Tumor-Stroma Interactions: How NSCLC and Radiotherapy Drive Resistance via MSC Senescence

Non-small cell lung cancer (NSCLC) is one of the deadliest cancers worldwide, responsible for a large number of cancer-related deaths each year. Even though diagnostic tools and treatments like surgery, chemotherapy, targeted therapies, and radiotherapy (RT) have improved, the outlook for most NSCLC patients remains bleak. Only about 20 percent of patients survive for five years after diagnosis, which shows just how aggressive this disease can be and how skilled it is at dodging the effects of treatment. With lung cancer rates continuing to rise globally, researchers face increasing pressure to figure out why NSCLC resists treatment and how it manages to progress so relentlessly. A big part of the problem lies in the tumor microenvironment. This is not just a static space where the cancer sits; it is a lively and complex mix of different cells, including immune cells, fibroblasts, endothelial cells, and mesenchymal stem cells (MSCs). These MSCs, which are multipotent stromal cells found in the lung’s vascular adventitia, play a particularly interesting role. Under normal conditions, MSCs help repair and regenerate tissue. However, in the context of cancer, they are essentially hijacked by the tumor. Instead of helping, they start supporting cancer growth, spreading it further, and even helping it fight off treatments. One especially tricky issue is the unintended side effects of therapies like radiotherapy. While radiotherapy is a cornerstone in treating NSCLC, it does not just target the cancer cells. It also affects nearby non-cancerous cells, including MSCs, and can unintentionally cause them to change in ways that make the tumor harder to kill. These changes can include shifts in how MSCs function and what they secrete, creating an environment that helps the cancer survive and resist further treatment. Understanding exactly how this happens has been a major challenge for researchers.

New research paper published in Frontiers in Oncology and conducted by Hanna Sentek, Annika Braun, Bettina Budeus, and led by Professor Diana Klein from the Institute of Cell Biology (Cancer Research), University of Duisburg-Essen, University Hospital in  Germany, investigated how NSCLC cells and therapies like RT interact with MSCs. The research identified key molecular signals and secretory factors, such as senescence-associated secretory phenotype (SASP) molecules that drive these changes and by this opens the door to new NSCLC treatment approaches that target the supportive role of MSCs. The researchers kicked things off by co-culturing NSCLC cell lines—NCI-H460 and A549—with MSCs. They used two methods: indirect co-cultures in transwell systems and direct three-dimensional spheroid models. These setups were designed to replicate the tumor microenvironment as closely as possible, allowing the team to carefully observe how the cancer cells and MSCs interacted. What they found was striking—when MSCs were exposed to tumor-conditioned media or co-cultured with cancer cells, their growth slowed, and their behavior started to change. Things got even more dramatic when radiotherapy was added, pushing the MSCs into a senescent state.

To study in more details what was driving these changes, the authors looked at what the MSCs were secreting after being treated with radiotherapy. Through RNA sequencing and gene set enrichment analysis, they spotted a significant increase in SASP factors. One factor, in particular, stood out: SERPINE1, also known as plasminogen activator inhibitor-1 (PAI-1). This protein was highly elevated in the senescent MSCs and was linked to making the cancer cells more resistant to radiotherapy. Functional tests showed that media from irradiated MSCs helped NSCLC cells survive and grow which confirm that these secreted factors were strengthening the tumor’s defenses. Afterward, the researchers wanted to study how these changes were affecting the MSCs themselves and by using flow cytometry and Western blot analysis, they found that the irradiated MSCs showed classic signs of senescence. Their appearance changed—they became larger and flatter—and they showed increased levels of proteins like p21 and cyclin D1, while their levels of PCNA, a marker for cell proliferation, dropped. On top of that, the senescent MSCs were releasing molecules like SERPINE1, which seemed to help remodel the tumor environment and support cancer cell survival. When the team analyzed patient data, they found that high levels of SERPINE1 were tied to worse outcomes, especially for patients receiving radiotherapy. The team confirmed their findings by running direct co-culture experiments and found that even when the MSCs had minimal contact with cancer cells, their proliferation slowed, and they became more resistant to radiotherapy. The researchers confirmed that radiotherapy-induced senescence was a key factor, with the SASP playing a central role in reshaping the MSCs’ behavior and metabolism. Finally, the team explored how senescent MSCs affected cancer cell movement and survival. Using wound-healing assays, they showed that the factors secreted by irradiated MSCs boosted the cancer cells’ ability to migrate—a critical step in cancer progression. At the same time, the senescent MSCs helped the cancer cells repair DNA damage from radiotherapy, as shown by fewer DNA double-strand breaks (reduced γH2A.X foci). This dual role of MSCs—both as victims of radiotherapy-induced stress and as active supporters of the tumor—painted a complex picture of how the tumor environment evolves during treatment.

In conclusion, Professor Diana Klein and her team demonstrated how  MSCs play a surprising role in helping tumors resist radiotherapy and identified that  NSCLC cells send out signals that can essentially “reprogram” MSCs into tumor-supporting allies, and this process becomes even more pronounced when radiotherapy induces senescence in these cells. This discovery marks a shift in thinking—it is not just about attacking cancer cells anymore. Instead, the focus is expanding to include the tumor’s entire ecosystem, where stromal cells like MSCs actively support cancer progression. One of the most important takeaways from this research is the identification of SERPINE1, a key factor in therapy resistance. This molecule does a lot: it helps cancer cells survive and repair damage caused by radiotherapy, and it reshapes the extracellular environment to make it easier for tumors to invade and spread. What makes this finding even more significant is its clinical relevance. Higher levels of SERPINE1 are closely tied to worse outcomes in NSCLC patients undergoing radiotherapy. This suggests that SERPINE1 is not just a marker of poor prognosis but also a promising target for new treatments aimed at weakening the tumor’s defenses.

The study also raises big questions about current cancer treatment approaches. Radiotherapy is a cornerstone of NSCLC therapy, but this research highlights its unintended side effects on the tumor’s surrounding stromal cells. These findings make a strong case for developing additional therapies to counteract the negative effects of radiotherapy, like preventing MSCs from becoming tumor-promoting or blocking harmful SASP factors such as SERPINE1. For instance, drugs that specifically target SERPINE1 could help make radiotherapy more effective without causing more damage to healthy tissues. Ultimately, this research points to the need for a more comprehensive strategy in cancer care. Addressing the stromal contribution to resistance could lead to longer-lasting and more effective treatments. By preventing MSCs from being turned into tumor allies, we could boost the effectiveness of not only radiotherapy but also other treatments like chemotherapy and immunotherapy. This holistic approach to targeting both cancer cells and their microenvironment offers new hope for improving outcomes in NSCLC.