Two Technetium-99m-Labeled Cholecystokinin-8 (CCK8) Peptides for Scintigraphic Imaging of CCK Receptors
详细信息 查看全文
- 作者：Peter Laverman ; Martin Bé ; hé ; Wim J. G. Oyen ; Peter H. G. M. Willems ; Frans H. M. Corstens ; Thomas M. Behr ; and Otto C. Boerman
- 刊名：Bioconjugate Chemistry
- 出版年：2004
- 出版时间：May 2004
- 年：2004
- 卷：15
- 期：3
- 页码：561 - 568
- 全文大小：89K
- 年卷期：v.15,no.3(May 2004)
- ISSN：1520-4812
文摘
A broad spectrum of radiolabeled peptides with high affinity for receptors expressed on tumor cells iscurrently under preclinical and clinical investigation for scintigraphic imaging and radionuclidetherapy. The present paper evaluates two 99mTc-labeled forms of the C-terminal octapeptide ofcholecystokinin (CCK8): sulfated (s)CCK8, with high affinity for CCK1 and CCK2 receptors, andnonsulfated (ns)CCK8, with high affinity for CCK2 receptors but low affinity for CCK1 receptors.Peptides were conjugated with the bifunctional chelator N-hydroxysuccinimidyl hydrazino niconitate(s-HYNIC). 99mTc-labeling, performed in the presence of nicotinic acid and tricine, was highly efficient(~95%) and yielded products with a high specific activity (~700 Ci/mmol) and good stability (~5%release of radiolabel during 16 h incubation in phosphate buffered saline at 37 
C). Chinese hamsterovary cells stably expressing the CCK1 receptor (CHO-CCK1 cells) internalized ~3% of added 99mTc-sCCK8 per confluent well during 2 h at 37 C. Internalization was effectively blocked by excessunlabeled sCCK8. CHO-CCK1 cells did not internalize 99mTc-nsCCK8. Displacement of 99mTc-sCCK8and -nsCCK8 by unlabeled CCK-8 (performed at 0 C to prevent internalization) revealed 50%inhibitory concentrations (IC50) of 8 nM and >1 
M, respectively. CHO-CCK2 cells internalized ~25%and ~5% of added 99mTc-sCCK8 and -nsCCK8, respectively. In both cases internalization was blockedby excess unlabeled peptide. IC50 values for the displacement of 99mTc-sCCK8 and -nsCCK8 were 3nM and 10 nM, respectively. CHO-CCK1 cell-derived tumors present in one flank of athymic miceaccumulated 2.0% of injected 99mTc-sCCK8 per gram tissue at 1 h postinjection. This value decreasedto 0.6% following coinjection with excess unlabeled peptide. Uptake of 99mTc-nsCCK8 was low (0.2%)and not did change by excess unlabeled peptide (0.3%). Accumulation of 99mTc-sCCK8 and -nsCCK8by CHO-CCK2 cell-derived tumors (present in the other flank) amounted to 4.2% and 0.6%, respectively.In both cases uptake was significantly reduced by excess unlabeled peptide to 1.0% and 0.4% forsCCK8 and nsCCK8, respectively. Accumulation of 99mTc-sCCK8 was also high in pancreas (11.7%),stomach (2.0%), and kidney (2.1%), whereas uptake of 99mTc-nsCCK8 was high in stomach (0.7%) andkidney (1.4%). Both radiolabeled peptides showed a rapid blood clearance. In conclusion, these datashow that CCK8 analogues can be efficiently labeled with 99mTc using s-HYNIC as chelator and nicotinicacid/tricine as coligand system without compromising receptor binding. Furthermore, the present studydemonstrates that CCK1 tumors hardly accumulate 99mTc-nsCCK8, CCK2 tumors accumulate 2 timesmore 99mTc-sCCK8 than CCK1 tumors, and CCK2 tumors accumulate 15 times more 99mTc-sCCK8than 99mTc-nsCCK8. Although accumulation in some nontarget organs was also higher with 99mTc-sCCK8, this may not reflect the human situation due to a different receptor expression pattern inhumans as compared to mice. Therefore, further studies are warranted to investigate the possibleuse of 99mTc-sCCK8 for scintigraphic imaging of CCK receptor-positive tumors in humans.
C). Chinese hamsterovary cells stably expressing the CCK1 receptor (CHO-CCK1 cells) internalized ~3% of added 99mTc-sCCK8 per confluent well during 2 h at 37 C. Internalization was effectively blocked by excessunlabeled sCCK8. CHO-CCK1 cells did not internalize 99mTc-nsCCK8. Displacement of 99mTc-sCCK8and -nsCCK8 by unlabeled CCK-8 (performed at 0 C to prevent internalization) revealed 50%inhibitory concentrations (IC50) of 8 nM and >1 M, respectively. CHO-CCK2 cells internalized ~25%and ~5% of added 99mTc-sCCK8 and -nsCCK8, respectively. In both cases internalization was blockedby excess unlabeled peptide. IC50 values for the displacement of 99mTc-sCCK8 and -nsCCK8 were 3nM and 10 nM, respectively. CHO-CCK1 cell-derived tumors present in one flank of athymic miceaccumulated 2.0% of injected 99mTc-sCCK8 per gram tissue at 1 h postinjection. This value decreasedto 0.6% following coinjection with excess unlabeled peptide. Uptake of 99mTc-nsCCK8 was low (0.2%)and not did change by excess unlabeled peptide (0.3%). Accumulation of 99mTc-sCCK8 and -nsCCK8by CHO-CCK2 cell-derived tumors (present in the other flank) amounted to 4.2% and 0.6%, respectively.In both cases uptake was significantly reduced by excess unlabeled peptide to 1.0% and 0.4% forsCCK8 and nsCCK8, respectively. Accumulation of 99mTc-sCCK8 was also high in pancreas (11.7%),stomach (2.0%), and kidney (2.1%), whereas uptake of 99mTc-nsCCK8 was high in stomach (0.7%) andkidney (1.4%). Both radiolabeled peptides showed a rapid blood clearance. In conclusion, these datashow that CCK8 analogues can be efficiently labeled with 99mTc using s-HYNIC as chelator and nicotinicacid/tricine as coligand system without compromising receptor binding. Furthermore, the present studydemonstrates that CCK1 tumors hardly accumulate 99mTc-nsCCK8, CCK2 tumors accumulate 2 timesmore 99mTc-sCCK8 than CCK1 tumors, and CCK2 tumors accumulate 15 times more 99mTc-sCCK8than 99mTc-nsCCK8. Although accumulation in some nontarget organs was also higher with 99mTc-sCCK8, this may not reflect the human situation due to a different receptor expression pattern inhumans as compared to mice. Therefore, further studies are warranted to investigate the possibleuse of 99mTc-sCCK8 for scintigraphic imaging of CCK receptor-positive tumors in humans.