Deep-Sea Sponge Compound Attacks Cancer Through Two Separate Pathways

Published in Journal of the American Chemical Society. DOI: 10.1021/jacs.5c13808. Research by Tokyo University of Agriculture and Technology and University of Tokyo.

In the waters off Yakushima Island, Japan, a deep-sea sponge produces a molecule that cancer researchers have been studying for years. The compound, called yaku'amide B, was already known to inhibit ATP synthase -- an enzyme that cells depend on for energy production. Shutting down the cellular power supply is a blunt but effective way to kill cancer cells. But the molecule seemed to do more than its known mechanism could explain.

Now, a collaborative team led by Professor Kaori Sakurai at Tokyo University of Agriculture and Technology, along with Associate Professor Hiroaki Itoh and Professor Masayuki Inoue at the University of Tokyo, has identified what else yaku'amide B does. Using a technique called photoaffinity labeling -- which captures molecules that interact briefly with a drug -- they discovered that the compound transiently binds to and triggers the degradation of CD9, a membrane protein identified as a cancer stem cell marker. The findings were published in the Journal of the American Chemical Society.

Capturing a fleeting interaction

Natural products derived from marine organisms often interact with multiple targets inside cells. Their structural complexity allows them to make brief, transient contacts with different biomolecules, each potentially triggering a distinct biological effect. The challenge is catching those interactions in the act.

Photoaffinity labeling works by attaching a chemical group to the drug molecule that, when activated by light, forms a permanent bond with whatever protein it is touching at that instant. This converts a fleeting interaction into a stable one that can be identified through standard biochemical techniques.

Using a designed photoaffinity probe based on yaku'amide B, Itoh and colleagues discovered that the compound binds to CD9. More remarkably, this binding event does not simply block CD9 function -- it promotes the protein's degradation inside cancer cells. The protein is not just inhibited; it is destroyed.

Why CD9 matters in cancer

CD9 belongs to a family of membrane proteins called tetraspanins, which sit on the cell surface and participate in cell adhesion, migration, and signaling. In cancer biology, CD9 has attracted attention as a marker for cancer stem cells -- the subset of tumor cells thought to be responsible for recurrence and metastasis after initial treatment.

Cancer stem cells are particularly problematic because they often resist conventional chemotherapy and radiation. A drug capable of degrading a cancer stem cell marker represents a different angle of attack -- one that targets the cells most responsible for treatment failure.

Sakurai described the discovery as opening new possibilities for drug development strategies that target cancer stem cells and their associated pathways. The fact that yaku'amide B is the first natural product reported to induce CD9 degradation makes it a unique starting point for medicinal chemistry efforts.

A dual mechanism with complementary effects

The picture that emerges is a molecule with two simultaneous modes of action. Yaku'amide B enters cancer cells and migrates to mitochondria, where it inhibits ATP synthase, depleting the cell's energy supply. At the same time, it interacts with CD9 on the cell membrane, triggering the protein's degradation.

Inoue noted that this dual mechanism -- ATP depletion and CD9 degradation -- provides a compelling explanation for the compound's ability to suppress both cancer cell proliferation and migration. These are distinct hallmarks of cancer: uncontrolled growth and the ability to spread to other tissues. Targeting both simultaneously with a single molecule is the kind of multi-target activity that drug designers increasingly seek but rarely achieve through rational design alone.

The study also validates photoaffinity labeling as a strategy for studying transient interactions between natural products and their cellular targets. Many bioactive natural products likely have multiple targets that remain unidentified because the interactions are too brief to detect with conventional methods.

From sponge to clinic: a long distance

Several substantial caveats apply. Yaku'amide B is a structurally complex peptide isolated from a deep-sea organism. Synthesizing it at scale is challenging, and the total synthesis required to produce enough material for biological studies was itself a significant achievement by Inoue's group.

All experiments in this study were conducted in cancer cell lines, not in animal models or humans. Whether yaku'amide B's dual mechanism translates to anti-tumor activity in living organisms -- where drug distribution, metabolism, and toxicity all come into play -- is entirely unknown.

CD9's role in cancer is also more complex than a simple on-off switch. In some cancer types, CD9 appears to suppress metastasis rather than promote it. The consequences of degrading CD9 may depend heavily on tumor type, stage, and molecular context. A drug that degrades CD9 broadly could have unintended effects in tissues where CD9 plays a protective role.

The selectivity of yaku'amide B for cancer cells versus normal cells has not been established. ATP synthase is essential for all cells, not just cancer cells, which raises obvious concerns about systemic toxicity. Whether the compound's effects are sufficiently selective to be therapeutically useful is a question that will require extensive preclinical testing.

A template for future molecules

The value of yaku'amide B may ultimately lie less in the molecule itself and more in the design principles it illustrates. Identifying a natural product that simultaneously depletes cellular energy and degrades a cancer stem cell marker provides a template for synthetic molecules that could achieve similar effects with better drug-like properties -- improved solubility, oral availability, and selectivity.

The study underscores a broader point about natural products as starting points for drug discovery. Marine organisms, having evolved in one of the planet's most competitive environments, produce molecules of extraordinary structural diversity. Mining that chemical diversity -- and then understanding the full range of cellular interactions through techniques like photoaffinity labeling -- remains one of the most productive strategies for finding new therapeutic leads.