Distinctive
TP53 mutation patterns and whole genome mutational signatures have been identified in human tumours and linked to environmental carcinogenesis. By performing the Hupki mouse embryo fibroblast (HUF) immortalisation assay (HIMA),
TP53-mutants are generated, selected and
TP53 mutation patterns for the respective carcinogen attained. These carcinogen-treated immortalised HUFs can be further subjected to whole genome sequencing (WGS) to extract characteristic mutational signatures defined by single base substitutions (SBS). Ultimately this can help to understand cancer aetiology by comparing carcinogen-specific mutation patterns and signatures to those harboured in tumours of exposed individuals. The main aim of this project was therefore to determine
TP53 mutation patterns and mutational signatures of suspected and known environmental as well as dietary carcinogens in HUF clones immortalised in the HIMA. The carcinogens tested were acrylamide, 2-amino-1-methyl-6-phenylimidazo[4,5-
b]pyridine (PhIP) and 4-aminobiphenyl (4-ABP) and their proximate metabolites glycidamide,
N-hydroxy-PhIP (
N-OH-PhIP) and
N-hydroxy-4-ABP (N-OH-4-ABP), respectively. To optimise treatment condition for the HIMA, cytotoxicity, carcinogen-DNA adduct formation and induction of mutations in the bacterial
lacZ reporter gene and DNA damage response proteins were assessed in primary HUFs. Treatment with
N-OH-PhIP induced the highest
TP53 and
lacZ mutant frequency, followed by glycidamide, and both activated metabolites also formed high levels of premutagenic DNA adducts. While
N-OH-4-ABP treatment led to formation of DNA adducts and
TP53-mutant HUFs were found, no mutagenicity was observed in the
lacZ gene. The observed
TP53 mutation frequencies were 6 (9/150 clones), 9 (17/198) and 10% (9/90) after 24 h+24 h treatment with 40 μM
N-OH-4-ABP, 1.1 mM glycidamide and 2.5 μM
N-OH-PhIP, respectively. Characteristic
TP53 mutation patterns were found for all proximate metabolites, which agree with the pre-mutagenic DNA adducts formed by the respective carcinogen and were resembled in many human tumours. While the mutation pattern for glycidamide was defined by A > T/T > A and A > G/T > C mutations, treatment with
N-OH-PhIP mostly induced G > T/C > A and
N-OH-4-ABP G > C/C > G transversions. Further, distinctive WGS mutational signatures were found for glycidamide and
N-OH-PhIP, which were characterised by the same mutation types as found in the
TP53 gene. Both WGS signatures showed high cosine similarities with COSMIC signatures previously observed in Abstract 4 human tumours, most notably SBS3 and 25 for glycidamide and SBS4, 18 and 25 for
N-OH-PhIP. Together with the
TP53 mutation data, results of the present study suggest that glycidamide may be involved in the development of breast, ovary and lung cancer, while
N-OH-PhIP could play a role in the aetiology of liver and colorectal cancer. Overall, this project has helped to advance our understanding how dietary and environmental exposures can impact on the development of human cancer and the underlying processes of mutagenicity.
| Date of Award | 1 Aug 2020 |
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| Original language | English |
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| Awarding Institution | |
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| Supervisor | Volker Arlt (Supervisor) & David Phillips (Supervisor) |
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