Controlled drug release: new water-soluble prodrugs of an HIV protease inhibitor

We designed and synthesized a series of highly water-soluble prodrugs of an HIV protease inhibitor, KNI-727 (1), containing tandem-linked two auxiliary units, a solubilizing moiety and a self-cleavable spacer. Prodrugs with an ionized amino group at the solubilizing moiety exhibited a remarkable increase of water-solubility (>10(4) fold) compared to the parent drug 1. These prodrugs released I not enzymatically, but chemically via an intramolecular cyclization-elimination reaction through an imide formation in physiological conditions. Diversified rates of parent drug release were observed when the chemical structure of both the solubilizing and the spacer moieties were modified. This new approach for water-soluble prodrugs will enable to control chemically the release of parent drug as well as to maintain high water-solubility.     

Enzymatic and structural analysis of the I47A mutation contributing to the reduced susceptibility to HIV protease inhibitor lopinavir

Lopinavir (LPV) is a second-generation HIV protease inhibitor (PI) designed to overcome resistance development in patients undergoing long-term antiviral therapy. The mutation of isoleucine at position 47 of the HIV protease (PR) to alanine is associated with a high level of resistance to LPV. In this study, we show that recombinant PR containing a single I47A substitution has the inhibition constant (K(i) ) value for lopinavir by two orders of magnitude higher than for the wild-type PR. The addition of the I47A substitution to the background of a multiply mutated PR species from an AIDS patient showed a three-order-of-magnitude increase in K(i) in vitro relative to the patient PR without the I47A mutation. The crystal structure of I47A PR in complex with LPV showed the loss of van der Waals interactions in the S2/S2' subsites. This is caused by the loss of three side-chain methyl groups due to the I47A substitution and by structural changes in the A47 main chain that lead to structural changes in the flap antiparallel beta-strand. Furthermore, we analyzed possible interaction of the I47A mutation with secondary mutations V32I and I54V. We show that both mutations in combination with I47A synergistically increase the relative resistance to LPV in vitro. The crystal structure of the I47A/I54V PR double mutant in complex with LPV shows that the I54V mutation leads to a compaction of the flap, and molecular modeling suggests that the introduction of the I54V mutation indirectly affects the strain of the bound inhibitor in the PR binding cleft.     

HIV protease inhibitor ritonavir increases endothelial monolayer permeability

HIV protease inhibitors (PIs) are often associated with metabolic and cardiovascular complications although they are effective anti-HIV drugs. In this study, we determined whether HIV PI ritonavir could increase endothelial permeability, one of the important mechanisms of vascular lesion formation. Human dermal microvascular endothelial cells (HMECs) treated with ritonavir showed a significant increase of endothelial permeability in a dose- and time-dependent manner assayed with a transwell system. Ritonavir significantly reduced the mRNA levels of tight junction proteins zonula occluden-1, occludin, and claudin-1 by 40-60% as compared to controls (P<0.05) by real-time PCR analysis. Protein levels of these tight junction molecules were also substantially reduced in the ritonavir-treated cells. In addition, HMECs treated with ritonavir (7.5, 15, and 30microM) showed a substantial increase of superoxide anion production by 10%, 32%, and 65%, respectively, as compared to controls. Antioxidants (EGCG and SeMet) effectively reduced ritonavir-induced endothelial permeability. Furthermore, ritonavir activated ERK1/2 (phosphorylation), but not P38 and JNK. Specific ERK1/2 inhibitor, PD89059, significantly abolished ritonavir-induced endothelial permeability by 92%. Thus, HIV PI ritonavir increases endothelial permeability, decreases levels of tight junction proteins, and increases superoxide anion production. ERK1/2 activation is involved in the signal transduction pathway of ritonavir-induced endothelial permeability.     

Darunavir, a conceptually new HIV-1 protease inhibitor for the treatment of drug-resistant HIV

Our structure-based design strategies which specifically target the HIV-1 protease backbone, resulted in a number of exceedingly potent nonpeptidyl inhibitors. One of these inhibitors, darunavir (TMC114), contains a privileged, structure-based designed high-affinity P2 ligand, 3(R),3a(S),6a(R)-bis-tetrahydrofuranylurethane (bis-THF). Darunavir has recently been approved for the treatment of HIV/AIDS patients harboring multidrug-resistant HIV-1 variants that do not respond to previously existing HAART regimens.     

