Self-Assembling Multifunctional Peptide Dimers for Gene Delivery

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  • Research ArticleSelf-Assembling Multifunctional PeptideDimers for Gene Delivery Systems

    Kitae Ryu,1 Gyeong Jin Lee,1 Ji-yeong Choi,1 Taewan Kim,1 and Tae-il Kim1,2

    1Department of Biosystems&Biomaterials Science andEngineering, College of Agriculture andLife Sciences, SeoulNationalUniversity,1 Gwanak-ro, Gwanak-gu, Seoul 151-921, Republic of Korea2Research Institute of Agriculture and Life Sciences, Seoul National University, 1 Gwanak-ro, Gwanak-gu,Seoul 151-921, Republic of Korea

    Correspondence should be addressed to Tae-il Kim; seal1004@snu.ac.kr

    Received 10 May 2015; Accepted 6 September 2015

    Academic Editor: Michele Iafisco

    Copyright 2015 Kitae Ryu et al.This is an open access article distributed under theCreativeCommonsAttribution License, whichpermits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

    Self-assembling multifunctional peptide was designed for gene delivery systems. The multifunctional peptide (MP) consists ofcellular penetrating peptide moiety (R

    8), matrix metalloproteinase-2 (MMP-2) specific sequence (GPLGV), pH-responsive moiety

    (H5), and hydrophobic moiety (palmitic acid) (CR

    8GPLGVH

    5-Pal). MP was oxidized to form multifunctional peptide dimer

    (MPD) by DMSO oxidation of thiols in terminal cysteine residues. MPD could condense pDNA successfully at a weight ratio of 5.MPD itself could self-assemble into submicronmicelle particles via hydrophobic interaction, of which criticalmicelle concentrationis about 0.01mM.MPDshowed concentration-dependent but low cytotoxicity in comparisonwith PEI25k.MPDpolyplexes showedlow transfection efficiency in HEK293 cells expressing low level of MMP-2 but high transfection efficiency in A549 and C2C12cells expressing high level of MMP-2, meaning the enhanced transfection efficiency probably due to MMP-induced structuralchange of polyplexes. Bafilomycin A1-treated transfection results suggest that the transfection of MPD is mediated via endosomalescape by endosome buffering ability. These results show the potential of MPD for MMP-2 targeted gene delivery systems due toits multifunctionality.

    1. Introduction

    Lots of peptides have been developed and used for genedelivery systems due to their advantages [13]. Buildingblocks of peptides, amino acids, are nontoxic and almostnonimmunogenic endogenous molecules possessing vari-ous functional side chains with the diversity for designinggene delivery carriers. Peptides can be synthesized by well-established solid-phase chemistry in sequence-controlledmanner, yielding almost monodispersed products. Peptidesalso can interact with cellular molecules or components,which induce biologically important events such as recogni-tion of RGD peptide by integrin receptors [4].

    Particularly, cellular penetrating peptides such as pene-tratin, Tat sequence, or oligoarginine have been extensivelyexamined in gene delivery field because they can formnanosized complexes with nucleic acids due to their cationicproperty and possess high cellular uptake efficiency [59].

    Besides oligopeptide forms, bioreducible cellular penetratingpeptides which are linked via disulfide bonds, also have beendeveloped for gene delivery systems [1013]. They can bedegraded in reductive environment such as cytosol, showingcontrolled release of nucleic acids and low cytotoxicity [14].

    In this work, we designed a self-assembling multifunc-tional peptide (MP, CR

    8GPLGVH

    5-Pal) in order to combine

    advantages of several functional peptides for gene deliverysystems. It is expected that R

    8moiety would condense

    pDNA into polyplex particles and facilitate the cellular uptakeof the polyplexes [15]. GPLGV is a substrate sequence ofmatrix metalloproteinase-2 (MMP-2), which is one of thecollagenases overexpressed from several tumor cells andplays important roles in tumor progression and metastasis[16]. It was introduced to cause structural change of thepolyplexes for efficient cellular uptake, responding toMMP-2of tumor cells. Many studies reported the potential of MMP-cleavable drug/gene delivery carriers for targeting tumor cells

    Hindawi Publishing CorporationAdvances in Materials Science and EngineeringVolume 2015, Article ID 852584, 9 pageshttp://dx.doi.org/10.1155/2015/852584

  • 2 Advances in Materials Science and Engineering

    [17, 18]. H5moiety was employed for endosome buffering

    ability of imidazole groups to escape from endosomes aftercellular uptake [19, 20]. Palmitic acid at C-terminal wouldinduce micelle formation via self-assembly of the peptide byhydrophobic interaction. H

    5moiety also would contribute to

    the micelle formation because of hydrophobicity at neutralpH. In addition, we cross-linked this peptide to dimer(MPD) for improvement ofmicelle formation and performedcharacterizations to examine the potential of MPD for genedelivery systems.

