Premature Fibroblast Senescence in Large Cell Carcinoma Provides Enhanced Growth and Invasive Advantages to Cancer Cells in Culture and in vivo

Tumor-associated fibroblasts (TAFs) are increasingly regarded as essential co-conspirators for tumor progression in all solid tumors including non-small cell lung cancer. While most TAFs exhibit activation markers indicative of a myofibroblast-like phenotype, senescence markers have been reported in a growing list of selected cancer types only. However, the presence of senescent TAFs in lung cancer remains undefined. Assessing senescence in lung TAFs is important because previous studies have reported that senescent TAFs enhances tumor growth, which is in marked contrast with the widely accepted tumor-suppressive role of senescence in cancer cells. We examined common senescence markers in patient derived lung TAFs from the 3 major non-small cell lung cancer (NSCLC) subtypes: adenocarcinoma (ADC), squamous cell carcinoma (SCC) and large cell carcinoma (LCC). Given the difficulties in gathering LCC-TAFs owing to the lower prevalence of LCC compared to the other subtypes, primary fibroblasts from 2 independent fibroblast collections were used. Senescence markers included senescence-associated beta-galactosidase, permanent growth arrest and spreading. We found an enrichment of the myofibroblast-like phenotype in TAFs regardless their histologic subtype, yet senescence was observed in LCC-TAFs only regardless their neuroendocrine status. Likewise, co-culturing normal lung fibroblasts with LCC (but not ADC or SCC) cancer cells was sufficient to induce senescence, and this induction was prevented in the presence of an antioxidant, indicating that it is mediated through oxidative stress. Remarkably, senescent fibroblasts provided growth and invasive advantages to LCC cells in culture and in vivo beyond those effects provided by control (non-senescent) fibroblasts. Our findings expand recent evidence that challenges the common assumption that lung TAFs are a heterogeneous myofibroblast-like cell population regardless their histologic subtype. Of note, because LCC often distinguishes itself in the clinic by its aggressive nature, our findings support that senescent or senescent-like TAFs may contribute to the selective aggressive behavior of LCC tumors.