When using HDAC isotype-specific substrates, R306465 showed poor inhibition of deacetylation of an HDAC6-specific synthetic substrate, which was confirmed while analysing HDAC1–3 (H3) and HDAC6 substrates (Tubulin, Hsp90) in A2780 ovarian carcinoma cells. The gene discussed is HDAC9; the disease is ovarian carcinoma.