    2. Materials and Methods

    2.1. Materials. Multifunctional peptide (CR8GPLGVH

    5-Pal)

    was purchased from GL Biochem (Shanghai, China). Thia-zolyl Blue Tetrazolium Bromide (MTT reagent), agarose, and5,5-dithiobis(2-nitrobenzoic acid) (Ellmans reagent) werepurchased from Sigma-Aldrich (St. Louis, MO). Dimethylsulfoxide (DMSO) was purchased from Merck (Germany).Luciferase assay systemwas purchased from Promega (Madi-son, WI). BCA protein assay kit was purchased fromPierce (Rockford, IL). Fetal bovine serum (FBS), 0.25%trypsin-EDTA,Dulbeccos phosphate buffered saline (DPBS),and Dulbeccos modified Eagles medium (DMEM) werepurchased from Invitrogen (Carlsbad, CA). The luciferasereporter gene-encoding plasmidDNA, pCN-Luci, was ampli-fied in Escherichia coli DH5 and isolated by NucleobondXtra Midi kit (Macherey-Nagel, Germany). MMP-2 enzymewas purchased from Calbiochem (San Diego, CA). All otherchemicals were purchased and used without any furtherpurification.

    2.2. Synthesis of Peptide Dimers. Multifunctional peptidedimer (MPD)was synthesized by usingDMSO autooxidationreaction [21]. Multifunctional peptide (MP) was dissolved inDMSO (0.5 wt%) and the solution was stirred under nitrogengas at room temperature for 24 h. After oxidation reaction,synthesized MPD was purified by diethyl ether precipitationand dried under vacuum at room temperature overnight.Finally, sticky and transparent product was obtained.

    2.3. Ellmans Assay. Ellmans assay was carried out to con-firm the synthesis of MPD by measuring residual thi-ols after dimerization of MPM. MPD was dissolved inDMSO (0.2mM). 50 L of Ellmans reagent solution (DMSO,4mg/mL) was added to 250 L of sample. After 15min ofincubation, the absorbance at 499 nm was measured by amicroplate reader (Synergy H1, BioTek, USA). Thiol amountof MPD was calculated based on calibration curve.

    2.4. Agarose Gel Electrophoresis. DNA condensation abilityof MPD was identified by agarose gel electrophoresis assay.Agarose gel (0.7 wt%) containing ethidium bromide wasprepared in Tris-Acetate-EDTA (TAE) buffer.TheMPDpoly-plexes (0.5 g pDNA) having various weight ratios (0.5, 1, 2,5, and 10) were prepared. After 30min of incubation at roomtemperature, electrophoresis was carried out for 15min at

    100V (Mupid-2plus, Takara Bio Inc., Japan).The locations ofpDNA bands were observed by UV illuminator (ChemiDocXRS+ gel documentation system, Bio-Rad, Hercules, CA).

    2.5. Critical Micelle Concentration (CMC) Measurements. Inorder to characterize CMC of MPD, pyrene was selectedas a model drug as previously reported [22]. 0.2mM ofpyrene solution was prepared by dilution of pyrene/ethanolsolution. 3 L of pyrene solutions was added to vials anddried under vacuum overnight in dark condition. Afterethanol evaporation, 1mL of MPD solution with variousconcentrations was added to the vials, giving the final pyreneconcentration of 6 107M. The MPD/pyrene solution wassonicated for 10min and incubated with gentle mixing atroom temperature for 24 h. Absorbance was measured byUV/Vis spectrometer (Optizen POP BIO, Mecasys, Korea)using quartz cuvettes in the range of 200 to 400 nm.The totalabsorbance was calculated by sum of four absorbance points(242, 272, 320, and 336 nm). CMC of theMPD sample was setto the center of the sigmoid.

    2.6. Average Particle Size and Zeta-Potential Measurements.Average sizes and Zeta-potential values of MPD and MPDpolyplexes were measured by Zetasizer Nano ZS (MalvernInstruments, UK) with He-Ne laser beam (633 nm) at 25C,respectively. 1mL of MPD (0.01 and 0.1mM) and MPDpolyplex solutions (5g pDNA, weight ratios: 2, 10, and 20)was prepared and used for analysis. Sizes of MPD polyplexesafter active MMP-2 cleavage were also examined. MPDpolyplexes (1 g pDNA, weight ratio: 20) were prepared asdescribed above. The polyplex solution was added to activeMMP-2 containing PBS buffer (pH 7.4, 10 g/mL MMP-2)and themixture was incubated at 37C for 4 hours with gentleshaking. After treatment, the sizes of the polyplexes samplewere analyzed by Zetasizer Nano ZS. Average sizes and Zeta-potential values ofMPD andMPDpolyplexes weremeasured3 times.

    2.7. Atomic Force Microscopy (AFM). The morphologies ofMPD particle structures were observed by using atomicforce microscopy (Park Systems, Korea). 100 L of MPDaqueous solution samples was prepared (0.01 and 0.1mM).10 L sample aliquots were dropped to fresh mica surfaceby pipette carefully and then excess of sample was removedby absorption of filter papers from the corner of the mica.The mica samples were dried at room temperature for 24 hand used for AFM observation. The imaging was set tononcontact tapping mode and the scanning rate was 1Hz.

    2.8. Cell Culture. Human lung adenocarcinoma epithelialcells (A549), human transformed primary embryonal kidneyepithelial cells (HEK293), and mouse myoblast cells (C2C12)were grown in DMEM supplemented with 10% FBS and1% penicil