Abstract 2083: Development of novel targeted adjuvant therapy for triple negative breast cancer
Authors: Bansal Nidhi , Farias Eduardo , Gonzalez Veronica , Nolan Garry , Waxman Samuel 
Published: July 2017

There is an unmet clinical need for targeted adjuvant therapy in Triple Negative Breast Cancer (TNBC) to overcome its poor prognosis, short disease-free interval and metastatic dissemination. We previously reported that blocking interactions between the PAH2 domain of chromatin regulator Sin3 and Sin3 interaction domain (SID) containing proteins like PF1 and TGIF1 by SID decoys (peptides and small molecule, C16) decreased the cancer stem cell population, invasion, EMT, and metastases. This, programmed upregulation of retinoid signaling that sensitized TNBC cells to AM80, a novel clinically available RARα-specific agonist. Here we report preclinical investigations on effects of SID decoys and AM80 treatments on cellular heterogeneity, primary tumors, metastatic dissemination, minimum residual disease (MRD) and host microenvironment. Using CyTOF2, we made single cell measurements of markers of differentiation, proliferation and stemness in CSC-enriched 4T1 tumorspheres. Treatment with SID peptide decreased cell populations expressing nanog, sox2, vimentin and β-catenin with increase in γH2AX. Addition of AM80 in combination with C16, resulted in populations with increased expression of differentiation marker CD24 with decrease in vimentin, β-catenin and Ki-67. To interrogate the neo-adjuvant effects of C16-AM80 treatments, primary 4T1 tumors in Balb/c mice were treated with C16 and AM80 alone or in combination. Compared to DMSO, ~40 % decrease in tumor weight, 60% decrease in ALDH activity and 60% decrease in lung metastasis was seen in mice treated with C16-AM80 combination. In post-surgical adjuvant settings, in both 4T1 and MMTV-myc xenografts, we observed 100% disease-free survival and absence of macrometastasis in mice receiving minimally toxic adjuvant therapy with the C16-AM80 combination for 90 days. However, MRD was found consisting of a small number of single CK8+ cells which failed to form colonies when recovered from the bone marrow and selectively cultured in vitro. Upon stopping the treatments, 20-40% animals developed macrometastases within the first three months. To test the influence of C16-AM80 to condition the host microenvironment to prevent macrometastases mice received only pretreatment with C16 and AM80 followed by 4T1 cells injected in the tail vein. The percentage of parenchyma occupied by metastatic nodules were: DMSO = 50%; AM80 = 25%; C16 &gt;10% and C16-AM = &lt;&lt;10%; the mitotic features were greatly reduce from 0-5 in DMSO to 0-1 per 400x/field in the C16-AM80 combination. The predominant effects were observed with C16 treatment, which was enhanced to a small degree in combination with AM80. These results suggest that C16 can potentially induce changes in the host microenvironment to prevent the colonization and metastatic growth of cancer cells in TNBC. Altogether, our preclinical studies merit expansion of a pre-clinical program for development of C16-AM80 combination as a targeted adjuvant therapy to treat TNBC.

Citation Format: Nidhi Bansal, Eduardo Farias, Veronica Gonzalez, Garry Nolan, Samuel Waxman. Development of novel targeted adjuvant therapy for triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2083. doi:10.1158/1538-7445.AM2017-2083