Drug resistance is a major cause of chemotherapy failure in breast cancer patients with metastatic disease. We previously demonstrated that autocrine human growth hormone (hGH) plays a key role in oncogenic transformation and progression of mammary carcinoma. The present study investigated the role of autocrine hGH in the development of resistance to mitomycin C (MMC), an alkylating agent utilised in the treatment of advanced metastatic breast cancer. Stable forced expression of the hGH gene was established in the mammary carcinoma cell lines MDA-MB-231, MCF-7 and T47D. Autocrine hGH reduced the sensitivity of mammary carcinoma cells to MMC in cell viability assays and reduced MMC-induced apoptotic cell death when compared to a control cell line. In addition, autocrine hGH enhanced MDA-MB-231 clonogenic survival, anchorage independent cell growth, growth in 3D Matrigel and protected MDA-MB-231 cells from induction of DNA double-strand breaks following MMC treatment. Functional antagonism of hGH in the endometrial carcinoma cell line RL95-2, which endogenously expresses hGH, significantly increased the sensitivity of these cells to MMC-induced DNA damage and cell death. Thus, autocrine hGH promotes mammary and endometrial carcinoma cell resistance to MMC. These studies indicate a potential role for antagonism of autocrine hGH in chemoresistant breast cancer.

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