Method development for [11C]carbon monoxide radiochemistry

Positron emission tomography (PET) is a non-invasive molecular imaging technique that has found extensive utility in biomedical research and in drug development. A fundamental pre-requisite for PET is the tracer, which is a biologically relevant molecule, labeled with a short-lived radionuclide. One of the most attractive radionuclides for PET is carbon-11 (11C) that has a half-life of only 20 minutes (11C, t1/2=20.3 min). This radionuclide can be introduced via transition-metal mediated carbonylation with [11C]carbon monoxide ([11C]CO), a reaction that has found utility in the production of a wide range of drug-like molecules and radioligands. Transition-metal mediated 11C-carbonylation is typically performed at high pressure and high temperature due to the poor solubility of [11C]CO in organic solvents and its high dilution in inert gas. Because of its radioactive nature, chemical processes with 11C not only need to be fast, but also need to be automated inside a lead-shielded fume cupboard to ensure operator safety. The current PhD thesis aimed to develop novel and simplified methods for the introduction of 11C into one of the most abundant functional groups in bioactive molecules, namely the carbonyl group. Paper I describes the development of a new stainless-steel loop method for 11C-carbonylation reactions, in which a thin film of reagents is created on the interior surface of the loop. This operation creates a large surface area, which facilitates exchange between the liquid and gas phase and thus enhances trapping and incorporation of [11C]CO into target compounds via reactive palladium complexes. The method was applied to a set of test compounds and proved to be useful to provide 11C-labeled amides, esters and carboxylic acids with good to excellent yields. As a proof of concept, the histamine‐3 receptor radioligand [11C]AZ13198083, the oncology drug [11C]olaparib, the dopamine D2 receptor radioligands [11C]raclopride and [11C]FLB457 were produced using the same method. To allow tracers labeled by 11C-carbonylation to be used in studies of human physiology and pathophysiology, Paper II described the development of a new automated system for [11C]CO radiochemistry that complies with all regulations associated with such studies (e.g. good manufacturing practice (GMP)). The aim was to develop the first commercially available [11C]CO system with the purpose of making [11C]CO radiochemistry accessible to the wider PET community. Following development and optimization of each part of the GMP system, the [11C]CO synthesizer was successfully used to produce the histamine type-3 radioligand, [11C]AZ13198083. In Paper III, a novel and simple method for the synthesis of 11C-labeled primary amides was developed. This process consists on the Pd-mediated 11C-aminocarbonylation of aryl halides via intermediate electrophilic aroyl-DMAP-salts (DMAP – 4-dimethylaminopyridine). The method provided a range of substrates with good to excellent yields and was finally successfully applied to the radiolabeling of the two cancer drugs [11C]niraparib and [11C]veliparib for preclinical studies. To conclude, a variety of new methodologies have been described for 11C-labeling carbonyl groups that have the potential to be widely implemented in the development of new tracer molecules for PET imaging

Optimized, automated and cGMP-compliant synthesis of the HER2 targeting [68Ga]Ga-ABY-025 tracer

Abstract Background The Affibody molecule, ABY-025, has demonstrated utility to detect human epidermal growth factor receptor 2 (HER2) in vivo, either radiolabelled with indium-111 (111In) or gallium-68 (68Ga). Using the latter, 68Ga, is preferred due to its use in positron emission tomography with superior resolution and quantifying capabilities in the clinical setting compared to 111In. For an ongoing phase II study (NCT05619016) evaluating ABY-025 for detecting HER2-low lesions and selection of patients for HER2-targeted treatment, the aim was to optimize an automated and cGMP-compliant radiosynthesis of [68Ga]Ga-ABY-025. [68Ga]Ga-ABY-025 was produced on a synthesis module, Modular-Lab PharmTracer (Eckert & Ziegler), commonly used for 68Ga-labelings. The radiotracer has previously been radiolabeled on this module, but to streamline the production, the method was optimized. Steps requiring manual interactions to the radiolabeling procedure were minimized including a convenient and automated pre-concentration of the 68Ga-eluate and a simplified automated final formulation procedure. Every part of the radiopharmaceutical production was carefully developed to gain robustness and to avoid any operator bound variations to the manufacturing. The optimized production method was successfully applied for 68Ga-labeling of another radiotracer, verifying its versatility as a universal and robust method for radiosynthesis of Affibody-based peptides. Results A simplified and optimized automated cGMP-compliant radiosynthesis method of [68Ga]Ga-ABY-025 was developed. With a decay corrected radiochemical yield of 44 ± 2%, a radiochemical purity (RCP) of 98 ± 1%, and with an RCP stability of 98 ± 1% at 2 h after production, the method was found highly reproducible. The production method also showed comparable results when implemented for radiolabeling another similar peptide. Conclusion The improvements made for the radiosynthesis of [68Ga]Ga-ABY-025, including introducing a pre-concentration of the 68Ga-eluate, aimed to utilize the full potential of the 68Ge/68Ga generator radioactivity output, thereby reducing radioactivity wastage. Furthermore, reducing the number of manually performed preparative steps prior to the radiosynthesis, not only minimized the risk of potential human/operator errors but also enhanced the process’ robustness. The successful application of this optimized radiosynthesis method to another similar peptide underscores its versatility, suggesting that our method can be adopted for 68Ga-labeling radiotracers based on Affibody molecules in general. Trial registration: NCT, NCT05619016, Registered 7 November 2022, https://clinicaltrials.gov/study/NCT05619016?term=HER2&cond=ABY025&rank=