Background Lead-212 (212Pb, t1/2 = 10.6 h) and lead-203 (203Pb, t1/2 = 51.9 h) are an element-equ... more Background Lead-212 (212Pb, t1/2 = 10.6 h) and lead-203 (203Pb, t1/2 = 51.9 h) are an element-equivalent, or a matched theranostic radioisotope pair that show great potential for application in targeted radionuclide therapy (TRT) and single-photon emission computed tomography (SPECT), respectively. At TRIUMF we have produced both 203Pb and 212Pb using TRIUMF’s TR13 (13 MeV) and 500 MeV cyclotrons, and subsequently purified and evaluated both radioisotopes using a series of pyridine-modified DOTA analogues in comparison to the commercially available chelates DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and TCMC (1,4,7,10-tetraaza-1,4,7,10-tetra(2-carbamoylmethyl)cyclododecane). Results Proton irradiation (12.8 MeV) of natural and enriched thallium-203 (203Tl) targets gave 203Pb saturation yields of 134 ± 25 and 483 ± 3 MBq/μA, respectively. Thorium-228 (228Th, t1/2 = 1.9 y), a by-product of 232Th proton spallation on TRIUMF’s main 500 MeV beamline (beamline 1A, BL1...
Background: Temperature-sensitive radiopharmaceutical precursors require lower reaction temperatu... more Background: Temperature-sensitive radiopharmaceutical precursors require lower reaction temperatures (<100 °C) during nucleophilic radiofluorination in order to avoid compound thermolysis, often resulting in sub-optimal radiochemical yields (RCYs). To facilitate nucleophilic aromatic substitution (SNAr) of nucleofuges commonly used in radiofluorination (e.g., nitro group), we explored the use of Lewis acids as nucleophilic activators to accelerate [18F]fluoride incorporation at lower temperatures, and thereby increasing RCYs for thermolabile activated precursors. Lewis acid-assisted radiofluorination was exemplified on the temperature-sensitive compound 1-(4-(4-morpholino-7-neopentyl-7H-pyrrolo[2,3-d]pyrimidin-2-yl)phenyl)-3-(6-nitropyridin-3-yl)urea (MN3PU, compound 3) targeting leucine-rich repeat kinase 2 (LRRK2), an important target in the study of Parkinson’s disease and various cancers. Methods: To a vessel containing dried K[18F]F-K222 complex, a solution of precursor MN3P...
H4pypa was conjugated to an antibody via a newly synthesized H4pypa-phenyl-NCS; promising immuno-... more H4pypa was conjugated to an antibody via a newly synthesized H4pypa-phenyl-NCS; promising immuno-PET imaging with 44Sc was demonstrated.
With recent impressive clinical results of targeted alpha therapy using 225Ac, significant effort... more With recent impressive clinical results of targeted alpha therapy using 225Ac, significant effort has been directed towards providing a reliable and sufficient supply of 225Ac to enable widespread using of 225Ac-radiopharmaceuticals. TRIUMF has begun production of 225Ac via spallation of thorium metal with 480 MeV protons. As part of this program, a new 225Ac-production target system capable of withstanding the power deposited by the proton beam was designed and its performance simulated over a range of potential operating parameters. Special attention was given to heat transfer and stresses within the target components. The target was successfully tested in two irradiations with a 72–73 µA proton beam for a duration of 36.5 h. The decay corrected activity at end of irradiation (average ± standard deviation) was (524 ± 21) MBq (14.2 mCi) and (86 ± 13) MBq (2.3 mCi) for 225Ac and 225Ra, respectively. These correspond to saturation yields of 72.5 MBq/µA for 225Ac and 17.6 MBq/µA for 2...
