Serving as a promising target, enzymes involved in the nucleotide metabolism have been chosen as an approach to selectively impair proliferating cells in cancer therapy, and the antimetabolites of the nucleotide metabolism have been widely used in clinics, such as 5-fluoro-2-deoxyuridine and methotrexate, the inhibitor to the thymidylate synthase and the dihydrofolate reductase, respectively (Hatse et al., 1999). The gene discussed is DHFR; the disease is cancer.