Abstract 2075: DNA damage on HPRT as a biomarker of susceptibility to tobacco-induced cancer
Authors: Chinnaiyan Mayilvanan , Brobst Daniel , Sadhasivam Balaji , Ganapathy Vengatesh , Johnston Sarah E. , Zhao Daniel , Krempl Greg A. , Queimado Lurdes 
Published: July 2021

Abstract
Background: The prevention of cancer and the development of more effective strategies to detect cancer precursor lesions and early-stage cancers remain critical goals. It has been estimated that 50% - 60% of cancers could be prevented if known strategies were optimally used. Cancer risk is not uniform, but varies based on age, genetic susceptibility, exposures, existence of preneoplastic conditions across the population. The DNA is constantly damaged by exogenous and endogenous sources. DNA repair mechanisms maintain the integrity of the genome. DNA damage has emerged as a major culprit in tumorigenesis and progression. There are numerous strategies with inherent advantages and disadvantages that may be used for the evaluation of DNA damage and repair. We have developed a novel and highly sensitive primer-anchored DNA damage detection assay (PADDA) to map and quantify DNA damage in p53, the most frequently mutated gene in human cancer. Here, we have extended this assay to HPRT (hypoxanthine-guanine phosphoribosyltransferase), the gene most frequently analyzed in DNA damage studies.
Aim: (1) To quantify the amount of DNA damage in HPRT in peripheral blood cells of never-smokers, smokers, and secondhand smokers. (2) To determine whether cancer patients have higher levels of DNA damage in HPRT than non-cancer patients.
Methods: The assay, PADDA was used on a high-throughput setting to quantify DNA damage (q-PADDA) on the HPRT gene. DNA was extracted and damage was quantified by q-PADDA in peripheral blood cells collected from non-cancer patients [never-smokers (n=28), tobacco smokers (n=25), secondhand smokers (n=18)], and cancer patients (n=66). Pairwise comparisons in DNA damage among the diverse groups were performed using the Tukey's adjustment in a one-way ANOVA model. Linear regression models were also used to test difference in DNA damage between cancer and non-cancer groups.
Results: Never-smokers, tobacco smokers, and secondhand smokers had similar age distribution. In non-cancer patients, the amount of DNA damage in the HPRT gene in smokers was significantly higher than in non-smokers (p=0.01). Secondhand smokers also showed higher levels of DNA damage than never-smokers but this difference did not reach significance. Among cancer patients (n=64), smokers (n=29) showed significantly higher levels of DNA damage (p=0.03) than non-smokers (n=16).
Conclusion: Our preliminary data document PADDA's ability to quantify DNA damage on HPRT gene. Damage was significantly higher in smokers than never-smokers, both in cancer and non-cancer patients. Application of this assay to a larger population sample has a major potential to establish biomarkers of susceptibility to tobacco-induced cancer, which can guide preventive and diagnostic strategies.
Funding: This work was supported by the NIH, NCI (1R33 CA202898-01, LQ). Dr. Queimado holds a Presbyterian Health Foundation Endowed Chair in Otorhinolaryngology.
Citation Format: Mayilvanan Chinnaiyan, Daniel Brobst, Balaji Sadhasivam, Vengatesh Ganapathy, Sarah E. Johnston, Daniel Zhao, Greg A. Krempl, Lurdes Queimado. DNA damage on HPRT as a biomarker of susceptibility to tobacco-induced cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2075.