Study finds blocking minor splicing curbs tumor growth in multiple cancer types

Australian researchers have discovered a promising new strategy to suppress the growth of aggressive and hard-to-treat cancers by targeting a specialized molecular process known as “minor splicing.”

Published in EMBO Reports, the study, titled “Inhibition of the minor spliceosome restricts the growth of a broad spectrum of cancers,” shows that blocking minor splicing can markedly slow tumor growth in liver, lung and stomach cancers, while leaving healthy cells largely unharmed.

The research in animal models and human cells, from Australian medical research institute WEHI, demonstrates the potential of this strategy to target cancers driven by mutations in common cancer-causing genes.

Why minor splicing matters

Splicing is how cells turn long strands of RNA into shorter pieces called messenger RNA, which provides the template for the production of proteins.

While major splicing carries out 99.5% of this work, minor splicing is an indispensable process for the remaining 0.05% of genes, affecting about 700 of the 20,000 genes in the human genome.

The new research reveals that blocking minor splicing causes the accumulation of DNA damage in cancer cells and activates a key tumor suppressor pathway that leads to cell death. Remarkably, healthy cells are largely unaffected.

Although it affects only a small sub-set of genes, minor splicing is crucial for the correct expression of genes that drive cell growth and division—making it a potential Achilles’ heel for cancer cells.

Importantly, many of these genes are commonly hijacked by cancers driven by KRAS mutations, which are among the most frequent genetic changes found in solid tumors.

WEHI laboratory head Professor Joan Heath said scientists have long known that KRAS is central to many aggressive cancers but have struggled to turn that knowledge into broadly effective treatments.

“KRAS mutations come in a variety of flavors, making them extremely hard to treat, so even with decades of scientific effort there has been only limited progress so far,” Prof Heath said.

“But our approach is different. Instead of trying to target specific mutations that may only apply to a subset of patients, we’re disrupting a fundamental process that these fast-growing cancers rely on.

“This research offers a new way to tackle a problem that’s long resisted conventional approaches, with the potential to help a much wider group of patients.”

Striking result reveals path towards new treatments

Using zebrafish and mouse models, as well as human lung cancer cells, the WEHI-led research is the first to demonstrate the impact of inhibiting minor splicing in in vivo models of solid tumors.

The study found reducing the activity of a protein encoded by the RNPC3 gene—an essential component of the minor splicing machinery—significantly slows tumor growth in liver, lung and stomach cancers.

“Just by halving the amount of this protein, we were able to significantly reduce tumor burden,” said Dr. Karen Doggett, first author of the study.

“That’s a striking result, especially given how resilient these cancers usually are.”

The study also revealed that disrupting minor splicing triggers the p53 tumor suppressor pathway, a critical defense mechanism in the body’s fight against cancer.

Dubbed the “guardian of the genome,” the p53 protein responds to DNA damage by stalling cell division, initiating DNA repair or triggering cell death. This well-known pathway is frequently mutated or disabled in many cancers, allowing these cells to grow unchecked.

“Blocking minor splicing leads to DNA damage and activates this critical defensive response, which means cancers with a functional p53 pathway are likely to be especially vulnerable to this strategy,” Dr. Doggett said.

“This opens the door to treatments that could be both more effective and less toxic, offering hope for patients with aggressive cancers that currently have limited options.”

Drug discovery collaboration

To search for compounds that might inhibit minor splicing, the research team turned to the National Drug Discovery Center headquartered at WEHI, with a screen of over 270,000 drug-like molecules identifying several promising hits.

“We’ve validated minor splicing as a compelling therapeutic target—now the challenge is to develop a drug compound that can safely and effectively inhibit it,” Prof Heath said.

The research draws on WEHI’s deep expertise in gene discovery and cancer biology, showcasing the power of collaboration across multiple labs and technologies.

“One of the strengths of this study is the breadth of models and tumor types we used,” Prof Heath said.

“We didn’t just test one kind of cancer or use one analysis method. This diversity in our approach gives us confidence that our strategy could be relevant across many forms of cancer, and not just in a narrow set of conditions.”