title: Progression of chromosomal damage induced by etoposide in G2 phase in a DNA-PKcs-deficient context.
abstract: Etoposide (ETO), a drug used for the treatment of human tumors, is associated with the development of secondary malignancies. Recently, therapeutic strategies have incorporated chemosensitizing agents to improve the tumoral response to this drug. ETO creates DNA double-strand breaks (DSB) via inhibition of DNA topoisomerase II (Top2). To repair DSB, homologous recombination (HR) and non-homologous end-joining (NHEJ), involving D-NHEJ (dependent of the catalytic subunit of DNA-dependent protein kinase, DNA-PKcs) and B-NHEJ (backup repair pathway) are activated. We evaluated the progression of the DNA damage induced by the Top2 poison ETO in G2 phase of human HeLa cells after chemical inhibition of DNA-PKcs with NU7026. Compared to ETO treatment alone, this combined treatment resulted in a twofold higher rate of chromatid breaks and exchanges when analysis was performed in the following metaphase. Moreover, when analysis was performed in the second metaphase following treatment, increases in the percentage of micronuclei with H2AX (biomarker for DSB) foci in binucleated cells and dicentric chromosomes were seen. In post-mitotic G1 phase, a close association between unresolved DSB and meiotic recombination 11 homolog A (MRE11) signals was observed, demonstrating the contribution of MRE11 in the DSB repair by B-NHEJ. Hence, chemical inhibition of DNA-PKcs impaired both D-NHEJ and HR repair pathways, altering the maintenance of chromosomal integrity and cell proliferation. Our results suggest that the chemosensitizing effectiveness of the DNA-PKcs inhibitor and the survival rate of aberrant cells may contribute to the development of therapy-related tumors.
authors.affiliation: Laboratorio de Mutagénesis, Instituto de Medicina Experimental, IMEX-CONICET, Academia Nacional de Medicina, J. A. Pacheco de Melo 3081, 1425, Buenos Aires, Argentina.
authors.forename: Micaela
authors.initials: M
authors.lastname: Palmitelli
authors.affiliation: Laboratorio de Mutagénesis, Instituto de Medicina Experimental, IMEX-CONICET, Academia Nacional de Medicina, J. A. Pacheco de Melo 3081, 1425, Buenos Aires, Argentina.
authors.forename: Marcelo
authors.initials: M
authors.lastname: de Campos-Nebel
authors.affiliation: Laboratorio de Mutagénesis, Instituto de Medicina Experimental, IMEX-CONICET, Academia Nacional de Medicina, J. A. Pacheco de Melo 3081, 1425, Buenos Aires, Argentina. margoncid@hematologia.anm.edu.ar.
authors.forename: Marcela
authors.initials: M
authors.lastname: González-Cid
mesh_terms: D000972:Antineoplastic Agents, Phytogenic / Q000633:toxicity*; D002869:Chromosome Aberrations / Q000139:chemically induced*; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D059766:DNA End-Joining Repair / Q000187:drug effects; D051747:DNA-Activated Protein Kinase / Q000172:deficiency*; D004268:DNA-Binding Proteins / Q000378:metabolism; D005047:Etoposide / Q000633:toxicity*; D016195:G2 Phase / Q000187:drug effects* / Q000235:genetics*; D015321:Gene Rearrangement; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism; D059765:Homologous Recombination; D006801:Humans; D000076228:MRE11 Homologue Protein; D008940:Mitotic Index; D011485:Protein Binding; D051135:Rad51 Recombinase / Q000378:metabolism; D012854:Sister Chromatid Exchange / Q000235:genetics
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D004268:DNA-Binding Proteins; D006657:Histones; C121766:MRE11 protein, human; D005047:Etoposide; D051747:DNA-Activated Protein Kinase; D051135:Rad51 Recombinase; D000076228:MRE11 Homologue Protein
keywords: DNA damage; DNA-PKcs chemical inhibition; DSB repair pathway; G2 phase; Topoisomerase II poison