European journal of medicinal chemistry, Jan 5, 2018
Herein we report the design and synthesis of a series of novel benzofuran-isatin hybrids, and in ... more Herein we report the design and synthesis of a series of novel benzofuran-isatin hybrids, and in vitro evaluation of their anti-mycobacterial activity against both drug-susceptible and multi-drug resistant (MDR) Mycobacterium tuberculosis (MTB) strains. In parallel, cytotoxicity of these hybrids was also tested in VERO cells. Preliminary results indicated that all hybrids with acceptable cytotoxicity in VERO cells (CC: 128->1024 μg/mL) exhibited considerable anti-mycobacterial activities against MTB HRv and MDR-TB with MIC ranging from 0.25 to 8 μg/mL. It is worth noting that hybrid 8f with no cytotoxicity towards VERO cells (CC: >1024 μg/mL) was found to be the most active compound (MIC: 0.25 and 0.5 μg/mL) against MTB HRv and MDR-TB strains. Comparing to the first-line anti-tuberculosis agents rifampicin and isoniazid, hybrid 8f has shown over two magnitude more active against MDR-TB. The hybrid 8f was further evaluated for its metabolic stability and in vivo pharmacokinetic...
In this study, we synthesized F-ASu-BF, a close boramino acid analog of 5-[F]fluoro-aminosuberic ... more In this study, we synthesized F-ASu-BF, a close boramino acid analog of 5-[F]fluoro-aminosuberic acid (F-ASu), via F-F isotope exchange reaction and evaluated its potential for imaging with positron emission tomography (PET). F-ASu-BF was stable in mouse plasma and taken up into PC3 prostate cancer cells via the system x amino acid transporter. The continuous use of isoflurane for anesthesia during dynamic imaging acquisition slowed down the excretion of F-ASu-BF and enabled visualization of PC3 tumor xenografts in mice. In contrast, no tumor visualization was observed from static images of F-BF-ASu due to its rapid renal excretion mediated in part by the organic anion transporter. Our data indicate that the pharmacokinetics of amino acids could be altered after being converted into their boramino acid analogs. Therefore, care should be taken when using the boramino acid strategy to design and prepare F-labeled tracers for imaging amino acid transporters/receptors with PET.
Functionalization of heterocyclic scaffolds with mono- or difluoroalkyl groups provides unique op... more Functionalization of heterocyclic scaffolds with mono- or difluoroalkyl groups provides unique opportunities to modulate drug p, influence potency and membrane permeability, and attenuate metabolism. While advances in the addition of fluoroalkyl radicals to heterocycles have been made, direct C(sp)-H heterobenzylic fluorination is comparatively unexplored. Here we demonstrate both mono- and difluorination of a range of alkyl heterocycles using a convenient process that relies on transient sulfonylation by the electrophilic fluorinating agent -fluorobenzenesulfonimide. We also report heterobenzylic trifluoromethylthiolation and F-fluorination, providing a suite of reactions for late-stage C(sp)-H functionalization of drug leads and radiotracer discovery.
Angewandte Chemie (International ed. in English), Jan 7, 2018
Peptides are often ideal ligands for diagnostic molecular imaging due to their ease of synthesis ... more Peptides are often ideal ligands for diagnostic molecular imaging due to their ease of synthesis and tuneable targeting properties. However, labelling peptides with 18F for positron emission tomography (PET) imaging presents a number of challenges. Here we show that a combination of photoactivated sodium decatungstate and [18F]-N-fluorobenzenesulfonimide effects site-selective 18F-fluorination at the branched position in leucine residues in unprotect-ed and unaltered peptides. This streamlined process provides a means to directly convert native peptides into PET imaging agents under mild aqueous conditions, enabling the rapid discovery and development of peptide-based molecular imaging tools.
