The Multifunctional Deoxynucleoside Kinase of Insect Cells Is a Target for the Development of New Insecticides

The antiherpetic agent ( E )-5-(2-bromovinyl)-2′-deoxyuridine (BVDU) was found to be an efficient substrate for recombinant Drosophila melanogaster -deoxyribonucleoside kinase with a K m of 4.5 μM and a V max of 400 nmol/μg protein/h compared with 1.3 μM and 62.5 nmol/μg protein/h, respectively, for the natural substrate thymidine. Mammalian cytosolic thymidine kinase-1 does not recognize BVDU as a substrate. In sharp contrast to mammalian cells, the insect D. melanogaster and Spodoptera frugiperda (Sf) embryonic cells proved highly sensitive to the cytostatic action of BVDU. BVDU was efficiently metabolized to its 5′-mono-, 5′-di- and 5′-triphosphate derivatives in the insect cell cultures and abundantly incorporated into the insect cell DNA. BVDU prevented the D. melanogaster cells to initiate the S phase of their cell cycle, and exposure of S. frugiperda cells to BVDU led to a dose-dependent retardation of the insect cells in the S phase of their cell cycle. Both inhibition of nucleic acid synthesis (through the 5′-triphosphate of BVDU) and inhibition of thymidylate synthase (through the 5′-monophosphate of BVDU) would account for the cytostatic activity of BVDU against the insect cells. Because of the virtual lack of cytotoxicity of BVDU against mammalian cells, the drug should be considered highly selective in its cytostatic action against the insect cells. When added to the food of S. frugiperda larvae, BVDU caused a remarkable decrease in the weight gain of the larvae and heavily compromised the transformation of the larvae to the pupae and their subsequent adult (moth) phase. Our data indicate that insect multifunctional deoxyribonucleoside kinase should be considered an entirely novel and attractive target in the development of new nucleoside types of highly selective insecticidal drugs.