Abstract 2985: Molecular mechanisms of dianhydrogalactitol (VAL-083) in cancer treatment

Abstract

Abstract Dianhydrogalactitol (VAL-083) is a unique bi-functional alkylating agent causing methylation of N7-guanine and inter-strand DNA crosslinks. VAL-083 is a small water-soluble molecule that readily crosses the blood-brain-barrier. In China, VAL-083 is approved as a chemotherapeutic drug for the treatment of chronic myelogenous leukemia (CML) and lung cancer. In the United States, VAL-083 has been evaluated in more than 40 National Cancer Institute (NCI)-sponsored phase I and phase II clinical trials. Preclinical studies and clinical trial data suggested antineoplastic effects of VAL-083 in a variety of malignancies, including lung cancer, brain tumors, leukemia, cervical cancer, and ovarian cancer. Here we report new insight into VAL-083 mechanism of action by showing that VAL-083 leads to irreversible cell cycle arrest and cell death caused by replication-dependent DNA damage. In lung (H2122, H1792, H23 and A549) and prostate (PC3 and LNCaP) cancer cell lines, VAL-083 treatment caused irreversible cell cycle arrest in late S and G2 phase as measured by propidium iodide (PI) and immunofluorescent (IF) staining in synchronized cultures. Importantly, VAL-083 was cytotoxic to all cell lines tested (IC50 range 3.06 - 25.7 μM). Western blot and IF analyses of DNA repair markers were employed to investigate the DNA damage response induced by VAL-083 in cancer cells. VAL-083 treatment led to phosphorylation of the proximal DNA double-strand break (DSB) sensor Ataxia Telangiectasia Mutated kinase (ATM), the single-strand DNA-binding Replication Protein A (RPA32), and the histone variant H2A.X (γH2A.X). Importantly, the DNA damage was specific to cells in S phase indicating that VAL-083-induced DNA cross-links translates into more severe DNA lesions during replication. Furthermore, S/G2 phase cell cycle arrest and increased phosphorylation of γH2A.X in cancer cells persisted after pulse-treatment with VAL-083, indicating irreversible DNA lesions. Taken together, VAL-083 displayed broad anti-neoplastic activity in lung and prostate cancer cells through the induction of replication-dependent DNA damage. Elucidation of the molecular mechanisms underlying VAL-083 cytotoxicity in cancer cells will offer help in identifying and predicting efficacy of combination treatments. Citation Format: Beibei Zhai, Anne Steino, Jeffrey Bacha, Dennis Brown, Mads Daugaard. Molecular mechanisms of dianhydrogalactitol (VAL-083) in cancer treatment. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2985.