title: Human monocytes undergo excessive apoptosis following temozolomide activating the ATM/ATR pathway while dendritic cells and macrophages are resistant.
abstract: Immunodeficiency is a severe therapy-limiting side effect of anticancer chemotherapy resulting from sensitivity of immunocompetent cells to DNA damaging agents. A central role in the immune system is played by monocytes that differentiate into macrophages and dendritic cells (DCs). In this study we compared human monocytes isolated from peripheral blood and cytokine matured macrophages and DCs derived from them and assessed the mechanism of toxicity of the DNA methylating anticancer drug temozolomide (TMZ) in these cell populations. We observed that monocytes, but not DCs and macrophages, were highly sensitive to the killing effect of TMZ. Studies on DNA damage and repair revealed that the initial DNA incision was efficient in monocytes while the re-ligation step of base excision repair (BER) can not be accomplished, resulting in an accumulation of DNA single-strand breaks (SSBs). Furthermore, monocytes accumulated DNA double-strand breaks (DSBs) following TMZ treatment, while DCs and macrophages were able to repair DSBs. Monocytes lack the DNA repair proteins XRCC1, ligase IIIα and PARP-1 whose expression is restored during differentiation into macrophages and DCs following treatment with GM-CSF and GM-CSF plus IL-4, respectively. These proteins play a key role both in BER and DSB repair by B-NHEJ, which explains the accumulation of DNA breaks in monocytes following TMZ treatment. Although TMZ provoked an upregulation of XRCC1 and ligase IIIα, BER was not enhanced likely because PARP-1 was not upregulated. Accordingly, inhibition of PARP-1 did not sensitize monocytes, but monocyte-derived DCs in which strong PARP activation was observed. TMZ induced in monocytes the DNA damage response pathways ATM-Chk2 and ATR-Chk1 resulting in p53 activation. Finally, upon activation of the Fas-receptor and the mitochondrial pathway apoptosis was executed in a caspase-dependent manner. The downregulation of DNA repair in monocytes, resulting in their selective killing by TMZ, might impact on the immune response during cancer chemotherapy.
authors: Department of Toxicology, University Medical Center, Mainz, Germany.
authors: Martina
authors: M
authors: Bauer
authors: Michael
authors: M
authors: Goldstein
authors: Daniel
authors: D
authors: Heylmann
authors: Bernd
authors: B
authors: Kaina
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D064007:Ataxia Telangiectasia Mutated Proteins; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects; D000071877:Checkpoint Kinase 1; D064447:Checkpoint Kinase 2; D053903:DNA Breaks, Double-Stranded / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism*; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D003713:Dendritic Cells / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D006657:Histones / Q000378:metabolism; D006801:Humans; D008264:Macrophages / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D009000:Monocytes / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D000077204:Temozolomide; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D019014:fas Receptor / Q000378:metabolism
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C468783:H2AX protein, human; D006657:Histones; D000067856:Poly(ADP-ribose) Polymerase Inhibitors; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D019014:fas Receptor; D003606:Dacarbazine; D011065:Poly(ADP-ribose) Polymerases; D011494:Protein Kinases; D064447:Checkpoint Kinase 2; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C000605867:CHEK1 protein, human; C578634:CHEK2 protein, human; D000071877:Checkpoint Kinase 1; D017346:Protein Serine-Threonine Kinases; D020169:Caspases; D000077204:Temozolomide