# Lactate‐mediated activation of GPR81 regulates BCR/Abl protein expression in chronic myeloid leukemia cells selected under low oxygen tension

## TL;DR

Lactate activates a receptor called GPR81, which suppresses a cancer-causing protein in leukemia cells under low oxygen conditions.

## Contribution

This study identifies lactate-mediated GPR81 activation as a novel mechanism suppressing BCR/Abl protein in CML cells under hypoxia.

## Key findings

- Lactate suppresses BCR/Abl protein expression in chronic myeloid leukemia cells under low oxygen.
- GPR81 receptor engagement by lactate is essential for BCR/Abl suppression in hypoxic environments.
- MCT inhibitors and 2-DG increase BCR/Abl expression, but this effect is reversed by adding lactate.

## Abstract

Chronic myeloid leukemia (CML) is a stem cell‐driven neoplasia characterized by the expression of the constitutively active tyrosine kinase (TK) BCR/Abl. Under low oxygen, a condition that characterizes stem cell niches (SCNs) in vivo, the oncogenic BCR/Ablprotein is suppressed. Consequently, leukemia stem cells (LSCs) residing within SCNs show resistance to TK inhibitors (TKIs), the first‐line therapy for CML, due to the lack of their molecular target. It is therefore important to deepen understanding of the mechanisms driving BCR/Ablprotein suppression to design new strategies able to repress TKI‐resistant LSCs. Our previous studies showed that BCR/Ablprotein suppression occurred when glucose approaches completed exhaustion in culture medium. As lactate is the main byproduct of glucose catabolism in low oxygen, in this study we addressed the role of lactate in regulating BCR/Ablprotein expression. We found that treatment of CML cells with 2‐DG, which blocks glycolysis and thereby lactate production, or monocarboxylate transporter (MCT) inhibitors, which reduce lactate excretion, enhanced BCR/Ablprotein expression and promoted maintenance of a BCR/Abl‐dependent/TKI‐sensitive stem cell phenotype. The effects of MCT inhibition were abolished when exogenous lactate was added to culture medium, resulting in the suppression of BCR/Ablprotein expression. Treatment with 3‐hydroxy‐butyrate acid, an antagonist of the GPR81 plasma membrane ‘lactate’ receptor, prevented lactate‐driven BCR/Ablprotein suppression, while the selective GPR81 agonist 3‐chloro‐5‐hydroxy‐BA counteracted the maintenance of BCR/Ablprotein induced by MCT inhibition. Our results indicate that GPR81 engagement by extracellular lactate determines BCR/Ablprotein suppression in low oxygen environments. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.