Treatment with inhibitors of polyamine biosynthesis, which selectively lower intracellular spermine, does not affect the activity of alkylating agents but antagonizes the cytotoxicity of DNA topoisomerase II inhibitors

Abstract

Summary Inhibitors of ornithine decarboxylase (ODC), such as a-difluoromethylornithine (DFMO), may influence the cytotoxicity of anti-tumour agents that interact with DNA. Intracellular levels of putrescine and spermidine were markedly reduced by ODC inhibitors while the level of spermine, which is the main polyamine in nuclei, was unchanged. By combining a novel inhibitor of ODC, such as (2R, 5R)-6-heptyne-2,5-diamine (MDL 72.175, MAP), with an inhibitor of S-adenosylmethionine decarboxylase (SAMDC), such as 5'-{[(Z)-4-aminobut-2-enyl]methylamino}-5'-deoxyadenosine (MDL 73.81 1, AbeAdo), spermine was selectively depleted in a human ovarian cancer cell line OVCAR-3 (i.e. spermine became almost undetectable whereas the levels of spermidine and putrescine were not affected). The . The addition of spermine before drug treatment restored the sensitivity to the DNA topoisomerase 11 inhibitors, thus indicating that the reduced effect was related to the intracellular spermine level. The reason for the reduction in cytotoxicity is unclear, but it does not appear to be related to a cell cycle effect or to a decrease in the intracellular level of DNA topoisomerase 11. Drugs that modify polyamine biosynthesis are under early clinical development as potential new anti-tumour agents. These findings illustrate the need for caution in combining such drugs with DNA topoisomerase 11 inhibitors.

Topoisomerase II is nonfunctional in polyamine-depleted cells

“…These results are supported by a number of studies, although none of those has directly estimated the topo II function in the cell [Dorr et al, 1986;Bakic et al, 1987;Desiderio et al, 1997]. The cytotoxicity of etoposide was found to be significantly lower in polyamine biosynthesis inhibitor-treated cells compared with control cells, as determined by colony forming efficiency assay [Desiderio et al, 1997]. Using Western blot, Desiderio and colleagues found that the enzyme protein level was not affected by the polyamine biosynthesis inhibitor treatment.…”

“…Taken together, these results show that the function of topo II in the cell was severely affected by polyamine depletion while the enzyme itself was not directly affected as reflected by the lack of difference in kDNA cleaving activity in crude nuclear extracts from the different treatment groups. These results are supported by a number of studies, although none of those has directly estimated the topo II function in the cell [Dorr et al, 1986;Bakic et al, 1987;Desiderio et al, 1997]. The cytotoxicity of etoposide was found to be significantly lower in polyamine biosynthesis inhibitor-treated cells compared with control cells, as determined by colony forming efficiency assay [Desiderio et al, 1997].…”

“…Our results imply that although present in the cell, topo II was less functional in polyamine-depleted cells, resulting in an insensitivity to etoposide. Desiderio et al [1997] have also speculated that a lowered cytotoxicity of etoposide in polyamine-depleted cells may be caused by changes in chromatin structure. Our results suggest that both spermine and spermidine have an important role in maintaining the chromatin structure in an optimal configuration for the function of topo II.…”

“…Polyamine biosynthesis inhibitors have indirectly been shown to affect topo II in cells in culture [Dorr et al, 1986;Bakic et al, 1987;Desiderio et al, 1997]. However, in none of these studies has the function of topo II in DNA cleavage in the cell been investigated.…”

The role of the polyamine catabolic enzymes SSAT and SMO in the synergistic effects of standard chemotherapeutic agents with a polyamine analogue in human breast cancer cell lines

“…In fact, polyamine analogues were found to result in DNA strand breaks [42], inhibit nucleosome formation in cell-free systems and alter the structure of chromatin and influence gene expression in cellular systems [2, 3, 27, 65]. Based on the hypothesis that polyamine analogues can synergize with standard DNA-reactive cytotoxic drugs, several studies evaluated the combination of chemotherapeutic agents with either polyamine analogues or drugs targeting the polyamine metabolic pathway [16, 22, 25, 33, 43, 47, 61, 63, 64, 68, 77]. The findings from these studies overall were mixed with results being agent-, schedule-, and cell-line-dependent.…”