Effects of methylacetylenic putrescine, an ornithine decarboxylase inhibitor and potential novel anticancer agent, on human and mouse cancer cell lines

Sensitivity of several human and mouse cancer cell lines to methylacetylenic putrescine (MAP) was evaluated using clonogenic, sulforhodamine B and cell counting assays. The effects of MAP on cell morphology, cell cycle phase distribution and changes in polyamine metabolism of xenografted MCF-7 and MDA-MB-231 human mammary tumor cells were also investigated. On the basis of IC50 values, BHT-101 human thyroid carcinoma cells were the most sensitive (9 micrograms/ml), followed by P388 mouse lymphoma (32 micrograms/ml), MCF-7 (48 micrograms/ml) and MDA-MB-231 (110 micrograms/ml) human breast carcinoma cell lines. MAP treatment led to accumulation of P388 cells in G1 phase. At higher doses, the cytoplasm of the cells became vacuolated followed by apoptosis. The foamy cytoplasm may suggest a rare type of cell death (Clarke III type) called non-apoptotic programmed cell death. MAP treatment resulted in a total inhibition of ornithine decarboxylase (ODC) activity with a concomitant decrease of intracellular polyamine (mostly putrescine and spermidine) content in the breast cancer cells, whilst the spermine concentration was shown to increase. MAP proved at least 10 times more potent than the formerly studied DL-alpha-difluoromethylornithine making it an attractive candidate for clinical testing.