Clinical pharmacology, metabolism, and tissue distribution of 90Y-labeled monoclonal antibody B72.3 after intraperitoneal administration.

B72.3 is a murine monoclonal antibody that recognizes a high-molecular-weight tumor-associated glycoprotein (TAG-72). Nine patients with TAG-72-positive ovarian carcinoma or papillary serous carcinoma of the peritoneum received an intraperitoneal infusion of 2, 4, or 10 mg B72.3 labeled with 0.5-1.2 (mean, 0.8) mCi 90Y. All patients had laparotomy, with multiple tissue and tumor samples removed 3-7 days later. The concentration of the total 90Y label in peritoneal fluid cleared with an extrapolated half-life of 68.6 +/- 4.5 hours. A low-molecular-weight 90Y-labeled species of metabolite was identified by high-performance liquid chromatography. The concentration of this low-molecular-weight species initially increased in the peritoneal fluid, with a half-life of 0.9 hour, and was rapidly cleared from the peritoneal cavity, with a half-life of 23.1 hours. Both the 90Y-labeled metabolite and the 90Y-labeled B72.3 were absorbed into the plasma, with half-lives of 16 +/- 2.2 hours and 25 +/- 5 hours, respectively. The clearance half-lives for these agents in plasma were 25 +/- 3 hours for the metabolite and 42 +/- 17 hours for B72.3. Approximately 8%-11% of the total injected 90Y label appeared in urine over 72 hours. Most of the label (about 70%) was present as the 90Y-labeled metabolite, but about 30% of the 90Y label in urine appeared identical to the authentic 90Y-labeled B72.3 standard when assayed by chromatography. Tissue distribution studies showed that normal tumor tissue and omentum contained the highest content of 90Y (about 0.017% of the injected dose per gram), followed in descending order by liver, normal lymph nodes, peritoneum, bone, and fascia. The lowest concentrations of 90Y were found in rectus abdominis muscle, bone marrow, and fat. There was substantial heterogeneity in the uptake of the 90Y label into tumor sites among patients and among different sites within the same patient. No correlation could be demonstrated between the TAG-72 content and the amount of 90Y label found in tumor sites. Preliminary radiation dosimetry estimates suggest that the tumor sites received about 82.8 cGy for each millicurie of 90Y administered. Thus, if an adequate total radiation dose can be achieved, 90Y-labeled B72.3 should be therapeutically useful for treating diffuse intraperitoneal disease.

Radioimaging of melanoma using 99mTc-labeled Fab fragment reactive with a high molecular weight melanoma antigen.

Twenty patients with metastatic malignant melanoma were studied with 99mTc-labeled monoclonal antibody (MoAb) Fab fragment (NR-Ml-05) reactive with a high molecular weight (Mr 240,000) melanoma associated antigen. Patients received 40 mg unlabeled irrelevant MoAb (NR-2AD-IgG) and 7.5 mg unlabeled NR-Ml-05 (whole IgG) prior to infusion of 10 mg 99mTc-labeled (10-25 mCi) NR-Ml-05 Fab. Unlabeled MoAb were given to block nonspecific and specific binding sites. Gamma camera scans and single photon emission computed tomography were performed at 8 and 24 h postadministration. Of 172 preexisting lesions, 136 were imaged for a sensitivity of detection of 79%. Imaging was site and size dependent with the greatest sensitivity for liver lesions (100%) and the least for bowel (0%). Six sites (2 skin, 1 lung, 3 liver) were detected by single photon emission computed tomography that were missed on routine planar images. Forty-one additional unconfirmed sites were seen. Of these, 7 (17%) have been confirmed as tumor after a median follow-up time of 6 months. False positive scans included scar tissue, areas of chronic inflammation, an infected femoral aneurysm, and septic emboli. Nonspecific uptake of radioactivity occurred in kidney, gallbladder, bowel, thyroid, and myocardium. Human anti-mouse antibodies were detected in up to 69% of patients. In summary, radioimaging with 99mTc-NR-Ml-05 is a sensitive test, especially for detecting liver lesions. It is safe, simple to administer, and convenient for the patient. Biodistribution and imaging sensitivity differ significantly from studies in which 111In-labeled anti-melanoma MoAb have been used.

Immunospecific saturable clearance mechanisms for indium-111-labeled anti-melanoma monoclonal antibody 96.5 in humans.

Liver uptake of 111In-labeled monoclonal antibodies (MoAb) remains a significant problem in radioimaging studies to date. To determine if the observed liver uptake of an 111In-labeled anti-melanoma antibody 96.5 (111In-96.5) was dependent on the presence of hepatic antigen or on recognition of circulating murine antibody, escalating doses of an unlabeled nonimmunoreactive MoAb (NIR-MoAb) were administered to 18 patients with metastatic malignant melanoma either 1 or 24 h prior to an infusion of 1 mg of 111In-96.5. The number of metastases imaged, pharmacokinetics, and the ratio of radioactivity (expressed as average counts/pixel) in liver (L), spleen (S), bone (B), and kidney (K) compared to blood pool (heart = H) were examined. Results were prospectively compared with data from six patients who received immunoreactive unlabeled 96.5 prior to 111In-96.5. Increasing dose or changes in the preinfusion time of NIR-MoAb had no significant effect on the biodistribution of 111In-96.5. In contrast, patients who received unlabeled, immunoreactive 96.5 prior to 111In-96.5 infusion demonstrated a significant drop [P less than 0.001] in the liver/heart ratio of radioactivity [2.81 +/- 0.35 (SEM)] compared to patients receiving the identical dose of NIR-MoAb [10.35 +/- 1.33]. Significant decreases in spleen/heart and bone/heart ratios were also observed. Pharmacokinetic studies showed that the volume of distribution (Vd) and the plasma t1/2 both decreased when 96.5 was administered compared to NIR-MoAb. In addition, a 4-fold increase in concentration X time was obtained after 96.5 antibody was administered compared to NIR-MoAb. More metastases were imaged in patients receiving preinfusions of 96.5 (23 of 28) than in patients receiving NIR-MoAb (10 of 18; P less than 0.05). Although tissue distribution of 111In-labeled antibody can be ascribed to nonspecific organ clearance of murine antibodies, a substantial component of tissue disposition of antibody 96.5 was shown to be a consequence of specific clearance of immunoreactive antibody which may cross-react with tissue antigens.

Metastatic colorectal cancer: radioimmunoscintigraphy with a stabilized In-111-labeled F(ab')2 fragment of an anti-CEA monoclonal antibody.

Metastatic colorectal cancer was detected with stabilized F(ab')2 fragments of ZCE-025, an anti-carcino-embryonic antigen (CEA) monoclonal antibody (MoAb). The fragments were prepared by cross-linking Fab' with a bifunctional cross-linking agent, bis-(maleimido)methyl ether. The authors labeled 2 mg of ZCE-025 with 5 mCi (185 MBq) of indium-111 and injected the material intravenously, either alone or with unlabeled F(ab')2, into 16 patients. Lesion detection, pharmacokinetics, and relative body distribution were evaluated and compared with those of the intact immunoglobulin (IgG1) antibody. Stabilized F(ab')2 fragments were more useful than the intact antibody in detection of lesions: Overall sensitivity of F(ab')2 fragments for all the patients was 79.4%, whereas overall sensitivity of the intact IgG1 antibody was 32%. This anti-CEA-stabilized F(ab')2 fragment may be a powerful diagnostic tool that can achieve higher sensitivity at smaller protein doses than the intact IgG1 antibody.