Raltegravir (MK-0518): an integrase inhibitor for the treatment of HIV-1

In the developed world, access to highly active antiretroviral therapy (HAART) has led to significant reductions in the morbidity and mortality attributed to HIV/AIDS. However, the continual emergence of HIV-1 strains resistant to currently available classes of antiretrovirals highlights the need to develop agents with novel mechanisms of action. Successful completion of the HIV-1 viral life cycle depends in part on the integration of complementary DNA mediated by the enzyme HIV-1 integrase, one of three essential enzymes encoded in the viral genome. The integrase inhibitors have demonstrated the ability to act specifically at the strand transfer step during integration, making HIV-1 integrase a valid and attractive chemotherapeutic target for the treatment of HIV/AIDS. In clinical trials, raltegravir has been shown to be a potent drug with a pharmacokinetic profile that supports a twice-daily dosing schedule. In addition, it has demonstrated a favorable side-effect profile in treatment-naive and -experienced patients and a subset of heavy treatment-experienced patients have been able a achieve virologic suppression with raltegravir as part of combination therapy despite limited treatment options. In October 2007, raltegravir was approved by the U.S. Food and Drug Administration (FDA) for the treatment of HIV-1 as part of combination antiretroviral therapy in treatment-experienced patients-providing an additional option for the management of the HIV-1 infected individual.     

Raltegravir (MK-0518): a novel integrase inhibitor for the treatment of HIV infection

Integrase is essential for HIV-1 replication; however, potent inhibition of the isolated enzyme in biochemical assays has not readily translated into antiviral activity in a manner consistent with inhibition of integration. Raltegravir is a novel HIV-1 integrase strand transfer inhibitor with potent in vitro activity against wild-type and multi-class resistant HIV-1 virus (in vitro IC(95) for HIV-1 in 50% normal human serum = 33 nM). Inhibition of integrase prevents insertion of HIV DNA into the human DNA genome, thus blocking the ability of HIV to replicate. Raltegravir is administered orally every 12 h and does not require boosting with low-dose ritonavir (RTV) to achieve therapeutic concentrations. Raltegravir is not a potent inhibitor or inducer of cytochrome P450 3A4, and it is predominantly metabolized by glucuronidation, specifically by the enzyme UDP-glucuronosyltransferase 1A1.     

Studies of metabolism and disposition of potent human immunodeficiency virus (HIV) integrase inhibitors using 19F-NMR spectroscopy

¹⁹F-nuclear magnetic resonance (NMR) has been extensively used in a drug-discovery programme to support the selection of candidates for further development. Data on an early lead compound, N-(4-fluorobenzyl)-5-hydroxy-1-methyl-2-(4-methylmorpholin-3-yl)-6-oxo-1,6-dihydropyrimidine-4-carboxamide (compound A (+)), and MK-0518 (N-(4-fluorobenzyl)-5-hydroxy-1-methyl-2-(1-methyl-1-{[(5-methyl-1,3,4-oxadiazol-2-yl)carbonyl]amino}ethyl)-6-oxo-1,6-dihydropyrimidine-4-carboxamide), a potent inhibitor of this series currently in phase III clinical trials, are described. The metabolic fate and excretion balance of compound A (+) and MK-0518 were investigated in rats and dogs following intravenous and oral dosing using a combination of ¹⁹F-NMR-monitored enzyme hydrolysis and solid-phase extraction chromatography and NMR spectroscopy (SPEC-NMR). Dosing with the ³H-labelled compound A (+) enabled the comparison of standard radiochemical analysis with ¹⁹F-NMR spectroscopy to obtain quantitative metabolism and excretion data. Both compounds were eliminated mainly by metabolism. The major metabolite identified in rat urine and bile and in dog urine was the 5-O-glucuronide.     

