✓ Rat glial tumors, induced by weekly injections of N-nitrosomethylurea for 8 months, were plated and propagated in culture. Cells grew as a glial tumor when injected back into various sites in newborn rats, and were then carried for many generations by transplantations from rat to rat or by alternate culture and animal passage. Light, phase, and electron microscopy of the cultured cells showed great variability among the glial types in all the primary tumors, in the cultures grown from them, and in the secondary in vivo tumors grown from the cultures. Many unmistakable stigmata of glia were conserved. Cloned cultures (derived from a single cell) were frozen and stored, and upon thawing resumed growth with their original histological appearance. Tumor lines from these cultured cloned strains showed much more constant growth rates and cell types; two stable lines were carried for many generations: a slow-growing astrocytoma and a faster growing glioblastoma. The distinctive neural protein called “S-100” was detected in soluble extracts of cultured cells from all five different primary tumors studied and the secondary tumors grown from them. It represented 0.2% to 0.4% of the soluble proteins extracted from the cultures, and was also present in some clonal strains and their derived tumors. One clonal strain after a few hundred generations continues to synthesize S-100. It is concluded that clonally derived cultures of gliomas histologically similar to those in man provide a stable and suitable model in rats for the study of human glia and gliomas.

✓ Experimental glial tumors were induced by weekly intravenous injections of N-nitrosomethylurea (NNMU) in rats. The tumors included low- and high-grade gliomas of the astrocytic series and mixed gliomas. The histology of the tumors did not vary significantly with serial passage through tissue culture, subcutaneous implantation, or freezing. These neoplasms provide reliable animal models of brain tumors common to man.

To a great extent there is a correlation between high aqueous/lipid solvent partition coefficients of a series of substituted aromatic boronic acids and the high tumor/brain ratios of these compounds in mice with subcutaneously transplanted gliomas. There are, however, exceptions to this observation and the mechanism of transport into the central nervous system of compounds with low lipid solubility remains obscure. The position of groups on an aromatic nucleus is of importance in determining the degree of penetration of brain. An attempt is made to correlate chemical and physical properties with biologic attributes.

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