THE HEXOSE MONOPHOSPHATE PATHWAY IN ETHYLNITROSOUREA INDUCED TUMORS OF THE NERVOUS SYSTEM

Respiration studies in vitro, in which tissue slices were incubated with [1-¹⁴C]glucose or [6-¹⁴C]glucose and ¹⁴CO₂ collected, resulted in C-1/C-6 ¹⁴CO₂ ratios that were higher in slices of tumor and newborn brain than in slices of adult brain. In adult brain, the C-1/C-6 ¹⁴CO₂ ratio averaged close to unity. In slices of tumor and newborn brain however, the mean C-1/C-6 ratio was greater than three. Addition of phenazine methosulfate (PMS) increased conversion of [1-¹⁴C]glucose to ¹⁴CO₂ in slices of normal adult brain 5-fold, and in slices of newborn brain and tumor, approx 12-fold. Injection of animals with 6-aminonicotinamide (6-AN) decreased conversion of [1-¹⁴C]glucose in slices of normal brain 30% but decreased conversion in tumor slices by 80%. Evidence supports the presence of an active hexose monophosphate pathway (HMP) in tumors of the nervous system regulated in part by available NADP⁺ levels. Inhibition by 6-AN was more effective in tumors than in normal adult brain.