumors. Consistent with previous reports, sensitivity to temsirolimus-mediated growth inhibition varied widely among different breast cancer cell lines and was primarily due to inhibition of proliferation with little, if any, effect on apoptosis induction. In the HER-2 gene-amplified breast cancer cell line BT474, temsirolimus inhibited vascular endothelial growth factor (VEGF) production in vitro under both normoxic and hypoxic conditions through inhibition of hypoxia-stimulated hypoxia-inducible factor (HIF)-1alpha expression and transcriptional activation. Interestingly, these effects were also observed in the MDA-MB-231 cell line, independent of its inherent sensitivity to the growth-inhibitory effects of temsirolimus. A central role for mTOR (and the critical regulator of cap-dependent protein translation, eIF4E) in the regulation of VEGF production by BT474 cells was further confirmed using a small interfering RNA approach to silence mTOR and eIF4E protein expression. In addition to its effect on HIF-1alpha-mediated VEGF production, temsirolimus also directly inhibited serum- and/or VEGF-driven endothelial cell proliferation and morphogenesis in vitro and vessel formation in a Matrigel assay in vivo. Overall, these results suggest that antiangiogenic effects may substantially contribute to the antitumor activity observed with temsirolimus in breast cancer.
authors.affiliation: Laboratory of Experimental Chemotherapy and Division of Medical Oncology A, Regina Elena National Cancer Institute, Rome, Italy.
authors.forename: Donatella
authors.initials: D
authors.lastname: Del Bufalo
authors.forename: Ludovica
authors.initials: L
authors.lastname: Ciuffreda
authors.forename: Daniela
authors.initials: D
authors.lastname: Trisciuoglio
authors.forename: Marianna
authors.initials: M
authors.lastname: Desideri
authors.forename: Francesco
authors.initials: F
authors.lastname: Cognetti
authors.forename: Gabriella
authors.initials: G
authors.lastname: Zupi
authors.forename: Michele
authors.initials: M
authors.lastname: Milella
mesh_terms: D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000098:blood supply* / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D048708:Cell Growth Processes / Q000187:drug effects; D045744:Cell Line, Tumor; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D009389:Neovascularization, Pathologic / Q000188:drug therapy / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D011494:Protein Kinases / Q000378:metabolism; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis
chemical_list: D020533:Angiogenesis Inhibitors; D047428:Protein Kinase Inhibitors; D042461:Vascular Endothelial Growth Factor A; C401859:temsirolimus; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus