Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Biological Sciences

Committee Chair/Advisor

Chen, Wen Y.

Committee Member

Rice , Charles D.

Committee Member

Temesvari , Lesly A.

Committee Member

Scott , Thomas R.


The tumor microenvironment is a crucial factor in breast tumorigenesis. Tumor epithelial cells maintain 3D structure in tumor stroma and they interact with soluble factors secreted by stromal cells such as cancer associated fibroblasts (CAFs) or directly with the extracellular matrix (ECM). Recent studies have shown that the hormone prolactin (PRL) promotes the proliferation and survival of breast cancer cells in part via the transactivation of human epidermal growth factor receptor 2 (HER2), also known as Neu in rodents. A PRL receptor (PRLR) antagonist, G129R, has been demonstrated not only to be able to directly inhibit PRLR activation but also indirectly inhibits the tyrosine phosphorylation of HER2 (p-HER2) in human breast cancer cell lines. However, there is an obvious discrepancy related to the inhibitory effects of G129R on p-HER2 between the monolayer cell culture system and in vivo.
In this dissertation, I investigated the potential mechanisms by which tumor stroma exert upon the cross talk between PRLR and HER2/Neu. To compare drug response to G129R between tumors and primary cultured cells, mammary tumors were resected and cultured as small tumor chunks (≈3 mm3) or were cultured in monolayer. G129R reduced p-Neu in a dose-dependent manner (IC50 ≈10 µg/ml) in tumor chunks, but had no significant effect upon primary tumor epithelial cells grown in monolayer. Similar to that observed in mouse tumor chunks, direct co-culture of mouse tumor
epithelial cells with CAFs restored the response of epithelial cells to G129R. The addition of PRL, as expected, induced p-Neu in both the tumor chunk and co-culture iiimodels. The inhibitory effect of G129R was absent when CAFs were physically separated from mouse tumor epithelial cells using a transwell system, or when CAFs
were replaced with normal fibroblasts in direct co-culture with human or mouse tumor epithelial cells. In human breast cancer cell lines, the activation of HER2 was reduced by G129R when co-cultured with mouse or human CAFs. Furthermore, 3D culture of just
mouse or human tumor epithelial cells with ECM components restored the same response to both G129R and PRL, suggesting that ECM components or 3D cell structure at least partially contributes to the cross talk between HER2/Neu and PRLR in breast cancer. Finally, G129R was tested in ex vivo and in vivo models. I demonstrated that G129R had an additive inhibitory effect on p-Neu in tumor chunks when combined with lapatinib, a HER1 and HER2/Neu tyrosine kinase inhibitor. Also, it reduced tyrosine phosphorylation of Neu (p-Neu) in primary mammary tumors of mice in a time- and dose-dependent manner.
In conclusion, tumor stroma play a critical role in modulating the cross talk between PRLR and HER2/Neu in both human and mouse models of breast cancer. The inhibitory effects of G129R on p-HER2/Neu are dependent, at least in part, upon interactions of tumor epithelium with stroma.



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