R-306465 is a sulfonyl-derivative patented by Janssen Pharmaceutica N.V. as class I histone deacetylase inhibitor with broad-spectrum antitumoral activity against solid and hematological malignancies. R-306465 rapidly induced histone 3 (H3) acetylation and strongly upregulated expression of p21waf1,cip1, a downstream component of HDAC1 signaling, in A2780 ovarian carcinoma cells. R306465 showed class I HDAC isotype selectivity as evidenced by poor inhibition of HDAC6 (class IIb) confirmed by the absence of downregulation of Hsp90 chaperone c-RAF protein expression and tubulin acetylation. R306465 potently inhibited cell proliferation of all main solid tumor indications, including ovarian, lung, colon, breast and prostate cancer cell lines. Hematological cell lines, including acute lymphoblastic leukemia, acute myeloid leukemia, chronic lymphoblastic leukemia, chronic myeloid leukemia, lymphoma, and myeloma, were potently inhibited at a similar concentration range. R306465 induced apoptosis and inhibited angiogenesis in cell-based assays and had potent oral in vivo antitumoral activity in xenograft models.