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1.  Lead-203-Labeled Alpha-Melanocyte Stimulating Hormone Peptide as an Imaging Probe for Melanoma Detection 
Peptide-targeted alpha therapy with 7.4 MBq of 212Pb-[1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-ReO-[Cys3,4,10, d-Phe7, Arg11]α-MSH3-13 {212Pb-DOTA-Re(Arg11)CCMSH} cured 45% of B16/F1 murine melanoma-bearing C57 mice in a 120-day study, highlighting its melanoma treatment potential. However, there is a need to develop an imaging surrogate for patient-specific dosimetry and to monitor the tumor response to 212Pb-DOTA-Re(Arg11)CCMSH therapy. The purpose of this study was to evaluate the potential of 203Pb-DOTA-Re(Arg11)CCMSH as a matched-pair SPECT imaging agent for 212Pb-DOTA-Re(Arg11)CCMSH.
DOTA-Re(Arg11)CCMSH was labeled with 203Pb in 0.5 M NH4OAc buffer at pH 5.4. The internalization and efflux of 203Pb-DOTA-Re(Arg11)CCMSH were determined in B16/F1 melanoma cells. The pharmacokinetics of 203Pb-DOTA-Re(Arg11)CCMSH was examined in B16/F1 melanoma-bearing C57 mice. A micro-SPECT/CT imaging study was performed with 203Pb-DOTA-Re(Arg11)CCMSH in a B16/F1 melanoma-bearing C57 mouse at 2 h post-injection.
Lead-203-DOTA-Re(Arg11)CCMSH was easily prepared in NH4OAc buffer and completely separated from the excess non-radiolabeled peptide by RP-HPLC. Lead-203-DOTA-Re(Arg11)CCMSH displayed fast internalization and extended retention in B16/F1 cells. Approximately 73% of 203Pb-DOTA-Re(Arg11)CCMSH activity internalized after a 20-min incubation at 25°C. After incubating the cells in culture media for 20 min, 78% of internalized activity remained in the cells. Lead-203-DOTA-Re(Arg11)CCMSH exhibited similar biodistribution pattern with 212Pb-DOTA-Re(Arg11)CCMSH in B16/F1 melanoma-bearing mice. Lead-203-DOTA-Re(Arg11)CCMSH exhibited the peak tumor uptake of 12.00±3.20 %ID/g at 1 h post-injection. The tumor uptake gradually decreased to 3.43±1.12 %ID/g at 48 h post-injection. Lead-203-DOTA-Re(Arg11)CCMSH exhibited a peak tumor to kidney uptake ratio of 1.53 at 2 h post-injection. The absorbed doses to the tumor and kidneys were 4.32 and 4.35 Gy/37 MBq, respectively. Whole-body clearance of 203Pb-DOTA-Re(Arg11)CCMSH was fast, with approximately 89% of the injected activity cleared through urinary system by 2 h post-injection. Lead-203 showed 1.6 mm SPECT imaging resolution, which was comparable to 99mTc. Melanoma lesions were visualized through SPECT/CT images of 203Pb-DOTA-Re(Arg11)CCMSH at 2 h post-injection.
Lead-203-DOTA-Re(Arg11)CCMSH exhibited favorable pharmacokinetic and tumor imaging properties, highlighting its potential as a matched-pair SPECT imaging agent for 212Pb-DOTA-Re(Arg11)CCMSH melanoma treatment.
PMCID: PMC3610567  PMID: 18413404
2.  A comparison of 111In- or 64Cu-DOTA-trastuzumab Fab fragments for imaging subcutaneous HER2-positive tumor xenografts in athymic mice using microSPECT/CT or microPET/CT 
EJNMMI Research  2011;1:15.
Our objective was to compare 111In- or 64Cu-DOTA-trastuzumab Fab fragments for imaging small or large s.c. tumor xenografts in athymic mice that display a wide range of human epidermal growth factor receptor-2 (HER2) expression using microSPECT/CT or microPET/CT.
Trastuzumab Fab were labeled with 111In or 64Cu by conjugation to 1,4,7,10-tetraazacyclododecane N, N', N'', N'''-tetraacetic acid (DOTA). The purity of 111In- and 64Cu-DOTA-trastuzumab Fab was measured by SDS-PAGE and HPLC. HER2 binding affinity was determined in saturation radioligand binding assays using SKBR-3 cells (1.3 × 106 HER2/cell). MicroSPECT/CT and microPET/CT were performed in athymic mice bearing s.c. BT-20 and MDA-MB-231 xenografts with low (0.5 to 1.6 × 105 receptors/cell), MDA-MB-361 tumors with intermediate (5.1 × 105 receptors/cell) or SKOV-3 xenografts with high HER2 expression (1.2 × 106 receptors/cell) at 24 h p.i. of 70 MBq (10 μg) of 111In-DOTA-trastuzumab Fab or 22 MBq (10 μg) of 64Cu-DOTA-trastuzumab Fab or irrelevant 111In- or 64Cu-DOTA-rituximab Fab. Tumor and normal tissue uptake were quantified in biodistribution studies.
111In- and 64Cu-DOTA-trastuzumab were > 98% radiochemically pure and bound HER2 with high affinity (Kd = 20.4 ± 2.5 nM and 40.8 ± 3.5 nM, respectively). MDA-MB-361 and SKOV-3 tumors were most clearly imaged using 111In- and 64Cu-DOTA-trastuzumab Fab. Significantly higher tumor/blood (T/B) ratios were found for 111In-DOTA-trastuzumab Fab than 111In-DOTA-rituximab Fab for BT-20, MDA-MB-231 and MDA-MB-361 xenografts, and there was a direct association between T/B ratios and HER2 expression. In contrast, tumor uptake of 64Cu-DOTA-trastuzumab Fab was significantly higher than 64Cu-DOTA-rituximab Fab in MDA-MB-361 tumors but no direct association with HER2 expression was found. Both 111In- and 64Cu-DOTA-trastuzumab Fab imaged small (5 to 10 mm) or larger (10 to 15 mm) MDA-MB-361 tumors. Higher blood, liver, and spleen radioactivity were observed for 64Cu-DOTA-trastuzumab Fab than 111In-DOTA-trastuzumab Fab.
We conclude that 111In-DOTA-trastuzumab Fab was more specific than 64Cu-DOTA-trastuzumab Fab for imaging HER2-positive tumors, especially those with low receptor density. This was due to higher levels of circulating radioactivity for 64Cu-DOTA-trastuzumab Fab which disrupted the relationship between HER2 density and T/B ratios. Use of alternative chelators that more stably bind 64Cu may improve the association between T/B ratios and HER2 density for 64Cu-labeled trastuzumab Fab.
PMCID: PMC3250982  PMID: 22214307
indium-111; copper-64; HER2; MicroSPECT; MicroPET; DOTA; trastuzumab Fab; breast cancer; ovarian cancer
3.  Evaluation of 111In-Labeled Cyclic RGD Peptides: Tetrameric Not Tetravalent 
Bioconjugate chemistry  2010;21(5):969-978.
