Anti-angiogenic therapy (AAT) targeting the vascular endothelial growth factor (VEGF) axis is an important component of treatment for recurrent glioblastoma (GBM). Many novel therapeutic strategies are being developed in combination with AAT in the next generation of clinical trials for GBM. Unfortunately, these combinations have been developed without an understanding of how AAT influences the integrity of the blood-brain barrier (BBB) in and around the tumor core and the subsequent delivery of novel chemotherapeutic agents across the BBB. During gliomagenesis, expression of VEGF and other pro-angiogenic factors promotes development of an immature tumor vasculature with partial BBB disruption. AAT-mediated inhibition of VEGF signaling can restore tight junction integrity and potentially promote expression of BBB drug efflux transporters, i.e., "normalize" the BBB vasculature. Many drugs being tested in GBM clinical trials in combination with AAT have limited BBB penetration. Studies in this application will test the central hypothesis that AAT-mediated restoration of BBB integrity may paradoxically reduce delivery of concomitantly administered drugs to the tumor, leading to reduced efficacy. This hypothesis will be tested both in the Mayo panel of primary GBM xenografts and in University of Minnesota-derived genetically engineered GBM models (GEMMs).
Aim one will determine the influence of the anti-VEGF antibody, Bev, the VEGFR inhibitor, cediranib, and a novel PI3K/mTOR inhibitor, GNE-317, on brain microvasculature function (perfusion, tight junctions and efflux transport) in primary GBM xenografts and GEMMs.
Aim two will examine how anti-angiogenic effects of Bev and GNE-317 alter drug delivery (site-specific pharmacokinetics) for relevant agents that have different BBB permeability characteristics (e.g., temozolomide, erlotinib, GDC-0980 and GNE-317). We hypothesize that AAT will have a variable detrimental impact on delivery and resultant efficacy depending on the combination therapy.
Aim three will test two distinct strategies to improve the efficacy of combination therapies: a) disruption of BBB efflux transporter activity to enhance the efficacy of AAT-transporter substrate combinations, and b) manipulation of chemical structure to reduce efflux liability and increase passive permeability to enhance efficacy of AAT + PI3K/mTOR inhibitor combinations. Many novel agents for GBM being developed in combination with AAT are excluded by the BBB. Thus, understanding the impact of AAT on BBB integrity and drug delivery is critical for successful development of AAT combination therapies for recurrent GBM. The planned studies will define critical parameters that influence the efficacy of AAT combination regimens and use that information to improve patient outcome in future trials that combine anti-angiogenic agents with other novel therapeutics.
Anti-angiogenic drugs, such as bevacizumab, block blood vessel growth and are important treatments for deadly brain tumors. However, bevacizumab and other anti-angiogenic drugs can also make blood vessels less leaky, especially in the brain, and might reduce the delivery of other chemotherapy drugs when given together in these brain cancers. This could reduce the effectiveness of certain combinations of drugs. The planned studies will test this possibility and identify methods to increase drug delivery and effectiveness of combined drug treatments. Ultimately, these studies will have an impact on improving the survival of patients with brain tumors.
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