Abstract 2562: Dianhydrogalactitol inhibits the growth of glioma stem and non-stem cultures, including temozolomide-resistant cell lines, in vitro and in vivo
Authors: Fouse Shaun D. , Steino Anne , Butowski Nicholas , Bacha Jeffrey A. , Kanekal Sarath , Santos Nancy Dos , Brown Dennis M. , Costello Joseph F. 
Published: August 2015

The standard of care for glioblastoma multiforme (GBM) patients is surgical resection followed by temozolomide (TMZ) and irradiation (XRT). However, TMZ-resistance has emerged as a significant unmet medical need, as DNA repair enzyme 0-6-methylguanine DNA methyltransferase (MGMT) removes the methyl-group adducts caused by TMZ. Dianhydrogalactitol (VAL-083) is a structurally unique alkylating agent causing DNA crosslinks at N7 position of guanine. Because VAL-083's N7 adducts are not subject to MGMT mediated repair, it may be an effective chemotherapeutic in the treatment of TMZ-resistant GBM. VAL-083 crosses the blood brain barrier and accumulates in brain tumor tissue. We have recently shown that TMZ activity is similar in cancer stem cells (CSC) and their paired non-CSC from primary GBM tissues, and that the activity is MGMT-dependent. We thus sought to investigate how our CSC and non-CSC panel would respond to VAL-083 alone or in combination with XRT. We further investigated the activity of VAL-083 in in vivo models of drug-resistant GBM in comparison to TMZ. Rag2 mice bearing intracranial human GBM xenograft tumors of either MGMT-positive and TMZ-resistant origin (BT74), or MGMT-negative and TMZ-sensitive origin (U251) were treated. VAL-083 was given i.p. 3 times/week x 3 weeks, and the efficacy of VAL-083 in controlling tumor growth compared to TMZ (30 mg/kg). Disease progression was evaluated by overall survival, clinical observations and body weight measurements. Our in vitro results show that VAL-083 is a potent inhibitor of all tested primary GBM cultures, irrespective of MGMT status. VAL-083 causes cell cycle arrest and loss of cell viability in TMZ-resistant cells, and at lower concentrations than TMZ in TMZ-sensitive cells. Furthermore, VAL-083 is not affected by cell culture condition (Stem vs. Non-Stem). Low dose VAL-083 combined with XRT exhibited an additive effect in all cultures tested, suggesting that VAL-083 might act as a radiosensitizer. In the in vivo U251 model, the median survival time for mice treated with 4 mg/kg VAL-083 was significantly increased to 72 days compared to 48 days for controls (p&lt;0.0001). Median survival time for 3 mg/kg VAL-083 was 54 days. Body weight loss was observed in mice treated with 5 mg/kg and treatment was stopped after 4 doses after which the animals recovered and their median survival was 57 days. Animals treated with TMZ were terminated at day 102 at the end of the study. BT74: study is ongoing, data will be presented at the meeting.In conclusion, VAL-083 is highly efficacious against both stem and non-stem GBM cell cultures in vitro, the activity is independent of MGMT and VAL-083 appears to act as a radiosensitizer in GBM. In vivo xenograft GBM models further validate the benefits of VAL-083 in the treatment of GBM and support ongoing clinical research with VAL-083, which is currently in a clinical trial for GBM patients with recurrent disease.

Citation Format: Shaun D. Fouse, Anne Steino, Nicholas Butowski, Jeffrey A. Bacha, Sarath Kanekal, Nancy Dos Santos, Dennis M. Brown, Joseph F. Costello. Dianhydrogalactitol inhibits the growth of glioma stem and non-stem cultures, including temozolomide-resistant cell lines, in vitro and in vivo. [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 2562. doi:10.1158/1538-7445.AM2015-2562