Antigenic modulation and internalization of monoclonal antibody to human colonic carcinoma cells detected by enzyme-linked immunosorbent assay

Binding and internalization of anti-sarcoma IgG and IgM antibodies

A variety of monoclonal antibodies directed against tumor cell surface antigens have been employed for tumor detection and delivery of toxins and radioisotopes to tumors in situ. The sequence of events following antibody binding to tumor cells may be critical to the success or failure of tumor imaging or therapy. Using indirect immunofluorescence, we have examined the binding and internalization of two different monoclonal antibodies (19-24 and MFH 4.10) by HT-1080, a cultured human sarcoma cell line. MAb 19-24 (IgG1) and MAb MFH 4.10 (IgM) are directed against surface antigens on cells from human malignant fibrous histiocytoma (MFH). For both of these antibodies, the initial binding on the surface of HT-1080 cells at 4 degrees C was uniform. After binding secondary fluorescent antibody, monoclonal antibodies underwent rapid internalization at 37 degrees C. Surface-bound antigen-antibody complexes were completely cleared from the cell surface in 30-60 min. In the absence of secondary fluorescent antibody, MAb 19-24 remained bound to the cell surface at 37 degrees C for up to 20 hr without being released or internalized. However, under these same conditions MAb MFH 4.10 was internalized completely within 30 min by HT-1080 cells and did not subsequently return to the cell surface. Such differences in the mechanisms of binding and uptake for these two antibodies may have significant implications for their future clinical or therapeutic uses.

Decreased renal accumulation of biotinylated chimeric monoclonal antibody-neocarzinostatin conjugate after administration of avidin

Murine monoclonal antibodies (mAbs) such as A7 administered to humans induce a human anti-mouse antibody response. Moreover, because Fab fragments of mAbs are able to penetrate target tumors easily, they may be more suitable than intact mAb to be carriers of anticancer agents such as neocarzinostatin (NCS), which are rapidly inactivated in the blood. To address these problems, chimeric A7 Fab fragment-NCS conjugate (chA7Fab-NCS) was produced. However, large amounts of 125I-labeled chA7Fab-NCS accumulate in the kidney and can lead to renal dysfunction. To decrease renal accumulation of chA7Fab-NCS, chA7Fab was biotinylated and administered with a subsequent injection of avidin. Human pancreatic carcinoma-bearing nude mice were injected with 125I-labeled biotinylated chA7Fab-NCS with or without subsequent administration of avidin. The accumulation of 125I-labeled biotinylated chA7Fab-NCS in tissue samples was measured at appropriate time intervals. 125I-labeled biotinylated chA7Fab-NCS was cleared more rapidly from the blood and the kidney with the administration of avidin than without it. There was no difference between tumor accumulation in these groups. The tumor/blood ratio of radioactivity of 125I-labeled biotinylated chA7Fab-NCS was significantly higher with subsequent administration of avidin than without avidin. The administration of biotinylated chA7Fab-NCS followed by avidin may enhance safety and permit the administration of larger doses of NCS without the subsequent development of renal failure. A larger amount of 125I-labeled biotinylated chA7Fab-NCS was retained in the liver and spleen with the subsequent administration of avidin than without avidin.

A critical comparison of three internalization assays applied to the evaluation of a given mAb as a toxin-carrier candidate

In the attempt to define a strategy for screening new monoclonal antibodies (mAb) that could be appropriate for clinical application in oncology, we evaluated the suitability of three methods: a direct internalization assay (DIA), an indirect internalization assay (IIA) and an indirect cytotoxicity assay (ICA), by applying them to already selected mAb. The latter were directed against three antigenic systems [38-kDa glycoprotein (gp38), epidermal growth factor receptor, and the neu oncogene product], which, according to their tumor selectivity, could be considered suitable for mAb-guided therapy. The dose-dependent and time-dependent binding, as well as the low intra-assay variability, demonstrated the reliability of the three tests. However, a certain degree of inter-assay variability was observed in each one, the highest value being that found when IIA was applied. Furthermore, the degree of variability, as well as the predictability, seemed to be more related to the mAb/antigen (Ag) combination used rather than to the test applied. From the overall data we suggest a procedure to be applied for screening purposes. As a first approach applied to the raw material, ICA is only suitable for screening in the case of an already selected toxin whereas IIA may be helpful to eliminate the true negative mAb. After purification of the relevant mAb a repeated analysis using DIA could allow the selection of true internalizing mAb. However, this second screening should be followed by a further analysis of the fate of the Ag-Ab complex after internalization.

Use of combination of monoclonal antibodies directed against three distinct epitopes of a tumor-associated antigen: analysis of cell binding and internalization

Three monoclonal antibodies (MAbs), MOv17, MOv18 and MOv19 with tumor-restricted specificity for human ovarian carcinoma, were tested alone or in double combination with the aim of analyzing their binding and internalization behavior on different in vitro cell lines. Biochemical studies indicated that the 3 MAbs were directed against 3 epitopes of the same 38 kDa surface molecule. By immuno-electron-microscopy they exhibited a different internalization behavior since MOv17 induced evident endocytosis through coated vesicles, whereas MOv18 gave rise to occasional uncoated vesicles and MOv19 was completely unable to promote internalization of the relevant molecule. When tested 2 by 2 there was a binding synergy in one of the 9 possible combinations (125I-labelled MOv18 and unlabelled MOv19), but no change in the internalization behavior. The binding synergy, which was highly reproducible, was temperature-dependent and was also evident on glutaraldehyde-fixed cells. A metabolism involvement is therefore unlikely. This could be attributed to an easier accessibility of the CaMOv18 due to a conformational change of the molecule after MOv19 MAb binding.