Study reveals a new facet of how pancreatic cancer cells regulate autophagy

A feature of pancreatic cancer cells' surroundings determines whether they grow fast or become resistant to chemotherapy, a new study shows. The ability of these cancer cells to adapt quickly and toggle between biological responses makes them more likely to survive and harder to treat, the study authors say.

Led by NYU Langone Health researchers, the study reveals a new facet of how pancreatic cancer cells regulate their levels of autophagy, a "self-eating" process in which they break down their own components into nutrients to survive. When turned on, cancer cells focus on surviving, instead of dividing and multiplying, which protects them from chemotherapies designed to attack fast-dividing cells. When autophagy is low, cells multiply faster.

Published online Feb. 16 in the journal Cell, the new work shows that a main factor determining whether pancreatic cancer cells increase autophagy levels is their ability to detect the extracellular matrix (ECM), the fibers that surround cancer cells in a tumor, and that cause worse outcomes for patients.

The authors say that both normal and cancer cells grow best when anchored to a specific, guiding ECM. Unanchored cancer cells that fail to detect the ECM increase their autophagy levels.

Our findings show that the sensing of the ECM by pancreatic cancer cells enables them to switch between states of active growth and autophagic survival."

Mohamad Assi, PhD, study first author, postdoctoral fellow in the Department of Radiation Oncology at NYU Langone

Specifically, the team found that cancer cells detect certain ECM structural proteins, such as laminin, through a protein on their surfaces called integrin subunit α3 (integrinα3). 

Forcing sameness

For the study, the research team grew clusters of pancreatic cancer cells in three-dimensional spheres embedded in gel-like substances, which mimic how tumors grow in the body. Using a fluorescent protein, the researchers tracked which cells had high or low autophagy levels.
The team found that autophagy levels in pancreatic cancer cells, which were historically known to be regulated by nutrient availability, can be also regulated by sensing local changes related to ECM type or structure.

In pancreatic tumors, the researchers found that the distance of cancer cells from the ECM creates two distinct populations in the same tumor. One group detects the ECM, and so has low autophagy levels and a high growth rate. A second population, more distant from the ECM, has high autophagy levels and can better survive chemotherapy. This makes it very unlikely that a single drug could successfully target most cancer cells in a pancreatic tumor, the authors say.

Along these lines, hydroxychloroquine, the only drug approved by the Food and Drug Administration to block autophagy in patients, has had limited success as a single agent. This is likely because only small amounts of it can reach the tumors, and because not all cancer cells are present in their high-autophagy mode, the authors say. 

With an eye on future treatment design, the researcher genetically suppressed integrinα3 in spheroid cultures, which forced nearly all the cancer cells into their high-autophagy mode. This made autophagy-interfering hydroxychloroquine much more effective at killing them. Indeed, removing integrinα3 led to a 50% reduction in cancer cell survival compared to hydroxychloroquine alone.

 In another set of experiments, the researchers engineered cancer cells to lack the protein NF2, which passes on the message inside a cancer cell when the activity of integrinα3 is changed. NF2 hinders the integrinα3 signal, so knocking it out significantly reduces autophagy in the cell. Importantly, it does so by slowing down the function of cellular structures called lysosomes, which are critical to the autophagic process, as well as to other survival pathways used by cancer cells. NF2-knockout-driven autophagic and lysosomal inhibition drastically reduced pancreatic tumor growth and triggered cancer cell death. 

The researchers say that current strategies designed to block autophagy are effective for a short time, but then fail as cancer cells adapt. They say their results suggest that targeting both the ECM-mediated regulation of autophagy levels, and lysosomal function, might provide longer-lasting antitumor responses. 

Along with Dr. Assi, authors in the Perlmutter Cancer Center at NYU Langone were Drs. Emily Kawale, Zahidunnabi Dewan, and Alec C. Kimmelman. Other NYU Langone authors include Dr. Robert Banh from the Department of Biochemistry and Molecular Pharmacology. Authors from the Dana-Farber Cancer Institute and Harvard Medical School include Drs. Andrew Aguirre, and Joao Paulo. Dr. Diane Simeone from Moores Cancer Center at UC San Diego is also a contributing author. 

The study was funded by National Cancer Institute grants P30CA016087, R37CA289040, P01CA117969, R35CA232124, P30CA016087-38, and 1R01CA251726-01A1. Also providing support were the Damon Runyon Cancer Research Foundation, the Lustgarten Foundation, and Stand Up to Cancer. Dr. Kimmelman is listed as an inventor on a patent targeting alanine transport and the autophagic control of iron metabolism. He is also on the scientific advisory board of Rafael/Cornerstone Pharmaceuticals and has been a consultant for Deciphera and AbbVie.