Peptidic Protease Inhibitors Research Articles

Plant Protease Inhibitors as Emerging Antimicrobial Peptide Agents: A Comprehensive Review.

Antimicrobial peptides (AMPs) are important mediator molecules of the innate defense mechanisms in a wide range of living organisms, including bacteria, mammals, and plants. Among them, peptide protease inhibitors (PPIs) from plants play a central role in their defense mechanisms by directly attacking pathogens or by modulating the plant's defense response. The growing prevalence of microbial resistance to currently available antibiotics has intensified the interest concerning these molecules as novel antimicrobial agents. In this scenario, PPIs isolated from a variety of plants have shown potential in inhibiting the growth of pathogenic bacteria, protozoans, and fungal strains, either by interfering with essential biochemical or physiological processes or by altering the permeability of biological membranes of invading organisms. Moreover, these molecules are active inhibitors of a range of proteases, including aspartic, serine, and cysteine types, with some showing particular efficacy as trypsin and chymotrypsin inhibitors. In this review, we provide a comprehensive analysis of the potential of plant-derived PPIs as novel antimicrobial molecules, highlighting their broad-spectrum antimicrobial efficacy, specificity, and minimal toxicity. These natural compounds exhibit diverse mechanisms of action and often multifunctionality, positioning them as promising molecular scaffolds for developing new therapeutic antibacterial agents.

Drug-Receptor Interaction of Peptidic HIV-1 Protease: The Hydrophobic Effect-I

When a drug interacts with its receptor, the nonpolar substituent of drug and receptor proteins attract each other because they have opposite magnitude with respect to each other. X-rays structure studies reflected that the S2/S2’ pocket in HIV-1 protease enzyme are essentially hydrophobic. The residues that make up these pockets are Val-32, Ile-47, Ile-50, and Ile-84 in each monomeric polypeptidic unit of the protease enzyme. Δπdr and ΔSASAdr have been used to measure the extent of hydrophobic interaction between peptidic protease inhibitors and receptor proteins (binding site: valine‒isoleucine; and catalytic site: glycine‒aspartic acid‒threonine) on the HIV-1 protease enzyme. For measurement of hydrophobic interaction, the molecular modeling and geometry optimization of all the inhibitors and the receptor amino acids have been carried out with CAChe Pro software by opting semiempirical PM3 methods. Log P was calculated using the atom-typing scheme of Ghose and Crippen, while solvent accessible surface area by conductor likes screening model. πd, πr, SASASd and SASASr well describe the hydrophobicities of the substituents and play the effective role for site selectivity for interaction of the drug with the receptor. Comparative study of values of Δπdr and ΔSASAdr show the order of hydrophobic interaction with respect to amino acids: Asp > Thr > Val > Ile and Thr > Val > Asp > Ile, respectively. Further, comparative study of the values of (ΣΔπdr)binding-site, (ΣΔπdr)catalytic-site, (ΣΔSASAdr)binding-site, (ΣΔSASAdr)catalytic-site shows that peptidic HIV-1-PRIs interact with binding site rather than catalytic site as binding site have lower value of ΣΔπdr and ΣΔSASAdr. Among the binding site, Val has maximum interaction than Ile, as it has lower vale of Δπdr and ΔSASAdr.

Enzymatic Cβ-H Functionalization of l-Arg and l-Leu in Nonribosomally Derived Peptidyl Natural Products: A Tale of Two Oxidoreductases.

