COMPARISON OF THE PHARMACOKINETICS, BIODISTRIBUTION AND DOSIMETRY OF MONOCLONAL-ANTIBODIES OC125, OV-TL 3, AND 139H2 AS IGG AND F(AB')2 FRAGMENTS IN EXPERIMENTAL OVARIAN-CANCER

Monoclonal antibody (MAb) 139H2 was previously shown to localise specifically into ovarian cancer xenografts in nude mice. MAb 139H2 was compared with MAbs OC125 and OV-TL 3, all reactive with ovarian carcinomas, for the binding characteristics as IgG and F(ab')2 fragments with the use of the OVCAR-3 cell line grown in vitro and as s.c. xenografts- Immunoperoxidase staining of OVCAR-3 tissue sections with MAbs OC125 and 139H2 was heterogeneous, whereas MAb OV-TL 3 showed homogeneity. No differences in binding were observed between IgG and F(ab')2. The avidity expressed as apparent affinity constants of MAbs OC125, OV-TL 3 and 139H2 for OVAR-3 cells were 1 x 10(9)m-1, 1 x 10(9)m-1, and 1 x 10(8) M-1. while the number of antigenic determinants were 5 x 10(6), 1 x 10(6) and 7 x 10(6), respectively. In OVCAR-3 bearing nude mice the blood half-lives of the MAbs as IgG and F(ab')2 were approximately 50 h and 6 h, respectively. Maximum tumour uptake for the whole MAbs OC125, OV-TL 3, 139H2 and a control MAb 2C7 was 8.5%, 17.7%, 11.1% and 2.5% of the injected dose g-1, reached at 72 h after injection. For the respective F(ab')2 fragments, the maximum values were 5.2%, 10.0%, 5.5% and 1.9% of the injected dose g-1, reached between 6 h and 15 h. Tumour to non-tumour ratios were more favourable for the F(ab')2 fragments as compared to those for MAbs as IgG. Biodistribution in mice bearing a control tumour confirmed the Specificity of tumour localisation of MAbs OC125, OV-TL 3 and 139H2. After injection of a tracer dose of 10-mu-Ci of radiolabelled MAbs OC125. OV-TL 3 and 139H2 as IgG, tumours received 38 cGy, 86 cGy and 39 cGy, respectively. For the respective F(ab')2 fragments, these doses were 6 cGy, 22 cGy and 9 cGy. In our OVCAR-3 model. a ranking in efficiency in tumour localisation would indicate MAb OV-TL 3 as most favourable MAb, but cross-reactivity with subpopulations of human white blood cells might hamper its clinical use. Dosimetric data indicate a 4-fold higher radiation absorbed dose to tumours for IgG compared with F(ab')2 fragments.