Effects of HIV protease inhibitor therapy on lipid metabolism

Highly active antiretroviral therapy, which includes a combination of protease inhibitors, is highly successful in controlling human immunodeficiency virus (HIV) infection and reducing the morbidity and mortality of autoimmune deficiency syndrome (AIDS). However, the benefits of HIV protease inhibitors are compromised by numerous undesirable side effects. These include peripheral fat wasting and excessive central fat deposition (lipodystrophy), overt hyperlipidemia, and insulin resistance. The mechanism associated with protease inhibitor-induced metabolic abnormalities is multifactorial. One major effect of the protease inhibitor is its suppression of the breakdown of the nuclear form of sterol regulatory element binding proteins (nSREBP) in the liver and adipose tissues. Hepatic accumulation of nSREBP results in increased fatty acid and cholesterol biosynthesis, whereas nSREBP accumulation in adipose tissue causes lipodystrophy, reduces leptin expression, and promotes insulin resistance. The HIV protease inhibitors also suppress proteasome-mediated breakdown of nascent apolipoprotein (apo) B, thus resulting in the overproduction and secretion of triglyceride-rich lipoproteins. Finally, protease inhibitor also suppresses the inhibition of the glucose transporter GLUT-4 activity in adipose and muscle. This latter effect also contributes directly to insulin resistance and diabetes. These adverse effects need to be alleviated for long-term use of protease inhibitor therapy in treatment of HIV infection.     

Stability analysis for HIV infection delay model with protease inhibitor

In this article, we considered a model of HIV-1 infection with a protease inhibitor therapy and three delays. The frequency of the bifurcating periodic solution as well as the threshold value is approximated numerically using realistic parameter. The estimated threshold value is realistic and the frequency of the oscillations is consistent with that of the observed viral blips.     

Nonpeptidic HIV protease inhibitors possessing excellent antiviral activities and therapeutic indices. PD 178390: a lead HIV protease inhibitor

With the insight generated by the availability of X-ray crystal structures of various 5,6-dihydropyran-2-ones bound to HIV PR, inhibitors possessing various alkyl groups at the 6-position of 5,6-dihydropyran-2-one ring were synthesized. The inhibitors possessing a 6-alkyl group exhibited superior antiviral activities when compared to 6-phenyl analogues. Antiviral efficacies were further improved upon introduction of a polar group (hydroxyl or amino) on the 4-position of the phenethyl moiety as well as the polar group (hydroxymethyl) on the 3-(tert-butyl-5-methyl-phenylthio) moiety. The polar substitution is also advantageous for decreasing toxicity, providing inhibitors with higher therapeutic indices. The best inhibitor among this series, (S)-6-[2-(4-aminophenyl)-ethyl]-(3-(2-tert-butyl-5-methyl-phenylsulfanyl)-4-hydroxy-6-isopropyl-5,6-dihydro-pyran-2-one (34S), exhibited an EC₅₀ of 200 nM with a therapeutic index of >1000. More importantly, these non-peptidic inhibitors, 16S and 34S, appear to offer little cross-resistance to the currently marketed peptidomimetic PR inhibitors. The selected inhibitors tested in vitro against mutant HIV PR showed a very small increase in binding affinities relative to wild-type HIV PR. C_max and absolute bioavailability of 34S were higher and half-life and time above EC₉₅ were longer compared to 16S. Thus 34S, also known as PD 178390, which displays good antiviral efficacy, promising pharmacokinetic characteristics and favorable activity against mutant enzymes and CYP3A4, has been chosen for further preclinical evaluation.     

