Prostate cancer, a leading health concern for men in the United States, is often linked to an imbalance between antioxidants and pro-oxidants, tipping the scales toward harmful oxidative stress. This connection sparked interest in whether dietary antioxidants could reduce oxidative stress and potentially lower prostate cancer risk. Two decades ago, the National Cancer Institute launched a large-scale study involving more than 35,000 men to determine whether selenium and vitamin E could help prevent prostate cancer. However, the results showed little benefit to either antioxidant supplementation and revealed an increase in prostate cancer risk with vitamin E.1,2
Lloyd Trotman explores the space between discovery and basic research to develop cancer models for functional analysis of how cancer arises and how clinicians may treat it.
Cold Spring Harbor Laboratory
These findings left a deep impression on Lloyd Trotman, a molecular biologist at Cold Spring Harbor Laboratory, who had eagerly followed the ongoing trial. Although the results did not meet the researchers’ expectations, Trotman remarked, “Unexpected results that go against what you think are the ones you probably can trust the most, because you were looking the other way.” Subsequent studies from other groups found that antioxidant response genes acted as oncogenes rather than tumor suppressors, prompting Trotman to explore an intriguing alternative: Could pro-oxidants be a viable alternative to slowing prostate cancer?
Trotman focused on the pro-oxidant menadione sodium bisulfate (MSB), a precursor to vitamin K, which is commonly found in leafy greens. Recently, in a paper published in Science, Trotman and his team found that MSB promotes prostate cancer cell death by targeting a key lipid kinase in the endosomal pathway.3 This disrupts cell sorting and results in oxidative cell death. The team also linked this kinase to X-linked myotubular myopathy, a severe muscle disease, highlighting the broader potential of this approach for pro-oxidants’ potential therapeutic benefits.
To test the effects of an MSB treatment, Trotman turned to a prostate cancer mouse model that his team previously developed.4 They gave the mice one of three drinking treatments: water, water-soluble MSB, or a combination of water-soluble MSB with vitamin C. Despite vitamin C’s reputation as a classic antioxidant, it exerts oxidative effects against cancer cells.5
Trotman hoped to see a synergistic effect between MSB and vitamin C; however, when the researchers measured their abundance in mouse prostates, only MSB was robustly present. Not only did the treatment effectively deliver MSB to the prostate, but MSB more effectively reduced prostate tumor progression. Subsequent analysis revealed that increased oxidative stress was driving the MSB-induced slowdown.
Using the same mouse model, Trotman’s team tested a standard-of-care surgical castration treatment. However, castration alone was insufficient to hold off the cancer’s attack; an initial therapeutic response was quickly followed by resistance and lethal disease progression. Cancer cells eventually mutate to resist treatment, so understanding this process can give researchers a clue into how these cancer cells defend themselves.
Trotman used single-nucleus whole-genome sequencing across 100 cancer cell lines to identify potential mechanisms behind MSB-induced disease regression and resistance. The researchers treated each cell line with increasing concentrations of MSB for 24 hours and then measured cell viability. They found that under MSB’s oxidative pressure, resistant cells ramped up antioxidant defenses. “We can therefore infer that the therapy did what we wanted it to do,” explained Trotman.
To better understand how MSB suppressed disease progression, the researchers sought to identify the target of this oxidative stress. First, Trotman and his team investigated whether MSB triggered mitochondrial or lysosomal cell death pathways. To his surprise, MSB triggered neither. “This [cellular] killing occurred through a mechanism that is not described and doesn’t fit any existing paradigm.”
To characterize this pathway, the researchers used CRISPR-Cas9 screens on two metastatic prostate cancer cell lines to identify key genes. One standout was a gene that encodes vacuolar protein sorting 34 (VPS34), which produces a signaling lipid that plays a role in trafficking proteins and lipids within the cell. In the endosome, this lipid, called phosphatidylinositol 3-phosphate (PI(3)P), acts like a molecular ID tag that helps guide cargo to the plasma membrane or marks it for lysosomal degradation.
Through human and mouse cell line experiments, the researchers discovered that MSB oxidized cysteines that are required for VPS34 function, which depleted PI(3)P levels on the endosomal membrane. Without this molecular ID tag, the cells failed to sort cellular material, accumulated untagged endosomes, and eventually burst. These findings revealed a distinct pathway by which MSB kills prostate cancer cells through lipid depletion. The researchers coined this redox-sensitive cell death process as triaptosis.
“There’s a lot we need to know about vitamin K and how it acts, since the more recently recognized action of vitamin K is that it acts as an antioxidant,” remarked JoEllen Welsh, a nutritional biochemist at the University of Albany. The study’s findings demonstrating pro-oxidant effects surprised her, but she said, “Nobody has really studied the different forms of vitamin K, so it’s nice to see that groups are looking at menadione.”
Intrigued by VPS34’s role in prostate cancer, Trotman wondered if MSB could tackle another condition tied to this protein: X-linked myotubular myopathy (XLMTM). This devastating disease, which stunts muscle growth, often claims the lives of boys before they reach adulthood. XLMTM stems from a mutated myotubularin 1 (MTM1) gene, causing PI(3)P production to run rampant.
To test MSB’s potential, the team used Mtm1 knockout mice, supplementing their drinking water with MSB to deplete PI(3)P levels. This treatment greatly extended the life span and improved muscle health. “It’s a pretty striking effect where they show the survival of those mice,” said Welsh. “This [XLMTM] model validates [VPS34] as one of the targets that menadione is hitting.”
Trotman aims to investigate whether MSB could complement existing treatments for various diseases. He plans to delve deeper into the molecular mechanisms behind pro-oxidant supplements and triaptosis, paving the way for innovative therapeutic strategies.
