Halting the Spread of Herpes Simplex Virus-1: The Discovery of an Effective Dual αvβ6/αvβ8 Integrin Ligand

Over recent years, αvβ6 and αvβ8 Arg-Gly-Asp (RGD) integrins have risen to prominence as interchangeable co-receptors for the cellular entry of herpes simplex virus-1 (HSV-1). In fact, the employment of subtype-specific integrin-neutralizing antibodies or gene-silencing siRNAs has emerged as a valuable strategy for impairing HSV infectivity. Here, we shift the focus to a more affordable pharmaceutical approach based on small RGD-containing cyclic pentapeptides. Starting from our recently developed αvβ6-preferential peptide [RGD-Chg-E]-CONH2 (1), a small library of N-methylated derivatives (2-6) was indeed synthesized in the attempt to increase its affinity toward αvβ8. Among the novel compounds, [RGD-Chg-(NMe)E]-CONH2 (6) turned out to be a potent αvβ6/αvβ8 binder and a promising inhibitor of HSV entry through an integrin-dependent mechanism. Furthermore, the renewed selectivity profile of 6 was fully rationalized by a NMR/molecular modeling combined approach, providing novel valuable hints for the design of RGD integrin ligands with the desired specificity profile.

Organoids to Study Intestinal Nutrient Transport, Drug Uptake and Metabolism - Update to the Human Model and Expansion of Applications

Intestinal transport and sensing processes and their interconnection to metabolism are relevant to pathologies such as malabsorption syndromes, inflammatory diseases, obesity and type 2 diabetes. Constituting a highly selective barrier, intestinal epithelial cells absorb, metabolize, and release nutrients into the circulation, hence serving as gatekeeper of nutrient availability and metabolic health for the whole organism. Next to nutrient transport and sensing functions, intestinal transporters including peptide transporter 1 (PEPT1) are involved in the absorption of drugs and prodrugs, including certain inhibitors of angiotensin-converting enzyme, protease inhibitors, antivirals, and peptidomimetics like β-lactam antibiotics. Here, we verify the applicability of 3D organoids for in vitro investigation of intestinal biochemical processes related to transport and metabolism of nutrients and drugs. Establishing a variety of methodologies including illustration of transporter-mediated nutrient and drug uptake and metabolomics approaches, we highlight intestinal organoids as robust and reliable tool in this field of research. Currently used in vitro models to study intestinal nutrient absorption, drug transport and enterocyte metabolism, such as Caco-2 cells or rodent explant models are of limited value due to their cancer and non-human origin, respectively. Particularly species differences result in poorly correlative data and findings obtained in these models cannot be extrapolated reliably to humans, as indicated by high failure rates in drug development pipelines. In contrast, human intestinal organoids represent a superior model of the intestinal epithelium and might help to implement the 3Rs (Reduction, Refinement and Replacement) principle in basic science as well as the preclinical and regulatory setup.

Enhancing Oral Bioavailability of Cyclic RGD Hexa-peptides by the Lipophilic Prodrug Charge Masking Approach: Redirection of Peptide Intestinal Permeability from a Paracellular to Transcellular Pathway

Hydrophilic peptides constitute most of the active peptides. They mostly permeate via tight junctions (paracellular pathway) in the intestine. This permeability mechanism restricts the magnitude of their oral absorption and bioavailability. We hypothesized that concealing the hydrophilic residues of the peptide using the lipophilic prodrug charge masking approach (LPCM) can improve the bioavailability of hydrophilic peptides. To test this hypothesis, a cyclic N-methylated hexapeptide containing Arg-Gly-Asp (RGD) and its prodrug derivatives, masking the Arg and Asp charged side chains, were synthesized. The library was evaluated for intestinal permeability in vitro using the Caco-2 model. Further investigation of metabolic stability ex vivo models in rat plasma, brush border membrane vesicles (BBMVs), and isolated CYP3A4 microsomes and pharmacokinetic studies was performed on a selected peptide and its prodrug (peptide 12). The parent drug analogues were found to have a low permeability rate in vitro, corresponding to atenolol, a marker for paracellular permeability. Moreover, palmitoyl carnitine increased the P_app of peptide 12 by 4-fold, indicating paracellular permeability. The P_app of the prodrug derivatives was much higher than that of their parent peptides. For instance, the P_app of the prodrug 12P was 20-fold higher than the P_app of peptide 12 in the apical to basolateral (AB) direction. Whereas the permeability in the opposite direction (BA of the Caco-2 model) was significantly faster than the P_app AB, indicating the involvement of an efflux system. These results were corroborated when verapamil, a P-gp inhibitor, was added to the Caco-2 model and increased the P_app AB of prodrug 12P by 3-fold. The prodrug 12P was stable in the BBMVs environment, yet degraded quickly (less than 5 min) in the plasma into the parent peptide 12. Pharmacokinetic studies in rats showed an increase in the bioavailability of peptide 12 > 70-fold (from 0.58 ± 0.11% to 43.8 ± 14.9%) after applying the LPCM method to peptide 12 and converting it to the prodrug 12P. To conclude, the LPCM approach converted the absorption mechanism of the polar peptides from a paracellular to transcellular pathway that tremendously affects their oral bioavailability. The LPCM method provides a solution for the poor bioavailability of RGD cyclohexapeptides and paves the way for other active hydrophilic and charged peptides with poor oral bioavailability.

