Purpose: The novel indirubin derivatives 5-nitro-5'-hydroxy- indirubinoxime (5-OH-NIO) was designed and tested for antitumor activity both in vitro and in vivo using breast cancer cell lines, MDA-MB-231 cells.
METHODS: Cell viability was examined by MTT assay. To examine apoptotic cell death, Annexin V/PI staining for flow cytometry and Western blot analysis and DAPI staining were performed. Necrotic cell death was determined by leakage of lactate dehydrogenase (LDH), HMGB1, and PI staining in 5-OH-NIO-treated MDA-MB-231 cells.
Six-week-old male nude mice were inoculated s.c. on the right flank with MDA-MB-231 cells. Indirubin derivatives were directly injected into the tumor every other day. Animals were monitored daily and tumor volume was measured by caliper.
Results: Indirubin derivatives showed potent antiproliferative activity on various human cancer cells. 5-OH-NIO inhibited cells proliferation in a dose dependent manner. The ratio of annexin V-positive cells and cleaved caspase-3/7 was increased by 5-OH-NIO treatment in MDA-MB-231 cells, suggesting that 5-OH-NIO induced cell death in MDA-MB-231 cells may be owing to apoptosis. In addition, LDH secretion and PI staining were detected in MDA-MB-231 cells treated with 5-OH-NIO, showing that 5-OH-NIO also induced necrotic cell death in the MDA-MB-231 cells. The inhibitory effect of 5-OH-NIO on tumor growth was confirmed by in vivo tumor xenograft model. 5-OH-NIO induced significant inhibition of tumor growth in nude mice bearing MDA-MB-231-induced tumors.
Conclusions: These data showed that novel indirubin derivatives 5-OH-NIO arrested the tumor growth by inhibiting cell proliferation and inducing apoptosis and necrosis. These findings provide the potential value of indirubin derivatives as novel candidates for antitumor agents.