Design of Potent Mannose 6‐Phosphate Analogues for the Functionalization of Lysosomal Enzymes To Improve the Treatment of Pompe Disease

Therapeutic antibody engineering for efficient targeted degradation of membrane proteins in lysosomes

Targeted degradation of pathological proteins is a promising approach to enhance the effectiveness of therapeutic monoclonal antibodies (mAbs) in cancer therapy. In this study, we demonstrate that this objective can be efficiently achieved by the grafting of mannose 6-phosphate analogues called AMFAs2 onto the therapeutic antibodies trastuzumab and cetuximab, both directed against membrane antigens. The grafting of AMFAs confers to these antibodies the novel property of being internalized via the mannose 6-phosphate receptor (M6PR) pathway. AMFA conjugation to these mAbs significantly increases their cellular uptake and leads to enhanced degradation of the target antigens in cancer cells. This results in a drastic inhibition of cancer cell proliferation compared to unconjugated mAbs, as demonstrated in various cancer cell lines, and an increased therapeutic efficacy in mouse and zebrafish xenografted models. These findings highlight the potential of this technology to improve therapeutic outcomes in cancer treatment.

Engineered therapeutic antibodies with mannose 6-phosphate analogues as a tool to degrade extracellular proteins

Inducing the degradation of pathological soluble antigens could be the key to greatly enhancing the efficacy of therapeutic monoclonal antibodies (mAbs), extensively used in the treatment of autoimmune and inflammatory disorders or cancer. Lysosomal targeting has gained increasing interest in recent years due to its pharmaceutical applications far beyond the treatment of lysosomal diseases, as a way to address proteins to the lysosome for eventual degradation. Mannose 6-phosphonate derivatives (M6Pn), called AMFA, are unique glycovectors that can significantly enhance the cellular internalization of the proteins conjugated to AMFA via the cation-independent mannose 6-phosphate receptor (M6PR) pathway. AMFA engineering of mAbs results in the generation of a bifunctional antibody that is designed to bind both the antigen and the M6PR. The improvement of the therapeutic potential by AMFA engineering was investigated using two antibodies directed against soluble antigens: infliximab (IFX), directed against tumor necrosis factor α (TNF-α), and bevacizumab (BVZ), directed against the vascular endothelial growth factor (VEGF). AMFA conjugations to the antibodies were performed either on the oligosaccharidic chains of the antibodies or on the lysine residues. Both conjugations were controlled and reproducible and provided a novel affinity for the M6PR without altering the affinity for the antigen. The grafting of AMFA to mAb increased their cellular uptake through an M6PR-dependent mechanism. The antigens were also 2.6 to 5.7 times more internalized by mAb-AMFA and rapidly degraded in the cells. Additional cell culture studies also proved the significantly higher efficacy of IFX-AMFA and BVZ-AMFA compared to their unconjugated counterparts in inhibiting TNF-α and VEGF activities. Finally, studies in a zebrafish embryo model of angiogenesis and in xenografted chick embryos showed that BVZ-AMFA was more effective than BVZ in reducing angiogenesis. These results demonstrate that AMFA grafting induces the degradation of soluble antigens and a significant increase in the therapeutic efficacy. Engineering with mannose 6-phosphate analogues has the potential to develop a new class of antibodies for autoimmune and inflammatory diseases.

Cation-independent mannose 6-phosphate receptor: From roles and functions to targeted therapies

The cation-independent mannose 6-phosphate receptor (CI-M6PR) is a ubiquitous transmembrane receptor whose main intracellular role is to direct enzymes carrying mannose 6-phosphate moieties to lysosomal compartments. Recently, the small membrane-bound portion of this receptor has appeared to be implicated in numerous pathophysiological processes. This review presents an overview of the main ligand partners and the roles of CI-M6PR in lysosomal storage diseases, neurology, immunology and cancer fields. Moreover, this membrane receptor has already been noted for its strong potential in therapeutic applications thanks to its cellular internalization activity and its ability to address pathogenic factors to lysosomes for degradation. A number of therapeutic delivery approaches using CI-M6PR, in particular with enzymes, antibodies or nanoparticles, are currently being proposed.

