MATERIALS AND METHODS: Four human
breast cancer cell lines (MDA-MB-231, MCF-7, Hs578t, and T47D) and one immortalized, non-tumorigenic mammary epithelial cell line (MCF-10A) were used for in vitro combination studies with
BENSpm and cytotoxic drugs. Xenograft mice models generated with MDA-MB-231 cells were used for in vivo studies with
BENSpm and
paclitaxel.
RESULTS AND CONCLUSION:
BENSpm exhibited synergistic inhibitory effect on cell proliferation in combination with
5-FU or
paclitaxel in human
breast cancer cell lines (MDA-MB-231 and MCF-7) and was either antagonistic or less effective in the non-tumorigenic MCF-10A cell line. Synergism was highest with 120 h concomitant treatment or pre-treatment with
BENSpm for 24 h followed by concomitant treatment for 96 additional hours. Since the cytotoxic effects of many
polyamine analogues and
cytotoxic agents are believed to act, in part, through induction of the
polyamine catabolic
enzymes SSAT and SMO, the role of these
enzymes on synergistic response was evaluated in MDA-MB-231 and MCF-7 treated with
BENSpm and
5-FU or
paclitaxel. Combination treatments of
BENSpm with
5-FU or
paclitaxel resulted in induction of SSAT
mRNA and activity in both cell lines compared to either
drug alone, while SMO
mRNA and activity were increased only in MDA-MB-231 cells. Induction was greater with
BENSpm/
paclitaxel combination than
BENSpm/5-FU. Further, RNAi studies demonstrated that both SSAT and SMO play a significant role in the response of MDA-MB-231 cells to treatment with
BENSpm and
5-FU or
paclitaxel. In MCF-7 cells, only SSAT appears to be involved in the response to these treatments. In an effort to translate combination studies from in vitro to in vivo, and to form a basis for clinical setting, the in vivo therapeutic efficacy of
BENSpm alone and in combination with
paclitaxel on
tumor regression was evaluated in xenograft mice models generated with MDA-MB-231 cells. Intraperitoneal exposure to
BENSpm or
taxol singly and in combination for 4 weeks resulted in significant inhibition in
tumor growth. These findings help elucidate the mechanisms involved in synergistic
drug response and support combinations of
polyamine analogues with chemotherapeutic agents which could potentially be used in the treatment of
breast cancer.