By Gabriel Paijo 
In a landmark study published on July 24, 2025, in the journal Cancer Cell, researchers at the NCI-Designated Cancer Center at Sanford Burnham Prebys have unveiled a transformative approach to treating pancreatic ductal adenocarcinoma (PDAC). By targeting a specific cellular scavenging process known as macropinocytosis, the scientific team demonstrated that they could effectively "reprogram" the protective environment surrounding a tumor, making it more susceptible to traditional chemotherapy and modern immunotherapy. This discovery addresses one of the most significant hurdles in oncology: the dense, impenetrable nature of pancreatic tumors that shields them from the body’s immune system and life-saving drugs.
Pancreatic cancer remains one of the most lethal malignancies, currently standing as the third leading cause of cancer-related deaths in the United States, despite accounting for only three percent of all cancer diagnoses. The high mortality rate is largely attributed to the tumor microenvironment (TME)—a complex "neighborhood" of immune cells, connective tissue, and blood vessels that PDAC manipulates to fuel its growth and evade destruction. The research led by Yijuan Zhang, PhD, and Cosimo Commisso, PhD, suggests that by disrupting how these cells "eat," doctors may finally be able to breach the fortress that protects pancreatic tumors.
The Biology of the Tumor Microenvironment
Cancer cells do not exist as isolated entities. Instead, they develop within a highly organized and altered milieu that provides the structural and nutritional support necessary for unchecked proliferation. In the case of PDAC, the tumor creates a particularly hostile environment characterized by a thick, fibrous layer of connective tissue known as the stroma. This stroma acts as a physical barrier, increasing the internal pressure of the tumor and compressing blood vessels, which in turn prevents chemotherapy drugs and immune cells from reaching their target.
Central to this environment are fibroblasts, cells that typically produce the extracellular matrix (ECM) and collagen needed for tissue structure. In a healthy body, fibroblasts are essential for wound healing and structural integrity. However, in the presence of a pancreatic tumor, these cells are coerced into becoming cancer-associated fibroblasts (CAFs). These CAFs serve as the tumor’s logistical support team, providing metabolites and growth signals while simultaneously building the dense collagen walls that protect the malignancy.
The Sanford Burnham Prebys study focused on how these CAFs maintain themselves in the nutrient-poor environment of the pancreas. Because PDAC tumors grow so rapidly, they often outstrip their blood supply, creating a "metabolic desert" where essential nutrients like glucose and glutamine are scarce. To survive, both the cancer cells and the CAFs resort to macropinocytosis—a process akin to a "fishing trawler" deploying a net to scoop up proteins and carbohydrates from the extracellular matrix to be broken down into fuel.
The Scavenging Mechanism: Macropinocytosis
Macropinocytosis is a form of endocytosis where the cell membrane folds inward to create large vesicles, capturing extracellular fluid and its contents. While this is a normal process for some immune cells, pancreatic cancer cells and their associated fibroblasts hijack this mechanism to scavenge for nutrients, particularly the amino acid glutamine.
Glutamine is a critical building block for proteins and a key source of nitrogen and carbon for rapidly dividing cells. PDAC is notoriously "addicted" to glutamine, and the competition for this resource within the tumor microenvironment is fierce. The researchers found that when CAFs are deprived of glutamine, they become even more reliant on macropinocytosis to survive. This scavenging not only fuels the CAFs but also contributes to the stiffness of the surrounding tissue, as the process of taking in the extracellular matrix leads to a remodeling of the connective tissue that further reinforces the tumor’s defenses.
By utilizing a macropinocytosis inhibitor known as EIPA (Ethylisopropyl amiloride), the research team was able to block this scavenging pathway. The results were immediate and profound: the metabolic stress caused by the lack of nutrients forced the CAFs to undergo a fundamental change in identity.
Subtype Reprogramming: From Myofibroblasts to Inflammatory CAFs
The study’s most significant finding lies in the "reprogramming" of the fibroblast population. Not all CAFs are identical; they generally fall into different subtypes with varying roles. Myofibroblastic CAFs (myCAFs) are responsible for the production of collagen and the physical hardening of the tumor microenvironment. Inflammatory CAFs (iCAFs), on the other hand, are associated with different signaling pathways.
"Most pancreatic CAFs are myofibroblasts that promote stiffness and density in the tumor microenvironment and make it more difficult for immune cells and drugs to reach the tumor," explained Dr. Cosimo Commisso, interim director and deputy director of the institute’s cancer center. "Our experiments led to a subtype reprogramming with fewer myofibroblasts and more inflammatory CAFs."
