Expression and Therapeutic Targeting of Dopamine Receptor Type-1 in Breast Cancer

Presentation Number: OR38-5
Date of Presentation: June 23rd, 2014

Dana C Borcherding*, David F Barnard, Eric R Hugo, Sejal R Fox, Kathleen LaSance and Nira Ben-Jonathan
University of Cincinnati, Cincinnati, OH

Abstract

Patients with advanced breast cancer often fail to respond to anti-hormonal treatment and/or to chemotherapy, creating an incentive to develop novel and effective treatments. Dopamine (DA) binds to five receptors (DAR), classified by the ability to increase (D1R and D5R) or decrease (D2R, D3R and D4R) cAMP levels. Fenoldopam (Fen) is a D1R agonist which does not penetrate the brain and is FDA-approved to treat renal hypertension.  The objectives were: 1) to determine if D1R is expressed in breast cancer cells (BCC) and carcinomas, and whether D1R expression correlates with disease severity, 2) to analyze effect of D1R agonists on cell viability and determine the signaling pathway(s) involved, and 3) to examine if Fen inhibits tumor growth in mice with xenografts. We discovered D1R expression, determined by PCR and western blotting, in aggressive BCC and primary tumors. Scoring of tissue microarrays by immunohistochemistry revealed moderate to strong D1R expression in 30% of 751 primary breast carcinomas. Such expression was associated with larger tumors, higher grades, and lymph node metastasis; D1R expression was undetected in 30 normal breast tissues.  Patients with D1R-expressing tumors had significantly shorter survival and recurrence-free survival. DA and three selective D1R agonists, but not a D2R agonist, reduced cell viability and inhibited cell invasion. The reduced cell viability was due to apoptosis, as determined by flow cytometry and TUNEL assay.  Unexpectedly,  Fen decreased intracellular cAMP while increasing cGMP. The role of the cGMP/protein kinase G (PKG) as mediators of D1R activation was supported by using PKG activators and inhibitors.  Fen induced rapid and dramatic suppression of tumor growth in mice with MDA-MB-231 xenografts. Tumor suppression was due to a combined effect of Fen on apoptosis and necrosis. Fluorescence imaging, following injection of anti-D1R antibody conjugated to a fluorescent marker, revealed location of tumors and metastases in mice with xenografts. In conclusion, D1R overexpression in breast cancer is associated with advanced disease and poor prognosis. The D1R agonist Fen induced apoptosis in vitro through the cGMP/PKG pathway, and caused marked inhibition of tumor growth in mice. These data suggest that D1R analysis in tumor biopsies could serve as a prognostic biomarker for advanced breast cancer. Fen should be exploited as a novel therapeutic agent in patients who do not respond to standard therapy.

 

Nothing to Disclose: DCB, DFB, ERH, SRF, KL, NB