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.

Graphical Abstract

Keywords:

• HDAC
• phosphate
• phosphoramidate
• phosphorothiolate
• SAHA

Acknowledgements

The authors extend their gratitude for technical assistance to Dr. G. Helms and Dr. W. Hiscox at the WSU Center for NMR Spectroscopy, Dr. G. Munske at the WSU Molecular Biology and Genomics Core, and to both Dr. A. Berim and Dr. B. M Lange at the WSU Institute of Biological Chemistry for assistance with high resolution mass spectrometric analysis.

Disclosure statement

The authors declare no competing financial or personal interest.

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.

Additional information

Funding

This work was supported in part by the National Institutes of Health [1R21CA185884-02] (C.E.B.) and [1R01GM138592-01] (J.W.P.). Partial salary support for J.W.P. was supported by the United States Department of Agriculture National Institute of Food and Agriculture, Hatch umbrella project #1015621.