Applicability of carcinoembryonic antigen-specific monoclonal antibodies to radioimmunoguided surgery for human colorectal carcinoma

Two carcinoembryonic antigen (CEA)-specific monoclonal antibodies (MAbs), P R1A3 and T84.66, were tested to determine whether they could accurately loc alize colorectal carcinoma and therefore be applicable in radioimmunoguided surgery (RIGS). Twenty-one tumors by three human colorectal carcinoma cell lines with various levels of CEA expression (KM-12c, C75, and Clone A) wer e successfully implanted in the intraabdominal organs of 15 nude mice. The tumors was localized using a portable radioisotope detector (Neoprobe 1000) 48 h after injection of radiolabeled MAbs (10 mCi/mouse) when the precordi al counts were <20 per 2 s, Histopathological identification of radiolabele d MAbs were also performed using immunohistochemistry and microautoradiogra phy. Radioactivity counted on a portable radioisotope detector correlated w ell with that on a gamma counter. The distribution in the blood was signifi cantly greater than in other organs (P < 0.001). Localization indices of th e tumor in various organs was from 1.1 to 8.5 in the PR1A3-pretreated mice and 3.0 to 8.6 in the T84.66-pretreated mice, Silver grains and immune stai ning were distributed in the tumor cells of the PR1A3-pretreated mice, wher eas they were in the necrotic debris as well as the tumor cells of the T84. 66-pretreated mice, There were significantly more silver grains in the live r in the T84.66-pretreated mice than in the PR1A3-pretreated mice (P = 0.00 4). The sensitivity and specificity of tumor localization by RIGS were 71.4 and 91.4% in the PR1A3-pretreated mice, whereas they were 60 and 76% in th e T84.66-pretreated mice, A study using specific anti-CEA MAbs suggested PR 1A3 as an efficient immune probe for RIGS in colorectal carcinoma with a lo w rate of false-positive detection.