# Potent Fluorescent Probe for Target‐Engagement Studies of Allosteric Pyruvate Kinase Modulators

## TL;DR

A new fluorescent probe called LumiPK was developed to study how drugs bind to a key metabolic enzyme in liver cells, improving drug development for metabolic diseases and cancer.

## Contribution

LumiPK is a novel fluorescent tracer that enables direct monitoring of allosteric ligand engagement with PKL in both recombinant and cellular settings.

## Key findings

- LumiPK has high affinity for PKL with a K_D of 37 ± 5 nM in recombinant assays.
- LumiPK maintains potency (EC50 = 18.4 nM) in cellular experiments using a PKL-Nluc fusion.
- LumiPK validates known PKL activators in both cellular and recombinant settings with consistent K_D values.

## Abstract

Pyruvate kinases (PKs) are highly allosterically regulated enzymes that play a central role in cellular metabolism and are increasingly recognized as valuable therapeutic targets in cancer, metabolic diseases, and diabetes. Despite their biological and clinical significance, methods to directly assess allosteric ligand engagement of PK isoforms remain limited. Here, we report the development of LumiPK, a novel, environment‐sensitive fluorescent tracer designed to monitor allosteric binding to the liver isoform of pyruvate kinase (PKL). LumiPK integrates an environment‐sensitive 4‐sulfamonyl‐7‐aminobenzoxadiazole fluorophore into a potent allosteric modulator scaffold. It emerged as the lead compound from a small ligand series, showing high affinity for PKL (K
D  =  37 ± 5 nM) in recombinant assays; the most potent fluorescent PK reporter reported to date. A NanoBRET assay using a PKL‐Nluc fusion (PKLNluc) enabled intracellular monitoring of unlabeled ligand engagement. LumiPK maintained high potency (EC50  =  18.4 nM) in cellular experiments. Competitive NanoBRET and fluorescence titration assays confirmed binding of known PKL activators (mitapivat, TEPP‐46, DASA‐58) in both cellular and recombinant settings, with K
D values remaining consistent across these methods. LumiPK thus provides a robust tool for probing PKL allosteric modulation and fills a key gap in target engagement technologies for PKL.

LumiPK, a novel environment‐sensitive fluorescent tracer, enables direct monitoring of allosteric ligand engagement with pyruvate kinase fused with nanoluciferase (Nluc), focusing on the liver isoform (PKL). In NanoBRET, and fluorescence indicator displacement assays, LumiPK shows high affinity and validates known allosteric modulators of PKL. This tool compound advances target engagement technologies and supports broader PK‐related therapeutic research.