Development of Clarstatin, a Novel Drug Lead for the Therapy of Autoimmune Uveitis.

We describe the design, synthesis, and activity of a potent thiourea-bridged backbone cyclic peptidomimetic known as Clarstatin, comprising a 5-amino acid sequence (Q/D)1-(R/K)2-X3-X4-A5-(Gln/Asp)1-(Arg/Lys)2-AA3-AA4-Ala5-based on a motif called "shared epitope (SE)", specifically present in specific alleles of the HLA-DRB1 gene. This SE binds to a particular site within the proline reach domain (P-domain) of the cell surface-calreticulin (CS-CRT). CS-CRT is a multifunctional endoplasmic reticulum (ER) calcium-binding protein that is located on the cell surface of T cells and triggers innate immune signaling, leading to the development of inflammatory autoimmune diseases. The development of Clarstatin was based on the parent peptide W-G-D1-K2-S3-G4-A5- derived from the active region of the SE. Following the design based on the cycloscan method, the synthesis of Clarstatin was performed by the Fmoc solid phase peptide synthesis (SPPS) method, purified by HPLC to 96% homogeneity, and its structure was confirmed by LC-MS. Clarstatin reduced calcium levels in Jurkat lymphocyte cultures, ameliorated uveitis in vivo in the experimental autoimmune uveitis (EAU) mice model, and was safe upon acute toxicity evaluation. These findings identify Clarstatin as a promising lead compound for future drug development as a novel class of therapeutic agents in the therapy of uveitis.

Treatment with αvß3-integrin-specific 29P attenuates pressure-overload induced cardiac remodelling after transverse aortic constriction in mice.

Heart failure remains one of the largest clinical burdens globally, with little to no improvement in the development of disease-eradicating therapeutics. Integrin targeting has been used in the treatment of ocular disease and cancer, but little is known about its utility in the treatment of heart failure. Here we sought to determine whether the second generation orally available, αvß3-specific RGD-mimetic, 29P , was cardioprotective. Male mice were subjected to transverse aortic constriction (TAC) and treated with 50 µg/kg 29P or volume-matched saline as Vehicle control. At 3 weeks post-TAC, echocardiography showed that 29P treatment significantly restored cardiac function and structure indicating the protective effect of 29P treatment in this model of heart failure. Importantly, 29P treatment improved cardiac function giving improved fractional shortening, ejection fraction, heart weight and lung weight to tibia length fractions, together with partial restoration of Ace and Mme levels, as markers of the TAC insult. At a tissue level, 29P reduced cardiomyocyte hypertrophy and interstitial fibrosis, both of which are major clinical features of heart failure. RNA sequencing identified that, mechanistically, this occurred with concomitant alterations to genes involved molecular pathways associated with these processes such as metabolism, hypertrophy and basement membrane formation. Overall, targeting αvß3 with 29P provides a novel strategy to attenuate pressure-overload induced cardiac hypertrophy and fibrosis, providing a possible new approach to heart failure treatment.

Structure-Activity Relationship of Synthetic Linear KTS-Peptides Containing Meta-Aminobenzoic Acid as Antagonists of α1ß1 Integrin with Anti-Angiogenic and Melanoma Anti-Tumor Activities.

To develop peptide drugs targeting integrin receptors, synthetic peptide ligands endowed with well-defined selective binding motifs are necessary. The snake venom KTS-containing disintegrins, which selectively block collagen α1ß1 integrin, were used as lead compounds for the synthesis and structure-activity relationship of a series of linear peptides containing the KTS-pharmacophore and alternating natural amino acids and 3-aminobenzoic acid (MABA). To ensure a better stiffness and metabolic stability, one, two and three MABA residues, were introduced around the KTS pharmacophore motif. Molecular dynamics simulations determined that the solution conformation of MABA peptide 4 is more compact, underwent larger conformational changes until convergence, and spent most of the time in a single cluster. The peptides' binding affinity has been characterized by an enzyme linked immunosorbent assay in which the most potent peptide 4 inhibited with IC50 of 324 ± 8 µM and 550 ± 45 µM the binding of GST-α1-A domain to collagen IV fragment CB3, and the cell adhesion to collagen IV using α1-overexpressor cells, respectively. Docking studies and MM-GBSA calculations confirmed that peptide 4 binds a smaller region of the integrin near the collagen-binding site and penetrated deeper into the binding site near Trp1. Peptide 4 inhibited tube formation by endothelial cell migration in the Matrigel angiogenesis in vitro assay. Peptide 4 was acutely tolerated by mice, showed stability in human serum, decreased tumor volume and angiogenesis, and significantly increased the survival of mice injected with B16 melanoma cells. These findings propose that MABA-peptide 4 can further serve as an α1ß1-integrin antagonist lead compound for further drug optimization in angiogenesis and cancer therapy.

