Abstract 4479: Influence of the blood-brain barrier on drug distribution and efficacy of PI3K/mTOR inhibitors

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Drug delivery to glioblastoma multiforme (GBM) is influenced by the presence of blood-brain barrier (BBB). PI3K/mTOR/AKT is frequently dysregulated in GBM and some agents targeting this pathway have limited distribution across the BBB due to activity of efflux transporters p-glycoprotein (P-gp) and breast cancer resistance protein1 (BCRP1). GNE-317 and GDC-0980 are structurally related PI3K/mTOR inhibitors with the former molecule optimized for brain delivery. Here the influence of the BBB on tumor distribution and resultant efficacy was evaluated in flank and intracranial tumors. Pharmacokinetic-pharmacodynamic approaches were used in GBM10 (patient-derived) and U87 (cell line) orthotopic xenograft models to evaluate the influence of delivery on efficacy. We investigated the brain distribution of GNE-317 and GDC-0980 in tumor-bearing (GBM10 and U87) athymic nu/nu mice and non-tumor-bearing (FVBn) mice. BBB-integrity in both GBM10 and U87-models was evaluated using Texas-Red(TR)-linked 3kD dextran prior to euthanasia. GNE-317 and GDC-0980 were administered orally at 30mg/kg and 7.5mg/kg, respectively, for all studies. Brain distribution studies were performed in FVB-wild type (WT) and P-gp/Bcrp knockout mice (TKO) and brain and plasma exposures (area-under-curve, AUC) were determined. Comparison of tumor pharmacokinetic-pharmacodynamic endpoints at 1- and 6-hr post single oral dose will be reported. GBM10 showed heterogeneous disruption of BBB-integrity, while U87 tumors exhibited homogenous and uniform disruption of BBB by analysis of TR-dextran accumulation within orthotopic xenografts. The brain-to-plasma AUC0-tlast ratio in FVBn-wild type was ∼10-fold higher in GNE-317(0.75) vs. GDC-0980 (0.07). Survival studies in intracranial tumors with U87 demonstrated no difference in survival between the GNE-317 vs. GDC-0980 treated groups (median survival∼26 days (GNE-317), 34 days(GDC-0980), p=0.07), and both treatments significantly extended survival compared to vehicle control (p<0.0003, ∼12 days). Survival with GNE-317 in GBM10 xenografts (median survival 42 days vs. 35 days for control, p<0.0003) was greater than the GDC-0980 treated group (median survival 32 days vs. 35 days in control, p=0.79); both treatments were not significantly different from each other (p=0.08). To evaluate the relative efficacy in the complete absence of the BBB, the effects on tumor growth are being evaluated in flank tumor models. These studies demonstrate that efficacy of a PI3K/mTOR inhibitor with low brain penetrance (GDC-0980) is marginally inferior to the related brain penetrant GNE-317 in tumor models with a partially intact BBB. Since GBM patients have regions of intact BBB, these data suggest that the brain penetration of targeted agents may be a critical factor that determines treatment efficacy in patients. Citation Format: Rajneet K. Oberoi, William F. Elmquist, Rajendar Mittapalli, Jenny Pokorny, Jann Sarkaria. Influence of the blood-brain barrier on drug distribution and efficacy of PI3K/mTOR inhibitors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4479. doi:10.1158/1538-7445.AM2014-4479