HDAC1 and colorectal carcinoma: Furthermore, regarding a dual HDAC6 inhibitor that contains an Hsp90 inhibitor, a compound identified as compound 12 (dual HDAC6 and Hsp90) displayed inhibitory effects toward the HDAC6 isoform and a 246-fold higher selectivity for HDAC6 over HDAC1, 3, and 8 isoforms and was endowed with significant cytotoxic effects against CRC cell lines [173] (Table 3).