This report presents the synthesis and evaluation of 111In(DOTA-6G-RGD4) (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracetic acid; 6G-RGD4 = E{G3-E[G3-c(RGDfK)]2}2 and G3 = Gly-Gly-Gly), 111In(DOTA-RGD4) (RGD4 = E{E[c(RGDfK)]2}2) and 111In(DOTA-3G-RGD2) (3G-RGD2 = G3-E[G3-c(RGDfK)]2) as new radiotracers for imaging integrin αvβ3–positive tumors. The IC50 values of DOTA-6G-RGD4, DOTA-RGD4 and DOTA-3G-RGD2 were determined to be 0.4 ± 0.1, 1.5 ± 0.2 and 1.3 ± 0.2 nM against 125I-c(RGDyK) bound to integrin αvβ3–positive U87MG human glioma cells. 111In(DOTA-6G-RGD4), 111In(DOTA-RGD4) and 111In(DOTA-3G-RGD2) were prepared by reacting 111InCl3 with the respective DOTA conjugate in NH4OAc buffer (100 mM, pH = 5.5). Radiolabeling could be completed by heating the reaction mixture at 100 °C for 15 – 20 min. The specific activity was ~1850 MBq/μmol for 111In(DOTA-3G-RGD2) and ~1480 MBq/μmol for 111In(DOTA-6G-RGD4). The athymic nude mice bearing U87MG human glioma xenografts were used to evaluate tumor uptake and excretion kinetics of 111In(DOTA-6G-RGD4), 111In(DOTA-RGD4) and 111In(DOTA-3G-RGD2). The results from both the integrin αvβ3 binding assay and biodistribution studies suggest that the tetrameric cyclic RGD peptides, such as RGD4 and 6G-RGD4, are most likely bivalent in binding to the integrin αvβ3. Both 111In(DOTA-6G-RGD4) and 111In(DOTA-RGD4) had significantly higher tumor uptake than 111In(DOTA-3G-RGD2) at 24 – 72 h post-injection due to the extra RGD motifs in RGD4 and 6G-RGD4. 111In(DOTA-3G-RGD2) had very little metabolism while 111In(DOTA-6G-RGD4) had a significant metabolism during its excretion via both renal and hepatobiliary routes over the 2 h period, probably due to its much larger size. The combination of high tumor uptake with long tumor retention suggests that their corresponding 90Y and 177Lu analogs M(DOTA-6G-RGD4) (M = 90Y and 177Lu) might be useful as therapeutic radiotracers for treatment of integrin αvβ3-positive solid tumors.
PMCID: PMC2874107  PMID: 20387808
integrin αvβ3; 111In-labeled cyclic RGD peptides; tumor imaging
4.  Evaluation of 64Cu Labeled GX1: A Phage Display Peptide Probe for PET Imaging of Tumor Vasculature 
Molecular imaging using positron emission tomography (PET) radiotracers targeted to tumor vasculature offers a noninvasive method for early detection of tumor angiogenesis and efficient monitoring of response to anti-tumor vasculature therapy. The previous in vitro results demonstrated that the GX1 peptide, identified by phage display technology, is a tumor vasculature endothelium-specific ligand. In this study, we evaluated a 64Cu-labeled GX1 peptide as a potential radiotracer for microPET imaging of tumor vasculature in a U87MG tumor xenografted mouse model.
Macrocyclic chelating agent 1,4,7,10-tetraazacyclododecane-N, N′, N″, N‴-tetraacetic acid (DOTA)-conjugated GX1 peptide was synthesized and radiolabeled with 64Cu (t1/2=12.7 h) in ammonium acetate buffer. The 64Cu-labeled GX1 peptide was then subjected to in vitro tumor cell uptake study, small animal PET and direct tissue sampling biodistribution studies in a U87MG tumor xenografted mouse model.
The in vitro experiment demonstrated that 64Cu-DOTA-GX1 is stable in PBS with more than 91% of 64Cu-DOTA-GX1 peptide remaining intact after 24 h of incubation. Cellular uptake and retention studies revealed 64Cu-DOTA-GX1 binds to U87MG glioma cells and has good tumor cell retention. For small animal PET imaging studies, the U87MG tumors were all clearly visible with high contrast to contralateral background at all measured time points after injection of 64Cu-DOTA-GX1 while high accumulation in liver and kidneys were also observed at early time points. The U87MG tumor uptake was determined to be the highest (7.97±0.75%ID/g) at 24 h pi. The blocking experiment was achieved by co-injection of 64Cu-DOTA-GX1 with non-radiolabeled GX1 peptide (20 mg/kg) at 24 h pi, suggesting 64Cu-DOTA-GX1 is a target-specific tracer. Furthermore, the biodistribution results were consistent with the quantification of microPET imaging, demonstrating the highest ratio (16.09±1.21) of tumor/muscle uptake of 64Cu-DOTA-GX1 at 24 h pi for non-blocking group and significant decreased ratio (6.57±0.58) for blocking group. Finally, metabolic studies suggested that 64Cu-DOTA-GX1 is stable in mouse blood and urine in vivo at early time point while the metal transchelation may also occur in mouse liver and kidneys.
Our studies demonstrate that 64Cu-DOTA-GX1 is a promising radiotracer for imaging tumor vasculature.
PMCID: PMC3629956  PMID: 21360213
64Cu-Labeled GX1 peptide; PET imaging; Tumor vasculature; Phage display
5.  Development of Novel Radiogallium-Labeled Bone Imaging Agents Using Oligo-Aspartic Acid Peptides as Carriers 
PLoS ONE  2013;8(12):e84335.
68Ga (T1/2 = 68 min, a generator-produced nuclide) has great potential as a radionuclide for clinical positron emission tomography (PET). Because poly-glutamic and poly-aspartic acids have high affinity for hydroxyapatite, to develop new bone targeting 68Ga-labeled bone imaging agents for PET, we used 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) as a chelating site and conjugated aspartic acid peptides of varying lengths. Subsequently, we compared Ga complexes, Ga-DOTA-(Asp)n (n = 2, 5, 8, 11, or 14) with easy-to-handle 67Ga, with the previously described 67Ga-DOTA complex conjugated bisphosphonate, 67Ga-DOTA-Bn-SCN-HBP. After synthesizing DOTA-(Asp)n by a Fmoc-based solid-phase method, complexes were formed with 67Ga, resulting in 67Ga-DOTA-(Asp)n with a radiochemical purity of over 95% after HPLC purification. In hydroxyapatite binding assays, the binding rate of 67Ga-DOTA-(Asp)n increased with the increase in the length of the conjugated aspartate peptide. Moreover, in biodistribution experiments, 67Ga-DOTA-(Asp)8, 67Ga-DOTA-(Asp)11, and 67Ga-DOTA-(Asp)14 showed high accumulation in bone (10.5±1.5, 15.1±2.6, and 12.8±1.7% ID/g, respectively) but were barely observed in other tissues at 60 min after injection. Although bone accumulation of 67Ga-DOTA-(Asp)n was lower than that of 67Ga-DOTA-Bn-SCN-HBP, blood clearance of 67Ga-DOTA-(Asp)n was more rapid. Accordingly, the bone/blood ratios of 67Ga-DOTA-(Asp)11 and 67Ga-DOTA-(Asp)14 were comparable with those of 67Ga-DOTA-Bn-SCN-HBP. In conclusion, these data provide useful insights into the drug design of 68Ga-PET tracers for the diagnosis of bone disorders, such as bone metastases.
PMCID: PMC3877283  PMID: 24391942
6.  Improving Tumor Uptake and Pharmacokinetics of 64Cu-Labeled Cyclic RGD Peptide Dimers with Gly3 and PEG4 Linkers 
Bioconjugate chemistry  2009;20(4):750-759.
Radiolabeled cyclic RGD (Arg-Gly-Asp) peptides represent a new class of radiotracers with potential for the early tumor detection and non-invasive monitoring of tumor metastasis and therapeutic response in cancer patients. This report describes the synthesis of two cyclic RGD peptide dimer conjugates, DOTA-PEG4-E[PEG4-c(RGDfK)]2 (DOTA-3PEG4-dimer: DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid; PEG4 = 15-amino-4,7,10,13-tetraoxapentadecanoic acid) and DOTA-G3-E[G3-c(RGDfK)]2 (DOTA-3G3-dimer: G3 = Gly-Gly-Gly). Integrin αvβ3 binding affinities of cyclic RGD peptides were determined by competitive displacement of 125I-echistatin bound to U87MG human glioma cells, and follow the order of DOTA-E{E[c(RGDfK)]2}2 (DOTA-tetramer: IC50 = 10 ± 2 nM) > DOTA-3G3-dimer (IC50 = 62 ± 6 nM) ~ DOTA-3PEG4-dimer (IC50 = 74 ± 3 nM) > DOTA-E[c(RGDfK)]2 (DOTA-dimer: IC50 = 102 ± 5 nM). The addition of PEG4 and G3 linkers between two cyclic RGD motifs in DOTA-3G3-dimer and DOTA-3PEG4-dimer makes it possible for them to achieve the simultaneous integrin αvβ3 binding in a bivalent fashion. Both 64Cu(DOTA-3PEG4-dimer) and 64Cu(DOTA-3G3-dimer) were prepared in high yield with specific activity being >50 Ci/mmol. Biodistribution and imaging studies were performed in athymic nude mice bearing U87MG human glioma xenografts. The results from those studies show that PEG4 and G3 linkers are particularly useful for improving tumor uptake and clearance kinetics of 64Cu radiotracers from the non-tumor organs, such as kidneys, liver and lungs. There is a linear relationship between the tumor size and %ID tumor uptake, suggesting that 64Cu(DOTA-3PEG4-dimer) and 64Cu(DOTA-3PEG4-dimer) might be useful for noninvasive monitoring of tumor growth or shrinkage during anti-angiogenic therapy. MicroPET imaging data clearly demonstrate the utility of 64Cu(DOTA-3G3-dimer) as a new PET radiotracer for imaging integrin αvβ3-positive tumors.
