Deconstruction of sulfonamide inhibitors of the urotensin receptor (UT) and design and synthesis of benzylamine and benzylsulfone antagonists.

Potent small molecule antagonists of the urotensin receptor are described. These inhibitors were derived via systematically deconstructing a literature inhibitor to understand the basic pharmacophore and key molecular features required to inhibit the protein receptor. The series of benzylamine and benzylsulfone antagonists herein reported display a combination of nanomolar molecular and cellular potency as well as acceptable in vitro permeability and metabolic stability.

Identification of a potent sodium hydrogen exchanger isoform 1 (NHE1) inhibitor with a suitable profile for chronic dosing and demonstrated cardioprotective effects in a preclinical model of myocardial infarction in the rat.

Sodium-hydrogen exchanger isoform 1 (NHE1) is a ubiquitously expressed transmembrane ion channel responsible for intracellular pH regulation. During myocardial ischemia, low pH activates NHE1 and causes increased intracellular calcium levels and aberrant cellular processes, leading to myocardial stunning, arrhythmias, and ultimately cell damage and death. The role of NHE1 in cardiac injury has prompted interest in the development of NHE1 inhibitors for the treatment of heart failure. This report outlines our efforts to identify a compound suitable for once daily, oral administration with low drug-drug interaction potential starting from NHE1 inhibitor sabiporide. Substitution of a piperidine for the piperazine of sabiporide followed by replacement of the pyrrole moiety and subsequent optimization to improve potency and eliminate off-target activities resulted in the identification of N-[4-(1-acetyl-piperidin-4-yl)-3-trifluoromethyl-benzoyl]-guanidine (60). Pharmacological evaluation of 60 revealed a remarkable ability to prevent ischemic damage in an ex vivo model of ischemia reperfusion injury in isolated rat hearts.

Rapid synthesis of an array of trisubstituted urea-based soluble epoxide hydrolase inhibitors facilitated by a novel solid-phase method.

A 270-membered library of trisubstituted ureas was synthesized and evaluated for inhibition of soluble epoxide hydrolase. Library design and reagent selection was guided by the use of a pharmacophore model and synthesis of the array was enabled with a general solid-phase method. This array approach facilitated multi-dimensional SAR around this series and identified functionality responsible for binding affinity, as well as opportunities for modulating the overall in vitro profiles of this class of soluble epoxide hydrolase inhibitors.

Optimization of piperidyl-ureas as inhibitors of soluble epoxide hydrolase.

Inhibition of sEH is hypothesized to lead to an increase in epoxyeicosatrienoic acids resulting in the potentiation of their anti-inflammatory and vasodilatory effects. In an effort to explore sEH inhibition as an avenue for the development of vasodilatory and cardio- or renal-protective agents, a lead identified through high-throughput screening was optimized, guided by the determination of a solid state co-structure with sEH. Replacement of potential toxicophores was followed by optimization of cell-based potency and ADME properties to provide a new class of functionally potent sEH inhibitors with attractive in vitro metabolic profiles and high and sustained plasma exposures after oral administration in the rat.

Structure-based optimization of arylamides as inhibitors of soluble epoxide hydrolase.

Inhibition of soluble epoxide hydrolase (sEH) is hypothesized to lead to an increase in circulating levels of epoxyeicosatrienoic acids, resulting in the potentiation of their in vivo pharmacological properties. As part of an effort to identify inhibitors of sEH with high and sustained plasma exposure, we recently performed a high throughput screen of our compound collection. The screen identified N-(3,3-diphenyl-propyl)-nicotinamide as a potent inhibitor of sEH. Further profiling of this lead revealed short metabolic half-lives in microsomes and rapid clearance in the rat. Consistent with these observations, the determination of the in vitro metabolic profile of N-(3,3-diphenyl-propyl)-nicotinamide in rat liver microsomes revealed extensive oxidative metabolism and a propensity for metabolite switching. Lead optimization, guided by the analysis of the solid-state costructure of N-(3,3-diphenyl-propyl)-nicotinamide bound to human sEH, led to the identification of a class of potent and selective inhibitors. An inhibitor from this class displayed an attractive in vitro metabolic profile and high and sustained plasma exposure in the rat after oral administration.

