A heterodimeric [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] αvβ3/GRPr-targeting antagonist radiotracer for PET imaging of prostate tumors.
BACKGROUND
In the present study, we describe a (64)Cu-radiolabeled heterodimeric peptide conjugate for dual αvβ3/GRPr (αvβ3 integrin/gastrin releasing peptide receptor) targeting of the form [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] (RGD: the amino acid sequence [Arg-Gly-Asp], a nonregulatory peptide used for αvβ3 integrin receptor targeting; Glu: glutamic acid; NO2A: 1,4,7-triazacyclononane-1,4-diacetic acid; 6-Ahx: 6-amino hexanoic acid; and RM2: (D-Phe-Gln-Trp-Ala-Val-Gly-His-Sta-Leu-NH2), an antagonist analogue of bombesin (BBN) peptide used for GRPr targeting).


METHODS
RGD-Glu-6Ahx-RM2] was conjugated to a NOTA (1,4,7-triazacyclononane-1,4,7-triacetic acid) complexing agent to produce [RGD-Glu-[NO2A]-6-Ahx-RM2], which was purified by reversed-phase high-performance liquid chromatography (RP-HPLC) and characterized by electrospray ionization-mass spectrometry (ESI-MS). Radiolabeling of the conjugate with (64)Cu produced [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2 in high radiochemical yield (≥95%). In vivo behavior of the radiolabeled peptide conjugate was investigated in normal CF-1 mice and in the PC-3 human prostate cancer experimental model.


RESULTS
A competitive displacement receptor binding assay in human prostate PC-3 cells using (125)I-[Tyr(4)]BBN as the radioligand showed high binding affinity of [RGD-Glu-[(nat)Cu-NO2A]-6-Ahx-RM2] conjugate for the GRPr (3.09±0.34 nM). A similar assay in human, glioblastoma U87-MG cells using (125)I-Echistatin as the radioligand indicated a moderate receptor-binding affinity for the αvβ3 integrin (518±37.5 nM). In vivo studies of [RGD-Glu-[(64)Cu-NO2A]-6-Ahx-RM2] showed high accumulation (4.86±1.01 %ID/g, 1h post-intravenous injection (p.i.)) and prolonged retention (4.26±1.23 %ID/g, 24h p.i.) of tracer in PC-3 tumor-bearing mice. Micro-positron emission tomography (microPET) molecular imaging studies produced high-quality, high contrast images in PC-3 tumor-bearing mice at 4h p.i.


CONCLUSIONS
The favorable pharmacokinetics and enhanced tumor uptake of (64)Cu-NOTA-RGD-Glu-6Ahx-RM2 warrant further investigations for dual integrin and GRPr-positive tumor imaging and possible radiotherapy.
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA; Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA; Department of Nuclear Applications, Ege University, 35100, Bornova, Izmir, Turkey. Electronic address: kubra.durkan@ege.edu.tr.
Kubra
K
Durkan
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA; Department of Chemistry, University of Missouri, Columbia, MO 65211, USA.
Zongrun
Z
Jiang
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA; Department of Internal Medicine, University of Missouri School of Medicine, Columbia, MO 65211, USA.
Tammy L
TL
Rold
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA.
Gary L
GL
Sieckman
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA; Department of Internal Medicine, University of Missouri School of Medicine, Columbia, MO 65211, USA; Department of Chemistry, University of Missouri, Columbia, MO 65211, USA.
Timothy J
TJ
Hoffman
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA; Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA.
Rajendra Prasad
RP
Bandari
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA.
Ashley F
AF
Szczodroski
College of Pharmacy, University of New Mexico, Albuquerque, NM87131, USA.
Liqin
L
Liu
College of Pharmacy, University of New Mexico, Albuquerque, NM87131, USA; Cancer Research and Treatment Center, University of New Mexico, , Albuquerque, NM 8713, 1USA; Department of Dermatology, University of New Mexico, Albuquerque, NM 87131, USA.
Yubin
Y
Miao
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA; Department of Veterinary Pathobiology, University of Missouri College of Veterinary Medicine, Columbia, MO 65211, USA.
Tamila Stott
TS
Reynolds
Research Division, Harry S. Truman Memorial Veterans' Hospital, Columbia, MO 65201, USA; Department of Radiology, University of Missouri School of Medicine, Columbia, MO 65211, USA; University of Missouri Research Reactor Center, University of Missouri, Columbia, MO 65211, USA. Electronic address: smithcj@health.missouri.edu.
Charles J
CJ
Smith
D015119:Aminocaproic Acid; D000818:Animals; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic; D003301:Copper Radioisotopes; D019281:Dimerization; D005260:Female; D006571:Heterocyclic Compounds / Q000737:chemistry; D006573:Heterocyclic Compounds, 1-Ring; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D008297:Male; D051379:Mice; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism / Q000493:pharmacokinetics; D049268:Positron-Emission Tomography / Q000379:methods*; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology*; D011849:Radioactive Tracers; D018004:Receptors, Bombesin / Q000037:antagonists & inhibitors* / Q000378:metabolism
D003301:Copper Radioisotopes; D006571:Heterocyclic Compounds; D006573:Heterocyclic Compounds, 1-Ring; D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D011849:Radioactive Tracers; D018004:Receptors, Bombesin; C048993:1,4,7-triazacyclononane-N,N',N''-triacetic acid; C047981:arginyl-glycyl-aspartic acid; D015119:Aminocaproic Acid
Bombesin; Copper-64; Gastrin-releasing peptide; Prostate cancer; Prostate-specific membrane antigen