Abstract B69: Mesenchymal stem cells promote tumor-skin involvement in inflammatory breast cancer models

Background: Inflammatory breast cancer (IBC) is an aggressive variant of breast cancer characterized by blocked breast lymphatics and clinically apparent involvement of the skin resulting in erythema, swelling and a high rate of resistance to therapy. Tumor-skin involvement in IBC patients, despite being a rare event, is an event that develops very rapidly, can spread throughout the upper body (chest and back) and ultimately results in breast cancer death. Very little is known about this event and how to prevent it. Mesenchymal stem cells (MSC) are multipotent progenitor cells which are found in normal tissues, including the bone marrow and adipose tissue. MSC exhibit a unique tropism for tumors, where they engraft, form tumor stroma, and alter the tumor microenvironment. MSC have been shown to increase the growth of certain cancers and the incidence of breast xenograft metastasis. Whether MSC directly modify the primary tumor microenvironment or the pre-metastatic niche remote from the primary tumor has not been addressed in IBC tumor models or patients. Methods and Results: Many IBC xenografts grow tumors but do not faithfully recapitulate the skin phenotype of IBC. In order to investigate whether direct exposure to MSC or paracrine exposure using the MSC-conditioned media (MSC-CM) would influence skin involvement and metastasis development and with this recapitulate the IBC phenotype in pre-clinical models, we performed two different in vivo experiments. In the first, we labeled SUM149 cells with luciferase reporter gene and then injected them into the cleared mammary fat pads of female immunocompromised mice (SCID/Beige) with or without 10% MSC (obtained from healthy donors). Transplants were allowed to grow until 300 mm3 in volume and then resected in a survival surgery. At resection time we found that there was a significant difference in the tumor-skin involvement (p=0.0189, Fisher's exact test) between the 0% MSC group (4/20) and 10% MSC group (11/18). Furthermore, we assessed metastasis development with live bioluminescence imaging and identified unexpected development of metastasis in the upper body skin plexus (31.6% vs. 58.8%, p = NS). In vitro, MSC co-culture is associated with increased EGFR signaling, and tumors in MSC co-injected animals had increased p-EGFR staining by IHC (70.6% vs. 50.0%, p =0.0455). In a second experiment, we cultured in vitro SUM149 cells (labeled with luciferase reporter gene) with or without MSC-CM for 5 days and then injected them into the cleared mammary fat pads of female immunocompromised mice (SCID/Beige), to determine whether the observed tumor-skin involvement was an effect of MSC secreted factors. Transplants were allowed to grow until 300 mm3 in volume and then resected in a survival surgery. MSC-CM increased significantly the tumor-skin involvement (p=0.0227, Fisher's exact test), between the control group (4/16) and MSC-CM group (9/13). We followed up metastasis development with live bioluminescence imaging after tumor resection and observed that several mice developed metastasis in the upper body skin plexus (20.0% vs. 27.2%, p=NS). Conclusion: Our studies show that MSC and MSC-CM increase tumor-skin involvement and metastasis development in an IBC pre-clinical model independent of growth rate. Understanding the role of MSC on the primary tumor microenvironment and the pre-metastatic niche is critical to further develop therapies that target and suppress the tumor-skin involvement and the rapid development of metastasis that IBC patients experience. Citation Format: Lara Lacerda, Daniel Smith, Bisrat Debeb, Travis Solley, Richard Larson, Wei Xu, Savitri Krishnamurthy, Naoto Ueno, Ann Klopp, Wendy Woodward. Mesenchymal stem cells promote tumor-skin involvement in inflammatory breast cancer models. [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 B69.