A tip to the tumor
The new therapy "warms up" the tumor tissue
Peter Kazimirov, PCR.news
Avoiding the activity of the immune system is one of the main defense mechanisms of a cancerous tumor. To overcome it, inhibitors of immune response checkpoints are used, which remove restrictions from immune cells. But not all cancers can serve as a target even for such "activated" immune cells — "cold" tumors are characterized by low cytokine expression and a low level of infiltration by immune cells. Agonists of the interferon gene stimulator (STINGa) are able to "warm up" tumor tissues by activating signaling pathways, resulting in the expression of the regulatory factor interferon 3 and autophagy. Scientists from the USA have developed a system that provides targeted delivery of STINGa to cancer cells, and tested its effectiveness on mouse models of cancer.
The authors used the pHLIP protein (pH Low Insertion Protein), which is embedded in the cell membrane of cells with an acid medium on the surface, which is typical for metabolically active cells, for example, cancer cells. The STINGa molecule was attached to the penetrating end of the protein, which is a chain of L- or D-amino acids, using a disulfide binder. Upon penetration into the cell, the binding link disintegrates, releasing STINGa into the cell. In in vitro experiments, 40% of pHLIP-STINGa complexes successfully released STINGa when incubated with mouse plasma. However, when incubated with human plasma, systems consisting of D-amino acids released STINGa only in 10% of cases. Scientists have also confirmed the ability of pHLIP-STINGa complexes to penetrate cells in vitro.
In the in vivo experiments, the researchers used the CT26 mouse model of colon cancer, which is widely used to evaluate the effectiveness of immunotherapies. To assess the pharmacokinetics of the system, a fluorescent label was attached to the non-penetrating end of the pHLIP. Next, the scientists evaluated the fluorescent response both in vivo and on the slaughtered animals from 2 to 96 hours after intravenous administration of the labeled pHLIP-STINGa complex. The study showed that the drug quickly accumulates in the tumor tissues and remains there for eight days. At the same time, the half-life of pHLIP-STINGa is 8.2 hours, which is about six times higher than the half-life of free STINGa molecules (1.4 hours). Scientists have also demonstrated that pHLIP-STINGa penetrates all types of cancer cells.
The untreated tumor (top left) is strongly acidic, as evidenced by its reaction to the fluorescent dye (top right). Just a few days after treatment (bottom left), the tumor stroma collapses and the pH decreases (bottom right).
To assess the therapeutic efficacy, the authors used animals whose tumor size reached 100 mm3. Mice were injected with one dose of pHLIP-STINGa (intravenously or by intraperitoneal injection), pHLIP or STINGa. The group that was injected with STINGa showed only a slight slowdown in tumor development compared to control animals. In all 20 animals that received pHLIP-STINGa in one way or another, the tumor disappeared. At the same time, in 18 out of 20 animals, the cancer did not return within 60 days after the injection. One of the animals received a second injection of pHLIP-STINGa after the tumor reappeared, but this did not affect the development of cancer.
The scientists also repeated the experiment on large-volume tumors (about 500 mm3), since they have a different cellular composition compared to small formations. In this case, tumors gradually disappeared in 7 out of 10 mice who received a pHLIP-STINGa injection.
To test the development of immunity, cancer cells were re-injected into animals that had successfully undergone treatment. Only in 5 out of 25 animals, this led to the development of a tumor.
The scientists also tested the drug's work on the 4T1 breast cancer line. In this case, it was only possible to slow down the growth of the tumor, but not completely destroy it.
The authors believe that targeting cells based on metabolic activity, rather than specific markers, can help fight tumors more effectively, since cancer tissues are a complex system with a large number of different cell types.
Article by Moshnikova et al. The eradication of tumors and development of anti-cancer immunity using STINGa targeted by pHLIP is published in the journal Frontiers in Oncology.
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