Inhibitory effect of CM on tumor cell proliferation correlates with Aβ concentrations in the CM. (A, B) 36 hr-, 60 hr- and 84 hr-CM from 7W, SKAPP, SW293 and CHO, SH-SY5Y, HEK293 cells were collected, and Aβ40 and Aβ42 concentrations were measured by ELISA. Much more Aβ40 (A) and Aβ42 (B) were produced by 7W, SKAPP and SW293 cells than their wild type parental cells (P < 0.05). The Aβ40 and Aβ42 concentrations in the SW293-CM were significantly higher than those in 7W-CM and SKAPP-CM(P < 0.05). All values represent means ± SEM (n = 12). (C) Relative levels of Aβ generated from each cell line were illustrated, based on the actual levels of Aβ (A, B). (D) Representative images from MDA-MB231-L cell cultured with 36 hr, 60 hr and 84 hr- CM from 7W/CHO, SKAPP/SH-SY5Y and SW293/HEK293 cells. (E, F) Persistent inhibitory effect of SW293-CM on MDA-MB231-L and B16F-L cells proliferation. The proliferation of the MDA-MB231-L and B16F-L cells were measured by BLI assay at 24, 48 and 72 hr post medium replacement. All values indicate means ± SEM (n = 6), and the difference between SW293 and control HEK293 cells is statistically significant, as indicated by *, P < 0.05.