Illuminated, warmed up…
CRISPR was activated in the tumor by heat and light
Daria Spasskaya, N+1
Chinese scientists have developed a means of delivering a genome editing system that allows you to turn it on in the animal's body only in the right place using infrared radiation. To do this, the Cas9 protein charged with guide RNA was sewn to the ap-conversion nanoparticles using a photosensitive linker. According to the authors of the article in Science Advances (Pan et al., Near-infrared upconversion–activated CRISPR-Cas9 system: A remote-controlled gene editing platform), with the help of such nanoparticles charged against one of the oncogenes, they managed to slow down tumor growth in mice.
Genome editing systems, in particular, CRISPR-Cas9, allow already in an adult organism to change gene expression only in a specific organ or tumor, however, for safe use it is desirable to limit their activity not only in space, but also in time. To do this, scientists are developing systems that are inactive by default, but they can be turned on by directed physical action. For example, we talked about magnetized viral nanoparticles with CRISPR-Cas9, which penetrate into cells only under the action of a magnet.
Another convenient way to start the process in a separate organ is near infrared radiation, which penetrates well through the tissues. This is the method chosen by researchers from Nanjing University (China) to release Cas9 complexes with RNA inside the tumor at the right time. As a means of delivering the editing system, the scientists chose ap-conversion nanoparticles with a small admixture of lanthanides, which convert infrared radiation into ultraviolet and visible light. Cas9 was sewn to the nanoparticles using a photo-separable linker (hydroxymethyl-nitrobenzoic acid). After entering the cells and exposure to infrared radiation, the particles turn it into ultraviolet, which cleaves the linker and releases Cas9. The Cas9-RNA complex already enters the nucleus and introduces a mutation into the desired gene.
Scheme of Cas9 release in cells by photoactivation on ap-conversion nanoparticles (figures from the article in Science Advances).
For the experiment on mice, the authors charged Cas9 with a guide RNA against the PLK-1 gene, the increased expression of which is associated with many types of cancer, and the suppression of which in tumor cells causes apoptosis. It turned out that during intravenous delivery of nanoparticles, they mainly accumulate in the liver and spleen, so it is most effective to inject them directly into the tumor. Mice with a grafted tumor from human lung adenocarcinoma cells were injected with nanoparticles, and then the tumor was exposed to near-infrared radiation for 20 days. As a result, the tumor did not disappear completely, but its growth in mice from the experimental group noticeably slowed down.
Tumor sizes in mice from the control groups (upper and middle row) and from the experimental group, which was injected with nanoparticles with Cas9-RNA and then heated the tumor (lower row).
The authors, however, recognized that tumors that can be injected can usually be removed by surgery, so now they face the task of modifying the particles so that they can deliver Cas to the right place during systemic administration.
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