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The radiation survival curves showed that the Caki-1 cell line was more sensitive to both HDR and ED LDR irradiation than A498 in vitro. The Caki-1 cell line, compared with A498, had a larger alpha (0.39 vs. 0.15 Gy following HDR and 0.32 vs. 0.21 Gy following ED LDR) and alpha-to-beta ratio (6.92 vs. 2.60 Gy for HDR and 40.0 vs. 19.2 Gy for ED LDR), a smaller n number (5.13 vs. 23 for HDR and 1.16 vs. 3.53 for ED LDR), a lower quasi-threshold dose (Dq) (1.60 vs. 3.15 Gy for HDR and 0.35 vs. 1.76 Gy for ED LDR), and a lower surviving fraction at 2 Gy (SF2) (0.37 vs. 0.60 for HDR and 0.51 vs. 0.61 for ED LDR), suggesting that Caki-1, compared with A498, had a steep initial slope and a small shoulder. The final slope represented by the beta value and D0 dose (the dose (Gy) required to reduce the fraction of surviving cells of 37% of its previous value in the exponential region of the survival curves) did not vary significantly between these two cell lines at either HDR or ED LDR irradiation. Tumor volume doubling times were 4.0 +/- 1.5 days for Caki-1 and 4.2 +/- 1.8 days for A498 tumor xenografts. One hundred microCi/50 microg of 90Y-labeled, isotype-matched irrelevant monoclonal antibody CCOO16-3 produced a tumor growth delay time (TGD) of 2.1 days in Caki-1 tumors but had no effect on A498 tumors (P< 0.05). RIT with 100 microCi of 90Y-NR-LU-10 resulted in a TGD of 4.8 days for Caki-1 tumors, whereas 100 microCi and 150 microCi of 90Y-NR-LU-10 produced a TGD of 1.9 and 2.7 days for A498 tumors, respectively. Estimated absorbed doses were 21.9 Gy in Caki-1 tumors treated with 100 microCi of 90Y-NR-LU-10 and 14.5 Gy and 21.8 Gy in A498 tumors treated with 100 microCi and 150 microCi of 90Y-NR-LU-10, respectively. The weighted normal tissue absorbed doses were 7.4 Gy for Caki-1 tumor-bearing mice and 9.0 Gy for A498 tumor-bearing mice (P > 0.05). To compare the responses of Caki-1 and A498 xenografts to RIT with external beam ED LDR and HDR irradiation, tumor-bearing mice were treated with equivalent doses (20-22 Gy) of 1) RIT with 90Y-NR-LU-10 (100 microCi for Caki-1 and 150 microCi for A498), 2) continuous ED LDR 137Cs irradiation with a initial dose rate of 22 cGy/hour, or 3) HDR X-irradiation (2 Gy x 10 fractions in 2 weeks). The TGDs produced by RIT, ED LDR, and HDR were 5.3, 9.7, and 8.3 days for Caki-1 and 2.7, 5.1, and 5.8 days for A498. The relative efficacy of RIT in these xenograft models correlated well with the radiobiologic parameters (i.e., the size of the initial slope and shoulder) of in vitro survival curves following HDR and ED LDR irradiation in these cell lines. (ABSTRACT TRUNCATED)

parameters and the relative sensitivity of tumor to RIT, exponentially decreasing low dose rate (ED LDR) irradiation and conventional high dose rate (HDR) fraction- and a computer FIT program was used to calculate the radiobiologic parameters.The antitumor efficacy of the different treatments was compared in vivo using a tumor regrowth delay assay in these two tumor xenograft models. RESULTS.The radiation survival curves showed that the Caki-1 cell line was more sensitive to both HDR and ED LDR irradiation than A498 in vitro. LDR irradiation. Tumor volume doubling times were 4.0 { 1.5 days for Caki-1 and 4.2 { 1.8 days for A498 tumor xenografts. One hundred mCi/50 mg of 90 Y-labeled, Presented at the Sixth Conference on Radioimisotype-matched irrelevant monoclonal antibody CCOO16-3 produced a tumor munodetection and Radioimmunotherapy of growth delay time (TGD) of 2.1 days in Caki-1 tumors but had no effect on A498 Cancer, Princeton, New Jersey, October 10-12, 1996.tumors ( tively. The weighted normal tissue absorbed doses were 7.4 Gy for Caki-1 tumorbearing miceand 9.0 Gy for A498 tumor-bearing mice (P ú 0.05). To compare the

Antibodies with nucleophilic or catalytic properties often have these characteristics encoded in their germ line genes. Because hydrolytic activity has been reported to be associated with light chain V regions, we have begun an analysis of germ line light chain proteins that could be the basis for affinity maturation into hydrolytic or other reactive antibodies. We produced the germ line A18b light chain and characterized its hydrolytic, nucleophilic, and tertiary structural activities. This light chain was purified to >99% purity and found to hydrolyze aminomethylcoumarin-peptide and larger protein substrates and bind a fluorophosphonate probe. Mutation of putative catalytic residues only resulted in loss of activity of a tetrameric but not dimeric form of the light chain. These biochemical properties provide a framework for understanding the structure-function relationships of germ line antibodies.Antibodies are responsible for defense against invading pathogens, but they can also be pathogenic in autoimmune disease. Antibody genes are partially hard-coded in the genome as gene modules known as V, D, and J segments for the heavy chain, or V and J segments for the light chain (1). Multiple modules allow for the diversity of the antibody repertoire through combinatorial rearrangement. During B-cell development, the germ line-encoded V, D, and J segments recombine to form functional heavy-and light-chain V region genes. Following exposure to antigen, B-cells activate an affinity maturation process that mutates V regions, and those B-cells with higher affinity variants are driven to survive and proliferate. Typically, germ line-derived antibodies have affinities in the mid nanomolar to micromolar range (2, 3), as opposed to nanomolar or less for affinity-matured antibodies. Germ line-derived antibodies contain unique properties, including polyspecificity and catalytic activity. The polyspecificity is thought to be due to an inherent flexibility in germ line antibody complementarity-determining regions (CDRs), 2 which allows them to adopt multiple conformations and bind different antigens (4 -6). The structural basis for catalytic activity is more obscure, however, structural studies of induced catalytic antibodies also show multiple structures in their germ line precursors (4,7,8).Recently, catalytic antibodies have been associated with positive or negative aspects of human disease (9, 10). In sepsis, catalytic antibodies were predictive of survival (11). In subsets of hemophilia, proteolytic antibodies against Factor VIII were associated with resistance to therapy (12, 13). Catalytic antibodies against myelin basic protein in multiple sclerosis have also been found and suggested to contribute to pathogenesis (14, 15). In multiple myeloma, Bence-Jones light-chain proteins can contribute to pathogenesis of the disease and in some cases have been reported to contain catalytic activity (16,17). The structural and biochemical details around such antibodies have not yet been studied in detail.We describe here a human g...

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