COMPARISON OF COPPER-67-LABELED AND IODINE-125-LABELED ANTI-CEA MONOCLONAL-ANTIBODY BIODISTRIBUTION IN PATIENTS WITH COLORECTAL TUMORS

Copper-67 has comparable beta-particle emissions to that of I-131, but it displays more favorable gamma emission characteristics for applica tion in radioimmunotherapy (RIT). This study investigates the potentia l of Cu-67-labeled monoclonal antibody (MAb) 35 for RIT of colorectal carcinoma. Methods: Biokinetics of simultaneously injected Cu-67- and I-125-labeled MAb35 were studied in six patients scheduled for surgery of primary colorectal cancer. Results: Whole-body clearance (T-1/2) o f Cu-67, estimated from sequential anterior and posterior whole-body s cans and corrected for decay of Cu-67, was 41 hr. Serum clearance of C u-67 was faster (27.41 hr) than that of I-125 (38.33 hr). Mean tumor u ptake of the Cu-67-labeled compound (0.0133 %ID/g) exceeded that of I- 125 (0.0095 %ID/g), and tumor-to-blood ratios were higher for Cu-67 th an for I-125, with averages of 6.07 and 2.41, respectively. The averag e Cu-67/I-125 ratio was 1.9 for tumor uptake, 0.7 for blood and 2.6 fo r tumor-to-blood ratios. Nonspecific liver uptake of Cu-67 as calculat ed from whole-body scans was high in four patients, up to 25% of resid ual whole-body activity at 48 hr, but did not increase with time. We a lso observed some nonspecific bowel activity, as well as moderate to h igh uptake in benign polyps. Conclusion: Copper-67-labeled MAb35 is mo re favorable than its radioiodine-labeled counterpart for RIT of color ectal carcinoma due to higher tumor-to-blood ratios, but the problem o f nonspecific liver and bowel uptake must first be overcome. The absol ute accumulation of activity in tumor remains low, however, so the pro bability of cure with this compound alone is questionable. The use of Cu-67 as one component of a multimodality adjuvant treatment seems to remain the most appropriate application for RIT.