Improved targeting of the alpha(v)beta (3) integrin by multimerisation of RGD peptides.
OBJECTIVE
The integrin alpha(v)beta(3) is expressed on sprouting endothelial cells and on various tumour cell types. Due to the restricted expression of alpha(v)beta(3) in tumours, alpha(v)beta(3) is considered a suitable receptor for tumour targeting. In this study the alpha(v)beta(3) binding characteristics of an (111)In-labelled monomeric, dimeric and tetrameric RGD analogue were compared.


METHODS
A monomeric (E-c(RGDfK)), dimeric (E-[c(RGDfK)](2)), and tetrameric (E{E[c(RGDfK)](2)}(2)) RGD peptide were synthesised, conjugated with DOTA and radiolabelled with (111)In. In vitro alpha(v)beta(3) binding characteristics were determined in a competitive binding assay. In vivo alpha(v)beta(3) targeting characteristics of the compounds were assessed in mice with SK-RC-52 xenografts.


RESULTS
The IC(50) values for DOTA-E-c(RGDfK), DOTA-E-[c(RGDfK)](2), and DOTA-E{E[c(RGDfK)](2)}(2)were 120 nM, 69.9 nM and 19.6 nM, respectively. At all time points, the tumour uptake of the dimer was significantly higher as compared to that of the monomer. At 8 h p.i., tumour uptake of the tetramer (7.40+/-1.12%ID/g) was significantly higher than that of the monomer (2.30+/-0.34%ID/g), p<0.001, and the dimer (5.17+/-1.22%ID/g), p<0.05. At 24 h p.i., the tumour uptake was significantly higher for the tetramer (6.82+/-1.41%ID/g) than for the dimer (4.22+/-0.96%ID/g), p<0.01, and the monomer (1.90+/-0.29%ID/g), p<0.001.


CONCLUSIONS
Multimerisation of c(RGDfK) resulted in enhanced affinity for alpha(v)beta(3) as determined in vitro. Tumour uptake of a tetrameric RGD peptide was significantly higher than that of the monomeric and dimeric analogues, presumably owing to the enhanced statistical likelihood for rebinding to alpha(v)beta(3).
Dijkgraaf
Ingrid
I
Department of Nuclear Medicine, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB, Nijmegen, The Netherlands. I.Dijkgraaf@nucmed.umcn.nl
Kruijtzer
John A W
JA
Liu
Shuang
S
Soede
Annemieke C
AC
Oyen
Wim J G
WJ
Corstens
Frans H M
FH
Liskamp
Rob M J
RM
Boerman
Otto C
OC
D000818:Animals; D019281:Dimerization; D016503:Drug Delivery Systems / Q000379:methods*; D005260:Female; D007205:Indium Radioisotopes / Q000493:pharmacokinetics; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009374:Neoplasms, Experimental / Q000000981:diagnostic imaging* / Q000378:metabolism*; D009842:Oligopeptides / Q000493:pharmacokinetics*; D009928:Organ Specificity; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D014018:Tissue Distribution
D007205:Indium Radioisotopes; D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D019275:Radiopharmaceuticals; C047981:arginyl-glycyl-aspartic acid