title: Lipid bilayer crossing--the gate of symmetry. Water-soluble phenylproline-based blood-brain barrier shuttles.
abstract: Drug delivery to the brain can be achieved by various means, including blood-brain barrier (BBB) disruption, neurosurgical-based approaches, and molecular design. Recently, passive diffusion BBB shuttles have been developed to transport low-molecular-weight drug candidates to the brain which would not be able to cross unaided. The low water solubility of these BBB shuttles has, however, prevented them from becoming a mainstream tool to deliver cargos across membranes. Here, we describe the design, synthesis, physicochemical characterization, and BBB-transport properties of phenylproline tetrapeptides, (PhPro)4, an improved class of BBB shuttles that operates via passive diffusion. These PhPro-based BBB shuttles showed 3 orders of magnitude improvement in water solubility compared to the gold-standard (N-MePhe)4, while retaining very high transport values. Transport capacity was confirmed when two therapeutically relevant cargos, nipecotic acid and l-3,4-dihydroxyphenylalanine (i.e., l-DOPA), were attached to the shuttle. Additionally, we used the unique chiral and conformationally restricted character of the (PhPro)4 shuttle to probe its chiral interactions with the lipid bilayer of the BBB. We studied the transport properties of 16 (PhPro)4 stereoisomers using the parallel artificial membrane permeability assay and looked at differences in secondary structure. Most stereoisomers displayed excellent transport values, yet this study also revealed pairs of enantiomers with high enantiomeric discrimination and different secondary structure, where one enantiomer maintained its high transport values while the other had significantly lower values, thereby confirming that stereochemistry plays a significant role in passive diffusion. This could open the door to the design of chiral and membrane-specific shuttles with potential applications in cell labeling and oncology.
authors.affiliation: †Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona E-08028, Spain.
authors.forename: Pol
authors.initials: P
authors.lastname: Arranz-Gibert
authors.affiliation: †Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona E-08028, Spain.
authors.forename: Bernat
authors.initials: B
authors.lastname: Guixer
authors.affiliation: †Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona E-08028, Spain.|‡Department of Chemistry, University of Isfahan, Isfahan 81746-73441, Iran.
authors.forename: Morteza
authors.initials: M
authors.lastname: Malakoutikhah
authors.affiliation: †Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona E-08028, Spain.
authors.forename: Markus
authors.initials: M
authors.lastname: Muttenthaler
authors.affiliation: §Núcleo de Biotecnología Curauma, Pontificia Universidad Católica de Valparaíso, Valparaíso, Chile.
authors.forename: Fanny
authors.initials: F
authors.lastname: Guzmán
authors.affiliation: †Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona E-08028, Spain.
authors.forename: Meritxell
authors.initials: M
authors.lastname: Teixidó
authors.affiliation: †Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona E-08028, Spain.|∥Department of Organic Chemistry, University of Barcelona, Martí i Franquès 1-11, Barcelona E-08028, Spain.
authors.forename: Ernest
authors.initials: E
authors.lastname: Giralt
mesh_terms: D001812:Blood-Brain Barrier / Q000378:metabolism*; D008051:Lipid Bilayers / Q000737:chemistry / Q000378:metabolism*; D015394:Molecular Structure; D011392:Proline / Q000737:chemistry* / Q000378:metabolism*; D012995:Solubility; D014867:Water / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D008051:Lipid Bilayers; D014867:Water; D011392:Proline