Design, synthesis, and biological evaluation of anti-HIV double-drugs. conjugates of HIV protease inhibitors with a reverse transcriptase inhibitor through spontaneously cleavable linkers

Hybrid Molecules as Potential Drugs for the Treatment of HIV: Design and Applications

Human immunodeficiency virus (HIV) infection is a major problem for humanity because HIV is constantly changing and developing resistance to current drugs. This necessitates the development of new anti-HIV drugs that take new approaches to combat an ever-evolving virus. One of the promising alternatives to combination antiretroviral therapy (cART) is the molecular hybrid strategy, in which two or more pharmacophore units of bioactive scaffolds are combined into a single molecular structure. These hybrid structures have the potential to have higher efficacy and lower toxicity than their parent molecules. Given the potential advantages of the hybrid molecular approach, the development and synthesis of these compounds are of great importance in anti-HIV drug discovery. This review focuses on the recent development of hybrid compounds targeting integrase (IN), reverse transcriptase (RT), and protease (PR) proteins and provides a brief description of their chemical structures, structure–activity relationship, and binding mode.

Small-sized human immunodeficiency virus type-1 protease inhibitors containing allophenylnorstatine to explore the S2' pocket

A series of HIV protease inhibitor based on the allophenylnorstatine structure with various P(2)' moieties were synthesized. Among these analogues, we discovered that a small allyl group would maintain potent enzyme inhibitory activity compared to the o-methylbenzyl moiety in clinical candidate 1 (KNI-764, also known as JE-2147, AG-1776, or SM-319777). Introduction of an anilinic amino group to 2 (KNI-727) improved water-solubility and anti-HIV-1 activity. X-ray crystallographic analysis of 13k (KNI-1689) with a beta-methallyl group at P(2)' position revealed hydrophobic interactions with Ala28, Ile84, and Ile50' similar to that of 1. The presence of an additional methyl group on the allyl group in compound 13k significantly increased anti-HIV activity over 1 while providing a rational drug design for structural minimization and improving membrane permeability.

FK506-binding protein (FKBP) partitions a modified HIV protease inhibitor into blood cells and prolongs its lifetime in vivo

HIV protease inhibitors are a key component of anti-retroviral therapy, but their susceptibility to cytochrome P(450) metabolism reduces their systemic availability and necessitates repetitive dosing. Importantly, failure to maintain adequate inhibitor levels is believed to provide an opportunity for resistance to emerge; thus, new strategies to prolong the lifetime of these drugs are needed. Toward this goal, numerous prodrug approaches have been developed, but these methods involve creating inactive precursors that require enzymatic processing. Using an alternative strategy inspired by the natural product FK506, we have synthetically modified an HIV protease inhibitor such that it acquires high affinity for the abundant, cytoplasmic chaperone, FK506-binding protein (FKBP). This modified protease inhibitor maintains activity against HIV-1 protease (IC(50) = 19 nM) and, additionally, it is partitioned into the cellular component of whole blood via binding to FKBP. Interestingly, redistribution into this protected niche reduces metabolism and improves its half-life in mice by almost 20-fold compared with the unmodified compound. Based on these findings, we propose that addition of FKBP-binding groups might partially overcome the poor pharmacokinetic properties of existing HIV protease inhibitors and, potentially, other drug classes.

Design of potent aspartic protease inhibitors to treat various diseases

In this retrospective, personal review covering our research from the late 1980s until 2007, we outline nearly two-decade worth of our own work on several aspartic protease inhibitors including those affecting renin, HIV-1 protease, plasmepsins, beta-secretase, and HTLV-I protease and we report on aspartic protease inhibitors as potential drugs to treat hypertension, AIDS, malaria, Alzheimer's disease and adult T-cell leukemia, HTLV-I associated myelopathy / tropical spastic paraparesis, and various, respectively, associated diseases. Herein, we describe our methods for rational substrate-based drug design of peptidomimetics that potently inhibit the activity of renin, HIV-1 protease, plasmepsins, beta-secretase, and HTLV-I protease accordingly, using an appropriately selected inhibitory residue that contained a hydroxymethylcarbonyl isostere. Although this non-hydrolyzable isostere mimics the transition state that is formed during protein cleavage of a substrate, the isostere-containing inhibitor is not cleaved. We highlight our optimization studies in which we used various techniques and tools such as truncation studies, natural and non-natural amino acid substitution studies, various moieties to promote chemical and pharmacological stability, X-ray crystallography, computer-assisted docking and dynamic simulations, quantitative structure-activity relationship studies, and various other methods that this review can barely mention.

Synthesis and Anti-HIV Activity of Some [Nucleoside Reverse Transcriptase Inhibitor]-C5′-Linker-[Integrase Inhibitor] Heterodimers as Inhibitors of HIV Replication

Selected for their expected ability to inhibit HIV replication, a series of eight heterodimers containing a Nucleoside Reverse Transcriptase Inhibitor (NRTI) and an Integrase Inhibitor (INI), bound by a linker, were designed and synthesized. For the NRTIs, d4U, d2U and d4T were chosen. For the INIs, 4-[1-(4-fluorobenzyl)-1H-pyrrol-2-yl]-2,4-dioxobutyric acid (6) and 4-(3,5-dibenzyloxyphenyl)-2,4-dioxobutyric acid (9) (belonging to the beta-diketo acids class) were chosen. The conjugation of the two different inhibitors (NRTI and INI) was performed using an amino acid (glycine or beta-alanine) as a cleavable linker.

