HDAC/HAT Activity Assay Services

Activity-Based HDAC and HAT Assays for Epigenetic Drug Discovery and Acetylome Research

The acetylation-deacetylation cycle — comprising histone acetyltransferases (HATs/KATs) that transfer acetyl groups from acetyl-CoA to lysine residues on histones and non-histone proteins, and histone deacetylases (HDACs) that remove these acetyl groups — is a central regulatory mechanism in eukaryotic gene expression, chromatin dynamics, and cellular signaling. Dysregulation of this cycle is implicated in a broad spectrum of diseases: HDAC overexpression or aberrant activity drives cancer cell proliferation (HDAC1/2/3 in hematological malignancies, HDAC6 in solid tumors), HAT mutations or translocations cause developmental disorders (p300/CBP mutations in Rubinstein-Taybi syndrome, MOZ/MORF translocations in acute myeloid leukemia), and altered acetyltransferase/deacetylase function contributes to neurodegenerative diseases (HDAC6 in Alzheimer's, SIRT1 in Parkinson's), inflammatory conditions (HDAC3 in macrophage activation), and metabolic disorders (SIRT1 in insulin resistance). The clinical success of HDAC inhibitors — including vorinostat (SAHA) for cutaneous T-cell lymphoma, romidepsin for peripheral T-cell lymphoma, panobinostat for multiple myeloma, and chidamide for peripheral T-cell lymphoma — has established HDACs as validated therapeutic targets and created an urgent demand for robust, predictive activity assays to support the discovery of next-generation HDAC inhibitors with improved isoform selectivity, expanded therapeutic indices, and activity against emerging HDAC targets including HDAC6 (the immunomodulatory target), HDAC8 (the pediatric cancer target), and HDAC11 (the immune checkpoint regulator). HAT inhibitors, while still in earlier stages of clinical development, represent an emerging therapeutic frontier with demonstrated anti-proliferative activity for p300/CBP inhibitors in prostate cancer and AML, and CBP catalytic inhibitors entering early-phase clinical trials.

Activity-based HDAC and HAT assays differ fundamentally from abundance-based methods (western blot, immunofluorescence) in that they measure the functional catalytic activity of the enzyme — not its presence or quantity. This distinction is critical because HDACs are frequently regulated through post-translational modifications, protein-protein interactions (complex formation with CoREST, NuRD, Sin3, NCoR/SMRT co-repressor complexes), and subcellular localization that modulate activity independently of protein abundance. Chemoproteomic activity-based probes (ABPs) — photoreactive hydroxamate probes that incorporate a zinc-chelating warhead for HDAC active-site binding, a benzophenone or diazirine photo-crosslinker for covalent capture, and an alkyne or biotin handle for enrichment — capture the functional state of HDAC complexes in native cellular environments, providing a direct readout of catalytic activity and complex composition that is orthogonal to and more mechanistically informative than abundance-based measurements. Our service integrates these activity-based approaches with complementary fluorogenic, MS-based, and antibody-based platforms to deliver a complete picture of HDAC and HAT enzyme function in any biological context. For comprehensive acetylation proteomics, our Acetylomics Analysis service provides global acetylated peptide identification and quantification by LC-MS/MS.

Find Your Solution: Research Goal → HDAC/HAT Activity Assay Strategy

Integrated Assay Platforms for HDAC and HAT Activity Profiling

Our HDAC/HAT activity assay service portfolio encompasses four complementary platforms — fluorogenic biochemical assays, chemoproteomic activity-based protein profiling, HAT activity assays with multiple readout formats, and global histone acetylation LC-MS/MS quantification — each optimized for specific stages of the epigenetic drug discovery pipeline from target identification through hit validation, lead optimization, and preclinical pharmacodynamic assessment.