The development of alpha-emitting radiopharmaceuticals using <sup>211</sup>At require... more The development of alpha-emitting radiopharmaceuticals using <sup>211</sup>At requires quantitative determination of the time-dependent nature of the <sup>211</sup>At biodistribution. However, imaging-based methods for acquiring this information with <sup>211</sup>At have not found wide-spread use because of its low abundance of decay emissions suitable for external detection. In this publication we demonstrate the theranostic abilities of the <sup>211</sup>At/<sup>209</sup>At isotope pair and present the first-ever <sup>209</sup>At SPECT Images. <b>Methods:</b> The VECTor microSPECT/PET/CT scanner was used to image <sup>209</sup>At with a collimator suitable for the 511 keV annihilation photons of PET isotopes. Data from distinct photopeaks of the <sup>209</sup>At energy spectrum (195 keV (22.6%), 239 keV (12.4%), 545 keV (91.0%), a combined 782/790 keV peak (147%), and…
Zirconium-89 (Zr, t=78.4h) liquid target (LT) production offers an approach to introduce this pos... more Zirconium-89 (Zr, t=78.4h) liquid target (LT) production offers an approach to introduce this positron-emitting isotope to cyclotron centres without the need for a separate solid target (ST) production set up. We compared the production, purification, and antibody radiolabeling yields ofZr-(LT) andZr-(ST), and assessed the feasibility ofZr-(LT) for preclinical PET/CT. Zr-(ST) production was performed with anY foil on a TR 19 cyclotron at 13.8MeV. For LT production; an aqueous solution of yttrium nitrate (Y(NO)·6HO) was irradiated on a TR 13 cyclotron at 12MeV.Zr was purified from the ST or LT material with hydroxamate resin, and used to radiolabel p-SCN-Bn-Deferoxamine (DFO)-conjugated Trastuzumab. MicroPET-CT imaging was performed at 1, 3 and 5days post-injection ofZr-DFO-Trastuzumab from ST or LT with biodistribution analysis on day 5. Irradiation of the ST yielded 2.88±1.07GBq/μA with a beam current of 14.0±3.8μA and irradiation time of 137±48min at end of bombardment while LT yi...
Angewandte Chemie (International ed. in English), Jan 29, 2017
H2macropa, an 18-membered macrocycle, was investigated for 225Ac chelation in targeted alpha ther... more H2macropa, an 18-membered macrocycle, was investigated for 225Ac chelation in targeted alpha therapy (TAT). Radiolabeling studies showed that macropa, at submicromolar concentration, complexed all 225Ac (26 kBq) in 5 min at RT. [225Ac(macropa)]+ remained intact over 7-8 days when challenged with either excess La3+ ions or human serum, and did not accumulate in any organ after 5 h in healthy mice. A bifunctional analogue macropa-NCS was conjugated to trastuzumab, as well as to the prostate-specific membrane antigen-targeting compound RPS-070. Both constructs rapidly radiolabeled 225Ac in just minutes at RT, and macropa-Tmab retained >99% of its 225Ac in human serum after 7 days. In LNCaP xenograft mice, 225Ac-macropa-RPS-070 was selectively targeted to tumors and did not release free 225Ac over 96 h. These findings establish macropa to be a highly promising ligand for 225Ac chelation that will facilitate the clinical development of 225Ac TAT for the treatment of soft-tissue metast...
Potentially nonadentate (NO) bifunctional chelator p-SCN-Bn-Hneunpa and its immunoconjugate Hneun... more Potentially nonadentate (NO) bifunctional chelator p-SCN-Bn-Hneunpa and its immunoconjugate Hneunpa-trastuzumab for In radiolabeling are synthesized. The ability of p-SCN-Bn-Hneunpa and Hneunpa-trastuzumab to quantitatively radiolabel InCl at an ambient temperature within 15 or 30 min, respectively, is presented. Thermodynamic stability determination with In, Bi, and La resulted in high conditional stability constant (pM) values. In vitro human serum stability assays have demonstrated both In complexes to have high stability over 5 days. Mouse biodistribution of [In][In(p-NO-Bn-neunpa)], compared to that of [In][In(p-NH-Bn-CHX-A″-diethylenetriamine pentaacetic acid (DTPA))], at 1, 4, and 24 h shows fast clearance of both complexes from the mice within 24 h. In a second mouse biodistribution study, the immunoconjugates In-neunpa-trastuzumab and In-CHX-A″-DTPA-trastuzumab demonstrate a similar distribution profile but with slightly lower tumor uptake of In-neunpa-trastuzumab compared to that of In-CHX-A″-DTPA-trastuzumab. These results were also confirmed by immuno-single photon emission computed tomography (immuno-SPECT) imaging in vivo. These initial investigations reveal the acyclic bifunctional chelator p-SCN-Bn-Hneunpa to be a promising chelator for In (and other radiometals) with high in vitro stability and also show Hneunpa-trastuzumab to be an excellent In chelator with promising biodistribution in mice.
