Seite - 15 - in Cancer Nanotheranostics - What Have We Learnd So Far?

Condeetal. Biofunctionalizationandsurfacechemistryof inorganicnanoparticles FIGURE5 |Goldnanoparticles functionalizedwithmultiple biomolecules:PEG,cellpenetrationpeptide (TAT),ammonium quaternarygroups,andsiRNA.Twodifferent approacheswereemployed toconjugate thesiRNAto theAuNPs: (A) ionic approach, interactionof the negatively chargedsiRNAto themodifiedsurfaceof theAuNPs through ionic interactions; (B)covalent approach,useof thiolatedsiRNAforgold thiol binding to theNPs. point-of-care testing, gene expression studies, high-throughput screening,andclinicaldiagnostics. WhenmodifiedwithDNA,QDswere successfully employed in the detection of respective complementary DNA strands via FRET.Sub-nanomolardetectionlimitshavebeenreported(Zhou et al., 2008a; Singh and Strouse, 2010). The strategy success is directly related to the covalent coupling of the nucleic acid molecule to the QD, controlling the donor-acceptor distance, fundamental inFRET-basedbiosensors. QDscanalsobeused ingenedelivery. Jin-MingLietal.devel- opeda series ofQDs functionalizedwithβ-cyclodextrin coupled toaminoacids.Usingtheβ-cyclodextrinasavector fordelivering doxorubicin (DOX) and electrostatically bindingMDR1 siRNA, this strategy allowed for simultaneous chemotherapy and gene silencing. The authors observed that in HeLa cells it was pos- sible to induce apoptosis due to the intracellular accumulation ofDox and also reduced levels ofMDR1gene expression.These multifunctional QDs are promising vehicles for the co-delivery of nucleic acids and chemotherapeutics, as well as for real-time trackingof treatment(Lietal., 2012). QDs-siRNA conjugates have also been used for imaging and gene silencing approaches (Derfus et al., 2007; Tan et al., 2007; Yezhelyev et al., 2008; Zhao et al., 2010; Li et al., 2011, 2012). For example, Yezhelyev et al. developedmultifunctional nanoparticles for siRNA delivery and imaging based on the use of QDs and proton-absorbing polymeric coatings (proton sponges). The authors demonstrated a dramatic improvement in gene silencing efficiency and simultaneous reduction in cel- lular toxicity, when comparedwith existing transfection agents. Additionally, QD-siRNA nanoparticles are also dual-modality opticalandelectron-microscopyprobes,allowingreal-timetrack- ing and ultrastructural localization ofQDs during delivery and transfection(Yezhelyevetal., 2008). MNPs have also been frequently used as platforms for the delivery of DNA or siRNA, as they can be used to track their biodistribution byMRI. For instance, Kumar et al. synthesized multifunctionalMNPs by attaching a near-infrared optical dye Cy5.5andapeptidethattargetsthetumorspecificantigenmucin- 1tocross-linkeddextrancoatedSPIONs(Kumaretal.,2010).The delivery of thenanosystem to tumors inmicewas imaged either invivoorexvivobyMRIandoptical imaging. Ontheotherhand, the functionalizationofplasmidDNAand siRNA toMNPs has been widely reported, as MNPs are used as tools for magnetofection, that is to say, the enhanced deliv- ery of nucleic acids associated toMNPsusing externalmagnetic fields (Scherer et al., 2002; Dobson, 2006; Plank et al., 2011). Using magnetofection the transfection efficiency can be highly improved when compared with transfections carried out with non-magnetic genedelivery systems in a variety of primary cells and cell lines (Mykhaylyk et al., 2007; Prijic and Sersa, 2011). Althoughmagnetofectionresults arepromising in vitro, andsev- eral studies have reported the systemic delivery of nucleic acids usingMNPs in vivo, notmanyof themuse anexternalmagnetic field to enhance the accumulation of theMNPs in the targeted area (Plank et al., 2011). Thus far, the most promising appli- cation ofmagnetofection as an in vivo cancer therapy has been reported byNamiki et al. (2009). The authors formulated oleic acid-coatedMNPsassembledwithcationic lipidshells, andfunc- tionalized themwith an appropriate siRNA sequence to knock down the epidermal growth factor receptor (EGFR)mRNA, as it is overexpressed in tumorbloodvessel endothelium.After sys- temicallyinjectingthecomplextomicetumors,theauthorsfound a50%reductionintumormasswhenamagneticfieldwasapplied comparedto thecontrolgroupwithoutmagneticfield. Peptides Peptides are short chains of amino acid monomers linked by amide bonds and are distinguished from proteins on the basis of size, once theyonly contain∼50aminoacidsor less. Peptides canbe foundnaturallyor syntheticallyandhave thepotential for the stabilization and biofunctionalization of NPs. For instance Wang et al. demonstrate thatmultiple functional peptide stabi- lized AuNPs are readily obtained in a one-step surface coating procedure and that the surface functionalities can be selectively addressedonamicroarray.The authors developed a straightfor- ward route to stableAuNPs, bothwith single andwithdual bio- logical functionality.Theparticlesexhibit thespecificrecognition Frontiers inChemistry | ChemicalEngineering July2014 |Volume2 |Article48 | 15