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The incorporation of non-covalent albumin binding moieties (ABMs) into radiotracers results in increased circulation time, leading to a higher uptake in the target tissues such as the tumor, and, in some cases, reduced kidney retention. We previously developed [ 18 F]AlF NOTA-K(ABM)-α v β 6 -BP, where α v β 6 -BP is a peptide with high affinity for the cell surface receptor integrin α v β 6 that is overexpressed in several cancers, and the ABM is an iodophenyl-based moiety. [ 18 F]AlF NOTA-K(ABM)-α v β 6 -BP demonstrated prolonged blood circulation compared to the non-ABM parent peptide, resulting in high, α v β 6 -targeted uptake with continuously improving detection of α v β 6 (+) tumors using PET/CT. To further extend the imaging window beyond that of fluorine-18 ( t 1/2 = 110 min) and to investigate the pharmacokinetics at later time points, we radiolabeled the α v β 6 = 12.7 h). Two peptides were synthesized without ( t 1/2 = 12.7 h). Two peptides were synthesized without ( 1 ) and with ( 2 ) the ABM and radiolabeled with copper-64 to yield [ 64 Cu] 1 and [ 64 Cu] 2 , respectively. The affinity of [ nat Cu] 1 and [ nat Cu] 2 for the integrin α v β 6 was assessed by enzyme-linked immunosorbent assay. [ 64 Cu] 1 and [ 64 Cu] 2 were evaluated in vitro (cell binding and internalization) using DX3puroβ6 (α v β 6 (+)), DX3puro (α v β 6 (-)), and pancreatic BxPC-3 (α v β 6 (+)) cells, in an albumin binding assay, and for stability in both mouse and human serum. In vivo (PET/CT imaging) and biodistribution studies were done in mouse models bearing either the paired DX3puroβ6/DX3puro or BxPC-3 xenograft tumors. [ 64 Cu] 1 and [ 64 Cu] 2 were synthesized in ≥97% radiochemical purity. In vitro , [ nat Cu] 1 and [ nat Cu] 2 maintained low nanomolar affinity for integrin α v β 6 (IC 50 = 28 ± 3 and 19 ± 5 nM, respectively); [ 64 Cu] 1 and [ 64 Cu] 2 showed comparable binding to α v β 6 (+) cells (DX3puroβ6: ≥70%, ≥42% internalized; BxPC-3: ≥19%, ≥12% internalized) and ≤3% to the α v β 6 (-) DX3puro cells. Both radiotracers were ≥98% stable in human serum at 24 h, and [ 64 Cu] 2 showed a 6-fold higher binding to human serum protein than [ 64 Cu] 1 . In vivo , selective uptake in the α v β 6 (+) tumors was observed with tumor visualization up to 72 h for [ 64 Cu] 2 . A 3-5-fold higher α v β 6 (+) tumor uptake of [ 64 Cu] 2 vs [ 64 Cu] 1 was observed throughout, at least 2.7-fold improved BxPC-3-to-kidney and BxPC-3-to-blood ratios, and 2-fold improved BxPC-3-to-stomach ratios were noted for [ 64 Cu] 2 at 48 h. Incorporation of an iodophenyl-based ABM into the α v β 6 -BP ([ 64 Cu] 2 ) prolonged circulation time and resulted in improved pharmacokinetics, including increased uptake in α v β 6 (+) tumors that enabled visualization of α v β 6 (+) tumors up to 72 h by PET/CT imaging.