Muraymycins are peptidyl nucleoside antibiotics that contain two Cβ-modified amino acids, (2S,3S)-capreomycidine and (2S,3S)-β-OH-Leu. The former is also a component of chymostatins, which are aldehyde-containing peptidic protease inhibitors that─like muraymycin─are derived from nonribosomal peptide synthetases (NRPSs). Using feeding experiments and in vitro characterization of 12 recombinant proteins, the biosynthetic mechanism for both nonproteinogenic amino acids is now defined. The formation of (2S,3S)-capreomycidine is shown to involve an FAD-dependent dehydrogenase:cyclase that requires an NRPS-bound pathway intermediate as a substrate. This cryptic dehydrogenation strategy is both temporally and mechanistically distinct in comparison to the biosynthesis of other capreomycidine diastereomers, which has previously been shown to proceed by Cβ-hydroxylation of free l-Arg catalyzed by a member of the nonheme Fe2+- and α-ketoglutarate (αKG)-dependent dioxygenase family and (eventually) a dehydration-mediated cyclization process catalyzed by a distinct enzyme(s). Contrary to our initial expectation, the sole nonheme Fe2+- and αKG-dependent dioxygenase candidate Mur15 encoded within the muraymycin gene cluster is instead demonstrated to catalyze specific Cβ hydroxylation of the Leu residue to generate (2S,3S)-β-OH-Leu that is found in most muraymycin congeners. Importantly, and in contrast to known l-Arg-Cβ-hydroxylases, the Mur15-catalyzed reaction occurs after the NRPS-mediated assembly of the peptide scaffold. This late-stage functionalization affords the opportunity to exploit Mur15 as a biocatalyst, proof of concept of which is provided.

SARS‐CoV‐2 main protease inhibitory efficacy of natural peptidic α‐hydroxy amides for therapeutic applications of COVID‐19

Background: COVID‐19, a disease caused by a novel coronavirus, is a major global human threat that has turned into a pandemic. Identification and development of drugs/vaccines is urgently needed for prevention and therapy of the COVID‐19 virus (SARS‐CoV‐2) infection. SARS‐CoV‐2 main protease (Mpro,) plays a key role in viral protein processing for its replication and inhibition of Mpro leads to prevention of viral replication. The SARS‐CoV‐2 Mpro is considered a promising drug target, as it is dissimilar to human proteases. Several peptidic protease inhibitors have been developed as SARS‐CoV‐2 Mpro inhibitors for COVID‐19 treatment. In this study, we screened naturally occurring peptidic α‐hydroxy amides (PHAs) (phebestin, probestin, bestatin) for SARS‐CoV‐2 Mpro inhibition.Materials and methods: In vitro COVID‐19 Mpro fluorometric assay was performed to evaluate its inhibitory efficacy by PHAs. Isothermal titration calorimetry technique was used to demonstrate the binding affinity between COVID‐19 Mpro and PHAs. Circular dichroism technique was used to determine the structural changes in secondary structure of COVID‐19 Mpro induced by PHAs. Molecular docking studies were performed to demonstrate the molecular level mechanism behind COVID‐19 Mpro inhibitory efficacy of PHAs. In addition, cytotoxic effects of PHAs were evaluated on lung epithelial cells of mice for its therapeutic applications for COVID‐19 through nasal delivery.Results and discussion: Phebestin (IC50 = 17.98 µM) Probestin (IC50 = 48.31 µM) and Bestatin (IC50 > 100 µM) significantly inhibited the COVID‐19 Mpro activity. The KD (dissociation constant) values of phebestin and probestin for COVID‐19 Mpro were 31.23 and 43.51 µM, respectively. CD spectrum analysis demonstrated that phebestin and probestin (10 µM) induced changes in the secondary structure of COVID‐19 Mpro. Molecular docking studies demonstrated that Interactions of phebestin and probestin with active site amino acids. Phebestin and probestin did not show any cytotoxicity on normal mouse lung epithelial cells up to 100 µM.Conclusion: Preliminary in vitro studies demonstrated that naturally occurring PHAs derivatives phebestin and probestin are SARS‐CoV‐2 Mpro inhibitors and warranted further studies to develop as drugs for COVID‐19.

