The anti-erbB3 antibody MM-121/SAR256212 in combination with trastuzumab exerts potent antitumor activity against trastuzumab-resistant breast cancer cells.
BACKGROUND
Elevated expression of erbB3 receptor has been reported to induce resistance to therapeutic agents, including trastuzumab in erbB2-overexpressing breast cancer. Our recent studies indicate that erbB3 interacts with both erbB2 and IGF-1 receptor to form a heterotrimeric complex in trastuzumab-resistant breast cancer cells. Herein, we investigate the antitumor activity of MM-121/SAR256212, a fully human anti-erbB3 antibody (Ab), against two erbB2-overexpressing breast cancer cell lines resistant to trastuzumab.


METHODS
MTS-based proliferation assays were used to determine cell viability upon treatment of trastuzumab and/or MM-121/SAR256212. Cell cycle progression was examined by flow cytometric analysis. Western blot analyses were performed to determine the expression and activation of proteins. Tumor xenografts were established by inoculation of the trastuzumab-resistant BT474-HR20 cells into nude mice. The tumor-bearing mice were treated with trastuzumab and/or MM-121/SAR256212 via i.p injection to determine the Abs' antitumor activity. Immunohistochemical analyses were carried out to study the Abs' inhibitory effects on tumor cell proliferation and induction of apoptosis in vivo.


RESULTS
MM-121 significantly enhanced trastuzumab-induced growth inhibition in two sensitive and two resistant breast cancer cell lines. MM-121 in combination with trastuzumab resulted in a dramatic reduction of phosphorylated erbB3 (P-erbB3) and Akt (P-Akt) in the in vitro studies. MM-121 combined with trastuzumab did not induce apoptosis in the trastuzumab-resistant cell lines under our cell culture condition, rather induced cell cycle G1 arrest mainly associated with the upregulation of p27(kip1). Interestingly, in the tumor xenograft model established from the trastuzumab-resistant cells, MM-121 in combination with trastuzumab as compared to either agent alone dramatically inhibited tumor growth correlated with a significant reduction of Ki67 staining and increase of cleaved caspase-3 in the tumor tissues.


CONCLUSIONS
The combination of MM-121 and trastuzumab not only inhibits erbB2-overexpressing breast cancer cell proliferation, but also promotes the otherwise trastuzumab-resistant cells undergoing apoptosis in an in vivo xenografts model. Thus, MM-121 exhibits potent antitumor activity when combined with trastuzumab under the studied conditions. Our data suggest that further studies regarding the suitability of MM-121 for treatment of breast cancer patients whose tumors overexpress erbB2 and become resistant to trastuzumab may be warranted.
Jingcao
J
Huang
Shuiliang
S
Wang
Hui
H
Lyu
Bo
B
Cai
XiaoHe
X
Yang
Department of Pathology, School of Medicine, University of Colorado Anschutz Medical Campus, MS-8104, 12801 E, 17th Ave,, Aurora, CO 80045, USA. wangjx@ihcams.ac.cn.
Jianxiang
J
Wang
Bolin
B
Liu
D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage; D061067:Antibodies, Monoclonal, Humanized / Q000008:administration & dosage; D000970:Antineoplastic Agents / Q000008:administration & dosage; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology* / Q000627:therapeutic use; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D045744:Cell Line, Tumor; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D004789:Enzyme Activation; D005260:Female; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020893:Receptor, ErbB-3 / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D000068878:Trastuzumab; D047368:Tumor Burden / Q000187:drug effects; D023041:Xenograft Model Antitumor Assays
D000911:Antibodies, Monoclonal; D061067:Antibodies, Monoclonal, Humanized; D000970:Antineoplastic Agents; C436291:CDKN1B protein, human; D050760:Cyclin-Dependent Kinase Inhibitor p27; C000589319:seribantumab; C581292:ERBB3 protein, human; D020893:Receptor, ErbB-3; D051057:Proto-Oncogene Proteins c-akt; D000068878:Trastuzumab