In vivo behavior of 111In-labeled monoclonal anti-prostatic acid phosphatase antibody after intraprostatic and intravenous injections.

The 111In-labeled monoclonal anti-prostatic acid phosphatase (PAP) monoclonal antibody F(ab')2 fragment was used for the radioimmunodetection of prostate cancer in two different patient groups: 15 patients with surgically verified T1-2 prostate cancer were imaged prior to staging lymphadenectomy and total prostatectomy using lymphatic administration (intraprostatic (ipr) injection), and 15 patients with verified metastatic prostatic cancer were imaged after intravenous (i.v.) injection. The patients were studied on several occasions (at 0-180 hours) after injecting a 1 mg MoAb fragment labeled with 75-150 MBq111In (DTPA-chelation). The extirpated tissues were counted for radioactivity, and studied immunohistochemically (IHC) and histologically. The anti-PAP MoAb was labeled with high efficiency (87-99%) and it demonstrated good immunoreactivity (90-95%) and a high affinity to the target antigen. In the excised prostates, cut into 12-18 smaller pieces, there was a clear correlation between the PAP content (as detected by IHC) and absolute radioactivity (% ID of 111In anti-PAP/g prostate). However, there was no correlation between radioactivity and the amount of cancer tissue (% of histological slices) inside the removed prostate tissue. In the pharmacokinetic studies, maximum activity in the serum was obtained within 3-5 hours after ipr injection; after that the kinetic behavior was similar to that after i.v. injection. After i.v. injection, two components could be distinguished the pharmacokinetic curves; the half-lives for mean distribution and elimination were 0.62 and 35.6 hours, respectively. The mean distribution half-life as well as the AUC from the pharmacokinetic curves correlated significantly with serum PAP (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)