Development and validation of simplified RP-HPLC method for quantification of Darunavir in commercial tablets

Darunavir (DRV) is a peptidic protease inhibitor class of antiretroviral drug which is regularly included in the antiretroviral therapy with several other drugs to treat Human immunodeficiency virus (HIV) patients to avoid those developing Acquired Immune Deficiency Syndrome (AIDS). In this research paper, an accurate, precise, reproducible, simple and rapid Reverse-Phase High-Performance Liquid Chromatography (RP-HPLC) method was developed and validated for quantifying DRV in the tablet dosage form (Danavir 600). The liquid chromatography was carried out on a Phenomenex C18 analytical column with dimensions of 250 × 4.6 mm, 5 µm using a mixture of acetonitrile (ACN) and water in the ratio of 30:70 v/v as mobile phase. The sample was injected in a volume of 20 µl and determined at 268 nm with a flow rate of 1 ml/min (ACN:water). The retention time of standard and sample drug was found to be 3.16 and 3.12 min respectively. The linearity in the calibration curve was achieved for DRV in the concentration range of 40–200 µg/ml and the regression coefficient (R2) was found to be 0.982. The percentage recovery of DRV was obtained in the range of 98.10–103.65% indicated the great accuracy of the current method. Reproducibility and recovery studies with % relative standard deviation (%RSD) with intra and inter-day precision was found to be less than 2%, which proven a developed method was reproducible. The limit of detection (LOD) and limit of quantification (LOQ) were found to be 0.31 and 0.96 µg/ml respectively. The method was validated as per the International Conference on Harmonization (ICH) guidelines and can be strongly adopted for routine analysis of DRV since it is the most reliable and rapid approach. Even though a lot of work has been performed for estimating DRV in dosage forms, this study was found to be under green chemistry with the rapid and economical condition. Thus, the statistical validation of the data showed that the proposed method can be applied for the estimation of DRV in commercial tablets.

Discovery of a Beetroot Protease Inhibitor to Identify and Classify Plant-Derived Cystine Knot Peptides.

Plant peptide protease inhibitors are important molecules in seed storage metabolism and to fight insect pests. Commonly they contain multiple disulfide bonds and are exceptionally stable molecules. In this study, a novel peptide protease inhibitor from beetroot (Beta vulgaris) termed bevuTI-I was isolated, and its primary structure was determined via mass spectrometry-based amino acid sequencing. By sequence homology analysis a few peptides with high similarity to bevuTI-I, also known as the Mirabilis jalapa trypsin inhibitor subfamily of knottin-type protease inhibitors, were discovered. Hence, we assessed bevuTI-I for inhibitory activity toward trypsin (IC50 = 471 nM) and human prolyl oligopeptidase (IC50 = 11 μM), which is an emerging drug target for neurodegenerative and inflammatory disorders. Interestingly, using a customized bioinformatics approach, bevuTI-I was found to be the missing link to annotate 243 novel sequences of M. jalapa trypsin inhibitor-like peptides. According to their phylogenetic distribution they appear to be common in several plant families. Therefore, the presented approach and our results may help to discover and classify other plant-derived cystine knot peptides, a class of plant molecules that play important functions in plant physiology and are currently being explored as lead molecules and scaffolds in drug development.

A structural and functional analogue of a Bowman–Birk-type protease inhibitor from Odorrana schmackeri

Frog skin secretions contain complex peptidomes and peptidic protease inhibitors that are one of the biologically and structurally described groups of components. In the present study, by use of molecular ‘shotgun’ cloning and LC MS/MS fractionation sequencing, a novel Bowman–Birk-type heptadecapeptide (AALKGCWTKSIPPKPCF-amide), named Odorrana schmackeri Trypsin Inhibitor (OSTI), with a canonical Cys6–Cys16 disulfide bridge, was isolated and identified in piebald odorous frog (O. schmackeri) skin secretion. A synthetic replicate of OSTI-exhibited trypsin inhibitory activity with a Ki value of 0.3 ± 0.04 nM and also a tryptase inhibitory effect with a Ki of 2.5 ± 0.6 μM. This is the first time that this property has been reported for a peptide originating from amphibian sources. In addition, substituting lysine (K) with phenylalanine (F) at the presumed P1 position, completely abrogated the trypsin and tryptase inhibition, but produced a strong chymotrypsin inhibition with a Ki of 1.0 ± 0.1 μM. Thus, the specificity of this peptidic protease inhibitor could be optimized through modifying the amino acid residue at the presumed P1 position and this novel native OSTI, along with its analogue, [Phe9]-OSTI, have expanded the potential drug discovery and development pipeline directed towards alleviation of serine protease-mediated pathologies.

