Phosphorus containing analogues of SAHA as inhibitors of HDACs

Abstract

Histone deacetylases (HDACs) are a family of enzymes responsible for regulating DNA transcription by modulating its binding to histone proteins. HDACs are overexpressed in several types of cancers and are recognised as drug targets. Vorinostat, or suberanilohydroxamic acid (SAHA), is an histone deacetylase (HDAC) inhibitor with a hydroxamic acid as a zinc-binding group (ZBG), and it has been FDA approved for the treatment of T-cell lymphoma. In this work, phosphorus-based SAHA analogues were synthesised to assess their zinc-binding effectiveness compared to the hydroxamic acid of SAHA. Specifically, we examined phosphate, phosphoramidate and phosphorothiolate groups as isosteres of the canonical hydroxamic acid motif of conventional HDAC inhibitors. The compounds were screened for binding to HDAC enzymes from HeLa cell lysate. The most potent derivatives were then screened against HDAC3 and HDAC8 isoforms. HDAC inhibition assays demonstrated that these phosphorus-based SAHA analogs exhibited slow binding to HDACs but with greater potency than phosphonate SAHA analogs examined previously. All compounds inhibited HDACs, the most potent having an IC₅₀ of 50 µM.

Keywords: HDAC; SAHA; phosphate; phosphoramidate; phosphorothiolate.

Graphical abstract

Figure 1.

Phosphorus containing SAHA analogues discovered by Kapustin et al. IC₅₀ values reported for Hela cell lysate and 10 h incubation time.

Figure 2.

Time-dependent inhibition of HDACs from HeLa cell lysates, HDAC8 and HDAC3 with inhibitor 2 (100 μM).

Scheme 1.

Synthesis of HDAC inhibitors 1–7. a) HBTU, DIPEA, aniline, DMF b) 4 N HCl in dioxane c) dibenzyl phosphite, BrCCl₃, Et₃N, CH₃CN d) H₂, Pd/C, MeOH, KHCO₃ e) 33% HBr in AcOH f) DCC, DMAP, aniline, DMF g) KOAc, DMF, 70 °C h) NaOH, MeOH i) NaOH, H₂O j) imidazole, TBDMS-Cl, DCM k) HBTU, DIPEA, aniline, DMF l) 4 N HCl in dioxane m) Dibenzyl N,N-diisopropylphosphoramidite, 5-(Ethylthio)-1H-tetrazole, ACN, tert-butyl hydrogen peroxide n) H₂, Pd/C, MeOH, KHCO₃ o) Bis(2-cyanoethyl)-N,N-diisopropylphosphoramidite, Sulphur, ACN p) KOH, MeOH.