Indirubin 3'-Epoxide Induces Caspase-Independent Cell Death in Human Neuroblastoma
Masahiro Kurita1, Satoshi Hanada, Yoshimi Ichimaru
1School of Pharmacy, Nihon University.
Abstract:
Indirubin inhibits cyclin-dependent kinases by binding to their ATP-binding site, thereby exerting potent cytotoxicity on some tumor cells. We examined the anti-tumor effect of indirubin 3'-epoxide on human neuroblastoma cell lines (IMR-32, SK-N-SH, and NB-39). The results revealed potent cytotoxicity of indirubin 3'-epoxide against the IMR-32 (IC50: 0.16 µM) and SK-N-SH (IC50: 0.07 µM) cells. Furthermore, it also induced an increase of the sub-G1 population in the IMR-32 cells. Examination by Hoechst 33342 staining revealed apoptosis characterized by cell shrinkage, nuclear condensation and nuclear fragmentation in a concentration-dependent manner. Furthermore, annexin V-propidium iodide (PI) double-staining revealed an increase in the percentage of early apoptotic cells following treatment of the cells with indirubin 3'-epoxide without activation of caspases. In addition, significant decreases in the protein level of survivin and poly(ADP-ribose)polymerase (PARP), and increase in that of apoptosis-inducing factor (AIF) were found in the nuclei of the cells. These results suggest that indirubin 3'-epoxide induced caspase-independent apoptosis through mechanisms involving DNA fragmentation and inhibition of DNA repair.
Insights
Indirubin 3'-epoxide shows strong anti-tumor effects against neuroblastoma cells by inducing apoptosis. This compound triggers programmed cell death independently of caspases, offering a potential new therapeutic strategy.
Area of Science:
- Pharmacology
- Molecular Biology
- Oncology
Background:
- Indirubin derivatives are known to inhibit cyclin-dependent kinases, leading to cytotoxicity in tumor cells.
- Neuroblastoma is a pediatric cancer with a need for effective therapeutic agents.
Purpose of the Study:
- To investigate the anti-tumor activity of indirubin 3 '-epoxide on human neuroblastoma cell lines.
- To elucidate the mechanism of cell death induced by indirubin 3 '-epoxide.
Main Methods:
- Cytotoxicity assays (IC50 determination) on IMR-32, SK-N-SH, and NB-39 neuroblastoma cells.
- Cell cycle analysis (sub-G1 population) and Hoechst 33342 staining for apoptosis.
- Annexin V-propidium iodide (PI) double-staining and Western blot analysis for apoptotic markers (survivin, PARP, AIF).
Main Results:
- Indirubin 3 '-epoxide exhibited potent cytotoxicity against IMR-32 (IC50: 0.16 µM) and SK-N-SH (IC50: 0.07 µM) cells.
- Apoptosis was observed, characterized by morphological changes and increased early apoptotic cells, independent of caspase activation.
- Decreased levels of survivin and PARP, and increased AIF were detected in the nuclei.
Conclusions:
- Indirubin 3 '-epoxide induces caspase-independent apoptosis in neuroblastoma cells.
- The mechanism involves DNA fragmentation and inhibition of DNA repair pathways.
- Indirubin 3 '-epoxide demonstrates potential as an anti-neuroblastoma agent.