Targeting Reactive Carbonyls for Identifying Natural Products and Their Biosynthetic Origins.

Natural products (NPs) serve important roles as drug candidates and as tools for chemical biology. However, traditional NP discovery, largely based on bioassay-guided approaches, is biased toward abundant compounds and rediscovery rates are high. Orthogonal methods to facilitate discovery of new NPs are thus needed, and herein we describe an isotope tag-based expansion of reactivity-based NP screening to address these shortcomings. Reactivity-based screening is a directed discovery approach in which a specific reactive handle on the NP is targeted by a chemoselective probe to enable its detection by mass spectrometry. In this study, we have developed an aminooxy-containing probe to guide the discovery of aldehyde- and ketone-containing NPs. To facilitate the detection of labeling events, the probe was dibrominated, imparting a unique isotopic signature to distinguish labeled metabolites from spectral noise. As a proof of concept, the probe was then utilized to screen a collection of bacterial extracts, leading to the identification of a new analogue of antipain, deimino-antipain. The bacterial producer of deimino-antipain was sequenced and the responsible biosynthetic gene cluster was identified by bioinformatic analysis and heterologous expression. These data reveal the previously undetermined genetic basis for a well-known family of aldehyde-containing, peptidic protease inhibitors, including antipain, chymostatin, leupeptin, elastatinal, and microbial alkaline protease inhibitor, which have been widely used for over 40 years.

Inhibition of Kallikrein-Related Peptidases 7 and 5 by Grafting Serpin Reactive-Center Loop Sequences onto Sunflower Trypsin Inhibitor-1 (SFTI-1).

Serpin proteins irreversibly inhibit serine proteases, but only a small part of the serpin reactive-center loop (RCL) is responsible for the initial protein-protein interaction (PPI). To develop peptidic protease inhibitors, kallikrein-related peptidases 7 (KLK7) and 5 (KLK5) were chosen. Firstly, we demonstrated that short peptides derived from RCL sequences can be cleaved by KLK7 in a substrate-like manner. Next, these substrates were grafted onto the protease-binding loop of sunflower trypsin inhibitor-1 (SFTI-1). Peptides based on kallistatin, α1 -antichymotrypsin, and protein C inhibitor (PCI) inhibited KLK7 with Ki =0.4, 0.5, and 0.7 μm, respectively. In contrast, the trypsin-like KLK5 was only blocked by the peptide derived from PCI (Ki =0.6 μm). Thus, serpin function can be mimicked by introducing its PPI site into the rigid structure of the SFTI-1 scaffold. This approach might be applicable not only to KLKs but also to other serine protease members, thus opening up new therapeutic fields.

Nostosins, Trypsin Inhibitors Isolated from the Terrestrial Cyanobacterium Nostoc sp. Strain FSN.

Two new trypsin inhibitors, nostosin A (1) and B (2), were isolated from a hydrophilic extract of Nostoc sp. strain FSN, which was collected from a paddy field in the Golestan Province of Iran. Nostosins A (1) and B (2) are composed of three subunits, 2-hydroxy-4-(4-hydroxyphenyl)butanoic acid (Hhpba), L-Ile, and L-argininal (1) or argininol (2). Nostosins A (1) and B (2) exhibited IC50 values of 0.35 and 55 μM against porcine trypsin, respectively, suggesting that the argininal aldehyde group plays a crucial role in the efficient inhibition of trypsin. Molecular docking of nostosin A (1) (449 Da), leupeptin (426 Da, IC50 0.5 μM), and spumigin E (610 Da, IC50 < 0.1 μM) with trypsin suggested prominent binding similarity between nostosin A (1) and leupeptin but only partial binding similarity with spumigin E. The number of hydrogen bonds between ligands and trypsin increased according to the length and size of the ligand molecule, and the docking affinity values followed the measured IC50 values. Nostosin A (1) is the first highly potent three-subunit trypsin inhibitor with potency comparable to the known commercial trypsin inhibitor leupeptin. These findings expand the known diversity of short-chain linear peptide protease inhibitors produced by cyanobacteria.