Synthesis of Novel Arginine Building Blocks with Increased Lipophilicity Compatible with Solid-Phase Peptide Synthesis.

Arginine, due to the guanidine moiety, increases peptides' hydrophilicity and enables interactions with charged molecules, but at the same time, its presence in a peptide chain might reduce its permeability through biological membranes. This might be resolved by temporary coverage of the peptide charge by lipophilic, enzyme-sensitive alkoxycarbonyl groups. Unfortunately, such a modification of a guanidine moiety has not been reported to date and turned out to be challenging. Here, we present a new, optimized strategy to obtain arginine building blocks with increased lipophilicity that were successfully utilized in the solid-phase peptide synthesis of novel arginine vasopressin prodrugs.

PH-Binding Motif in PAR4 Oncogene: From Molecular Mechanism to Drug Design.

While the role of G-protein-coupled receptors (GPCR) in cancer is acknowledged, their underlying signaling pathways are understudied. Protease-activated receptors (PAR), a subgroup of GPCRs, form a family of four members (PAR1-4) centrally involved in epithelial malignancies. PAR4 emerges as a potent oncogene, capable of inducing tumor generation. Here, we demonstrate identification of a pleckstrin-homology (PH)-binding motif within PAR4, critical for colon cancer growth. In addition to PH-Akt/PKB association, other PH-containing signal proteins such as Gab1 and Sos1 also associate with PAR4. Point mutations are in the C-tail of PAR4 PH-binding domain; F347 L and D349A, but not E346A, abrogate these associations. Pc(4-4), a lead backbone cyclic peptide, was selected out of a mini-library, directed toward PAR2&4 PH-binding motifs. It effectively attenuates PAR2&4-Akt/PKB associations; PAR4 instigated Matrigel invasion and migration in vitro and tumor development in vivo. EGFR/erbB is among the most prominent cancer targets. AYPGKF peptide ligand activation of PAR4 induces EGF receptor (EGFR) Tyr-phosphorylation, effectively inhibited by Pc(4-4). The presence of PAR2 and PAR4 in biopsies of aggressive breast and colon cancer tissue specimens is demonstrated. We propose that Pc(4-4) may serve as a powerful drug not only toward PAR-expressing tumors but also for treating EGFR/erbB-expressing tumors in cases of resistance to traditional therapies. Overall, our studies are expected to allocate new targets for cancer therapy. Pc(4-4) may become a promising candidate for future therapeutic cancer treatment.

Synthesis and Pharmacological Characterization of Visabron, a Backbone Cyclic Peptide Dual Antagonist of α4ß1 (VLA-4)/α9ß1 Integrin for Therapy of Multiple Sclerosis.

