Taxol reduces circulating tumor cells to prevent bone metastases in SCID mice

The correlative effects of taxol on the reduction of circulating PC-3 ML human prostatic tumor cells and bone metastasis have been examined in SCID mice. Normally, following injection of 2 x 10(5) cells i.v., the circulating levels in peripheral blood drop by about 50 and 100%, after 8 and 24 h, respectively. In contrast, in taxol-treated mice (40-60 mg/m2/injection given 0, 3, 7 and 23 h following injection of the cells) the numbers of circulating human prostatic PC-3 ML tumor cells were reduced by 100% at 8 h. In similar experiments were mice were injected with taxol 2 h prior to injecting the cells, dosages of 40 and 60 mg/m2/injection reduced circulating tumor cells about 91 and 100%, respectively, by 8 h. Alternatively, if PC-3 Ml cells were pretreated with taxol (0.5 and 1.0 microM for 8 and 24 h) prior to injection, tumor cell clearance by 7 h was also significantly increased (80-100%). Correlative studies showed that the incidence of bone metastases (observed after 40 days) was reduced significantly (a) in mice treated with 40 and 60 mg/m2/injection (i.e. from 73-80% in controls to 15-0% in treated mice) and (b) in mice injected with PC-3 ML cells pre-exposed to 0.5-1.0 microM taxol for 7 h. Immunofluorescence studies with tubulin antibodies showed that the microtubules were disrupted in cells exposed to taxol in vivo and in vitro under conditions that significantly increased cellular clearance from the blood. Taken together, the data suggests that taxol at nontoxic dosages (to mice) can prevent metastases by directly reducing the circulating levels of tumor cells.