Abstract 1843: Dianhydrogalactitol (VAL-083) for the treatment of glioblastoma multiforme (GBM): Impact of glucose transporters for crossing the blood brain barrier (BBB)

Glucose transporters at the blood brain barrier (BBB) maintain the continuous high glucose and energy demands of the brain. These transporters have been targets for the creation of therapeutic molecules as a means to cross the BBB. The BBB has been a major limitation for the successful development of treatments for brain tumors. To date, only a limited number of lipophilic small chemical entities, which can cross the BBB, have been approved for the treatment of GBM. These include the nitrosoureas such as carmustine (BCNU) and lomustine (CCNU) and temozolomide (TMZ). VAL-083 is a di-epoxide substituted hexitol sugar (galactitol). It has a molecular weight of 146 and is highly water soluble. VAL-083 is active against several GBM cell lines and animal models and acts as a DNA targeting agent rapidly forming cross-links at the N7 position of guanine, resulting in lethal DNA double strand breaks and cancer cell death. Its is active in GBM patients, both newly diagnosed and recurrent. Furthermore, its activity is independent of the DNA repair enzyme MGMT which limits the effectiveness of O6 guanine alkylating agents such as the nitrosoureas and TMZ.In clinical pharmacology studies, VAL-083 rapidly accumulates in the cerebrospinal fluid (CSF) and brain tumor tissue. Studies with radiolabeled VAL-083 have shown a half-life of ~ 20 h in CSF vs 2h for plasma post-IV infusion. Recent clinical studies in newly diagnosed GBM patients demonstrated levels of VAL-083 in CSF at least as high as in plasma two hours post infusion (ratio 1.24 ± 0.35). In comparison, peak TMZ concentrations in the CSF are ~30% of that of the plasma.Due to its structural similarity with glucose, we have initiated in vitro glucose transporter studies to identify if SGLTs (sodium dependent glucose cotransporters) or GLUTs (glucose transporters) are contributing to brain penetration. Our initial studies evaluated VAL-083 as a substrate of the human SGLT1 and SGLT2 SLC (solute carrier) transporters. HEK293 cells expressing either the SGLT1 or SGLT2 transporter were exposed to VAL-083 at 3 and 15 µM for 2 and 20 min. The probe substrate methyl-α-D- glucopyranoside (AMG) was used as a positive control, as well as comparison against the reference inhibitors phloridzin dihydrate (100 µM, 20 min) for SGLT1 and dapagliflozin (0.3 µM, 10 min) for SGLT2. Surprisingly, no transporter-specific accumulation of VAL-083 by SGLT1 or SGLT2 was observed. Ongoing studies in CaCo-2 cells are investigating whether VA