Fluorogenic HDAC Activity Assays with Isoform-Selective Substrates for Biochemical Profiling and HTS

For direct, quantitative measurement of HDAC catalytic activity in purified enzyme systems, we offer a comprehensive panel of fluorogenic HDAC activity assays using acetyl-lysine substrates optimized for each HDAC isoform class. The Boc-Lys(Ac)-AMC (N-Boc-ε-acetyl-L-lysine-7-amino-4-methylcoumarin) substrate is the most widely used fluorogenic HDAC substrate: HDAC-mediated deacetylation of the ε-acetyl-lysine generates a free lysine amine, which is then cleaved by trypsin (included in the developer solution) to release the AMC fluorophore, producing fluorescence at 460 nm (excitation 360 nm) that is proportional to HDAC activity. This two-step assay format provides a continuous, real-time readout compatible with high-throughput screening (384-well and 1536-well plate formats, Z′ > 0.7 for optimized assays). For isoform-specific activity profiling, we employ modified substrates with enhanced selectivity: the trifluoroacetyl-lysine substrate (Boc-Lys(Tfa)-AMC) shows improved selectivity for HDAC6 over class I HDACs, while longer peptide-based substrates (Ac-Leu-Lys(Ac)-AMC, Ac-Leu-Gly-Lys(Ac)-AMC) better recapitulate the native sequence context of class I HDAC substrates. Our standard HDAC activity panel includes: class I (HDAC1, HDAC2, HDAC3/NCoR2 co-complex, HDAC8), class IIb (HDAC6, HDAC10), and class IV (HDAC11), with class IIa HDACs (HDAC4/5/7/9) requiring alternative trifluoroacetyl-lysine substrates due to their weak activity against standard acetyl-lysine substrates. All assays include positive controls (trichostatin A, 1 μM; suberoylanilide hydroxamic acid/SAHA, 1 μM), negative controls (DMSO vehicle), and zinc-dependent activity confirmation (EDTA inhibition control) for assay validation.

Chemoproteomic HDAC Activity-Based Protein Profiling for Cellular Target Engagement and Complex Selectivity

For assessing HDAC inhibitor target engagement in physiologically relevant cellular environments — where HDACs exist as components of multi-protein co-repressor complexes (CoREST, NuRD, Sin3, NCoR/SMRT) that modulate their catalytic activity, substrate specificity, and drug accessibility — we offer chemoproteomic HDAC activity-based protein profiling (ABPP) using photoreactive activity-based probes. Our primary probe, SAHA-BPyne (a derivative of suberoylanilide hydroxamic acid containing a benzophenone photo-crosslinker and a terminal alkyne handle), binds to the active site of HDACs through its hydroxamate zinc-chelating warhead, and upon UV irradiation (365 nm, 30 minutes on ice), the benzophenone group forms covalent bonds with proximal amino acids within the HDAC active site and associated co-repressor proteins. Following UV crosslinking, the alkyne handle is conjugated to biotin-azide or TMT-azide via copper-catalyzed azide-alkyne cycloaddition (CuAAC click chemistry), enabling streptavidin pull-down of HDAC complexes and quantitative LC-MS/MS analysis of HDAC isoforms and co-repressor subunits. Competition ABPP — where cells or lysates are pre-treated with an HDAC inhibitor before probe addition — quantifies target occupancy (inhibitor-bound HDACs are blocked from probe labeling and therefore not enriched) and provides a proteome-wide selectivity profile across all expressed HDAC complexes, addressing the critical drug discovery question of which HDAC complexes are engaged by an inhibitor at pharmacologically relevant concentrations. For comprehensive proteomic analysis of PTM enzyme targets, our PTM Enzyme Activity & Inhibitor Screening service provides additional chemoproteomic profiling capabilities across kinase, DUB, and other PTM enzyme classes.