Studies of metabolism and disposition of potent human immunodeficiency virus (HIV) integrase inhibitors using 19F-NMR spectroscopy

(19)F-nuclear magnetic resonance (NMR) has been extensively used in a drug-discovery programme to support the selection of candidates for further development. Data on an early lead compound, N-(4-fluorobenzyl)-5-hydroxy-1-methyl-2-(4-methylmorpholin-3-yl)-6-oxo-1,6-dihydropyrimidine-4-carboxamide (compound A (+)), and MK-0518 (N-(4-fluorobenzyl)-5-hydroxy-1-methyl-2-(1-methyl-1-{[(5-methyl-1,3,4-oxadiazol-2-yl)carbonyl]amino}ethyl)-6-oxo-1,6-dihydropyrimidine-4-carboxamide), a potent inhibitor of this series currently in phase III clinical trials, are described. The metabolic fate and excretion balance of compound A (+) and MK-0518 were investigated in rats and dogs following intravenous and oral dosing using a combination of (19)F-NMR-monitored enzyme hydrolysis and solid-phase extraction chromatography and NMR spectroscopy (SPEC-NMR). Dosing with the (3)H-labelled compound A (+) enabled the comparison of standard radiochemical analysis with (19)F-NMR spectroscopy to obtain quantitative metabolism and excretion data. Both compounds were eliminated mainly by metabolism. The major metabolite identified in rat urine and bile and in dog urine was the 5-O-glucuronide.     

Metabolism and disposition of the antihypertensive agent moxonidine in humans.

The metabolism and pharmacokinetics of moxonidine, a potent central-acting antihypertensive agent, were studied in four healthy subjects after a single oral administration of approximately 1 mg (approximately 60 muCi) of [(14)C(3)]moxonidine. Moxonidine was rapidly absorbed, with peak plasma concentration achieved between 0.5 to 2 h postdose. The maximal plasma concentration and the area under the curve of unchanged moxonidine are lower than those determined for radioactivity, indicating presence of circulating metabolite(s). The total recovery of radiocarbon over 120 h ranged from 99.6 to 105.2%, with 92.3 to 103.3% of the radioactivity excreted in the urine and only 1.9 to 7.3% of the dose excreted in the feces. Thus, renal elimination represented the principal route of excretion of radioactivity. Metabolites of moxonidine were identified in urine and plasma samples by high performance liquid chromatography and liquid chromatography-tandem mass spectrometry. Oxidation of moxonidine on the methyl group or on the imidazoline ring resulted in the formation of hydroxymethyl moxonidine, hydroxy moxonidine, dihydroxy moxonidine, and dehydrogenated moxonidine. Metabolite profiling results indicated that parent moxonidine was the most abundant component in the urine. The dehydrogenated moxonidine was the major urinary metabolite as well as the major circulating metabolite. Moxonidine also underwent phase II metabolism, generating a cysteine conjugate. In summary, moxonidine is well absorbed after oral administration. The major clearance pathway for moxonidine in humans is via renal elimination. Furthermore, seven metabolites were identified with three metabolites unique to humans.     

Selection of diverse and clinically relevant integrase inhibitor-resistant human immunodeficiency virus type 1 mutants

Resistance passage studies were conducted with five INIs (integrase inhibitors) that have been tested in clinical trials to date: a new naphthyridinone-type INI S/GSK-364735, raltegravir, elvitegravir, L-870,810 and S-1360. In establishing the passage system and starting from concentrations several fold above the EC(50) value, resistance mutations against S-1360 and related diketoacid-type compounds could be isolated from infected MT-2 cell cultures from day 14 to 28. Q148R and F121Y were the two main pathways of resistance to S/GSK-364735. Q148R/K and N155H, which were found in patients failing raltegravir treatment in Phase IIb studies, were observed during passage with raltegravir with this method. The fold resistance of 40 mutant molecular clones versus wild type virus was compared with these five INIs. The overall resistance pattern of S/GSK-364735 was similar to that of raltegravir and other INIs. However, different fold resistances of particular mutations were noted among different INIs, reflecting a potential to develop INIs with distinctly different resistant profiles.     