PMCID: PMC2676896  PMID: 19320477
integrin αvβ3; 64Cu-labeled cyclic RGD peptides; PET tumor imaging
7.  Evaluation of 111In-Labeled Cyclic RGD Peptides: Effects of Peptide and Linker Multiplicity on Their Tumor Uptake, Excretion Kinetics and Metabolic Stability 
Theranostics  2011;1:322-340.
Purpose: The purpose of this study was to demonstrate the valence of cyclic RGD peptides, P-RGD (PEG4-c(RGDfK): PEG4 = 15-amino-4,710,13-tetraoxapentadecanoic acid), P-RGD2 (PEG4-E[c(RGDfK)]2, 2P-RGD4 (E{PEG4-E[c(RGDfK)]2}2, 2P4G-RGD4 (E{PEG4-E[G3-c(RGDfK)]2}2: G3 = Gly-Gly-Gly) and 6P-RGD4 (E{PEG4-E[PEG4-c(RGDfK)]2}2) in binding to integrin αvβ3, and to assess the impact of peptide and linker multiplicity on biodistribution properties, excretion kinetics and metabolic stability of their corresponding 111In radiotracers.
Methods: Five new RGD peptide conjugates (DOTA-P-RGD (DOTA =1,4,7,10-tetraazacyclododecane-1,4,7,10-tetracetic acid), DOTA-P-RGD2, DOTA-2P-RGD4, DOTA-2P4G-RGD4, DOTA-6P-RGD4), and their 111In complexes were prepared. The integrin αvβ3 binding affinity of cyclic RGD conjugates were determined by a competitive displacement assay against 125I-c(RGDyK) bound to U87MG human glioma cells. Biodistribution, planar imaging and metabolism studies were performed in athymic nude mice bearing U87MG human glioma xenografts.
Results: The integrin αvβ3 binding affinity of RGD conjugates follows the order of: DOTA-6P-RGD4 (IC50 = 0.3 ± 0.1 nM) ~ DOTA-2P4G-RGD4 (IC50 = 0.2 ± 0.1 nM) ~ DOTA-2P-RGD4 (IC50 = 0.5 ± 0.1 nM) > DOTA-3P-RGD2 (DOTA-PEG4-E[PEG4-c(RGDfK)]2: IC50 = 1.5 ± 0.2 nM) > DOTA-P-RGD2 (IC50 = 5.0 ± 1.0 nM) >> DOTA-P-RGD (IC50 = 44.3 ± 3.5 nM) ~ c(RGDfK) (IC50 = 49.9 ± 5.5 nM) >> DOTA-6P-RGK4 (IC50 = 437 ± 35 nM). The fact that DOTA-6P-RGK4 had much lower integrin αvβ3 binding affinity than DOTA-6P-RGD4 suggests that the binding of DOTA-6P-RGD4 to integrin αvβ3 is RGD-specific. This conclusion is consistent with the lower tumor uptake for 111In(DOTA-6P-RGK4) than that for 111In(DOTA-6P-RGD4). It was also found that the G3 and PEG4 linkers between RGD motifs have a significant impact on the integrin αvβ3-targeting capability, biodistribution characteristics, excretion kinetics and metabolic stability of 111In-labeled cyclic RGD peptides.
Conclusion: On the basis of their integrin αvβ3 binding affinity and tumor uptake of their corresponding 111In radiotracers, it was conclude that 2P-RGD4, 2P4G-RGD4 and 6P-RGD4 are most likely bivalent in binding to integrin αvβ3, and extra RGD motifs might contribute to the long tumor retention times of 111In(DOTA-2P-RGD4), 111In(DOTA-2P4G-RGD4) and 111In(DOTA-6P-RGD4) than that of 111In(DOTA-3P-RGD3) at 72 h p.i. Among the 111In-labeled cyclic RGD tetramers evaluated in the glioma model, 111In(DOTA-2P4G-RGD4) has very high tumor uptake with the best tumor/kidney and tumor/liver ratios, suggesting that 90Y(DOTA-2P4G-RGD4) and 177Lu(DOTA-2P4G-RGD4) might have the potential for targeted radiotherapy of integrin αvβ3-positive tumors.
PMCID: PMC3157017  PMID: 21850213
integrin αvβ3; 111In-labeled cyclic RGD peptides; tumor imaging
8.  Effects of the Amino Acid Linkers on the Melanoma-Targeting and Pharmacokinetic Properties of Indium-111-labeled Lactam Bridge-Cyclized α-MSH Peptides 
The purpose of this study was to examine the profound effects of the amino acid linkers on the melanoma targeting and pharmacokinetic properties of novel 111In-labeled lactam bridge-cyclized DOTA-[X]-CycMSHhex {1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid-[X]-c[Asp-His-dPhe-Arg-Trp-Lys]-CONH2, X=GlyGlyNle, GlyGluNle or NleGlyGlu} peptides.
Three novel DOTA-GGNle-CycMSHhex, DOTA-GENle-CycMSHhex and DOTA-NleGE-CycMSHhex peptides were designed and synthesized. The melanocortin-1 (MC1) receptor binding affinities of the peptides were determined in B16/F1 melanoma cells. The melanoma targeting and pharmacokinetic properties of 111In-DOTA-GGNle-CycMSHhex and 111In-DOTA-GENle-CycMSHhex were determined in B16/F1 melanoma-bearing C57 mice.
DOTA-GGNle-CycMSHhex and DOTA-GENle-CycMSHhex displayed 2.1 and 11.5 nM MC1 receptor binding affinities, whereas DOTA-NleGE-CycMSHhex showed 873.4 nM MC1 receptor binding affinity. The introduction of the -GlyGly- linker maintained high melanoma uptake while decreased the renal and liver uptakes of 111In-DOTA-GlyGlyNle-CycMSHhex. The tumor uptake values of 111In-DOTA-GGNle-CycMSHhex were 19.05 ± 5.04 and 18.6 ± 3.56 % injected dose/gram (%ID/g) at 2 and 4 h post-injection. 111In-DOTA-GGNle-CycMSHhex exhibited 28, 32 and 42% less renal uptake values than 111In-DOTA-Nle-CycMSHhex we reported previously, and 61, 65 and 68% less liver uptake values than 111In-DOTA-Nle-CycMSHhex at 2, 4 and 24 h post-injection, respectively.
The amino acid linkers exhibited the profound effects on the melanoma targeting and pharmacokinetic properties of the 111In-labeled lactam bridge-cyclized α-MSH peptides. Introduction of the -GlyGly- linker maintained high melanoma uptake while reducing the renal and liver uptakes of 111In-DOTA-GlyGlyNle-CycMSHhex, highlighting its potential as an effective imaging probe for melanoma detection, as well as a therapeutic peptide for melanoma treatment when labeled with a therapeutic radionuclide.
PMCID: PMC3065533  PMID: 21421725
Alpha-melanocyte stimulating hormone; Radiolabeled cyclic peptide; Melanoma imaging
9.  Metastatic Melanoma Imaging with an 111In-labeled Lactam Bridge-cyclized Alpha-Melanocyte Stimulating Hormone Peptide 
Nuclear medicine and biology  2009;36(3):267-276.
