Oxidative modifications control aberrant tyrosine kinase activity

Therapy resistance is a major reason for the fatal consequences of cancer. The tumor microenvironment (TME) often is associated with the production of excess reactive oxygen species (ROS). ROS are capable of introducing oxidative post-translational modifications (oxPTMs) to proteins targeted in cancer therapy, such as tyrosine kinases (TKs), and ROS could render their functionality. However, little is known about the occurrence or magnitude of such processes, partially because mimicking the TME producing several short-lived ROS types at once is technically challenging. Gas plasma technology, a partially ionized gas generating a multitude of ROS types simultaneously and at high concentrations, was used to model pro-oxidative conditions in the TME and study the functional consequences in three TKs (epidermal growth factor receptor, sarcoma, and vascular endothelial growth factor receptor 2) targeted clinically. TKs dissolved in liquids were exposed to gas plasma, and a drastic reduction in their activity was observed. Hypothesizing that this was due to gas plasma-generated ROS, plasma-treated TKs were analyzed by high-resolution mass spectrometry for the type and quantity of oxPTM types using an in-house database. Preferred oxidation targets were identified as sulfur-containing and aromatic amino acids. OxPTMs were detected on amino acid residues that have important structural or catalytic functions in TKs, such as the adenosine triphosphate-binding site, but also on amino acid residues that are targets for therapeutic applications, such as TK inhibitors. While the practical relevance of these findings remains to be discovered, our results suggest that excessive ROS concentrations potentially contribute to TK activity reduction in the TME. The mass spectrometry data are available via ProteomeXchange with identifier PXD056912.