Dicaffeoyltartaric acid analogues inhibit human immunodeficiency virus type 1 (HIV-1) integrase and HIV-1 replication at nontoxic concentrations

The human immunodeficiency virus type 1 (HIV-1) is a major health problem worldwide. In this study, 17 analogues of L-chicoric acid, a potent inhibitor of HIV integrase, were studied. Of these analogues, five submicromolar inhibitors of integrase were discovered and 13 compounds with activity against integrase at less than 10 microM were identified. Six demonstrated greater than 10-fold selectivity for HIV replication over cellular toxicity. Ten analogues inhibited HIV replication at nontoxic concentrations. Alteration of the linkages between the two bis-catechol rings, including the use of amides, mixed amide esters, cholate, and alkyl bridges, was explored. Amides were as active as esters but were more toxic in tissue culture. Alkyl and cholate bridges were significantly less potent against HIV-1 integrase in vitro and were inactive against HIV-1 replication. Two amino acid derivates and one digalloylderivative of L-chicoric acid (L-CA) showed improved selectivity over L-CA against integration in cell culture. These data suggest that in addition to the bis-catechols and free carboxylic acid groups reported previously, polar linkages are important constituents for optimal activity against HIV-1 integrase and that new derivatives can be developed with increased specificity for integration over HIV entry in vivo.     

Metabolism of the antipsychotic drug tiospirone in humans.

Metabolism of the antipsychotic drug tiospirone was studied in humans after a single 60-mg oral dose of [14C]tiospirone. Metabolites were isolated from a 0-24 hr pooled urine from eight subjects, which represented 39% of the dose, and purified to homogeneity by HPLC. Purified metabolites were identified by desorption chemical ionization mass spectrometry in the positive ion mode with methane as a reagent gas. Structures of the metabolites were confirmed by coelution on HPLC in several systems with synthetic standards. In addition to unchanged tiospirone, five metabolites of tiospirone were identified and one additional metabolite was partially identified. Based on the structures of these metabolites, five routes of metabolism of tiospirone were identified: N-dealkylation of the butyl side chain attached to the piperazinyl nitrogen, hydroxylation alpha to the glutarimidyl carbonyl at the 6'-position on the spiro ring, hydroxylation at the 3'-position on the spiro ring, oxidation at sulfur resulting in the formation of sulfones, and oxidation at carbon alpha to the piperazinyl nitrogen resulting in the formation of a lactam-sulfone. The major urinary metabolites were benzisothiazole piperazine sulfone and its lactam derivative, accounting for 5.0 and 4.3% of the dose, respectively. The identified metabolites accounted for 50% of the total radioactivity in the urine (approximately 20% of the dose). The remaining radioactive components were extremely heterogeneous and could not be isolated in sufficient quantities to characterize. A scheme for the metabolism of tiospirone in humans is proposed.     

Inhibition of human immunodeficiency virus type I integrase by naphthamidines and 2-aminobenzimidazoles

Retroviral integrases catalyze two of the steps of insertion of proviral DNA into the host genomic DNA. Inhibitors that target the second step, strand transfer into the host DNA, have been demonstrated to have antiviral activity in cell culture. We describe two classes of HIV-1 integrase inhibitors that block strand transfer, one based on a naphthamidine core and one on a benzimidazole core. While the naphthamidine compounds showed some propensity to interact with the DNA substrate, both classes were shown to bind directly to integrase. The naphthamidine compounds showed activity in cell culture, and a direct effect on integrase was indicated by an increase in 2-LTR products in the presence of a naphthamidine compound. These two classes of compounds represent potential starting points for the development of new classes of integrase inhibitors.     

Enalapril maleate (MK-421), a potent, nonsulfhydryl angiotensin-converting enzyme inhibitor: absorption, disposition, and metabolism in man

Animal studies (particularly in dogs) on enalapril maleate have served to predict the patterns of absorption and elimination observed in man. Enalapril is more readily absorbed in man than the active inhibitor form MK-422. Estimates of minimum absorption of enalapril are of the order of 60-70%, based on urinary recovery. Metabolism of enalapril to MK-422 appears to be largely a postabsorptive process. From urinary recovery data, a minimum of 43% of a 10-mg dose of enalapril is available as MK-422. Excretion of enalapril and MK-422 is principally renal. The excellent mass balance obtained in human studies precludes extensive metabolism beyond hydrolysis to MK-422. Data in hand suggest that any metabolism other than to MK-422 is of a trace nature.     

