Combined Src and aromatase inhibition impairs human breast cancer growth in vivo and bypass pathways are activated in AZD0530-resistant tumors.
OBJECTIVE
Antiestrogens are used to treat estrogen receptor (ER)-alpha-positive breast cancers and cause a p27-dependent G(1) arrest. Estrogen-bound ER recruits Src to mediate proteolysis of p27 and drive cell proliferation. Here, we tested the antitumor efficacy of combined Src and aromatase inhibition for ER-positive breast cancer.


METHODS
Antiproliferative effects of the aromatase inhibitor, anastrozole, and Src inhibitor, AZD0530, alone or in combination were tested in vitro and in vivo on aromatase-transfected MCF-7Arom5 xenografts. Xenografts were analyzed by immunohistochemistry and proteomic analysis to identify potential biomarkers of drug response and resistance.


RESULTS
AZD0530 and anastrozole together increased p27 and caused greater G(1) cell cycle arrest than either drug alone. AZD0530 monotherapy initially retarded xenograft growth in vivo, but drug resistance rapidly emerged. Combined anastrozole/AZD0530 reduced drug resistance and showed greater antitumor efficacy in vivo with greater Src and epidermal growth factor receptor inhibition and a greater increase in p27 and reduction of Ki-67 than either drug alone, supporting further evaluation of these putative predictors of response to combined Src/aromatase inhibition in vivo. Anastrozole alone stimulated Src activity both in vitro and in vivo. AZD0530-resistant tumors showed activation of bypass pathways including MEK and phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin, raising the possibility that MEK, mammalian target of rapamycin (mTOR), or PI3K inhibitors may augment Src inhibitor efficacy.


CONCLUSIONS
These data support clinical investigation of anastrozole-AZD0530 therapy for postmenopausal ER-positive breast cancer. Loss of p27 and increased Ki-67 may predict response and further clinical studies should evaluate for activation of bypass pathways including MEK and PI3K pathways during Src inhibitor therapy.
Chen
Yi
Y
Braman Family Breast Cancer Institute, Sylvester Comprehensive Cancer Center, University of Miami Miller School of Medicine, Miami, FL 33136, USA.
Guggisberg
Natalia
N
Jorda
Merce
M
Gonzalez-Angulo
Ana
A
Hennessy
Bryan
B
Mills
Gordon B
GB
Tan
Chen-Keat
CK
Slingerland
Joyce M
JM
D000077384:Anastrozole; D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D047072:Aromatase Inhibitors / Q000008:administration & dosage; D052117:Benzodioxoles / Q000008:administration & dosage; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D000081247:CSK Tyrosine-Protein Kinase; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D019394:Ki-67 Antigen / Q000378:metabolism; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009570:Nitriles / Q000008:administration & dosage; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011799:Quinazolines / Q000008:administration & dosage; D015398:Signal Transduction / Q000187:drug effects*; D014230:Triazoles / Q000008:administration & dosage; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays; D019061:src-Family Kinases
D000077384:Anastrozole; D047072:Aromatase Inhibitors; D052117:Benzodioxoles; D000081247:CSK Tyrosine-Protein Kinase; D050760:Cyclin-Dependent Kinase Inhibitor p27; D019394:Ki-67 Antigen; D020928:Mitogen-Activated Protein Kinases; D009570:Nitriles; D019869:Phosphatidylinositol 3-Kinases; D011505:Protein-Tyrosine Kinases; D011799:Quinazolines; D014230:Triazoles; D019061:src-Family Kinases; C515233:saracatinib; C000631346:CSK protein, human