UCLA Scientists Discover Synthetic Lethality Between RB Loss and E2F3 in Deadly Small Cell Cancers, Opening Door to Drug Repurposing
核心洞察
UCLA researchers identified that small cell neuroendocrine cancers (搜索) lacking the RB (搜索) gene become critically dependent on the E2F3 (搜索) protein, creating a synthetic lethality vulnerability.
Genome-wide CRISPR screens across novel organoid models revealed nearly 1,400 essential genes, with E2F3 (搜索) dependence conserved across lung, prostate, and ovarian small cell cancers.
Blocking the DHODH (搜索) enzyme with FDA-approved drugs leflunomide and teriflunomide reduced E2F3 (搜索) levels and slowed tumor growth, offering a potential repurposing shortcut.
Small cell neuroendocrine cancers (搜索) — aggressive malignancies that arise in the lung, prostate, and ovary — have stubbornly resisted therapeutic progress for more than half a century. Now, a team at UCLA has uncovered a hidden genetic dependency that could finally offer a way to attack these tumors, and existing FDA-approved drugs may help accelerate the path to the clinic.
The study, published March 20, 2026 in Proceedings of the National Academy of Sciences, reveals that cancer cells lacking the tumor suppressor gene RB (搜索) become exquisitely dependent on a protein called E2F3 (搜索). When both are disabled simultaneously, the cancer cells cannot survive — a phenomenon known as synthetic lethality.
A Vulnerability Decades in the Making
“Discovering a vulnerability like this opens the door to thinking about entirely new treatment strategies,” said senior author Dr. Owen N. Witte, who holds the Presidential Chair in Developmental Immunology in the Department of Microbiology, Immunology, and Molecular Genetics at UCLA and is a member of the UCLA Health Jonsson Comprehensive Cancer Center (搜索). “That’s especially important because there has not been a major change in how we treat these cancers for decades. When I first encountered these tumors as a medical student more than 50 years ago, the survival statistics were essentially the same as they are today.”
Small cell neuroendocrine cancers (搜索) are defined by rapid growth, early metastasis, and profound resistance to existing targeted therapies. A hallmark of these malignancies is the loss of RB (搜索), a gene that normally restrains cell proliferation. Without RB, tumor cells multiply unchecked — but the new findings suggest this very loss also creates an Achilles’ heel.
Building Better Models to Find Hidden Dependencies
Progress against small cell cancers, particularly those of the prostate, has been hampered by a shortage of faithful laboratory models. To bridge this gap, the UCLA team engineered normal human prostate cells with five major cancer-driving genetic alterations, including loss of RB (搜索) and TP53. These cells were grown into three-dimensional organoids and then implanted into mice, generating tumors that closely recapitulate human small-cell prostate cancer. The effort builds on more than a decade of work in Witte’s laboratory to develop specialized models of small-cell neuroendocrine prostate cancer.
Using these models, the researchers performed genome-wide CRISPR screens, systematically interrogating thousands of genes to determine which ones are essential for cancer cell survival. The screen identified nearly 1,400 critical genes. Crucially, small cell cancers originating from different organs — lung, prostate, and ovary — all converged on a shared dependence on E2F3 (搜索).
When the team experimentally reduced E2F3 (搜索) levels in RB (搜索)-deficient cancer cells, the cells stopped dividing, lost the ability to form clusters, and in some cases underwent cell death.
“It’s not that the two genes do the same thing,” Witte explained. “But the combination of what they do together becomes essential for the cancer cell. Losing one gene may not matter much, but losing both has a dramatic effect on tumor growth.”
First author Dr. Evan Abt, an assistant professor of Molecular and Medical Pharmacology at the David Geffen School of Medicine at UCLA, added: “These new model systems allowed us to uncover a genetic vulnerability that would have been very difficult to find otherwise.”
A Drug Repurposing Shortcut Through DHODH (搜索) Inhibition
Because no drugs currently target E2F3 (搜索) directly, the researchers explored an indirect strategy. They discovered that inhibiting the enzyme DHODH (搜索) — a key player in the metabolic pathway that produces DNA building blocks — led to reduced E2F3 levels and slowed tumor growth.
Notably, DHODH (搜索) inhibitors including leflunomide and teriflunomide are already FDA-approved for the treatment of autoimmune diseases. This existing regulatory status could substantially shorten the timeline for evaluating these agents as cancer therapies.
“What’s exciting is that our findings open the door to applying existing drugs in a new way,” Abt said. “By understanding how these cancers depend on E2F3 (搜索), we can start to think about strategies that might work much more quickly in patients.”
Cautious Optimism and Next Steps
While the research remains at an early stage, the study provides a foundational insight into the biology of these recalcitrant cancers and highlights a concrete therapeutic direction. The synthetic lethality between RB (搜索) loss and E2F3 (搜索) inhibition, combined with the availability of approved DHODH (搜索) inhibitors, creates a rationale for further preclinical and potentially clinical investigation.
The study was conducted by Evan R. Abt, Liang Wang, Grigor Varuzhanyan, Jack Freeland, Tian He, Guadalupe M. Peña-Garcia, Lauryn Ruegg, Jami McLaughlin, Donghui Cheng, Nikolas G. Balanis, Chia-Chun Chen, Yang Xu, Yi Xing, Sanaz Memarzadeh, Caius G. Radu, Thomas G. Graeber, and Owen N. Witte.