Bicyclic Peptide Inhibitor of Urokinase‐Type Plasminogen Activator: Mode of Action

The development of protease inhibitors for pharmacological intervention has taken a new turn with the use of peptide-based inhibitors. Here, we report the rational design of bicyclic peptide inhibitors of the serine protease urokinase-type plasminogen activator (uPA), based on the established monocyclic peptide, upain-2. It was successfully converted to a bicyclic peptide, without loss of inhibitory properties. The aim was to produce a peptide cyclised by an amide bond with an additional stabilising across-the-ring covalent bond. We expected this bicyclic peptide to exhibit a lower entropic burden upon binding. Two bicyclic peptides were synthesised with affinities similar to that of upain-2, and their binding energetics were evaluated by isothermal titration calorimetry. Indeed, compared to upain-2, the bicyclic peptides showed reduced loss of entropy upon binding to uPA. We also investigated the solution structures of the bicyclic peptide by NMR spectroscopy to map possible conformations. An X-ray structure of the bicyclic-peptide-uPA complex confirmed an interaction similar to that for the previous upain-1/upain-2-uPA complexes. These physical studies of the peptide-protease interactions will aid future designs of bicyclic peptide protease inhibitors.

New Structural Variants of Aeruginosin Produced by the Toxic Bloom Forming Cyanobacterium Nodularia spumigena

Nodularia spumigena is a filamentous diazotrophic cyanobacterium that forms blooms in brackish water bodies. This cyanobacterium produces linear and cyclic peptide protease inhibitors which are thought to be part of a chemical defense against grazers. Here we show that N. spumigena produces structurally novel members of the aeruginosin family of serine protease inhibitors. Extensive chemical analyses including NMR demonstrated that the aeruginosins are comprised of an N-terminal short fatty acid chain, L-Tyr, L-Choi and L-argininal and in some cases pentose sugar. The genome of N. spumigena CCY9414 contains a compact 18-kb aeruginosin gene cluster encoding a peptide synthetase with a reductive release mechanism which offloads the aeruginosins as reactive peptide aldehydes. Analysis of the aeruginosin and spumigin gene clusters revealed two different strategies for the incorporation of N-terminal protecting carboxylic acids. These results demonstrate that strains of N. spumigena produce aeruginosins and spumigins, two families of structurally similar linear peptide aldehydes using separate peptide synthetases. The aeruginosins were chemically diverse and we found 11 structural variants in 16 strains from the Baltic Sea and Australia. Our findings broaden the known structural diversity of the aeruginosin peptide family to include peptides with rare N-terminal short chain (C2–C10) fatty acid moieties.

The Binding Mechanism of a Peptidic Cyclic Serine Protease Inhibitor

Serine proteases are classical objects for studies of catalytic and inhibitory mechanisms as well as interesting as therapeutic targets. Since small-molecule serine protease inhibitors generally suffer from specificity problems, peptidic inhibitors, isolated from phage-displayed peptide libraries, have attracted considerable attention. Here, we have investigated the mechanism of binding of peptidic inhibitors to serine protease targets. Our model is upain-1 (CSWRGLENHRMC), a disulfide-bond-constrained competitive inhibitor of human urokinase-type plasminogen activator with a noncanonical inhibitory mechanism and an unusually high specificity. Using a number of modified variants of upain-1, we characterised the upain-1–urokinase-type plasminogen activator complex using X-ray crystal structure analysis, determined a model of the peptide in solution by NMR spectroscopy, and analysed binding kinetics and thermodynamics by surface plasmon resonance and isothermal titration calorimetry. We found that upain-1 changes both main-chain conformation and side-chain orientations as it binds to the protease, in particular its Trp3 residue and the surrounding backbone. The properties of upain-1 are strongly influenced by the addition of three to four amino acids long N-terminal and C-terminal extensions to the core, disulfide-bond-constrained sequence: The C-terminal extension stabilises the solution structure compared to the core peptide alone, and the protease-bound structure of the peptide is stabilised by intrapeptide contacts between the N-terminal extension and the core peptide around Trp3. These results provide a uniquely detailed description of the binding of a peptidic protease inhibitor to its target and are of general importance in the development of peptidic inhibitors with high specificity and new inhibitory mechanisms.

