as the phosphate masking groups are designed to be quickly removed in cells, which hampers deep tissue penetration. Likewise, clinically used aryl amidate prodrugs, such as sofosbuvir, tenofovir alafenamide, and remdesivir are also based on enzymatic hydrolysis, in which the activation of the prodrugs are not potentially subject to an extracellular trigger. Recent developments rely on lipophilic modifications of γ-phosphates of NTP analogues, which facilitate uptake and release the active molecules by enzymatic cleavage at physiological pH. Polymer-based drug carriers containing positive charges are also capable of loading and delivering molecules into cells via formation of non-covalent complexes. In another study, a polyamine linker was introduced to an ATP-biotin covalently, resulting in a cell-permeable ATP analogue, however in this design, release of the native NTP cargo is not possible. A more general NTP transporter was established based on a combination of using a per-6-amino-β-cyclodextrin as a receptor, which forms complexes with NTPs and an arginine-rich molecular transporter as a cellpenetrating agent. These efforts have greatly contributed to the study of NTPs and their analogues inside cells.