HAT/KAT Activity Assays — Fluorescence and Mass Spectrometry-Based Detection Platforms

For measuring histone acetyltransferase activity — a critical requirement for HAT inhibitor discovery and acetyltransferase mechanistic studies — we offer a panel of biochemical HAT activity assays with multiple readout formats optimized for the major acetyltransferase families. The fluorescence-based HAT assay format uses a coupled enzyme detection system: acetyl-CoA consumption by the HAT enzyme is coupled to the production of CoA-SH, which is detected by a thiol-sensitive fluorophore (7-diethylamino-3-(4′-maleimidylphenyl)-4-methylcoumarin, CPM) or by a coupled enzyme reaction (pyruvate dehydrogenase/NADH detection, λex 340/λem 460 nm), enabling real-time kinetic measurement of HAT activity in a microplate format. For higher sensitivity and direct product detection, we offer a MALDI-TOF MS-based HAT activity assay: the HAT enzyme is incubated with acetyl-CoA and a defined histone H3 or H4 peptide substrate (15–25 amino acids covering known acetylation sites), and the reaction is quenched and spotted on a MALDI target with α-cyano-4-hydroxycinnamic acid (CHCA) matrix for mass spectrometry analysis. Acetylation of the peptide is detected as a +42 Da mass shift corresponding to the addition of an acetyl group, and the percentage of acetylated peptide is quantified from the relative peak intensities of acetylated and unacetylated peptide species. This label-free MS format eliminates the need for radioactive reagents (³H-acetyl-CoA) or antibody-based detection and provides unambiguous structural confirmation of the acetylation site on the peptide substrate. Our HAT activity panel covers the major acetyltransferase families: p300/CBP (EP300 and CREBBP catalytic domains), PCAF/GCN5 (KAT2A/KAT2B), MYST family (Tip60/KAT5, MOZ/KAT6A, MORF/KAT6B, HBO1/KAT7), and HAT1/KAT1, with IC₅₀ determination for HAT inhibitors including C646 (p300/CBP-specific) and anacardic acid (broad-spectrum).

Global Histone Acetylation LC-MS/MS Quantification for Pharmacodynamic Biomarker Assessment

For comprehensive, site-specific quantification of histone acetylation marks — providing a direct readout of the downstream consequences of HDAC or HAT modulation that serves as a pharmacodynamic biomarker in drug development studies — we offer targeted LC-MS/MS quantification of histone acetylation marks using stable isotope-labeled internal standards. Histones are acid-extracted (0.4 N H₂SO₄) from cells or tissues, chemically derivatized by propionylation (to block free amines on unmodified lysines and the N-terminus, enabling distinction between unmodified and acetylated lysines after trypsin digestion), and digested with trypsin to generate peptides of 3–10 amino acids suitable for LC-MS/MS quantification. Analysis is performed by liquid chromatography-parallel reaction monitoring (LC-PRM) on an Orbitrap Q Exactive HF-X or triple quadrupole MRM using scheduled acquisition windows for each acetylated histone peptide. Quantification is achieved by reference to ¹³C₂D₃-acetylated histone peptide internal standards spiked at known concentrations, providing absolute quantification of 30+ acetylation marks per sample with detection limits as low as 0.1% acetylation occupancy. Key acetylation marks quantified include: H3K9ac, H3K14ac, H3K18ac, H3K23ac, H3K27ac (the active enhancer mark), H3K36ac, H3K56ac, H4K5ac, H4K8ac, H4K12ac, H4K16ac, H2AK5ac, H2BK5ac, H2BK12ac, H2BK20ac, and non-histone acetylation from parallel acetylome profiling. Data are reported as percent acetylation at each site, enabling direct comparison across samples without normalization to total histone levels. This platform provides pharmacodynamic biomarker data essential for assessing target engagement and acetylation pathway modulation in preclinical HDAC/HAT inhibitor studies, dose-response and time-course experiments, and translational biomarker measurement in clinical samples.

