Study Provides Insights into NLRP3 Inflammasome

Although tyrosine kinase inhibitors (TKI) can be very useful in fighting certain cancers, they also cause serious inflammatory side effects that limit their use. In a paper published last month in The Journal of Immunology, researchers from Tohoku University revealed the underlying mechanism that causes this inflammation..

From earlier studies, the team had learned that a TKI called Gefitinib (GF) causes lung inflammation. GF works by targeting the epidermal growth factor receptors, but when it is used to treat cancer, it can also cause inflammation in the patient's lungs through the NLRP3 inflammasome. The NLRP3 inflammasome is part of the body's immune system and plays an important role in innate immunity. But when the NLRP3 inflammasome is improperly activated, it can contribute to the development of a wide range of inflammatory diseases.

Until now, scientists have not fully understood why the NLRP3 inflammasome is activated, but the evidence seems to point to mitochondrial dysfunction. In their earlier study, the team learned that GF activated the NLRP3 inflammasome through mitochondrial damage that led to the interstitial pneumonitis in patients. However, they had not understood how GF initiates the mitochondrial damage and whether or not other TKIs shared this mechanism.

To conduct their study, the team specifically studied the Src family kinases. SFKs are nonreceptor tyrosine kinases that regulate many cell processes. There are 11 types of SFKs in the human genome. Some of these SFKs are in the mitochondria and they play an essential role in the function of the mitochondria. The team found that all the TKIs they tested inhibit the kinase activity of the SKFs in the mitochondria, which is responsible for the NLRP3 inflammasome.

The team's comprehensive analysis of the TKIs they tested revealed that these TKIs act as powerful agonists. In addition, the team observed off-target activity that could contribute to the side effects. "As an important finding, all TKIs we tested share a common off-target activity against the mitochondrial SFKs. Therefore, blocking the access of TKIs to mitochondria is a good way to prevent the inflammation," said Atsushi Matsuzawa, senior author of the paper. They also noted that the other TKIs that do not affect the activity of the mitochondrial SFKs may overcome the inflammatory-based side effects. As another approach, when effective inhibitors of the NLRP3 inflammasome are developed, administering the TKIs at the same time as the NLRP3 inhibitors can counteract the side effects. The team's results provide insight into both the biological and the clinical significance of the NLRP3 inflammasome and the SFKs.