Purpose: The α v β 6 -BP peptide selectively targets the integrin α v β 6 , a cell surface receptor recognized as a prognostic indicator for several challenging malignancies. Given that the 4-[ 18 F]fluorobenzoyl (FBA)-labeled peptide is a promising PET imaging agent, radiolabeling via aluminum [ 18 F]fluoride chelation and introduction of an albumin binding moiety (ABM) have the potential to considerably simplify radiochemistry and improve the pharmacokinetics by increasing biological half-life., Procedures: The peptides NOTA-α v β 6 -BP (1) and NOTA-K(ABM)-α v β 6 -BP (2) were synthesized on solid phase, radiolabeled with aluminum [ 18 F]fluoride, and evaluated in vitro (integrin ELISA, albumin binding, cell studies) and in vivo in mouse models bearing paired DX3puroβ6 [α v β 6 (+)]/DX3puro [α v β 6 (-)], and for [ 18 F]AlF 2, BxPC-3 [α v β 6 (+)] cell xenografts (PET imaging, biodistribution)., Results: The peptides were radiolabeled in 23.0 ± 5.7 % and 22.1 ± 4.4 % decay-corrected radiochemical yield, respectively, for [ 18 F]AlF 1 and [ 18 F]AlF 2. Both demonstrated excellent affinity and selectivity for integrin α v β 6 by ELISA (IC 50 (α v β 6 ) = 3-7 nM vs IC 50 (α v β 3 ) > 10 μM) and in cell binding studies (51.0 ± 0.7 % and 47.2 ± 0.7 % of total radioactivity bound to DX3puroβ6 cells at 1 h, respectively, vs. ≤ 1.2 % to DX3puro for both compounds). The radiotracer [ 18 F]AlF 1 bound to human serum at 16.3 ± 1.9 %, compared to 67.5 ± 1.0 % for the ABM-containing [ 18 F]AlF 2. In vivo studies confirmed the effect of the ABM on blood circulation (≤ 0.1 % ID/g remaining in blood for [ 18 F]AlF 1 as soon as 1 h p.i. vs. > 2 % ID/g for [ 18 F]AlF 2 at 6 h p.i.) and higher α v β 6 (+) tumor uptake (4 h: DX3puroβ6; [ 18 F]AlF 1: 3.0 ± 0.7 % ID/g, [ 18 F]AlF 2: 7.2 ± 0.7 % ID/g; BxPC-3; [ 18 F]AlF 2: 10.2 ± 0.1 % ID/g)., Conclusion: Both compounds were prepared using standard chemistries; affinity and selectivity for integrin α v β 6 in vitro remained unaffected by the albumin binding moiety. In vivo, the albumin binding moiety resulted in prolonged circulation and higher α v β 6 -targeted uptake.

Unlabelled: Radiotracers based on the peptide A20FMDV2 selectively target the cell surface receptor integrin αvβ6. This integrin has been identified as a prognostic indicator correlating with the severity of disease for several challenging malignancies. In previous studies of A20FMDV2 peptides labeled with 4-(18)F-fluorobenzoic acid ((18)F-FBA), we have shown that the introduction of poly(ethylene glycol) (PEG) improves pharmacokinetics, including increased uptake in αvβ6-expressing tumors. The present study evaluated the effect of site-specific C-terminal or dual (N- and C-terminal) PEGylation, yielding (18)F-FBA-A20FMDV2-PEG28 (4) and (18)F-FBA-PEG28-A20FMDV2-PEG28 (5), on αvβ6-targeted tumor uptake and pharmacokinetics. The results are compared with (18)F-FBA -labeled A20FMDV2 radiotracers (1- 3) bearing either no PEG or different PEG units at the N terminus., Methods: The radiotracers were prepared and radiolabeled on solid phase. Using 3 cell lines, DX3puroβ6 (αvβ6+), DX3puro (αvβ6-), and BxPC-3 (αvβ6+), we evaluated the radiotracers in vitro (serum stability; cell binding and internalization) and in vivo in mouse models bearing paired DX3puroβ6-DX3puro and, for 5, BxPC-3 xenografts., Results: The size and location of the PEG units significantly affected αvβ6 targeting and pharmacokinetics. Although the C-terminally PEGylated 4 showed some improvements over the un-PEGylated (18)F-FBA-A20FMDV2 (1), it was the bi-terminally PEGylated 5 that displayed the more favorable combination of high αvβ6 affinity, selectivity, and pharmacokinetic profile. In vitro, 5 bound to αvβ6-expressing DX3puroβ6 and BxPC-3 cells with 60.5% ± 3.3% and 48.8% ± 8.3%, respectively, with a significant fraction of internalization (37.2% ± 4.0% and 37.6% ± 4.1% of total radioactivity, respectively). By comparison, in the DX3puro control 5: showed only 3.0% ± 0.5% binding and 0.9% ± 0.2% internalization. In vivo, 5: maintained high, αvβ6-directed binding in the paired DX3puroβ6-DX3puro model (1 h: DX3puroβ6, 2.3 ± 0.2 percentage injected dose per gram [%ID/g]; DX3puroβ6/DX3puro ratio, 6.5:1; 4 h: 10.7:1). In the pancreatic BxPC-3 model, uptake was 4.7 ± 0.9 %ID/g (1 h) despite small tumor sizes (20-80 mg)., Conclusion: The bi-PEGylated radiotracer 5 showed a greatly improved pharmacokinetic profile, beyond what was predicted from individual N- or C-terminal PEGylation. It appears that the 2 PEG units acted synergistically to result in an improved metabolic profile including high αvβ6+ tumor uptake and retention., (© 2015 by the Society of Nuclear Medicine and Molecular Imaging, Inc.)

