Autoradiographic study of peripheral benzodiazepine receptors in animal brain tumor models and human gliomas

In vitro binding of ³H]PK-11195 (1-(2-chlorophenyl)-N-methyl-(1-methylpropyl)-3-isoquinoline carboxamide) in rodent AA ascites and C6 glioma as well as in human gliomas was investigated. The B_max (mean ± S.D.) of AA ascites tumor and C6 glioma is 1.39 ± 0.15 pmol/mg tissue and 4.50 ± 0.76 pmol/mg tissue, respectively. This B_max is 9 and 30 times, respectively, higher than the one found in the rat cortex (0.15 ± 0.03 pmol/mg tissue). A B_max of 1.26 ± 0.24 pmol/mg tissue and 0.64 ± 0.08 pmol/mg tissue was found in human malignant and low grade gliomas respectively. This B_max value should be compared to 0.35 ± 0.04 pmol/mg tissue found in the normal human cortex. There are significant (P < 0.05) differences between B_max in tumors and normal cortex. There was no significant difference in K_D between the malignant and low grade gliomas. C6 glioma has a K_D significantly greater than rat cortex. In some cases of human low grade gliomas, kinetic measurements suggested the presence of two affinity receptor sites. However, at this time, heterogeneity of the tissue cannot be excluded as being at least in part a source of this.