# Hypochlorous Acid-Gated Hydrolysis of a Phosphinate Ester Dye in Living Cells

## TL;DR

This paper introduces a new fluorescent dye system that can deliver drug-like molecules to cancer cells in a controlled way using a chemical signal linked to disease.

## Contribution

The first direct evidence of HOCl-gated delivery of small-molecule cargos using phosphinate ester dyes in living cells.

## Key findings

- NR-HOCl-TFMU is stable until it reacts with hypochlorous acid, triggering hydrolysis and fluorescence.
- The dye selectively delivers its cargo to AML cells in vitro and in a tumor model.
- The system integrates reporter, linker, and ligand into one molecule, simplifying theranostic design.

## Abstract

Theranostic fluorescent platforms are capable of the
selective
delivery of small molecules to target cells with simultaneous optical
monitoring. Such technologies promise to significantly reduce off-target
effects compared with 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 developed NR-HOCl-TFMU, which responds to hypochlorous acid (HOCl), an analyte detected
in 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) fluorescence signal. NR dye fluorescence
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 vitro and in a localized tumor model in an HOCl-gated
manner. In the long term, we envision the potential use of this technology
to afford HOCl-gated delivery systems with selectivity toward HOCl-positive
AML cells. More broadly, this approach provides a potentially generalizable
strategy for the development of simplified theranostic agents targeted
toward small-molecule analytes and enzymatic activities associated
with disease.