Radioimmunoscintigraphy of gynecologic tumors with 131I-labeled anti-PLAP monoclonal antibodies.

Radioimmunoscintigraphy (RIS) was performed in 20 patients with gynecologic tumors, 14 ovarian, 5 cervical, and one endometrial carcinoma. One murine monoclonal antibody (mab) against placental alkaline phosphatase (H7) was used after radiolabeling with 131I. The labeling procedure yielded antibodies with specific activity varying between 60 and 73 MBq/mg mab. Each patient received 57 to 100 MBq of the preparation. RIS was performed 7 to 35 days later. Patients with ovarian adenocarcinoma had an accumulation of activity on RIS at tumor sites (79%, 11/14) verified by ultrasonography, CT, and clinical examination. A low or absent accumulation of activity was seen in patients with cervical tumors. The patient with an endometrial adenocarcinoma was seen to have an activity accumulation at RIS corresponding to tumor sites determined by ultrasound and/or CT. It is concluded that RIS using monoclonal antibodies against placental alkaline phosphatase can provide information which will supplement that gained from other investigations of patients with ovarian adenocarcinomas.

Inhibition of growth of HeLa cell tumours in nude mice by 125I-labeled anticytokeratin and antiPLAP monoclonal antibodies.

The radiommunotherapeutic potential of 125I-labeled monoclonal antibodies was investigated in 48 nude mice (BALB/c, nu/nu) inoculated s.c. with the HeLa Hep 2 human adenocarcinoma cell line. This isotope, 125I, which is not commonly used for therapeutic purposes caused significant decrease in tumour growth from day 10 to day 42, when coupled to monoclonal antibodies directed against placental alkaline phosphatase (H7) or cytokeratins (TS1). The average growth rate was approximately 50-60% of that observed in the untreated control group after 42 days. The specific radioactivity in each organ 42 days after injection of radiolabeled monoclonal antibodies, indicated that these target antigens retain significant amounts of radiolabeled antibody in the tumours for at least 6 weeks after injection. No weight loss was seen in the animals during this experiment. By use of autoradiographic techniques, the labeled monoclonal antibodies were visualized deep in tumours in characteristic patterns representative of viable tumour cells (H7) and necrotic areas (TS1). The therapeutic approach using 125I labeled antibodies is encouraging and may offer new dimensions in radioimmunotherapy.

Experimental radioimmunotherapy of HeLa tumours in nude mice with 131I-labeled monoclonal antibodies.

The radioimmunotherapeutic potential of 131I-labeled monoclonal antibodies was investigated in 36 nude mice (BALB/c nu/nu) inoculated s.c. with the HeLa Hep 2 human adenocarcinoma cell line. The membrane bound tumour associated antigen placental alkaline phosphatase and several intracellular cytokeratins served as targets for the antibodies. The specific radioactivity in each organ was determined after i.p. injection of the 131I-labeled antibodies (0.2-0.3 mg, approximately 15 MBq/animal), and high localization to the tumours was seen. Significant growth inhibition was observed after injection of the radiolabeled monoclonal antibody H7 against the placental alkaline phosphatase, which reduced the tumour growth to only 12% during a 3 week period compared to a growth of more than 100% for the controls. Animal weight losses were seen. Synthesis of endogenous antibodies to the target antigens was found to be significant. Morphometric evaluation of the relations between stroma, tumour cells and necrotic areas in the tumours after radioimmunotherapy demonstrated a significant increase of the mean relative connective tissue volume and a significant decreased mean of relative volume of tumour cells in the group treated with iodinated antiplacental alkaline phosphatase antibody. This therapeutic principle is encouraging and may offer new possibilities for future treatment of some malignant diseases.