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

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.

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.

We found that PLDR combined with chemotherapy induced a functional shift in the extracellular matrix (ECM) produced by chemoradiotherapy-treated CAFs. These functional units of CAFs and their self-generated ECMs (CAFu) are key drivers of pancreatic cancer desmoplasia. ECMs from PLDR-treated CAFu 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.

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.