OBJECTIVETo investigate the effect and explore its possible mechanisms of epidermal growth factor receptor(EGFR) expression in macrophages on the anti-cancer effect of berberine (BER) on the growth of colorectal cancer.

METHODSMice with EGFR gene defects in macrophages (Egfr(fl/fl) LysM-Cre) and with EGFR gene expression in macrophages (LysM-Cre) (control group) were treated with azoxymethane (AOM) to establish colorectal tumor models. These models were treated with or without berberine (BER) intervention. The number of colorectal tumors and the gut length in the two groups were measured. The proliferation of tumor cells was detected by Ki-67 immunohistochemistry and apoptosis was detected by annexin V-FITC fluorescence labeling. Western blot was used to detect the expression of cleaved-caspase-3 protein.

RESULTSAfter treated with AOM, the colorectal tumor number was 10.26 ± 1.43 in the LysM-Cre group and 7.62 ± 1.05 in the Egfr(fl/fl) LysM-Cre group, showing a significant difference (P = 0.021). The gut length was (6.04 ± 1.06) cm in the LysM-Cre group and (6.39 ± 0.92) cm in the gfrfl/flLysM-Cre group, with a non-significant difference between the two groups (P = 0.075). After treated with AOM plus BER intervention, the colorectal tumor number of the LysM-Cre group was 8.35 ± 1.22 and that in the Egfr(fl/fl) LysM-Cre group was 2.66 ± 0.38, showing a very significant difference between the two groups (P = 0.006). The gut length of the LysM-Cre group was (7.34 ± 1.16) cm and that of the Egfr(fl/fl) LysM-Cre group was (10.01 ± 1.72) cm (P = 0.028). After treated with AOM, the ratio of Ki-67-positive tumor cells in the LysM-Cre group was (78.31 ± 3.43)% and that in the Egfr(fl/fl) LysM-Cre group was (75.85 ± 2.92)% (P = 0.282). After AOM plus BER treatment, the ratio of Ki-67-positive tumor cells in the LysM-Cre group was (42.43 ± 3.09)% and that in the Egfr(fl/fl) LysM-Cre group was significantly lower (29.65 ± 2.47)% (P = 0.018). The ratio of annexin V-positive tumor cells was (0.95 ± 0.13)% in the LysM-Cre group, not significantly different from (1.13 ± 0.16)% in the Egfr(fl/fl) LysM-Cre group (P = 0.175). After AOM plus BER treatment, the ratio of annexin V-positive tumor cells in the LysM-Cre group was (32.10 ± 1.97)%, significantly lower than the (47.08 ± 2.83)% in the Egfr(fl/fl) LysM-Cre group (P = 0.010). The level of cleaved-caspase-3 protein expression was 235.92 ± 19.73 in the Egfr(fl/fl) LysM-Cre group, significantly higher than the 119.71 ± 12.87 in the LysM-Cre group (P = 0.012).

CONCLUSIONSThe growth of colorectal cancer cells in mice can be inhibited by BER treatment, and this anti-cancer effect of BER can be further enhanced by EGFR gene knockout in macrophages. The mechanisms may be related to the inhibition of proliferation and promotion of apoptosis in colorectal cancer cells.