Abstract 1344: HMGA2-targeted drug discovery for breast cancer brain metastasis
Authors: Burnett Riesa , Appaiah Hitesh , Bhat-Nakshatri Poornima , Wikel Jim , Crooks Peter , Mathews William , Nakshatri Harikrishna 
Published: June 2012

Breast cancer is a major health concern for women in the United States, with nearly 200,000 women diagnosed annually. An estimated 10-16% of women with breast cancer will develop symptomatic brain metastases and the incidence of brain metastasis has increased in recent years mainly due to the inability of current therapies to cross the blood-brain barrier (BBB). It is suggested that metastatic tumors contain a unique subpopulation of cancer cells with stem cell properties (CSCs), and these CSCs are enriched in metastatic tumors and express genes that enhance self-renewal and prevent differentiation. We used the MDA-MB-231 breast cancer cell line (MD-231) and its variant brain metastasis (231-BR) isolated from a xenograft model to characterize signaling molecules uniquely active in brain metastatic cells and to identify drugs that may target these molecules. 231-BR cells expressed lower levels of Let-7 microRNA, which is known to suppress levels of H-ras and high mobility group AT hook 2 (HMGA2) proteins, compared to parental MD-231 cells. H-ras is associated with self-renewal, whereas HMGA2 blocks differentiation of CSCs and effects the epithelial-to-mesenchymal transformation (EMT). HMGA2 binds to the minor grove of DNA and alters the expression of target genes, which include EMT-associated and NF-κB-driven genes. Reduced levels of Let-7 correlated with elevated HMGA2 in 231-BR cells, as evidenced by quantitative RT-PCR and western blot analysis. Although both MD-231 and 231-BR cells displayed CSC phenotype based on their CD44 and CD24 cell marker expression pattern (CD44+/CD24-), 231-BR cells contained higher numbers of a unique subset of CSCs compared to MD-231 cells based on CFSE-1 dye retention assay. Given these unique characteristics of 231-BR cells, we hypothesized that netropsin, a Streptomyces-derived antimicrobial agent with anti-tumoral properties, capable of crossing the BBB, and that interferes with the binding of proteins to DNA's minor groove, might be effective in targeting HMGA2 over-expressing cells. 231-BR cells, but not the MD-231 cells, were highly sensitive to netropsin, as evidenced by BrdU cell proliferation assay. Given that NF-κB is a downstream effector of HMGA2, we also tested LC-1, a parthenolide derived compound developed by this laboratory as an inhibitor of NF-κB, for its effects on 231-BR cells. As predicted, the 231-BR cells were more sensitive to LC-1 than the MD-231 cells. In contrast, salinomycin, a recently discovered drug that targets CD44+/CD24- CSCs, was effective in reducing proliferation of both cell types. Based on these results, we propose netropsin or an NF-κB inhibitor as potential new therapies for the growing problem of breast cancer brain metastases. Further testing is currently underway to establish the efficacy of netropsin and LC-1 in addressing the two main issues with brain metastases; cancer cell specificity, particularly CSCs, and ability to cross the BBB.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1344. doi:10.1158/1538-7445.AM2011-1344