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2026-07-20 PubMed

FBAL acts as S1PR2 β-arrestin1-biased ligand, upregulating DPD and driving 5-FU resistance.

α-fluoro-β-alanine functions as a β-arrestin1-biased ligand of S1PR2 to upregulate DPD expression in cancer cells.
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Background

Resistance to the chemotherapeutic agent 5-fluorouracil (5-FU) is a significant challenge in colorectal cancer treatment, limiting its efficacy and patient outcomes. While α-fluoro-β-alanine (FBAL), a catabolite of 5-FU, is known for its cardiotoxicity and neurotoxicity, its direct role in 5-FU resistance has been largely unexplored. This study addresses this critical gap by investigating FBAL's interaction with sphingosine 1-phosphate receptor 2 (S1PR2), a G protein-coupled receptor (GPCR), and its downstream effects on drug resistance mechanisms.

Study Design

Researchers identified FBAL as a β-arrestin1-biased ligand of S1PR2 using in vitro cell models. They investigated the mechanistic pathway in HCT116 colorectal cancer cells, including S1PR2 knockout (HCT116S1PR2KO-ΔC) and specific phosphorylation site mutants (HCT116S1PR2KO-S343A). IP-MS analysis was used to pinpoint key phosphorylation sites. In vivo, mice bearing orthotopic xenografts of HCT116S1PR2KO-WT and HCT116S1PR2KO-S343A cells were exposed to FBAL and subsequently treated with 5-FU to assess changes in chemosensitivity.

Results

FBAL exposure led to S1PR2 phosphorylation, specifically at Ser343 within its C-terminal domain, mediated by G protein-coupled receptor kinase 6 (GRK6). This phosphorylation event selectively recruited β-arrestin1, rather than G proteins, to activate the MEK/ERK/AP-1 pathway. This activation subsequently promoted DPYD (dihydropyrimidine dehydrogenase) transcription, leading to increased DPD expression. Elevated DPD is a known mechanism of 5-FU resistance. > Mice bearing HCT116S1PR2KO-S343A orthotopic xenografts exhibited significantly enhanced sensitivity to 5-FU treatment compared to HCT116S1PR2KO-WT cells following FBAL exposure, directly linking S1PR2 phosphorylation at Ser343 to overcoming resistance. This confirms that the β-arrestin1-dependent ERK pathway, activated by FBAL via S1PR2, drives 5-FU resistance.

Key Findings

  • FBAL acts as a β-arrestin1-biased ligand for S1PR2 in colorectal cancer cells.
  • S1PR2 is phosphorylated at Ser343 by GRK6 upon FBAL exposure.
  • Phosphorylated S1PR2 couples with β-arrestin1 (not G proteins) to activate the MEK/ERK/AP-1 pathway.
  • Activation of the MEK/ERK/AP-1 pathway promotes DPYD transcription, upregulating DPD expression.
  • Disrupting S1PR2 phosphorylation at Ser343 significantly enhances 5-FU sensitivity in vivo.

Why It Matters

This study fundamentally shifts our understanding of 5-FU resistance by identifying FBAL's role and the S1PR2-β-arrestin1 pathway as a critical driver. Targeting S1PR2, particularly its phosphorylation at Ser343 or its interaction with β-arrestin1, represents a promising therapeutic strategy to resensitize colorectal cancers to 5-FU. This could lead to novel adjuvant therapies that block FBAL-induced resistance, improving the efficacy of existing chemotherapy. While preclinical, this work lays the groundwork for developing small molecule inhibitors or peptide mimetics that disrupt the S1PR2-β-arrestin1 coupling, potentially translating into more effective clinical protocols for patients facing chemoresistance.

fbal 5-fu-resistance colorectal-cancer s1pr2 beta-arrestin1 dpd
Source: pubmed:42475555 · Ingested 2026-07-20 · Digest: gemini-2.5-flash