DIHYDROPYRIMIDINE DEHYDROGENASE-ACTIVITY IN HUMAN PERIPHERAL-BLOOD MONONUCLEAR-CELLS AND LIVER - POPULATION CHARACTERISTICS, NEWLY IDENTIFIED DEFICIENT PATIENTS, AND CLINICAL IMPLICATION IN 5-FLUOROURACIL CHEMOTHERAPY

Dihydropyrimidine dehydrogenase (DPD) is the initial and rate-limiting enzyme in the catabolism of 5-fluorouracil (FUra), one of the most wi dely used anticancer drugs. Previous studies from our laboratory demon strated the clinical importance of DPD in cancer patients (G. D. Heggi e, J-P. Sommadossi, D. S. Cross, W. J. Huster, and R. B. Diasio. Cance r Res., 47: 2203-2206, 1987; B. E. Harris, R. Song, S-j. Soong, and R. B. Diasio. Cancer Res., 50: 197-201, 1990), particularly in those wit h DPD deficiency who experience severe FUra toxicity (including death) following FUra treatment [R. B. Diasio, T. L. Beavers, and J. T. Carp enter. J. Clin. Invest., 81: 47-51, 1988; B. E. Harris, J. T. Carpente r, and R. B. Diasio. Cancer (Phila.), 68: 499-501, 1991]. We now sugge st that measurement of DPD activity may be useful in routine screening of cancer patients prior to FUra treatment. In this paper, we describ e the following serial studies: (a) we developed a sensitive, accurate , and precise DPD assay and a storage method to stabilize DPD activity , permitting large scale DPD screening in cancer patients; (b) we demo nstrated a normal distribution (Gaussian distribution) of human DPD ac tivity from peripheral blood mononuclear cells (PBM-DPD) in a populati on study. Baselines for PBM-DPD with fresh and frozen samples were 0.4 25 +/- 0.124 (SD) and 0.189 +/- 0.064 nmol/min/mg protein, respectivel y. The 95% and 99% distribution ranges for both fresh and frozen sampl es were also determined, providing criteria for detection of DPD-defic ient patients; (c) we identified nine new patients with profound or pa rtial DPD deficiency; (d) we determined a baseline for human liver DPD activity, which was shown to be 0.360 +/- 0.182 nmol/min/mg protein ( frozen samples); (e) we did a preliminary evaluation of liver DPD from deficient patients. Low liver DPD activity in two deficient patients correlated with low PBM-DPD activity. Using a polyclonal antibody rais ed against human liver DPD in our laboratory (Z. Lu, R. Zhang, and R. B. Diasio. J. Biol. Chem., 267: 17102-17109, 1992), Western blot analy sis demonstrated decreased DPD protein in the liver cytosol from DPD-d eficient patients compared to normal subjects. These results may be us eful in improving the effectiveness and/or lessening the toxicity of F Ura chemotherapy.