THU545 Growth Hormone Receptor Antagonist As A Novel Combination Therapy Against Triple Negative Breast Cancer

Disclosure: P. Mora-Criollo: None. R. Basu: None. J.J. Kopchick: None. Triple Negative breast (TNBC) cancer is classified based on the absence of ER-, PR-, and HER2- receptors and is associated with high metastatic potential. TNBC accounts for approximately 15-20% of new breast cancer diagnoses and is responsible for most breast cancer-related deaths. First-line treatment of anticancer drugs can be effective in 30-70% of patients with TNBC, but during treatment, more than half of the patients develop resistance and progress into metastatic disease. Previous studies have demonstrated the link between growth hormone receptor (GHR) expression and mammary carcinogenesis and established that GHR signaling promotes breast cancer development and progression. Conversely, inhibition of GHR expression has been shown to arrest tumor initiation and reduce metastasis of mammary carcinoma cells. Here we present the feasibility studies for employing GHR as a target for novel combination therapeutic approaches in TNBC. We performed retrospective analysis of GHR transcript expression and survival in TNBC patients, followed by experimental data in cellular models using combinations of Pegvisomant (an FDA-approved GHR antagonist) with chemotherapeutic agents, as a potential therapeutic option in TNBC. Survival probability plots from the TCGA dataset of 405 TNBC samples showed that patients expressing high levels of the GHR showed a significantly poor survival (27 months, p=0.038) compared to patients expressing low GHRs (40.37 months). Additionally, human breast cancer MDA-MB-453 cells, when treated with human (hGH)(2.5 nM) increased activation of JAK2, STAT5, SRC, ERK1/2, and AKT, associated with cancer progression. Importantly, treatment of the cells with Paclitaxel (1 nM) + (hGH)(2.5 nM) increased ABCG2 expression and the epithelial-to-mesenchymal transition (EMT) makers (SLUG, SNAIL, N-cad) associated with drug resistance and tumor progression. On the contrary, when cells were treated with Pegvisomant (500 nM) in combination with Paclitaxel + GH, a significant decrease in protein and RNA expression of ABCG2 as well as EMT markers was observed. Next, serum collected from GH antagonist (GHA) mice and WT as control, were used to treat PY8119 mouse cells in combination with Paclitaxel (1 nM) + bovine (bGH)(2.5 nM). Downregulation of protein and RNA expression levels of ABCG2 as well EMT makers in GHA serum treatment compared to WT was also found. This preliminary data shows that the GHR antagonist, Pegvisomant, in combination with anticancer drugs, can be effective in attacking drug resistance in TNBC. Key words: Pegvisomant, growth hormone receptor Presentation: Thursday, June 15, 2023