Taxanes represent a treatment of choice for metastatic breast cancer. Their combination with bevacizumab improved response rate and progression-free survival. We studied in vitro the effect on cell survival of the combination of either paclitaxel or nab-paclitaxel with bevacizumab and we investigated the biological factors involved in the response to treatments. We used two breast cancer cell lines, MCF7 (ER+/HER2-) and MDA-MB-231 (ER-/HER2-), co-cultured with or without HUVEC cells. We analysed cell survival by MTT test, VEGF secretion by ELISA and VEGFR, SPARC, MDR1 expression by western blot. Doses of both taxanes causing a 50 % growth inhibition were higher in MCF7 than MDA-MB-231, suggesting that taxanes are more effective in ER- cell lines. When both cell lines were grown as single culture, the combination bevacizumab+paclitaxel showed a similar anti-proliferative effect compared to paclitaxel alone. The association bevacizumab+nab-paclitaxel was more effective than nab-paclitaxel alone. An increased anti-proliferative effect of bevacizumab+paclitaxel was observed when MDA-MB-231 cells were cultured with HUVEC. We detected an induction of VEGF secretion when MDA-MB-231 cells were treated with either taxanes. Paclitaxel caused a reduction of VEGF in MCF7. SPARC resulted up-regulated in both cell lines treated with bevacizumab+nab-paclitaxel. Nab-paclitaxel seems to play an important role in inhibiting tumor proliferation through albumin-SPARC bound in association with bevacizumab compared to taxanes alone in both breast cancer cells. The addition of bevacizumab to paclitaxel increased its activity only in ER- cells. This difference might be due to their ER status.
