Comparative in vitro and in vivo evaluation of two 64Cu-labeled bombesin analogs in a mouse model of human prostate adenocarcinoma.
Bombesin (BBN), an analog of human gastrin-releasing peptide (GRP), binds to the GRP receptor (GRPR) with high affinity and specificity. Overexpression of GRPR has been discovered in mostly androgen-independent human prostate tissues and, thus, provides a potential target for prostate cancer diagnosis and therapy. We have previously demonstrated the feasibility of the positron emission tomography (PET) imaging using 64Cu-1,4,7,10-tetraazadodecane-N,N',N'',N'''-tetraacetic acid (DOTA)-[Lys3]BBN to detect GRPR-positive prostate cancer. In this study, we compared the receptor affinity, metabolic stability, tumor-targeting efficacy, and pharmacokinetics of a truncated BBN analog 64Cu-DOTA-Aca-BBN(7-14) with 64Cu-DOTA-[Lys3]BBN. Binding of each DOTA conjugate to GRPR on PC-3 and 22Rv1 prostate cancer cells was evaluated with competitive binding assay using 125I-[Tyr4]BBN as radioligand. In vivo pharmacokinetics was determined on male nude mice subcutaneously implanted with PC-3 cells. Dynamic microPET imaging was performed to evaluate the systemic distribution of the tracers. Metabolic stability of the tracers in blood, urine, tumor, liver and kidney was studied using high-performance liquid chromatography. The results showed that 125I-[Tyr4]BBN has a K(d) of 14.8+/-0.4 nM against PC-3 cells, and the receptor concentration on PC-3 cell surface is approximately 2.7+/-0.1 x 10(6) receptors per cell. The 50% inhibitory concentration value for DOTA-Aca-BBN(7-14) is 18.4 +/- 0.2 nM, and that for DOTA-[Lys3]BBN is 2.2 +/- 0.5 nM. DOTA-[Lys3]BBN shows a better tumor contrast and absolute tumor activity accumulation compared to DOTA-Aca-BBN(7-14). Studies on metabolic stability for both tracers on organ homogenates showed that 64Cu-DOTA-[Lys3]BBN is relatively stable. This study demonstrated that both tracers are suitable for targeted PET imaging to detect the expression of GRPR in prostate cancer, while 64Cu-DOTA-[Lys3]BBN may have a better potential for clinical translation.
Yang
Yi-Shan
YS
Department of Radiology and Bio-X Program, The Molecular Imaging Program at Stanford (MIPS), Stanford University School of Medicine, Stanford, CA 94305-5484, USA.
Zhang
Xianzhong
X
Xiong
Zhengming
Z
Chen
Xiaoyuan
X
D000230:Adenocarcinoma / Q000000981:diagnostic imaging / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001839:Bombesin / Q000031:analogs & derivatives; D003301:Copper Radioisotopes; D004195:Disease Models, Animal; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008819:Mice, Nude; D049268:Positron-Emission Tomography; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism; D018004:Receptors, Bombesin / Q000378:metabolism; D014018:Tissue Distribution
D003301:Copper Radioisotopes; D018004:Receptors, Bombesin; D001839:Bombesin