Pronukleotydy o strukturze amidofosforanów i ich wewnątrzkomórkowy mechanizm aktywacji

Nucleoside analogues have great therapeutic potential for the treatment of cancer and viral diseases. Once inside the cell, they are activated by a series of intracellular phosphorylation steps to produce 5’-triphosphate derivatives, which can be incorporated to DNA or RNA and act as terminators of growing polynucleotide chains [1c]. In many cases, nucleoside analogues are poor substrates for the cellular kinases needed for their activation [5]. It is clear that intracellular introduction of nucleoside analogues as phosphorylated metabolites (so called pronucleotides) could circumvent difficulties associated with the use of non-phosphorylated nucleoside analogues and could even activate inactive compounds or could increase the activity of the nucleoside analogues. However, polarity and a ready degradation by phosphatases make the use of free nucleotide analogues impractical. Therefore, much of the recent efforts have been focused on finding suitable prodrugs of nucleoside analogue monophosphates. Among the current diverse prodrug approaches, nucleoside phosphoramidate derivatives appear to be an interesting class of antiviral and anticancer agents [1c]. These prodrugs, as are devoid of negative charge, should be able to cross the cell membrane either by diffusion or utilizing transport protein [1c]. Conducted cell extract studies have provided evidence of a bioactivation mechanism that relies on enzyme-catalyzed P-N bond hydrolysis in phosphoramidate pronucleotides [1a,b]. It was assumed that phosphoramidate derivatives should generate nucleoside monophosphates inside the cell at rates that are influenced by both the nature of the amino group and the pH of the medium. Then nucleoside monophosphates should be phosphorylated in two different steps to the corresponding 5’-O-triphosphates (NTP) which can inhibit polymerase or be incorporated into the DNA strand being synthesized in the cell. Over the last decade extensive studies has been carried out to establish the mechanism of action of phosphoramidates and identification of enzymes responsible for bioactivation this pronucleotides to phosphorylated nucleosides [7, 21, 24]. Investigation of metabolism pathways provided evidence that phosphoramidase activity of Hint (histidine triad nucleotide-binding proteins) play a key role in the activation of phosphoramidate pronucleotides [23–27].