Metabolism and disposition of the dipeptidyl peptidase IV inhibitor teneligliptin in humans

Abstract

1. The absorption, metabolism and excretion of teneligliptin were investigated in healthy male subjects after a single oral dose of 20?mg [¹⁴C]teneligliptin.

2. Total plasma radioactivity reached the peak concentration at 1.33?h after administration and thereafter disappeared in a biphasic manner. By 216?h after administration, ≥90% of the administered radioactivity was excreted, and the cumulative excretion in the urine and faeces was 45.4% and 46.5%, respectively.

3. The most abundant metabolite in plasma was a thiazolidine-1-oxide derivative (designated as M1), which accounted for 14.7% of the plasma AUC (area under the plasma concentration versus time curve) of the total radioactivity. The major components excreted in urine were teneligliptin and M1, accounting for 14.8% and 17.7% of the dose, respectively, by 120?h, whereas in faeces, teneligliptin was the major component (26.1% of the dose), followed by M1 (4.0%).

4. CYP3A4 and FMO3 are the major enzymes responsible for the metabolism of teneligliptin in humans.

5. This study indicates the involvement of renal excretion and multiple metabolic pathways in the elimination of teneligliptin from the human body. Teneligliptin is unlikely to cause conspicuous drug interactions or changes in its pharmacokinetics patients with renal or hepatic impairment, due to a balance in the elimination pathways.     

Metabolism and disposition of calcimimetic agent cinacalcet HCl in humans and animal models.

The metabolism and disposition of calcimimetic agent cinacalcet HCl was examined after a single oral administration to mice, rats, monkeys, and human volunteers. In all species examined, cinacalcet was well absorbed, with greater than 74% oral bioavailability of cinacalcet-derived radioactivity in monkeys and humans. In rats, cinacalcet-derived radioactivity was widely distributed into most tissues, with no marked gender-related differences. In all animal models examined, radioactivity was excreted rapidly via both hepatobiliary and urinary routes. In humans, radioactivity was cleared primarily via the urinary route (80%), with 17% excreted in the feces. Cinacalcet was not detected in the urine in humans. The primary routes of metabolism of cinacalcet were N-dealkylation leading to carboxylic acid derivatives (excreted in urine as glycine conjugates) and oxidation of naphthalene ring to form dihydrodiols (excreted in urine and bile as glucuronide conjugates). The plasma radioactivity in both animals and humans was primarily composed of carboxylic acid metabolites and dihydrodiol glucuronides, with <1% circulating radioactivity accounting for the unchanged cinacalcet. Overall, the circulating and excreted metabolite profile of cinacalcet in humans was qualitatively similar to that observed in preclinical animal models.     

Metabolism and disposition of a selective alpha(7) nicotinic acetylcholine receptor agonist in humans.

The metabolism and disposition of N-(3R)-1-azabicyclo[2.2.2]oct-3-ylfuro[2,3-c]pyridine-5-carboxamide (1), an alpha(7) nicotinic acetylcholinergic receptor agonist, were elucidated in humans (4 female, 4 male; all white) after an oral dose of [(3)H]1. Overall, 1 was well tolerated, with >94% of administered radioactivity excreted renally by 48 h postdose; lyophilization of all urine and plasma samples confirmed (3)H stability within [(3)H]1. Across genders, 1 underwent low-to-moderate oral clearance comprising both renal (67%) and metabolic (33%) components, with the biotransformation of 1 occurring predominantly via oxidation of its furanopyridine moiety to carboxylic acid 2, and minimally by modification of its quinuclidine nitrogen to N-oxide 4 or N-glucuronide M5. Experiments using human in vitro systems were undertaken to better understand the enzyme(s) involved in the phase 1 biotransformation pathways. The formation of 2 was found to be mediated by CYP2D6, a polymorphically expressed enzyme absent in 5 to 10% of white people, whereas the generation of 4 was catalyzed by CYP2D6, FAD-containing monooxygenase 1 (FMO1), and FMO3. It is of interest that, although no overall gender-related differences in excretory routes, mass recoveries, pharmacokinetics, or metabolite profiles of 1 were evident, the observation of one of eight subjects (13%) showing disparate (relative to all other volunteers) systemic exposures to 1, and urinary and plasma quantitative profiles nearly devoid of 2 with the highest levels of 1, seem consistent with both the identification of CYP2D6 as the only major recombinant cytochrome P450 transforming 1 to 2 and the demographics of white CYP2D6 poor metabolizers. Data also reported herein suggest that 4 is generated predominantly by renal FMO1 in humans.     