Evolution of cyclic peptide protease inhibitors

We report a bacterial system for the evolution of cyclic peptides that makes use of an expanded set of amino acid building blocks. Orthogonal aminoacyl-tRNA synthetase/tRNA(CUA) pairs, together with a split intein system were used to biosynthesize a library of ribosomal peptides containing amino acids with unique structures and reactivities. This peptide library was subsequently used to evolve an inhibitor of HIV protease using a selection based on cellular viability. Two of three cyclic peptides isolated after two rounds of selection contained the keto amino acid p-benzoylphenylalanine (pBzF). The most potent peptide (G12: GIXVSL; X=pBzF) inhibited HIV protease through the formation of a covalent Schiff base adduct of the pBzF residue with the ε-amino group of Lys 14 on the protease. This result suggests that an expanded genetic code can confer an evolutionary advantage in response to selective pressure. Moreover, the combination of natural evolutionary processes with chemically biased building blocks provides another strategy for the generation of biologically active peptides using microbial systems.

Mangiferin, an Anti-HIV-1 Agent Targeting Protease and Effective against Resistant Strains

The anti-HIV-1 activity of mangiferin was evaluated. Mangiferin can inhibit HIV-1ⅢB induced syncytium formation at non-cytotoxic concentrations, with a 50% effective concentration (EC50) at 16.90 μM and a therapeutic index (TI) above 140. Mangiferin also showed good activities in other laboratory-derived strains, clinically isolated strains and resistant HIV-1 strains. Mechanism studies revealed that mangiferin might inhibit the HIV-1 protease, but is still effective against HIV peptidic protease inhibitor resistant strains. A combination of docking and pharmacophore methods clarified possible binding modes of mangiferin in the HIV-1 protease. The pharmacophore model of mangiferin consists of two hydrogen bond donors and two hydrogen bond acceptors. Compared to pharmacophore features found in commercially available drugs, three pharmacophoric elements matched well and one novel pharmacophore element was observed. Moreover, molecular docking analysis demonstrated that the pharmacophoric elements play important roles in binding HIV-1 protease. Mangiferin is a novel nonpeptidic protease inhibitor with an original structure that represents an effective drug development strategy for combating drug resistance.

A Novel Trypsin and &amp;#945;-Chymotrypsin Inhibitor from Maclura pomifera Seeds

A new peptidic protease inhibitor (MpI) has been isolated from Maclura pomifera seeds, being the first trypsin and chymotrypsin inhibitor from a species belonging to the family Moraceae. MpI was purified by acetone precipitation, gel filtration and ion exchange chromatography, successively, with purification factors of 112 and 109 for the aforementioned enzymes, which are infrequent high values for inhibitors isolated from seeds. MpI showed a unique band in SDSTricine PAGE (Mr 11 kDa) and isoelectric focusing (pI = 5.2), inhibited the serine proteases trypsin and α-chymotrypsin (IC50 0.17 and 0.7 μg/ml, respectively), but not cathepsin B (cysteine protease), cathepsin D (aspartic protease) nor carboxypeptidase A (metallo protease). The N-terminal sequence was determined (AREPKFSTHCEEEESR) but no homology was detected with other peptide inhibitors isolated from seeds. Preliminary assays related to blood clotting reactions showed that the isolated inhibitor significatively increased the activated partial thromboplastin time (APTT), suggesting its potential use in the treatment of blood coagulation disorders. Keywords: Maclura pomifera seeds, Peptide trypsin inhibitor, Peptide α-chymotrypsin inhibitor, Moraceae

Quantification of darunavir (TMC114) in human plasma by high-performance liquid chromatography with ultra-violet detection

