Application of carbamyl in structural optimization.

Carbamyl is considered a privileged structure in medicinal chemistry. It has a wide range of biological activities such as antimicrobial, anticancer, anti-epilepsy, for which the best evidence is a number of marketed carbamyl-containing drugs. Carbamyl is formed of primary amine and carbonyl moieties that act as hydrogen bond donors and hydrogen acceptors with residues of targets respectively, which are benefit for improving pharmacological activities. In other cases, the introduced carbamyl improves drug-like properties including oral bioavailability. In this review, we introduce the carbamyl-containing drugs and the application of carbamyl in structural optimization as a result of enhancing activities or/and drug-like properties.

Multifunctional Tumor-Targeting Cathepsin B-Sensitive Gemcitabine Prodrug Covalently Targets Albumin in Situ and Improves Cancer Therapy.

We report a new type of amide bond-bearing cathepsin B-sensitive gemcitabine (GEM) prodrugs, capable of in situ covalently targeting circulating albumin and then making a hitchhike to the tumor. Specially, less plasma-enzyme deactivation, long plasma half-life, independence on nucleoside transporters, outstanding tumor targeting, and site-specific drug release are achieved, and as such these multifunctional advantages contribute to the dramatically increased in vivo antitumor efficacy.

Design, synthesis, and evaluation of carboxyl-modified oseltamivir derivatives with improved lipophilicity as neuraminidase inhibitors.

In this study, a series of carboxyl-modified oseltamivir analogs with improved lipophilicity were designed and synthesized, and their inhibitory activities against neuraminidase from influenza A virus H5N1 subtype were evaluated. The results demonstrated that compound 5m exhibited potent inhibitory activity (IC50 = 1.30 ±â€¯0.23 µM), and it targeted the recently discovered 430-cavity. Compound 5m (LogD = -0.12) is more lipophilic than oseltamivir carboxylate (LogD = -1.69) at pH 7.4, which is potentially propitious to improved membrane permeability and oral drug absorption. Meanwhile, 5m showed high stability in human liver microsomes. The findings of this study can be valuable in identifying neuraminidase inhibitors with optimal lipophilicity and in the exploration of 430-cavity.

The current strategies of optimization of oseltamivir against mutant neuraminidases of influenza A：A review.

Influenza with a tendency to cause pandemic and epidemic is an infectious disease with a high of morbidity and mortality. Neuraminidase (NA) inhibitors are proved to prevent and treat influenza. Among the four Neuraminidase inhibitors (NAIs) licensed, oseltamivir is most commonly used. With the extensive usage, several variants containing mutant NAs especially H274Y point mutation exhibit reduced susceptibility. In this review, we covered the current drugs available for influenza, the analysis of active site of NA, the mutant types of NAs and the molecular mechanism of drug resistance brought by H274Y mutant NAs. For recovering the susceptibility to oseltamivir, many series of oseltamivir analogues were designed. We present the details of the strategies of strengthening the interactions with S2 via introducing strong basic fragment, targeting additional subpockets and making full use of Zone X by modifying 3-pentyl of OC. PROTAC targeting NA and combination therapies are also introduced. Further, the advantages and disadvantages of these methods are also discussed.

Discovery of hydrazide-containing oseltamivir analogues as potent inhibitors of influenza A neuraminidase.

Neuraminidase (NA) inhibitors play a prime role in treating influenza. However, a variety of viruses containing mutant NAs have developed severe drug resistance towards NA inhibitors, so it is of crucial significance to solve this problem. Encouraged by urea-containing compound 12 disclosed by our lab, we designed a series of oseltamivir derivatives bearing hydrazide fragment for targeting the 150 cavity. Among the synthesized compounds, compound 17a showed 8.77-fold, 4.12-fold, 203-fold and 6.23-fold more potent activity than oseltamivir carboxylate against NAs from H5N1, H1N1, H5N1-H274Y, H1N1-H274Y, respectively. Meanwhile, the best compound 17a exhibited satisfactory metabolic stability in vitro. This study offers an important reference for the structural optimization of oseltamivir aiming at potent inhibition against H274Y mutant of NAs.