Integrins α4ß1/ α9ß1 are important in the pathogenesis and progression of inflammatory and autoimmune diseases by their roles in leukocyte activation and trafficking. Natalizumab, a monoclonal antibody selectively targeting α4ß1 integrin and blocking leukocyte trafficking to the central nervous system, is an immunotherapy for multiple sclerosis (MS). However, due to its adverse effects associated with chronic treatment, alternative strategies using small peptide mimetic inhibitors are being sought. In the present study, we synthesized and characterized visabron c (4-4), a backbone cyclic octapeptide based on the sequence TMLD, a non-RGD unique α4ß1 integrin recognition sequence motif derived from visabres, a proteinous disintegrin from the viper venom. Visabron c (4-4) was selected from a minilibrary with conformational diversity based on its potency and selectivity in functional adhesion cellular assays. Visabron c (4-4)'s serum stability, pharmacokinetics, and therapeutic effects following ip injection were assessed in an experimental autoimmune encephalomyelitis (EAE) animal model. Furthermore, visabron c (4-4)'s lack of toxic effects in mice was verified by blood analysis, tissue pathology, immunogenicity, and "off-target" effects, indicating its significant tolerability and lack of immunogenicity. Visabron c (4-4) can be delivered systemically. The in vitro and in vivo data justify visabron c (4-4) as a safe alternative peptidomimetic lead compound/drug to monoclonal anti-α4 integrin antibodies, steroids, and other immunosuppressant drugs. Moreover, visabron c (4-4) design may pave the way for developing new therapies for a variety of other inflammatory and/or autoimmune diseases.

Cyclizing Painkillers: Development of Backbone-Cyclic TAPS Analogs.

Painkillers are commonly used medications. Native peptide painkillers suffer from various pharmacological disadvantages, while small molecule painkillers like morphine are highly addictive. We present a general approach aimed to use backbone-cyclization to develop a peptidomimetic painkiller. Backbone-cyclization was applied to transform the linear peptide Tyr-Arg-Phe-Sar (TAPS) into an active backbone-cyclic peptide with improved drug properties. We designed and synthesized a focused backbone-cyclic TAPS library with conformational diversity, in which the members of the library have the generic name TAPS c(n-m) where n and m represent the lengths of the alkyl chains on the nitrogens of Gly and Arg, respectively. We used a combined screening approach to evaluate the pharmacological properties and the potency of the TAPS c(n-m) library. We focused on an in vivo active compound, TAPS c(2-6), which is metabolically stable and has the potential to become a peripheral painkiller being a full µ opioid receptor functional agonist. To prepare a large quantity of TAPS c(2-6), we optimized the conditions of the on-resin reductive alkylation step to increase the efficiency of its SPPS. NMR was used to determine the solution conformation of the peptide lead TAPS c(2-6).

Novel humanin analogs confer neuroprotection and myoprotection to neuronal and myoblast cell cultures exposed to ischemia-like and doxorubicin-induced cell death insults.

Humanin (HN) is a 24-amino acid mitochondrial-derived peptide, best known for its ability to protect neurons from damage caused by ischemic stroke and neurodegenerative insults and cardiomyocytes from myocardial infarction or doxorubicin (Dox)-induced cardiotoxicity. This study examines the neuroprotective and myoprotective effects of HN novel synthetic analogs HUJInin and c(D-Ser14-HN), prepared by solid-phase peptide synthesis. The cellular models employed were oxygen-glucose-deprivation (OGD) followed by reoxygenation (R)-induced neurotoxicity in PC12 and SH-SY5Y neuronal cell cultures and Dox-induced cardiotoxicity in H9c2 and C2C12 myoblast cell cultures, respectively. Necrotic and apoptotic cell death was measured by LDH release and caspase-3 activity. Erk 1/2 and AKT phosphorylations were examined by western blotting. Mitochondrial calcium and mitochondrial membrane potential were measured using the fluorescent dye tetramethylrhodamine-methyl ester. It was found that HUJInin and c(D-Ser14-HN) conferred significant dose-dependent neuroprotection, a phenomenon related to attenuation of OGD insult-induced Erk 1/2 phosphorylation, stimulation of AKT phosphorylation and improvement of mitochondrial functions. These peptides also conferred myoprotective effect towards Dox-induced apo-necrotic cell death insults. HUJInin and c(D-Ser14-HN) synthetic analogs may provide new lead compounds for the development of a potential candidate drug for stroke treatment and/or Dox-induced cardiotoxicity therapy in cancer patients.

The tripartite mechanism as the basis for a biochemical memory engram.

