ProTide-enabled antibody-drug conjugates: A novel platform for the targeted delivery of phosphorylated drugs

: Herein, we report the first integration of ProTide technology with antibody-drug conjugates (ADCs) to create a novel platform that enables the targeted delivery of active, phosphorylated drugs. Our ADCs contain a specially designed ProTide linker that exploits the ProTide enzymatic activation pathway to release monophosphorylated nucleoside analogues directly into target cells. Using gemcitabine as a model drug conjugated to trastuzumab lysines, we demonstrated good antiproliferative activity in HER2-positive cancer cell lines (SKBR3 and MIA PaCa-2) compared to the unconjugated antibody and existing ProTide formulations. The lead compound achieved IC₅₀ values of 0.25 μM (SKBR3) and 0.19 μM (MIA PaCa-2), which represent a significant improvement over current therapies. Mechanistic studies confirmed the successful enzymatic release of the drug and the maintenance of the internalization properties of the antibody. This platform fulfils the requirement to deliver phosphorylated drugs while minimising resistance and systemic toxicity. Beyond nucleoside analogues, this approach opens up new possibilities for the targeted delivery of other phosphate-containing therapeutics, potentially expanding the scope of ADC technology.