Figure 8.

Rapamycin suppresses the tumour-promoting activity of senescent cells. (a,b) Percentage of BPH1, M12 and PC3 prostate cancer cell migration (a) and invasion (b) was determined on co-culture with conditioned media from irradiated PSC27 fibroblasts that were treated with rapamycin (Rapa) or vehicle (control). The human cervical cancer line HeLa was used as a positive control in both experiments. (c) The indicated prostate epithelial cells were incubated with conditioned media from PSC27 human prostate fibroblasts, non-senescent (NS) or induced to senesce by irradiation (Sen (IR)), untreated or treated with rapamycin. Epithelial cell numbers were determined 3 days later. (d) PC3 prostate cancer cells were implanted subcutaneously with non-senescent (PSC27-NS) or senescent (ionizing radiation; PSC27-Sen (IR)) prostate fibroblasts that had been pretreated for 8 days in culture with DMSO or rapamycin. Tumour volumes were determined as described in the Methods (mean ± s.e.m., n = 8 animals). (e) Prostate cancer cell viability was determined by MTT assays following exposure to mitoxantrone for 72 h at twice the IC₅₀ dose for each cell line in the presence of conditioned media from non-senescent (PSC27-NS) or senescent (PSC27-Sen (IR)) PSC27 fibroblasts that were co-treated with rapamycin or vehicle. (f) In vivo effect of rapamycin on chemotherapy resistance was determined by injecting PC3 cancer cells with or without PSC27 prostate fibroblasts into SCID mice followed by treatment with mitoxantrone or vehicle and co-administration of rapamycin or vehicle. Tumour volumes were determined after an 8-week treatment period (mean ± s.e.m., n = 10 animals). For a–c and e shown is one representative of three independent experiments, each with triplicate cell culture samples. For d and f, a standard t-test served to determine P values. For raw data, see Supplementary Table 4.