Neoplastic transformation of newborn rat oligodendrocytes in culture

We have developed a model to study the neoplastic transformation of rat oligodendrocytes in culture. This procedure utilizes a technique previously developed by McCarthy and de Vellis which allows the preparation of 99% pure astrocyte and oligodendrocyte populations from 1- to 2-day-old rat cerebral cortices. Pregnant rats on the 19th day of gestation were given injections with either ethyl nitrosourea (10 µg/g body weight) in phosphate-buffered saline or phosphate-buffered saline, and oligodendrocyte cultures were prepared. Oligodendrocytes appear to be unstable in culture since transformation was observed with cells derived from either pups from pregnant rats either treated with nitrosourea or phosphate-buffered saline. Transformation required 78 to 108 days and 3 to 9 passages, at which time a marked increase in cellular proliferation was observed. The possibility that the transformed cells were derived from a nonoligodendroglial cell was excluded by the following evidence. Light and scanning electron micrographs of the transformed cells revealed cytological features essentially similar to those of primary oligodendroglial cultures. Furthermore, 2 biochemical oligodendroglial markers, the induction of lactate dehydrogenase by N⁶, O⁶-dibutyryl cyclic adenosine 3́:5́-monophosphate and the presence of 2́, 3́-cyclic nucleotide 3́ phosphohydrolase, were also retained. Conversely, another oligodendroglial marker, the hydrocortisone induction of glycerol phosphate dehydrogenase, was not found in any of the cell lines. These transformed cells grew as tumors when injected intracranially into 21-day-old rats. Histologically, these tumors did not appear as classical oligodendrogliomas, but their oligodendroglial origin was confirmed since the tumor tissue contained 2́:3́-cyclic nucleotide 3́-phosphohydrolase activity, and the cells which grew from tumor explant cultures morphologically appeared similar to the parent cell line. The transformed cells were also characterized for in vitro properties which correlate with the expression of tumorigenicity. The transformed cells exhibited anchorage-independent growth and were agglutinated by concanavalin A treatment. Changes in fibrinolytic activity were not an exclusive property of transformed glial cells. This model should now allow us to study various mechanisms involved in the neoplastic transformation of oligodendrocytes.