Pulsed Low-Dose-Rate Chemoradiation Induces Stromal Reprogramming in Pancreatic CAF-Generated ECM: Quantification by the HOST-Factor

Background and Aims: Pancreatic cancer remains highly lethal, with limited treatment options, in part due to its extensive and complex desmoplastic tumor microenvironment (TME). We investigated the in vitro use of pulsed low-dose-rate radiation (PLDR) as an alternative to conventional radiotherapy, aiming to counteract a key pro-tumoral effect of standard chemoradiation on the TME. Additionally, we introduced a novel approach for quantifying pro- vs anti-tumoral stromal function in vitro. Methods: We utilized an established 3-dimensional, in vivo-mimetic cancer-associated fibroblast (CAF) functional unit culture system to model and alter TME behavior. To comprehensively assess the impact of PLDR, we developed the Harmonic Output of Stromal Traits Factor (HOST-Factor), a composite score integrating multiple function-informing stromal biomarkers. Results: lost their capacity to support de novo CAF activation, instead acquiring a restrictive phenotype. A positive-to-negative shift in HOST-Factor values corresponded to this functional transition, predicting the ECM's ability to limit further CAF activation. Conclusion: Our findings suggest that PLDR may restrict desmoplastic expansion and improve the therapeutic efficacy of chemoradiotherapy. The HOST-Factor provides a novel, quantitative tool for assessing stromal function and may inform future treatment strategies. These results support the ongoing NCT04452357 clinical trial, which is evaluating the safety and impact of escalated PLDR-based chemoradiation in the neoadjuvant treatment of pancreatic cancer.