This shift had a cascade of positive effects on the tumor microenvironment:
- Reduced Fibrosis: There were significantly fewer deposits of collagen, meaning the "fortress walls" around the tumor began to crumble.
- Vascular Expansion: The blood vessels within the tumor neighborhood widened. In a typical PDAC tumor, blood vessels are often collapsed by the pressure of the dense stroma. Widening these vessels allows for better delivery of oxygen and, crucially, chemotherapy drugs.
- Immune Infiltration: With the physical barriers reduced, CD4+ and CD8+ T cells—the "soldiers" of the immune system—were able to infiltrate the tumor in much higher numbers.
Experimental Results and Synergistic Therapies
To test the clinical potential of these findings, the investigators conducted a series of experiments using mouse models of PDAC. They focused on combining the macropinocytosis inhibitor with existing treatments that are often ineffective against pancreatic cancer when used alone.
One of the primary challenges in treating PDAC with immunotherapy is that the tumors are "cold," meaning they do not trigger a strong immune response. This is partly because T cells cannot get into the tumor, and those that do are often suppressed by proteins like PD-1. When the researchers combined the inhibitor EIPA with an anti-PD-1 antibody, they observed a significant suppression of tumor metastasis and a marked increase in the survival rates of the mice.
"Infiltrating T cells are rich in a cell surface protein called PD-1 that dampens the immune response," Dr. Commisso noted. "By blocking macropinocytosis, we allowed those T cells to enter the tumor, and the anti-PD-1 antibody prevented the tumor from turning them off."
The team also tested the inhibitor as a pre-treatment for chemotherapy. When mice were treated with EIPA before receiving gemcitabine—a standard chemotherapy for pancreatic cancer—the results showed a synergistic effect. Not only did the primary tumor growth slow down, but the spread of micrometastases in the lungs was also reduced. This suggests that "softening" the tumor environment before administering drugs can significantly enhance the efficacy of the treatment.
Chronology of the Research
The path to this discovery involved several years of incremental steps in understanding the metabolic landscape of the pancreas.
- Initial Observations: The team began by studying the metabolic "addiction" of PDAC cells to glutamine and how they survive in nutrient-poor environments.
- Identification of Scavenging: Research identified macropinocytosis as a primary survival mechanism for cancer cells, but the role of the surrounding fibroblasts remained unclear.
- Focus on CAFs: The Sanford Burnham Prebys team shifted focus to the "neighborhood," investigating how CAFs utilize the same scavenging techniques to support the tumor.
- Discovery of the "Switch": Through genetic and pharmacological inhibition, the team discovered that blocking this pathway didn’t just starve the CAFs—it changed their fundamental nature, switching them from a structural (myofibroblastic) role to an inflammatory one.
- Therapeutic Testing (2024-2025): Preclinical trials in mouse models confirmed that this biological switch could be exploited to improve the delivery and effectiveness of chemotherapy and immunotherapy.
Broader Implications and Future Outlook
The implications of this study extend beyond pancreatic cancer. Many other aggressive "solid" tumors, such as certain types of lung and breast cancer, also utilize macropinocytosis and develop dense stromal environments. The strategy of "reprogramming" the tumor microenvironment rather than simply attempting to kill the cancer cells directly represents a paradigm shift in oncology.
For patients with PDAC, these findings offer a glimmer of hope for a disease that has seen little improvement in survival rates over the last several decades. The current five-year survival rate for pancreatic cancer remains approximately 13%, largely because the disease is often diagnosed at an advanced stage and is resistant to most therapies.
"We believe this is a very promising strategy to pursue for developing combination therapies for cancer patients," said Dr. Commisso. "Especially for pancreatic cancer that is the third leading cause of cancer deaths despite accounting for only three percent of cases."
The next steps for the research team involve identifying more potent and specific inhibitors of macropinocytosis that can be safely used in humans. While EIPA served as an effective tool for this laboratory study, the development of clinical-grade drugs will be necessary for human trials. Additionally, the team plans to explore the timing of these treatments, investigating whether "priming" the tumor environment with scavenging inhibitors could become a standard first step in oncological protocols.
The study was supported by the National Institutes of Health (NIH) and the National Cancer Institute (NCI), highlighting the federal commitment to finding innovative solutions for high-mortality cancers. As the scientific community continues to peel back the layers of the tumor microenvironment, the transition from viewing a tumor as a single entity to viewing it as a complex, manageable ecosystem may finally turn the tide against pancreatic cancer.