The mechanism of insulin resistance caused by HIV protease inhibitor therapy

Retroviral protease inhibitors used as therapy for HIV-1 infection have been causally associated with serious metabolic side effects, including peripheral lipodystrophy, hyperlipidemia, insulin resistance, and in some cases, overt type 2 diabetes. The etiology of this characteristic clinical syndrome remains unknown. We demonstrate that the HIV protease inhibitor, indinavir, dramatically inhibits insulin-stimulated glucose uptake in 3T3-L1 adipocytes in a dose-dependent manner (63% inhibition observed with 100 micrometer indinavir). Indinavir treatment did not affect early insulin signaling events or the translocation of intracellular Glut1 or Glut4 glucose transporters to the cell surface. To determine whether indinavir may be directly affecting the intrinsic transport activity of glucose transporters, the Glut1 and Glut4 isoforms were heterologously expressed and analyzed in Xenopus laevis oocytes. Indinavir at 100 microm had no effect on Glut1 transport activity in Xenopus oocytes, whereas Glut4 activity was significantly inhibited (45% inhibition). Similar effects on glucose transport were observed for other HIV protease inhibitors. We conclude that HIV protease inhibitors as a class are capable of selectively inhibiting the transport function of Glut4 and that this effect may be responsible for a major iatrogenic complication frequently observed in HIV patients.     

The solution structures of the HIV protease inhibitor DG35-VIII

NMR spectroscopy techniques have been used to determine the conformation of DG35-VIII in DMSO, acetone, and methanol. COSY and Heteronuclear Correlation experiments were used to confirm the proton spectral assignments. NOESY experiments were used to identify proton internuclear distances which were used to determine the 3D structure. The NOESY data identified a single "U-shaped" conformer of DG35-VIII in acetone, and an alternate "extended" conformer in methanol and two possible conformations in DMSO. Restrained molecular minimization methods using the Molecular Mechanics Program "DISCOVER" and "DYANA" were used to determine a low energy structure consistent with the NMR data. The extended structure of DG35-VIII was compared with closely related HIV protease inhibitors (VX-478 and ABT-538) and showed similar backbone structures, with the functional isostere groups superimposed on each other. The binding energy of DG35-VIII with HIV protease was examined and found to be comparable with VX-478 and ABT-538.     

Species-dependent enantioselective pharmacokinetics of PNU-103017, a Pyrone HIV protease inhibitor

PNU-103017, 4-Cyano-N-(3-(cyclopropyl(5,6,7,8,9,10-hexahydro-4-hydroxy-2-oxo-2H-cycloocta(b) pyran-3-yl)methyl)phenyl)-benzenesulfonamide, is a selective HIV aspartyl protease inhibitor under evaluation as a potential oral treatment of Acquired Immunodeficiency Diseases. PNU-103017 is a racemic mixture of two enantiomers, designated PNU-103264 (R-) and PNU-103265 (S-). Stereoselective pharmacokinetics of the two enantiomers of PNU-103017 were observed in the dog, rat, and human after single and multiple dose administration of the racemate and were apparently species-dependent. Mean enantiomeric ratios of plasma concentrations (R-/S-) at each time point were greater than 1 in the dog, ranging from 1.22 to 3.06, but less than 1 in the rat and in the human, ranging from 0.44 to 0.80 and 0.23 to 0.73, respectively. A trend towards increased or decreased (farther from 1:1, R-/S-) enantiomeric ratio of plasma concentrations with time after each administration was also observed. The enantiomeric ratio remained unchanged after multiple dose administration in the rat, dog, and human although enzyme induction and increased plasma clearance were observed for both enantiomers. Chirality 10:210–216, 1998. © 1998 Wiley-Liss, Inc.     

Ginsenosides block HIV protease inhibitor ritonavir-induced vascular dysfunction of porcine coronary arteries

Human immunodeficiency virus (HIV) protease inhibitor ritonavir (RTV) may induce vascular dysfunction through oxidative stress. Ginsenosides have been shown to have potential benefits on the cardiovascular system through diverse mechanisms, including antioxidative property. The objective of this study was to determine whether ginsenosides could prevent coronary arteries from RTV-induced dysfunction. Porcine coronary artery rings were incubated with RTV and ginsenosides Rb1, Rc, and Re for 24 h. Vasomotor function was recorded by a myograph tension system. In response to the thromboxane A(2) analog U-46619, the contraction of the vessel rings was significantly reduced. When cocultured with Rb1, Rc, and Re, the contractility significantly increased. In response to bradykinin at 10(-5) M, the endothelium-dependent relaxation of vessel rings was significantly reduced by 59% for RTV compared with controls (P < 0.05). When cocultured with Rb1, Rc, and Re, the relaxation significantly increased 100%, 90%, and 134%, respectively, compared with the RTV-alone groups (P > 0.05). In response to sodium nitroprusside, RTV significantly reduced vasorelaxation. In addition, the endothelial nitric oxide synthase (eNOS) mRNA levels were significantly reduced by 78% for RTV group (P < 0.05) by real-time PCR analysis. The eNOS protein levels measured by Western blot analysis and nitrite concentrations measured by Griess assay were also decreased, whereas O(2)(-) production by lucigenin-enhanced chemiluminescence was significantly increased in the RTV-treated group. These effects of RTV were effectively blocked by ginsenosides. Thus HIV protease inhibitor RTV significantly impaired the vasomotor function of porcine coronary arteries. This effect may be mediated by the downregulation of eNOS and overproduction of O(2)(-). These results suggest that ginsenosides can effectively block RTV-induced vascular dysfunction.     

