Abstract 1680: Modulation of MDM2 in context of DNA damage enhances cell death in a metastatic breast-to-lung xenograft model
Authors: Tonsing-Carter Eva , Shannon Harlan E. , Bailey Barbara J. , Sinn Anthony L. , Peterman Kacie M. , Mayo Lindsey D. , Pollok Karen E. 
Published: May 2015

Abstract
Metastatic breast cancer is highly refractive to current treatment strategies, and new multi-targeted treatments need to be elucidated. In metastatic disease, inhibiting key protein-protein interactions with the murine double minute 2 (MDM2) could be beneficial for developing new treatment modalities since this signaling pathway is a critical regulatory point in cancer progression. Inhibition of protein binding to the hydrophobic pocket of MDM2 by Nutlin-3a can activate pro-apoptotic proteins such p73 and E2F1 as well as decrease pro-angiogenic Hif-1α. Since the DNA damaging agent carboplatin is currently being studied in clinical trials of triple-negative breast cancers (TNBCs), our objective was to evaluate the effects of carboplatin and Nutlin-3a in combination in TNBC in a mutant p53 background. Using a TNBC cell line TMD231 derived from the MDA-MB-231 human breast cancer cell line, we performed combination studies using different ratios of carboplatin to Nutlin-3a in vitro to evaluate the range of carboplatin-mediated DNA damage required to obtain synergism with inhibition of MDM2 function. A fixed ratio of 1:1 carboplatin:Nutlin-3a was strongly synergistic with a combination index of &lt;0.5. In cell proliferation assays there was increased sensitivity to the drugs when given in combination (p&lt;0.05). TMD231 cells implanted into the mammary fat pad of NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) mice showed enhanced tumor growth, and metastasis was evident in the lungs. Dose-finding studies were performed to determine an optimal carboplatin dosing schema. NSG mice were randomized based on fluorescent imaging of E2-crimson expressing TMD231 cells allowing for a sensitive measurement of early tumor burden. Following Nutlin-3a and carboplatin combination treatment in vivo, there was a statistically significant reduction in tumor volume and lung metastases compared to vehicle and single drug treated mice (p&lt;0.001). Following Kaplan-Meier analysis, the combination treated mice had a significant increase in survival, (54.3±1.5 days) compared to the vehicle (39.3±0.6 days) and each single drug (Nutlin-3a: 39±1 and carboplatin: 47.5±1.8 days) (p&lt;0.001). While there was a decrease in bone-marrow cellularity, this did not lead to bone-marrow aplasia, and body weights recovered to normal levels within 7 days post-treatment. Pharmacodynamic studies are ongoing to further understand at the molecular level how the DNA damage response and repair is modulated by MDM2 resulting in a robust synergistic response. These studies will lead to a better understanding of how to potentiate DNA damage and may lead to new clinical therapies in the future for metastatic breast cancer.
Citation Format: Eva Tonsing-Carter, Harlan E. Shannon, Barbara J. Bailey, Anthony L. Sinn, Kacie M. Peterman, Lindsey D. Mayo, Karen E. Pollok. Modulation of MDM2 in context of DNA damage enhances cell death in a metastatic breast-to-lung xenograft model. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1680. doi:10.1158/1538-7445.AM2014-1680