Michael-addition of a thiol to a maleimide is commonly used for bioconjugation of drugs to macromolecules. Indeed, both current FDA-approved antibody-drug conjugates-Brentuximab vedotin and Trastuzumab emtansine-and one approved PEGylated conjugate-Cimzia-contain a thiol-maleimide adduct. However, the ultimate in vivo fate of such adducts is to undergo disruptive cleavage by thiol exchange or stabilizing ring opening. Therapeutic efficacy of a conjugate can be compromised by thiol exchange and the released drug may show toxicities. However, if the succinimide moiety of a maleimide-thiol conjugate is hydrolyzed, the ring-opened product is stabilized toward cleavage. We determined rates of ring-opening hydrolysis and thiol exchange of a series of N-substituted succinimide thioethers formed by maleimide-thiol conjugation. Ring-opening of conjugates prepared with commonly used maleimides were too slow to serve as prevention against thiol exchange. However, ring-opening rates are greatly accelerated by electron withdrawing N-substituents, and ring-opened products have half-lives of over two years. Thus, conjugates made with electron-withdrawing maleimides may be purposefully hydrolyzed to their ring-opened counterparts in vitro to ensure in vivo stability.

ObjectivesTo synthesise current evidence for the effects of exenatide and liraglutide on heart rate, blood pressure and body weight.DesignMeta-analysis of available data from randomised controlled trials comparing Glucagon-like peptide-1 (GLP-1) analogues with placebo, active antidiabetic drug therapy or lifestyle intervention.ParticipantsPatients with type 2 diabetes.Outcome measuresWeighted mean differences between trial arms for changes in heart rate, blood pressure and body weight, after a minimum of 12-week follow-up.Results32 trials were included. Overall, GLP-1 agonists increased the heart rate by 1.86 beats/min (bpm) (95% CI 0.85 to 2.87) versus placebo and 1.90 bpm (1.30 to 2.50) versus active control. This effect was more evident for liraglutide and exenatide long-acting release than for exenatide twice daily. GLP-1 agonists decreased systolic blood pressure by −1.79 mm Hg (−2.94 to −0.64) and −2.39 mm Hg (−3.35 to −1.42) compared to placebo and active control, respectively. Reduction in diastolic blood pressure failed to reach statistical significance (−0.54 mm Hg (−1.15 to 0.07) vs placebo and −0.50 mm Hg (−1.24 to 0.24) vs active control). Body weight decreased by −3.31 kg (−4.05 to −2.57) compared to active control, but by only −1.22 kg (−1.51 to −0.93) compared to placebo.ConclusionsGLP-1 analogues are associated with a small increase in heart rate and modest reductions in body weight and blood pressure. Mechanisms underlying the rise in heart rate require further investigation.

Conjugation to macromolecular carriers is a proven strategy for improving the pharmacokinetics of drugs, with many stable polyethylene glycol conjugates having reached the market. Stable conjugates suffer several limitations: loss of drug potency due to conjugation, confining the drug to the extracellular space, and the requirement for a circulating conjugate. Current research is directed toward overcoming such limitations through releasable conjugates in which the drug is covalently linked to the carrier through a cleavable linker. Satisfactory linkers that provide predictable cleavage rates tunable over a wide time range that are useful for both circulating and noncirculating conjugates are not yet available. We describe such conjugation linkers on the basis of a nonenzymatic β-elimination reaction with preprogrammed, highly tunable cleavage rates. A set of modular linkers is described that bears a succinimidyl carbonate group for attachment to an amine-containing drug or prodrug, an azido group for conjugation to the carrier, and a tunable modulator that controls the rate of β-eliminative cleavage. The linkers provide predictable, tunable release rates of ligands from macromolecular conjugates both in vitro and in vivo, with half-lives spanning from a range of hours to >1 y at physiological pH. A circulating PEG conjugate achieved a 56-fold half-life extension of the 39-aa peptide exenatide in rats, and a noncirculating s.c. hydrogel conjugate achieved a 150-fold extension. Using slow-cleaving linkers, the latter may provide a generic format for once-a-month dosage forms of potent drugs. The releasable linkers provide additional benefits that include lowering C max and pharmacokinetic coordination of drug combinations. metronomic chemotherapy | implant M any drugs and drug candidates are suboptimal or ineffective because of a short duration of action. For example, peptides and proteins with promising therapeutic value often have serum half-lives of only minutes to hours. One solution to this problem involves conjugation to carriers such as polyethylene glycol (PEG), the Fc portion of IgG, serum albumin, and other longlived macromolecules. The large carriers retard kidney filtration and hence increase plasma half-life of the attached drug. Much success has been realized thus far with PEG as the macromolecular carrier. PEG is nontoxic and nonimmunogenic, and the plasma half-life is a function of hydrodynamic size. Conjugation of drugs to PEG with molecular mass ∼40 kDa has been successfully used with peptides, nucleic acids, and small molecules and can afford half-lives of up to ∼7 d in humans; as of 2011, 10 PEGylated peptide-based drugs were approved by the Food and Drug Administration (FDA) and ∼40 were in clinical trials (1, 2).All of the currently marketed PEG-protein conjugates are permanently PEGylated. Attachment of large PEG moieties often reduces activity of the drug, and higher concentrations of conjugate are necessary to achieve the required biological activity. A further limitation is that permanen...

We recently reported a chemical approach for half-life extension that utilizes sets of releasable linkers to attach drugs to macromolecules via a cleavable carbamate group (Santi et al., Proc. Nat. Acad. Sci. U.S.A. 2012, 109, 6211-6216). The linkers undergo a β-elimination cleavage to release the free, native amine-containing drug. A limitation of the technology is the requirement for an amino group on the drug in order to form the carbamate bond, since most small molecules do not have an amine functional group. Here, we describe an approach to adapt these same β-elimination carbamate linkers so they can be used to connect other acidic heteroatoms, in particular, phenolic hydroxyl groups. The approach utilizes a methylene adaptor to connect the drug to the carbamate nitrogen, and an electron-withdrawing group attached to carbamate nitrogen to stabilize the system against a pH-independent spontaneous cleavage. Carbamate cleavage is driven by β-elimination to give a carboxylated aryl amino Mannich base which rapidly collapses to give the free drug, an aryl amine, and formaldehyde.

This article describes a new methodology for the parallel synthesis of 3,4-dihydroquinoxalin-2-ones containing three points of diversity. The synthesis begins with commercially available resin-bound alpha-amino acids as the source of the first diversity element and employs a combination of solid- and solution-phase chemistry to introduce the other two. The key step is an intramolecular cyclization and simultaneous traceless cleavage from the solid support to give a disubstituted 3,4-dihydroquinoxalin-2-one. The third substituent is introduced in solution by N-alkylation of the aniline nitrogen using a scavenger resin to dispose of excess reagent. All the reactions in the sequence take place at room temperature without the need to use strong acids or to maintain an inert atmosphere, thereby preserving the chiral integrity of the starting alpha-amino acid and facilitating the generation of libraries in a high-throughput parallel format.