Water-soluble version of SCR7-pyrazine inhibits DNA repair and abrogates tumor cell proliferation

• Main Authors: Monica Pandey, Vidya Gopalakrishnan, Hassan A Swarup, Sujeet Kumar, Radha Gudapureddy, Anjana Elizabeth Jose, Supriya V Vartak, Robin Sebastian, Mrinal Srivastava, Bibha Choudhary, Mantelingu Kempegowda, Subhas S Karki, Sathees C Raghavan
• Format: Article
• Language: English
• Published: Wolters Kluwer Medknow Publications 2019-01-01
• Series: Journal of Radiation and Cancer Research
• Subjects: Cancer therapeutics; CRISPR; DNA ligase; double-strand break; end-joining; genome editing; homologous recombination; nonhomologous end-joining
• Online Access: http://www.journalrcr.org/article.asp?issn=2588-9273;year=2019;volume=10;issue=1;spage=27;epage=43;aulast=Pandey

Aim: Mammalian DNA Ligases play pivotal role in processes such as DNA replication, recombination, and repair, which qualifies them as potent therapeutic targets to eradicate cancer cells. Recently, we have identified a small molecule inhibitor, SCR7 and its oxidized form SCR7-pyrazine (2-mercapto-6,7-diphenylpteridin-4-ol) (SCR7-P), which can inhibit nonhomologous end-joining (NHEJ) in a Ligase IV-dependent manner. In the present study, we describe a water-soluble version of ligase inhibitor, sodium salt of SCR7-P (Na-SCR7-P) and its anti-tumor effects. Materials and Methods: Water soluble version of SCR7-P was synthesised. To study the inhibitory effect of Na-SCR7-P on ligases, we did in vitro DNA end joining assays using double strand DNA substrates. For this, different concentrations of Na-SCR7-P was used along with purified ligases or cell-free extracts. Further, cytotoxicity induced by Na-SCR7-P was evaluated through trypan blue exclusion assay, JC-1 assay and cell cycle analysis. Anti-tumor activity of Na-SCR7-P was investigated in Swiss albino mice and its off-target effects were studied by conducting kidney and liver test and histological evaluation. Further, the anti-angiogenic effect of the compound was studied using in ovo chorioallantoic membrane assay. Results: Na-SCR7-P inhibited NHEJ in a Ligase IV-dependent manner. However, unlike SCR7 and SCR7-P, it blocked joining catalyzed by all three ligases in vitro, making it an ideal cancer therapeutic agent, as it may target multiple DNA transaction processes within the cancer cells. Na-SCR7-P decreased mitochondrial membrane potential (MMP) leading to cell death in cancer cells. Importantly, the administration of Na-SCR7-P led to a significant reduction in tumor growth from 12th day of treatment, and its impact was significantly higher than previously described SCR7, which targets Ligase IV within cells. Antitumor activity of Na-SCR7-P in mice resulted in enhanced lifespan, with minimal side effects. In addition, the in ovo chorioallantoic membrane assay revealed potent antiangiogenic property of Na-SCR7-P. Conclusion: Our results suggest that Na-SCR7-P can target NHEJ and other DNA repair pathways by disrupting Ligase mediated joining and can potentially be used as a strategy for cancer treatment, owing to its water solubility.