J.D. Barnett, A. Sharma, J. Stewart, F. Bunz, R. Ivkov
The Johns Hopkins University School of Medicine,
Keywords: DNA damage response, signal transduction, cancer cell, reactive oxygen species, iron oxide
Summary:This study explores the potential genotoxicity of metal oxide nanoparticles and their involvement in the activation of signal transduction pathways of DNA damage response (DDR). DDR is an extensive system of signaling pathways that responds largely to double (DSB) and single strand breaks (SSB). This repair network is essential for genomic stability, replication, cellular homeostasis and normal physiological development. ATM (ataxia-telangiectasia mutated) and ATR (ataxia-telangiectasia and Rad3–related) protein kinase are the regulators of DNA damage checkpoints that manage the progression, delay and arrest of the cell cycle during the G1/S, intra-S and G2/M phase. When activated, these homeostatic kinases phosphorylate key downstream effectors that ultimately result in fork replication arrest, apoptosis or DNA repair. More knowledge of DDR is imperative in advancing therapeutic modalities, such as radiotherapy and chemotherapy. Metal oxide nanoparticles are used in biomedicine for their chemical, physical and biological properties. Although some exhibit certain degrees of biocompatibility, they have the potential to generate reactive oxygen species that may serve as endogenous DNA damaging agents. Metallic oxide nanoparticles, most specifically iron oxide nanoparticles, were screened for their ability to elicit DNA damage and cytotoxicity in human colorectal cancer (HCT116) cells. Those particles exhibiting cytotoxic activity through clonogenic survival assays were further biologically characterized. Western blot analysis was used to determine downstream phosphorylation of checkpoint proteins CHK-2 and CHK-1 (phosphorylated by ATM and ATR, respectively). ATM/ATR activation was investigated and visualized through confocal microscopy. Results of this and evidence of DSBs will be presented along with examination of gamma-H2AX foci abundance.