A precise and accurate high-performance liquid chromatography (HPLC) method with UV detection has been developed and validated for darunavir, a peptidic protease inhibitor. An internal standard, methylclonazepam, was added to 100 μL of plasma before a solid-phase extraction on C18 Bond Elut column. The eluted solutions were evaporated to dryness and reconstitued with 100 μL of mobile phase before being injected in the chromatographic system. The separation was performed on a C8 column using an acetonitrile and ultrapure water mixture (40:60, v/v) as mobile phase. All compounds were detected at a wavelength of 266 nm. The method was linear and validated over a concentration range of 0.25–20 mg/L. The within-day precision, ranged from 3.0 to 7.9%, while the within-day accuracy ranged from −11.4 to 0.5%. The between day precision and accuracy were respectively less than 13.7 and −11.4%. The mean recovery was 75.7% for darunavir and 66.7% for methylclonazepam. This method provides a useful tool for therapeutic drug monitoring in HIV patients.

Non-peptide protease inhibitors as vovel antiHIV agents

The human immunodeficiency virus has been shown to be the causative agent for acquired immunodeficiency syndrome (AIDS). The human immunodeficiency virus encodes for unique aspartyl protease that is essential for the production of enzymes and proteins in the final stages of maturation. Protease inhibitors act by preventing the formation of functional proteins from precursor proteins, which are vital for production of mature infectious viral particles. This review summarizes the data documenting the pharmacology and chemistry of non-peptide protease inhibitors that may be used as therapeutic agents against the human immunodeficiency virus infection. These agents are structural mimics of peptides with little or no peptidic character, thus overcoming various pharmacological problems of peptidic protease inhibitors. Structure-based drug designs of potent protease inhibitors, discovered through broad screening, have been developed into various clinical candidates for the treatment of AIDS. Non-peptide protease inhibitors could provide a useful model in the further search for novel compounds with even more pertinent pharmacological and pharmacokinetic profiles.

Unraveling Sub-Site Specificities of Peptidic Serine Protease Inhibitors by Substitutional and Structural Analysis

The interaction of peptidic inhibitors with serine proteases is investigated using peptide spot synthesis on cellulose sheets. This method permits a highly parallel analysis of subsite specificities and an optimization of peptidic inhibitors towards higher affinity and specificity for a given target protease. Information from crystal structures of corresponding protease/inhibitor complexes may help to explain the observed binding pattern.

Tipranavir: a novel non-peptidic protease inhibitor for the treatment of HIV infection

Tipranavir (TPV) is a non-peptidic protease inhibitor belonging to the class of 4-hydroxy-5,6-dihydro-2-pyrones, which exhibits potent and specific activity against HIV type I (HIV-1) and 2 (HIV-2). Clinically effective plasma levels of TPV are achieved by concomitant administration of ritonavir (RTV). Therefore, TPV has been coadministered with RTV in clinical trials. TPV has demonstrated antiviral activity against HIV-1 isolates that are resistant to reverse-transcriptase and selected peptidic protease inhibitors. Therefore, TPV is emerging as one of the newer drugs in the armamentarium against HIV-1 in patients demonstrating multi-drug resistance. TPV administered orally to humans exhibits linear pharmacokinetics at doses of 100 – 2000 mg. Steady-state plasma levels are attained within 7 days of initiating multiple dosing. The half-life of the drug is ∼ 6 h at steady-state. The plasma concentration is lower with repeated dosing than predicted from single-dose studies due to induction of the cytochrome P450 3A4 isoform of the liver microsomal enzyme system. Phase II clinical trials have shown that the administration of TPV and RTV in combination is safe and generally well-tolerated in HIV-1-infected adults. Phase III trials are underway to compare the efficacy of this drug versus other antiretroviral regimens. Gastrointestinal toxicity has been described with TPV, the most frequently reported side effects being diarrhoea, nausea, vomiting and abdominal pain. There is no known evidence of teratogenicity or effect on fertility. TPV dosed twice-daily, in the range of 500 – 1250 mg and combined with 100 – 200 mg of RTV has been shown to substantially and durably reduce viral load in HIV-1-infected drug-naive and experienced patients.