Abstract 1369: Dianhydrogalactitol (VAL-083) synergizes with topoisomerase inhibitors to overcome homologous recombination repair activity in glioblastoma and prostate cancer cells
Authors: Zhai Beibei , Kotapalli Sudha Sravanti , Bacha Jeffrey A. , Brown Dennis M. , Steino Anne , Daugaard Mads 
Published: September 2020

Abstract
Dianhydrogalactitol (VAL-083) is a bi-functional DNA-damaging agent that targets N7-guanines and causes DNA inter-strand crosslinks. VAL-083 is a small water-soluble molecule that readily crosses blood-brain-barrier and accumulates in brain tumor tissue, making it a good candidate for targeting brain malignancies, such as glioblastoma multiforme (GBM). VAL-083 has demonstrated anti-tumor activity in prior NCI-sponsored clinical trials in brain tumors and other cancer types. Previous research in our group demonstrates VAL-083-induced DNA inter-strand crosslinks lead to replication-dependent DNA double strand break (DSB) lesions that are preferentially repaired by homologous recombination (HR) in non-small cell lung cancer (NSCLC) cells. To investigate if the observed effects of VAL-083 in NSCLC cells translate to other cancer indications as well, we tested the cytotoxic activity of VAL-083 in a panel of GBM and prostate cancer cell lines. Crystal violet cell proliferation assay showed broad cytotoxicity of VAL-083 in low concentration (µM) range in all the cell lines tested. Immunofluorescent and propidium iodide staining followed by flow cytometric analysis furthermore showed that VAL-083 treatment induced replication-dependent S/G2 cell cycle arrest. DNA repair markers were investigated by western blot and confocal microscopy analyses and confirmed the activation of HR DNA repair pathway after VAL-083 treatment in cancer cells. Using lentiviral transduction of MLH1 and MSH2 expression vectors in HCT116 and LoVo cell lines, we investigated if VAL-083 activity was affected by DNA mismatch repair (MMR), which is the secondary temozolomide (TMZ)-resistance mechanism in GBM patients. Our data showed that VAL-083 cytotoxicity was independent of MMR, suggesting that VAL-083 is able to overcome MMR-mediated TMZ-resistance in GBM patients. Additionally, we demonstrated synergistic effects between VAL-083 and inhibitors of both topoisomerase I and II (camptothecin, irinotecan and etoposide) in GBM and prostate cancer cells. Taken together. our present study validated the broad cytotoxic effect and mechanism-of-action of VAL-083 in a variety of cancer cells and suggested that VAL-083 is able to overcome MMR-mediated TMZ resistance in GBM. We further demonstrated synergy between VAL-083 and topoisomerase inhibitors in GBM, prostate cancer and NSCLC cell lines. This provides good guidance for improved treatment strategies to use VAL-083 either as single agents or as part of combination regimens in the treatment of cancer patients.
Citation Format: Beibei Zhai, Sudha Sravanti Kotapalli, Jeffrey A. Bacha, Dennis M. Brown, Anne Steino, Mads Daugaard. Dianhydrogalactitol (VAL-083) synergizes with topoisomerase inhibitors to overcome homologous recombination repair activity in glioblastoma and prostate cancer cells [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1369.