Abstract: This invention relates to novel multi-substrate deoxyribonucleoside kinase variants. More specifically the invention provides novel deoxyribonucleoside kinase variants derived from insects or lower vertebrates, in particular from Drosophila melanogaster, from Bombyx mori, or from Xenopus laevis, novel polynucleotides encoding multi-substrate nucleoside kinase variants, vector constructs comprising the polynucleotide, host cells carrying the polynucleotide or vector, methods of sensitising cells to prodrugs, method of inhibiting pathogenic agents in warm-blooded animals, and pharmaceutical compositions comprising deoxyribonucleoside kinase variants of the invention.