title: Combined Src and ER blockade impairs human breast cancer proliferation in vitro and in vivo.
abstract: Antiestrogen therapies arrest susceptible estrogen receptor (ER)-positive breast cancers by increasing p27. Since Src phosphorylates p27 to promote p27 proteolysis, Src activation observed in up to 40% of ER-positive cancers may contribute to antiestrogen resistance. In this article, we show that treatment with the Src-inhibitor saracatinib (AZD0530) together with ER-blocking drugs increased breast cancer cell cycle arrest via p27. Saracatinib and fulvestrant together more effectively increased p27, reduced Ki67, and impaired MDA-MB-361 xenograft tumor growth in vivo than either of the drugs alone. In contrast, saracatinib monotherapy rapidly gave rise to drug resistance. Since combined ER and Src inhibition delays development of resistance in vivo, these data support further clinical investigation of saracatinib in combination with fulvestrant for women with ER-positive breast cancer. Proteomic analysis revealed striking bypass activation of the mTOR pathway in saracatinib-resistant tumors. mTORC1 activation also arose following long-term culture of ER-positive breast cancer lines in the presence of saracatinib. These data indicate the utility of proteomic analysis of drug-resistant tumors to identify potential means of drug resistance. The use of mTOR kinase inhibitors with saracatinib may subvert drug resistance and prove to be more effective than saracatinib alone.
authors.affiliation: Braman Family Breast Cancer Institute, University of Miami Sylvester Comprehensive Cancer Center, Miami, FL, 33136, USA. ychen@jding.dhs.org
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.forename: Edwin A
authors.initials: EA
authors.lastname: Alvarez
authors.forename: Diana
authors.initials: D
authors.lastname: Azzam
authors.forename: Seth A
authors.initials: SA
authors.lastname: Wander
authors.forename: Natalia
authors.initials: N
authors.lastname: Guggisberg
authors.forename: Mercè
authors.initials: M
authors.lastname: Jordà
authors.forename: Zhenlin
authors.initials: Z
authors.lastname: Ju
authors.forename: Bryan T
authors.initials: BT
authors.lastname: Hennessy
authors.forename: Joyce M
authors.initials: JM
authors.lastname: Slingerland
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D052117:Benzodioxoles / Q000494:pharmacology*; D001943:Breast Neoplasms; D045744:Cell Line, Tumor; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D066246:ErbB Receptors / Q000378:metabolism; D004958:Estradiol / Q000031:analogs & derivatives* / Q000494:pharmacology; D047628:Estrogen Receptor alpha / Q000037:antagonists & inhibitors* / Q000378:metabolism; D005260:Female; D000077267:Fulvestrant; D016193:G1 Phase / Q000187:drug effects; D006801:Humans; D019394:Ki-67 Antigen / Q000378:metabolism; D051379:Mice; D008819:Mice, Nude; D009376:Neoplasms, Hormone-Dependent; D011799:Quinazolines / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology*; D023041:Xenograft Model Antitumor Assays; D019061:src-Family Kinases / Q000037:antagonists & inhibitors*
chemical_list: D000970:Antineoplastic Agents; D052117:Benzodioxoles; D019927:Cyclin E; D047628:Estrogen Receptor alpha; D019394:Ki-67 Antigen; D011799:Quinazolines; D013629:Tamoxifen; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000077267:Fulvestrant; D004958:Estradiol; C515233:saracatinib; C546842:MTOR protein, human; D066246:ErbB Receptors; D019061:src-Family Kinases; D058570:TOR Serine-Threonine Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2