Pericyte drives the formation of circulating tumour cell-neutrophil clusters to promote colorectal cancer metastasis

Background Circulating tumour cell (CTC)-neutrophil clusters represent a key driver and a hallmark of tumour metastasis; however, efficient approaches for their elimination are still lacking. Objective This study sought to elucidate the location and mechanisms of CTC-neutrophil cluster formation and develop more effective antimetastasis strategies. Design Immunofluorescence staining of clinical colorectal cancer (CRC) samples was performed to identify the location of CTC-neutrophil clusters. The correlation between the expression of nicotinamide N-methyltransferase (NNMT) in pericytes and patient prognosis, as well as its association with CTC-neutrophil cluster formation, was assessed using clinical specimens and public CRC datasets. The formation process of CTC-neutrophil clusters was visualised using intravital microscope and microfluidic vascular chip models. Bulk RNA sequencing, xenograft and allograft models and pericyte-specific genetic Nnmt deficiency mice were used to investigate the effect of pericyte NNMT on CTC-neutrophil cluster formation and CRC metastasis. Results CTC-neutrophil clusters formed at the vascular-immune interface of CRC primary tumours. Pericytes with high NNMT expression could serve as a poor prognostic biomarker that indicated an increased risk of developing metastasis in CRC. NNMT highly expressing pericytes facilitated the formation of CTC-neutrophil clusters by mediating the cellular interaction among CRC cells, neutrophils and endothelial cells through activating the CXCL5/CXCR2 axis. Genetic and pharmacological inhibition of NNMT in pericytes eliminated CTC-neutrophil clusters and suppressed CRC liver metastasis. Conclusion This study uncovers the previously undefined location and mechanism of CTC-neutrophil cluster formation and underscores the potential of pericyte-driven CTC-neutrophil clusters as a valuable prognostic indicator and therapeutic target for CRC metastasis.