Purpose: The integrin αvβ6 is overexpressed in a variety of aggressive cancers and serves as a prognosis marker. This study describes the conjugation, radiolabeling, and in vitro and in vivo evaluation of four chelators to determine the best candidate for (64)Cu radiolabeling of A20FMDV2, an αvβ6 targeting peptide., Procedures: Four chelators were conjugated onto PEG28-A20FMDV2 (1): 11-carboxymethyl-1,4,8,11-tetraazabicyclo[6.6.2]hexadecane-4-methanephosphonic acid (CB-TE1A1P), 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA), 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA), and 4,4'-((3,6,10,13,16,19-hexazazbicyclo[6.6.6]ico-sane-1,8-diylbis(aza-nediyl))bis(methylene)dibenzoic acid (BaBaSar). All peptides were radiolabeled with (64)Cu in ammonium acetate buffer at pH 6 and formulated to pH 7.2 in PBS for use. The radiotracers were evaluated using in vitro cell binding and internalization assays and serum stability assays. In vivo studies conducted include blocking, biodistribution, and small animal PET imaging. Autoradiography and histology were also conducted., Results: All radiotracers were radiolabeled in good radiochemical purity (>95 %) under mild conditions (37-50 °C for 15 min) with high specific activity (0.58-0.60 Ci/μmol). All radiotracers demonstrated αvβ6-directed cell binding (>46 %) with similar internalization levels (>23 %). The radiotracers (64)Cu-CB-TE1A1P-1 and (64)Cu-BaBaSar-1 showed improved specificity for the αvβ6 positive tumor in vivo over (64)Cu-DOTA-1 and (64)Cu-NOTA-1 (+/- tumor uptake ratios-3.82 +/- 0.44, 3.82 ± 0.41, 2.58 ± 0.58, and 1.29 ± 0.14, respectively). Of the four radiotracers, (64)Cu-NOTA-1 exhibited the highest liver uptake (10.83 ± 0.1 % ID/g at 4 h)., Conclusions: We have successfully conjugated, radiolabeled, and assessed the four chelates CB-TE1A1P, DOTA, NOTA, and BaBaSar both in vitro and in vivo. However, the data suggests no clear "best candidate" for the (64)Cu-radiolabeling of A20FMDV2, but instead a trade-off between the different properties (e.g., stability, selectivity, pharmacokinetics, etc.) with no obvious effects of the individual chelators.

Introduction: Incorporation of fluorine-18 ((18)F) into radiotracers by capturing ionic [(18)F]-species can greatly accelerate and simplify radiolabeling for this important positron emission tomography (PET) radioisotope. Among the different strategies, the incorporation of aluminum [(18)F]fluoride (Al[(18)F](2+)) into NOTA chelators has recently emerged as a robust approach to peptide radiolabeling. This study presents Al[(18)F](2+)-radiolabeling of an α(v)β₆ integrin-targeted peptide (NOTA-PEG₂₈-A20FMDV2) and its in vitro and in vivo evaluation., Methods: Aluminum [(18)F]fluoride was prepared at r.t. from [(18)F]fluoride (40 MBq-11 GBq) and introduced into NOTA-PEG₂₈-A20FMDV2 (1) in sodium acetate (pH 4.1; 100°C, 15 min). The radiotracer Al[(18)F] NOTA-PEG₂₈-A20FMDV2 (2) was purified by HPLC, formulated in PBS and evaluated in vitro (stability; binding and internalization in α(v)β₆(+) and α(v)β₆(-) cells) and in vivo (paired α(v)β₆(+) and α(v)β₆(-) xenograft mice: PET/CT, biodistribution, tumor