Research Grants Awarded
The Role of Beta1 and Beta4 Integrins in Endocrine and Anti-HER Therapy Resistance in Breast Cancer
Tumor Cell Biology III
Background: Crosstalk between the HER family and the estrogen receptor (ER) plays a key role in breast cancer endocrine resistance. HER inhibition circumvents this resistance, but secondary resistance to this combination therapy further develops, presenting a new serious clinical challenge. There are clearly missing components to what is probably a multicausal basis behind endocrine and anti-HER resistance. In particular, the integrins, especially the beta1 and beta4 subunits of the alpha6beta1 and alpha6beta4 heterodimers, have been strongly implicated in mammary tumorigenesis. These adhesion receptors crosstalk extensively with HER1/2 and may be a key component in therapy resistance, a hypothesis that has not been investigated until now. Objective/Hypothesis: We therefore hypothesize that beta1 and beta4 integrins, at least partly via their crosstalk with the HER and perhaps also ER pathways, are important determinants in endocrine and HER therapy resistance, and that these receptors may thus serve as diagnostic and therapeutic targets to circumvent resistance. Our goal is to investigate the role and the therapeutic potential integrins may have in influencing endocrine and anti-HER therapy efficacy, and to examine the molecular basis for this association. Specific Aims: To investigate (1) whether endocrine and anti-HER therapies are correlated with alterations in beta1/beta4 integrin expression and signaling; (2) whether overexpression or (3) inhibition of these integrins can accelerate or delay these therapy resistance types; and (4) the molecular mechanisms by which beta1/beta4 can modulate ER and HER signaling and therapy outcome. Study Design: Studies will be done in our in vivo and 3D culture models of endocrine and anti-HER therapy resistance, using ER+ human breast cancer lines with low or high HER2 levels. (1) RNA and total/phospho-protein levels of beta1/beta4 integrins and their downstream kinases will be studied in sensitive and resistant xenograft tumor specimens. (2) Inducible beta1 and beta4 transfectant clones will be generated and examined in vivo and in 3D cultures for their ability to accelerate resistance to endocrine therapy, alone or with anti-HER therapy. (3) Beta1 and beta4 signaling will be inhibited by antibody or by dominant-negative or shRNA expression. These inhibitors? ability to circumvent therapy resistance will be studied as above. (4) The molecular mechanisms by which beta1 and beta4 modulate ER activity, HER signaling, and therapy resistance will be studied via analysis of biomarkers related to these pathways in the tumors and cultures that were collected from Aims 2&3. We expect to provide definitive evidence on the therapeutic potential of beta1 and beta4 integrins as targets for circumventing endocrine and HER/dual therapy resistance, to identify new predictive biomarkers for this resistance, and to elucidate the mechanisms by which integrins interact with and modulate ER and HER signaling and therapy.
Endocrine therapy to target the estrogen receptor (ER) is the most common treatment for breast cancer, but resistance sooner or later abolishes its efficacy. Revealing the underlying resistance mechanisms will have profound clinical implications for alternative and improved treatment strategies. In a tumor cell, ER can be activated by growth factor receptors (GFRs) such as HER1 and HER2, potentially overwhelming the estrogen antagonist activity of endocrine drugs like tamoxifen or aromatase inhibitors, and thereby resulting in endocrine resistance. HER inhibitors like lapatinib and trastuzumab (Herceptin) added to the endocrine therapy can inhibit tumor growth and stave off resistance in our human breast cancer models grown in mice, but resistance still eventually develops (dual therapy resistance). Clearly there are missing components to the molecular etiology of endocrine and HER or dual therapy resistance. The integrin family of cell surface receptors, specifically beta1 and beta4 integrins, show particular promise as therapeutic targets due to their excess activity in breast cancer cells and their involvement in cancer cell survival, proliferation, and metastasis. While endocrine, HER, and dual resistance probably have multiple molecular causes, evidence strongly suggests a link between integrins, GFRs, and ER itself that has not been investigated until now in the context of endocrine and anti-HER therapy resistance. We thus suggest that beta1 and beta4 integrins are involved in endocrine and HER therapy resistance and that these integrins may serve as therapeutic targets to overcome resistance and improve therapy outcome. Our goals are first to examine the relationship between integrin expression, signaling, and resistance to endocrine, anti-HER, and dual therapies, and then to investigate the molecular basis of this relationship. To do so, we will look at integrin signaling in relation to resistance in tumor specimens harvested at sensitive and resistant phases from our various in vivo (in mice) human breast cancer models of endocrine/anti-HER therapy. We will then see whether inducible beta1 and beta4 can accelerate resistance onset, in cultures and in mice. In complement, we will inhibit beta1 and beta4 integrin activity to determine if their suppression can delay or overcome resistance onset. To investigate the molecular mechanisms behind beta1 and beta4 integrin activity, we will also study other biological parameters, including various ER and HER signaling intermediates and downstream kinases which may hold keys that tether the above components more tightly together. We expect to provide experimental evidence of the important role of beta1/beta4 integrins in endocrine, HER, and dual therapy resistance. We believe that targeting beta1 and beta4 integrin activity may represent a novel treatment strategy for ER-positive breast cancer, and if successful, we will translate our findings promptly to the clinic.