In a study published in Science Translational Medicine, a team of researchers led by Dr. WANG Yu from the Shenzhen Institutes of Advanced Technology of the Chinese Academy of Sciences developed PRINCE and Little Prince, dual small-molecule-controlled genome editing systems that allow CRISPR activity to be switched on by drug inducers and kept largely silent in their absence.
Current therapeutic CRISPR strategies often rely on passive control: RNA or protein editors are delivered, act for a limited time, and gradually disappear as they degrade. "Natural decay is not the same as active control. For therapeutic genome editing, DNA edits often remain after editing is complete, but the editor itself does not need to stay active indefinitely. Our goal is to make genome editing not only efficient, but also controllable in time," said Dr. WANG.
PRINCE takes a more active approach by coordinating two regulatory layers at once. The nuclease protein is controlled by a small-molecule-responsive nuclear localization module, while guide RNA expression is regulated by a doxycycline-responsive system. This dual control is designed to reduce background editing while preserving efficient editing after induction.
In human cells, PRINCE showed stringent control even after stable genomic integration and long-term culture. After two years of continuous culture, a brief 24-hour exposure to drug inducers efficiently activated editing, whereas uninduced cells showed minimal background activity. Whole-genome analyses detected substantially less off-target activity than constitutive CRISPR systems. The same control principle was also successfully extended to prime editing.
To support in vivo, particularly in situ delivery, researchers developed Little Prince, a compact version based on miniature nucleases that can be packaged into a single adeno-associated virus vector. The name "Little Prince" was inspired by Antoine de Saint-Exupéry's classic novel. Researchers hope that safer and more controllable genome editing technologies may one day become a meaningful gift for patients, especially children with rare diseases.
In a humanized mouse model of hypercholesterolemia, AAV8-delivered Little Prince targeted human PCSK9 in the liver. Drug induction produced robust in situ editing, while uninduced mice showed background editing comparable to negative controls. Serum total cholesterol and low-density lipoprotein (LDL) cholesterol were both reduced by roughly half.
Along with collaborators from Fudan University, researchers tested Little Prince in a humanized mouse model of neovascular age-related macular degeneration by targeting human VEGFA in the retina. They found that drug induction reduced pathological vascular leakage and lesion size and improved retinal function measured by electroretinography.
By enabling a 'start' and 'stop' button for gene editing, this work shows how small molecules act as a safety harness, allowing to actively control the editing process. Further studies are needed to assess long-term safety and broader applicability. PRINCE and Little Prince provide proof of concept for pharmacologically controlled genome editing directly in native tissues.
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