DNA Damage

The US National Academy of Sciences/National Research Council report on TT21C (Krewski et al 2010) proposes an in-vitro approach to toxicity testing that aims to describe perturbations in critical cellular processes that lead to adverse events (toxicity pathways), and a safety assessment approach that ensures human exposure is kept below a level that is expected to cause adverse effects.  Using the p53 DNA damage repair pathway as a prototype toxicity pathway, Unilever and the Hamner Institutes have an ongoing collaborative project to investigate what a TT21C-based risk assessment may look like in practice for an ingredient in a consumer product.

The p53 pathway was chosen for its known relationship to the development of human cancer.  Briefly p53 is a tumour suppressor protein which is found to be mutated in a variety of several cancers and is considered to be the guardian of the genome. DNA damage can be caused by a variety of agents such as ultraviolet radiation, gamma radiation, genotoxic compounds and oxidative stress.  This damage is then ‘sensed’ by a number of sensor kinases such as ATM and ATR which phosphorylate p53 into its active form. Active p53 transcribes genes involved in DNA repair, inhibiting the cell cycle (to prevent propagation of the damage into daughter cells) and apoptosis to inactivate the cell. The aim of the project is to describe perturbations of the p53 pathway, in human cell lines, in response to various concentrations of case study chemicals and to determine if this approach can be applied to risk assessment.

We developed a number of tools such as high throughput flow cytometry to measure key components of the p53 pathway such as ATM, ATR, and MDM2 to assess dose dependent transitions for case study chemicals. In addition, we have investigated the formation of micronuclei, nuclear anomalies that are biomarkers of genotoxic events, as measure of an adverse outcome i.e. mutation.

Computational systems biology models of the circuitry of the p53 pathway have been constructed to examine the dose-dependent transitions (using experimental data) in mutational efficiency. These models will help in our understanding of basal function, response to small and large perturbations (the so called tipping point between adaptive and adverse responses) and to provide a mechanistic understanding of the dose responses observed within the in vitro assays.

Finally, a PBPK (physiologically based pharmacokinetic)  model describing exposure to case study chemicals was developed to enable us to perform an in-vitro to in-vivo extrapolation, and so compare changes in the pathway with expected human exposure in tissues and plasma arising from consumer use of products containing the case study chemicals.

Latest Presentation

Characterization of Threshold Dose Response of Genotoxicity from Chemicals with Diverse Mechanisms of Damage

Latest Publication

Clewell RA, Sun B, Adeleye Y, Carmichael P, Efremenko A, McMullen PD, Pendse S, Trask OJ, White A, Andersen ME (2014) Profiling dose-dependent activation of p53-mediated signaling pathways by chemicals with distinct mechanisms of DNA damage, Toxicological Sciences, 142(1), 56-73

Adeleye Y, Andersen M, Clewell R, Davies M, Dent M, Edwards S, Fowler P, Malcomber S, Nicol B, Scott A, Scott S, Sun B, Westmoreland C, White A, Zhang Q, Carmichael PL (2014) Implementing Toxicity Testing in the 21st Century (TT21C): making safety decisions using toxicity pathways, and progress in a prototype risk assessment, Toxicology, doi:10.1016/j.tox.2014.02.007

Li Z, Sun B, Clewell RA, Adeleye Y, Andersen ME, Zhang Q (2014) Dose response modeling of etoposide-induced DNA damage response, Toxicological Sciences, 137, 371-84

Sun B, Ross SM, Trask JO, Carmichael PL, Dent M, White A, Andersen ME, Clewell RA (2013). Assessing dose-dependent differences in DNA-damage, p53 response and genotoxicity for quercetin and curcumin, Toxicology in Vitro, 27, 1877-1887.

Yeyejide Adeleye