[Utidelone induces apoptosis and autophagy in small cell lung cancer cells through the ROS/AMPK signaling pathway]

Objective: To investigate the effects and underlying molecular mechanisms of Utidelone (UTD1) in small cell lung cancer (SCLC). Methods: The study utilized small cell lung cancer H446 and H1048 cell lines along with animal models. Cell proliferation, cell cycle progression, apoptosis, autophagy, and related activities following UTD1 treatment were assessed using Cell Counting Kit-8 (CCK-8), flow cytometry, immunofluorescence staining, reactive oxygen species (ROS) generation assay, and Western blot analysis. The involvement of the ROS/adenosine monophosphate-activated protein kinase (AMPK) signaling pathway was also examined. Data analysis was performed using GraphPad Prism version 8 software. Results: UTD1 inhibited the viability of H446 and H1048 cells in a dose- and time-dependent manner. The half inhibitory concentrations (IC₅₀) of UTD1 for H446 and H1048 cells were 0.675 and 0.439 μg/ml, respectively. The proportion of cells in the G₂/M phase for H446 and H1048 cells in the UTD1 group at 6 h, 12 h, and 24 h was [(53.86±4.54)%, (68.59±5.49)%, (60.89±3.26)%] and [(46.83±2.20)%, (60.67±3.44)%, (57.88±5.11)%], which were significantly higher than that in the control group, except for the proportion of H1048 cells at 6 h [(38.99±2.60)% vs. (40.73±2.50)%, P＜0.05]. The apoptosis rates were [(23.57±0.12)%, (35.79±1.59)%, and (46.15±4.57)%] for H446 cells and [(23.05±2.70)%, (37.73±2.97)%, and (43.39±3.31)% for H1048 cells], all of which were significantly higher than those in the control group [(6.44±0.96)%, (6.31±0.75)%, respectively; all P＜0.05]. The number of LC3 fluorescent spots was [(56±11), (69±8), and (66±8)] for H446 cells and [(39±7), (56±12), and (50±11)] for H1048 cells, both significantly higher than those in the control group [(13±6) and (12±5), respectively; both P＜0.05]. The relative fluorescence intensity of ROS was 2.54±0.48, 2.85±0.68, and 5.03±0.72 for H446 cells and 2.26±0.51, 4.17±0.35, and 4.66±0.51 for H1048 cells, which were also significantly higher than those in the control group (P＜0.05). The expression levels of cyclin B1, cyclin A2, and P21 of H446 cells in the three time points were [(0.63±0.07, 0.33±0.05, 0.23±0.04), (0.68±0.08, 0.46±0.03, 0.27±0.06), and (0.64±0.03, 0.32±0.05, 0.22±0.03), respectively], all significantly lower compared to the control group (P＜0.05). The apoptosis rates of H446 and H1048 cells in the UTD1+Z-VAD-FMK group were (19.97±3.19)% and (17.68±3.14)%, both lower than those in the UTD1 group [(40.73±3.35)% and (39.82±2.45)%, respectively; all P＜0.05]. The absorbance values of H446 and H1048 cells in the UTD1+3-MA group were significantly higher than those in the UTD1 group at 6h, 12h, and 24h (all P＜0.05). The levels of p-AMPKα/AMPKα, LC3-II expression, and the percentage of apoptotic cells in the H446 and H1048 cells of the UTD1+NAC group were [(1.33±0.09, 1.33±0.11), (1.49±0.16, 1.55±0.05), (17.24±2.15)%, and (19.40±4.28)%], all of which were lower than those observed in the UTD1 group [(1.98±0.17, 2.23±0.23), (2.81±0.19, 2.49±0.38), (38.07±3.53)%, and (41.20±1.87)%, all P＜0.05]. The number of LC3 fluorescence points and the percentage of apoptotic cells in the H446 and H1048 cells of the UTD1+si-AMPKα group [(24±5, 23±3), (18.35±1.15)%, and (19.15±3.46)%] were all lower than those in the UTD1+si-NC group [(46±6, 36±6), (39.34±1.77)%, and (39.50±2.15)%, all P＜0.05]. The tumor inhibition rates in small cell lung cancer tumor-bearing nude mice for the 2.5 mg/kg UTD1 group and the 5 mg/kg UTD1 group were 46.43% and 58.33%, respectively. Furthermore, the proportions of apoptosis-positive cells and p-AMPKα-positive cells in the UTD1 group were significantly higher compared to the control group, while the levels of Ki-67 positivity were significantly reduced. Conclusion: UTD1 inhibits SCLC cell proliferation, induces G₂/M phase arrest, and promotes cell apoptosis and autophagy through the activation of the ROS/AMPK signaling pathway.