The analysis consistently pointed toward PCSK9. The protein appeared to function as a regulatory valve for how the cancer cells obtained cholesterol, a vital building block for cell membranes and a necessary resource for rapid cell division. The researchers found that when PCSK9 levels were low, the cancer cells were primed to thrive in the liver. In this state, the cells did not need to expend energy producing their own cholesterol; instead, they became highly efficient at absorbing the cholesterol that is naturally plentiful in the liver’s environment.
Conversely, when the researchers examined cells that had successfully colonized the lungs, they found high levels of PCSK9. In the cholesterol-poor environment of the lungs, cancer cells cannot rely on external sources to fuel their growth. High levels of PCSK9 signaled the cells to undergo a dramatic metabolic shift, triggering them to synthesize their own cholesterol internally. Perhaps even more importantly, the researchers discovered that this high-PCSK9 state also prompted the production of specific antioxidant molecules. These molecules act as a shield, protecting the cancer cells from the damaging effects of reactive oxygen species, which are prevalent in the oxygen-rich tissues of the lung.
To test whether PCSK9 was merely a marker of where the cancer went or the actual cause of its destination, the UCSF team conducted a series of "forced expression" experiments. They took pancreatic cancer cells that were genetically predisposed to migrate to the liver—cells with naturally low PCSK9—and artificially boosted their PCSK9 production. The results were striking: the cells that would have normally settled in the liver instead made a metabolic detour, successfully colonizing the lungs. This demonstrated that PCSK9 is a functional switch that determines the metastatic fate of the cell.
"Cancers persist by adapting to live in new tissues and organs, and we found that pancreatic tumors use PCSK9 to adapt as they spread," said Rushika Perera, PhD, the Deborah Cowan Endowed Associate Professor of Anatomy at UCSF and the senior author of the paper. Dr. Perera emphasized that this discovery provides a new perspective on the resilience of metastatic tumors. By understanding the metabolic requirements of a cell in a specific organ, scientists can begin to look for ways to "starve" the cancer or prevent it from adapting to its new home. "It opens the door to fighting metastatic cancer growth by manipulating how cells acquire their cholesterol," she added.
The implications for treatment are significant. Pancreatic cancer has earned a reputation for being "notoriously resistant" to conventional chemotherapy and targeted treatments. Much of this resistance stems from the tumor’s ability to create a protective microenvironment and its capacity to pivot its internal chemistry when under attack. If clinicians can target the PCSK9 pathway, they might be able to prevent the cancer from establishing itself in the lungs or make liver metastases more vulnerable to existing drugs.
