Abstract A103: Investigation of novel therapeutic and diagnostic strategies for the management of triple-negative breast cancer

Approximately 10-24% of invasive breast cancers (BCs) are characterized as ‘triple-negative’ breast cancer (TNBC), a specific BC subtype that lacks expression of the estrogen and progesterone receptors, as well as that of Her2 over expression. TNBC is one of the most clinically aggressive forms of BC, exhibiting elevated rates of metastasis, disease recurrence, and poor overall survival. Metastatic TNBCs rapidly progress through multiple lines of chemotherapy and currently there are no targeted therapies approved for the treatment of TNBC highlighting the importance of investigating novel druggable targets for this highly aggressive disease. Previously, we demonstrated that the heterologous expression of a constitutively active (CST) c-Abl, a non-receptor tyrosine kinase, mutant morphologically and phenotypically reverted late-stage murine BC cells both in vitro and in vivo. We further showed that CST-Abl enhanced cytostatic activity in part by elevating p21 expression levels thereby preventing TNBC tumorigenesis when implanted into the mammary fat pads of mice. Additionally, we found c-Abl expression to associate with invasive BC patient9s response to docetaxel treatment through Oncomine in silico data. Recently the natural product, Securinine, has been shown to mediate an anti-cancer response through modulating p53 family member expression in leukemic and colorectal carcinoma cells. We have shown a strong induction of c-Abl expression in response to Securinine administration in highly aggressive late stage murine BC cells suggestive of its involvement in the mechanism of Securinine-mediated cell death. Our studies tested the hypothesis that c-Abl is a biomarker for a TNBC response to docetaxel and furthermore targeted activation of c-Abl utilizing DPH, a novel pharmacological allosteric c-Abl activator, will inhibit the tumorigenicity of TNBCs in vitro. We additionally hypothesized that Securinine would be an effective novel therapy for the treatment of TNBCs. We found DPH to inhibit the proliferation of highly aggressive 4T1 murine metastatic TNBC cells in a 3D-organotypic culture model. In addition, DPH suppressed the up-regulation of β3-integrin, a robust marker of epithelial to mesenchymal transitions (EMT), in response to TGF-β, in normal murine mammary gland (NMuMG) cells. Through phalloidin staining, DPH was shown to partially blunt a morphological EMT, induced by TGF-β, in NMuMGs and enhanced a basal epithelial morphology that was reminiscent of CST-Abl activity. Furthermore, we have recapitulated that DPH is specific to the kinase activity of c-Abl. Utilizing cell lines expressing a lentiviral shRNA construct targeting c-Abl in dormant and metastatic D2 hyperaveolar nodule (D2.HAN) cells, we have shown through clonogenic assays and 3D-organotypic culturing models, that the loss of c-Abl expression directly correlates with a blunted response to docetaxel. Finally, Securinine was found to strongly induce p73 expression in both dormant and metastatic TNBCs and suppressed their proliferation in 3D-culture, but did not have an effect on their normal counterparts. These innovative findings suggest that c-Abl expression associates with a TNBC response to docetaxel and Securinine and that its targeted activation could lead to an effective treatment for TNBCs. Citation Format: Chevaun Danielle Morrison, William Schiemann. Investigation of novel therapeutic and diagnostic strategies for the management of triple-negative breast cancer. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr A103.