Brian G. Rowan, Ph.D.

Estrogen receptor phosphorylation: A major focus of the laboratory is understanding the role of estrogen receptor alpha (ERα) phosphorylation in regulating receptor function and the mechanisms by which signaling pathway kinases/phosphatases alter function. Our studies identify phosphorylation fingerprints for ERα and coregulators that impact tumor growth, migration/metastasis and response to endocrine therapy (J. Biol. Chem., 2000; Mol.Cell.Biol., 2000; Molecular Endocrinology, 2005, Molecular Endocrinology 2007, Endocrine Related Cancer 2010, Endocrinology, 2011, Mol Cell Endocrinol. 2015). Related to these studies, we have also have examined active kinase expression (Clinical Cancer Research, 2004, PLoS One, 2012) and coregulator expression (Gynecologic Oncology, 2004) in normal and cancerous tissue. We have also demonstrated that targeted disruption of one phosphorylation site in ERα resulted in breast cancer cells that exhibited increased growth, migration and tumor formation (Endocrinology, 2012). Another research emphasis is on novel phosphorylation sites in ERα (BMC Biochemistry 2009). These collective studies will provide the mechanistic groundwork for rational design of preclinical therapeutic combinations of endocrine therapy (selective estrogen receptor modulators (SERMs) and aromatase inhibitors (AIs)) with agents that block or activate specific kinase signaling pathways. To this end we have evaluated the in vitro and in vivo efficacy of a clinical Src kinase inhibitor, KXO1, in combination with tamoxifen for estrogen receptor positive breast cancer (Breast Cancer Research and Treatment, 2012). Our ongoing work will continue to discern molecular mechanisms by which altered ERα phosphorylation impacts breast cancer growth/metastasis and normal physiological systems.

Experimental therapeutics for breast cancer: c-Src is an oncogenic non-receptor tyrosine kinase that is up-regulated in approximately half of all breast cancers. Inhibition of Src has recently been identified as a therapeutic target for ER/PR/HER2-negative breast cancer.  KX-01 (clinical reference, KX2-391) was developed as a ‘first in class’ peptidomimetic Src kinase inhibitor that inhibits Src kinase with more specificity than ATP analogue src inhibitors. Preclinical studies in the laboratory demonstrated that KX-01 resulted in a dose dependent inhibition of ERα positive and ERa negative breast tumors (Breast Cancer Research and Treatment, 2011, Molecular Cancer Therapeutics, 2012). Low dose KX-01 resulted in re-expression of ERα in MDA-MB-231, MDA-MB-157 and MDA-MB-468 ‘triple negative’ breast tumor xenografts and sensitization of tumors to tamoxifen.

Breast cancer metastasis to bone is a major source of morbidity and mortality in patients. The local erosion of bone increases the risk of fracture and decreases the mean survival time. Drugs that could prevent bone metastatic breast cancer would significantly reduce the mortality of this disease. Breast cancer bone metastases secrete high local concentrations of a parathyroid hormone (PTH) analog termed parathyroid hormone-related peptide (PTHrP). PTHrP stimulates osteoblasts to activate osteoclasts causing bone turnover that releases stored tumor-promoting growth factors, and creates cavities in bone allowing the tumor to grow in the resulting space. We have synthesized two novel classes of PTHrP antagonists that are fused to the inert collagen binding domain (CBD) of ColG collagenase from Clostridium histolyticum. The CBD directs the concentration of the drugs to the bone and provide competitive blockade of PTHrP produced locally by invading tumor cells, thereby preventing bone turnover and release of tumor stimulating factors.

Ongoing studies will determine the optimal dosing/schedule for these agents, continue to discern the mechanisms of action, and identify surrogate biomarkers for drug efficacy with the goal of rapid advance of these agents to clinical trials with breast cancer patients.

Circadian regulation of estrogen receptor function: The impact of the circadian system on nuclear receptor function is incompletely described and the role of circadian disruption by light on nuclear receptor function is unknown. Artificial light at night is classified as a "probable human carcinogen" that contributes to circadian disruption. Extending this concept to estrogen receptor function during circadian disruption, in collaboration with Dr. Steven Hill female nude rats were implanted with “tissue-isolated” MCF-7 breast cancer xenografts housed in light boxes at 12/light:12/dark or exposed to dim light (0.2 lux) during the dark phase. Exposure to dim light resulted in markedly increased tumor growth and de novo resistance to tamoxifen that coincided with elevation of specific ERα phosphorylation sites. These results demonstrated that ERα phosphorylation at specific sites is a direct outcome of circadian disruption (Cancer Research, 2014). We have further demonstrated that ERα protein levels and phosphorylation is regulated by the circadian system using both in vitro and in vivo models.  Our research will continue to discern the mechanisms of circadian control of ERα function and the reciprocal control of the peripheral clocks by ERα.

Adipocyte tissue-derived stromal/stem cells in reconstructive surgery and soft tissue repair: Adipocyte-derived stromal/stem cells (ASCs) are present in adipose tissue and serve as precursors for mature adipocytes. ASCs are used in various applications of regenerative medicine and soft tissue repair. In collaboration with Drs. Ernest Chiu, M.D., Paul Friedlander, M.D. and Jeffrey Gimble, M.D./Ph.D., our research group is evaluating the applied use of ASCs in reconstructive surgery following tumor resection in breast cancer and head/neck cancer patients. We found that the body mass index (BMI) of the patient donor profoundly impacts the viability, morphology and osteogenic differentiation of ASCs which would impact efficacy in applied uses (BMC Cell Biology 2013). In related studies, we found that the low oxygen environment in fat grafts influenced the ASC secretome of fibrotic proteins, and stimulated T regulatory cells (Tregs) that would impair immune response in tissues (Biochimie, 2014; Stem Cells and Development, 2014).  These findings may be related to the role of ASCs in stimulating metastasis of both breast cancer and head/neck xenografts in mice suggesting caution when applying these cell-based therapeutics for reconstruction after tumor resection/treatments (PloS One, 2014, Aesthetic Surgery Journal, 2015). Future studies are aimed at understanding the mechanisms by which ASCs promote head/neck cancer metastasis, and the impact of ASCs in a low oxygen environment on fibrosis and immunomodulation.

Metastatic breast tumor model developed from patient biopsies:

Metastatic breast cancer is the leading cause of death in breast cancer patients.  We developed a reproducible, hetero-transplant breast tumor model derived from primary needle biopsies from patients diagnosed with primary invasive ductal carcinoma. Tumors formed in mice exhibited a highly metastatic phenotype and enhanced tumorigenesis during metastatic latency in bone marrow.