Inflammatory breast cancer (IBC) comprises only 2.0% of all breast cancer cases; however it accounts for 8.0% of breast cancer-specific deaths. IBC is highly aggressive, appears at a younger age, and is more difficult to treat than the common forms of breast cancer. By the time the disease is diagnosed, IBC is usually stage 3 and has already metastasized to neighboring lymphatics. Though many tumors are p53 wild type and/or Her2 positive, the median overall survival among women with IBC is less than 4 years even with aggressive multimodal therapy. To develop IBC-specific therapies, we have compared the effects of two hydroxamic acid histone deacetylase (HDAC) inhibitors, Trichostatin A (TSA) and CG-1521 on the biology of the triple negative SUM149PT IBC cell line. In these cells, CG-1521 and TSA induce dose (0–10 µM) and time dependent (0–96 h) increases in the proportion of cells undergoing cell cycle arrest and cell death, in the presence or absence of 17β-estradiol. To identify the genomic targets of CG-1521, we have performed concurrent microarray analyses of mRNA and miRNA expression followed by qPCR validation. In SUM149PT cells, CG-1521 modulates the expression of approximately 935 transcripts: 341 of these transcripts are up-regulated and 594 are down-regulated after 48h of treatment. Gene ontology analysis demonstrates that many of the down-regulated mRNA transcripts encode proteins that are associated with the spindle assembly checkpoint, chromosome segregation and microtubule based processes including KIF4, PRC1, AURKB and KIF23 (MKLP-1). Strikingly, many genes in these ontologies are potentially targeted by a small number of miRNAs (miR-22, miR-1207-5p & miR-494) which are significantly up-regulated by CG-1521, suggesting that the ability of CG-1521 to down-regulate the transcripts associated with spindle formation and cytokinesis may be significantly modulated by miRNA expression. Immunofluorescence microscopy demonstrates that treatment of SUM149PT cells with CG-1521 results in the appearance of elongated midzone structures visualized by phalloidin staining, similar to the phenotype seen by others after siRNA-mediated knockdown of KIF4 in HeLa cells. These data suggest that CG-1521 affects the central mitotic spindle formation, disrupts furrow formation and abscission, arresting the cells in cytokinesis ultimately leading to cell death. Whether these effects are solely mediated through transcriptional mechanisms or whether CG-1521 also directly affects the activity of these proteins through acetylation remains to be determined. Nevertheless, the data show that histone deacetylase inhibitors induce cell death in IBC cells, and suggest that these small molecules may be useful addition to the armamentarium as adjuvants for the treatment of IBC.
Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P3-10-02.