Radioimmunolocalization of human brain tumours: biodistribution of radiolabelled monoclonal antibody UJ13A.

Monoclonal antibody UJ13A, radiolabelled with 131I, was intravenously administered to patients with primary brain tumours. The antigen recognised by UJ13A is present on most neuroectodermally derived tissue. The ratio of uptake in tumour to normal brain, assessed by scintigraphy, improved with time. Maximal tumour uptake occurred between 4 and 48 h. Dynamic and static scintigrams indicated some early sequestration of radiolabelled antibody by the liver. Tumours were surgically resected in seven patients at various intervals after antibody administration showing tissue to blood ratios increasing with time in all parts of the lesion (viable and necrotic tumour, cyst fluid), and in normal brain. The highest tissue to blood ratio in viable tumour was 5.1 at 16 days after injection. In tissues resected 2-3 days after injection there was relatively greater uptake in the viable tumour compared to necrotic tumour and cyst fluid. In contrast, tissues resected later (6-16 days) showed greater uptake in ischaemic tissue than viable tumour, suggesting diffusion was an important factor influencing tumour uptake. The amount of radioactivity per gram of tumour tissue was less than 0.005% of the injected dose. Future studies are needed using different antibodies, antibody fragments and additional methods of optimising delivery.