autoradiography and metabolites)., Results: The radiotracer 2 was prepared in 90 ± 6 min (incl. formulation; n=3) in 19.3 ± 5.4% decay corrected radiochemical yield (radiochemical purity: >99%; specific activity: 158 ± 36 GBq/μmol) and was stable in PBS and serum (2 h). During in vitro cell binding studies, 2 showed high, α(v)β₆-targeted binding (α(v)β₆(+): 42.4 ± 1.2% of total radioactivity, ratio (+)/(-)=8.4/1) and internalization (α(v)β₆(+): 28.3 ± 0.5% of total radioactivity, (+)/(-)=11.7/1). In vivo, 2 maintained α(v)β₆-targeted binding (biodistribution; 1 h: α(v)β₆(+): 1.74 ± 0.38% ID/g, (+)/(-)=2.72/1; 4 h: α(v)β₆(+): 1.21 ± 0.56% ID/g, (+)/(-)=4.0/1; 11% intact 2 in tumor at 1 h), with highest uptake around the tumor edge (autoradiography). Most of the radioactivity cleared rapidly in the urine within one hour, but a significant fraction remained trapped in the kidneys (4 h: 229 ± 44% ID/g)., Conclusion: The Al[(18)F]/NOTA-based radiolabeling was rapid and efficient, and the radiotracer 2 showed good α(v)β₆-selectivity in vitro and in vivo. However, in contrast to A20FMDV2 labeled with covalently bound [(18)F]-prosthetic groups (e.g., [(18)F]fluorobenzoic acid), 2 demonstrated significant trapping in kidneys, similar to radiometal-labeled chelator-analogs of 2., (© 2013.)

Introduction: Click chemistry, particularly the Huisgen 1,3-dipolar cycloaddition of an alkyne with an azide, has quickly become popular for site-specific radiolabeling. Recently, strain-promoted click chemistries have been developed, eliminating the need for potentially toxic copper catalysts. This study presents radiolabeling of an α(v)β(6) integrin targeting peptide (A20FMDV2) via strain-promoted click using a fluorine-18 prosthetic group, and in vitro and in vivo evaluation., Methods: The radiotracer was prepared from and N(3)-PEG(7)-A20FMDV2 (ethanol; 10 min; 35-45 °C). HPLC-purified and formulated radiotracer 1 was evaluated in vitro by cell binding (DX3puroβ6, α(v)β(6)-positive; and DX3puro, α(v)β(6)-negative control) and serum stability, and in vivo using PET/CT imaging and biodistribution studies in mice., Results: The radiotracer 1 was readily prepared and purified (from 2: 40±4 min including HPLC, 11.9±3.2% decay corrected isolated radiochemical yield, >99% radiochemical purity, n=4) and displayed good stability (1 h: >99%, saline; 94.6%, serum). Strong α(v)β(6)-targeted binding was observed in vitro (DX3puroβ6 cells, 15 min: 43.2% binding, >6:1 for DX3puroβ6:DX3puro). In the mouse model DX3puroβ6-tumor binding was low (1 h: 0.47±0.28% ID/g, 4h: 0.14±0.09% ID/g) and clearing from the bloodstream was via the renal and hepatobiliary routes (urine: 167±84% ID/g at 1 h, 10.3±4.8% ID/g at 4 h; gall bladder: 95±33% ID/g at 1 h, 63±11% ID/g at 4 h)., Conclusion: Copper-free, strain-promoted click chemistry is an attractive, straightforward approach to radiolabeling. Although the [(18)F]FBA-C(6)-ADBIO-based prosthetic group did not interfere with α(v)β(6)-targeted binding in vitro, it did influence the pharmacokinetics, possibly due to its size and lipophilic nature., (Copyright © 2013 Elsevier Inc. All rights reserved.)

