Structural Change from Nonparallel to Parallel G-Quadruplex Structures in Live Cancer Cells Detected in the Lysosomes Using Fluorescence Lifetime Imaging Microscopy

Time-gated fluorescence lifetime imaging microscopy with the o-BMVC fluorescent probe provides a visualizing method for the study of exogenous G-quadruplexes (G4s) in live cancer cells. Previously, imaging results showed that the parallel G4s are accumulated and that nonparallel G4s are not detected in the lysosomes of CL1-0 live cells. In this work, the detection of the G4 signals from exogenous GTERT-d(FN) G4s in the lysosomes may involve a structural change in live cells from intramolecular nonparallel G4s to intermolecular parallel G4s. Moreover, the detection of the G4 signals in the lysosomes after the 48 h incubation of HT23 G4s with CL1-0 live cells indicates the occurrence of structural conversion from the nonparallel G4s to the parallel G4s of HT23 in the live cells. In addition, the detection of much stronger G4 signals from ss-GTERT-d(FN) than ss-HT23 in the lysosomes of CL1-0 live cells may be explained by the quick formation of the intermolecular parallel G4s of ss-GTERT-d(FN) and the degradation of ss-HT23 before its intramolecular parallel G4 formation. This work provides a new approach to studying G4-lysosome interactions in live cells.