Trans-nasal mucosal delivery of BDNF antagoNAT oligonucleotides using heterotopic mucosal engrafting for Parkinson's disease

Abstract

Chronic neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's diseases (PD) are currently the major health care challenge around the world [1]. The currently used levodopa therapy leads to motor complications like dyskinesias. Invasive techniques like deep brain stimulation used for treating PD leads to nerve cell damage in patients. Delivering drugs in the brain is limited by the presence of the blood brain barrier (BBB). Despite many new developments in the field of CNS drug delivery, overcoming the BBB continues to pose a serious challenge. Parkinson's disease is characterized by the loss of nigrostriatal dopaminergic neurons in turn reducing dopamine levels in brain. Brain-derived neurotropic factor (BDNF) is a high molecular weight protein, responsible for dopaminergic neuron survival [2]. However, the therapeutic applications of BDNF in CNS diseases are limited by the BBB, its complex structure, off-target toxicity, immunogenicity and post-translational modifications. BDNF AntagoNATs (AT's) are small oligonucleotides that can up regulate endogenous BDNF protein expression by inhibiting the natural antisense transcripts (NAT's) and could be a potential therapy for neurodegenerative diseases like AD and PD. The AT's are highly locus specific and are highly stable structures that can improve the uptake of these oligonucleotides in cells. Despite several advantages and significant promise of AT's, they cannot pass through the BBB. In my doctoral project we have successfully developed an innovative endonasal heterotopic mucosal grafting technique that can provide a permanent way of delivering high molecular weight therapeutics like proteins and oligonucleotides to the brain bypassing the BBB. This method is based on human endoscopic skull base surgeries which are currently in practice in the clinic. Using the endonasal mucosal grafting technique, we successfully showed that a model protein like ovalbumin (45 kDa) can be delivered to the brain in spite of its high molecular weight. We utilized a liposome-in gel system to protect the protein from degradation and to allow to sustained drug release. The results of this study were published in PLOS-1 in December 2018 [3]. Regarding BDNF AT's, we have successfully shown the liposomes encapsulating BDNF AT's can up regulate the BDNF mRNA and protein levels in rat schwannoma cells and our results also demonstrate the grafts are capable of delivering therapeutic levels of AT's in rat brain which further resulted in significant protein up regulation in striatum and substantia nigra. We have also shown that the liposomes encapsulating BDNF AT's are capable of protecting dopaminergic neurons in a 6-hydroxydopamine rat model of PD further confirming the therapeutic effect of trans-nasal delivery of BDNF AT's. A manuscript comprising of the results from this study is currently in review in the journal Science Advances. Considering one of the limitations of the mucosal engrafting model being that it allows the delivery of therapeutics from the top of the head in a rat model instead of through the nose, we developed an olfactory depot surgery rat model which is closer to mimicking the proposed drug delivery strategy in humans. In this particular model, our aim was to create a drug depot using a liposome-in-gel system right above the nasal grafts in a rat and deliver the drug directly through it. We have successfully shown that the depot surgery model can also deliver therapeutic amounts of BDNF AT's in rat brain. As a platform technique these results suggest that the surgical techniques for CNS drug delivery developed during the course of my thesis project could be potentially used to deliver other high molecular weight therapeutics to the brain by passing the BBB completely which could open door to additional treatment options for CNS diseases.