The purpose of this study was to examine whether a novel lactam bridge-cyclized 111In-labeled 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid-Gly-Glu-c[Lys-Nle-Glu-His-dPhe-Arg-Trp-Gly-Arg-Pro-Val-Asp] {DOTA-GlyGlu-CycMSH} could be an effective imaging probe for metastatic melanoma detection.
111In-DOTA-GlyGlu-CycMSH was prepared and purified by reverse phase high performance liquid chromatography (RP-HPLC). The internalization and efflux of 111In-DOTA-GlyGlu-CycMSH were examined in B16/F10 melanoma cells. The biodistribution of 111In-DOTA-GlyGlu-CycMSH was determined in B16/F10 pulmonary metastatic melanoma-bearing and normal C57 mice. Pulmonary metastatic melanoma imaging was performed by small animal SPECT/CT (Nano-SPECT/CT®) using 111In-DOTA-GlyGlu-CycMSH as an imaging probe and compared with 18F-FDG PET imaging.
111In-DOTA-GlyGlu-CycMSH was readily prepared with greater than 95% radiolabeling yield. 111In-DOTA-GlyGlu-CycMSH displayed rapid internalization and extended efflux in B16/F10 cells. 111In-DOTA-GlyGlu-CycMSH exhibited significantly (p<0.05) higher uptakes (2.00±0.74 %ID/g at 2 h post-injection and 1.83±0.12 %ID/g at 4 h post-injection) in metastatic melanoma-bearing lung than that in normal lung (0.08±0.08 %ID/g and 0.05±0.05 %ID/g at 2 and 4 h post-injection, respectively). The activity accumulation in normal organs were low (<0.5 %ID/g) except for the kidneys 2 and 4 h post-injection. B16/F10 pulmonary melanoma metastases were clearly visualized with 111In-DOTA-GlyGlu-CycMSH 2 h post-injection rather than with 18F-FDG 1 h post-injection.
111In-DOTA-GlyGlu-CycMSH exhibited favorable metastatic melanoma targeting and imaging properties, highlighting its potential as an effective imaging probe for metastatic melanoma detection.
PMCID: PMC2685149  PMID: 19324272
Metastatic melanoma imaging; radiolabeled lactam bridge-cyclized peptide; alpha-melanocyte stimulating hormone
10.  Synthesis and Evaluation of Novel Gonadotropin-Releasing Hormone Receptor-Targeting Peptides 
Bioconjugate chemistry  2011;22(8):1682-1689.
The purpose of this study was to develop novel radiolabeled gonadotropin-releasing hormone (GnRH) receptor-targeting peptides for breast cancer imaging. Three novel 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)-conjugated GnRH peptides were designed and synthesized. The radiometal chelator DOTA was conjugated to the epsilon or alpha amino group of D-lysine, or the epsilon amino group of L-lysine via an Ahx {aminohexanoic acid} linker to generate DOTA-Ahx-(D-Lys6-GnRH1), DOTA-Ahx-(D-Lys6-GnRH2) and DOTA-Ahx-(L-Lys6-GnRH3), respectively. The conjugation of the DOTA to the epsilon amino group of D-lysine (rather than alpha amino group of D-lysine nor epsilon amino group of L-lysine) maintained the nanomolar GnRH receptor binding affinity. The IC50 values of DOTA-Ahx-(D-Lys6-GnRH1), DOTA-Ahx-(D-Lys6-GnRH2) and DOTA-Ahx-(L-Lys6-GnRH3) were 36.07 nM, 10.6 mM and 4.3 mM, respectively. Since only DOTA-Ahx-(D-Lys6-GnRH1) displayed nanomolar receptor binding affinity, the specific GnRH receptor binding of 111In-DOTA-Ahx-(D-Lys6-GnRH1) was determined in human GnRH receptor membrane preparations. Furthermore, the biodistribution and tumor imaging properties of 111In-DOTA-Ahx-(D-Lys6-GnRH1) were examined in MDA-MB-231 human breast cancer-xenografted nude mice. 111In-DOTA-Ahx-(D-Lys6-GnRH1) exhibited specific GnRH receptor binding and rapid tumor uptake (1.76 ± 0.58 %ID/g at 0.5 h post-injection) coupled with fast whole-body clearance through the urinary system. The MDA-MB-231 human breast cancer-xenografted tumor lesions were clearly visualized by single photon emission computed tomography (SPECT)/CT at 1 h post-injection of 111In-DOTA-Ahx-(D-Lys6-GnRH1). The profound impact of DOTA position on the binding affinity of the GnRH peptide provided a new insight into the design of novel radiolabeled GnRH peptides. The successful imaging of MDA-MB-231 human breast cancer-xenografted tumor lesions using 111In-DOTA-Ahx-(D-Lys6-GnRH1) suggested its potential as a novel imaging probe for human breast cancer imaging.
PMCID: PMC3157568  PMID: 21749045
Gonadotropin-releasing hormone receptor; receptor-targeting peptide
11.  111In-labeled Lactam Bridge-cyclized Alpha-Melanocyte Stimulating Hormone Peptide Analogues for Melanoma Imaging 
Bioconjugate chemistry  2008;19(2):539-547.
The purpose of this study was to examine the influence of the lactam bridge cyclization on melanoma targeting and biodistribution properties of the radiolabeled conjugates. Two novel lactam bridge-cyclized α-MSH peptide analogues, DOTA-CycMSH (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-c[Lys-Nle-Glu-His-DPhe-Arg-Trp-Gly-Arg-Pro-Val-Asp]) and DOTA-GlyGlu-CycMSH (DOTA-Gly-Glu-c[Lys-Nle-Glu-His-DPhe-Arg-Trp-Gly-Arg-Pro-Val-Asp]), were synthesized and radiolabeled with 111In. The internalization and efflux of 111In-labeled CycMSH peptides were examined in B16/F1 melanoma cells. The melanoma targeting properties, pharmacokinetics and SPECT/CT imaging of 111In-labeled CycMSH peptides were determined in B16/F1 melanoma-bearing C57 mice. Both 111In-DOTA-CycMSH and 111In-DOTA-GlyGlu-CycMSH exhibited fast internalization and extended retention in B16/F1 cells. The tumor uptake values of 111In-DOTA-CycMSH and 111In-DOTA-GlyGlu-CycMSH were 9.53±1.41 %injected dose/gram (%ID/g) and 10.40±1.40 %ID/g at 2 h post-injection, respectively. Flank melanoma tumors were clearly visualized with 111In-DOTA-CycMSH and 111In-DOTA-GlyGlu-CycMSH by SPECT/CT images at 2 h post-injection. Whole-body clearance of the peptides was fast, with greater than 90% of the radioactivities cleared through urinary system by 2 h post-injection. There was low radioactivity (<0.8 %ID/g) accumulated in blood and normal organs except kidneys at all time points investigated. Introduction of a negatively-charged linker (-Gly-Glu-) into the peptide sequence decreased the renal uptake by 44% without affecting the tumor uptake at 4 h post-injection. High receptor-mediated melanoma uptakes coupled with fast whole-body clearance in B16/F1 melanoma-bearing C57 mice demonstrated the feasibility of using 111In-labeled lactam bridge-cyclized α-MSH peptide analogues as a novel class of imaging probes for receptor-targeting melanoma imaging.
PMCID: PMC3617549  PMID: 18197608
Melanoma imaging; lactam bridge cyclization; alpha-MSH; melanocortin-1
12.  64Cu-Labeled Lissamine Rhodamine B: A Promising PET Radiotracer Targeting Tumor Mitochondria 
Molecular pharmaceutics  2011;8(4):1198-1208.
