Objective To investigate the effect of metformin on ALDH1 expression in pancreatic cancer cells and pancreatic cancer stem cells, and explore its mechanism.

Methods PANC-1 cells were used to detect the inhibition rate and the expression levels of ALDH1 and p-mTOR by CCK-8 and Western blot after the intervention of metformin in different concentrations, respectively. Rapamycin is an inhibitor of mTOR; Western blot, immunofluorescence and qRT-PCR were employed to detect the protein expression and mRNA level of ALDH1, 4EBP1, p-mTOR among metformin group, rapamycin group and combination group. We used ultra low adhesion culture plate to culture PANC-1 cell, the number of spheroid body cells were observed and the expression of ALDH1 protein level were detected by Western blot in pancreatic cancer stem cells. The tumorigenicability between pancreatic cancer cells and spheroid body cells were compared by establishing nude mouse transplantation tumor model of pancreatic cancer.

Results Metformin could inhibit the proliferation of PANC1 along with the increase of treatment time and metformin concentrations, the optimal concentration and respond time of metformin were 20mmol/L and 48h; Compared with control group, the protein expression and mRNA level of ALDH1, 4EBP1 and p-mTOR among metformin group, rapamycin group and combination group were suprressed significantly (P < 0.05). The tumorigenic potential in spheroid body cells was significantly higher than that in parental cells; Compared with control group, the tumor sphere forming capability and the expression of ALDH1 in pancreatic cancer stem cells were inhibited among metformin group, rapamycin group and combination group (P < 0.05).

Conclusion Metformin and rapamycin significantly inhibit the expression of ALDH1 in pancreatic cancer PANC-1 cells and pancreatic cancer stem cells, and the mechanism may be through suprressing mTOR pathway.