64Cu production via the 68Zn(p,nα)64Cu nuclear reaction: An untapped, cost-effective and high energy production route.

INTRODUCTION: Copper-64 (64Cu, t1/2 = 12.7 h) is a positron emitter well suited for theranostic applications with beta-emitting 67Cu for targeted molecular imaging and radionuclide therapy. The present work aims to evaluate the radionuclidic purity and radiochemistry of 64Cu produced via the 68Zn(p,nα)64Cu nuclear reaction. Macrocyclic chelators DOTA, NOTA, TETA, and prostate-specific membrane antigen ligand PSMA I&T were radiolabeled with purified 64Cu and tested for in vitro stability. [64Cu]Cu-PSMA I&T was used to demonstrate in vivo PET imaging using 64Cu synthesized via the 68Zn(p,nα)64Cu production route and its suitability as a theranostic imaging partner alongside 67Cu therapy. METHODS: 64Cu was produced on a 24 MeV TR-24 cyclotron at a beam energy of 23.5 MeV and currents up to 70 µA using 200 mg 68Zn encapsulated within an aluminum­indium-graphite sealed solid target assembly. 64Cu semi-automated purification was performed using a NEPTIS Mosaic-LC synthesis unit employing CU, TBP, and TK201 (TrisKem) resins. Radionuclidic purity was measured by HPGe gamma spectroscopy, while ICP-OES assessed elemental purity. Radiolabeling was performed with NOTA at room temperature and DOTA, TETA, and PSMA I&T at 95 °C. 64Cu incorporation was studied by radio-TLC. 64Cu in vitro stability of [64Cu]Cu-NOTA, [64Cu]Cu-DOTA, [64Cu]Cu-TETA, and [64Cu]Cu-PSMA I&T was assessed at 37 °C from 0 to 72 h in human blood serum. Preclinical PET imaging was performed at 1, 24, and 48 h post-injection with [64Cu]Cu-PSMA I&T in LNCaP tumor-bearing mice and compared with [68Ga]Ga-PSMA I&T. RESULTS: Maximum purified activity of 4.9 GBq [64Cu]CuCl2 was obtained in 5 mL of pH 2-3 solution, with 2.9 GBq 64Cu concentrated in 0.5 mL. HPGe gamma spectroscopy of purified 64Cu detected <0.3 % co-produced 67Cu at EOB with no other radionuclidic impurities. ICP-OES elemental analysis determined <1 ppm Al, Zn, In, Fe, and Cu in the [64Cu]CuCl2 product. NOTA, DOTA, TETA, and PSMA I&T were radiolabeled with 64Cu, resulting in maximum molar activities of 164 ± 6 GBq/µmol, 155 ± 31 GBq/µmol, 266 ± 34 GBq/µmol, and 117 ± 2 GBq/µmol, respectively. PET imaging in PSMA-expressing LNCaP xenografts resulted in high tumor uptake (SUVmean = 1.65 ± 0.1) using [64Cu]Cu-PSMA I&T, while [68Ga]Ga-PSMA I&T yielded an SUVmean of 0.76 ± 0.14 after 60 min post-injection. CONCLUSIONS: 64Cu was purified in a small volume amenable for radiolabeling, with yields suitable for preclinical and clinical application. The 64Cu production and purification process and the favourable PET imaging properties confirm the 68Zn(p,nα)64Cu nuclear reaction as a viable 64Cu production route for facilities with access to a higher energy proton cyclotron, compared to using expensive 64Ni target material and the 64Ni(p,n)64Cu nuclear reaction. ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: Our 64Cu production technique provides an alternative production route with the potential to improve 64Cu availability for preclinical and clinical studies alongside 67Cu therapy.

Synthesis and Analysis of 64Cu-Labeled GE11-Modified Polymeric Micellar Nanoparticles for EGFR-Targeted Molecular Imaging in a Colorectal Cancer Model.

Polymeric micellar nanoparticles represent versatile and biocompatible platforms for targeted drug delivery. However, tracking their biodistribution, stability, and clearance profile in vivo is challenging. The goal of this study was to prepare surface-modified micelles with peptide GE11 for targeting the epidermal growth factor receptor (EGFR). In vitro fluorescence studies demonstrated significantly higher internalization of GE11 micelles into EGFR-expressing HCT116 colon cancer cells versus EGFR-negative SW620 cells. Azo coupling chemistry of tyrosine residues in the peptide backbone with aryl diazonium salts was used to label the micelles with radionuclide 64Cu for positron emission tomography (PET) imaging. In vivo analysis of 64Cu-labeled micelles showed prolonged blood circulation and predominant hepatobiliary clearance. The biodistribution profile of EGFR-targeting GE11 micelles was compared with nontargeting HW12 micelles in HCT116 tumor-bearing mice. PET revealed increasing tumor-to-muscle ratios for both micelles over 48 h. Accumulation of GE11-containing micelles in HCT116 tumors was higher compared to HW12-decorated micelles. Our data suggest that the efficacy of image-guided therapies with micellar nanoparticles could be enhanced by active targeting, as demonstrated with cancer biomarker EGFR.

Radiometal-Containing Aryl Diazonium Salts for Chemoselective Bioconjugation of Tyrosine Residues.

Tyrosine is an attractive target for chemo- and site-selective protein modification. The particular chemical nature of tyrosine residues allows bioconjugation chemistry with reactive aryl diazonium salts via electrophilic aromatic substitution to produce diazo compounds. In this work, we describe the preparation of 64Cu- and 68Ga-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA)-diazonium salts as building blocks for azo coupling chemistry with tyrosine and tyrosine-containing peptides and proteins under mild conditions. 2-S-(4-aminobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (p-NH2-Bn-NOTA) was used to form the corresponding 64Cu- and 68Ga-labeled complexes, followed by diazotization with NaNO2 in the presence of HCl. 64Cu- and 68Ga-labeled NOTA complexes were prepared in high radiochemical yields >80% starting from 20 µg of p-NH2-Bn-NOTA. Conversion of p-NH2-Bn-NOTA complexes into diazonium salts followed by azo coupling with l-tyrosine afforded 64Cu- and 68Ga-labeled tyrosine in radiochemical yields of 80 and 56%, respectively. Azo coupling with tyrosine-containing hexapeptide neurotensin NT(8-13) afforded 64Cu- and 68Ga-labeled NT(8-13) in radiochemical yields of 45 and 11%, respectively. Azo coupling of 64Cu-labeled NOTA-diazonium salt with human serum albumin (HSA) gave 64Cu-labeled HSA in radiochemical yields of 20%. The described azo coupling chemistry represents an innovative and versatile bioconjugation strategy for selective targeting of tyrosine residues in peptides and proteins.