In vivo evaluation of epidermal growth factor (EGF) receptor density on human tumor xenografts using radiolabeled EGF and anti-(EGF receptor) mAb 425.

In order to study the potential of non-invasive scintigraphic evaluation of the epidermal growth factor (EGF) receptor status in vivo, the biokinetics and tumor binding of 125I-EGF and anti-(EGF receptor) mAb 425 were investigated in nude mice bearing human tumor xenografts with different EGF-receptor densities as determined by a radioreceptor assay. The results demonstrated a tumor uptake for both substances depending on the receptor level. The EGF receptor status, however, was reflected slightly better by the binding of EGF to tumor tissue compared to the mAb. The rapid blood clearance of EGF with a plasma half-life of less than 1 min led to a tumor-to-blood ratio of approximately 3 within 6 h after injection in tumors with a high receptor expression. A similar ratio for the mAb was not obtained before day 6 after injection. The absolute concentration of EGF, however, was low compared to the mAb. Therefore, it can be concluded that the EGF receptor status as a target for (radio)immunotherapy can be evaluated in vivo with EGF labeled with a short-life positron-emitting radionuclide or with monoclonal antibodies to the EGF receptor or their fragments.

Curative radioimmunotherapy of human mammary carcinoma xenografts with iodine-131-labeled monoclonal antibodies.

The radioiodinated monoclonal antibody BW 495/36 showed an exceptionally high uptake and long residence time in human ductal mammary carcinoma xenografts in nude mice. There was a mean tumor uptake of 82%/g 24 hr p.i., decreasing with a biologic half-life of approximately 6 days, to 15%/g by Day 16. The tumor-to-blood ratio increased from 2.8 to 21.4 and the percentage of the whole-body retention recovered in the tumor from 47% to 80% during the same time interval. The therapeutic efficiency of two injections of 7.4 MBq 131I-BW 495/36 was evaluated by comparing the tumor size with that in mice injected with either the same amount of the unlabeled MoAb, the same radioactivity of an 131I-labeled nonspecific MoAb, or with saline only. The high tumor accumulation of 131I-BW 495/36 led to a total tumor dose of 77 Gy resulting in a mean reduction in tumor diameter of 50%, corresponding to a reduction in tumor volume of 88% within 42 days p.i. Unlabeled MoAb had no effect on tumor growth compared with controls, whereas 131I nonspecific antibody caused a slight inhibition of tumor growth. Histologic tumor sections showed large areas of necrosis and a pronounced vacuolation of the tumor cell cytoplasm between Days 7 and 30 p.i. By Day 42 all remaining tissue in the tumor was identified as mouse connective tissue.

Improved radioimmunoscintigraphy of human mammary carcinoma xenografts after injection of an anti-antibody.

The low tumor-to-background ratio obtained after administration of radiolabeled whole monoclonal antibodies (MAbs) is one of the major problems in immunoscintigraphy and -therapy. To reduce the blood pool label caused by the circulation of radiolabeled MAb we have investigated the advantage of injecting an anti-antibody after administration of a tumor-specific MAb in nude mice bearing human mammary carcinoma xenografts. The MAb MA 10-11 of rat origin, used in these studies, had shown a high affinity to human mammary carcinoma tissue on frozen sections and low cross-reactivity with various normal human tissues. 24 h after injection of 1.5 MBq 131I-labeled MAb containing 10 micrograms IgG2a one group of mice received an additional injection of 100 micrograms anti-rat antibody. Blood taken 2 min after the second antibody injection showed nearly the whole activity bound to antibody aggregates, that cleared very rapidly from the circulation and accumulated in liver and spleen. The transitory high liver activity decreased within several hours because of rapid deiodination of the antibody-complex in this organ. The release of radioactivity from the spleen, however, was found to be much slower. The rapid excretion of the radioactivity from the blood pool combined with a nearly constant tumor activity allowed early tumor detection with tumor-to-blood ratios of 250:1 at 48 h after anti-antibody injection compared to 1.1:1 obtained for the control animals. In addition the results may explain the reported reduction of imaging quality and high uptake of radioactivity in the spleen of patients having repeated injections of mouse MAbs due to complex formation after development of human anti-mouse antibodies.

Uptake mechanism of interstitially injected 99mTc-labeled antimony trisulphide colloid in the popliteal lymph node of rabbits.

The right popliteal lymph node was studied in rabbits by well counting, histoautoradiography and electron microscopy, after interstitial injection of 99mTc-labeled antimony trisulphide (Sb2S3) colloid into the right hind pad. The highest radioactivity concentration (96.8%/g) was measured 6 hr following injection. At 24 hr, the concentration had dropped to nearly half of the maximum (51.5%/g). At each time, only a single or a few lymph node sectors were found to contain 99mTc. Initially, the radioactivity distribution pattern in the draining lymph node was stripy. Beginning at 15 min p.i., there was a progressive change from stripy to focal radioactivity distribution pattern. Until 6 hr after injection, the bulk of radioactivity was trapped by macrophages in the lumen and wall of the lymph node sinus system, predominantly in medullary sinuses. Surprisingly, at 24 hr the majority of labeled cells were eosinophilic polymorphonuclear leukocytes located in medullary sinuses and medullary cords. Up to 24 hr p.i., no accumulation of radioactivity could be detected in the cortical and paracortical lymph node parenchyma. In conclusion, interstitially injected 99mTc-Sb2S3 colloid is not homogeneously but sectorially distributed in the draining lymph node. Moreover, both macrophages and eosinophilic polymorphonuclear leukocytes are involved in the filtration process.