The enhanced mitochondrial potential in carcinoma cells is an important characteristic of cancer. It is of great current interest to develop a radiotracer that is sensitive to the mitochondrial potential changes at the early stage of tumor growth. In this report, we present the synthesis and evaluation of 64Cu-labeled Lissamine Rhodamine B (LRB), 64Cu(DOTA-LRB) (DOTA-LRB = 2-(6-(diethylamino)-3-(diethyliminio)-3H-xanthen-9-yl)-5-(N-(2-(2-(4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclo-dodecan-1-yl)acetamido)ethyl)-sulfamoyl)benzenesulfonate), as a new radiotracer for imaging tumors in athymic nude mice bearing U87MG human glioma xenografts by positron emission tomography (PET). We also explored its localization mechanism using Cu(DOTA-LRB) as the fluorescent probe in both U87MG human glioma cell line and the cultured primary U87MG glioma cells. It was found that 64Cu(DOTA-LRB) had the highest tumor uptake (6.54 ± 1.50, 6.91 ± 1.26, 5.68 ± 1.13, 7.58 ± 1.96, and 5.14 ± 1.50 %ID/g at 0.5, 1, 2, 4 and 24 h post-injection, respectively) among many 64Cu-labeled organic cations evaluated in the same animal model. The cellular staining study indicated that Cu(DOTA-LRB) was able to localize in mitochondria of U87MG glioma cells due to the enhanced negative mitochondrial potential. This statement is completely supported by the results from decoupling experiment with carbonylcyanide-m-chlorophenylhydrazone (CCCP). MicroPET data showed that the U87MG glioma tumors were clearly visualized as early as 30 min post-injection with 64Cu(DOTA-LRB). 64Cu(DOTA-LRB) remained stable during renal excretion, but underwent extensive degradation during hepatobiliary excretion. On the basis of the results from this study, it was concluded that 64Cu(DOTA-LRB) represents a new class of promising PET radiotracers for noninvasive imaging of the MDR-negative tumors.
PMCID: PMC3148415  PMID: 21545131
64Cu PET radiotracers; mitochondrial potential and tumor imaging
13.  Radiolabeled Affibody-Albumin Bioconjugates for HER2 Positive Cancer Targeting 
Bioconjugate chemistry  2011;22(3):413-421.
Affibody molecules have received significant attention in the fields of molecular imaging and drug development. However, Affibody scaffolds display an extremely high renal uptake, especially when modified with chelators and then labeled with radiometals. This unfavorable property may impact their use as radiotherapeutic agents in general and as imaging probes for the detection of tumors adjacent to kidneys in particular. Herein, we present a simple and generalizable strategy for reducing the renal uptake of Affibody molecules while maintaining their tumor uptake. Human serum albumin (HSA) was consecutively modified by 1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid mono-N-hydroxysuccinimide ester (DOTA-NHS ester) and the bifunctional crosslinker sulfosuccinimidyl 4-[N-maleimidomethyl]cyclohexane-1-carboxylate (Sulfo-SMCC). The HER2 Affibody analog, Ac-Cys-ZHER2:342, was covalently conjugated with HSA, and the resulting bioconjugate DOTA-HSA-ZHER2:342 was further radiolabeled with 64Cu and 111In and evaluated in vitro and in vivo. Radiolabeled DOTA-HSA-ZHER2:342 conjugates displayed a significant and specific cell uptake into SKOV3 cell cultures. Positron emission tomography (PET) investigations using 64Cu-DOTA-HSA-ZHER2:342 were performed in SKOV3 tumor-bearing nude mice. High tumor uptake values (> 14% ID/g at 24 h and 48 h) and high liver accumulations but low kidney accumulations were observed. Biodistribution studies and single-photon emission computed tomography (SPECT) investigations using 111In-DOTA-HSA-ZHER2:342 validated these results. At 24 h post injection, the bio distribution data revealed high tumor (16.26% ID/g) and liver uptake (14.11% ID/g) but relatively low kidney uptake (6.06% ID/g). Blocking studies with co-injected, non-labeled Ac-Cys-ZHER2:342 confirmed the in vivo specificity of HER2. Radiolabeled DOTA-HSA-ZHER2:342 Affibody conjugates are promising SPECT and PET-type probes for the imaging of HER2 positive cancer. More importantly, DOTA-HSA-ZHER2:342 is suitable for labeling with therapeutic radionuclides (e.g. 90Y or 177Lu) for treatment studies. The approach of using HSA to optimize the pharmacokinetics and biodistribution profile of Affibodies, may be extended to the design of many other targeting molecules.
PMCID: PMC3059402  PMID: 21299201
14.  Effect of DOTA Position on Melanoma Targeting and Pharmacokinetic Properties of 111In-labeled Lactam Bridge-Cyclized Alpha-Melanocyte Stimulating Hormone Peptide 
Bioconjugate chemistry  2009;20(11):2162-2168.
The purpose of this study was to examine the effect of DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) position on melanoma targeting and pharmacokinetics of radiolabeled lactam bridge-cyclized alpha-melanocyte stimulating hormone (α-MSH) peptide.
A novel lactam bridge-cyclized α-MSH peptide, Ac-GluGlu-CycMSH[DOTA] {Ac-Glu-Glu-c[Lys(DOTA)-Nle-Glu-His-DPhe-Arg-Trp-Gly-Arg-Pro-Val-Asp]}, was synthesized using standard 9-fluorenylmethyloxycarbonyl (Fmoc) chemistry. DOTA was directly attached to the alpha amino group of Lys in the cyclic ring while the N-terminus of the peptide was acetylated to generate Ac-GluGlu-CycMSH[DOTA]. The MC1 receptor binding affinity of Ac-GluGlu-CycMSH[DOTA] was determined in B16/F1 melanoma cells. Melanoma targeting and pharmacokinetic properties of Ac-GluGlu-CycMSH[DOTA]-111In were determined in B16/F1 melanoma-bearing C57 mice and compared to that of 111In-DOTA-Gly-Glu-c[Lys-Nle-Glu-His-DPhe-Arg-Trp-Gly-Arg-Pro-Val-Asp] (111In-DOTA-GlyGlu-CycMSH, DOTA was coupled to the N-terminus of the peptide).
Ac-GluGlu-CycMSH[DOTA] displayed 0.6 nM MC1 receptor binding affinity in B16/F1 cells. Ac-GluGlu-CycMSH[DOTA]-111In was readily prepared with greater than 95% radiolabeling yield. Ac-GluGlu-CycMSH[DOTA]-111In exhibited high tumor uptake (11.42 ± 2.20% ID/g 2 h post-injection) and prolonged tumor retention (9.42 ± 2.41% ID/g 4 h post-injection) in B16/F1 melanoma-bearing C57 mice. The uptake values for non-target organs were generally low (<1.3% ID/g) except for the kidneys 2, 4 and 24 h post-injection.
DOTA position exhibited profound effect on melanoma targeting and pharmacokinetic properties of Ac-GluGlu-CycMSH[DOTA]-111In, providing a new insight into the design of lactam bridge-cyclized peptide for melanoma imaging and therapy.
PMCID: PMC2786309  PMID: 19817405
Melanoma detection; lactam bridge cyclization; alpha-melanocyte stimulating hormone peptide; melanocortin-1 receptor
15.  High-throughput flow injection analysis of labeled peptides in cellular samples – ICP-MS analysis versus fluorescence based detection 
A high throughput method based on flow injection analysis was developed and validated for the quantification of the peptide Bβ15-42 in cellular samples comparing different labeling strategies and detection methods. The used labels were 1,4,7,10-tetraazacyclododecane-N, N′, N′′, N′′′-tetraaceticacid (In-DOTA) and 2-(4-isothiocyanatobenzyl) - 1,4,7,10-tetraazacyclododecane-N, N′, N′′, N′′′-tetraacetic acid (In-DOTA-Bn) for elemental labeling. 6-Hydroxy-9-(2-carboxyphenyl)- (3H)-xanthen-3-on (fluorescein) was employed as fluorescence label. The explored peptide (mass = 3 kD) is a novel candidate drug, which shows an anti-inflammatory effect after an event of myocardial infarction. The analysed samples were fractioned cell compartments of human umbilical cord vein endothelial cells (HUVEC) maintained via lysis with Triton X buffer. In order to enhance sensitivity and selectivity of peptide quantification via flow injection the peptide was labeled prior to incubation using elemental and fluorescence labels. Quantification of the elemental and fluorescence labeled peptide was performed via flow injection analysis combined with inductive coupled plasma sector field mass spectrometry (FIA-ICP-SFMS) or fluorescence detection (FIA-FLD), respectively. The employed quantification strategies were external calibration in the case of fluorescence detection and external calibration with and without internal standardization and on-line IDMS in the case of ICP-MS detection
The limit of detection (LOD) for FIA-ICP-MS was 9 pM In-DOTA-Bβ15-42 (0.05 fmol absolute) whereas FIA-FLD showed a LOD of 100 pM (3 fmol absolute) for the fluorescein labeled peptide. Short term precision of FIA-ICP-MS was superior for all ICP-MS based quantification strategies compared to FIA-FLD (FIA-ICP-SFMS: 0.3-3.3%; FIA-FLD: 6.5%). Concerning long term precision FIA-ICP-SFMS with on-line IDMS and internal standardization showed the best results (3.1 and 4.6%, respectively) whereas the external calibration of both applied methodological approaches was only in the range of 10 %.
