FIG 7.

XBP1-overexpressing tumors are resistant to tamoxifen in human breast cancer cell xenografts. (A) XBP1(S)-, XBP1(U)-ES48-, or LacZ control-overexpressing MCF-7 cells (2 × 10⁶) were injected into the mammary fat pad of athymic nude mice, and tumors were measured weekly. The graph shows the average tumor volumes at weeks 1 to 3 after tumor injection. (B) Xenografts were harvested at necropsy, and tumor lysates were obtained and subjected to Western blot hybridization with the antibodies indicated. (C) After any tumor in an animal reached 6 mm in diameter, that animal was randomly assigned to a group and treated with either the tamoxifen diet or parthenolide injection, or both; animals receiving a diet without tamoxifen or administered ethanol injections served as controls. After randomization, each group contained 4 to 8 animals; two tumor inoculation sites were used for each animal. Day 0 was taken as the day that drug treatment started. Once treatments started, tumor sizes were measured twice weekly. Data represent the mean tumor volumes in each group. *, P < 0.05; **, P < 0.01. For the Western blots, representative images from three independent experiments are shown.