Background Lead-212 (212Pb, t1/2 = 10.6 h) and lead-203 (203Pb, t1/2 = 51.9 h) are an element-equ... more Background Lead-212 (212Pb, t1/2 = 10.6 h) and lead-203 (203Pb, t1/2 = 51.9 h) are an element-equivalent, or a matched theranostic radioisotope pair that show great potential for application in targeted radionuclide therapy (TRT) and single-photon emission computed tomography (SPECT), respectively. At TRIUMF we have produced both 203Pb and 212Pb using TRIUMF’s TR13 (13 MeV) and 500 MeV cyclotrons, and subsequently purified and evaluated both radioisotopes using a series of pyridine-modified DOTA analogues in comparison to the commercially available chelates DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid) and TCMC (1,4,7,10-tetraaza-1,4,7,10-tetra(2-carbamoylmethyl)cyclododecane). Results Proton irradiation (12.8 MeV) of natural and enriched thallium-203 (203Tl) targets gave 203Pb saturation yields of 134 ± 25 and 483 ± 3 MBq/μA, respectively. Thorium-228 (228Th, t1/2 = 1.9 y), a by-product of 232Th proton spallation on TRIUMF’s main 500 MeV beamline (beamline 1A, BL1...
Background: Temperature-sensitive radiopharmaceutical precursors require lower reaction temperatu... more Background: Temperature-sensitive radiopharmaceutical precursors require lower reaction temperatures (<100 °C) during nucleophilic radiofluorination in order to avoid compound thermolysis, often resulting in sub-optimal radiochemical yields (RCYs). To facilitate nucleophilic aromatic substitution (SNAr) of nucleofuges commonly used in radiofluorination (e.g., nitro group), we explored the use of Lewis acids as nucleophilic activators to accelerate [18F]fluoride incorporation at lower temperatures, and thereby increasing RCYs for thermolabile activated precursors. Lewis acid-assisted radiofluorination was exemplified on the temperature-sensitive compound 1-(4-(4-morpholino-7-neopentyl-7H-pyrrolo[2,3-d]pyrimidin-2-yl)phenyl)-3-(6-nitropyridin-3-yl)urea (MN3PU, compound 3) targeting leucine-rich repeat kinase 2 (LRRK2), an important target in the study of Parkinson’s disease and various cancers. Methods: To a vessel containing dried K[18F]F-K222 complex, a solution of precursor MN3P...
H4pypa was conjugated to an antibody via a newly synthesized H4pypa-phenyl-NCS; promising immuno-... more H4pypa was conjugated to an antibody via a newly synthesized H4pypa-phenyl-NCS; promising immuno-PET imaging with 44Sc was demonstrated.
With recent impressive clinical results of targeted alpha therapy using 225Ac, significant effort... more With recent impressive clinical results of targeted alpha therapy using 225Ac, significant effort has been directed towards providing a reliable and sufficient supply of 225Ac to enable widespread using of 225Ac-radiopharmaceuticals. TRIUMF has begun production of 225Ac via spallation of thorium metal with 480 MeV protons. As part of this program, a new 225Ac-production target system capable of withstanding the power deposited by the proton beam was designed and its performance simulated over a range of potential operating parameters. Special attention was given to heat transfer and stresses within the target components. The target was successfully tested in two irradiations with a 72–73 µA proton beam for a duration of 36.5 h. The decay corrected activity at end of irradiation (average ± standard deviation) was (524 ± 21) MBq (14.2 mCi) and (86 ± 13) MBq (2.3 mCi) for 225Ac and 225Ra, respectively. These correspond to saturation yields of 72.5 MBq/µA for 225Ac and 17.6 MBq/µA for 2...
