Triphosphate and diphosphate nucleoside prodrugs: broadening the therapeutic potential of nucleoside-based treatments

Multiple prodrug strategies have been developed to deliver nucleoside monophosphates (NMPs) and thereby overcome the initial kinase-mediated intracellular phosphorylation of nucleoside analogues (NAs), a major bottleneck in their activation. However, some NAs are limited by a second and/or third slow and inefficient phosphorylation step, which can lead to accumulation of mono- and diphosphate intermediates with associated toxicity. In addition, the metabolic pathways leading to the formation of the active nucleoside triphosphates remain poorly characterised for many reported analogues. Consequently, di- and triphosphate prodrug strategies for NAs have gained increasing attention in recent years. Here, we provide a comprehensive overview of the current approaches for development of these higher phosphorylated nucleotide analogues, including their activation pathways in different media, biological activity, synthetic methodologies, and their applicability across a broad range of NAs. Taken together, this review highlights both the potential of NDP and NTP prodrug strategies and the challenges associated with their development, providing a framework to guide future advances in their rational design and broader application.