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Thymidylate synthase (TS; EC 2.1.1.45), a prominent target for fluoropyrimidines and antifolates, catalyzes the N5,10-methylenetetrahydrofolate-dependent C(5) methylation of dUMP, resulting in the de novo synthesis of thymidylate. Anticancer activity of 5-fluorodeoxyuridine (FdUrd) is based on conversion of 5FdUrd to FdUMP, a potent TS inhibitor. Clinical effectiveness of antineoplastic drugs is hampered by development of various types of drug resistance, for example expression of a changed target enzyme, less sensitive to inhibition by drug active form. A FdUrd-resistant mouse leukemia L1210 cell line (L1210R) was developed in our laboratory (1). TS purified from L1210R cells was less sensitive to FdUMP slow-binding inhibition than the enzyme from the parental cells (L1210P) (Table 1). The two TS forms also showed different mobilities under conditions of denaturing polyacrylamide gel electrophoresis, indicating differing molecular weights, 34,000 ± 0 (N = 3) and 31,000 ± 0 (N = 3) for L1210P TS and L1210R TS, respectively (Figure 1). In order to learn the molecular mechanism of different FdUMP interactions with the two TS forms, efforts were made to clone their cDNAs and compare amino acid sequences.

Trichinella spiralis is a parasitic nematode causing trichinellosis in mammals. The muscle larvae develop from the newborn larvae, delivered by females after mating in the host small intestine of the adult forms, originating from consumed infected meat. The larval growth in the muscles is completed within 20 days post infection. Therefore it was surprising to find high thymidylate synthase (TS; EC 2.1.1.45) activity in non-growing T. spiralis muscle larvae, isolated up to two years post infection (1), as expression of activity of this enzyme (catalyzing the C(5) methylation of dump, yielding dTMP) has been correlated with cell proliferation (2). In order to learn more about regulation of thymidylate synthase expression in the parasite, molecular cloning of T. spiralis thymidylate synthase gene was performed, and expression of the corresponding mRNA studied.

A number of reports for the past few years have shown that higher plants can be important and useful tools for production and delivery of viral antigens. Oral route represents one of the most efficient and safe ways for administration of therapeutic proteins [1]. Among protein antigens expressed in transgenic plants is hepatitis B surface antigen as reported by several laboratories.