In this paper, we address the enigma of the memory engram, the physical trace of memory in terms of its composition, processes, and location. A neurochemical approach assumes that neural processes hinge on the same terms used to describe the biochemical functioning of other biological tissues and organs. We define a biochemical process, a tripartite mechanism involving the interactions of neurons with their neural extracellular matrix, trace metals, and neurotransmitters as the basis of a biochemical memory engram. The latter inextricably link physiological responses, including sensations with affective states, such as emotions.

Deciphering Direct and Indirect Effects of Neurokinin B and GnRH in the Brain-Pituitary Axis of Tilapia.

Neurokinin B (NKB) and its cognate receptor (NK3R) are emerging as important components of the neuroendocrine regulation of reproduction. Unlike mammalian tac3, which encodes only one mature peptide (namely NKB), two mature peptides are predicted for each tac3 gene in fish and frogs. Therefore, it was designated as Neurokinin F (NKF). Hormone analogs with high and long-lasting biological activity are important tools for physiological and biological research; however, the availability of piscine-specific analogs is very limited. Therefore, we have developed specific NKB and NKF analogs based on the structure of the mammalian NKB analog-senktide. These analogs, specifically designed for longer half-lives by methylation of proteolysis sites, exhibited activity equal to those of the native NKB and NKF in short-term signal-transduction assays of tilapia NKB receptors. However, the analogs were found to be able to significantly increase the release of luteinizing hormone (LH), follicle stimulating hormone (FSH) and growth hormone (GH) in tilapia, as fast as 1 h after intraperitoneal (IP) injection. The impact of the analogs on LH and FSH secretion lasted longer compared to the effect of native peptides and salmon GnRH analog (sGnRHa). In addition, we harvested pituitaries 24 h post injection and measured LH, FSH and GH mRNA synthesis. Both analogs elevated mRNA levels of LH and GH, but only NKB analog increased FSH mRNA levels in the pituitary and all GnRH forms in the brain. NKB receptors were co-localized with all three types the GnRH neurons in tilapia brain in situ. We previously showed a direct effect of NKB at the pituitary level, and these new results suggest that the stronger impact of the NKB analog on GTH release is also due to an indirect effect through the activation of GnRH neurons. These results suggest that novel synthetic NKB analogs may serve as a tool for both research and agricultural purposes. Finally, the biological activity and regulatory role of NKB in tilapia brain and pituitary suggest that the NKB/NKBR system in fish is an important reproductive regulator in a similar way to the kisspeptin system in mammals.

Myristoylation Confers Oral Bioavailability and Improves the Bioactivity of c(MyD 4-4), a Cyclic Peptide Inhibitor of MyD88.

Myeloid differentiation primary response 88 (MyD88) is an intracellular adaptor protein central to the signaling of multiple receptors involved in inflammation. Since innate immune inflammation promotes autoimmunity, MyD88 is an attractive target in autoimmune disease. We previously developed c(MyD 4-4), a novel cyclic peptide competitive inhibitor of MyD88 dimerization that is metabolically stable. Parenteral administration of c(MyD 4-4) reduces disease severity in a mouse model of the human autoimmune disease multiple sclerosis. We now show that N-terminal myristoylation of c(MyD 4-4) enhances the competitive inhibition of MyD88 dimerization in living cells, leading to improved inhibition of the Toll-like receptor and IL-1 receptor signaling. Importantly, myristoylation converts c(MyD 4-4) to an orally bioavailable inhibitor of MyD88. Oral administration of c(MyD 4-4) significantly lowered the inflammatory cytokines secreted by peripheral autoimmune T cells in mice immunized with myelin antigens and ameliorated disease severity in the mouse model of multiple sclerosis. Taken together, we show the conversion of a protein active region to a metabolically stable, selective cyclic peptide that is orally bioavailable.

Orally Active Peptides: Is There a Magic Bullet?

