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A number of polyamine analogs are currently used in various clinical trials as cancer treatment and it is important to investigate their effects not only on cancer cells but also on normal cells. Treatment with polyamine analogs depletes cells of polyamines and inhibits cell proliferation, but the analogs cannot take over the normal function of the natural polyamines in the cell. In this study, the normal-like breast epithelial cell line MCF-10A was treated with the polyamine analog N',N"-diethylnorspermine (DENSPM). The cells were then studied using a bromodeoxyuridine- DNA flow cytometry method as well as western blot. The ability of both normal-like and breast cancer cells to recover from DENSPM treatment was also studied. DENSPM treatment of MCF-10A cells resulted in a prolongation of the S and G2 +M phases, followed by a G1/S block. The p53/p21/RB1 pathway was involved in the G1/S block as shown by increased levels of p53 and p21 detected by western blot. Decreased levels of cyclin E1, cyclin A2, and cyclin B1 in DENSPM-treated cells can explain the prolongation of cell cycle phases that occurred before the G1/S block. We also show that MCF-10A cells rapidly recover from DENSPM-induced growth inhibition in contrast to four human breast cancer cell lines. The goal of cancer treatment is to cause minimal and reversible damage to normal cells, while cancer cells should be eliminated. Altogether, the data show that treatment with polyamine analogs spares normal cells, while negatively affecting the cancer cells.

Combination of selecting agents that act on different cellular mechanisms is a common strategy in cancer chemotherapy. GL331 is a new potent topoisomerase II (Topo II) poison; distinctly, paclitaxel is a microtubule-interfering cancer chemotherapeutic agent. In this study, we intended to evaluate the efficacy of combining GL331 with paclitaxel in cell killing and apoptotic induction in nasopharyngeal carcinoma NPC-TW01 cells. By MTT and internucleosomal DNA cleavage assays, we found that pretreatment or simultaneous treatment of NPC-TW01 cells with GL331 could significantly interfere with paclitaxel's cell killing and apoptosis-inducing activity. When the administration schedule was reversed, the cytotoxicity of GL331 was attenuated by paclitaxel pretreatment. The anti-cancer activity produced by combining GL331 with paclitaxel was obviously lower than the addition of the activities of two individual agents. NPC-TW01 cells were treated with GL331 and 3H-labeled paclitaxel simultaneously or with GL331 before 3H-labeled paclitaxel. In both conditions, GL331 did not reduce the [3H]paclitaxel level in the cells, suggesting that GL331's interference with paclitaxel's cell-killing and apoptosis-inducing efficacy did not result from any inhibition of cellular uptake or retention of paclitaxel. In addition, we found that GL331-induced perturbation of cell cycle progression dramatically over-rode the patterns of mitotic arrest induced by paclitaxel, and the mechanism could be the inhibition of cyclin B1/CDC2 kinase and MAD2 checkprotein activities.

UCN-01 (7-hydroxystaurosporine) and CGP 41 251 (4'-N-benzoyl staurosporine), both of which were discovered as protein kinase C selective inhibitors, have entered in phase 1 clinical trials as anti-cancer drugs. In this study, we have directly compared the effects of these drugs as well as staurosporine (STP) on cell cycle progression of A431 human epidermoid carcinoma cells synchronized at M phase by treatment with nocodazole. The nocodazole-synchronized cells progressed from M to G1 phase in the absence of the drug, which was accompanied by a decrease of cyclin B1 protein expression, disappearance of the complex formation of CDC2 with cyclin B1 and reduction of the kinase activity. Treatments of the M phase cells with UCN-01, STP and CGP 41 251 at 80% growth-inhibitory concentrations (IC80S) resulted in specific G1 block, G2M block and polyploidy, respectively. Decreases of cyclin B1 protein expression was partially prevented by treatments with STP and CGP 41 251 but not with UCN-01 at IC80S. Reductions of active complex and kinase activity of CDC2/cyclin B1 were also observed in the presence of the three drugs. In addition, augmentation of CDC2 protein tyrosine phosphorylation was induced only when the cells were treated with STP. These observations demonstrated that higher concentrations of UCN-01, STP and CGP 41 251 showed different effects on cell cycle progression as well as CDC2/cyclin B1 regulation in A431 cells synchronized at M phase. The data suggest that UCN-01 and CGP 41 251 may act at quite different points on the cell cycle.