Design and synthesis of substituted nicotinamides as inhibitors of soluble epoxide hydrolase.

A series of potent nicotinamide inhibitors of soluble epoxides hydrolase (sEH) is disclosed. This series was designed using structure-based deconstruction and a combination of two HTS hit series, resulting in hybrid analogs that retained the optimal potency from one series, and acceptable in vitro metabolic stability from the other. Structure-guided optimization of these analogs gave rise to nanomolar inhibitors of human sEH that had acceptable plasma exposure to qualify them as probes to determine the in vivo phenotypic consequences of sEH inhibition.

Structure-activity relationship study on a simple cationic peptide motif for cellular delivery of antisense peptide nucleic acid.

Improving cellular uptake and biodistribution remains one of the major obstacles for a successful and broad application of peptide nucleic acids (PNAs) as antisense therapeutics. Recently, we reported the identification and functional characterization of an antisense PNA, which redirects splicing of murine CD40 pre-mRNA. In this context, it was discovered that a simple octa(l-lysine) peptide covalently linked to the PNA is capable of promoting free uptake of the conjugate into BCL1 cells as well as primary murine macrophages. On the basis of this peptide motif, the present study aimed at identifying the structural features, which define effective peptide carriers for cellular delivery of PNA. While the structure-activity relationship study revealed some clear correlations, only a few modifications actually led to an overall improvement as compared to the parent octa(l-lysine) conjugate. In a preliminary PK/tissue distribution study in healthy mice, the parent conjugate exhibited relatively broad tissue distribution and only modest elimination via excretion within the time frame of the study.

Inhibitory effect of 2'-substituted nucleosides on hepatitis C virus replication correlates with metabolic properties in replicon cells.

Nucleosides have been widely used in the treatment of viral diseases, but relatively few have been identified as inhibitors of hepatitis C virus (HCV). The modified ribonucleosides, 2'-C-methyl-adenosine and 2'-O-methyl-cytidine, are potent inhibitors of HCV replication which specifically target the NS5B polymerase. Herein, a more extensive characterization of the effect of these compounds upon HCV replication in subgenomic replicons is reported. A highly selective antireplicative effect induced by the nucleosides in replicon-containing cell lines was maintained during an exponential growth period with potencies which paralleled the reduction of both positive- and negative-strand RNA replication. Moreover, the inhibitory effect closely correlated with the intrinsic metabolic properties of differing replicon clonal lines. Interestingly, while 2'-C-methyl-adenosine elicited similar inhibitory potencies in different cell lines, 2'-O-methyl-cytidine was found to be inactive in one replicon cell line tested, although the corresponding triphosphates comparably inhibited the in vitro activity of replication complexes isolated from these cells and the activity of NS5B polymerase using synthetic templates. The lack of antireplicative effect, attributed to poor intracellular conversion of the 2'-O-methyl-cytidine nucleoside to the active 5'-triphosphate, was reversed using a monophosphate prodrug. Thus, although replicon cells are useful for evaluating the effect of inhibitors upon HCV replication, these findings have important implications for their use in the identification and characterization of nucleosides and other chemotherapeutic agents requiring cellular metabolism.

Synthesis and evaluation of S-acyl-2-thioethyl esters of modified nucleoside 5'-monophosphates as inhibitors of hepatitis C virus RNA replication.