The concentrations in the Triton X soluble fraction relative to the applied amount of Indium in the cell culture were in the range of 0.75-1.8% for In-DOTA or 0.30-0.79% for the 2-(4-isothiocyanatobenzyl) - 1,4,7,10-tetraazacyclododecane-N, N′, N′′, N′′′-tetraacetic acid (In-DOTA-Bn) labeled peptide Bβ15-42. In the Triton X insoluble fraction the relative concentrations of Indium were 0.03-0.18% for the In-DOTA labeled peptide and 0.03-0.13% for Bβ15-42-In-DOTA-Bn.
PMCID: PMC3378036  PMID: 22723737
ICP-MS; quantification; peptide; labeling; fluorescence
16.  Imaging carotid body chemodectomas with 68Ga-DOTA-NOC PET-CT 
The British Journal of Radiology  2012;85(1016):1140-1145.
The purpose of the present study was to evaluate the role of 68-gallium-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid-1-Nal3-octreotide (68Ga-DOTA-NOC) positron emission tomography CT (PET-CT) in carotid body chemodectomas (CBCs).
: 5 patients with known CBCs (conventional imaging and angiography) were evaluated retrospectively (3 males, 2 females; mean age 36.6 years). All underwent PET-CT after injection of 148 MBq (4 mCi) of 68Ga-DOTA-NOC.
: At baseline there were four bilateral CBCs and one unilateral CBC with an additional glomus tympanicum and bilateral glomus jugulare tumour in these five patients. All these lesions showed intense uptake on 68Ga-DOTA-NOC PET-CT. Apart from these known lesions, additional tumours were detected in three patients; glomus jugulare in one, aortic body tumour and multiple abdominal paragangliomas in another and unsuspected vertebral metastasis in the last. Overall it led to a change in management in 3 of the 5 patients (60%).
: 68Ga-DOTA-NOC PET-CT is a promising non-invasive imaging modality in the detection and characterisation of CBCs.
PMCID: PMC3587100  PMID: 22096221
17.  Reduction of the Ring Size of Radiolabeled Lactam Bridge-Cyclized Alpha-MSH Peptide Resulting in Enhanced Melanoma Uptake 
The purpose of this study was to examine the profound effect of the ring size of the radiolabeled lactam bridge-cyclized α-melanocyte stimulating hormone (α-MSH) peptide on its melanoma targeting properties.
A novel cyclic α-MSH peptide, DOTA-Nle-CycMSHhex {1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetic acid-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH2}, was synthesized and radiolabeled with 111In. The melanocortin-1 (MC1) receptor binding affinity of DOTA-Nle-CycMSHhex was determined in B16/F1 melanoma cells. The internalization and efflux of 111In-DOTA-Nle-CycMSHhex were examined in B16/F1 cells. The melanoma targeting properties and single photon emission computed tomography (SPECT)/CT imaging of 111In-DOTA-Nle-CycMSHhex were determined in B16/F1 melanoma-bearing C57 mice.
DOTA-Nle-CycMSHhex displayed 1.77 nM receptor binding affinity. 111In-DOTA-Nle-CycMSHhex exhibited rapid internalization and extended retention in B16/F1 cells. The tumor uptake of 111In-DOTA-Nle-CycMSHhex was 24.94 ± 4.58 and 10.53 ± 1.11% injected dose/gram (%ID/g) at 0.5 and 24 h post-injection, respectively. Greater than 82% of the injected radioactivity was cleared through the urinary system by 2 h post-injection. The tumor/kidney uptake ratios reached 2.04 and 1.70 at 2 and 4 h post-injection, respectively. Flank melanoma tumors were clearly visualized by SPECT/CT using 111In-DOTA-Nle-CycMSHhex as an imaging probe at 2 and 24 h post-injection. The radioactivity accumulation in normal organs was low except for the kidneys at 2, 4 and 24 h post-injection.
The reduction of the peptide ring size dramatically increased the melanoma uptake and decreased the renal uptake of 111In-DOTA-Nle-CycMSHhex, providing a new insight into the design of novel radiolabeled lactam bridge-cyclized α-MSH peptide for melanoma imaging and treatment.
PMCID: PMC2998183  PMID: 20150256
Melanoma imaging; radiolabeled cyclic peptide; alpha-melanocyte stimulating hormone; small animal imaging
18.  Peptoid-based PET imaging of vascular endothelial growth factor receptor (VEGFR) expression 
Non-invasive detection of vascular endothelial growth factor receptor 2 (VEGFR2) by positron emission tomography (PET) would allow the evaluation of tumor vascular activity in vivo. Recently, a dimeric peptoid, GU40C4, was reported as a highly potent antagonist of VEGFR2 activation inhibiting angiogenesis and tumor growth in vivo. The purpose of this work was to evaluate the potential of this peptoid for PET imaging of VEGFR2 expression. To label GU40C4 and a control peptoid with a positron emitter, 64Cu (t1/2 = 12.7 h; β+: 0.653 MeV, 17.4%), a cysteine was introduced to the C-terminus of the peptoids and then conjugated to a bifunctional chelator (DOTA: 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) through the maleimide-thiol coupling chemistry. The in vitro binding assay showed a negligible effect of the DOTA conjugation on the VEGFR2 binding affinity of GU40C4. Both peptoid conjugates were efficiently labeled with 64Cu in high radiochemical yields (> 90%); the specific activity was in the range of 10 – 80 GBq/μmol. PET imaging evaluation using a prostate cancer xenograft (PC3) mouse model showed that 64Cu-DOTA-GU40C4 had a prominent and steady accumulation in the VEGFR2 positive PC3 tumors (2.25 ± 0.24, 2.15 ± 0.34, and 1.90 ± 0.18 %ID/g at 1, 4, and 20 h p.i., respectively; n = 3), which is significantly higher than the control peptoid conjugate (0.3 – 0.5 %ID/g; p < 0.001 at 1, 4, and 20 h p.i.). Interestingly, the mouse salivary glands were also clearly visualized by 64Cu-DOTA-GU40C4 (3.17 ± 0.25, 3.00 ± 0.36, and 1.83 ± 0.21 %ID/g at 1, 4, and 20 h p.i., respectively; n = 3) rather than its control peptoid conjugate. VEGFR2 expression in the salivary glands was shown by polymerase chain reaction (PCR) assay. Our results demonstrate that 64Cu-DOTA-GU40C4 can be used to image the expression of VEGFR2 in vivo.
PMCID: PMC3477717  PMID: 23133797
VEGFR2; peptoid; PET; 64Cu; prostate cancer; tumor angiogenesis
19.  DOTA-Functionalized Polylysine: A High Number of DOTA Chelates Positively Influences the Biodistribution of Enzymatic Conjugated Anti-Tumor Antibody chCE7agl 
PLoS ONE  2013;8(4):e60350.
