Review Article

Targeted Delivery of siRNA Therapeutics to Malignant Tumors

Table 2

Ligands targeting tumor cells.

Ligand/target1CarriersiRNA and/or active moietyCellsResultsOther commentsReferences

High MW endogenous ligands

Transferrin (Tfr)/TfR receptorPolymer (cyclodextrin)siRRM2Neuro2A, murine neuroblastoma, implanted SCGreater tumor inhibition with targeted than nontargeted NPDose-related efficacy using transferrin ligand[59]

Hyaluronic acid/CD44LiposomessiPLK1U87MG, human glioblastoma, orthotopicProlonged survival, reduced PLK1 mRNA by 80% in tumor xenografts versus control siRNACD44 increased on cell surfaces of many cancers[63]

ApoA1/SR-B1LiposomessiVEGFMCF-7, SCInhibited tumor size and prolonged survivalHepatocellular carcinomas have been targeted[72]

Aptamers

Aptamer/PSMA2ā€‰Aptamer-siRNA chimerasiPLK1PSMA+ (22Rv) versus PSMA- (PC-3) cells, SCTumor regression of 22Rv xenografts treated with apta-mer-PLK1 siRNAPSMA upregulated in prostate cancer[78]
Aptamer/PSMAAptamer- dsRNA binding domain- polyhistidine chimerasiGFPPSMA+ (LNCaP) versus PSMA- (PC-3) cells, in vitro study onlySilenced GFP efficiently in LNCaP cellsdsRNA-binding domain binds to siRNA; chimera may not efficiently lyse endosomes in vivo[80]

Aptamer/PSMAPolymer (atelocollagen)(miR15a and miR-16-1)Bone metastatic prostate model-LNCap cellsProlonged mouse survival versus nontargeted NPReduced expression of Bcl-2, cyclin D1, and Wnt3a in vitro with targeted NP[86]

Antibodies

scFv/Her2+scFv-protamine-conjugatesiPLK1Her2+ versus Her2- breast cancer, orthotopicMarked tumor inhibition on Her2+ tumors in vivo versus no/little effect on Her2- tumors Ionic interaction between siRNA and protamine; siRNA cocktail targeting PLK1, CCND1, and AKT more effective than PLK1 alone[89]

scFv/Her2+Polymer (PLA) siPLK1Her2+ (BT474) versus Her 2- (MCF7) breast cancer, orthotopicTargeted NP inhibited both Her2+/- xenografts but showed the most efficacy toward Her2+ tumorsDose-dependent antitumor response of the targeted NP was observed[95]
Small molecule nonpeptide ligands

Folate/folate receptorLow MW PEI cross-linked with by cyclodextrinsiVEGFHeLa xenografts, SCTargeted NP reduced tumor size more than nontargetedFolate receptor is widely distributed in epithelial cancers[109]
Tetrahedral DNA siGFPā€‰
siLuciferase
KB expressing GFP (in vitro) or luciferase, SCFolate NP, given IV or IT, reduced tumor luciferase expression by 60%3 ligands on same face of tetrahedron to maximize uptake; well-defined NPs[119]
Polymer (oligoamine amides)siEG5KB xenografts, SCMethotrexate/siEG5 NP enhanced survivalMethotrexate targets folate receptor, small NPs (~6 nm) delivered IT[120]

Anisamide/sigma-1, -2 receptorsLiposomesiMDM2, sic-MYC, and siVEGFB16F10 murine melanoma, SC, and lung metastasesReduced primary and metastatic tumor burden and prolonged survivalReceptor widely distributed in tumors and proliferating cells; sigma-2 ligands induce apoptosis in tumors[125, 144]

Galactose/asialoglycoprotein receptorsMultilayered NP (mesoporous silica NP, polymers)siVEGF/doxorubicinQGY-7703, a hepatocarcinoma, SCMarked inhibition with targeted NP (91.3%) versus nontargeted NP (75.2%)Ligand targets primarily liver cells[130]

Peptide ligands

T73/transferrin receptorCholesterol-grafted polymer/lipid hybridsiEGFRMC7 xenografts, SCAbout 50% greater reduction in tumor size with targeted than nontargeted NPsBinding of T7 to receptor is independent of endogenous transferrin concentration[134]

MMP2-cleavable peptidePEI-lipid hybrid micelleFluorescently-labeled siRNA and paclitaxelA549 lung cancer xenografts, SCEnhanced tumor uptake by 2.4-fold with MMP2-micelleMMP2-triggered PEG deshielding[135]

CP15/unknownPolymer (chitosan)siPLK1, biotin-labeled RNASW480 colon cancer cells, SCModest increase in tumor uptake/specificity of targeted NP (versus nontargeted NP)Identified by phage display; primarily targets colon cancer; study requires validation[136]

LHRH/LHRH receptorPolymer (PPI)siCD44/paclitaxelOvarian cancer xenograft, SCTargeted therapy significantly more effective than nontargeted therapyCombination of paclitaxel and siCD44 NP most effective in reducing tumor size[139]

GRP/BB2 receptorConjugateFluorescently-labeled siRNA, siSurvivinMDA-MB-231 xenografts (in vitro)Competitive inhibition indicates specific uptake of GRP-siRNA conjugates into cells; marked reduction of survivin with targeted NPRequires in vivo validation; BB2 reported to be on breast, prostate, lung, and colon cancers[140]

RVG/acetylcholine receptorPolymer (cyclodextrin)siGADPHU87 glioblastoma, HeLa (RVG- control), (in vitro)Targeted NP reduced GADPH mRNA about 25% more than nontargeted NP in U87Requires in vivo validation; in vitro efficacy is modest[142]

Selected representatives of targeted nanoparticles. 2PSMA, prostate specific membrane antigen; scFv, single-chain variable fragment antibody; MMP2, metalloproteinase-2; LHRH, luteinizing-hormone releasing hormone; GRP, gastrin-releasing peptide; BB2, a subtype of the bombesin receptor; RVG, rabies virus glycoprotein; dsRNA, double-stranded RNA binding domain; PLA, poly(D,L-lactide); PEI, polyethylenimine; PPI, polypropylenimine; RRM2, ribonucleoside-diphosphate reductase subunit M2; PLK1, polo-like kinase-1; EG5, eglin 5; GFP, green fluorescent protein; EGFR, epidermal growth factor receptor; GADPH, glyceraldehyde-3 phosphate dehydrogenase; SC, subcutaneous; NP, nanoparticle; IT, intratumoral. 3See text for amino acid sequences of ligands.