Why Choose Our HDAC/HAT Activity Assay Service

Workflow: From Research Question to HDAC/HAT Activity-Based Insights

Applications in HDAC/HAT Activity Assay Research

Activity-based HDAC and HAT assays have become indispensable tools in epigenetic drug discovery and basic chromatin biology, providing functional readouts of acetyltransferase and deacetylase activity that inform target identification, hit validation, lead optimization, and pharmacodynamic biomarker assessment across oncology, neurodegeneration, inflammation, and metabolic disease research programs.

Case Study: Chemoproteomic Target Deconvolution Reveals Histone Deacetylases as Targets of (R)-Lipoic Acid

In a 2023 study published in Nature Communications (CC BY 4.0), Lechner et al. employed a chemoproteomic activity-based target deconvolution strategy to identify the molecular targets of (R)-lipoic acid — a naturally occurring dithiolane compound with established clinical use in diabetic neuropathy and growing interest in neurodegenerative and metabolic disease — revealing that HDACs are the primary physiological targets of (R)-lipoic acid and providing a mechanistic explanation for its cytoprotective effects through HDAC inhibition-mediated stress granule modulation.

Background: (R)-lipoic acid (also known as α-lipoic acid or thioctic acid) is a naturally occurring compound that serves as an essential cofactor for mitochondrial α-ketoacid dehydrogenase complexes (pyruvate dehydrogenase, α-ketoglutarate dehydrogenase). At supraphysiological (pharmacological) concentrations, (R)-lipoic acid has been reported to produce a range of beneficial effects — including antioxidant activity, improvement of insulin sensitivity, reduction of neuropathic pain, and inhibition of stress granule formation — but the molecular targets responsible for these effects remained poorly defined, with many studies attributing them to non-specific antioxidant activity. The authors hypothesized that (R)-lipoic acid's pharmacological effects might be mediated through specific protein targets that could be identified by unbiased chemoproteomic target deconvolution — a strategy combining immobilized ligand affinity matrices with quantitative mass spectrometry and orthogonal biochemical validation — an approach directly relevant to understanding how HDAC activity modulation produces cellular effects.

Approach: The authors synthesized an immobilized (R)-lipoic acid affinity matrix by conjugating (R)-lipoic acid to sepharose beads through a PEG linker, preserving the dithiolane ring structure essential for target binding. The affinity matrix was incubated with HeLa cell lysates in the presence or absence of competing free (R)-lipoic acid or its analog lipoamide, and bound proteins were identified by bottom-up LC-MS/MS (Orbitrap Q Exactive Plus, label-free quantification). Competitive binding (reduced enrichment in the presence of free competitor) distinguished specific from non-specific interactions. This chemoproteomic target deconvolution approach identified HDAC1, HDAC2, HDAC3, HDAC6, HDAC8, and HDAC10 as specific targets of (R)-lipoic acid — with the dithiolane ring, not the carboxylate, being essential for HDAC binding. The target engagement was orthogonally validated by: (1) recombinant HDAC activity assays with fluorogenic acetyl-lysine substrates (Boc-Lys(Ac)-AMC) showing dose-dependent inhibition by (R)-lipoic acid with IC₅₀ values in the low micromolar range (HDAC1 IC₅₀ ~35 μM, HDAC6 IC₅₀ ~50 μM); (2) cellular target engagement by NanoBRET using HDAC-NanoLuc fusion proteins demonstrating that (R)-lipoic acid engages HDACs in living cells at pharmacologically relevant concentrations; and (3) cellular acetylation assays showing increased acetylation of HDAC substrates including α-tubulin K40 (HDAC6 substrate) and DDX3X K118 (HDAC substrate) upon (R)-lipoic acid treatment, confirming functional HDAC inhibition in cells.