Insulin-like Growth Factor 2 (IGF2)-Fused Lysosomal Targeting Chimeras for Degradation of Extracellular and Membrane Proteins

Targeted degradation of the cell-surface and extracellular proteins via the endogenous lysosomal degradation pathways, such as lysosome-targeting chimeras (LYTACs), has recently emerged as an attractive tool to expand the scope of extracellular chemical biology. Herein, we report a series of recombinant proteins genetically fused to insulin-like growth factor 2 (IGF2), which we termed iLYTACs, that can be conveniently obtained in high yield by standard cloning and bacterial expression in a matter of days. We showed that both type-I iLYTACs, in which IGF2 was fused to a suitable affibody or nanobody capable of binding to a specific protein target, and type-II iLYTAC (or IGF2-Z), in which IGF2 was fused to the IgG-binding Z domain that served as a universal antibody-binding adaptor, could be used for effective lysosomal targeting and degradation of various extracellular and membrane-bound proteins-of-interest. These heterobifunctional iLYTACs are fully genetically encoded and can be produced on a large scale from conventional E. coli expression systems without any form of chemical modification. In the current study, we showed that iLYTACs successfully facilitated the cell uptake, lysosomal localization, and efficient lysosomal degradation of various disease-relevant protein targets from different mammalian cell lines, including EGFR, PD-L1, CD20, and α-synuclein. The antitumor properties of iLYTACs were further validated in a mouse xenograft model. Overall, iLYTACs represent a general and modular strategy for convenient and selective targeted protein degradation, thus expanding the potential applications of current LYTACs and related techniques.

Lysosomal Targeting of β-Cyclodextrin

β-Cyclodextrin (β-CD) and derivatives are approved therapeutics in >30 clinical settings. β-CDs have also shown promise as therapeutics for treatment of some lysosomal storage disorders, such as Niemann-Pick disease type C, and other disease states which involve metabolite accumulation in the lysosome. In these cases, β-CD activity relies on transport to the lysosome, wherein it can bind hydrophobic substrate and effect extraction. The post-translational attachment of N-glycans terminated in mannose-6-phosphate (M6P) residues is the predominant method by which lysosomal enzymes are targeted to the lysosome. In this work we covalently attach a synthetic biantennary bis-M6P-terminated N-glycan to β-CD and study the effect of the added glycans in a mammalian cell line. The formation of a host guest complex with a Cy5 fluorophore allows study of both cellular internalisation and transport to the lysosome by fluorescence microscopy. Results indicate that the rates of both internalisation and lysosomal transport are increased by the attachment of M6P-glycans to β-CD, indicating that M6P-glycan conjugation may improve the therapeutic effectiveness of β-CD for the treatment of disorders involving hydrophobic metabolite accumulation in the lysosome.

The new horizons for treatment of Late-Onset Pompe Disease (LOPD)

Late-onset Pompe disease (LOPD) is a genetic myopathy causing skeletal muscle weakness and severe respiratory impairment, due to the deficiency of the lysosomal enzyme acid alpha-glucosidase (GAA) leading to lysosomal glycogen accumulation along with other complex pathophysiological processes. A major step for treatment of Pompe disease was reached in 2006 with the marketing of alglucosidase alfa, a first enzyme replacement therapy (ERT) that showed a significant motor and respiratory benefit. However, efficacy of alglucosidase alfa is limited in LOPD with a loss of efficacy over time, promoting research on new treatments. Next-generation ERT are new enzymes biochemically modified to increase the uptake of exogenous enzyme by target tissues, and the benefit of two recombinant enzymes (avalglucosidase alfa and cipaglucosidase alfa) has been recently studied in large phase III clinical trials, the latest combined with miglustat. Several innovative therapies, based on GAA gene transfer, antisense oligonucleotides or inhibition of glycogen synthesis with substrate reduction therapy, are currently under study, but are still at an early stage of development. Overall, active research for new treatments raises hope for LOPD patients but challenges remain for the clinician with the need for reliable efficacy assessment tools, long-term registry data, and evidence-based recommendations for the best use of these new molecules recently available or under development.

