Fig. 1

Nintedanib exhibits intracellular and cell-free intrinsic fluorescence activity. a Full excitation-emission 3D landscape was obtained by fluorescence spectroscopy to elucidate cell-free fluorescence properties of nintedanib. Spectra are shown for excitation wavelengths from 220 nm to 420 nm. Emission was measured from 240 to 700 nm. 1st and 2nd order Rayleigh scattering can be seen as diagonal ridges. b Viability of DMS114, NCI-H520 and NCI-H1703 lung cancer cells was analyzed by MTT assay after 72 h exposure to the indicated concentrations of nintedanib. c Intracellular fluorescence activity of 10 μM nintedanib in DMS114, NCI-H1703 and NCI-H520 cells after 1 h exposure was measured by flow cytometry. Fluorescence emission was analyzed using the Horizon V450 channel (450/40 nm bandpass filter) for the 405 nm laser and the FITC channel (530/30 nm bandpass filter) for the 488 nm laser. *** p < 0.001, students’s t-test. d Blue and green fluorescence activity in NCI-H1703 cells, treated for 1 h with 10 μM nintedanib was analyzed by live cell microscopy. The scale bar indicates 10 μm