Several triphosphates of modified nucleosides (1-6) were identified as inhibitors (IC(50) = 0.08-3.8 microM) of hepatitis C virus RNA-dependent RNA polymerase (RdRp). Although the initial SAR developed by determining the ability of the triphosphates to inhibit the in vitro activity of the HCV RdRp identified several potent inhibitors, none of the corresponding nucleosides exhibited significant inhibitory potency in a cell-based replicon assay. To improve upon the activity, bis(tBu-S-acyl-2-thioethyl) nucleoside 5'-monophosphate esters (7-12) were synthesized, and these derivatives exhibited improved potency compared to the corresponding nucleosides in the cell-based assay. Analysis of the intracellular metabolism demonstrated that the S-acyl-2-thioethyl (SATE) prodrug is metabolized to the 5'-triphosphate 40- to 155-fold more efficiently compared to the corresponding nucleoside. The prodrug approach involving bis(tBuSATE)cytidine 5'-monophosphate ester significantly reduced the deamination of cytidine derivatives by cellular deaminases. Additionally, chromosomal aberration studies with the SATE prodrug in cells showed no statistically relevant increase in aberrations compared to the concurrent controls.

Synthesis and biological evaluation of 5R- and 5S-methyl substituted D- and L-configuration 1,3-dioxolane nucleoside analogs.

1,3-Dioxolane and 1,3-oxathiolane nucleoside analogs play an important role in anti-viral and anti-neoplastic chemotherapy. We report here the synthesis of 2-hydroxymethyl-5-methyl-1,3-dioxolanylpurine nucleosides from 4-acetoxy-2-(benzyloxymethyl)-5-methyldioxolane. Dioxolanes of alpha-D-, beta-D-, alpha-L-, and beta-L-configuration were prepared, that included 5-methyl derivatives of both 5R and 5S configuration. Molecular mechanics calculations indicate that the 5S and 5R diastereoisomeric 1,3-dioxolanes possess distinct conformational bias, suggesting that methyl substitution may alter the conformational preference of 1,3-dioxolanes. The ability of the 1,3-dioxolanes to inhibit HCV RNA replication was evaluated in a cell-based, subgenomic replicon assay. In addition, activity against vaccinia and HIV was evaluated in cell-based assays. The 2-hydroxymethyl-5-methyl-1,3-dioxolanes were found to be inactive.

Structure-activity relationship of heterobase-modified 2'-C-methyl ribonucleosides as inhibitors of hepatitis C virus RNA replication.

Hepatitis C virus infection constitutes a significant health problem in need of more effective therapies. We have recently identified 2'-C-methyladenosine and 2'-C-methylguanosine as potent nucleoside inhibitors of HCV RNA replication in vitro. However, both of these compounds suffered from significant limitations. 2'-C-Methyladenosine was found to be susceptible to enzymatic conversions by adenosine deaminase and purine nucleoside phosphorylase, and it displayed limited oral bioavailability in the rat. 2'-C-Methylguanosine, on the other hand, was neither efficiently taken up in cells nor phosphorylated well. As part of an attempt to address these limitations, we now report upon the synthesis and evaluation of a series of heterobase-modified 2'-C-methyl ribonucleosides. The structure-activity relationship within this series of nucleosides reveals 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine as potent and noncytotoxic inhibitors of HCV RNA replication. Both 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine display improved enzymatic stability profiles as compared to that of 2'-C-methyladenosine. Consistent with these observations, the most potent compound, 4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidine ribonucleoside, is orally bioavailable in the rat. Together, the potency of the 2'-C-methyl-4-amino-pyrrolo[2,3-d]pyrimidine ribonucleosides and their improved pharmacokinetic properties relative to that of 2'-C-methyladenosine suggests that this class of compounds may have clinical utility.

A 7-deaza-adenosine analog is a potent and selective inhibitor of hepatitis C virus replication with excellent pharmacokinetic properties.