European journal of medicinal chemistry, Jan 5, 2018
Herein we report the design and synthesis of a series of novel benzofuran-isatin hybrids, and in ... more Herein we report the design and synthesis of a series of novel benzofuran-isatin hybrids, and in vitro evaluation of their anti-mycobacterial activity against both drug-susceptible and multi-drug resistant (MDR) Mycobacterium tuberculosis (MTB) strains. In parallel, cytotoxicity of these hybrids was also tested in VERO cells. Preliminary results indicated that all hybrids with acceptable cytotoxicity in VERO cells (CC: 128->1024 μg/mL) exhibited considerable anti-mycobacterial activities against MTB HRv and MDR-TB with MIC ranging from 0.25 to 8 μg/mL. It is worth noting that hybrid 8f with no cytotoxicity towards VERO cells (CC: >1024 μg/mL) was found to be the most active compound (MIC: 0.25 and 0.5 μg/mL) against MTB HRv and MDR-TB strains. Comparing to the first-line anti-tuberculosis agents rifampicin and isoniazid, hybrid 8f has shown over two magnitude more active against MDR-TB. The hybrid 8f was further evaluated for its metabolic stability and in vivo pharmacokinetic...
In this study, we synthesized F-ASu-BF, a close boramino acid analog of 5-[F]fluoro-aminosuberic ... more In this study, we synthesized F-ASu-BF, a close boramino acid analog of 5-[F]fluoro-aminosuberic acid (F-ASu), via F-F isotope exchange reaction and evaluated its potential for imaging with positron emission tomography (PET). F-ASu-BF was stable in mouse plasma and taken up into PC3 prostate cancer cells via the system x amino acid transporter. The continuous use of isoflurane for anesthesia during dynamic imaging acquisition slowed down the excretion of F-ASu-BF and enabled visualization of PC3 tumor xenografts in mice. In contrast, no tumor visualization was observed from static images of F-BF-ASu due to its rapid renal excretion mediated in part by the organic anion transporter. Our data indicate that the pharmacokinetics of amino acids could be altered after being converted into their boramino acid analogs. Therefore, care should be taken when using the boramino acid strategy to design and prepare F-labeled tracers for imaging amino acid transporters/receptors with PET.
Functionalization of heterocyclic scaffolds with mono- or difluoroalkyl groups provides unique op... more Functionalization of heterocyclic scaffolds with mono- or difluoroalkyl groups provides unique opportunities to modulate drug p, influence potency and membrane permeability, and attenuate metabolism. While advances in the addition of fluoroalkyl radicals to heterocycles have been made, direct C(sp)-H heterobenzylic fluorination is comparatively unexplored. Here we demonstrate both mono- and difluorination of a range of alkyl heterocycles using a convenient process that relies on transient sulfonylation by the electrophilic fluorinating agent -fluorobenzenesulfonimide. We also report heterobenzylic trifluoromethylthiolation and F-fluorination, providing a suite of reactions for late-stage C(sp)-H functionalization of drug leads and radiotracer discovery.
Angewandte Chemie (International ed. in English), Jan 7, 2018
Peptides are often ideal ligands for diagnostic molecular imaging due to their ease of synthesis ... more Peptides are often ideal ligands for diagnostic molecular imaging due to their ease of synthesis and tuneable targeting properties. However, labelling peptides with 18F for positron emission tomography (PET) imaging presents a number of challenges. Here we show that a combination of photoactivated sodium decatungstate and [18F]-N-fluorobenzenesulfonimide effects site-selective 18F-fluorination at the branched position in leucine residues in unprotect-ed and unaltered peptides. This streamlined process provides a means to directly convert native peptides into PET imaging agents under mild aqueous conditions, enabling the rapid discovery and development of peptide-based molecular imaging tools.