PurposeThe αvβ6-BP peptide selectively targets the integrin αvβ6, a cell surface receptor recognized as a prognostic indicator for several challenging malignancies. Given that the 4-[18F]fluorobenzoyl (FBA)-labeled peptide is a promising PET imaging agent, radiolabeling via aluminum [18F]fluoride chelation and introduction of an albumin binding moiety (ABM) have the potential to considerably simplify radiochemistry and improve the pharmacokinetics by increasing biological half-life.ProceduresThe peptides NOTA-αvβ6-BP (1) and NOTA-K(ABM)-αvβ6-BP (2) were synthesized on solid phase, radiolabeled with aluminum [18F]fluoride, and evaluated in vitro (integrin ELISA, albumin binding, cell studies) and in vivo in mouse models bearing paired DX3puroβ6 [αvβ6(+)]/DX3puro [αvβ6(-)], and for [18F]AlF 2, BxPC-3 [αvβ6(+)] cell xenografts (PET imaging, biodistribution).ResultsThe peptides were radiolabeled in 23.0 ± 5.7 % and 22.1 ± 4.4 % decay-corrected radiochemical yield, respectively, for [18F]AlF 1 and [18F]AlF 2. Both demonstrated excellent affinity and selectivity for integrin αvβ6 by ELISA (IC50(αvβ6) = 3-7 nM vs IC50(αvβ3) > 10 μM) and in cell binding studies (51.0 ± 0.7 % and 47.2 ± 0.7 % of total radioactivity bound to DX3puroβ6 cells at 1 h, respectively, vs. ≤ 1.2 % to DX3puro for both compounds). The radiotracer [18F]AlF 1 bound to human serum at 16.3 ± 1.9 %, compared to 67.5 ± 1.0 % for the ABM-containing [18F]AlF 2. In vivo studies confirmed the effect of the ABM on blood circulation (≤ 0.1 % ID/g remaining in blood for [18F]AlF 1 as soon as 1 h p.i. vs. > 2 % ID/g for [18F]AlF 2 at 6 h p.i.) and higher αvβ6(+) tumor uptake (4 h: DX3puroβ6; [18F]AlF 1: 3.0 ± 0.7 % ID/g, [18F]AlF 2: 7.2 ± 0.7 % ID/g; BxPC-3; [18F]AlF 2: 10.2 ± 0.1 % ID/g).ConclusionBoth compounds were prepared using standard chemistries; affinity and selectivity for integrin αvβ6 in vitro remained unaffected by the albumin binding moiety. In vivo, the albumin binding moiety resulted in prolonged circulation and higher αvβ6-targeted uptake.

UnlabelledRadiotracers based on the peptide A20FMDV2 selectively target the cell surface receptor integrin αvβ6. This integrin has been identified as a prognostic indicator correlating with the severity of disease for several challenging malignancies. In previous studies of A20FMDV2 peptides labeled with 4-(18)F-fluorobenzoic acid ((18)F-FBA), we have shown that the introduction of poly(ethylene glycol) (PEG) improves pharmacokinetics, including increased uptake in αvβ6-expressing tumors. The present study evaluated the effect of site-specific C-terminal or dual (N- and C-terminal) PEGylation, yielding (18)F-FBA-A20FMDV2-PEG28 (4) and (18)F-FBA-PEG28-A20FMDV2-PEG28 (5), on αvβ6-targeted tumor uptake and pharmacokinetics. The results are compared with (18)F-FBA -labeled A20FMDV2 radiotracers (1- 3) bearing either no PEG or different PEG units at the N terminus.MethodsThe radiotracers were prepared and radiolabeled on solid phase. Using 3 cell lines, DX3puroβ6 (αvβ6+), DX3puro (αvβ6-), and BxPC-3 (αvβ6+), we evaluated the radiotracers in vitro (serum stability; cell binding and internalization) and in vivo in mouse models bearing paired DX3puroβ6-DX3puro and, for 5, BxPC-3 xenografts.ResultsThe size and location of the PEG units significantly affected αvβ6 targeting and pharmacokinetics. Although the C-terminally PEGylated 4 showed some improvements over the un-PEGylated (18)F-FBA-A20FMDV2 (1), it was the bi-terminally PEGylated 5 that displayed the more favorable combination of high αvβ6 affinity, selectivity, and pharmacokinetic profile. In vitro, 5 bound to αvβ6-expressing DX3puroβ6 and BxPC-3 cells with 60.5% ± 3.3% and 48.8% ± 8.3%, respectively, with a significant fraction of internalization (37.2% ± 4.0% and 37.6% ± 4.1% of total radioactivity, respectively). By comparison, in the DX3puro control 5: showed only 3.0% ± 0.5% binding and 0.9% ± 0.2% internalization. In vivo, 5: maintained high, αvβ6-directed binding in the paired DX3puroβ6-DX3puro model (1 h: DX3puroβ6, 2.3 ± 0.2 percentage injected dose per gram [%ID/g]; DX3puroβ6/DX3puro ratio, 6.5:1; 4 h: 10.7:1). In the pancreatic BxPC-3 model, uptake was 4.7 ± 0.9 %ID/g (1 h) despite small tumor sizes (20-80 mg).ConclusionThe bi-PEGylated radiotracer 5 showed a greatly improved pharmacokinetic profile, beyond what was predicted from individual N- or C-terminal PEGylation. It appears that the 2 PEG units acted synergistically to result in an improved metabolic profile including high αvβ6+ tumor uptake and retention.

