Showing papers by "Otto C. Boerman published in 1999"

Pretargeting of renal cell carcinoma: improved tumor targeting with a bivalent chelate.

Abstract: Radiolabeled monoclonal antibodies (mAbs) can target tumors selectively. Sustained activity levels in nontarget tissues limit their application. Pretargeting approaches using bispecific mAbs (bsmAbs) or the biotin-avidin interaction have been proposed to improve tumor:nontumor ratios. Pretargeting a tumor and subsequently administering the radioactivity as a low molecular weight ligand fundamentally changes the pharmacokinetics of the radiolabel. In previous studies, we have shown successful radioimmunotargeting of diethylenetriaminepentaacetic acid (DTPA) labeled with indium-111 to renal cell carcinoma (RCC) after pretargeting in nude mice. In this study, we aimed to optimize further a pretargeting strategy in nude mice with RCC xenografts based on a bispecific anti-RCC × anti-DTPA mAb. Using this two-step approach, we studied whether the use of a bivalent chelate (111In-diDTPA) could improve radioimmunotargeting. The 111In-diDTPA dose greatly affected the uptake of the radiolabeled chelate in the tumor. At a low 111In-diDTPA dose (≤7 pmol), tumor uptake of 111In-diDTPA was very high [>50% injected dose (ID)/g, 1 h postinjection (p.i.)], whereas at higher doses (≥20 pmol), tumor uptake of 111In-diDTPA decreased (<30% ID/g). With monovalent 111In-DTPA uptake of the radiolabel in the tumor was much lower (<10% ID/g, 1 h p.i.). Furthermore, the bivalent chelate accreted rapidly in the tumor (78% ID/g, 4 h p.i.) and was virtually completely retained in the tumor during several days p.i. (92% ID/g, 72 h p.i.). Clearance of the 111In-diDTPA from the blood and kidneys was rapid and complete without the need to clear the bsmAb from the blood, probably due to the relative lability of the univalent bsmAb-diDTPA complexes in the blood. As a result, with this two-step pretargeting approach tumor:blood ratios increased up to values as high as 3500 at 72 h p.i. High doses of diDTPA could be targeted preferentially to the tumor, indicating that this approach could also be used for radioimmunotherapy. Tumors could be imaged up to 1 week p.i. of 50 μCi of 111In-diDTPA. Quantitative analysis of the images confirmed the biodistribution data and indicated that, at 20 h p.i., 50 ± 15% of the whole-body activity was localized in the tumor. In conclusion, these studies indicate that the use of bivalent chelates can very effectively optimize two-step targeting of tumors with bsmAbs. Our data indicate that this approach could optimize radioimmunotherapy.

In vivo and in vitro characterizations of three 99mTc-labeled monoclonal antibody G250 preparations.

Abstract: In previous clinical studies, excellent visualization of tumor lesions has been observed with 131 I-labeled monoclonal antibody (mAb) G250 in patients with renal cell carcinoma (RCC). In several cases, 131 I-cG250 immunoscintigraphy disclosed tumor lesions that were not visualized by radiography or CT. To improve image quality, we aimed to develop a 99m Tc-labeled mAb G250 preparation for radioimmunodetection of RCC. We studied in vitro stability, biodistribution and imaging potential of three 99m Tc-labeled G250 preparations in nude mice with subcutaneous RCC xenografts. 125 I-G250 and the nonspecific mAb 131 I-MN14 were used as control antibodies. Methods: The mAb G250 was labeled with 99m Tc according to three methods using: (a) S-hydrazinonicotinamide (HYNIC), (b) S-benzoylmercapto-acetyltriglycine (MAG3) and (c) a direct labeling method (Schwarz method). The stability of all preparations was tested in serum at 37°C during 48 h. In addition, diethylenetriamine pentaacetic acid, cysteine and glutathione challenge assays were performed. Results: All preparations showed good stability in serum during the 48-h incubation period. 99m Tc-G250 (Schwarz) showed release of the radiolabel at a 100-fold or higher molar excess of cysteine and at a 10,000-fold or higher molar excess of glutathione. 99m Tc-MAG3-G250 showed release of the radiolabel at a 10,000-fold molar excess of cysteine. 99m Tc-HYNIC-G250 was stable under all conditions. Tumors were clearly visualized with all preparations. 99m Tc-G250 (Schwarz) showed significantly lower blood levels (3.8 %ID/g) compared with all other preparations (11.2, 13.4 and 13.4 %ID/g for 99m Tc-HYNIC-G250, 99m Tc-MAG3-G250 and 125 I-G250, respectively, 48 h postinjection). At 48-h postinjection, mean tumor uptake was very high with all mAb G250 preparations: 92.4 ( 99m Tc-HYNIC-G250), 125.9 ( 99m Tc-MAG3-G250), 29.4 ( 99m Tc-G250 Schwarz) and 75.4 ( 125 I-G250) %ID/g. Mean tumor uptake of the nonspecific 131 I-MN14 mAb was 6.6 %ID/g. Conclusion: In this study, 99m Tc-HYNIC-G250 showed excellent in vitro stability and tumor targeting. Moreover, this preparation could be labeled with high efficiency (>95%) at room temperature within 15 min. Therefore, 99m Tc-HYNIC-G250 seems to be an ideal candidate for radioimmunodetection of RCC.

Immunohistochemical analysis of tumor antigen saturation following injection of monoclonal antibody G250.

Abstract: Clinical tumor targeting studies with monoclonal antibody (mAb) G250 showed excellent targeting of primary renal cell carcinomas (RCC). However, tumor uptake decreased at higher mAb G250 doses, suggesting saturation of the G250 antigenic determinants. In this immunohistochemical study we investigated the saturability of G250 antigen sites after i.v. administration of mAb G250 at various protein doses in nude mice with RCC xenografts. Five groups of mice received five different protein doses (1, 3, 10, 30 or 100 micrograms) of murine mAb G250. Three days post injection mice were killed and the tumors were removed. Free G250 antigen sites, i.e., not targeted by the i.v. injected murine mAb G250 were determined by immunohistochemical staining with chimeric mAb G250. Distinct staining of the G250 antigen was observed only at the 1 and 3 micrograms dose whereas G250 antigen staining at higher doses was virtually negative. The results of this study indicate that saturation of antigen occurs at relatively low doses of i.v. administered mAb G250. Apparently, all antigenic determinants present on the RCC tumor cells were targeted, while previous preclinical studies suggested that i.v. administration of mAb G250 only saturated the accessible antigen sites.