For decades, the development of peptides as potential drugs was aimed solely at peptides with the highest affinity, receptor selectivity, or stability against enzymatic degradation. However, optimization of their oral availability is highly desirable to establish orally active peptides as potential drug candidates for everyday use. A twofold optimization process is necessary to produce orally active peptides: 1) optimization of the affinity and selectivity and 2) optimization of the oral availability. These two steps must be performed sequentially for the rational design of orally active peptides. Nevertheless, additional knowledge is required to understand which structural changes increase oral availability, followed by incorporation of these elements into a peptide without changing its other biological properties. Considerable efforts have been made to understand the influence of these modifications on oral availability. One approach is to improve the oral availability of a peptide that has been previously optimized for biological activity, as described in (1) above. The second approach is to first identify an intestinally permeable, metabolically stable peptide scaffold and then introduce the functional groups necessary for the desired biological function. Previous approaches to achieving peptide oral availability have been claimed to have general applicability but, thus far, most of these solutions have not been successful in other cases. This Review discusses diverse chemical modifications, model peptides optimized for bioavailability, and orally active peptides to summarize the state of the research on the oral activity of peptides. We explain why no simple and straightforward strategy (i.e. a "magic bullet") exists for the design of an orally active peptide with a druglike biological function.

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 Papp of peptide 12 by 4-fold, indicating paracellular permeability. The Papp of the prodrug derivatives was much higher than that of their parent peptides. For instance, the Papp of the prodrug 12P was 20-fold higher than the Papp 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 Papp 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 Papp 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.

Development of a Novel Backbone Cyclic Peptide Inhibitor of the Innate Immune TLR/IL1R Signaling Protein MyD88.

MyD88 is a cytoplasmic adaptor protein that plays a central role in signaling downstream of the TLRs and the IL1R superfamily. We previously demonstrated that MyD88 plays a critical role in EAE, the murine model of multiple sclerosis, and showed that the MyD88 BB-loop decoy peptide RDVLPGT ameliorates EAE. We now designed and screened a library of backbone cyclized peptides based on the linear BB loop peptide, to identify a metabolically stable inhibitor of MyD88 that retains the binding properties of the linear peptide. We identified a novel cyclic peptide protein mimetic that inhibits inflammatory responses to TLR ligands, and NFκB activation in response to IL-1 activation. The inhibitor, c(MyD 4-4), is metabolically stable in comparison to the linear peptide, blocks MyD88 in a specific manner, and inhibits MyD88 function by preventing MyD88 dimerization. Finally, treatment of mice with c(MyD 4-4) reduced the severity of clinical disease in the murine EAE model of multiple sclerosis. Thus, modulation of MyD88-dependent signaling using c(MyD 4-4) is a potential therapeutic strategy to lower innate immune inflammation in autoimmune CNS disease.

Conversion of Protein Active Regions into Peptidomimetic Therapeutic Leads Using Backbone Cyclization and Cycloscan - How to Do it Yourself!

Protein-protein Interactions (PPIs) are particularly important for controlling both physiologic and pathologic biological processes but are difficult to target due to their large and/or shallow interaction surfaces unsuitable for small molecules. Linear peptides found in nature interact with some PPIs, and protein active regions can be used to design synthetic peptide compounds for inhibition of PPIs. However, linear peptides are limited therapeutically by poor metabolic and conformational stability, which can compromise their bioactivity and half-life. Cyclic peptidomimetics (modified peptides) can be used to overcome these challenges because they are more resistant to metabolic degradation and can be engineered to adopt desired conformations. Backbone cyclization is a strategy that we developed to improve drug-like properties of linear peptide leads without jeopardizing the integrity of functionally relevant side-chains. Here, we provide the first description of an entire approach for developing backbone cyclized peptide compounds, based upon two straightforward 'ABC' and 'DEF' processes. We present practical examples throughout our discussion of revealing active regions important for PPIs and identifying critical pharmacophores, as well as developing backbone cyclized peptide libraries and screening them using cycloscan. Finally, we review the impact of these advances and provide a summary of current ongoing work in the field.

Overcoming the Lack of Oral Availability of Cyclic Hexapeptides: Design of a Selective and Orally Available Ligand for the Integrin†αvß3.

