Answer Explanations

• Yes (please provide)

  Expert 5
  In considering the cytotoxic MOA for liver tumors it may be important to review some of the chloroform and carbon tertrachloride  liver tumor mode of action studies.   Except for the concept of metabolic saturation in the case of DX, chloroform and carbon tetrachloride exhibit the same subsequent key events as DX.   
  For example the key events in the carbon tetrachloride rodent liver tumor MOA include
   KE1  Metabolism of CCl4 to trichloromethyl and trichloromethyl peroxy radicals, resulting in KE2 Hepatocellular cytotoxicity (cell death), followed by KE3 Induction of hepatocyte proliferation via compensatory hyperplasia, leading to KE4 Induction of preneoplastic cells with theproduction of hepatocellular foci, leading to KE5  Formation of hepatocellular neoplasms(adenomas and carcinomas in the
  
   
  Cohen et al  Evaluation of the carcinogenicity of carbon tetrachloride. J Toxicol Environ Health B Crit Rev. 2023 Aug 18;26(6):342-370.
  Golden RJ, et al Chloroform mode of action: implications for cancer risk assessment. Regul Toxicol Pharmacol. 1997 Oct;26(2):142-55
  Holsapple, M. P., et al 2006. Mode of action in relevance of rodent liver tumors to human cancer risk. Toxicol. Sci. 89 (1):51–56.
  doi:10.1093/ toxsci/kfj001
  Andersen et al Lessons Learned in Applying the U.S. EPA Proposed Cancer Guidelines to Specific Compounds, Toxicological Sciences, Volume 53, Issue 2, February 2000, Pages 159–172, https://doi.org/10.1093/toxsci/53.2.159
   
• Yes (please provide)

  Expert 6
  TRPV1 and 1,4-D: Mo et al., 2022

  Human relevance of mesothelioma in Fischer 344 rats: Maronpot et al., 2016

  Tumors of the nasal mucosa in rodents: Nishikawa et al., 2024

  TRPV1 and cell death: Reilly et al., 2003

  
  

  
  

  
  

  
  
• No

  Expert 4
  While not essential (the reason for the "no" response), the following reviews provide additional perspective or important background on interpretation of the 1,4-DX dataset:
  
  1. Regulatory perspective:
  
  Maximum Contaminant Level Recommendation for 1,4-Dioxane in Drinking Water. New Jersey Drinking Water Quality Institute September 24, 2021. https://www.nj.gov/dep/watersupply/pdf/14dioxane-rec-sum.pdf
  
  2. Interpretation of recent mechanistic studies (cited also in Lafranconi et al., 2023). 
  
  

  Wang et al. (2022) Oxidative stress, glutathione, and CYP2E1 in 1,4-dioxane liver cytotoxicity and genotoxicity: insights from animal models.  https://doi.org/10.1016/j.coesh.2022.100389
  
  

  Ginsberg et al. (2022) Mechanistic considerations in 1,4-dioxane cancer risk assessment. https://doi.org/10.1016/j.coesh.2022.100407
   
  3. Biological plausibility of an oxidative stress/DNA damage/regenerative proliferation mode of action (also cited in Lafranconi et al., 2023): 
   

  OECD 220: Cyp2E1 Activation Leading to Liver Cancer.  https://aopwiki.org/aops/2200
  
  

  Cho et al. (2022) AOP report: Development of an adverse outcome pathway for oxidative DNA damage leading to mutations and chromosomal aberrations. DOI: 10.1002/em.22479 
   

  4. The following reference briefly considers 1,4-DX as an example of hypothesized key events in an AOP/MOA in which there is moderate confidence: 
   

  Perkins et al., (2022) Adverse Outcome Pathways for Regulatory Applications: Examination of Four Case Studies With  Different Degrees of Completeness and Scientific Confidence. doi: 10.1093/toxsci/kfv181
• Yes (please provide)

  Expert 2
  The literature on the role of "oval cells" and nonparenchymal cells during liver carcinogenesis is substantive. The contribution of cell interactions, e.g., fibrocytes and inflammatory cells producing various growth-regulatory cytokines in hepatic oncogenesis has also been accumulating. The mechanisms in hepatic oncogenesis in the setting of hepatic growth arrest for specific clinical conditions in people constitute a substantive literature too.   
• Expert 1
  AOP 220 Cyp2E1 Activation Leading to Liver Cancer
  AOP 296 Oxidative DNA damage, chromosomal aberrations and mutation
  
  Both AOP support threshold based extrapolation of risk.
  
  

  
  

• Yes (please provide)

  Expert 3
  The data describing the effects of DX in cyp2e1 KO mice were only very briefly highlighted in Wang etal. 2022.  It would be useful to access the complete study as a report and/or publication in order to determine whether further experimental refinements might be useful in this mouse strain.