Abstract 2550: FANCA protein is involved in the homologous recombination repair of sapacitabine-induced DNA damage

Fanconi anemia (FA) is an autosomal disorder characterized by developmental abnormalities, early-onset bone marrow failure, and a predisposition to cancer. FA cells are defective in DNA repair, and exhibit hypersensitivity to DNA interstrand cross-links (ICLs) and a high degree of chromosomal aberrations. A majority of the FA proteins have been shown to act as signal transducers and scaffolding proteins to employ other pathways to repair DNA. Specifically the FA group A (FANCA) protein has been indicated as an integral component in the early step of homologous recombination (HR) of double strand breaks (DSB). Sapacitabine, the orally bioavailable prodrug of the nucleoside analog CNDAC, has presented favorable clinical activity in advanced acute leukemias and myelodysplastic syndromes. CNDAC kills cells by a unique mechanism of action. Incorporation of CNDAC triphosphate into DNA results in a beta elimination reaction that causes single-strand break (SSB) that is terminated by the analogue. DNA replication over this nick converts the nick to a one-ended double-strand break (DSB) upon collapse of the DNA replication fork. The CNDAC-induced DSBs, which are potentially lethal, are repaired predominantly through homologous recombination (HR), relative to other repair pathways, such as base excision repair, transcription-coupled nucleotide excision repair and non-homologous end-joining. CNDAC greatly sensitizes cells lacking HR components, such as ATM, RAD51D, XRCC3 and BRCA2. Based on the evidence that FANCA associates with proteins involved with HR, we hypothesize that loss of FANCA may also sensitize cells to CNDAC. FANCA-deficient cells from an individual with Fanconi anemia as well FANCA repleted cells were utilized to investigate the role of the FANCA protein in the repair of damage caused by CNDAC. Cells were treated with CNDAC or mitomycin C (MMC), a crosslinking agent. We found that FANCA deficient cells were sensitized to CNDAC about 5-fold as compared with FANCA repleted cells, while they were sensitized by 6-fold when treated with MMC. Cells were treated with 1 μM CNDAC for either 24 or 48 hr before chromosome spread samples were collected to examine the genome integrity. Chromosome aberrations were increased in response to CNDAC treatment, and cells lacking FANCA protein exhibited more chromosomal abnormalities compared with FANCA repleted cells. Rad51 foci, diagnostic indicators of active HR, were present in both lines after 24 or 48 hr of CNDAC treatment; however, FANCA deficient cells displayed attenuated accumulation of Rad51 foci in response to CNDAC as compared with the FANCA repleted cells. These findings indicate that FANCA is involved in the HR repair of CNDAC-induced DNA lesions. Because FANCA is one component of the core complex of the Fanconi repair pathway, other proteins in this group may confer similar sensitization. Citation Format: Yingjun Jiang, Xiaojun Liu, William Plunkett. FANCA protein is involved in the homologous recombination repair of sapacitabine-induced DNA damage. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2550. doi:10.1158/1538-7445.AM2015-2550