title: Prolonged cell cycle response of HeLa cells to low-level alkylation exposure.
abstract: Alkylation chemotherapy has been a long-standing treatment protocol for human neoplasia. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) is a direct-acting monofunctional alkylator. Temozolomide is a clinical chemotherapeutic equivalent requiring metabolic breakdown to the alkylating agent. Both chemicals have similar mechanistic efficacy against DNA mismatch repair-proficient tumor cells that lack expression of methylguanine methyltransferase. Clinically relevant concentrations of both agents affect replicating cells only after the first cell cycle. This phenomenon has been attributed to replication fork arrest at unrepaired O(6)-methyldeoxyguanine lesions mispaired with thymine during the first replication cycle. Here, we show, by several different approaches, that MNNG-treated tumor cells do not arrest within the second cell cycle. Instead, the population slowly traverses through mitosis without cytokinesis into a third cell cycle. The peak of both ssDNA and dsDNA breaks occurs at the height of the long mitotic phase. The majority of the population emerges from mitosis as multinucleated cells that subsequently undergo cell death. However, a very small proportion of cells, <1:45,000, survive to form new colonies. Taken together, these results indicate that multinucleation within the third cell cycle, rather than replication fork arrest within the second cell cycle, is the primary trigger for cell death. Importantly, multinucleation and cell death are consistently avoided by a small percentage of the population that continues to divide. This information should prove clinically relevant for the future design of enhanced cancer chemotherapeutics.
authors.affiliation: Department of Biochemistry and Cancer Biology, University of Toledo College of Medicine, Toledo, Ohio 43614, USA.
authors.forename: Allen G
authors.initials: AG
authors.lastname: Schroering
authors.forename: Anbarasi
authors.initials: A
authors.lastname: Kothandapani
authors.forename: Steve M
authors.initials: SM
authors.lastname: Patrick
authors.forename: Saravanan
authors.initials: S
authors.lastname: Kaliyaperumal
authors.forename: Vishal P
authors.initials: VP
authors.lastname: Sharma
authors.forename: Kandace J
authors.initials: KJ
authors.lastname: Williams
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D016203:CDC2 Protein Kinase; D002453:Cell Cycle / Q000187:drug effects* / Q000235:genetics; D019926:Cyclin B / Q000378:metabolism; D018844:Cyclin-Dependent Kinases; D053843:DNA Mismatch Repair; D015254:DNA Modification Methylases / Q000172:deficiency; D045643:DNA Repair Enzymes / Q000172:deficiency; D004305:Dose-Response Relationship, Drug; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D008769:Methylnitronitrosoguanidine / Q000494:pharmacology*; D010766:Phosphorylation; D025521:Tumor Suppressor Proteins / Q000172:deficiency
chemical_list: D018906:Antineoplastic Agents, Alkylating; D019926:Cyclin B; D006657:Histones; D025521:Tumor Suppressor Proteins; D008769:Methylnitronitrosoguanidine; D015254:DNA Modification Methylases; C515491:MGMT protein, human; D016203:CDC2 Protein Kinase; C528899:CDK1 protein, human; D018844:Cyclin-Dependent Kinases; D045643:DNA Repair Enzymes