The RAS Dialogue Blog posts are written by RAS experts sharing the latest research, updates, and scientific RAS news. The content is curated by the RAS Initiative.
Pancreatic ductal adenocarcinoma (PDAC) remains one of the deadliest malignancies, and the frequent failure of conventional therapies underscores the urgent need for novel treatment strategies.
PDAC is characterized by a very high prevalence of oncogenic KRAS mutations and, consequently, a strong dependence on downstream signaling, importantly the MAPK-pathway. Signaling pathways are networks made of proteins that pass information through the cell, similar to a relay system, guiding how cells grow, divide, and survive. Mutations in KRAS hyperactivate this important signaling molecule.
Accordingly, the recent breakthrough and rapidly expanding field of direct KRAS inhibition has generated considerable optimism. However, it has already become evident that cancer cells can rapidly adapt to this targeted treatment by shifting their cellular programs and activating alternative survival pathways. As a result, resistance to MAPK- and RAS-targeted therapies almost invariably develops rapidly.
Putting the screws on KRAS
Rather than targeting a single protein, we have been focusing on what can be termed vertical RAS pathway inhibition. The idea is simple: instead of blocking one node, you target two levels of the same signaling cascade, addressing important signaling nodes in those invariably evolving adaptive circuits.
Already some time ago, we discovered that tyrosine phosphatase SHP2, encoded by the gene PTPN11, is critical for PDAC oncogenesis and a valuable target in the context of therapeutic pressure. Specifically, combined inhibition of MEK1/2, key downstream effectors of KRAS, and SHP2 upstream of KRAS led to durable therapeutic impact in both mouse and human PDAC models [1].
Disturb KRAS, and metabolism is rewired
Yet even this dual inhibition strategy ultimately resulted in resistant tumors - only later than with MEK inhibition alone. Because PDAC cells rely on KRAS not just for signaling but also for reshaping their metabolism to fuel rapid growth, we wondered:
What happens to this metabolic machinery during the initial response, and later as tumors adapt and become resistant to vertical RAS pathway inhibition?
We set out to explore this question and to see whether these changes might reveal new therapeutically exploitable vulnerabilities.
The answer was complex:
Not surprisingly, after dual SHP2/MEK inhibition, proliferation-associated metabolic programs were downregulated. Amino acid uptake decreased. DNA and RNA synthesis slowed. At the same time, autophagy - a protective recycling process that PDAC cells switch on under stress - increased, confirming earlier studies [2].
In addition, the most prominent changes were observed in mitochondria, the cell’s energy-producing organelles. Across multiple experiments, both in vitro and in vivo, we observed clear structural and functional alterations in and related to mitochondria.
These experiments included studies in cultured cells, as well as analysis of material derived from patients and mouse tumors, allowing us to assess changes in gene and protein activity. The changes we observed in mitochondrial size and metabolism were consistent and reproducible. And they pointed toward one critical consequence: increased oxidative stress.
A metabolic “fire” inside the cell
Mitochondria are a major source of reactive oxygen species (ROS). Under normal conditions, cells tightly control ROS levels. But after vertical RAS pathway inhibition, we observed a significant increase in lipid peroxidation, a type of oxidative damage to membrane lipids.
This form of damage has serious consequences. When lipid peroxidation exceeds a certain threshold, it can trigger a specific type of cell death called ferroptosis. Unlike other forms of cell death, ferroptosis is characterized by an iron-dependent accumulation of lipid peroxides in cell membranes, leading to disintegration of the membrane, the skin of the cell. Cancer cells protect themselves from this fate using antioxidant systems, most importantly the enzyme GPX4, which detoxifies lipid peroxides within membranes.
PDAC cells resistant to dual SHP2/MEK and to targeted RAS inhibition demonstrated increased levels of lipid peroxidation, but at the same time upregulated the protective machinery, allowing survival and continued proliferation. We therefore wondered:
What happens if we remove the cell’s protective shield? Could this reveal an additional vulnerability to make RAS/MAPK pathway inhibition more durable?
And yes: When we inhibited GPX4, PDAC cells that had undergone dual RAS/MAPK inhibition were no longer able to handle elevated lipid peroxidation.
In other words, RAS pathway inhibition appears to ignite a metabolic “fire” within the tumor cell. Initially, the cell can still cope, controlling the situation through its antioxidant defenses, including GPX4. Inhibiting GPX4 removes this protective “fire extinguisher,” pushing the cells beyond a survivable threshold and may ultimately lead to ferroptotic cell death.
Not all pancreatic cancers are the same
Pancreatic cancer is not a uniform disease. Molecular profiling studies have identified distinct subtypes, including classical and basal-like tumors, which differ in signaling activity, metabolic programs, and therapeutic responses.
Despite the differences in pancreatic cancer subtypes we found that the metabolic stress and increased lipid peroxidation were not restricted to a particular molecular subtype. This may represent a new therapeutic avenue for targeting pancreatic cancers, no matter what the particular form of the disease.
From adaptation to vulnerability
Cancer cells are masters of adaptation. When one survival pathway is blocked, they often find another way. But sometimes, adaptation itself creates stress. Our work brings together several ideas that had previously been explored independently.
First, ablation of oncogenic KRAS in PDAC can create a dependency on mitochondrial function and oxidative phosphorylation [3].
Second, inducing ferroptosis has previously been shown to effectively inhibit tumor growth in PDAC [4].
And third, a concept of a resistance continuum was introduced by the work of Franca et al., demonstrating cell state shifts along prolonged exposure to therapeutic pressure, establishing a cell characterized by the upregulation of cytoprotective programs against oxidative stress and ferroptosis in advanced forms of adaptive resistance [5].
Our work suggests that strong vertical inhibition of the RAS-MAPK pathway does more than suppress proliferation signals. It alters mitochondrial function, increases oxidative pressure, and moves tumor cells closer to a ferroptotic threshold. By combining pathway inhibition with metabolic targeting, we may be able to turn a survival mechanism into a liability.
It is important to note, however, that no compound is yet available for induction of ferroptosis in patient tumors in a clinical setting. As a result, our in vivo experiments have faced limitations, and translating our findings will not only require further confirmation but also the development of suitable therapeutic agents.
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References
Author note: BioRender was used for figure generation
[1] Ruess, D. A. et al. Mutant KRAS-driven cancers depend on PTPN11/SHP2 phosphatase. Nat. Med. 24, 954-960, (2018).
[2] Bryant, K. L. et al. Combination of ERK and autophagy inhibition as a treatment approach for pancreatic cancer. Nat. Med. 25, 628-640, (2019).
[3] Viale, A. et al. Oncogene ablation-resistant pancreatic cancer cells depend on mitochondrial function. Nature. 514, 628-632, (2014).
[4] Badgley, M. A. et al. Cysteine depletion induces pancreatic tumor ferroptosis in mice. Science. 368, 85-89, (2020).
[5] Franca, G. S. et al. Cellular adaptation to cancer therapy along a resistance continuum. Nature. 631, 876-883, (2024).
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