G9a blockade uncovers therapeutic vulnerabilities in advanced prostate cancer

Prostate cancer is a disease that often grows slowly, but in its advanced stages, it becomes a formidable opponent. The standard treatment for these advanced cases involves cutting off the body's supply of male hormones, a strategy that usually works well at first because the cancer cells rely on these hormones to survive. However, over time, many tumors learn to bypass this blockade, evolving into a form of the disease that no longer responds to hormone therapy. This shift, known as becoming castration-resistant, is a major hurdle for doctors and patients alike. To understand how to stop this evolution, scientists are looking deeper than just the genes themselves. They are examining the packaging of those genes. Inside every cell, DNA is wrapped around spool-like proteins to form a structure called chromatin. The tightness of this wrapping determines whether a gene is active or silent. Enzymes act as the hands that tighten or loosen this packaging, and when these enzymes malfunction, they can lock cancer cells into a state of uncontrolled growth. One such enzyme, known as G9a, has been found in high amounts in prostate tumors, where it helps keep the cancer locked in a dangerous, aggressive state.

A team of researchers at the University of Bern and the Bern University Hospital set out to see what would happen if they blocked this specific enzyme, G9a, in advanced prostate cancer. They used a sophisticated model where human prostate tumors were grown inside mice, allowing them to watch the disease behave as it would in a real patient. The scientists treated these tumors with a drug called CM-272, which stops G9a from working. Their goal was not just to see if the tumors shrank, but to understand exactly how the cancer cells changed their behavior when this enzyme was disabled. They discovered that the effect of the drug depended entirely on how long the cancer cells were exposed to it. This time-dependent response revealed two distinct ways the treatment could be used to outsmart the disease.

When the researchers treated the tumors for a short period, just ten days, the drug acted as a powerful brake. It stopped the cancer cells from dividing and, more importantly, it made them vulnerable to a specific type of cell death. The drug triggered a pathway that the cancer cells usually ignore, effectively disarming their defenses against self-destruction. In laboratory tests, combining this short-term treatment with a protein that naturally kills cancer cells resulted in a massive increase in cell death. This suggests that for a brief window, the drug can turn a resistant tumor into one that is highly sensitive to being eliminated.

However, the story changed when the treatment was extended over a longer period of about three weeks. Instead of just killing the cells, the drug fundamentally rewired the tumor's internal instructions. The researchers found that the enzyme G9a normally helps hide the instructions for tumor-suppressing genes while keeping the instructions for cancer-promoting genes active. When G9a was blocked for a long time, the packaging of the DNA loosened in a way that allowed the tumor to hear the "good" instructions again. Specifically, the tumor began to respond to male hormones in a different way. Instead of using those hormones to grow aggressively, the cells started using them to activate genes that suppress the tumor. This shift made the cancer cells dependent on the very hormone therapy that they had previously learned to ignore.

This discovery is significant because it suggests a new strategy for patients whose cancer is still sensitive to hormone treatment but is at high risk of becoming resistant. By using the G9a-blocking drug alongside standard hormone therapies, doctors might be able to keep the cancer in a state where it is easier to control. The researchers tested this idea in the lab by combining the G9a blocker with a common hormone therapy drug called enzalutamide. The combination worked much better than either drug alone, shrinking the tumors more effectively. This synergy indicates that the G9a blocker does not just attack the cancer directly; it changes the cancer's nature, making it more susceptible to existing treatments.

The study also clarified what this approach is not. The researchers tested the drug on a model of prostate cancer that had already become resistant to hormone therapy, a stage where the tumor no longer relies on male hormones to grow. In these cases, the drug had no effect on tumor growth. This finding is crucial because it defines the specific group of patients who would benefit: those with high-risk, hormone-sensitive tumors that have not yet fully evolved into the resistant form. It suggests that the best use of this strategy is to delay the progression to a resistant state rather than to cure a disease that has already become fully resistant.

Throughout the experiments, the researchers observed that the drug was safe for the mice, causing no damage to healthy organs like the liver or kidneys. The changes were specific to the tumor cells, where the enzyme was blocked and the DNA packaging was altered. The team also confirmed that the drug was not working by changing the amount of the hormone receptor protein itself, but by changing where that protein could bind to the DNA. In short, the drug did not remove the engine of the cancer; it changed the map the engine was following, steering it away from destruction and toward a state where it could be managed.

These findings offer a fresh perspective on how to fight advanced prostate cancer. Rather than viewing the disease as a static enemy that must be destroyed, the research highlights the plasticity of cancer cells and how they can be nudged back into a more manageable state. By targeting the epigenetic machinery that controls gene expression, specifically the enzyme G9a, it may be possible to extend the time patients remain responsive to standard therapies. While this work is still in the pre-clinical stage and has not yet been tested in humans, it provides a clear roadmap for future clinical trials. It points toward a future where combining epigenetic drugs with hormone therapies could delay the onset of resistance, giving patients more time and better outcomes in the ongoing battle against prostate cancer.