Doxorubicin-enriched, ALDH^br Mouse Breast Cancer Stem Cells Are Sensitive To The Oncolytic Activity Of HSV1

Purpose:Cancer stem cells (CSCs) are responsible for resistance to conventional chemotherapy. The primary objective of the current investigation was to test the anticancer effect of oncolytic herpes simplex virus type1(HSV1) and whether it could eradicate CSCs left behind following chemotherapy. Anti-cancer effect of the combined therapy was evaluated for further clinical use.Methods:The fluorescent aldefluor reagent-based technique was used to identify and isolate ALDHbr CSCs from the4T1murine breast cancer cell line.4T1ALDHbr cells were compared with their correspondent ALDH10cells in the abilities of tumor sphere formation in vitro and tumorigenicity in vivo. The presence of ALDHbr4T1cells was also examined in4T1breast cancer transplanted in immune-competent syngeneic mice after different treatments. We further investigated the treatment modalities with respect to their overall anti-tumor effects in vivo.Results:In the bulk tumor cells, nearly13%were ALDHbr cells. Compared with ALDHlo cells, they had a markedly higher ability to form tumor spheres in vitro and higher tumorigenic potential in vivo. ALDHbr4T1cells exhibited increased resistance to doxorubicin in vitro, which correlated with a selective increase in the percentage of ALDHbr cells after doxorubicin treatment and increased expression of P-glycoprotein (P-gp), a known chemoresistance factor. However, the ALDHbr cells could be reduced uniformly in vitro and even more in vivo by oncolytic HSV1compared with ALDHlo cells. Furthermore, in in vivo studies, systemic administration of doxorubicin followed by intratumoral injection of oncolytic HSV1resulted in much more significant suppression of tumor growth with increased median survival period compared with each treatment given alone (p<0.05).Conclusion:Taken together, these results suggested that the use of oncolytic HSV1may eradicate general tumor cells and residual chemoresistant CSCs with similar efficacy. The treatment of4T1breast tumors with oncolytic HSV1following doxorubicin chemotherapy generated a better anticancer effect in vivo.