Synthesis and application of phosphorylated saccharides in researching carbohydrate-based drugs

Phosphorylated saccharides are valuable targets in glycochemistry and glycobiology, which play an important role in various physiological and pathological processes. The current research on phosphorylated saccharides primarily focuses on small molecule inhibitors, glycoconjugate vaccines and novel anti-tumour targeted drug carrier materials. It can maximise the pharmacological effects and reduce the toxicity risk caused by nonspecific off-target reactions of drug molecules. However, the number and types of natural phosphorylated saccharides are limited, and the complexity and heterogeneity of their structures after extraction and separation seriously restrict their applications in pharmaceutical development. The increasing demands for the research on these molecules have extensively promoted the development of carbohydrate synthesis. Numerous innovative synthetic methodologies have been reported regarding the continuous expansion of the potential building blocks, catalysts, and phosphorylation reagents. This review summarizes the latest methods for enzymatic and chemical synthesis of phosphorylated saccharides, emphasizing their breakthroughs in yield, reactivity, regioselectivity, and application scope. Additionally, the anti-bacterial, anti-tumour, immunoregulatory and other biological activities of some phosphorylated saccharides and their applications were also reviewed. Their structure-activity relationship and mechanism of action were discussed and the key phosphorylation characteristics, sites and extents responsible for observed biological activities were emphasised. This paper will provide a reference for the application of phosphorylated saccharide in the research of carbohydrate-based drugs in the future.

Olefin Metathesis Catalysts Generated In Situ from Molybdenum(VI)-Oxo Complexes by Tuning Pendant Ligands

Tailored molybdenum(VI)‐oxo complexes of the form MoOCl₂(OR)₂(OEt₂) catalyse olefin metathesis upon reaction with an organosilicon reducing agent at 70 °C, in the presence of olefins. While this reactivity parallels what has recently been observed for the corresponding classical heterogeneous catalysts based on supported metal oxide under similar conditions, the well‐defined nature of our starting molecular systems allows us to understand the influence of structural, spectroscopic and electronic characteristics of the catalytic precursor on the initiation and catalytic proficiency of the final species. The catalytic performances of the pre‐catalysts are determined by the highly electron withdrawing (σ‐donation) character of alkoxide ligands, O^tBu_F9 being the best. This activity correlates with both the ⁹⁵Mo chemical shift and the reduction potential that follows the same trend: O^tBu_F9>O^tBu_F6>O^tBu_F3.

Chemoenzymatic glycan-selective remodeling of a therapeutic lysosomal enzyme with high-affinity M6P-glycan ligands. Enzyme substrate specificity is the name of the game

Functionalization of therapeutic lysosomal enzymes with mannose-6-phosphate (M6P) glycan ligands represents a major strategy for enhancing the cation-independent M6P receptor (CI-MPR)-mediated cellular uptake, thus improving the overall therapeutic efficacy of the enzymes. However, the minimal high-affinity M6P-containing N-glycan ligands remain to be identified and their efficient and site-selective conjugation to therapeutic lysosomal enzymes is a challenging task. We report here the chemical synthesis of truncated M6P-glycan oxazolines and their use for enzymatic glycan remodeling of recombinant human acid α-glucosidase (rhGAA), an enzyme used for treatment of Pompe disease which is a disorder caused by a deficiency of the glycogen-degrading lysosomal enzyme. Structure-activity relationship studies identified M6P tetrasaccharide oxazoline as the minimal substrate for enzymatic transglycosylation yielding high-affinity M6P glycan ligands for the CI-MPR. Taking advantage of the substrate specificity of endoglycosidases Endo-A and Endo-F3, we found that Endo-A and Endo-F3 could efficiently deglycosylate the respective high-mannose and complex type N-glycans in rhGAA and site-selectively transfer the synthetic M6P N-glycan to the deglycosylated rhGAA without product hydrolysis. This discovery enabled a highly efficient one-pot deglycosylation/transglycosylation strategy for site-selective M6P-glycan remodeling of rhGAA to obtain a more homogeneous product. The Endo-A and Endo-F3 remodeled rhGAAs maintained full enzyme activity and demonstrated 6- and 20-fold enhanced binding affinities for CI-MPR receptor, respectively. Using an in vitro cell model system for Pompe disease, we demonstrated that the M6P-glycan remodeled rhGAA greatly outperformed the commercial rhGAA (Lumizyme) and resulted in the reversal of cellular pathology. This study provides a general and efficient method for site-selective M6P-glycan remodeling of recombinant lysosomal enzymes to achieve enhanced M6P receptor binding and cellular uptake, which could lead to improved overall therapeutic efficacy of enzyme replacement therapy.

