NMPRTase inhibitor screen. A. NMPRTase assay was carried out as described in the methods section with extracts obtained from U87 with indicated amounts of either FK866 or compound 1 to 6. B. The amount of C14NAD+ formed in the experiment described above (A) is measured and shown. Please note that compound 5 and 4 inhibited the NMPRTase activity.