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Conditions are described for the preparation of 188Re-RC-160, a radiolabeled synthetic peptide derived from an analogue of somatostatin, using a lyophilized labeling kit containing RC-160 (200 μg) and stannous tartrate to which is added carrier-free 188 Re (β, E max , 2,12 MeV ; γ, 155 KeV , 10%, T 1 2 = 16.7 h ) . The 3its have been radiolabeled with > 2960 Mbq (80 mCi) with a high labeling efficiency and no need for subsequent purification. Radiolabeling results in one major peak when analyzed by reverse-phase (RP) HPLC. Presumptive radiolysis was detected at 2.5 h post-labeling; however, a convenient method is described for stabilizing the kits against radiolysis by the post-labeling addition of ascorbic acid.

Monoclonal antibodies can be directly labelled with 188Re using a simple one-step radiolabelling kit. Using B72.3 as a model antibody, the formulation was optimized and kits were made and tested and compared to data previously reported for the same antibody labelled with other radioisotopes. Labelling with Re-188 was carried out with the eluate of a W-188/Re-188 generator from Oak Ridge National Laboratory. Fresh generator eluate was added to the pre-reduced lyophilized antibody and the mixture allowed to incubate overnight at room temperature. The radiochemical purity, immunoreactive fraction, and biodistribution in normal and LS174T tumor bearing nude mice was determined. The radiochemical purity was 88 ± 7%, the immunoreactive fraction was 68.46 ± 3.8%. The immunoreactive fraction was higher than any previously reported for this antibody when labelled with other radioisotopes. At 48 h, 7.9 ± 2.4% of the injected dose per gram was found in the tumor. The biodistribution and tumor uptake of Re-188 labelled B72.3 was similar to that previously reported for Re-186 and In-111 labelled B72.3.

Kits for direct labeling of IgG with 99mTc were used without modification for the preparation of [67Cu]IgG. The IgG was pre-treated to generate thiolate groups which would bind 67Cu. The direct labeling of reduced IgG with 67Cu was highly efficient, resulting in approx. 95% 67Cu binding. Non-reduced IgG (negative control) had labeling efficiencies of less than 10%. IgG pre-exposed to Cu(II) had reduced amounts of 99mTc bound to it. The results demonstrate a direct relationship between copper- and 99mTc-binding sites in IgG.

High grade gliomas may have amplified expression of the epidermal growth factor receptor (EGFR) gene c-erb-B, which often is associated with increased expression of transmembrane EGFR. The purpose of the present study was to develop a method for labeling EGF with 99mTc and to determine whether the resulting radioligand would localize, following intracerebral injection, in rats bearing EGFR-positive gliomas. EGF has a relatively low molecular mass (approximately 6 kDa) compared to monoclonal antibodies, and this has allowed smaller bioconjugates, which should diffuse more rapidly within the brain and more effectively target disseminated glioma cells, to be constructed. In the present study, EGF has been labeled with either 131I or 99mTc, and in vitro uptake of the resulting radioligand has been investigated using C6EGFR rat glioma cells, which had been transfected with the EGFR gene. Cellular uptake of 131I radioactivity peaked after approximately 30 min of incubation with [131I]EGF, following which time it declined, while 99mTc radioactivity continued to increase over a 6 h incubation with [99mTc]-EGF. To determine if radiolabeled EGF had in vivo tumor-localizing properties, C6EGFR glioma cells were implanted stereotactically into the brains of Fischer rats. Four weeks later, either 99mTc- or 131I-labeled EGF was injected intracerebrally into normal or glioma-bearing animals using the same stereotactic coordinates. External gamma scintigraphy revealed that 131I radioactivity disappeared rapidly from the brain regions of tumor-bearing animals compared to 99mTc, approximately 50% of which remained in the tumor for up to 12 h. In contrast, only approximately 20% remained in the brains of non-tumor-bearing animals after 6 h. These studies are the first to describe a method for radiolabeling EGF with 99mTc and to detect it by external scintigraphy in the brains of tumor-bearing animals.

Thin layer chromatography (TLC) was used to monitor binding of radiolabeled antibodies to cells. Labeled antibodies were reacted with cells and aliquots chromatographed on serum-blocked, ITLC strips. The cell-antibody complexes remain at the origin and unbound antibody migrates with the solvent front. The antibody binding was estimated from the ratio of radioactivity at the origin compared to the total applied. Separations are completed in about 10 min. This method does not use centrifugation or wash steps, and provides an inexpensive and self-contained system to evaluate radioligand binding. Cell binding assay results using this method are approximately the same as those obtained using bead- or cell-type assays.

Regulated reduction, a controlle method for direct labelling of proteins, is defined. This procedure optimizes separate, but interdependent, parameters in the formulation of protein or peptide based radiopharmaceutical kits to increase radiochemical yields. Various analytical methods that can be used to establish radiochemical yields, radiochemical purity, and the immunoreactive fraction of the final labeled product will be summarized.