Preclinical development of a vaccine 'against smoking'

BACKGROUND

Nicotine is the main culprit for dependence on tobacco-containing products, which in turn are a major etiologic factor for cardiovascular diseases and cancer. This publication describes a vaccine, which elicits antibodies against nicotine. The antibodies in the blood stream intercept the nicotine molecule on its way to its receptors and greatly diminish the nicotine influx to the brain shortly after smoking.

METHODS

The nicotine molecule is chemically linked to cholera toxin B as a carrier protein in order to induce antibodies. The potential to elicit antibodies after subcutaneous as well as intranasal immunization is evaluated. In order to simulate realistic conditions, nicotine pumps delivering the nicotine equivalent of 5 packages of cigarettes for 4 weeks are implanted into the mice 1 week prior to vaccination. The protective effect of the vaccine is measured 5 weeks after vaccination by comparing the influx of radiolabeled nicotine in the brains of vaccinated and non-vaccinated animals 5 min after challenge with the nicotine equivalent of 2 cigarettes.

RESULTS

The polyclonal antibodies induced by the vaccine show a mean avidity of 1.8 x 10(7) l/Mol. Subcutaneous immunization elicits high antibody levels of the IgG class, and significant IgA antibody levels in the saliva of vaccinated mice can be found after intranasal vaccination. The protective effect also in the animals with implanted nicotine pumps is significant: less than 10% of radiolabeled nicotine found in the brains of non-vaccinated animals can be found in the brains of vaccinated animals.

CONCLUSIONS

These data provide credible evidence that a vaccine can break the vicious circle between smoking and instant gratification by intercepting the nicotine molecule. Astonishingly, there is no sign of exhaustion of specific antibodies even under extreme conditions, which makes it highly unlikely that a smoker can overcome the protective effect of the vaccine by smoking more. Finally, the high titers of specific antibodies after 1 year let us hope that booster vaccinations are probably only necessary in intervals of years.

Evolutionary principles for generating protein mimetics: directed assembly of peptide loops on topological templates

A novel methodology for the reversible competitive condensation of peptide loops to chemoreactive topological templates is presented.

Evolutionary principles for generating protein mimetics: directed assembly of peptide loops on topological templates

A novel methodology for the reversible competitive condensation of peptide loops to chemoreactive topological templates is presented.

Pseudoproline-containing analogues of morphiceptin and endomorphin-2: evidence for a cis Tyr-Pro amide bond in the bioactive conformation

Analogues of the opioid peptides [D-Phe(3)]morphiceptin (H-Tyr-Pro-D-Phe-Pro-NH(2)) and endomorphin-2 (H-Tyr-Pro-Phe-Phe-NH(2)) containing the pseudoproline (Psi Pro) (4R)-thiazolidine-4-carboxylic acid (Cys[Psi(R1,R2)pro]) or (4S)-oxazolidine-4-carboxylic acid (Ser[Psi(R1,R2)pro]) in place of Pro(2) were synthesized. The pseudoproline ring in these compounds was either unsubstituted (R(1), R(2) = H) or dimethylated (R(1), R(2) = CH(3)) at the 2-C position. 2-C-dimethylated pseudoprolines are known to be quantitative or nearly quantitative inducers of the cis conformation around the Xaa(i-1)-Xaa(i)[Psi(CH(3),CH)(3)pro)] imide bond. All dihydropseudoproline-containing analogues (R(1), R(2) = H) showed good mu opioid agonist potency in the guinea pig ileum (GPI) assay, high mu receptor binding affinity in the rat brain membrane binding assay, and, like their parent peptides, excellent mu receptor binding selectivity. (1)H NMR spectroscopic analysis of the Cys[Psi(H,H)pro](2)- and Ser[Psi(H,H)pro](2)-containing analogues in DMSO-d(6) revealed that they existed in a conformational equilibrium around the Tyr-Xaa[Psi(H,H)pro] peptide bond with cis/trans ratios of 40:60 and 45:55, respectively. The dimethylated thiazolidine- and oxazolidine-containing [D-Phe(3)]morphiceptin- and endomorphin-2 analogues (R(1), R(2) = CH(3)) all retained full mu agonist potency in the GPI assay and displayed mu receptor binding affinities in the nanomolar range and high mu receptor selectivity. As expected, no conformers of the latter analogues with a trans conformation around the Tyr-Xaa[Psi(CH(3),CH(3)pro)] imide bond were detected by (1)H NMR spectral analysis, indicating that in these compounds the cis conformation is highly predominant (>98%). These results represent the most direct evidence obtained so far to indicate that morphiceptin and endomorphin-2 have the cis conformation around the Tyr-Pro peptide bond in their bioactive conformations.

