Recent work from the Engelward Lab has been published in Cell Reports and featured in the MIT News on March 16, 2021. This research highlights increased concerns of the contaminant, N-nitrosodimethylamine or more commonly known by its abbreviation NDMA. NDMA is a probable carcinogen identified in exceedingly high levels at the Olin Chemical Superfund Site in Wilmington, MA. This chemical is also present in food that is known to be carcinogenic (namely, processed meat), and is sometimes present in heavily chloraminated municipal drinking water. Coincidently, last week the Massachusetts Department of Public Health released its findings from a 20 year study that showed an association between exposure to NDMA in utero and a childhood cancer cluster in Wilmington. Additionally, over the past couple of years several types of drugs were found to be contaminated with NDMA or to contain precursors that break down to form NDMA. Tens of millions of people in the United States alone were exposed to high levels of NDMA from taking Zantac, Metformin and Valsartan. In fact, the public health crisis that has stemmed from NDMA contamination is alarming enough that the FDA held a two-day public workshop focused on addressing this issue this past week. (https://www.fda.gov/drugs/news-events-human-drugs/nitrosamines-impurities-drugs-health-risk-assessment-and-mitigation-public-workshop-03292021).
The Engelward lab’s research project stems from studies by Leona Samson showing the cost-benefit of the DNA repair pathway known as base excision repair (BER), and it brings sophisticated mouse models to bear on understanding the role of BER in the context of NDMA exposure. NDMA is a DNA damaging agent that creates methylated DNA bases, that can be mutagenic. The focus of this most recent study is on the Alkyladenine DNA Glycosylase (AAG), which initiates the BER pathway by removing damaged bases, including those created by NDMA. After removal of damaged bases by AAG, downstream enzymes process the abasic site, and single strand breaks must be created to allow polymerase to replace the damaged base. While removal of the mutagenic lesion helps to prevent cancer, the resulting strand breaks can be toxic.
Led by Dr. Jennifer Kay, Engelward’s team discovered that the AAG plays a pivotal role in response to NDMA, literally creating a “pivot” wherein low levels of AAG lead to cancer and high levels of AAG lead to tissue toxicity.
The underlying mechanism for these observations is that AAG removes potentially mutagenic DNA lesions such as 3-methyladenine (3MeA). Having low amounts of AAG therefore results in increased mutations and cancer. Increasing the level of AAG at first glance appears advantageous, because mutations go down and so does cancer incidence. However, having high levels of AAG is also problematic, because excess activity can create pathway imbalance, which is associated with an increase in BER intermediates, some of which are toxic, like single strand DNA breaks.
This work highlights the importance of gene-environment interactions that dictate disease outcome, raising the possibility that people with low levels of AAG protein may be more susceptible to NDMA-induced cancer. An exciting opportunity for application of this research is that methods developed by the Samson and Engelward Labs, using plasmids and the CometChip platform, respectively, enable monitoring of AAG activity in people, thus potentiating precision prevention. Advanced by the Nagel laboratory promise to make the plasmid-based assay accessible to many labs.
Additionally, the study involved the use of the RaDR mouse model developed in the Engelward Lab, which makes it possible to monitor mutation frequency in tissues via fluorescent imaging. RaDR imaging using a standard epifluorescent microscope provides singly the most high-throughput and least expensive method available for mutation studies, and the results from this work show its utility. In particular, the tight correlation between RaDR mutations and cancer points to the potential for using the RaDR mice to screen conditions that might suppress mutations, identifying leads that can then be explored with a longer term cancer study.
Several MIT Superfund Research Program laboratories contributed in essential ways in collaboration of this study, including the White and Essigmann labs. The research project was led by Jennifer Kay (Engelward Lab) with key contributions from Joshua Corrigan (Engelward Lab), Amanda Armijo (Essigmann Lab), and Ishwar Kohale (White Lab). This is an excellent example of collaborative research made possible by the NIEHS Superfund Research Program, shedding light on some of the molecular processes that drive cancer and the methods our genes use to protect us from environmental contaminants.
Cell Reports Publication: https://www.cell.com/cell-reports/fulltext/S2211-1247(21)00178-9
MIT Press: https://news.mit.edu/2021/dna-repair-enzyme-ndma-cancer-0316