BIOLOGICAL PROPERTIES OF CHIMERIC DOMAIN-DELETED ANTICARCINOMA IMMUNOGLOBULINS

CC49 is a second-generation monoclonal antibody (MAb) that has high affinity for the tumor-associated pancarcinoma antigen tumor-associated glycoprotein-72, In clinical trials using gamma scanning, radiolabeled CC49 has facilitated the detection of more than 90% of carcinomas, We report here the development of a constant heavy-chain 2 (C(H)2) domain-deleted chimeric (c) CC49 MAb by transfecting an expression construct consisting of the CC49 murine variable region and a C(H)2 domain-deleted human IgG1 constant region into cCC49 kappa producing SP2/0 murine myeloma cells, As determined by SDS-PAGE, the intact cCC49 Delta C(H)2 has a molecular weight of 153,000 and, under reducing conditions, molecular weights of 43,000 and 27,000, The plasma clearance and tumor-targeting properties of cCC49 Delta C(H)2 were evaluated and compared with those of mouse/human chimeric forms cCC49 Delta C(H)1 and intact cCC49. Previous studies have shown that the in vitro antigen-binding properties of cCC49 Delta C(H)1 are similar to those of cCC49. Biodistribution studies reported here, using I-131-labeled cCC49 Delta C(H)1 and I-125-labeled cCC49 in athymic mice bearing human colon carcinoma xenografts, demonstrated that both cMAbs localized to the tumor and cleared from the normal tissues similarly, However, in comparison with I-125-labeled cCC49, I-131-labeled cCC49 Delta C(H)2 localized to tumors earlier and had a significantly lower percentage of the injected dose of cMAb/g (%ID/g) in normal tissues than cCC49, Immunoscintigraphy of I-131-labeled cCC49 Delta C(H)2 and I-125-labeled cCC49 in athymic mice bearing human tumor xenografts demonstrated a clear image of the tumor by 24 h after i,v, administration of the Delta C(H)2 cMAb versus the 72 h required for cCC49, Biodistribution studies using Lu-177-conjugated cCC49 Delta C(H)1 and cCC49 showed no significant difference between the radiolocalization indices (% ID/g in tumor divided by %ID/g in normal tissue), Lu-177-conjugated cCC49 Delta C(H)2, however, had lower %ID/g values in tumor xenografts and lower radiolocalization indices than either Lu-177-conjugated cCC49 Delta C(H)1 or Lu-177-conjugated cCC49, Pharmacokinetic studies in non-tumor-bearing athymic mice using cCC49 Delta C(H)1 and cCC49 revealed no significant difference between these cMAbs, However, the plasma clearance of cCC49 Delta C(H)2 in non-tumor-bearing mice was significantly faster than that of cCC49, These results were similar when the cMAbs were labeled with either iodine or lutetium, In nonhuman primates, I-131-labeled cCC49 Delta C(H)2 cleared significantly faster than I-125-labeled cCC49, The similar plasma clearance and tumor localization of cCC49 and cCC49 Delta C(H)1 suggest that these two cMAbs may be used in similar clinical settings, However, because of the unique pharmacokinetics and tumor targeting of cCC49 Delta C(H)2 versus cCC49 or ECC49 Delta C(H)1, this chimeric immunoglobulin form may be useful in clinical settings that require efficient tumor targeting and rapid serum and whole-body clearance.