S4‐02‐06: Gene therapy utilizing growth factors

Abstract

Brain-derived neurotrophic factor (BDNF) potently prevents the death and stimulates the function of cortical neurons in several rodent and primate models of Alzheimer's disease (AD). We previously reported that BDNF administration to the entorhinal cortex improved hippocampal-dependent learning and memory, enhanced synaptic function, and reduced neuronal loss (Nagahara et al., Nature Medicine 2009). Effects were observed in both the entorhinal cortex and hippocampus. We are now assessing the safety and toxicity of adeno-associated virus serotype 2 (AAV2) BDNF gene delivery at escalating doses in rodent and primate models. As part of potential clinical translation, it is essential to develop methods to accurately target AAV2-BDNF vector delivery to the entorhinal cortex. We have developed a “real-time” magnetic resonance imaging delivery system that enables accurate identification of vector infusion sites in the entorhinal cortex in rhesus monkeys, and that monitors spread of vector in each subjects at the time of active infusion. This system may be essential both in this AAV2-BDNF infusion program, and in other gene delivery programs targeting AD and other neurodegenerative brain disorders. Young rhesus monkeys underwent delivery of BDNF-AAV2 into the entorhinal cortex with the Clearpoint system (Surgivision) that uses a MRI-compatible head mounted frame (Smartframe), cannula system, and software to establish the cannula trajectory based real-time MRI. Using the real-time MRI, convection-enhanced delivery of BDNF-AAV2 mixed with 1mM gadoteridol (MRI contrast agent) into the entorhinal cortex is monitored during the infusion procedure. 1 month following vector delivery, monkeys are perfused and the brain is examined to confirm delivery of the BDNF-AAV2 to the targeted region. Real-time MRI during the infusion procedure allowed accurate targeting of BDNF-AAV2 to the entorhinal cortex. Comparison of BDNF immunolabeling in brain tissue and MR images of the vector infusion during surgery confirmed that real-time MRI accurately reflects targeting and spread of BDNF-AAV2. BDNF-AAV2 transduced only neurons, resulting in accurate vector delivery to the intended cellular targets. These findings demonstrate that real-time MRI during the infusion procedure can enable accurate targeting of gene delivery into entorhinal cortex of non-human primates. This represents a feasible method to deliver vectors into specific brain regions with 0.5 mm accuracy. The use of this system can allow accurate delivery of vector into this brain region in AD.