Small Molecule Delivery in Living Cells by Gated Hydrolysis of Phosphinate Ester Dyes: Application to Acute Myeloid Leukemia

Theranostic fluorescent platforms are capable of selective delivery of small molecules to target cells with simultaneous optical monitoring. Such technologies promise to significantly reduce off-target effects compared to cytotoxic chemotherapy. However, small molecule approaches are often hindered by relatively complex designs that are required to incorporate a fluorescent reporter, reactive linker, targeting ligand, and cargo into a single molecule. Herein, we provide the first direct evidence for the ability to gate the delivery of small molecule cargos from phosphinate ester-containing Nebraska Red (NR) dyes in vitro and in living cells. This simplified system integrates the fluorescent reporter, reactive linker, and targeting ligand into one species – a phosphinate ester dye. As a proof-of-principle for delivery of drug-like molecules to cells, we develop NR-HOCl-TFMU, which responds to hypochlorous acid (HOCl), a marker of acute myeloid leukemia (AML). NR-HOCl-TFMU is stable for days prior to reaction with HOCl, leading to phosphinate ester hydrolysis and production of a NIR (near-infrared, NR dye) and blue (cargo) fluorescent signal. NR dye fluorescence produced upon reaction with HOCl is directly proportional to cargo release, and NR-HOCl-TFMU is capable of selectively delivering its drug-like, small molecule cargo to AML cells in an HOCl-gated manner. In the long term, we envision the use of this technology to develop HOCl-gated cytotoxin delivery systems targeted towards AML cells. More broadly, this approach provides a potentially generalizable strategy for the development of simplified theranostic agents targeted towards small molecule analytes and enzymatic activities associated with disease.