Study by Electrospray Ionization Mass Spectrometry of the Complexation of Histone Deacetilase Inhibitors With Divalent Metal Ions

GASTÓN E. SILESS; CABRERA GABRIELA M.

Ginebra

Conferencia; 20th International Mass Spectrometry Conference; 2014

International Mass Spectrometry Foundation

IntroductionHistone deacetylase inhibitors (HDACIs) are a class of anticancerdrugs which act as epigenetic modi ers. The HDACfamily of enzymes consists of 18 known members divided intofour classes, three of which are metalloenzymes that require adivalent metal ion for substrate binding and catalysis. Differentclasses of HDACIs are known, some of which are hydroxamicacids that chelate active Zn2+ in a bidentate manner. Since themode of action of these compounds is related to its bindingcapacity of Zn2+, and they are known to chelate other metalssuch as Co, Cu or Ni, the goal of this study was the analysis byElectrospray of the complexes obtained from HDACIs in thepresence of Zn2+ and other metals and compare their differences.MethodsMass spectrometric analyses were performed using a BrukermicrOTOF-Q IImass spectrometer equipped with ESI.The analyte solutions of the HDACIs vorinostat (suberoylanilidehydroxamic acid, SAHA), octyl hydroxamic acid (OHA) andsodium valproate (VPA), at a concentration of 10 mM, wereprepared using methanol. The metal ion stock solutions (10 mM)were prepared from the metal salts of Zn (II), Ca (II), Co (II), Ni(II) and Cu (II) in the form of chlorides or sulphate (Cu).ResultsCharacteristic spectra were obtained in all the cases (the threeinhibitors with the  ve metals). [M + Me -H]+ and [2M + Me-H]+ were the most abundant metal adducts observed where Meis Zn (II), Co (II) and Ni (II) and M is SAHA or OHA.The spectra of the HDACIs with Ca2+ showed deprotonatedadducts with up to 3 ligands and other dicharged species with 3to 5 ligands. The base peak was different for the three inhibitors.The spectra in the presence of Cu2+ showed more ions, includingthose mentioned above, [3M + 2Cu -3H]+ and [M + Cu(I)]+ .VPA generally showed much more complex spectra, with a greatnumber of species, including adducts with water, chlorine and upto 5 ligands.All the ions were characterized by their accurate molecularweight, their characteristic isotopic pro les and MS/MS.ConclusionsAlthough some generalizations could be made on the type ofadducts observed in the MS spectra of SAHA, OHA or VPA in thepresence of different metal cations, the spectra were in generalcharacteristic, with the presence of some particular adduct orwith a different relative abundance among the formed species.Although the studied HDACIs have the same type of bioactivity,they exhibit a clearly different behavior in the presence of differentmetals which may help explain their dissimilar enzymaticspeci city. The activity of HDACIs has been previously related tothe formation of bidentate chelates, but in the present study otherspecies are also formed in high relative abundance.Novel AspectMetal complexation of HDACIs allows understanding of howthese compounds bind to metals and may contribute to explainthe different selectivity in their activity.