title: Probing label-free intracellular quantification of free peptide by MALDI-ToF mass spectrometry.
abstract: Cell-penetrating peptides are promising reagents for gene and drug delivery. They can efficiently traverse the plasma membrane and deliver various cargo materials ranging from genes to nanoparticles. The functional efficiency of cargo often depends on the completeness of intracellular peptide uptake, which can be measured, but its quantification remains largely inconclusive. Existing approaches rely on the use of radioactive and fluorescent labels or tags which allow colorimetric, fluorescent or spectrometric detection, but lack the ability to detect free peptide. Herein we describe a generic label- and tag-free method to measure the concentration of internalised peptide by matrix-assisted laser desorption/ionisation time of flight mass spectrometry. Quantification is preceded by two-dimensional chromatography and is performed at benign temperatures for the lysates of human dermal fibroblasts transfected with cell penetrating peptides in free form. Isotopically labelled peptides of the same structure are used as internal standards to enable accurate determination of concentration of the recovered free peptide. The method offers a minimalistic approach for intracellular quantification, which can be used as a correlative measure for fluorescence-based imaging methods.
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, UK.
authors.forename: Paulina D
authors.initials: PD
authors.lastname: Rakowska
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, UK.
authors.forename: Baptiste
authors.initials: B
authors.lastname: Lamarre
authors.affiliation: National Physical Laboratory, Hampton Road, Teddington TW11 0LW, UK; School of Physics and Astronomy, University of Edinburgh, EH9 3JZ, UK. Electronic address: max.ryadnov@npl.co.uk.
authors.forename: Maxim G
authors.initials: MG
authors.lastname: Ryadnov
mesh_terms: D000595:Amino Acid Sequence; D057846:Cell-Penetrating Peptides / Q000737:chemistry*; D003593:Cytoplasm / Q000378:metabolism; D016503:Drug Delivery Systems; D006801:Humans; D053758:Nanoparticles / Q000737:chemistry* / Q000627:therapeutic use; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
chemical_list: D057846:Cell-Penetrating Peptides
keywords: Cell penetrating peptides; Gene therapy; Mass spectrometry; Transfection