Aldehyde dehydrogenase activity in cancer stem cells from canine mammary carcinoma cell lines

Increasing evidence suggests that diverse solid tumours arise from a small population of cells known as cancer stem cells or tumour-initiating cells. Cancer stem cells in several solid tumours are enriched for aldehyde dehydrogenase (ALDH) activity. High levels of ALDH activity (ALDHhigh) were detected in four cell lines derived from canine mammary carcinomas. ALDHhigh cells were enriched in a CD44+CD24− population having self-renewal capacity. Xenotransplantation into immunodeficient mice demonstrated that 1 × 104 ALDHhigh cells were sufficient for tumour formation in all injected mice, whereas 1 × 104 ALDHlow cells failed to initiate any tumours. ALDHhigh-derived tumours contained both ALDH+ and ALDH− cells, indicating that these cells had cancer stem cell-like properties.