A study of inter-individual differences in the DNA damage response

Abstract

Agents that damage our DNA are omnipresent in our environment and inside our cells themselves. Left unrepaired, DNA damage can lead to premature aging, neurodegeneration and cancer. Humans have thus evolved intricate and widespread mechanisms to repair and manage this damage. These mechanisms-called the DNA damage response-often involve cell cycle arrest. Cell cycle arrest gives the cells precious extra time to utilize its diverse set of repair pathways. Among these is the homologous recombination pathway, which repairs DNA double-strand breaks. When the damage is deemed irreparable, a cell can choose to die: this allows for the maintenance of genomic integrity of the organism. Humans share 99.9% of the same genetic information. The remaining 0.1% is responsible for all genetic variations between individuals. This includes differences in disease susceptibility. In this study, we examined the inter-individual differences in the DNA damage response. To do so, we used a panel of twenty-four B lymphoblastoid cell lines derived from twenty-four healthy individuals of diverse ancestries. This panel had already been shown to display a broad range of sensitivity to several DNA damaging agents. We focused our attention on the alkylating agents temozolomide and methylnitronitrosoguanidine (MNNG). While MNNG has been extensively studied as a model DNA damaging drug, temozolomide is used in the clinic today to treat astrocytoma and glioblastomas. The two drugs are often referred to as functional analogues. We wanted to see if the cell lines' relative sensitivities to both drugs would be similar, which would support the analogy made between the drugs, or different, which would refute it. Furthermore, we measured the amounts of sister chromatid exchanges (SCEs) induced by temozolomide treatment to determine if the sensitivity measured by growth inhibition post-treatment was correlated with the amount of temozolomide-induced SCEs. For the cell lines tested, we found that the MNNG-induced sensitivity was similar to that induced by temozolomide. We also found a cell line in which temozolomide induced a large growth inhibition, all the while inducing no detectable SCEs.