In Vivo Imaging of Intracranial Human Glioma Xenografts Comparing Specific with Nonspecific Radiolabeled Monoclonal Antibodies

Current diagnostic and therapeutic modalities for malignant human gliomas are largely nonspecific. The development of monoclonal antibodies (MA's) with their high degree of specificity may allow precise tumor imaging and selective administration of therapeutic agents. However, the ability of these antibodies to specifically localize tumor tissue in vivo remains speculative. This study compares the localization and imaging properties of two MA's: a specific human glioma-associated extracellular matrix glycoprotein MA, 81C6, and a nonspecific control MA, 45.6, against a human glioma cell line, D-54 MG, intracranially inoculated into athymic rats. Forty-one animals received MA's labeled with iodine-131 (131I) or 125I and underwent imaging with a gamma camera. The images were independently evaluated and compared to tissue radioactivity levels. Radiolabeled antiglioma MA 81C6 specifically localized in intracranial xenografts. The percent of injected dose per gram of tissue for tumor was 1.707 +/- 0.405/gm for 81C6 and 0.118 +/- 0.056/gm for 45.6. All other organs had equivalent levels of specific and nonspecific MA's. For brain, these were 0.004 +/- 0.002/gm and 0.005 +/- 0.005/gm, respectively, and for the other organs, the range was from 0.053 to 0.284/gm. Statistically, 45.6 achieved levels in tumor that were significantly higher than normal brain (p less than 0.05) but significantly less than that achieved with 81C6 (p less than 0.005). With 81C6, the degree of localization was high enough to allow imaging of intracranial tumors at sizes as small as 20 mg. Intracranial tumors were imaged with 45.6 only when they achieved sizes greater than 300 mg. In this imaging study, radiolabeled 81C6, a specific antiglioma MA, proved to be significantly better for imaging small and intermediate-sized tumors than the control MA's. Large tumors were visualized by both MA's, although higher quality scans were obtained earlier and more frequently with specific MA's than with nonspecific immunoglobulin G. These data suggest that specific MA's have a role to play in both the diagnosis and treatment of primary intracranial human tumors.