Notch signaling regulates normal stem cells and is also thought to regulate cancer stem cells (CSCs). Recent data indicate that Notch signaling plays a role in the development and progression of
osteosarcoma, however the regulation of Notch in chemo-resistant stem-like cells has not yet been fully elucidated. In this study we generated
cisplatin-resistant
osteosarcoma cells by treating them with sub-lethal dose of
cisplatin, sufficient to induce DNA damage responses.
Cisplatin-resistant
osteosarcoma cells exhibited lower proliferation, enhanced spheroid formation and more mesenchymal characteristics than
cisplatin-sensitive cells, were enriched for Stro-1+/CD117+ cells and showed increased expression of stem cell-related genes. A similar effect was observed in vivo, and in addition in vivo tumorigenicity was enhanced during serial
transplantation. Using several publicly available datasets, we identified that Notch expression was closely associated with
osteosarcoma stem cells and
chemotherapy resistance. We confirmed that
cisplatin-induced enrichment of
osteosarcoma stem cells was mediated through Notch signaling in vitro, and immunohistochemistry showed that cleaved Notch1 (NICD1) positive cells were significantly increased in a relapsed xenograft which had received
cisplatin treatment. Furthermore, pretreatment with a γ-
secretase inhibitor (GSI) to prevent Notch signalling inhibited
cisplatin-enriched
osteosarcoma stem cell activity in vitro, including Stro-1+/CD117+ double positive cells and spheroid formation capacity. The Notch inhibitor
DAPT also prevented
tumor recurrence in resistant xenograft
tumors. Overall, our results show that
cisplatin induces the enrichment of
osteosarcoma stem-like cells through Notch signaling, and targeted inactivation of Notch may be useful for the elimination of CSCs and overcoming drug resistance.