Dual-Mode HDAC Prodrug for Covalent Modification and Subsequent Inhibitor Release

Abstract

Histone deacetylase inhibitors (HDACi) target abnormal epigenetic states associated with a variety of pathologies, including cancer. Here, the development of a prodrug of the canonical broad-spectrum HDACi suberoylanilide hydroxamic acid (SAHA) is described. Although hydroxamic acids are utilized universally in the development of metalloenzyme inhibitors, they are considered to be poor pharmacophores with reduced activity in vivo. We developed a prodrug of SAHA by appending a promoiety, sensitive to thiols, to the hydroxamic acid warhead (termed SAHA-TAP). After incubation of SAHA-TAP with an HDAC, the thiol of a conserved HDAC cysteine residue becomes covalently tagged with the promoiety, initiating a cascade reaction that leads to the release of SAHA. Mass spectrometry and enzyme kinetics experiments validate that the cysteine residue is covalently appended with the TAP promoiety. SAHA-TAP demonstrates cytotoxicity activity against various cancer cell lines. This strategy represents an original prodrug design with a dual mode of action for HDAC inhibition.

Epigenetic polypharmacology: from combination therapy to multitargeted drugs

“…These molecules should not be considered as pro-drugs, which are those designed to correct the pharmacokinetic and pharmacodynamic profiles of a valuable lead. For example, the hydroxamic acid functionality of the approved histone deacetylase inhibitor (HDACi) vorinostat (also known as SAHA, suberoylanilide hydroxamic acid, 1 ) was covalently bound to a thiol-sensitive group in the design of a dual-mode HDAC prodrug (SAHA-TAP, 2 ) in order to facilitate the delivery of the drug, which itself has poor pharmacokinetics [ 7 ]. Selective activation by glutathione 3 , which is present at higher concentrations in cancer cells (1 mM) than in the intracellular compartment (1 μM), would release the hydroxamate of 1 upon conjugate addition to the quinone giving 4 (Scheme 1 ).…”

How do we improve histone deacetylase inhibitor drug discovery?

“…Many factors are responsible for this nonoptimal response, such as side effects, fast elimination, poor tissue penetration caused by the metabolically labile and polar hydroxamic acid group. Several prodrug approaches, using carbamates [19], quinonebased moieties [20] and boron [21]-masked hydroxamic acid have been proposed. However, this approach is still in its infancy, and many studies are needed to demonstrate its proof of concept in clinical studies.…”

Targeting Non-Catalytic Cysteine Residues Through Structure-Guided Drug Discovery

“…The HDAC inhibitor suberoylanilide hydroxamic acid (SAHA) was modified to include a covalent moiety that reacted with a conserved cysteine 5.6A from the enzyme active site [34]. This dual-action inhibitor did not achieve isoform selectivity or increased potency, but represented an interesting example of using structure-guided design and cysteine modification to develop a novel drug-targeting scheme.…”