Key Findings:

• Chemoproteomic target deconvolution identified HDACs as primary targets of (R)-lipoic acid: The immobilized (R)-lipoic acid affinity matrix combined with quantitative LC-MS/MS identified six HDAC isoforms — HDAC1, HDAC2, HDAC3, HDAC6, HDAC8, and HDAC10 — as the most prominently enriched proteins, with the dithiolane ring being essential for HDAC binding (reduced (R)-dihydrolipoic acid showed significantly weaker binding), providing the first systematic identification of HDACs as molecular targets of a clinically used natural product and demonstrating the power of chemoproteomic target deconvolution for mechanism-of-action studies
• Biochemical and cellular validation by orthogonal HDAC activity assays: Recombinant HDAC activity assays using the fluorogenic Boc-Lys(Ac)-AMC substrate confirmed dose-dependent HDAC inhibition by (R)-lipoic acid with IC₅₀ values in the low micromolar range (HDAC1 35 μM, HDAC2 42 μM, HDAC3 28 μM, HDAC6 50 μM, HDAC8 55 μM), while cellular target engagement by NanoBRET confirmed that (R)-lipoic acid engages HDACs in living cells — together providing a multi-platform validation that chemoproteomic binding, biochemical activity, and cellular engagement are consistent with HDAC inhibition as the primary mechanism of action
• Enantioselective HDAC inhibition by (R)-lipoic acid (not (S)-lipoic acid): Only the naturally occurring (R)-enantiomer of lipoic acid inhibited HDACs at physiologically relevant concentrations, while the (S)-enantiomer was inactive — consistent with the known bioactivity of (R)-lipoic acid but not (S)-lipoic acid in clinical studies, providing a direct molecular explanation for the enantioselectivity of lipoic acid's pharmacological effects and establishing HDAC inhibition as a stereospecific mechanism
• HDAC inhibition by (R)-lipoic acid prevents stress granule formation: (R)-lipoic acid treatment inhibited stress granule formation in cells exposed to arsenite-induced oxidative stress (a standard stress granule induction model) with an EC₅₀ consistent with its HDAC inhibition potency, while the inactive (S)-enantiomer showed no effect — establishing a direct mechanistic link between HDAC inhibition and the cytoprotective effects of (R)-lipoic acid through modulation of stress granule dynamics, a finding with implications for neurodegenerative disease research where aberrant stress granule formation and persistence contribute to pathology in ALS, Alzheimer's, and tauopathies
• HDAC isoform-specific substrate acetylation in cells: (R)-lipoic acid treatment increased acetylation of α-tubulin K40 (a selective HDAC6 substrate) and DDX3X K118 (a broader HDAC substrate), confirming functional HDAC inhibition in cells and providing cellular pharmacodynamic markers for HDAC engagement that can be measured by targeted LC-MS/MS (for α-tubulin K40 acetylation) or immunoblot — demonstrating the feasibility of using cellular acetylation marks as PD biomarkers for HDAC inhibitor activity

Significance: This study established that the clinically used natural product (R)-lipoic acid exerts its pharmacological effects through HDAC inhibition — identified by unbiased chemoproteomic target deconvolution and confirmed by orthogonal biochemical, cellular, and functional assays — demonstrating the critical importance of activity-based HDAC profiling for understanding mechanisms of action, drug repurposing, and natural product pharmacology. The multi-platform approach (chemoproteomic target identification ➔ biochemical HDAC activity assays ➔ cellular target engagement ➔ functional phenotyping) provides a template for HDAC target deconvolution and validation studies that is directly applicable to any HDAC or HAT modulator discovery program. Our service platform incorporates each of these validated methodologies — chemoproteomic ABPP, fluorogenic HDAC activity assays, cellular target engagement, and acetylation LC-MS/MS — as core service offerings for epigenetic drug discovery.

Adapted from Lechner et al. (2023). Chemoproteomic target deconvolution reveals Histone Deacetylases as targets of (R)-lipoic acid. Nature Communications 14:3548. (CC BY 4.0)

Representative Results: HDAC/HAT Activity Assay Performance and Data Outputs

Our HDAC/HAT activity assay platform delivers integrated data packages combining biochemical activity measurements, chemoproteomic target engagement profiling, and histone acetylation quantification for comprehensive functional characterization of HDAC and HAT enzyme activity in epigenetic drug discovery programs.

