The pretargeting methods jointly developed with IBC Pharmaceuticals, Inc., are producing very high tumor/normal tissue ratios. As a result, we have developed a rapid and facile method for the radiolabeling of peptides with F-18 via a conjugate with aluminum or other metals.
In the new labeling method, F-18 was first allowed to react with aluminum in solution, which occurred instantaneously and in a quantitative manner to form an aluminum-F-18 complex. The complex was then bound or chelated to a chemical group attached to a peptide. By manipulating the chemical structure of the group that the aluminum-F-18 complex attaches to in the peptide, we were able to improve the yield of the reaction to 87%. The entire process is rapid, requiring only 15-20 minutes. This is the first method of binding F-18 to peptides via an aluminum conjugate.
The method has since been successfully applied to bispecific antibody pretargeting studies in animals injected with human colorectal cancer. Moreover, F-18 labeled peptides were shown to be stable enough to produce exceptional positron-emission tomography (PET) images of receptor-expressing tumors in animals by labeling of specific peptides binding such receptors. Scientists at the National Institutes of Health and outside third parties have also successfully applied the new F-18 labeling method for the PET imaging of tumor angiogenesis in mice, angiogenesis imaging in a myocardial infarction/reperfusion animal model, hypoxia imaging, and the imaging of growth factor receptors in animal models of gastrointestinal and ovarian cancers.
PET is one of the most prominent imaging tools in diagnostic medicine. F-18 is a positron-emitting radioisotope usually given to patients as F-18 fluoro-2-deoxyglucose (F-18 FDG), a sugar analog. Increased glucose metabolism, which leads to higher uptake of F-18 FDG, is the premise of F-18 FDG PET imaging. F-18 FDG is the most widely used radiopharmaceutical in PET to determine abnormal glucose metabolism. In the United States, F-18 FDG has been approved for use in detecting certain tumors, coronary artery disease, and epilepsy. However, F-18 FDG uptake is also enhanced during inflammatory processes and in rapidly-proliferating normal cells (such as bone marrow), which may lead to false-positive results and lower specificity.
Our goal is to improve the labeling process to the point where we will be capable of radiolabeling these peptides at clinical-scale using single-vial kits, then license the platform technology to companies on a product-by-product basis. To that end, we have improved the labeling method such that commercial F-18 in saline solution can be used and the labeling of temperature-sensitive and insensitive peptides or proteins, including antibodies, were achieved. In order to further simplify the procedure and make the process more consistent and for broader use, we have formulated and published a lyophilized kit that could be validated and manufactured under Good Manufacturing Practice conditions.
The kit, which contains aluminum, a radioprotectant, a non-volatile buffer, and a bulking agent, was able to F-18-label a peptide with approximately 70% yield under non-optimized condition using a semi-automated machine. With a fully automated microfluidics machine, the reaction time was reduced to 1.5 minutes. More importantly, F-18-labeled peptide was produced in amounts that are in the range of a single-patient dose. We are also pursuing the commercial development of radiopharmacy manufacturing to prepare multi-dose 18F labeled peptides and proteins based on the new labeling method through a corporate partnership.
In related work, similar synthetic methods have also been used to prepare peptides that can be radiolabeled with technetium-99m, gallium-68, indium-111, lutetium-177, and yttrium-90, which are being applied to the bispecific pretargeting technology that is being developed through IBC.
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- Lütje S, Franssen GM, Sharkey RM, Laverman P, Rossi EA, Goldenberg DM, Oyen WJG, Boerman OC, McBride WJ. Anti-CEA antibody fragments labeled with [F]AIF for PET imaging of CEA-expressing tumors. Bioconjugate Chem. 2014 Feb 19;25(2):335-41.
- Franssen GM, Laverman P, Chatalic KLS, Oyen WJG, Sharkey RM, Goldenberg DM, Rossi E, McBride WJ, Boerman OC. Anti-CEA antibody fragments labeled with [18F]AIF for PET imaging of CEA-expressing tumors. Annual Congress of the European Association of Nuclear Medicine (EANM), Oct 22, 2013 (Abstr. #PW138). Eur J Nucl Med Mol Imaging (2013) 40 (Suppl 2): S89-S567.
- Chatalic KLS, Franssen GM, McBride WJ, van der Graaf LM, Sharkey RM, Laverman P, Goldenberg DM, Hajjaj B, Fehrentz JA, Martinez J, Boerman OC, de Jong M. Preclinical Evaluation of AI F- and Ga-labeled GRPR-antagonist for PET Imaging of Gastrin-Releasing Peptide Receptor Expression in Prostate Cancer. Annual Congress of the European Association of Nuclear Medicine (EANM), Oct 20, 2013 (Abstr. #OP060). Eur J Nucl Med Mol Imaging (2013) 40 (Suppl 2): S89-S567.
- McBride WJ, Sharkey RM, Goldenberg DM. Radiofluorination using aluminum-fluoride (Al18F). Eur J Nucl Med Mol Imaging Res. 3(1):36, 8 May, 2013.
- McBride WJ, D’Souza CA, Sharkey RM, Goldenberg DM. The radiolabeling of proteins by the [18F]AlF method. Appl Radiat Isot. 70(1):200-4, 2012.
- McBride WJ, D’Souza CA, Karacay H, Sharkey RM, Goldenberg DM. New lyophilized kit for rapid radiofluorination of peptides. Bioconjug Chem. 23(3):538-47, 2012.