Targeting Macromolecules to CNS and Other Hard-to-Treat Organs Using Lectin-Mediated Delivery

Abstract

The greatest challenges for therapeutic efficacy of many macromolecular drugs that act on intracellular are delivery to key organs and tissues and delivery into cells and subcellular compartments. Transport of drugs into critical cells associated with disease, including those in organs protected by restrictive biological barriers such as central nervous system (CNS), bone, and eye remains a significant hurdle to drug efficacy and impacts commercial risk and incentives for drug development for many diseases. These limitations expose a significant need for the development of novel strategies for macromolecule delivery. RTB lectin is the non-toxic carbohydrate-binding subunit B of ricin toxin with high affinity for galactose/galactosamine-containing glycolipids and glycoproteins common on human cell surfaces. RTB mediates endocytic uptake into mammalian cells by multiple routes exploiting both adsorptive-mediated and receptor-mediated mechanisms. In vivo biodistribution studies in lysosomal storage disease models provide evidence for the theory that the RTB-lectin transports corrective doses of enzymes across the blood–brain barrier to treat CNS pathologies. These results encompass significant implications for protein-based therapeutic approaches to address lysosomal and other diseases having strong CNS involvement.

GLB1-related disorders: GM1 gangliosidosis and Morquio B disease

“…RTB lectin is the non-toxic carbohydrate-binding subunit B of ricin toxin that has a high affinity for galactose/galactosaminecontaining glycolipids and glycoproteins that are commonly found on human cell surfaces. In vivo biodistribution studies in lysosomal storage disease models provide evidence that RTB-lectin transports corrective doses of enzymes across the blood-brain barrier to treat CNS pathologies [45]. Plant-made b-gal:RTB was efficiently taken into GM1 patient fibroblasts and mediated the reduction of GM1 ganglioside substrate [46].…”

CNS-Targeting Therapies for Lysosomal Storage Diseases: Current Advances and Challenges

“…To investigate the potential of large-molecular weight compounds to treat neurological disorders, novel approaches are required to surmount the BBB. Based on the ability of the adsorptive-mediated endocytosis of plant RTB-lectin, plant-based bioproduction of a fusion enzyme of ERT agent and lectin were accomplished, preserving the lysosomal enzymatic activity (Acosta and Cramer, 2020 ). Two murine LSD models, IDUA −/− (MPS I), GM1 gangliosidosis mice, treated with the ERT agent-RTB-lectin showed significant normalization of substrate levels in CNS, and correction of learning and memory deficits of the mouse model (Condori et al, 2016 ; Ou et al, 2018 ).…”

Preclinical Enzyme Replacement Therapy with a Recombinant β-Galactosidase-Lectin Fusion for CNS Delivery and Treatment of GM1-Gangliosidosis

“…As a lectin, RTB binds to diverse and abundant surface glycoproteins (including receptors) and glycolipids to direct endocytosis, lysosomal delivery and transcytosis. In contrast to other lysosomal enzyme delivery strategies, RTB-mediated uptake is not dependent upon the presence or abundance of a specific receptor for efficient delivery of its cargo enzyme into target cells, resulting in distinct pharmacokinetics, low cell uptake saturability, and access to “hard-to-treat” tissues, including the CNS [ 17 ].…”

“…Here, we sought to experiment with a minimally invasive ERT approach, producing a recombinant β-Gal protein fused to the RTB in the leaves of Nicotiana benthamiana plants [ 16 ]. This novel lysosomal delivery approach supports distinct in vivo biodistribution and has the potential to reach hard-to-treat organs, such as the brain [ 16 , 17 ]. A recombinant fusion protein composed of RTB and human β-Gal (hβ-Gal:RTB) has been previously shown to maintain all the biochemical characteristics of the endogenous enzyme and to restore β-Gal activity when used in vitro to correct GM1-gangliosidosis fibroblasts [ 16 ].…”