Discovery of a non-zwitterionic oseltamivir analogue as a potent influenza a neuraminidase inhibitor.

The most of potent neuraminidase inhibitors as zwitterions with poor lipophilicity suffered from the poor oral bioavailability. Herein, we describe a rational journey to discover a non-zwitterionic neuraminidase inhibitor 24a containing urea. It showed potent inhibitions against neuraminidases from group 1(H5N1 and H1N1) and group 2 (H3N2) subtypes and exhibited more strong inhibitory activities against neuraminidases from H274Y mutants than oseltamivir carboxylate. Whether administrated by orally or intravenous injection, the pharmacokinetic profile of compound 24a in SD rats were improved compared to oseltamivir carboxylate.

Design, synthesis and biological evaluation of oseltamivir derivatives containing pyridyl group as potent inhibitors of neuraminidase for influenza A.

Influenza A neuraminidase plays an indispensable role in the process of replication and transmission of influenza, so the neuraminidase inhibition can prevent the reproduction of the viruses therefore achieve the effect of treatment of influenza. However, drug resistance of neuraminidase inhibitors such as oseltamivir highlights the need to develop novel structural neuraminidase inhibitors. Here we explored a series of oseltamivir derivatives bearing pyridyl group. Among them, compound 23b exhibiting potent inhibitory activity against neuraminidase from H5N1 subtype was comparable to oseltamivir carboxylate. Cytopathic effect inhibition assay in MDCK cells indicated that compound 23b exerted powerful inhibitions on influenza viruses. And compound 23b were nontoxic to MDCK cells. Meanwhile, compound 23b showed high stability towards rat liver microsomes, human liver microsomes and human plasma. This research enriched the structural type of neuraminidase inhibitors.

Striking a Balance between Carbonate/Carbamate Linkage Bond- and Reduction-Sensitive Disulfide Bond-Bearing Linker for Tailored Controlled Release: In Situ Covalent-Albumin-Binding Gemcitabine Prodrugs Promote Bioavailability and Tumor Accumulation.

To address the challenges of rapid enzyme inactivation, poor tumor targeting, and acquired drug resistance in gemcitabine (GEM) application, we report two groups of maleimide-functionalized GEM prodrugs conjugating covalently in situ with Cys-34 of blood-circulating albumin and then resulting in macromolecular prodrugs after intravenous administration. Tailored and accurate controlled release was achieved through different combinations of linkage bonds, relatively stable and labile (carbamate and carbonate, respectively), and linkers with or without insertion of a disulfide bond. Interestingly, we found that the overall advantages or disadvantages brought by a disulfide bond varied with the stability of the linkage bond. Finally, the carbonate linkage bond-bearing group, especially the one with a linker lacking a disulfide bond, stood out with remarkably increased bioavailability (21-fold greater than GEM) and efficient tumor free-GEM accumulation (8-fold of GEM), which consequently contributed to excellent in vivo antitumor efficacy.

Synthesis and biological evaluation of NH2-acyl oseltamivir analogues as potent neuraminidase inhibitors.

Neuraminidase inhibitors can deter nascent viruses from infecting intact cells by preventing their release from host cells. Herein, a neuraminidase inhibitor 11b absent of basic moieties was discovered in the process of searching for inhibitors targeting 150 cavity. It exhibited potent inhibitions against wild-type neuraminidases from group 1 (H5N1 and H1N1) and group 2 (H7N9) subtypes with IC50 values similar to those of oseltamivir carboxylate. Moreover, 11b showed moderate inhibitions against mutant neuraminidases from H5N1-H274Y and H1N1-H274Y with IC50 values of 2075 nM and 1382 nM, which were inferior to those of oseltamivir carboxylate (6095 nM and 4071 nM). The results were not consistent with the recognized SARs that a basic moiety was an indispensable part of a potent inhibitor.

