Imaging of alpha(v)beta(3) expression by a bifunctional chimeric RGD peptide not cross-reacting with alpha(v)beta(5).
OBJECTIVE
To test whether a novel bifunctional chimeric peptide comprising a cyclic Arg-Gly-Asp pentapeptide covalently bound to an echistatin domain can discriminate alpha(v)beta(3) from alpha(v)beta(5) integrin, thus allowing the in vivo selective visualization of alpha(v)beta(3) expression by single-photon and positron emission tomography (PET) imaging.


METHODS
The chimeric peptide was preliminarily tested for inhibition of alpha(v)beta(3)-dependent cell adhesion and competition of 125I-echistatin binding to membrane of stably transfected K562 cells expressing alpha(v)beta(3) (Kalpha(v)beta(3)) or alpha(v)beta(5) (Kalpha(v)beta(5)) integrin. The chimeric peptide was then conjugated with diethylenetriaminepentaacetic acid and labeled with 111In for single-photon imaging, whereas a one-step procedure was used for labeling the full-length peptide and a truncated derivative, lacking the last five C-terminal amino acids, with 18F for PET imaging. Nude mice bearing tumors from Kalpha(v)beta(3), Kalpha(v)beta(5), U87MG human glioblastoma, and A431 human epidermoid cells were subjected to single-photon and PET imaging.


RESULTS
Adhesion and competitive binding assays showed that the novel chimeric peptide selectively binds to alpha(v)beta(3) integrin and does not cross-react with alpha(v)beta(5). In agreement with in vitro findings, single-photon and PET imaging studies showed that the radiolabeled chimeric peptide selectively localizes in tumor xenografts expressing alphavbeta3 and fails to accumulate in those expressing alpha(v)beta(5) integrin. When 18F-labeled truncated derivative was used for PET imaging, alphavbeta3- and alpha(v)beta(5)-expressing tumors were visualized, indicating that the five C-terminal amino acids are required to differentially bind the two integrins.


CONCLUSIONS
Our findings indicate that the novel chimeric Arg-Gly-Asp peptide, having no cross-reaction with alphavbeta5 integrin, allows highly selective alphavbeta3 expression imaging and monitoring.
Zannetti
Antonella
A
Institute of Biostructures and Bioimages, National Research Council, Naples, Italy.
Del Vecchio
Silvana
S
Iommelli
Francesca
F
Del Gatto
Annarita
A
De Luca
Stefania
S
Zaccaro
Laura
L
Papaccioli
Angela
A
Sommella
Jvana
J
Panico
Mariarosaria
M
Speranza
Antonio
A
Grieco
Paolo
P
Novellino
Ettore
E
Saviano
Michele
M
Pedone
Carlo
C
Salvatore
Marco
M
D000595:Amino Acid Sequence; D000818:Animals; D005909:Glioblastoma / Q000000981:diagnostic imaging* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000032:analysis / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes / Q000378:metabolism; D020014:K562 Cells; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009842:Oligopeptides / Q000032:analysis / Q000378:metabolism*; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D049268:Positron-Emission Tomography / Q000379:methods*; D011485:Protein Binding; D019030:Receptors, Vitronectin / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013379:Substrate Specificity; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
D039302:Integrin alphaVbeta3; D036341:Intercellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D009842:Oligopeptides; D010455:Peptides; D019030:Receptors, Vitronectin; D011993:Recombinant Fusion Proteins; C064660:integrin alphaVbeta5; C057986:echistatin; C047981:arginyl-glycyl-aspartic acid