Overcoming the Lack of Oral Availability of Cyclic Hexapeptides: Design of a Selective and Orally Available Ligand for the Integrin αvβ3

A highly systematic approach for the development of both orally bioavailable and bioactive cyclic N-methylated hexapeptides as high affinity ligands for the integrin αvβ3 is based on two concepts: a) screening of systematically designed libraries with spatial diversity and b) masking of the peptide charge with a lipophilic protecting group. The key steps of the method are 1) initial design of a combinatorial library of N-methylated analogues of the stem peptide cyclo(d-Ala-Ala5 ); 2) selection of cyclic peptides with the highest intestinal permeability; 3) design of sublibraries with the bioactive RGD sequence in all possible positions; 4) selection of the best ligands for RGD-recognizing integrin subtypes; 5) fine-tuning of the affinity and selectivity by additional Ala to Xaa substitutions; 6) protection of the charged functional groups according to the prodrug concept to regain intestinal and oral permeability; 7) proof of biological effects in mice after oral administration.

(r)-, but not (s)-alpha lipoic acid stimulates deficient brain pyruvate dehydrogenase complex in vascular dementia, but not in Alzheimer dementia

In dementia of Alzheimer type (DAT), cerebral glucose metabolism is reduced in vivo, and enzymes involved in glucose breakdown are impaired in post-mortem brain tissue. Pyruvate dehydrogenase complex activity (PDHc) is one of the enzymes known to be reduced, while succinate dehydrogenase activity (SDH), another enzyme of oxidative glucose metabolism is unchanged. In dementia of vascular type (DVT), variable changes in glucose metabolism have been demonstrated in vivo, while changes of enzyme activities in post-mortem brain tissue are unknown. Here, PDHc and SDH activity were stimulated with each of the two stereoisomers of alpha lipoic acid in post-mortem parietal brain cortex of patients with DAT, DVT, and one case of Pick's disease and compared to stimulation effects in a control group, matched for age, sex, post-mortem delay, and storage time of brain tissue. PDHc in DAT and DVT, but not in Pick's disease was reduced. PDHc activity could be slightly stimulated by 10 micro M of the physiological stereoisomer (r)-alpha-lipoic acid, in controls and DVT (possibly also in Pick's disease), but not in DAT. In all groups investigated SDH was activated by 100 micro M and 1 mM of both isomers of alpha-lipoic acid, whereas 10 mM of both stereoisomers of alpha-lipoic acid caused an inhibition of both, PDHc and SDH activity. The loss of basal and of (r)-alpha-lipoic acid stimulated PDHc activity indicate that a functional or structural impairment of PDHc may exist in DAT and DVT which is not merely attributable to loss of mitochondria since basal and stimulated SDH activities are similar in controls, DVT and DAT, thus indicating selective vulnerability of PDHc.

Effect of lipoic acid on redox state of coenzyme Q in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine and diethyldithiocarbamate

We investigated the effects of a combined treatment of male C57Bl/6 mice with diethyldithiocarbamate and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in the absence or presence of different forms of lipoic acid (Thioctacid TR; commonly used for treatment of diabetic polyneuropathies) on levels and redox states of alpha-tocopherol and coenzyme Q in vivo and on activities of various enzymes of energy metabolism ex vivo. Treatment of mice with diethyldithiocarbamate plus MPTP resulted in a decrease in dopamine (67%) and its major metabolites dihydroxyphenylacetic acid (38%) and homovanillic acid (37%) in striatum. alpha-Tocopherol levels were unaltered in striatum; however, the reduced forms of coenzyme Q were decreased in frontal cortex and hippocampus following diethyldithiocarbamate plus MPTP. In frontal cortex activity of NADH dehydrogenase was significantly inhibited by diethyldithiocarbamate plus MPTP ex vivo, suggesting that the neurotoxic metabolite of MPTP, 1-methyl-4-phenylpyridinium ion, is acting in brain regions other than striatum as well. Lipoic acid, administered 6 times, each at 90 min prior to MPTP, could not restore dopamine in striatum but in contrast maintained a normal ratio of the reduced form to the oxidized form of coenzyme Q, suggesting an interaction of lipoic acid with energy metabolism which seems, however, not only to be due to an activation of pyruvate dehydrogenase.