Simultaneous Measurement of HDAC1 and HDAC6 Activity in HeLa Cells Using UHPLC-MS

Summary

The present method serves to identify isoform-specific inhibitors of histone deacetylases (HDAC) in HeLa cells by the UHPLC-MS analysis of multiple substrates. This is an antibody-free method developed to reflect HDAC1 and HDAC6 activity in the living cell environment, in contrast to single-isoform cell-free assays.

Abstract

The search for new histone deacetylase (HDAC) inhibitors is of increasing interest in drug discovery. Isoform selectivity has been in the spotlight since the approval of romidepsin, a class I HDAC inhibitor for cancer therapy, and the clinical investigation of HDAC6-specific inhibitors for multiple myeloma. The present method is used to determine the inhibitory activity of test compounds on HDAC1 and HDAC6 in cells. The isoform activity is measured using the ultra-high-performance liquid chromatography – mass spectrometry (UHPLC-MS) analysis of specific substrates incubated with treated and untreated HeLa cells. The method has the advantage of reflecting the endogenous HDAC activity within the cell environment, in contrast to cell-free biochemical assays conducted on isolated isoforms. Moreover, because it is based on the quantification of synthetic substrates, the method does not require the antibody recognition of endogenous acetylated proteins. It is easily adaptable to several cell lines and an automated process. The method has already proved useful in finding HDAC6-selective compounds in neuroblasts. Representative results are shown here with the standard HDAC inhibitors trichostatin A (non-specific), MS275 (HDAC1-specific), and tubastatin A (HDAC6-specific) using HeLa cells.

Introduction

HDACs belong to a family of enzymes able to deacetylate histones within the chromatin structure. They also have other protein substrates in the cytosol and are located in various cell compartments. A total of 18 HDAC isoforms have been identified so far and have been related to several cell mechanisms, including the regulation of transcription factors and gene expression, as well as cell signaling and transport^{1,2,3,4,5,6,7}. HDAC catalyti....

Protocol

1. Cell Culture

NOTE: The following steps are performed in a standard tissue culture hood. Familiarity with sterile technique is expected.

1. Culture HeLa cells to 80% confluency in a T75 cell culture flask in MEM supplemented with 10% fetal bovine serum, penicillin G (100 U/mL), and streptomycin (100 mg/mL).
   NOTE: Cell culture, treatment, and lysis steps are conducted under laminar flow, with cell incubation steps at 37 °C performed in a humidified atmosphere of 5% CO₂ under sterile conditions.
2. Wash the cells twice with 5 mL of DPBS, aspirate the DPBS, and add 1 mL of cell dissociation reagent. Incubate a....

Results

To demonstrate the application of the method to identifying non-selective and selective inhibitors for HDAC1 (class I) and HDAC6 (class IIb), HeLa cells were treated with known standard compounds: trichostatin A (non-selective between HDAC1 and HDAC6)¹⁸, MS275 (HDAC1-selective inhibitor)¹⁹, and tubastatin A (HDAC6-selective inhibitor)²⁰. By using the present method (Figure 1), IC₅₀

Discussion

HDAC inhibition is a hot topic in drug discovery, with a current focus on HDAC6-selective inhibitors for cancer therapy²¹. HDAC selectivity is usually assessed by a series of high-throughput, cell-free assays, which intend to determine the inhibitory potency towards individual HDAC isoforms²¹. However, the selectivity of an inhibitor must be additionally confirmed in living cells by evaluating the acetylation status of endogenous protein substrates, such as histones (for cl.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
BATCP	Sigma-Aldrich	B4061
MAL	Sigma-Aldrich	SCP0168	Synonym: BOC-Ac-Lys-AMC
MOCPAC	Sigma-Aldrich	M2195
MS275	Sigma-Aldrich	EPS002
Trichostatin A	Sigma-Aldrich	T8552
Tubastatin A	Sigma-Aldrich	SML0044
Acetonitrile, HPLC grade	Fisher Scientific	10660131
Formic acid, LC/MS grade	Fisher Scientific	10596814
H2O, HPLC grade			distilled H2O filtered through a Milli-Q purification system
HeLa cells	ATCC	ATCC CRM-CCL-2
Cell dissociation reagent TrypLE Express	ThermoFisher Scientific	12604013
DMSO, cell culture grade	Applichem	146463
DPBS	ThermoFisher Scientific	14190144
Fetal bovine serum	Biowest	S1810
MEM	ThermoFisher Scientific	22561021
Penicillin-Streptomycin	Bioconcept	4-01F00-H
10x RIPA buffer	Abcam	ab156034
SigmaFast protease inhibitor tablets	Sigma-Aldrich	S8820
96-well plates, sterile, flat-bottom, tissue culture treated Corning	VWR	29442-058
96-well plates, non-sterile, V-bottom Corning	VWR	29442-404	used in the centrifugation step
96-well plate, conical bottom, Nunc	ThermoFisher Scientific	249944	compatible with the Acquity UHPLC system
T75 cell culture flasks Corning	Sigma-Aldrich	CLS430641
Peelable heat sealing foil	Waters	186002789
Acquity UPLC system	Waters
Eppendorf Centrifuge 5810 R	Fisher Scientific	05-413-323
Integration software: MassLynx V4.1	Waters		Catalog number not available
Combi thermo-sealer SP-0669/240	Waters		Catalog number not available
Quattro micro API Tandem Quadrupole System	Waters		Catalog number not available