The development of alpha-emitting radiopharmaceuticals using <sup>211</sup>At require... more The development of alpha-emitting radiopharmaceuticals using <sup>211</sup>At requires quantitative determination of the time-dependent nature of the <sup>211</sup>At biodistribution. However, imaging-based methods for acquiring this information with <sup>211</sup>At have not found wide-spread use because of its low abundance of decay emissions suitable for external detection. In this publication we demonstrate the theranostic abilities of the <sup>211</sup>At/<sup>209</sup>At isotope pair and present the first-ever <sup>209</sup>At SPECT Images. <b>Methods:</b> The VECTor microSPECT/PET/CT scanner was used to image <sup>209</sup>At with a collimator suitable for the 511 keV annihilation photons of PET isotopes. Data from distinct photopeaks of the <sup>209</sup>At energy spectrum (195 keV (22.6%), 239 keV (12.4%), 545 keV (91.0%), a combined 782/790 keV peak (147%), and…
Zirconium-89 (Zr, t=78.4h) liquid target (LT) production offers an approach to introduce this pos... more Zirconium-89 (Zr, t=78.4h) liquid target (LT) production offers an approach to introduce this positron-emitting isotope to cyclotron centres without the need for a separate solid target (ST) production set up. We compared the production, purification, and antibody radiolabeling yields ofZr-(LT) andZr-(ST), and assessed the feasibility ofZr-(LT) for preclinical PET/CT. Zr-(ST) production was performed with anY foil on a TR 19 cyclotron at 13.8MeV. For LT production; an aqueous solution of yttrium nitrate (Y(NO)·6HO) was irradiated on a TR 13 cyclotron at 12MeV.Zr was purified from the ST or LT material with hydroxamate resin, and used to radiolabel p-SCN-Bn-Deferoxamine (DFO)-conjugated Trastuzumab. MicroPET-CT imaging was performed at 1, 3 and 5days post-injection ofZr-DFO-Trastuzumab from ST or LT with biodistribution analysis on day 5. Irradiation of the ST yielded 2.88±1.07GBq/μA with a beam current of 14.0±3.8μA and irradiation time of 137±48min at end of bombardment while LT yi...
Angewandte Chemie (International ed. in English), Jan 29, 2017
H2macropa, an 18-membered macrocycle, was investigated for 225Ac chelation in targeted alpha ther... more H2macropa, an 18-membered macrocycle, was investigated for 225Ac chelation in targeted alpha therapy (TAT). Radiolabeling studies showed that macropa, at submicromolar concentration, complexed all 225Ac (26 kBq) in 5 min at RT. [225Ac(macropa)]+ remained intact over 7-8 days when challenged with either excess La3+ ions or human serum, and did not accumulate in any organ after 5 h in healthy mice. A bifunctional analogue macropa-NCS was conjugated to trastuzumab, as well as to the prostate-specific membrane antigen-targeting compound RPS-070. Both constructs rapidly radiolabeled 225Ac in just minutes at RT, and macropa-Tmab retained >99% of its 225Ac in human serum after 7 days. In LNCaP xenograft mice, 225Ac-macropa-RPS-070 was selectively targeted to tumors and did not release free 225Ac over 96 h. These findings establish macropa to be a highly promising ligand for 225Ac chelation that will facilitate the clinical development of 225Ac TAT for the treatment of soft-tissue metast...
Potentially nonadentate (NO) bifunctional chelator p-SCN-Bn-Hneunpa and its immunoconjugate Hneun... more Potentially nonadentate (NO) bifunctional chelator p-SCN-Bn-Hneunpa and its immunoconjugate Hneunpa-trastuzumab for In radiolabeling are synthesized. The ability of p-SCN-Bn-Hneunpa and Hneunpa-trastuzumab to quantitatively radiolabel InCl at an ambient temperature within 15 or 30 min, respectively, is presented. Thermodynamic stability determination with In, Bi, and La resulted in high conditional stability constant (pM) values. In vitro human serum stability assays have demonstrated both In complexes to have high stability over 5 days. Mouse biodistribution of [In][In(p-NO-Bn-neunpa)], compared to that of [In][In(p-NH-Bn-CHX-A″-diethylenetriamine pentaacetic acid (DTPA))], at 1, 4, and 24 h shows fast clearance of both complexes from the mice within 24 h. In a second mouse biodistribution study, the immunoconjugates In-neunpa-trastuzumab and In-CHX-A″-DTPA-trastuzumab demonstrate a similar distribution profile but with slightly lower tumor uptake of In-neunpa-trastuzumab compared to that of In-CHX-A″-DTPA-trastuzumab. These results were also confirmed by immuno-single photon emission computed tomography (immuno-SPECT) imaging in vivo. These initial investigations reveal the acyclic bifunctional chelator p-SCN-Bn-Hneunpa to be a promising chelator for In (and other radiometals) with high in vitro stability and also show Hneunpa-trastuzumab to be an excellent In chelator with promising biodistribution in mice.
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Papers by Paul Schaffer