UCLA researchers have identified a critical vulnerability in some of the most lethal and drug-resistant cancers on record, a discovery that could unlock treatment options using medications already approved for other diseases.
Small cell neuroendocrine cancers are brutal killers. They develop in the lungs, prostate, and ovaries, spread early, and multiply with alarming speed. For more than half a century, survival rates have barely budged. The reason lies in a missing gene called RB, which normally acts as a cellular brake. Without it, cancer cells accelerate uncontrollably and shrug off most targeted therapies.
The new research, published in Proceedings of the National Academy of Sciences, reveals that this genetic loss also creates an unexpected trap. Cancer cells without RB become utterly dependent on a protein called E2F3 to stay alive. Block that protein, and the tumors collapse through what scientists call synthetic lethality, a process where losing two genes together is lethal even though losing one alone is survivable.
"These cancers haven't changed in my lifetime," said Dr. Owen N. Witte, the study's senior author at UCLA's Jonsson Comprehensive Cancer Center. "That's what makes this so significant. We're finally seeing a different path forward."
The breakthrough emerged from years of painstaking lab work. For decades, scientists lacked realistic models of small cell prostate cancer, making it nearly impossible to identify the genes these tumors actually depend on. The UCLA team engineered human prostate cells with five major cancer mutations, including the RB loss, then grew them into three-dimensional organoids and implanted them in mice. The resulting tumors closely mimicked the disease in humans.
Using CRISPR gene-editing technology to screen thousands of genes, researchers identified nearly 1,400 that play roles in cancer cell survival. The standout finding was that small cell cancers from different organs, regardless of where they started, all showed the same intense dependence on E2F3.
When E2F3 levels dropped in RB-deficient cells, tumors stopped dividing, lost the ability to form clusters, and sometimes died outright. "The two genes don't do the same job," Witte explained. "But together, their combined functions become absolutely essential for the cancer cell."
What makes the discovery especially promising is that no drug currently targets E2F3 directly. So the team pivoted. They found that blocking DHODH, an enzyme involved in DNA production, lowered E2F3 levels and halted tumor growth. The payoff comes from the fact that DHODH inhibitors already exist as FDA-approved medications. Leflunomide and teriflunomide are already prescribed to treat autoimmune diseases.
"What's exciting is that our findings open the door to applying existing drugs in a new way," said Dr. Evan Abt, the study's lead author. "By understanding how these cancers depend on E2F3, we can start thinking about strategies that might work much more quickly in patients."
Repurposing medications could accelerate the path from laboratory discovery to clinical trials, potentially bringing new hope to patients with cancers that have historically resisted every approach. While the research remains early stage, it marks the first major conceptual shift in treating these tumors in decades.
Author Jessica Williams: "This isn't a cure yet, but it's the kind of fundamental insight that changes the game when doctors finally have a weapon that actually works against killers like this."
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