Cells are built like old city blocks: load-bearing walls, backup wiring, repair crews, and at least one suspicious side entrance nobody noticed until the inspector showed up with a flashlight. In this story, that side entrance belongs to USP1, a protein cancer cells seem very happy to keep propped open.
The new paper by Cheng and colleagues is not just about finding a drug. It is about building the thing that helps you find the drug faster: a fluorescence polarization probe, basically a tiny glowing tag that lets scientists tell when a molecule has latched onto USP1's allosteric site, which is the sneaky side pocket rather than the enzyme's main workbench [1].
Why does that matter? Because if you want to stop a cancer-friendly protein, it helps to know whether your compound is actually grabbing the right handle instead of just loitering nearby like a guy at a velvet rope saying he "knows the owner."
Meet USP1, the Repair Guy Who Joined the Villains
USP1 is a deubiquitinating enzyme. Translation: it removes little molecular tags called ubiquitin from proteins. Those tags often act like cellular Post-its saying "deal with this," "move this," or "throw this out." When USP1 erases the wrong notes at the wrong time, trouble follows.
Cancer likes that arrangement. USP1 helps regulate DNA damage response pathways, including Fanconi anemia signaling and translesion synthesis, which are both involved in how cells survive genetic chaos [2]. In several tumor types, including difficult diffuse large B-cell lymphoma, high USP1 activity has been linked to bad behavior, drug resistance, or both [3].
That makes USP1 an attractive target. But here was the plot twist: scientists already had promising allosteric inhibitors, yet lacked a good direct binding assay for that allosteric site. In drug discovery terms, that is like having a treasure map with no compass and a flashlight held together with tape.
The Glow Stick That Speeds Up the Search
Cheng et al. designed the first allosteric fluoroprobe for USP1 and built a fluorescence polarization assay around it [1]. If that phrase sounds like science trying to win a spelling bee, the basic idea is simpler than it looks.
A small fluorescent tracer spins quickly when it is free in solution. When it binds a larger protein, it slows down. Scientists can measure that change. So instead of asking, "Did this candidate drug maybe sort of affect the enzyme somehow?" they can ask the much cleaner question: "Did it kick the tracer off the allosteric site or not?"
That is a big upgrade. It lets researchers separate compounds that hit USP1's hidden regulatory pocket from compounds that mess with the catalytic site. In other words, it tells you whether your suspect picked the side lock or just yelled at the front door.
Then the Paper Pulled Out a Better Weapon
The authors did not stop at the assay. Using this platform, they identified a new tetrahydroisoquinoline class of USP1 inhibitors. Their lead compound, called 14a, outperformed the clinical USP1 candidate KSQ-4279 in enzyme and cell-based tests and showed potent anti-tumor activity in a mouse model of diffuse large B-cell lymphoma [1].
That is the part that makes this more than a methods paper. The probe is useful on its own, but the study also serves up a lead compound with real bite.
This fits a broader trend. In 2024, researchers reported that KSQ-4279 could overcome PARP inhibitor resistance in homologous recombination-deficient tumors, including BRCA-mutant settings [4]. Structural work published the same year showed how KSQ-4279 binds a cryptic allosteric pocket on USP1, helping explain why this strategy can be selective [5]. A 2025 review traced USP1's rise from interesting target to real clinical contender, with early human data suggesting manageable safety but plenty left to prove [2].
So the field is moving. Not "cure next Tuesday" moving. More like "the blueprints finally make sense and the contractors have stopped arguing" moving.
Why Regular Humans Should Care
If these findings hold up, the impact could be pretty practical. Better USP1 screening tools could speed the discovery of next-generation drugs for tumors that lean hard on DNA repair or evolve resistance to other treatments. That includes not just lab-famous BRCA-related cancers, but potentially aggressive blood cancers too [1-4].
Diffuse large B-cell lymphoma is a particularly relevant villain here. It is the most common non-Hodgkin lymphoma in adults, and while many patients do well with standard therapy, relapsed or resistant disease remains a brutal problem [6]. A smarter way to disable one of the tumor's backup repair or survival systems is exactly the kind of move oncology needs more of.
The catch, because biology never misses a chance to be humbling, is that this is still early. Compound 14a looks strong in preclinical models, not in people yet. Tumors are notorious for rewriting the script halfway through the third act.
Still, this paper gives the field two valuable things at once: a better metal detector and a promising coin in the sand. In cancer research, that counts as a very good day at the construction site.
References
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Cheng J, Wang P, Wang P, et al. Discovery of a Potent Fluorescence Polarization Probe for Identifying USP1 Allosteric Inhibitors. Advanced Science. 2026; e75350. DOI: https://doi.org/10.1002/advs.75350. PubMed: https://pubmed.ncbi.nlm.nih.gov/42017803/
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Singh S, Cadzow L, Yap TA. USP1 inhibition: A journey from target discovery to clinical translation. Drug Resistance Updates. 2025;271:108865. PubMed: https://pubmed.ncbi.nlm.nih.gov/40274197/
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Li XY, Wu JC, Liu P, et al. Inhibition of USP1 reverses the chemotherapy resistance through destabilization of MAX in the relapsed/refractory B-cell lymphoma. Leukemia. 2023;37:164-177. DOI: https://doi.org/10.1038/s41375-022-01747-2
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Cadzow L, Blake SM, Goulet M, et al. The USP1 Inhibitor KSQ-4279 Overcomes PARP Inhibitor Resistance in Homologous Recombination-Deficient Tumors. Cancer Research. 2024;84(20):3419-3434. DOI: https://doi.org/10.1158/0008-5472.CAN-24-0293. PubMed: https://pubmed.ncbi.nlm.nih.gov/39402989/
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Rennie ML, Gundogdu M, Arkinson C, et al. Structural and Biochemical Insights into the Mechanism of Action of the Clinical USP1 Inhibitor, KSQ-4279. Journal of Medicinal Chemistry. 2024;67(17):15557-15568. DOI: https://doi.org/10.1021/acs.jmedchem.4c01184. PMCID: https://pmc.ncbi.nlm.nih.gov/articles/PMC11403619/
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Nussinov R, Zhang M, Maloney R, et al. Allostery: Allosteric Cancer Drivers and Innovative Allosteric Drugs. Journal of Molecular Biology. 2022;434(17):167569. DOI: https://doi.org/10.1016/j.jmb.2022.167569. PMCID: https://pmc.ncbi.nlm.nih.gov/articles/PMC9398924/
Disclaimer: The image accompanying this article is for illustrative purposes only and does not depict actual experimental results, data, or biological mechanisms.