Dual KRAS-EGFR Targeted Therapy Resistance Mechanism Revealed in Colorectal Cancer

Tumor cells exhibit remarkable adaptive capabilities under therapeutic pressure, a phenomenon scientifically termed cellular plasticity. Without relying on genetic mutations, they can alter their differentiation states to evade drug attacks and regain vitality. This survival strategy appears prominently in colorectal cancer treatment. Combined KRAS and EGFR inhibitor therapy has been regarded as a key approach to combat KRAS-mutant colorectal cancer. However, tumor cells still develop escape mechanisms to resist this dual suppression.

A recent study published in Cancer Cell by researchers from Sun Yat-sen University in China reveals that under the dual pressure of KRAS and EGFR inhibitors, surviving tumor cells undergo lineage plasticity, acquiring molecular features typically found in healthy small intestinal Paneth cells-a Paneth-like cell state.

Mechanistically, they identified the SMAD1-FGFR3 signaling pathway as the key pathway mediating this Paneth cell-like transformation in colorectal cancer cells. Activation of this pathway further enhanced the survival ability of these Paneth cell-like cells, enabling tumor cells to evade dual inhibition. Targeting FGFR3 effectively blocked this lineage plasticity and showed significant synergistic anti-tumor effects with KRAS-EGFR inhibitors in preclinical models.

To investigate residual tumor states post-combination therapy, researchers first utilized an inducible KRAS G12D-driven mouse colorectal cancer model. After two weeks of combined treatment with the KRAS G12D inhibitor MRTX1133 and the EGFR antibody cetuximab, tumor burden was significantly reduced but not completely eradicated. Transcriptomic analysis of residual lesions revealed marked enrichment of Paneth cell-associated pathways (e.g., defensin and antimicrobial peptide synthesis). Gene set enrichment analysis further confirmed that Paneth cell signature genes were the most upregulated epithelial cell type post-treatment. These findings were consistently validated across multiple human KRAS G12D/G12C-mutant colorectal cancer cell lines, patient-derived organoids, and xenograft models, indicating that Paneth-like cell state acquisition is a common adaptive response to KRAS-EGFR dual inhibition.

To trace the origin of Paneth-like cells, researchers developed a lineage-tracing system driven by the DEFA5 gene promoter. Once cells activated DEFA5 (a Paneth cell marker gene), they switched from red to green fluorescence. This system clearly captured tumor cells transitioning from red to green under drug pressure, confirming that Paneth-like cells arise directly from tumor cell transdifferentiation. Notably, this process was reversible-upon drug withdrawal, green cell proportions rapidly declined, as if tumor cells shed their disguise.

Subsequent functional assessments revealed that Paneth-like cells were less sensitive to KRAS-EGFR inhibitors. Experiments selectively eliminating Paneth-like cells demonstrated that their depletion significantly enhanced combination therapy efficacy.

To elucidate the upstream regulatory network driving this plasticity, researchers conducted genome-wide CRISPR knockout screens of transcription factors (TFs) in 3D tumor spheroid models. They identified 34 TFs whose loss increased drug sensitivity. Cross-referencing these with Paneth cell signature-associated TFs from public colorectal cancer cohorts and integrating functional and expression data pinpointed SMAD1 as the key candidate.

Validation experiments showed that combination therapy induced upregulation of SMAD1 at both transcript and protein levels, with SMAD1 protein co-localizing with Paneth marker DEFA5 in residual lesions. Genetic knockout of SMAD1 not only blocked therapy-induced Paneth marker expression but also restored tumor sensitivity to KRAS-EGFR dual inhibition in vitro and in vivo.

Mechanistically, SMAD1 directly binds to the fibroblast growth factor receptor 3 (FGFR3) gene promoter, activating its transcription and forming the SMAD1-FGFR3 signaling axis. This pathway promotes Paneth-like phenotype acquisition while reactivating MAPK survival signaling in these cells, enabling tumors to evade KRAS-EGFR inhibition. Genetic knockdown or pharmacological inhibition of FGFR3 effectively blocked Paneth-like transition, suppressed MAPK rebound, and reversed therapy resistance.

Figure 1. SMAD1 drives resistance to KRAS-EGFR combination therapy by promoting Paneth-like state transition. (Zhang Y, et al., 2025)

Finally, in KRAS G12D-mutant human tumor xenograft models, adding the FGFR inhibitor futibatinib to the MRTX1133-cetuximab dual regimen (forming a triple therapy) nearly completely prevented therapy-induced Paneth-like cell enrichment and induced profound, durable tumor regression, far surpassing dual therapy efficacy. Additionally, analysis of paired biopsies from two patients who progressed after KRAS G12C inhibitor-EGFR antibody therapy revealed significant Paneth-like cell enrichment post-treatment, providing clinical evidence for this resistance mechanism.

Reference

Zhang Y, et al. Paneth-like transition drives resistance to dual targeting of KRAS and EGFR in colorectal cancer. Cancer Cell, 2025.