A highly systematic approach for the development of both orally bioavailable and bioactive cyclic N-methylated hexapeptides as high affinity ligands for the integrin αvß3 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.

DMAP-assisted sulfonylation as an efficient step for the methylation of primary amine motifs on solid support.

Several multistep strategies were developed to ensure single methylation of amines on solid support. These strategies rely on the introduction of the o-NBS protecting/activating group as a key step. We found that the state-of-the-art strategies fail for the methylation of several primary amine motifs, largely due to inefficient sulfonylation. Here we show that using the superior nucleophilic base DMAP instead of the commonly used base collidine as a sulfonylation additive is essential for the introduction of the o-NBS group to these amine motifs. DFT calculations provide an explanation by showing that the energy barrier of the DMAP intermediate is significantly lower than the one of the collidine. We demonstrate that using DMAP as a sole additive in the sulfonylation step results in an overall effective and regioselective N-methylation. The method presented herein proved highly efficient in solid-phase synthesis of a somatostatin analogue bearing three Nα-methylation sites that could not be synthesized using the previously described state-of-the-art methods.

Oxytocin-Monolayer-Based Impedimetric Biosensor for Zinc and Copper Ions.

Zinc and copper are essential metal ions for numerous biological processes. Their levels are tightly maintained in all body organs. Impairment of the Zn2+ to Cu2+ ratio in serum was found to correlate with many disease states, including immunological and inflammatory disorders. Oxytocin (OT) is a neuropeptide, and its activity is modulated by zinc and copper ion binding. Harnessing the intrinsic properties of OT is one of the attractive ways to develop valuable metal ion sensors. Here, we report for the first time an OT-based metal ion sensor prepared by immobilizing the neuropeptide onto a glassy carbon electrode. The developed impedimetric biosensor was ultrasensitive to Zn2+ and Cu2+ ions at physiological pH and not to other biologically relevant ions. Interestingly, the electrochemical impedance signal of two hemicircle systems was recorded after the attachment of OT to the surface. These two semicircles suggest two capacitive regions that result from two different domains in the OT monolayer. Moreover, the change in the charge-transfer resistance of either Zn2+ or Cu2+ was not similar in response to binding. This suggests that the metal-dependent conformational changes of OT can be translated to distinct impedimetric data. Selective masking of Zn2+ and Cu2+ was used to allow for the simultaneous determination of zinc to copper ions ratio by the OT sensor. The OT sensor was able to distinguish between healthy control and multiple sclerosis patients diluted sera samples by determining the Zn/Cu ratio similar to the state-of-the-art techniques. The OT sensor presented herein is likely to have numerous applications in biomedical research and pave the way to other types of neuropeptide-derived sensors.

Superiority of the S,S conformation in diverse pharmacological processes: Intestinal transport and entry inhibition activity of novel anti-HIV drug lead.

Chirality is an important aspect in many pharmacological processes including drug transport and metabolism. The current investigation examined the stereospecific transport and entry inhibitory activity of four diastereomers derived from a small (macrocyclic) molecule that has two chiral centers. These molecules were designed to mimic the interaction between CD4 and gp120 site of HIV-1 and thereby to function as entry inhibitor(s). Intestinal permeability was assessed by ex-vivo model using excised rat intestine mounted in side-by-side diffusion chambers. The entry inhibitory activity was monitored using indicator HeLa-CD4-LTR-beta-gal cells (MAGI assay). The (S/S) diastereomer, named CG-1, exhibited superiority in both unrelated tested biological processes: (I) high transport through the intestine and (II) entry inhibition activity (in the low µM range). The permeability screening revealed a unique transporter-mediated absorption pathway of CG-1, suggesting a significant role of the molecule's conformation on the mechanism of intestinal absorption. Here we highlight that only the S,S enantiomer (CG-1) has both (I) promising anti HIV-1 entry inhibitory properties and (II) high transporter mediated intestinal permeability. Hence we suggest preference in pharmacological processes to the S,S conformation. This report augments the knowledge regarding stereoselectivity in receptor mediated and protein-protein interaction processes.