The Aryl Hydrocarbon Receptor Repressor (AhRR) Methylation Status as a Smoking Biomarker in Urothelial Bladder Cancer Tumors

Abstract

Urinary Bladder Cancer (BCa) is the 10th most incidental malignancy worldwide, with higher rates in industrialized countries. Smoking is considered one of the most important risk factors for BCa. In addition, studies have shown that cigarette smoking results in the demethylation of the AhRR gene in blood cells, establishing AhRR demethylation as a specific serum smoking biomarker. This study aimed to investigate the value of this biomarker in the target tissue and its possible role in bladder carcinogenesis. We sub-selected 180 tumor-based DNA samples from 263 histologically confirmed BCa patients diagnosed between 2013 and 2017 in two major medical centers in Beirut. AhRR % methylation in tumor DNA was determined by bisulfite conversion, pre-amplification by PCR, and differential methylation by droplet digital PCR. Associations between AhRR % methylation, patient’s smoking status, and tumorigenic outcome indicators were examined using the two-tail Student’s t-test. Our results show that muscle-invasiveness is significantly associated with a higher AhRR % methylation compared to non-muscle invasive tumors (42.86 ± 23.85% vs. 33.98 ± 20.36%; p=0.011). In addition, oncogenic FGFR3 E7 C248 mutant genotype was also found to be significantly associated with a lower AhRR % methylation compared to wild-type (28.11 ± 9.44% vs. 37.87 ± 22.53%; p=0.036). All other tested associations were not statistically significant. Further research investigating the role of AhRR in muscle-invasive bladder cancer tumors (MIBC) and bladder carcinogenesis is recommended.