A potent TPase inhibitor (IC50 = 35 nM for human placental TPase); selective for TPase over other pyrimidine-metabolizing enzymes (IC50s = >1 mM for UPase, OPRTase, TK, and DPDase); inhibits the phosphorolysis and degradation of trifluorothymidine in human breast and colon carcinoma tumor samples; enhances anti-tumor activity of trifluorothymidine in a mouse AZ-521 stomach cancer xenograft model