Depletion of cellular polyamines by α-difluoromethylornithine increases 1,3-bis(20chloroethyl)-1-nitrosourea-induced sister-chromatid exchanges

Abstract

Treatment of cells with α-difluoromethylornithine (DFMO), which leads to the intracellular depletion of the polyamnes putrescine and spermidine, is known to increase the cell kiling induced by the DNA cross-linking chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU0. This has been attributed to a change in DNA conformation that is related to the intracellular polyamine content and a concomitant change in accessibility of BCNU to reactive sites in DNA. Cytogenetic experiments were previously carried out showin that DFMO pretreatment also increased sister chromatid exchanges (SCEs) induced by BCNU. Subsequently, there was difficulty in repeating this phenomenon, which led to retraction of the results. More recent information indicates, however, that a change in protocol occurred between the time of the original experiments and the repeat experiments. Because cell killing by genotoxic agents, such as X-rays, can be related to cytogenetic damage, and agents that cause deformation of DNA do leads to SCEs, experiments have now been carried out to see whether or not the subtle deformation caused by polyamine depletion could, indeed, lead to the induction of increased SCEs by BCNU, as had been originally postulated. When the experiments were carried out with the original protocols, pretreatment with DFMO did increase BCNU-induced SCEs. Modification of the protocols, especially washing of the cells before the addition of BCNU, which reduces the toxicity, reduced the DFMO effect and in some experiments even obliterated it.