Quantitative Measurements of Regional Glucose Utilization and Rate of Valine Incorporation into Proteins by Double-Tracer Autoradiography in the Rat Brain Tumor Model

We examined the rate of glucose utilization and the rate of valine incorporation into proteins using 2-[¹⁸F]fluoro-2-deoxyglucose and L-[1-¹⁴C]-valine in a rat brain tumor model by quantitative double-tracer autoradiography. We found that in the implanted tumor the rate of valine incorporation into proteins was about 22 times and the rate of glucose utilization was about 1.5 times that in the contralateral cortex. (In the ipsilateral cortex, the tumor had a profound effect on glucose utilization but no effect on the rate of valine incorporation into proteins.) Our findings suggest that it is more useful to measure protein synthesis than glucose utilization to assess the effectiveness of antitumor agents and their toxicity to normal brain tissue. We compared two methods to estimate the rate of valine incorporation: “kinetic” (quantitation done using an operational equation and the average brain rate coefficients) and “washed slices” (unbound labeled valine removed by washing brain slices in 10% thrichloroacetic acid). The results were the same using either method. It would seem that the kinetic method can thus be used for quantitative measurement of protein synthesis in brain tumors and normal brain tissue using [¹¹C]-valine with positron emission tomography.