Abstract
2451
The inhibitors of histone deacetylase (HDAC) have potential as a new class of antitumor agents. So far, 18 HDACs have been identified and classified into 3 classes, Class I (HDACs 1, 2, 3, 8 and 11), Class II (HDACs 4, 5, 6, 7, 9 and 10) and Class III (SIRTs 1, 2, 3, 4, 5, 6 and 7). Although several classes of HDAC inhibitors such as short chain fatty acids, hydroxamic acids, cyclic peptides and benzamides have been reported, detailed analysis on isozyme selectivity has not been reported. MS-275 is an orally active benzamide compound with antitumor activity in vivo. In this study, we examined in vitro the isozyme spectrum of MS-275 in comparison with trichostatin A (TSA) and sodium butyrate (NaBu) by using recombinant human isozyme proteins, HDACs 1, 3, 4, 6, 8 and 10 and SIRT1. MS-275 strongly inhibited HDACs 1 and 3 (IC50values were 0.51 μM and 1.7 μM, respectively) compared with other HDACs (IC50values of HDACs 4, 6, 8 and 10 were >100 μM, >100 μM, 82.5 μM and 94.7 μM, respectively). On the other hand, TSA and NaBu showed different spectra in comparison to MS-275. TSA inhibited Class II isozymes as well as Class I isozymes at around nanomolar concentrations (IC50values of HDAC1, 3, 4, 6 and 10 were 4.99 nM, 5.21 nM, 27.6 nM, 16.4 nM and 24.3 nM, respectively), except HDAC8 (IC50 value was 486 nM) that needed a much higher concentration for the inhibition than the others. NaBu inhibited Class I enzymes including HDAC8 at sub-millimolar concentrations (IC50values of HDACs 1, 3 and 8 were 0.351 mM, 0.916 mM and 0.284 mM, respectively) and HDACs 4 and 10 at millimolar concentrations (IC50values were 3.10 mM and 3.14 mM, respectively), although much higher concentrations were needed to inhibit HDAC6 (IC50 value was 79.5 mM). The Class III enzyme SIRT1 was not inhibited by any of the 3 HDAC inhibitors. The finding that TSA, but neither NaBu nor MS-275, inhibited HDAC6 was consistent with the result showing that only TSA induced α-tubulin acetylation, for which inhibition of HDAC6 is needed. These results suggest that MS-275 is selective to structurally close subfamily members of Class I enzymes, HDAC1 and HDAC3, which are considered to be most important for tumor cell cycling and proliferation, whereas TSA and NaBu demonstrated broader spectra spread to Class I and Class II isozymes.
[Proc Amer Assoc Cancer Res, Volume 45, 2004]