The enhancement by caffeine of alkylation-induced cell death, mutations and chromosomal aberrations in Chinese hamster cells, as a result of inhibition of post-replication DNA repair

Abstract

Summary It can be convincingly argued that alkylation of DNA is a causal event in the death of alkylated mammalian cells. However, there are numerous chemical, biochemical and biological observations which indicate that mammalian cells can recover from the otherwise lethal effects of DNA alkylations which therefore implies the existence of a mechanism for repairing alkylation lesions in mammalian cell DNA. Various indications of “excision” or “cut and patch” repair can be detected in mammalian cells following alkylation by both mono- and difunctional alkylating agents. However, manifestations of excision repair do not correlate with the sensitivities of different cell types to various chemical agents, which suggests that an alternative DNA repair mechanism is also present in mammalian cells. Evidence has been adduced that this could be related to that proposed for the repair of UV-irradiation damage to DNA, in which lesions are by-passed during DNA replication. Caffeine has been found to potentiate the lethal action of alkylating agents and it appears that this results from inhibition of this proposed alternative form of DNA repair. MNU has been found to increase the yield of mutations to 8-azaguanine resistance in Chinese hamster cells and the relationships between the increase in induced mutation frequency and the extent of methylation of DNA and the effect of MNU, on cellsurvival, have been determined. Mutations were only observed with concentrations of MNU which produced some cell killing. Caffeine increased the alkylation-induced mutation frequency in a manner which did not support the concept that caffeine inhibits an error-prone repair mechanism. The number of MNU-induced chromosomal aberrations in Chinese hamster cells has been found to be dramatically increased when alkylated cells were grown subsequently in medium containing a non-toxic concentration of caffeine, which on its own failed to produce any chromosomal damage. It is proposed therefore that there are common steps in the repair of alkylation damage to cellular DNA which is responsible for the lethal, mutagenic and chromosomal effects of alkylating agents in mammalian cells. Moreover it seems likely that the common mechanism involves the repair of post-replication lesions in DNA.