X-ray crystallographic structure of ABT-378 (lopinavir) bound to HIV-1 protease

The crystal structure of ABT-378 (lopinavir), bound to the active site of HIV-1 protease is described. A comparison with crystal structures of ritonavir, A-78791, and BILA-2450 shows some analogous features with previous reported compounds. A cyclic urea unit in the P(2) position of ABT-378 is novel and makes two bidentate hydrogen bonds with Asp 29 of HIV-1 protease. In addition, a previously unreported shift in the Gly 48 carbonyl position is observed. A discussion of the structural features responsible for its high potency against wild-type HIV protease is given along with an analysis of the effect of active site mutations on potency in in vitro assays.     

Characterizing and optimizing protease/peptide inhibitor interactions, a new application for spot synthesis

A new method is presented that uses parallel peptide array synthesis on cellulose membranes to characterize protease/peptide inhibitor interactions. A peptide comprising P5-P4' of the third domain of turkey ovomucoid inhibitor was investigated for both binding to and inhibition of porcine pancreatic elastase. Binding was studied directly on the cellulose membrane, while inhibition was measured by an assay in microtiter plates with punched out peptide spots. The importance of each residue for binding or inhibition was determined by substitutional analyses, exchanging every original amino acid with all other 19 coded amino acids. Seven hundred eighty individual peptides were investigated for binding behavior to porcine pancreatic elastase, and 320 individual peptides were measured in inhibition experiments. The results provide new insights into the interaction between the ovomucoid derived peptide and subsites in the active site of elastase. Combining these data with length analysis we designed new peptides in a step-wise fashion which in the end not only inhibited elastase 400 times more strongly than the original peptide, but are highly specific for the enzyme. In addition, the optimized inhibitor peptide was protected against exopeptidase attack by substituting D-amino acids at both termini.     

A bis-[N-3-(1-hydroxy-1-methyl-ethyl)-benzyl)-cyclic urea as a HIV protease inhibitor

Synthetic efforts to overcome the metabolic oxidative degradation of the HIV protease inhibitory cyclic urea DMP323, a benzyl alcohol, have led to the discovery of a tertiary carbinol with superior affinity for the viral protease and more potent inhibitory activity against viral replication. Synthetic approaches to this new carbinol and comparative analysis of its pharmacology and pharmacokinetics are presented.     

The human immunodeficiency virus (HIV) protease inhibitor indinavir directly affects the opportunistic fungal pathogen Cryptococcus neoformans

Highly active antiretroviral therapy (HAART), that includes human immunodeficiency virus (HIV) protease inhibitors (PIs), has been remarkably efficacious including against some opportunistic infections. In this report we investigated the effect(s) of the PI indinavir on protease activity by Cryptococcus neoformans, an opportunistic fungal pathogen responsible for recurrent meningoencephalitis in AIDS patients. Indinavir was also tested for potential effects on other parameters, such as fungal viability, growth ability and susceptibility to immune effector cells. It was found that indinavir impaired cryptococcal protease activity in a time- and dose-dependent fashion. The phenomenon was similarly detectable in ATCC/laboratory strains and clinical isolates. C. neoformans growth rate was also significantly reduced upon exposure to indinavir, while fungal viability was not affected and mitochondrial toxicity not detected. Furthermore, as assessed by an in vitro infection model, indinavir significantly and consistently augmented C. neoformans susceptibility to microglial cell-mediated phagocytosis and killing. Overall, by providing the first evidence that indinavir directly affects C. neoformans, these data add new in vitro insights on the wide-spectrum efficacy of PIs, further arguing for the clinical relevance of HAART against opportunistic infections in AIDS.