Previously, we developed novel amide-bearing hydroxamic acid derivatives as class-selective HDAC inhibitors termed SL142 and SL325 (Fig. 1A) and reported that these small molecules show more significant HDAC1, HDAC4 and HDAC6 inhibitory activity in human prostate cancer cells LNCaP than SAHA [17]. This evidence concerns the gene HDAC6 and prostate cancer.