Purpose: A group of histone deacetylase inhibitors has been shown to be effective in suppressing the growth of a variety of transformed cell lines in vitro and in vivo. The effects of two of these agents, suberoylanilide hydroxamic acid (SAHA) and suberoyl-3-aminopyridineamide hydroxamic acid (pyroxamide), were investigated for their growth-suppressive effects on rhabdomyosarcoma (RMS) cells.

Experimental Design and Results: Dose-response experiments of two RMS cell lines, RD (embryonal) and RH30B (alveolar), were performed with SAHA (0.25–3.0 μm) and pyroxamide (1.25–20.0 μm). Both agents caused a dose-dependent decrease in viable cell number and an increase in percentage of dead cells over time. Exposure of the RMS cells to SAHA and pyroxamide resulted in an accumulation of acetylated histones with increasing doses by Western blot analysis. Additionally, there was an induction of p21/WAF1 at 15 and 24 h when the cells were cultured with SAHA (2.0 μm) or pyroxamide (20.0 μm), concentrations that were tested because they successfully induced inhibition of cell growth and initiated cell death in both RMS cell lines. An increase in nuclei with hypodiploid or sub-G₁ fraction was found by flow cytometry with increasing doses of both SAHA (0.25–3.0 μm) and pyroxamide (1.25–20.0 μm) over time. This finding is consistent with DNA fragmentation and cell death by apoptosis.

Conclusions: SAHA and pyroxamide induce growth suppression and cell death in human RMS in vitro. Accumulation of acetylated histones and induction of p21/WAF1 expression are observed in cells exposed to either agent.