Cyclization-activated prodrugs

Many drugs suffer from an extensive first-pass metabolism leading to drug inactivation and/or production of toxic metabolites, which makes them attractive targets for prodrug design. The classical prodrug approach, which involves enzyme-sensitive covalent linkage between the parent drug and a carrier moiety, is a well established strategy to overcome bioavailability/toxicity issues. However, the development of prodrugs that can regenerate the parent drug through non-enzymatic pathways has emerged as an alternative approach in which prodrug activation is not influenced by inter- and intraindividual variability that affects enzymatic activity. Cyclization-activated prodrugs have been capturing the attention of medicinal chemists since the middle-1980s, and reached maturity in prodrug design in the late 1990 s. Many different strategies have been exploited in recent years concerning the development of intramoleculary-activated prodrugs spanning from analgesics to anti-HIV therapeutic agents. Intramolecular pathways have also a key role in two-step prodrug activation, where an initial enzymatic cleavage step is followed by a cyclization-elimination reaction that releases the active drug. This work is a brief overview of research on cyclization-activated prodrugs from the last two decades.

Identification of peptidomimetic HTLV-I protease inhibitors containing hydroxymethylcarbonyl (HMC) isostere as the transition-state mimic

Towards the development of chemotherapy for the infection by human T-cell leukemia virus type I (HTLV-I), we have established evaluation systems for HTLV-I protease (PR) inhibitors using both recombinant and chemically synthesized HTLV-I PRs. Newly synthesized substrate-based inhibitors containing hydroxymethylcarbonyl (HMC) isostere showed potent anti-HTLV-I PR activity.

Chemoenzymatic syntheses of homo- and heterodimers of AZT and d4T, and evaluation of their anti-HIV activity

Homo- and heterodimers of AZT and d4T, possessing carbonate and carbamate linkers, have been synthesized with the aim to enhance the antiviral activity of their components. Homo- and heterodimer carbamates showed weak anti-HIV activity. On the other hand, dinucleoside carbonates showed marked antiviral activity.

Fragrance release from the surface of branched poly (amide)s

Enzymes are powerful tools in organic synthesis that are able to catalyse a wide variety of selective chemical transformations under mild and environmentally friendly conditions. Enzymes such as the lipases have also found applications in the synthesis and degradation of polymeric materials. However, the use of these natural catalysts in the synthesis and the post-synthetic modification of dendrimers and hyperbranched molecules is an application of chemistry yet to be explored extensively. In this study the use of two hydrolytic enzymes, a lipase from Candida cylindracea and a cutinase from Fusarium solani pisii, were investigated in the selective cleavage of ester groups situated on the peripheral layer of two families of branched polyamides. These branched polyamides were conjugated to simple fragrances citronellol and L-menthol via ester linkages. Hydrolysis of the ester linkage between the fragrances and the branched polyamide support was carried out in aqueous buffered systems at slightly basic pH values under the optimum operative conditions for the enzymes used. These preliminary qualitative investigations revealed that partial cleavage of the ester functionalities from the branched polyamide support had occurred. However, the ability of the enzymes to interact with the substrates decreased considerably as the branching density, the rigidity of the structure and the bulkiness of the polyamide-fragrance conjugates increased.

Plasmepsin II inhibition and antiplasmodial activity of Primaquine-Statine 'double-drugs'

Statine-based inhibitors of Plasmepsin II (PLMII) coupled with Primaquine have been designed using the 'double-drug' approach. The IC50 values for PLMII inhibition ranged from 0.59 to 400 nM and the best IC50 value for inhibition of Plasmodium falciparum growth in vitro was 0.4 microM, which represent a remarkable improvement compared to other statine-based PLMII inhibitors.

New bicyclam-GalCer analogue conjugates: synthesis and in vitro anti-HIV activity

The synthesis of bipharmacophore anti-HIV compounds which, in a single molecule, combine two ligands, that is, the bicyclam AMD3100 and a GalCer analogue, that might inhibit several steps of the complex virus/cell cascade interactions has been performed. The 'double-drug' Gal-AMD3100 conjugates elicited inhibitory effects on T (or X4)-tropic HIV-1 replication in all CXCR4 expressing cell lines with EC(50) values ranging from 0.25 to 6.0 microM which were however approximately 40- to 125-fold lower than that of AMD3100. Concerning the mechanism of inhibition of the Gal-AMD3100 conjugates, experiments performed with X4 or R5HIV-1 strains and GHOST cells genetically modified to express CD4 and CXCR4 or CCR5 indicated clearly that the conjugates interact with CXCR4 and not with CCR5.

Search for substrate-based inhibitors fitting the S2? space of malarial aspartic protease plasmepsin II

Plasmepsin (Plm) has been identified as an important target for the development of new antimalarial drugs, since its inhibition leads to the starvation of Plasmodium falciparum. A series of substrate-based dipeptide-type Plm II inhibitors containing the hydroxymethylcarbonyl isostere as a transition-state mimic were synthesized. The general design principle was provision of a conformationally restrained hydroxyl group (corresponding to the set residue at the P2' position in native substrates) and a bulky unit to fit the S2' pocket.