Phosphate-based linkers with tunable stability for intracellular delivery of drug conjugates are described. The phosphate-based linkers comprise a monophosphate, diphosphate, triphosphate, or tetraphosphate group (phosphate group) and a linker arm comprising a tuning element and optionally a spacer. A payload is covalently linked to the phosphate group at the distal end of the linker arm and the functional group at the proximal end of the linker arm is covalently linked to a cell-specific targeting ligand such as an antibody. These phosphate-based linkers have a differentiated and tunable stability in blood vs. an intracellular environment (e.g. lysosomal compartment).
