263 - Single-Cell Transcriptomic Analysis Unveils CAF-Mediated Mechanical Microenvironment Remodeling of Radiotherapy Resistance of LARC

01:00pm - 01:10pm ET

Room 107

Presenter(s)

Yinan Chen, PhD - Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, Beijing

Y. Chen¹, T. Xu², N. Wang³, H. Li², J. Shuai², M. Liu⁴, J. Zhang⁴, Y. Wang⁴, J. Jin⁵, and Y. Tang⁶; ¹State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College (PUMC), Beijing, China, ²State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences (CAMS) and Peking Union Medical College (PUMC), Beijing, China, ³State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China, ⁴Department of Ultrasound, National CancerCenter/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing,100021, China Beijing, Beijing,CN 100021, Beijing, China, ⁵Department of Radiation Oncology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, China, ⁶State Key Laboratory of Molecular Oncology and Department of Radiation Oncology, National Cancer Center/ National Clinical Research Center for Cancer/ Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, China

Purpose/Objective(s):

Emerging evidence highlights the biomechanical environment as a critical modulator of tumor behavior and therapeutic efficacy. However, its role in rectal cancer remains unclear. We aim to investigate baseline tumor stiffness and dynamic changes during neoadjuvant chemoradiotherapy (TNT) or TNT plus anti-PD1 therapy (iTNT), establish stiffness evaluation criteria, and identify key cancer-associated fibroblast (CAF) subtypes driving mechanical remodeling to influence therapeutic outcomes.

Materials/Methods:

Biomechanical properties of patients from the STELLAR II trial were assessed via ultrasound elastography (UE) and nanoindentation. Elastic modulus (Em) was measured pre-treatment(pre), post radiotherapy (on), and 4 weeks post-TNT(post). Baseline biopsy tissues were cryosectioned for nanoindentation. ROC analysis determined optimal baseline UE stiffness cutoff value. Pathological/radiologic assessments classified patients as complete responders (CR) or non-complete responders (NCR).Utilize single-cell RNA sequencing (scRNA-seq) data to explore mechanosensitive cues by high-resolution clustering, STARTRAC-dist index, AUCell/GO enrichment, and transcription factor (TF) analysis.

Results:

Among 146 patients (73 TNT vs. 73 iTNT), tissue stiffness measured by ultrasound elastography (UE) progressively decreased throughout treatment (p < 0.001), with significantly higher Emean values observed in non-complete responders (NCRs) compared to complete responders (CRs; p < 0.001). UE-derived stiffness showed strong correlation with ECM stiffness validated by nanoindentation (n = 16). ScRNA-seq analysis of 21 tissue samples identified mesenchymal cells as the primary contributors to tumor stiffness (p = 0.03). High-stiffness tissues exhibited increased infiltration of SOX6^high CAF, a subpopulation characterized by hyperactivation of pro-tumorigenic PI3K/Akt and TGF-ß signaling. Furthermore, SOX6 expression promoted Th cell infiltration but negatively correlated with plasmacytoid dendritic cell (pDC) activation; notably, pDCs in stiff environments showed marked suppression of fluid shear stress and related mechanosensitive pathways.

Conclusion:

In conclusion, our study demonstrated that tumor stiffness as a predictive biomarker for LARC therapeutic response, with stiffer tissues correlating with resistance. Mechanical remodeling involves CAF-driven mesenchymal reprogramming, where SOX6^high CAF emerge as pivotal regulators. These findings provide a framework for targeting biomechanical cues to improve treatment strategies in LARC.