ABSTRACT
INTRODUCTION: The androgen receptor (AR) is the most highly expressed steroid receptor in breast cancer with 75-95% of estrogen receptor (ER)-positive and 40-70% of ER-negative breast cancers expressing AR. Though historically breast cancers were treated with steroidal androgens, their use fell from favor because of their virilizing side effects and the emergence of tamoxifen. Nonsteroidal, tissue selective androgen receptor modulators (SARMs) may provide a novel targeted approach to exploit the therapeutic benefits of androgen therapy in breast cancer. MATERIALS AND METHODS: Since MDA-MB-453 triple-negative breast cancer cells express mutated AR, PTEN, and p53, MDA-MB-231 triple-negative breast cancer cells stably expressing wildtype AR (MDA-MB-231-AR) were used to evaluate the in vitro and in vivo anti-proliferative effects of SARMs. Microarray analysis and epithelial:mesenchymal stem cell (MSC) co-culture signaling studies were performed to understand the mechanisms of action. RESULTS: Dihydrotestosterone and SARMs, but not bicalutamide, inhibited the proliferation of MDA-MB-231-AR. The SARMs reduced the MDA-MB-231-AR tumor growth and tumor weight by greater than 90%, compared to vehicle-treated tumors. SARM treatment inhibited the intratumoral expression of genes and pathways that promote breast cancer development through its actions on the AR. SARM treatment also inhibited the metastasis-promoting paracrine factors, IL6 and MMP13, and subsequent migration and invasion of epithelial:MSC co-cultures. CONCLUSION: 1. AR stimulation inhibits paracrine factors that are important for MSC interactions and breast cancer invasion and metastasis. 2. SARMs may provide promise as novel targeted therapies to treat AR-positive triple-negative breast cancer.
Subject(s)
Mesenchymal Stem Cells/drug effects , Mesenchymal Stem Cells/metabolism , Receptors, Androgen/metabolism , Selective Estrogen Receptor Modulators/pharmacology , Signal Transduction/drug effects , Triple Negative Breast Neoplasms/metabolism , Animals , Cell Line, Tumor , Cell Proliferation/drug effects , Disease Models, Animal , Female , Gene Expression Regulation, Neoplastic/drug effects , Humans , Mice , Mice, Nude , Neoplasm Metastasis , Paracrine Communication/drug effects , Triple Negative Breast Neoplasms/genetics , Triple Negative Breast Neoplasms/pathology , Tumor Burden/drug effects , Xenograft Model Antitumor AssaysABSTRACT
MDM2 is an oncoprotein best characterized for its role in the inactivation and degradation of the p53 tumor suppressor. However, MDM2 has many other binding partners and its p53-independent role in the regulation of cell growth and survival appears to be extremely complex. This report describes the expression of MDM2 in two rhabdomyosarcoma cell lines, both expressing a mutant p53 gene. Expression of MDM2 in Rh30 cells enhanced cell growth whereas expression of MDM2 in RD cells suppressed their growth and enhanced the rate of spontaneous apoptosis. The mechanism for these opposite phenotypes was demonstrated to be due to differential effects on the NFkappaB pathway. Previously MDM2 has been shown to activate NFkappaB through activation of transcription of the p65RelA subunit. In Rh30 cells MDM2 acted similarly to previously described, thereby promoting growth of Rh30 cells. In untreated RD cells p65RelA was constitutively overexpressed resulting in activation of the NFkappaB pathway. Expression of MDM2 in RD cells transcriptionally repressed p65RelA and suppressed NFkappaB activity, resulting in a reduced growth rate and enhanced apoptosis. The MDM2-sensitive region of the p65 promoter was localized to a 225 bp fragment to which MDM2 protein was shown to bind. The observation that MDM2 induces apoptosis under certain circumstances may help to explain the apparently surprising clinical studies that have shown that MDM2 expression in tumors is often associated with a favorable prognosis.