Objective      To investigate whether Huaier ointment

a paste based on Huaier aqueous extract

has the inhibitory or lethal effect on the stem cells derived from human breast cancer cell line SUM-159.       Methods      CCK-8 assay was used to determine IC

50

values of Huaier ointment. The morphological changes

colony forming ability and sphere forming ability were observed in SUM-159 cells before and after drug treatment at a dose of 0

1

10

and 100 mg/mL. The percentag

e of ALDH1

high

cells was detected by flow cytometry before and after administration.       Results       CCK-8 assay showed that IC

50

value of Huaier ointment in SUM-159 cells was approximately 10 mg/mL. After Huaier ointment were applied on SUM-159 cells at a dose of 0

1

and 10 mg/mL

the number of formed colonies was gradually reduced as the dose increased (

P

0.05)

and the number and size of cell spheres were also decreased (

P

0.05). The percentage of ALDH1

high

cells was decreased from 2.8% to 1.5% after the treatment of 10 mg/mL Huaier ointment

while the percentage was increased to 9.1% after the administration of 1 μg/mL paclitaxel.       Conclusion      Huaier ointment exerts significant inhibitory effect on the colony and sphere formation abilities of SUM-159 cells

and reduces the percentage of ALDH1

high

cells

which suggesting the agent might inhibit or kill breast cancer stem cells.