Synergistic effect of sequential administration of mitoguazone (MGBG) and gemcitabine in treating tissue cultured human breast cancer cells and mammary rat tumors.

Modulation of cancer chemotherapeutic drugs has been attempted to increase efficacy and overcome resistance to the chemotherapeutic agent. Studies have shown schedule-dependent interactions in combined use of chemotherapeutic drugs. Mitoguazone (MGBG), an old drug with possible modulating activity, was used in combination with gemcitabine, a relatively new cancer drug, in treating tissue cultured human breast cancer cells and mammary rat tumors. Tissue cultured BOT-2 cancer cells were first treated with varying concentrations of gemcitabine and MGBG, independently. Combinations of the two drugs were then used with different scheduled administrations. Marked synergistic activity was found between gemcitabine and MGBG when the MGBG was given first, followed by gemcitabine 24 hours later. A non-toxic dose of MGBG enhanced the toxicity of gemcitabine by eight orders of magnitude using MTT assays in the tissue cultured human breast cancer cell study. The sequential administration of MGBG and gemcitabine also increased the survival rate of rats bearing mammary tumors in our pilot animal study.