FSTL3+ cancer-associated fibroblasts promote vasculogenic mimicry and drive malignant progression in colorectal cancer

This study reveals the critical role of FSTL3 in colorectal cancer-associated fibroblasts (CCAFs) promoting vasculogenic mimicry (VM) through the TfR1/AKT/mTOR signaling pathway. It also demonstrates the synergistic effect of combining FSTL3-targeting antibodies with bevacizumab in suppressing VM and metastasis.

 

Literature Overview
This article titled 'Cancer-associated fibroblasts expressing FSTL3 promote vasculogenic mimicry formation and drive colon cancer malignancy', published in Cell Death & Disease, reviews FSTL3's mechanism in promoting VM through regulation of the tumor microenvironment in colorectal cancer-associated fibroblasts, and its correlation with poor patient prognosis. The study further explores the synergistic anti-tumor effects of FSTL3-targeting antibodies combined with bevacizumab, offering novel solutions for drug resistance in anti-angiogenic therapies.

Background Knowledge
Colorectal cancer (CRC) is a highly heterogeneous, vascular-rich malignancy where traditional anti-angiogenic treatments (e.g., VEGF-targeted therapies) often face resistance limitations. Vasculogenic mimicry (VM) refers to endothelial cell-independent vascular-like structures formed by tumor cells, which correlate with tumor invasiveness and poor prognosis. While cancer-associated fibroblasts (CAFs) in the tumor microenvironment are known to contribute to VM formation, their specific mechanisms remain unclear. FSTL3 (Follistatin-like 3), a secretory glycoprotein, promotes epithelial-mesenchymal transition (EMT) in gastric cancer through the BMP/SMAD pathway and participates in tumor progression by antagonizing factors like activin and TGF-β. This study first reveals FSTL3's high expression in colorectal cancer fibroblasts, its hypoxia-induced regulation, and its activation of the AKT/mTOR pathway via TfR1 (transferrin receptor 1) to enhance endothelial-like transformation and VM formation, providing a novel therapeutic target for colorectal cancer.

 

 

Research Methods and Experiments
The study integrated multiple public colorectal cancer datasets (TCGA-COAD, GSE39582, GSE17536) and employed WGCNA analysis to identify core genes associated with CAF infiltration and VM. Single-cell sequencing data confirmed FSTL3's specific expression in CAFs and its significant correlation with poor prognosis. Immunohistochemistry and immunofluorescence validated FSTL3's co-localization with VM structures in 157 patient samples. In vitro and in vivo models demonstrated that FSTL3 silencing or antibody blockade significantly inhibited VM formation, with combined bevacizumab treatment further enhancing therapeutic efficacy.

Key Conclusions and Perspectives

• FSTL3 is highly expressed in colorectal cancer-associated fibroblasts, with its expression significantly correlated with VM formation, intratumoral vascular density, and poor patient prognosis.
• Hypoxic microenvironment induces FSTL3 expression, which promotes ECM remodeling and endothelial-like transformation of tumor cells.
• FSTL3 activates the AKT/mTOR pathway through TfR1 binding, upregulates VE-Cadherin expression, and facilitates VM formation.
• FSTL3-targeting antibody (aFSTL3) effectively suppresses VM and angiogenesis, synergizing with bevacizumab to enhance anti-tumor effects.
• In animal models, FSTL3 knockout significantly inhibits tumor growth, VM formation, and metastasis while prolonging survival.

Research Significance and Prospects
This study establishes FSTL3+ CCAFs as central players in VM formation in colorectal cancer, revealing a non-VEGF-dependent angiogenic mechanism between hypoxic CAFs and tumor cells. These findings explain resistance to anti-angiogenic therapies and support dual intervention strategies targeting both FSTL3 and VEGF. Future research should explore FSTL3/TfR1 pathway regulatory mechanisms and its conservation across tumor types. Additionally, FSTL3 serves as a potential plasma biomarker for early CRC diagnosis and therapeutic monitoring.

 

 

Conclusion
This systematic investigation elucidates FSTL3's mechanism in promoting VM through TfR1/AKT/mTOR signaling regulation in colorectal cancer-associated fibroblasts. FSTL3 functions as a hypoxia-induced tumor-promoting factor significantly linked to poor prognosis. Targeting FSTL3 antibodies effectively inhibit VM formation and demonstrate strong synergy with bevacizumab, offering novel intervention strategies for anti-angiogenic therapy resistance. The study expands understanding of fibroblast heterogeneity in tumor microenvironments and their pro-VM mechanisms, establishing foundations for developing FSTL3- or TfR1-based combination therapies.

 

Leqian Ying, Yini Zhu, Lu Zhang, Jinbing Xie, and Lin Liu. Cancer-associated fibroblasts expressing FSTL3 promote vasculogenic mimicry formation and drive colon cancer malignancy. Cell Death & Disease.