Expanded Application of a Photoaffinity Probe to Study Epidermal Growth Factor Receptor Tyrosine Kinase with Functional Activity.

The abnormal activation of the epidermal growth factor receptor (EGFR) is strongly associated with cancer invasion and metastasis. Tools and methods are required to study and visualize EGFR activation under (patho)physiological conditions. Here, we report the development of a two-step photoaffinity probe (HX101) by incorporation of a diazirine as a photoreactive group and an alkyne as a ligation handle to quantitively study EGFR kinase activity in native cellular contexts and human tissue slices. HX101 is a multifunctional probe based on the pharmacophore of the EGFR tyrosine kinase inhibitor (EGFR-TKI) and can covalently target the EGFR upon photoactivation. The incorporated alkyne serves as a versatile ligation handle and enables HX101 to introduce distinct reporter groups (e.g., fluorophore and biotin) via click chemistry. With variable reporter tags, HX101 enables visualization and target engagement studies of the active EGFR in a panel of cancer cells using flow cytometry, confocal microscopy, and mass spectrometry. Furthermore, as a proof of concept study, we applied HX101 in stochastic optical reconstruction microscopy super-resolution imaging to study EGFR activation in live cells. Importantly, HX101 was also applied to visualize EGFR mutant activity in tumor tissues from lung cancer patients for prediction of EGFR-TKI sensitivity. Altogether, our results demonstrate the wide application of a selective photoaffinity probe in multi-modal assessment/visualization of EGFR activity in both live cells and tissue slices. We anticipate that these diverse applications can facilitate the translation of a strategically functionalized probe into medical use.