Partial characterization of a brain extract factor(s) inhibitory to transformed neural cells

The factor(s) present in extracts prepared from the brains of newborn A/J or C57B1/6 mice, with inhibits S20Y neuroblastoma cell growth in vitro, was partially characterized. Twice as much ingibitory activity was extracted per gram wet weight of brain than torso, and inhibitor recovery was greatest in extracts prepared from brains of mice 1 week or less in age. The inhibitory factor(s) was water‐soluble and was stable to heating at 100°C, to freezing, and to lyophilization. It was susceptible to the action of pronase. The factor(s) behaved like a molecule of molecular weight ˜ 700 upon passage through ultrafiltration membranes. Growth of rat hepatoma (H4), murine melanoma (B16), and transformed murine fibroblasts (WT19 and B6‐HCMV) was not significantly inhibited by brain extract. Growth of rat glioma cells (C6) was significantly reduced but to a lesser degree than that of murine neuroblastoma cells (S20Y and N 115) and glioma cells (G26‐20). These results suggest that the inhibitor expresses a cell specificity.