β1 integrin mediates an alternative survival pathway in breast cancer cells resistant to lapatinib
- Baylor University, Houston, TX (United States)
- University of California, San Francisco, CA (United States)
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
The overexpression of human epidermal growth factor receptor (HER)-2 in 20% of human breast cancers and its association with aggressive growth has led to widespread use of HER2-targeted therapies, such as trastuzumab (T) and lapatinib (L). Despite the success of these drugs, their efficacy is limited in patients whose tumors demonstrate de novo or acquired resistance to treatment. The b1 integrin resides on the membrane of the breast cancer cell, activating several elements of breast tumor progression including proliferation and survival. We developed a panel of HER2-overexpressing cell lines resistant to L, T, and the potent LT combination through long-term exposure and validated these models in 3D culture. Parental and L/T/LT-resistant cells were subject to HER2 and b1 integrin inhibitors in 3D and monitored for 12 days, followed by quantification of colony number. Parallel experiments were conducted where cells were either stained for Ki-67 and Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) or harvested for protein and analyzed by immunoblot. Results were subjected to statistical testing using analysis of variance and linear contrasts, followed by adjustment with the Sidak method. Using multiple cell lines including BT474 and HCC1954, we reveal that in L and LT resistance, where phosphorylation of EGFR/HER1, HER2, and HER3 are strongly inhibited, kinases downstream of b1 integrin– including focal adhesion kinase (FAK) and Src–are up-regulated. Blockade of b1 by the antibody AIIB2 abrogates this up-regulation and functionally achieves significant growth inhibition of L and LT resistant cells in 3D, without dramatically affecting the parental cells. SiRNA against b1 as well as pharmacologic inhibition of FAK achieve the same growth inhibitory effect. In contrast, trastuzumab-resistant cells, which retain high levels of phosphorylated EGFR/HER1, HER2, and HER3, are only modestly growth-inhibited by AIIB2. Our data suggest that HER2 activity, which is suppressed in resistance involving L but not T alone, dictates whether b1 mediates an alternative pathway driving resistance. Our findings justify clinical studies investigating the inhibition of b1 or its downstream signaling moieties as strategies to overcome acquired L and LT resistance.
- Research Organization:
- Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), Biological and Environmental Research (BER); Susan G. Komen Race for the Cure; National Cancer Institute (NCI); National Institutes of Health (NIH); American Cancer Society
- Grant/Contract Number:
- AC02-05CH11231; BCTR0708226; P50 CA058183; 1R01CA124891-01; RSG-07-1110-01-CCE
- OSTI ID:
- 1626696
- Journal Information:
- Breast Cancer Research, Vol. 13, Issue 4; ISSN 1465-542X
- Publisher:
- BioMed CentralCopyright Statement
- Country of Publication:
- United States
- Language:
- English
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