Cholinergic signals regulate acute myeloid leukemia and chemotherapy response

Deep within the hollows of our bones lies a bustling, microscopic city known as the bone marrow. This is where the body's blood supply is manufactured, a process driven by specialized stem cells that constantly divide and differentiate into the red blood cells, white blood cells, and platelets we need to survive. However, these stem cells do not work in isolation; they reside in a carefully constructed neighborhood called a niche, supported by a network of structural cells and regulated by the body's nervous system. The nervous system acts as a master conductor, sending chemical signals that tell these cells when to rest, when to multiply, and when to move. For decades, scientists have understood how one branch of this nervous system, the sympathetic system, influences blood cell production. But a second branch, the parasympathetic system, which uses a different chemical messenger, has remained a mystery in the context of blood cancers.

Acute myeloid leukemia is a dangerous disease where the bone marrow becomes overrun with immature, malfunctioning white blood cells that crowd out healthy ones. A particularly stubborn subset of these cancer cells, known as leukemia stem cells, can hide in the bone marrow, sleeping quietly to avoid chemotherapy drugs that only kill active, dividing cells. When the treatment stops, these sleeping cells wake up and cause the cancer to return. Understanding how the nervous system talks to these cancer cells and their protective neighborhood is crucial for finding new ways to wake them up and destroy them before they can relapse.

A team of researchers from universities in Switzerland, the United Kingdom, and Spain has now uncovered a surprising and complex role for the parasympathetic nervous system in this disease. They discovered that acute myeloid leukemia actively manipulates the body's own nerve signals to its advantage. By analyzing blood samples from patients and conducting experiments in mice, the team found that the disease causes a significant rise in a chemical called acetylcholine. This chemical is the primary signal used by the parasympathetic nervous system. In healthy people, this system helps regulate daily rhythms, but in leukemia, the cancer cells appear to hijack this signal to fuel their own growth and survival.

The researchers observed that in mice with leukemia, the nerve fibers that usually release a different chemical, noradrenaline, were disappearing. In contrast, the fibers releasing acetylcholine remained intact and active. Further investigation revealed that the leukemia cells themselves were producing high levels of a protein called interleukin-6, which acted as a switch, forcing nearby nerve cells to change their behavior. These nerves, which normally release noradrenaline, were reprogrammed to release acetylcholine instead. This shift created a flood of acetylcholine in the bone marrow, which the cancer cells eagerly absorbed.

When the researchers blocked the receptors that leukemia cells use to receive these acetylcholine signals, the cancer cells lost their ability to multiply and maintain their stem-like properties. The study showed that this chemical signal directly activates a specific pathway inside the cancer cells that drives their growth. It is as if the cancer cells have found a way to turn the body's own "growth" signal into a constant command to expand. This finding suggests that the high levels of acetylcholine found in the blood of patients could serve as a warning sign, indicating a more aggressive disease and a poorer chance of survival.

However, the story is not entirely one-sided. The researchers also discovered that the nervous system plays a dual role, acting differently on the cancer cells themselves versus the protective neighborhood they live in. While acetylcholine directly encourages the leukemia cells to grow, it also acts on the structural cells of the bone marrow niche to make the leukemia cells sleep. These structural cells, which support the stem cells, have their own receptors for acetylcholine. When these receptors are activated, they release a chemical that tells the leukemia stem cells to enter a deep, dormant state. This dormancy is a double-edged sword: it protects the cancer cells from chemotherapy, which targets dividing cells, but it also keeps them from growing.

To test this, the team used mice that lacked the specific nerve fibers responsible for sending these signals. Without the nerve fibers, the leukemia stem cells could not enter this protective sleep mode. Instead, they remained active and dividing. When these mice were treated with chemotherapy, the drugs were far more effective because the cancer cells were awake and vulnerable. The treatment eliminated a much larger portion of the cancer, and the mice survived significantly longer without the disease returning.

The researchers then tried a different approach, using a drug that blocks the acetylcholine receptors on the leukemia cells and their supporting neighborhood. When combined with standard chemotherapy, this drug prevented the cancer cells from hiding in a dormant state. The combination therapy was highly successful, doubling the time the mice remained free of disease compared to chemotherapy alone. Yet, the study also revealed a cautionary note. In the few cancer cells that managed to survive this aggressive combination treatment, the lack of the protective signal made them grow back faster and more aggressively. This suggests that while blocking these signals can wake up the sleeping cancer cells and make them vulnerable to drugs, the timing and dosage must be precise to ensure all the dangerous cells are eliminated before they can rebound.

This work paints a vivid picture of how a cancer can rewire the body's own communication network to sustain itself. It shows that the disease does not just grow on its own; it actively recruits the nervous system to create a safe haven and a growth engine. By identifying the specific chemical signals and receptors involved, the researchers have opened a new door for treatment. Targeting these cholinergic signals could potentially force leukemia stem cells out of their hiding spots, making them susceptible to existing drugs and offering a new strategy to prevent the disease from returning. The findings suggest that the future of treating this aggressive cancer may lie not just in attacking the tumor directly, but in disrupting the very nerve signals that allow it to survive.