| Inflammatory breast cancer (IBC) is a rare and particularly lethal form of breast cancer. Despite aggressive therapeutic approaches, the 5-year survival rate is only 34%. As this disease is severely understudied, we have investigated the therapeutic potential of the novel hydroxamic acid-derived histone deacetylase inhibitor (HDACi), CG-1521 in comparison to a structurally similar compound, Trichostatin A (TSA) in two IBC cell lines: SUM149PT and SUM190PT. In these cells, CG-1521 and TSA induce dose- and time-dependent induction of cell cycle arrest and apoptosis regardless of the presence of 17beta-estradiol (E 2). Interestingly, the cell lines have considerably different sensitivities to these treatments despite their common disease origin.;To identify the genomic targets of CG-1521, microarray analysis of mRNA and miRNAs followed by qPCR validation was performed. CG-1521 modulates the expression of 876 mRNAs (316 up, 560 down) in SUM149PT cells and 1227 mRNAs (651 up, 576 down) in SUM190PT cells. Only 9% of the genes are commonly modulated in both cell lines, indicating that the expression of different cellular targets between the two cell lines significantly influences their response to CG-1521. Analysis of steady state miRNA levels demonstrates that CG-1521 modulates the expression of 63 miRNAs (35 up, 28 down) in SUM149PT cells and 35 miRNAs (14 up, 21 down) in SUM190PT cells. Gene ontology analysis demonstrates that CG-1521 affects the expression of numerous mRNA transcripts which encode proteins associated with the spindle assembly checkpoint, chromosome segregation and microtubule based processes in both cell lines, while also having cell-type specific effects on lipid biosynthesis, response to DNA damage and cell death. Specifically in SUM149PT cells, these mRNAs appear to modulate the metaphase transition, induce mitotic catastrophe, and cell death by destabilizing the transcripts encoding the proteins required for proper mitotic spindle formation. In SUM190PT cells, the HDAC inhibitors induce interphase (G 0/G1) cell death through the direct modulation of transcripts associated with cell death.;The appearance of elongated midzone structures evidenced by phalloidin staining, suggest that CG-1521 affects the mitotic spindle and prevents abscission during cytokinesis. In contrast, TSA treatment causes an increase in cell size, while both treatments increase acetylated-&agr;-tubulin. The expression and localization of key proteins involved in the spindle assembly checkpoint and cytokinesis were evaluated in SUM149PT cells after treatment with CG-1521 and TSA. Overall, TSA is more potent than CG-1521 in SUM149PT cells, especially with respect to KIF4, Aurora B, PLK-1 and Nek2 levels, causing significant decreases in these proteins. However, alterations in the localization or staining intensity of these proteins was not detected using confocal microscopy. Overall, CG-1521 is an attractive novel chemotherapeutic and may be useful for the treatment of IBC either as a monotherapy on in combination with other therapies including irradiation, cytotoxic and targeted chemotherapy. |