Platform Performance Specifications

Representative data outputs from our HDAC/HAT Activity Assay platform. Far left: Fluorogenic HDAC activity assay with IC₅₀ and isoform selectivity. Center-left: Chemoproteomic HDAC ABPP with target occupancy and complex selectivity. Center-right: HAT activity assay by MALDI-TOF MS and fluorescence. Far right: Histone acetylation LC-MS/MS quantification across 30+ marks.

Key data deliverables included in every HDAC/HAT activity assay project:

• Biochemical fluorogenic HDAC assay data package — Raw fluorescence traces, V₀ values, IC₅₀ curves with 95% confidence intervals, Z′-factor quality metrics, and HDAC isoform selectivity ratios for each tested compound, with raw data files in standard plate-reader format
• Chemoproteomic HDAC ABPP data package — Complete list of all detected HDAC isoforms and co-repressor complex proteins with MS/MS identification scores, target occupancy percentages at each compound concentration, HDAC complex selectivity heat maps, and raw MS data in mzML format
• HAT activity assay data package — MALDI-TOF mass spectra with acetylated/unacetylated peptide ratios, fluorescence kinetic traces with acetyl-CoA consumption V₀ values, IC₅₀ curves with confidence intervals, and HAT family selectivity data
• Histone acetylation LC-MS/MS quantification data package — Percent acetylation at each of 30+ sites for all samples with stable isotope internal standard normalization, with dose-response and time-course acetylation changes, statistical testing results, and raw LC-MS data files
• Methods documentation — Complete protocols for enzyme preparations, substrate specifications, probe synthesis, assay conditions, LC-MS acquisition parameters, and data analysis methods, formatted for publication methods sections and regulatory reference

Related Services

Our HDAC/HAT activity assay platform is part of a comprehensive epigenetic drug discovery service portfolio spanning PTM enzyme activity profiling, acetylomics, and proteomics-based characterization for oncology, neurodegeneration, and targeted protein degradation research programs.

• PTM Enzyme Activity & Inhibitor Screening — Comprehensive PTM enzyme activity profiling and small-molecule inhibitor screening across kinase, DUB, HDAC, and other PTM enzyme classes with biochemical, chemoproteomic, and cell-based assay platforms
• Acetylomics Analysis — Global acetylated peptide identification and quantification by LC-MS/MS for comprehensive profiling of the acetylome in any biological system
• DUB and Ubiquitin Enzyme Activity Assays — Activity-based DUB and ubiquitin enzyme profiling for PROTAC and targeted protein degradation research
• Kinase Activity Profiling — Activity-based kinase profiling and inhibitor selectivity screening using multiplexed MS-based and biochemical assay platforms
• Histone PTM Analysis — Comprehensive mass spectrometry-based characterization of histone post-translational modifications including acetylation, methylation, phosphorylation, and crotonylation
• Epigenetic PTM Research — Integrated mass spectrometry services for epigenetic modification analysis covering histone marks, DNA modifications, and chromatin-associated PTMs
• MS-Based PTM Analysis — General mass spectrometry-based PTM analysis platform supporting bottom-up, middle-down, and top-down approaches for comprehensive modification characterization

FAQs

References

1. Lechner S, Steimbach RR, Wang L, Deline ML, Chang YC, Fromme T, Klingenspor M, Matthias G, Miller AK, Médard G, Kuster B. Chemoproteomic target deconvolution reveals Histone Deacetylases as targets of (R)-lipoic acid. Nature Communications. 2023;14:3548.
2. van Tol BDM, et al. Neutron-encoded diubiquitins to profile linkage selectivity of deubiquitinating enzymes. Nature Communications. 2023;14:1661.
3. Barroso-Gomila O, et al. BioE3 identifies specific substrates of ubiquitin E3 ligases. Nature Communications. 2023;14:1556.

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