Epigenetic regulation of gene expression plays a fundamental role in tumor development and growth. Because of this, drugs that affect gene expression such as histone deacetylase inhibitors (HDACi) have been developed and used as an adjunct treatment to other standard anti-cancer drugs. Currently, three FDA-approved HDACi have shown promise in the treatment of specific lymphoid cancers by reducing tumor cell proliferation and inducing apoptosis. However, a significant downside to using HDACi is their lack of cell specificity as they can affect both tumor and normal cells. Furthermore, the approved HDACi affect both nuclear and cytoplasmic HDACs and thus can alter cytoplasmic protein acetylation and function in addition to gene expression. We hypothesized that treatment with these non-specific HDACi will result in increased normal lymphocyte death. To identify off-target effects, normal mature leukocyte populations harvested from wild-type mice were treated with different doses of two FDA-approved HDAC inhibitors, FK228 and pinobinostat, or vehicle control. After 24 or 48 hours of treatment, the cells were labeled with fluorochrome-conjugated antibodies and analyzed by flow cytometry to identify T lymphocyte and B lymphocyte subsets, and myeloid cells. Cell counts and viability were also determined by flow cytometry following addition of propidium iodide. Initial results indicate that FK228 has more off-target effects than pinobinostat and that the cytotoxic CD8+ T lymphocyte population was the most severely affected.