A gene delivery system containing nuclear localization signal: Increased nucleus import and transfection efficiency with the assistance of RanGAP1.

In the present report, a degradable gene delivery system (PAMS/DNA/10NLS) containing nucleus location signal peptide (NLS) was prepared. The agarose gel electrophoresis, particle size and zeta potential of PAMS/DNA/10NLS were similar to those of PAMS/DNA, which proved that NLS did not affect the interaction between PAMS and DNA. PAMS/DNA/10NLS exhibited marked extracellular and intracellular degradation under acidic conditions. The degradation was believed to allow NLS to come into contact with importins easily, which was able to mediate the nucleus import. With the help of NLS, PAMS/DNA/10NLS exhibited a higher transfection capability than PAMS/DNA. Moreover, the transfection of PAMS/DNA/10NLS was less dependent on the breakdown of the nucleus envelope than PAMS/DNA. Considering that GTPase-activating protein 1 (RanGAP1) was able to activate the endogenous GTPase, which was necessary for NLS-mediated nucleus import, RanGAP1 overexpressed cells (RanGAP1 cells) were produced. This result showed that RanGAP1 cells had higher GTPase activities than normal cells. Both the nucleus import and transfection efficiency of PAMS/DNA/10NLS were markedly higher in RanGAP1 cells than that in normal cells. The in vivo transfection results also showed that the transfection efficiency of PAMS/DNA/10NLS was higher in RanGAP1 pre-treated mice than that in normal mice. These findings showed that PAMS/DNA/10NLS is a promising gene delivery system with the assistance of RanGAP1. STATEMENT OF SIGNIFICANCE: The present report describes the increased transfection efficiency of a degradable gene delivery system (PAMS/DNA/10NLS) containing nuclear location signal (NLS) with the assistance of GTPase-activating protein 1 (RanGAP1). The physicochemical properties of PAMS/DNA/10NLS were similar to those of PAMS/DNA. PAMS/DNA/10NLS exhibited great extracellular and intracellular degradations, which might allow NLS to contact with importins easily. With the help of NLS, PAMS/DNA/10NLS exhibited a higher transfection capability than PAMS/DNA. The transfection of PAMS/DNA/10NLS had less dependence on the breakdown of nuclear envelope. Both the nuclear import and transfection efficiency of PAMS/DNA/10NLS were higher in RanGAP1 overexpressed cells than that in normal cells. Moreover, the transfection efficiency of PAMS/DNA/10NLS was higher in RanGAP1 pre-treated mice than that in normal mice.

Synthesis and characterization of a PAMAM-OH derivative containing an acid-labile ß-thiopropionate bond for gene delivery.

The present report describes the synthesis of a hydroxyl terminal PAMAM dendrimer (PAMAM-OH) derivative (PAMSPF). The hydroxyls of PAMAM-OH were attached to S-Methyl-l-cysteine (SMLC) via an acid-labile ester bond, named as ß-thiopropionate bond, followed by modification with folic acid (FA) through a polyethylene glycol (PEG) linker. The degrees of attachment of SMLC and FA to the PAMAM-OH backbone were 83.9% and 12.8%, respectively. PAMSPF could condense DNA to form spherical nanoparticles with particle sizes of ∼200nm and remain stable in the presence of heparin and nuclease. The ß-thiopropionate bond in PAMSPF was hydrolyzed completely and the DNA release rate was 95.8±3.3% after incubation under mildly acidic conditions at 37°C for 3h. PAMSPF/DNA was less cytotoxic to KB and HepG2 cells and exhibited a higher gene transfection efficiency than native PAMAM/DNA. The uptake assays showed that PAMSPF/DNA entered KB cells within 0.5h through folate receptor-mediated endocytosis and escaped from endosomes within 2h. In addition, PAMSPF/DNA displayed long circulation time along with excellent targeting of tumor sites in vivo. These findings demonstrate that PAMSPF is an excellent carrier for safe and effective gene delivery.