7-Fluorosialyl Glycosides Are Hydrolysis Resistant but Readily Assembled by Sialyltransferases Providing Easy Access to More Metabolically Stable Glycoproteins.

The maintenance of therapeutic glycoproteins within the circulatory system is associated, in large part, with the integrity of sialic acids as terminal sugars on the glycans. Glycoprotein desialylation, either by spontaneous cleavage or through host sialidases, leads to protein clearance, mainly through the liver. Thus, the installation of minimally modified sialic acids that are hydrolysis-resistant yet biologically equivalent should lead to increased circulatory half-lives and improved pharmacokinetic profiles. Here we describe the chemoenzymatic synthesis of CMP-sialic acid sugar donors bearing fluorine atoms at the 7-position, starting from the corresponding 4-deoxy-4-fluoro-N-acetylhexosamine precursors. For the derivative with natural stereochemistry we observe efficient glycosyl transfer by sialyltransferases, along with improved stability of the resultant 7-fluorosialosides toward spontaneous hydrolysis (3- to 5-fold) and toward cleavage by GH33 sialidases (40- to 250-fold). Taking advantage of the rapid transfer of 7-fluorosialic acid by sialyltransferases, we engineered the O-glycan of Interferon α-2b and the N-glycans of the therapeutic glycoprotein α1-antitrypsin. Studies of the uptake of the glyco-engineered α1-antitrypsin by HepG2 liver cells demonstrated the bioequivalence of 7-fluorosialic acid to sialic acid in suppressing interaction with liver cell lectins. In vivo pharmacokinetic studies reveal enhanced half-life of the protein decorated with 7-fluorosialic acid relative to unmodified sialic acid in the murine circulatory system. 7-Fluorosialylation therefore offers considerable promise as a means of prolonging circulatory half-lives of glycoproteins and may pave the way toward biobetters for therapeutic use.

Development of Novel Monoamine Oxidase-B (MAO-B) Inhibitors with Reduced Blood-Brain Barrier Permeability for the Potential Management of Noncentral Nervous System (CNS) Diseases.

Studies indicate that MAO-B is induced in peripheral inflammatory diseases. To target peripheral tissues using MAO-B inhibitors that do not permeate the blood-brain barrier (BBB) the MAO-B-selective inhibitor deprenyl was remodeled by replacing the terminal acetylene with a CO2H function, and incorporating a para-OCH2Ar motif (compounds 10a-s). Further, in compound 32 the C-2 side chain corresponded to CH2CN. In vitro, 10c, 10j, 10k, and 32 were identified as potent reversible MAO-B inhibitors, and all four compounds were more stable than deprenyl in plasma, liver microsomal, and hepatocyte stability assays. In vivo, they demonstrated greater plasma bioavailability. Assessment of in vitro BBB permeability showed that compound 10k is a P-glycoprotein (P-gp) substrate and 10j displayed mild interaction. Importantly, compounds 10c, 10j, 10k, and 32 displayed significantly reduced BBB permeability after intravenous, subcutaneous, and oral administration. These polar MAO-B inhibitors are pertinent leads for evaluation of efficacy in noncentral nervous system (CNS) inflammatory disease models.

Detection of amyloid-ß protein precursor homo-interactions using beta-galactosidase enzyme fragment complementation.

Amyloidogenic processing of the amyloid-ß protein precursor (AßPP) produces amyloid-ß peptides (Aß), the major constituent of amyloid plaques in the brains of Alzheimer's disease (AD) patients. Experimental evidence suggests that increased dimerization of AßPP increases Aß while decreased dimerization of AßPP decreases Aß production. If true, developing tools for detecting AßPP-AßPP interactions to understand AßPP processing leading to Aß production would be important. Here, we developed the method of ß-galactosidase (ß-gal) enzyme fragment complementation as a means to detect AßPP-AßPP interactions. Inactive ß-gal fragments are independently tagged to the C-terminal ends of monomeric AßPPs, and will come together to form a functional enzyme upon AßPP-AßPP interactions. Successful detection of ß-gal activity has been used to qualitatively visualize and quantify the amount of AßPP dimers or higher oligomers. This method can be used to enhance our understanding of the biological processes dependent upon AßPP-AßPP interactions.

Inhibition of alkaline phosphatase by cysteine: implications for calcium pyrophosphate dihydrate crystal deposition disease.

OBJECTIVE: Calcium pyrophosphate dihydrate (CPPD) crystal deposition disease, a common arthritis affecting the elderly, is characterized by the deposition of CPPD crystals in articular joints. The mechanism underlying disease expression is unknown, but factors contributing to the pathogenesis may involve changes in enzymatic activities involving pyrophosphate and phosphate metabolism. Tissue nonspecific alkaline phosphatase (TNAP) is one of the major enzymes regulating pyrophosphate concentrations in articular joints. We hypothesized that inhibition of TNAP activity at pH = 7.4 by endogenous molecules can lead to CPPD disease pathogenesis. METHODS: We investigated the inhibitory effects of the amino acid cysteine on TNAP's phosphatase, inorganic pyrophosphatase, and CPPD crystal dissolution activities. Kinetic parameters V(max), K(M), concentration for 50% inhibition (I(50)), inhibitor constant (K(I)), and specific activities calculated from Initial Velocity, Eadie-Hofstee, Simple, Dixon, and Secondary plots were used to assess enzyme inhibition. RESULTS: Cysteine inhibited TNAP's phosphatase activity uncompetitively and its inorganic pyrophosphatase activity mix-competitively. CPPD crystal dissolution activity was also inhibited. I(50) values demonstrated that high cysteine concentration is required to inhibit 50% of enzyme activity. K(I) values suggested that inorganic pyrophosphatase activity is inhibited more than the phosphatase activity. Ca(++) and Mg(++) ion concentrations may regulate this inhibition. CONCLUSION: The control of endogenous inhibitors, such as cysteine, that interfere with TNAP's ability to regulate CPPD crystal formation and dissolution in joints could be a potential therapeutic option for CPPD crystal deposition disease.