Lysosomal dysfunction and autophagy blockade contribute to IMB-6G-induced apoptosis in pancreatic cancer cells

Abstract

Targeting the autophagic pathway is currently regarded as an attractive strategy for cancer drug discovery. Our previous work showed that IMB-6G is a novel N-substituted sophoridinic acid derivative with potent cytotoxicity against tumor cells, yet the effect of IMB-6G on autophagy and pancreatic cancer cell death remains unknown. Here, we show that IMB-6G inhibits the growth of MiaPaCa-2 and HupT-3 pancreatic cancer cells and induces caspase-mediated apoptosis, which is correlated with an accumulation of autophagic vacuoles. IMB-6G promotes autophagosome accumulation from the early stage of treatment but blocks autophagic flux in the degradation stage, mainly through attenuation of lysosomal cathepsin activity in pancreatic cancer cells. Moreover, IMB-6G triggers lysosomal membrane permeabilization (LMP), followed by cathepsin B/CTSB and cathepsin D/CTSD release from lysosomes into the cytoplasm. Inhibition of autophagosome formation with siRNA against autophagy protein 5 (Atg5) attenuates IMB-6G-induced LMP and apoptosis. Furthermore, cathepsin inhibitors relieve IMB-6G-induced apoptosis as well. Altogether, our findings demonstrate that IMB-6G is a novel autophagy inhibitor, which induces autophagy-dependent apoptosis through autophagosomal-cathepsin axis in pancreatic cancer cells and indicate the potential value of IMB-6G as a novel antitumor drug candidate.

Resibufogenin suppresses transforming growth factor‐β‐activated kinase 1‐mediated nuclear factor‐κB activity through protein kinase C‐dependent inhibition of glycogen synthase kinase 3

“…The effect of RB on the cell viability of pancreatic cancer cells was determined by MTT assay as previously described . Observation of the chromatin shrinking in pancreatic cancer cells induced by RB was carried out by Hoechst 33342 staining assay .…”

“…The effect of RB on the cell viability of pancreatic cancer cells was determined by MTT assay as previously described. 25,26 Observation of the chromatin shrinking in pancreatic cancer cells induced by RB was carried out by Hoechst 33342 staining assay. 27 Detection of apoptotic cell rate was measured using an annexin V-FITC/propidium iodide apoptosis detection kit (KeyGen, Nanjing, China) as described previously.…”

“…27 Detection of apoptotic cell rate was measured using an annexin V-FITC/propidium iodide apoptosis detection kit (KeyGen, Nanjing, China) as described previously. 25,27…”

MPB, a novel berberine derivative, enhances lysosomal and bactericidal properties via TGF‐β–activated kinase 1‐dependent activation of the transcription factor EB

“…TAK1 WT, and TAK1 K34R, K72R, and K209R mutants were kindly provided by Prof. Jianhua Yang (Dan L. Duncan Cancer Center, Baylor College of Medicine, Houston, TX, USA). of 20 mg/ml DQ-Red bovine serum albumin (BSA; Thermo Fisher Scientific, Waltham, MA, USA) for 30 min (22). Cells were then scraped from wells in PBS and analyzed for whole-cell fluorescence with the BD FACSCalibur flow cytometer (BD Biosciences, San Jose, CA, USA).…”

How can Tricyclic Sophoridinic Derivatives Be Used as Autophagy Inhibitors for Cancer Treatments?

“…In addition, sophoridinic ester IMB-6G promotes autophagosome accumulation from the early stage of treatment but blocks autophagic flux in the degradation stage, mainly through attenuation of lysosomal cathepsin activity in pancreatic cancer cells [16]. Compound IMB-6G caused LMP in pancreatic cancer cells after treatment for 12 h. Induction of LMP has been abundantly linked to cell death [17].…”