New first and second generation inhibitors of human immunodeficiency virus-1 integrase

INTRODUCTION: The use of inhibitors of HIV-1 integrase for treating HIV-1 infection has proven to be very beneficial. Raltegravir, a strand transfer inhibitor, has been approved for use both as a first-line therapy and in treatment-experienced patients. A second compound in this class, elvitegravir, is in Phase III clinical trials and is being developed as part of a once daily fixed dose combination pill. With widespread use of raltegravir, viral resistance has emerged with surprising facility. Attempts to use raltegravir on a once daily dosing regimen have been unsuccessful whilst elvitegravir cannot be delivered daily without the aid of a pharmacokinetic (PK)-enhancing agent. Thus, there is a need for second generation compounds to address these issues. AREAS COVERED: Patent applications claiming compounds useful as inhibitors of HIV-1 integrase are reviewed in this paper, along with compounds related to the strand transfer inhibitors. EXPERT OPINION: The field appears to be more focused on developing compounds which address the issues identified for the first generation compounds, raltegravir and elvitegravir. Patent activity around new strand transfer inhibitors claims compounds active against first generation resistant mutations and having PK profiles suitable for daily dosing. Advancements in this area have been rapid and several compounds described in these patent applications are currently in clinical trials. Bolstered by recent mechanistic discoveries, compounds inhibiting processes other than strand transfer have begun to emerge. It is foreseeable that a second generation integrase inhibitor could be approved for treatment in the coming years.     

Investigations on the 4-quinolone-3-carboxylic acid motif. 1. Synthesis and structure-activity relationship of a class of human immunodeficiency virus type 1 integrase inhibitors

A set of 4-quinolone-3-carboxylic acids bearing different substituents on the condensed benzene ring was designed and synthesized as potential HIV-1 integrase inhibitors structurally related to elvitegravir. Some of the new compounds proved to be able to inhibit the strand transfer step of the virus integration process in the micromolar range. Docking studies and quantum mechanics calculations were used to rationalize these data.     

From ligand to complexes: inhibition of human immunodeficiency virus type 1 integrase by beta-diketo acid metal complexes

beta-Diketo acid-containing compounds are a promising class of human immunodeficiency virus type 1 (HIV-1) integrase (IN) inhibitors. Starting from the hypothesis that these inhibitors are able to coordinate ions in solution before interacting on the active site, a series of potentiometric measurements have been performed to understand the coordination ability of the diketo acid pharmacophore toward the biologically relevant Mg(2+). Moreover, by using beta-diketo acid/ester as model ligands with a set of divalent metal ions (Mg, Mn, Ni, Co, Cu, and Zn), we obtained a series of complexes and tested them for anti-HIV-1 IN activity. Results demonstrate that the diketo acid functionality chelates divalent metal ions in solution, and complexes with metals in different stoichiometric ratios are isolated. We postulate that the diketo acids act as complexes in their active form. In particular, they predominantly form species such as Mg(2)L(2+) and Mg(2)L(2) (derived from diketo acids, H(2)L), and MgL(+) and MgL(2) (derived from diketo esters, HL) at physiological pH. Furthermore, the synthesized mono- and dimetallic complexes inhibited IN at a high nanomolar to low micromolar range, with metal dependency in the phenyl diketo acid series. Retrospective analysis suggests that the electronic properties of the aromatic framework influence the metal-chelating ability of the diketo acid system. Therefore, the difference in activities is related to the complexes they preferentially form in solution, and these findings are important for the design of a new generation of IN inhibitors.