Cerenkov luminescence imaging (CLI) is an emerging preclinicalmolecular imagingmodality that tracks the radiation emitted in the visible spectrum by fast moving charged decay products of radionuclides. The aim of this study was in vitro and in vivo evaluation of the two radiotracers, 90Y-DOTA-PEG28-A20FMDV2 (90Y-1) and 90Y-DOTA-Ahx-A20FMDV2 (90Y-2) (>99% radiochemical purity, 3.7GBq/μmol specific activity) for noninvasive assessment of tumors expressing the integrin αvβ6 and their future use in tumor targeted radiotherapy. Cell binding and internalization in αvβ6-positive cells was 90Y-1: 10.1 ± 0.8%, 50.3± 2.1%; 90Y-2: 22.4 ± 1.7%, 44.7± 1.5% with <5% binding to αvβ6-negative control cells. Biodistribution studies showed maximum αvβ6-positive tumor uptake of the radiotracers at 1-h post injection (p.i.) (90Y-1: 0.64 ± 0.15%ID/g; 90Y-2: 0.34± 0.11%ID/g) with high renal uptake (>25%ID/g at 24h). Because of the lower tumor uptake and high radioactivity accumulation in kidneys (that could not be reduced by pre-administration of either lysine or furosemide), the luminescence signal from the αvβ6-positive tumor was not clearly detectable in CLI images. The studies suggest that CLI is useful for indicating major organ uptake for both radiotracers; however, it reaches its limitation when there is low signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Introduction: Incorporation of fluorine-18 (18F) into radiotracers by capturing ionic [18F]-species can greatly accelerate and simplify radiolabeling for this important positron emission tomography (PET) radioisotope. Among the different strategies, the incorporation of aluminum [18F]fluoride (Al[18F]2+) into NOTA chelators has recently emerged as a robust approach to peptide radiolabeling. This study presents Al[18F]2+-radiolabeling of an αvβ6 integrin-targeted peptide (NOTA-PEG28-A20FMDV2) and its in vitro and in vivo evaluation. Methods: Aluminum [18F]fluoride was prepared at r.t. from [18F]fluoride (40 MBq–11 GBq) and introduced into NOTA-PEG28-A20FMDV2 (1) in sodium acetate (pH 4.1; 100°C, 15 min). The radiotracer Al[18F] NOTA-PEG28-A20FMDV2 (2) was purified by HPLC, formulated in PBS and evaluated in vitro (stability; binding and internalization in αvβ6(+) and αvβ6(−) cells) and in vivo (paired αvβ6(+) and αvβ6(−) xenograft mice: PET/CT, biodistribution, tumor autoradiography and metabolites). Results: The radiotracer 2 was prepared in 90±6 min (incl. formulation; n= 3) in 19.3±5.4% decay corrected radiochemical yield (radiochemical purity: >99%; specific activity: 158±36 GBq/μmol) and was stable in PBS and serum (2 h). During in vitro cell binding studies, 2 showed high, αvβ6-targeted binding (αvβ6(+): 42.4±1.2% of total radioactivity, ratio (+)/(−) = 8.4/1) and internalization (αvβ6(+): 28.3±0.5% of total radioactivity, (+)/(−) = 11.7/1). In vivo, 2 maintained αvβ6-targeted binding (biodistribution; 1 h: αvβ6(+): 1.74±0.38% ID/g, (+)/(−) = 2.72/1; 4 h: αvβ6(+): 1.21±0.56% ID/g, (+)/(−) = 4.0/1; 11% intact 2 in tumor at 1 h), with highest uptake around the tumor edge (autoradiography). Most of the radioactivity cleared rapidly in the urine within one hour, but a significant fraction remained trapped in the kidneys (4 h: 229±44% ID/g). Conclusion: The Al[18F]/NOTA-based radiolabeling was rapid and efficient, and the radiotracer 2 showed good αvβ6-selectivity in vitro and in vivo. However, in contrast to A20FMDV2 labeled with covalently bound [18F]-prosthetic groups (e.g., [18F]fluorobenzoic acid), 2 demonstrated significant trapping in kidneys, similar to radiometal-labeled chelator-analogs of 2. [ABSTRACT FROM AUTHOR]