α,β-Unsaturated γ-Peptide Foldamers

Despite their concomitant emergence in the 1990s, γ-peptide foldamers have not developed as fast as β-peptide foldamers and to date, only a few γ-oligomer structures have been reported, and with sparse applications. Among these examples, sequences containing α,β-unsaturated γ-amino acids have recently drawn attention since the Z/E configurations of the double bond provide opposite planar restrictions leading to divergent conformational behaviors, from helix to extended structures. In this Review, we give a comprehensive overview of the developments of γ-peptide foldamers containing α,β-unsaturated γ-amino acids with examples of applications for health and catalysis, as well as materials science.

Multivalent, Stabilized Mannose-6-Phosphates for the Targeted Delivery of Toll-Like Receptor Ligands and Peptide Antigens

Mannose-6-phosphate (M6P) is recognized by the mannose-6-phosphate receptor and plays an important role in the transport of cargo to the endosomes, making it an attractive tool to improve endosomal trafficking of vaccines. We describe herein the assembly of peptide antigen conjugates carrying clusters of mannose-6-C-phosphonates (M6Po). The M6Po's are stable M6P mimics that are resistant to cleavage of the phosphate group by endogenous phosphatases. Two different strategies for the incorporation of the M6Po clusters in the conjugate have been developed: the first relies on a "post-assembly" click approach employing an M6Po bearing an alkyne functionality; the second hinges on an M6Po C-glycoside amino acid building block that can be used in solid-phase peptide synthesis. The generated conjugates were further equipped with a TLR7 ligand to stimulate dendritic cell (DC) maturation. While antigen presentation is hindered by the presence of the M6Po clusters, the incorporation of the M6Po clusters leads to increased activation of DCs, thus demonstrating their potential in improving vaccine adjuvanticity by intraendosomally active TLR ligands.

Moss-Derived Human Recombinant GAA Provides an Optimized Enzyme Uptake in Differentiated Human Muscle Cells of Pompe Disease

Pompe disease is an autosomal recessive lysosomal storage disorder (LSD) caused by deficiency of lysosomal acid alpha-glucosidase (GAA). The result of the GAA deficiency is a ubiquitous lysosomal and non-lysosomal accumulation of glycogen. The most affected tissues are heart, skeletal muscle, liver, and the nervous system. Replacement therapy with the currently approved enzyme relies on M6P-mediated endocytosis. However, therapeutic outcomes still leave room for improvement, especially with regard to skeletal muscles. We tested the uptake, activity, and effect on glucose metabolism of a non-phosphorylated recombinant human GAA produced in moss (moss-GAA). Three variants of moss-GAA differing in glycosylation pattern have been analyzed: two with terminal mannose residues in a paucimannosidic (Man3) or high-mannose (Man 5) configuration and one with terminal N-acetylglucosamine residues (GnGn). Compared to alglucosidase alfa the moss-GAA GnGn variant showed increased uptake in differentiated myotubes. Moreover, incubation of immortalized muscle cells of Gaa^-/- mice with moss-GAA GnGn led to similarly efficient clearance of accumulated glycogen as with alglucosidase alfa. These initial data suggest that M6P-residues might not always be necessary for the cellular uptake in enzyme replacement therapy (ERT) and indicate the potential of moss-GAA GnGn as novel alternative drug for targeting skeletal muscle in Pompe patients.

Mannose 6-phosphonate labelling: A key for processing the therapeutic enzyme in Pompe disease

In the search of a better enzyme therapy in Pompe disease, the conjugation of mannose 6‐phosphonates to the recombinant enzyme appeared as an enhancer of its efficacy. Here, we demonstrated that the increased efficacy of the conjugated enzyme is partly due to a higher intracellular maturation because of its insensitiveness to acid phosphatases during the routing to lysosomes.