Abstract #2051

Background: Excess histone deacetylase (HDAC) activity can induce global hypoacetylation of histone and non-histone protein substrates, altering gene expression patterns and cell behavior potentially associated with malignant transformation. However, HDAC expression and protein acetylation have not previously been studied in the context of breast cancer progression.
 Materials and Methods: We performed immunohistochemistry (IHC) to assess expression levels of acetylated histone H4 (acH4), acH4K12, acTubulin, HDAC1, HDAC2 and HDAC6 in formalin fixed paraffin embedded sections with synchronous normal epithelium (N), ductal carcinoma in situ (DCIS), and invasive ductal carcinoma (IDC) components from 58 archived samples at UCSF. Staining was assessed on the basis of H-score, defined as the sum of the intensity of staining (0-3) multiplied by % of stained cells for each intensity (score range 0-300). H-score differences between groups were tested for significance using either the Mann-Whitney test or the Wilcoxon signed rank test for paired samples.
 Results: From N to DCIS, there was a marked reduction in histone acetylation (acH4, acH4K12). Tubulin acetylation, a marker of non-histone protein acetylation, showed a smaller reduction. Expression of all three HDACs was also reduced, but to a lesser extent than histone acetylation. Moreover, from DCIS to IDC, the same pattern of changes in acetylation and HDAC expression was seen, although these differences were of smaller magnitude than between N and DCIS. All markers were significantly different between N and DCIS (all p<0.0001) and between DCIS and IDC (all p<0.03). ER-negative tumors exhibited greater changes from N to DCIS than did ER-positive tumors, particularly for acH4 and HDAC1 (p=0.05 and 0.0001 respectively). High-grade invasive tumors showed more significant changes from N to DCIS than low/intermediate grade tumors for acH4, acH4K12, acTubulin, and HDAC1 (p=0.0009, 0.006, 0.05, and <0.0001 respectively). The change in protein acetylation and HDAC expression with cancer progression did not differ by HER2 status or age (≤50 or >50).

Conclusions: Overall there was a pattern of hypoacetylation associated with malignant progression, with normal epithelium exhibiting the highest acH4, acH4K12, and acTubulin levels and IDC exhibiting the lowest levels. Paradoxically, expression of HDAC 1, 2 and 6 was not increased; thus, our data support that histone hypoacetylation is not regulated by HDAC expression but rather by modulation of HDAC activity. Outcome studies and clinical trials are needed to assess the prognostic significance of these findings and to determine how effectively HDAC inhibitors could reverse the hypoacetylation observed in progression from N to DCIS and IDC.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2051.

Thirty-first San Antonio Breast Cancer Symposium Dec 10-14, 2008; San Antonio, TX