Breast cancer is a heterogeneous disease exhibiting diverse biological characteristics and clinical responses. Gene expression profiling has defined genetic signatures corresponding to at least five distinct molecular subtypes of breast cancer including an aggressive form known as triple negative (TN; also called basal-like. TN breast cancers are typically high grade (poorly differentiated) and rapidly progressive, with a higher risk of relapse and lower survival than other subtypes of the disease. Additionally, for unknown reasons, TN breast cancers are often diagnosed in younger women and women of African-American descent. Although TN breast cancer represents a relative small percentage of all breast cancers (~20%), it is associated with a disproportionate number of deaths. By definition, TN breast cancers fail to express three molecules shown to promote many breast cancers: estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). Current clinical approaches for breast cancer include agents that target these three molecules; endocrine therapies and the monoclonal antibody targeting HER2, Trastuzumab. Because TN breast cancer is defined as absence of these targets, conventional cytotoxic chemotherapies are currently the mainstay of systemic treatment for these patients. However, conventional systemic treatments are limited by poor therapeutic response, high toxicity, and the development of resistance. Although new approaches in the treatment of TN breast cancer such as targeting DNA repair with PARP inhibitors have emerged, there have been relatively fewer advances in TN breast cancer when compared to other subtypes of the disease. Thus, there is a pressing need for both new therapeutic approaches, and mechanistic understandings, of TN breast cancer. Our studies will directly address both of these needs. We have developed AMPI-109, a novel drug with the characteristic of specifically killing TN breast cancer cells. Moreover, AMPI-109 exerts its potent pro-apoptotic actions through a novel mode of action providing insight into the patterns of signaling peculiar to TN breast cancer. Our preliminary studies, designed to identify targets of AMPI-109, demonstrate that AMPI-109 promotes apoptotic death of TN breast cancer cells through alterations of MAPK and bioenergetics cellular signaling pathways. Mechanistically, this contribution is significant because it 1) identifies cellular pathway(s) that can be exploited in pharmacologic strategies of targeted therapies of TN breast cancer and 2) identifies AMPI-109 as a “molecular tool” that will aid in our understanding of the unique and aggressive nature of this disease. These studies also have the added significance of providing a fundamental understanding of cancer cell targeting in general. The striking observation that AMPI-109 has no effect on untransformed cells suggests a critical “cancer-specific” mode of this drug’s action. Our research will lay the ground work of our understanding of this unique mechanism of action. Finally, these studies are also expected to provide the necessary pre-clinical knowledge on the use of AMPI-109 that will allow us to move AMPI-109 into clinical trials for TN breast cancer patients and potentially, other cancer types.