Background: Arsenic trioxide is currently used to treat acute promyelocytic leukemia and is known as a cytotoxic agent. Arsenic is also known as a carcinogen. However, a cytoprotective effect of low-dose arsenic (LDA) has also been observed in some studies. Our previous studies have found that pretreatment with LDA before DNA damaging agents such as chemotherapy and radiation therapy protects normal cells without impairing the cancer killing effects. We have demonstrated that intact p53 function is required in this process, and therefore, LDA does not protect cancer cells as most of them have mutated or dysfunctional p53 pathway. We have also reported that LDA helps protect the telomere from enhanced erosion by DNA damaging agents in ConA-activated normal human lymphocytes. As enhanced telomere shortening is associated with genomic instability, we decided to investigate the effect of LDA in genomic integrity.

Methods: Mouse embryonic stem cells (mESCs) with a mutator phenotype in DNA repair pathways (MSH2-/-, Rad51KA and Ku70null) and their wildtype counterparts were utilized for cell viability studies and HPRT minigene mutation assay. Cell viability under different doses of LDA (0-1000nM) and radiation (0-4Gy) was firstly examined by colony formation assay. DNA damage and DNA repair capacity were also measured by comet assay in MSH2-/- mESCs. TailDNA% was analyzed by OpenComet and used to describe the comet feature.

Results: Arsenic had little effect on the cell viability at doses ≤200nM in all tested cell lines. In MSH2-/- mESCs, there was no significant difference between the tailDNA% of cells treated with 200nM LDA (11.41±0.52%) and the control (10.82±0.49%) immediately after radiation. However, LDA treatment significantly decreased the tailDNA% 30 minutes after radiation (4.68±0.35% vs. 7.29±0.51%, Student’s test P<0.0014). While HPRT mutation frequency was not detectable in radiation-treated Rad51KA, Rad51wt and MSH2wt mESCs, LDA decreased the fraction of 6-Thioguanine resistant cells after radiation in MSH2-/-, Ku70null and Ku70res mESCs, suggesting fewer radiation-induced mutants were formed after LDA treatment.

Discussion: Our data suggest that brief use of LDA enhances DNA repair activities and provides protection from radiation-induced mutations in mESCs. The inability to correctly repair DNA damage from chemotherapy and radiation therapy has been attributed to the development of therapy related secondary malignancy. Helping maintain genomic integrity with LDA during chemotherapy and radiation therapy may have a role in reducing therapy related secondary malignancy. Further work is in progress to test the potential use of LDA as a genome protector in vivo.

Citation Format: Hang Su, Meijun Long, Mi Young Son, Teresa C Marple, Paul Hasty, Chul Soo Ha. An unexpected effect of low-dose arsenic on genomic integrity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3509.