Pseudoprolines (psiPro) in drug design: direct insertion of psiPro systems into cyclosporin C

The insertion of acetals that exhibit variable structural features into complex peptides such as cyclosporin C (CsC) results in oxazolidine derivatives (pseudoprolines, psiPro) of tailored physico-chemical and biological properties. N,O-Acetalation of the 2-threonine hydroxyl group and the preceding amide nitrogen of CsC is achieved by treating the molecule with a number of both arylated and non-arylated dimethyl acetals. The psiPro-containing CsC derivatives exhibit enhanced conformational backbone rigidity, as suggested by analytical HPLC, NMR spectroscopy and by kinetic measurements on binding with their receptor protein cyclophilin A (CypA) that were not time-dependent. IC50 values for calf-thymus CypA were obtained by kinetic evaluation of its cis-->trans isomerase activity. The choice of the para-substituted aryl dimethyl acetals allows the inhibitory properties of the corresponding derivatives to be modulated to either prodrugs or moderately strongly binding cyclosporin C derivatives.

One-wedge convention for stereochemical representations

We propose that various bonds (see figure below) used for specification of absolute configuration, e.g. the two types (I and II) of solid wedge and broken wedge representation most frequently seen in literature, can be replaced by only one kind of wedge, namely the solid wedge (III and IV). Only one wedge should be used when representing a quadrivalent center (IV). The three normal bonds are distributed on a cone opposite to the wedge. The flexibility, simplicity, unambiguity and usefulness for R-S specification of the one-wedge system are discussed, as well as its esthetic appeal.

Design and synthesis of substrate analogue inhibitors of peptide deformylase

Series of substrates derivatives of peptide deformylase were systematically synthesized and studied for their capacities to undergo hydrolysis. Data analysis indicated the requirement for a hydrophobic first side chain and for at least two main chain carbonyl groups in the substrate. For instance, Fo-Met-OCH3 and Fo-Nle-OCH3 were the minimal substrates of peptide deformylase obtained in this study, while positively charged Fo-Nle-ArgNH2 was the most efficient substrate (kcat/Km = 4.5 x 10(5) M-1.s-1). On the basis of this knowledge, 3-mercapto-2-benzylpropanoylglycine (thiorphan), a known inhibitor of thermolysin, could be predicted and further shown to inhibit the deformylation reaction. The inhibition by this compound was competitive and proved to depend on the hydrophobicity at the P1' position. Spectroscopic evidence that the sulfur group of thiorphan binds next to the active site metal ion on the enzyme could be obtained. Consequently, a small thiopseudopeptide derived from Fo-Nle-OCH3 was designed and synthesized. This compound behaved as a competitive inhibitor of peptide deformylase with KI = 52 +/- 5 microM. Introduction of a positive charge to this thiopeptide via addition of an arginine at P2' improved the inhibition constant up to 2.5 +/- 0.5 microM, a value 4 orders of magnitude smaller than that of the starting inhibitors. Evidence that this inhibitor, imino[(5-methoxy-5-oxo-4-[[2-(sulfanylmethyl)hexanoyl]amino]pentyl )am ino]methanamine, binds inside the active site cavity of peptide deformylase, while keeping intact the 3D fold of the protein, was provided by NMR. A fingerprint of the interaction of the inhibitor with the residues of the enzyme was obtained.