Site-specific enzymatic reactions with microbial transglutaminase (mTGase) lead to a homogenous species of immunoconjugates with a defined ligand/antibody ratio. In the present study, we have investigated the influence of different numbers of 1,4,7,10-tetraazacyclododecane-N-N′-N′′-N′′′-tetraacetic acid (DOTA) chelats coupled to a decalysine backbone on the in vivo behavior of the chimeric monoclonal anti-L1CAM antibody chCE7agl. The enzymatic conjugation of (DOTA)1-decalysine, (DOTA)3-decalysine or (DOTA)5-decalysine to the antibody heavy chain (via Gln295/297) gave rise to immunoconjugates containing two, six or ten DOTA moieties respectively. Radiolabeling of the immunoconjugates with 177Lu yielded specific activities of approximately 70 MBq/mg, 400 MBq/mg and 700 MBq/mg with increasing numbers of DOTA chelates. Biodistribution experiments in SKOV3ip human ovarian cancer cell xenografts demonstrated a high and specific accumulation of radioactivity at the tumor site for all antibody derivatives with a maximal tumor accumulation of 43.6±4.3% ID/g at 24 h for chCE7agl-[(DOTA)-decalysine]2, 30.6±12.0% ID/g at 24 h for chCE7agl-[(DOTA)3-decalysine]2 and 49.9±3.1% ID/g at 48 h for chCE7agl-[(DOTA)5-decalysine)]2. The rapid elimination from the blood of chCE7agl-[(DOTA)-decalysine]2 (1.0±0.1% ID/g at 24 h) is associated with a high liver accumulation (23.2±4.6% ID/g at 24 h). This behavior changed depending on the numbers of DOTA moieties coupled to the decalysine peptide with a slower blood clearance (5.1±1.0 (DOTA)3 versus 11.7±1.4% ID/g (DOTA)5, p<0.005 at 24 h) and lower radioactivity levels in the liver (21.4±3.4 (DOTA)3 versus 5.8±0.7 (DOTA)5, p<0.005 at 24 h). We conclude that the site-specific and stoichiometric uniform conjugation of the highly DOTA-substituted decalysine ((DOTA)5-decalysine) to an anti-tumor antibody leads to the formation of immunoconjugates with high specific activity and excellent in vivo behavior and is a valuable option for radioimmunotherapy and potentially antibody-drug conjugates (ADCs).
PMCID: PMC3614955  PMID: 23565233
20.  Trackable and Targeted Phage as Positron Emission Tomography (PET) Agent for Cancer Imaging 
Theranostics  2011;1:371-380.
The recent advancement of nanotechnology has provided unprecedented opportunities for the development of nanoparticle enabled technologies for detecting and treating cancer. Here, we reported the construction of a PET trackable organic nanoplatform based on phage particle for targeted tumor imaging. Method: The integrin αvβ3 targeted phage nanoparticle was constructed by expressing RGD peptides on its surface. The target binding affinity of this engineered phage particle was evaluated in vitro. A bifunctional chelator (BFC) 1,4,7,10-tetraazadodecane-N,N',N",N"'-tetraacetic acid (DOTA) or 4-((8-amino-3,6,10,13,16,19-hexaazabicyclo [6.6.6] icosane-1-ylamino) methyl) benzoic acid (AmBaSar) was then conjugated to the phage surface for 64Cu2+ chelation. After 64Cu radiolabeling, microPET imaging was performed in U87MG tumor model and the receptor specificity was confirmed by blocking experiments. Results: The phage-RGD demonstrated target specificity based on ELISA experiment. According to the TEM images, the morphology of the phage was unchanged after the modification with BFCs. The labeling yield was 25 ± 4% for 64Cu-DOTA-phage-RGD and 46 ± 5% for 64Cu-AmBaSar-phage-RGD, respectively. At 1 h time point, 64Cu-DOTA-phage-RGD and 64Cu-AmBaSar-phage-RGD have comparable tumor uptake (~ 8%ID/g). However, 64Cu-AmBaSar-phage-RGD showed significantly higher tumor uptake (13.2 ± 1.5 %ID/g, P<0.05) at late time points compared with 64Cu-DOTA-phage-RGD (10 ± 1.2 %ID/g). 64Cu-AmBaSar-phage-RGD also demonstrated significantly lower liver uptake, which could be attributed to the stability difference between these chelators. There is no significant difference between two tracers regarding the uptake in kidney and muscle at all time points tested. In order to confirm the receptor specificity, blocking experiment was performed. In the RGD blocking experiment, the cold RGD peptide was injected 2 min before the administration of 64Cu-AmBaSar-phage-RGD. Tumor uptake was partially blocked at 1 h time point. Phage-RGD particle was also used as the competitive ligand. In this case, the tumor uptake was significantly reduced and the value was kept at low level consistently. Conclusion: In this report, we constructed a PET trackable nanoplatform based on phage particle and demonstrated the imaging capability of these targeted agents. We also demonstrated that the choice of chelator could have significant impact on imaging results of nano-agents. The method established in this research may be applicable to other receptor/ligand systems for theranostic agent construction, which could have an immediate and profound impact on the field of imaging/therapy and lay the foundation for the construction of next generation cancer specific theranostic agents.
PMCID: PMC3248641  PMID: 22211143
phage particle; positron emission tomography; integrin αvβ3; RGD; Cu-64.
21.  Anti-EGFRvIII monoclonal antibody armed with 177Lu: in vivo comparison of macrocyclic and acyclic ligands 
Nuclear medicine and biology  2010;37(7):741-750.
Monoclonal antibody (mAb) L8A4 binds specifically to the epidermal growth factor receptor variant III (EGFRvIII) that is present on gliomas but not normal tissues, and is internalized rapidly after receptor binding. Because of the short range of its β-emissions, labeling this mAb with177Lu would be an attractive approach for the treatment of residual tumor margins remaining after surgical debulking of brain tumors.
Materials and Methods
L8A4 mAb was labeled with 177Lu using the acyclic ligands [(R)-2-Amino-3-(4-isothiocyanatophenyl)propyl]-trans-(S,S)-cyclohexane-1,2-diamine- pentaacetic acid (CHX-A″-DTPA) and 2-(4-Isothiocyanatobenzyl)-6-methyldiethylene- triaminepentaacetic acid (1B4M-DTPA), and the macrocyclic ligands S-2-(4- Isothiocyanatobenzyl)-1,4,7,10-tetraazacyclododecane-tetraacetic acid (C-DOTA) and α-(5-isothiocyanato-2-methoxyphenyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10- tetraacetic acid (MeO-DOTA). Paired-label tissue distribution experiments were performed in athymic mice bearing subcutaneous EGFRvIII-expressing U87.)EGFR glioma xenografts over a period of 1 to 8 days to directly compare 177Lu-labeled L8A4 to L8A4 labeled with 125I using N-succinimidyl 4-guanidinomethyl-3-[125I]iodobenzoate ([125I]SGMIB).
Except with C-DOTA, tumor uptake for the 177Lu-labeled mAb was significantly higher than the co-administered radioiodinated preparation; however, this was also the case for spleen, liver, bone and kidneys. Tumor:normal tissue ratios for 177Lu-1B4M-DTPA-L8A4 and to an even greater extent, 177Lu-MeO-DOTA-L8A4, were higher than those for [125I]SGMIB-L8A4 in most other tissues.
Tumor and normal tissue distribution patterns for this anti-EGFRvIII mAb were dependent on the nature of the bifunctional chelate used for 177Lu labeling. Optimal results were obtained with 1B4M-DTPA and MeO-DOTA, suggesting no clear advantage for acyclic vs. macrocyclic ligands for this application.
PMCID: PMC2946893  PMID: 20870149
Lu-177; radioimmunotherapy; MeO-DOTA; 1B4M-DTPA
22.  Influence of Macrocyclic Chelators on the Targeting Properties of 68Ga-Labeled Synthetic Affibody Molecules: Comparison with 111In-Labeled Counterparts 
PLoS ONE  2013;8(8):e70028.
