Approaches to transport therapeutic drugs across the blood–brain barrier to treat brain diseases

The central nervous system is protected by barriers which control the entry of compounds into the brain, thereby regulating brain homeostasis. The blood-brain barrier, formed by the endothelial cells of the brain capillaries, restricts access to brain cells of blood-borne compounds and facilitates nutrients essential for normal metabolism to reach brain cells. This very tight regulation of the brain homeostasis results in the inability of some small and large therapeutic compounds to cross the blood-brain barrier (BBB). Therefore, various strategies are being developed to enhance the amount and concentration of therapeutic compounds in the brain. In this review, we will address the different approaches used to increase the transport of therapeutics from blood into the brain parenchyma. We will mainly concentrate on the physiologic approach which takes advantage of specific receptors already expressed on the capillary endothelial cells forming the BBB and necessary for the survival of brain cells. Among all the approaches used for increasing brain delivery of therapeutics, the most accepted method is the use of the physiological approach which takes advantage of the transcytosis capacity of specific receptors expressed at the BBB. The low density lipoprotein receptor related protein (LRP) is the most adapted for such use with the engineered peptide compound (EPiC) platform incorporating the Angiopep peptide in new therapeutics the most advanced with promising data in the clinic.