Suitability of Tumor-Bearing Mice for Predicting Relative Usefulness of Isotopes in Brain Tumors

Abstract

IN CONNECTION with investigations being pursued in this laboratory on the application of atomic energy methods to the diagnosis, localization, and treatment of brain tumors,1 it has been necessary to screen a variety of radioactive isotopes and compounds of stable isotopes having useful nuclear properties, to determine which among them possess superior biological characteristics in regard to concentration in brain, brain tumor, and muscle. This screening of isotopes was carried out at first mainly in selected brain tumor patients. However, the paucity of suitable patients, the wide variations in their physiological status, the variety of tumor types encountered, and the frequent compromises of experimental discipline imposed by transcendent clinical necessity rendered this method of study slow, tedious, and at times difficult to interpret. As a means of circumventing these problems, it occurred to us that most of the desired information about a given isotope might be obtained through carefully controlled studies of distribution and concentration ratios in the organs and tumors of purestrain mice bearing transplantable subcutaneous brain tumors. Furthermore, the uniformity of the pure-strain mice and their tumors as an experimental substrate offered a possibility of a rapid method of screening without the necessity for a large statistical sampling. Although there is no assurance at the outset that data obtained in mice will carry over entirely to man, it is a relatively simple matter to check a small group of patients in order to establish a "factor of correlation" which integrates such differences as excretion, species metabolic rate, and characteristics of the particular mouse tumor studied.To establish the validity of this principle for the study of brain tumors, we have undertaken a comparative study in mice and patients of the distribution and relative concentrations of the physiological intracellular ions 32 4 and K42, of the extra-From the