Affibody molecules are a class of small (7 kDa) non-immunoglobulin scaffold-based affinity proteins, which have demonstrated substantial potential as probes for radionuclide molecular imaging. The use of positron emission tomography (PET) would further increase the resolution and quantification accuracy of Affibody-based imaging. The rapid in vivo kinetics of Affibody molecules permit the use of the generator-produced radionuclide 68Ga (T1/2 = 67.6 min). Earlier studies have demonstrated that the chemical nature of chelators has a substantial influence on the biodistribution properties of Affibody molecules. To determine an optimal labeling approach, the macrocyclic chelators 1,4,7,10-tetraazacylododecane-1,4,7,10-tetraacetic acid (DOTA), 1,4,7-triazacyclononane-N,N,N-triacetic acid (NOTA) and 1-(1,3-carboxypropyl)-1,4,7- triazacyclononane-4,7-diacetic acid (NODAGA) were conjugated to the N-terminus of the synthetic Affibody molecule ZHER2:S1 targeting HER2. Affibody molecules were labeled with 68Ga, and their binding specificity and cellular processing were evaluated. The biodistribution of 68Ga-DOTA-ZHER2:S1, 68Ga-NOTA-ZHER2:S1 and 68Ga-NODAGA-ZHER2:S1, as well as that of their 111In-labeled counterparts, was evaluated in BALB/C nu/nu mice bearing HER2-expressing SKOV3 xenografts. The tumor uptake for 68Ga-DOTA-ZHER2:S1 (17.9±0.7%IA/g) was significantly higher than for both 68Ga-NODAGA-ZHER2:S1 (16.13±0.67%IA/g) and 68Ga-NOTA-ZHER2:S1 (13±3%IA/g) at 2 h after injection. 68Ga-NODAGA-ZHER2:S1 had the highest tumor-to-blood ratio (60±10) in comparison with both 68Ga-DOTA-ZHER2:S1 (28±4) and 68Ga-NOTA-ZHER2:S1 (42±11). The tumor-to-liver ratio was also higher for 68Ga-NODAGA-ZHER2:S1 (7±2) than the DOTA and NOTA conjugates (5.5±0.6 vs.3.3±0.6). The influence of chelator on the biodistribution and targeting properties was less pronounced for 68Ga than for 111In. The results of this study demonstrate that macrocyclic chelators conjugated to the N-terminus have a substantial influence on the biodistribution of HER2-targeting Affibody molecules labeled with 68Ga.This can be utilized to enhance the imaging contrast of PET imaging using Affibody molecules and improve the sensitivity of molecular imaging. The study demonstrated an appreciable difference of chelator influence for 68Ga and 111In.
PMCID: PMC3731330  PMID: 23936372
23.  Comparative gallium-68 labeling of TRAP-, NOTA-, and DOTA-peptides: practical consequences for the future of gallium-68-PET 
EJNMMI Research  2012;2:28.
Currently, 68Ga-labeled 1,4,7,10-tetraazacyclododecane-tetraacetic acid (DOTA)-peptides are the most widely used class of 68Ga radiotracers for PET, although DOTA is not optimal for 68Ga complexation. More recently, 1,4,7-triazacyclononane-triacetic acid (NOTA) and particularly triazacyclononane-phosphinate (TRAP) chelators have been shown to possess superior 68Ga binding ability. Here, we report on the efficiency, reproducibility, and achievable specific activity for fully automated 68Ga labeling of DOTA-, NOTA-, and TRAP-peptide conjugates.
Compared to NOTA- and DOTA-peptides, achievable specific activity (AS) for TRAP-peptide is approximately 10 and 20 times higher, respectively. AS values in the range of 5,000 GBq/μmol were routinely obtained using 1 GBq of 68Ga, equivalent to 0.11 μg of cold mass for a 185-MBq patient dose of a 3-kDa conjugate. The TRAP-peptide could be 68Ga-labeled with excellent reproducibility and > 95% radiochemical yield for precursor amounts as low as 1 nmol.
High 68Ga labeling efficiency of TRAP-peptides could facilitate realization of kit labeling procedures. The good reproducibility of the automated synthesis is of relevance for GMP production, and the possibility to provide very high specific activities offers a high degree of safety in first clinical trials, due to reduction of cold mass content in tracer formulations.
PMCID: PMC3538506  PMID: 22682112
macrocyclic ligands; gallium-68; positron-emission tomography; peptides; bioconjugates; radiolabeling
24.  Monoclonal antibodies for copper-64 PET dosimetry and radioimmunotherapy 
Cancer Biology & Therapy  2011;11(12):1001-1007.
We previously described a two-antibody model of 64Cu radioimmunotherapy to evaluate low-dose, solid-tumor response. This model was designed to test the hypothesis that cellular internalization is critical in causing tumor cell death by mechanisms in addition to radiation damage. The purpose of the present study was to estimate radiation dosimetry for both antibodies (mAbs) using positron emission tomography (PET) imaging and evaluate the effect of internalization on tumor growth.
Dosimetry was similar between therapy groups. Median time to tumor progression to 1 g ranged from 7–12 days for control groups and was 32 days for both treatment groups (p < 0.0001). No statistically significant difference existed between any control group or between the treatment groups.
Material and Methods
In female nude mice bearing LS174T colon carcinoma xenografts, tumor dosimetry was calculated using serial PET images of three mice in each group of either internalizing 64Cu-labeled DOTA-cBR96 (DOTA = 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) or non-internalizing 64Cu-labeled DOTA-cT84.66 from 3 to 48 h. For the therapy study, controls (n = 10) received saline, DOTA-cBR96 or DOTA-cT84.66. Treatment animals (n = 9) received 0.890 mCi of 64Cu-labeled DOTA-cBR96 or 0.710 mCi of 64Cu-labeled DOTA-cT84.66. Tumors were measured daily.
PET imaging allows the use of 64Cu for pre-therapy calculation of tumor dosimetry. In spite of highly similar tumor dosimetry, an internalizing antibody did not improve the outcome of 64Cu radioimmunotherapy. Radio-resistance of this tumor cell line and copper efflux may have confounded the study. Further investigations of the therapeutic efficacy of 64Cu-labeled mAbs will focus on interaction between 64Cu and tumor suppressor genes and copper chaperones.
PMCID: PMC3142363  PMID: 21464612
monoclonal antibodies; copper-64; positron emission tomography; tumor dosimetry; radioimmunotherapy; colon cancer; nude mice
25.  PET imaging of CXCR4 using copper-64 labeled peptide antagonist 
Theranostics  2011;1:251-262.
Expression of CXCR4 in cancer has been found to correlate with poor prognosis and resistance to chemotherapy. In this study we developed a derivative of the CXCR4 peptide antagonist, T140-2D, that can be labeled easily with the PET isotope copper-64, and thereby enable in vivo visualization of CXCR4 in tumors. T140 was conjugated to 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid mono (N-hydroxysuccinimide ester) (DOTA-NHS) to give T140-2D, which contains a DOTA molecule on each of the two lysine residues. 64Cu-T140-2D was evaluated in vitro by migration and binding experiments, and in vivo by microPET imaging and biodistribution, in mice bearing CXCR4-positive and CXCR4-negative tumor xenografts. T140-2D was labeled with copper-64 to give 64Cu-T140-2D in a high radiochemical yield of 86 ± 3% (not decay-corrected) and a specific activity of 0.28 - 0.30 mCi/μg (10.36 – 11.1 MBq/μg). 64Cu-T140-2D had antagonistic and binding characteristics to CXCR4 that were similar to those of T140. In vivo, 64Cu-T140-2D tended to bind to red blood cells and had to be used in a low specific activity form. In this new form 64Cu-T140-2D enabled specific imaging of CXCR4-positive, but not CXCR4-negative tumors. Undesirably, however, 64Cu-T140-2D also displayed high accumulation in the liver and kidneys. In conclusion, 64Cu-T140-2D was easily labeled and, in its low activity form, enabled imaging of CXCR4 in tumors. It had high uptake, however, in metabolic organs. Further research with imaging tracers targeting CXCR4 is required.
PMCID: PMC3085282  PMID: 21544263
T140 peptide; CXCR4 imaging; PET; copper-64

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