Improved treatments for chronic hepatitis C virus (HCV) infection are needed due to the suboptimal response rates and deleterious side effects associated with current treatment options. The triphosphates of 2'-C-methyl-adenosine and 2'-C-methyl-guanosine were previously shown to be potent inhibitors of the HCV RNA-dependent RNA polymerase (RdRp) that is responsible for the replication of viral RNA in cells. Here we demonstrate that the inclusion of a 7-deaza modification in a series of purine nucleoside triphosphates results in an increase in inhibitory potency against the HCV RdRp and improved pharmacokinetic properties. Notably, incorporation of the 7-deaza modification into 2'-C-methyl-adenosine results in an inhibitor with a 20-fold-increased potency as the 5'-triphosphate in HCV RdRp assays while maintaining the inhibitory potency of the nucleoside in the bicistronic HCV replicon and with reduced cellular toxicity. In contrast, while 7-deaza-2'-C-methyl-GTP also displays enhanced inhibitory potency in enzyme assays, due to poor cellular penetration and/or metabolism, the nucleoside does not inhibit replication of a bicistronic HCV replicon in cell culture. 7-Deaza-2'-C-methyl-adenosine displays promising in vivo pharmacokinetics in three animal species, as well as an acute oral lethal dose in excess of 2,000 mg/kg of body weight in mice. Taken together, these data demonstrate that 7-deaza-2'-C-methyl-adenosine is an attractive candidate for further investigation as a potential treatment for HCV infection.

Identification and functional validation of PNAs that inhibit murine CD40 expression by redirection of splicing.

Cognate recognition between the CD40 receptor and its ligand, CD154, is thought to play a central role in the initiation and propagation of immune responses. We describe the specific down regulation of cell surface associated CD40 protein expression by use of a peptide nucleic acid (PNA) antisense inhibitor, ISIS 208529, that is designed to bind to the 3' end of the exon 6 splice junction within the primary CD40 transcript. Binding of ISIS 208529 was found to alter constitutive splicing, leading to the accumulation of a transcript lacking exon 6. The resulting protein product lacks the transmembrane domain. ISIS 208529-mediated CD40 protein depletion was found to be sequence specific and dose dependent, and was dependent on the length of the PNA oligomer. CD40-dependent induction of IL-12 in primary murine macrophages was attenuated in cells treated with ISIS 208529. Oligolysine conjugation to the PNA inhibitor produced an inhibitor, ISIS 278647, which maintained its specificity and displayed efficacy in BCL1 cells and in primary murine macrophages in the absence of delivery agents. These results demonstrate that PNA oligomers can be effective inhibitors of CD40 expression and hence may be useful as novel immuno-modulatory agents.

Structure-activity relationship of purine ribonucleosides for inhibition of hepatitis C virus RNA-dependent RNA polymerase.

As part of a continued effort to identify inhibitors of hepatitis C viral (HCV) replication, we report here the synthesis and evaluation of a series of nucleoside analogues and their corresponding triphosphates. Nucleosides were evaluated for their ability to inhibit HCV RNA replication in a cell-based, subgenomic replicon system, while nucleoside triphosphates were evaluated for their ability to inhibit in vitro RNA synthesis mediated by the HCV RNA-dependent RNA polymerase, NS5B. 2'-C-Methyladenosine and 2'-C-methylguanosine were identified as potent inhibitors of HCV RNA replication, and the corresponding triphosphates were found to be potent inhibitors of HCV NS5B-mediated RNA synthesis. The data generated in the cell-based assay demonstrated a fairly stringent structure-activity relationship around the active nucleosides. Increase in steric bulk beyond methyl on C2, change in the stereo- or regiochemistry of the methyl substituent, or change of identity of the heterobase beyond that of the endogenous adenine or guanine was found to lead to loss of inhibitory activity. The results highlight the importance of the ribo configuration 2'- and 3'-hydroxy pharmacophores for inhibition of HCV RNA replication in the cell-based assay and demonstrate that inclusion of the 2'-C-methylribonucleoside pharmacophore leads to increased resistance to adenosine deaminase and purine nucleoside phosphorylase mediated metabolism.

Synthesis and evaluation of optically pure dioxolanes as inhibitors of hepatitis C virus RNA replication.

A series of optically pure 1,3-dioxolane nucleoside mimics was synthesized by a synthetic route that allowed incorporation of a 5R-methyl substituent from commercially available starting materials. The pyrrolo[2,3-d]pyrimidine heterocycle was chosen as a substitute for the purine derivative. Coupling of the pyrrolo[2,3-d]pyrimidine and the dioxolane was performed under solid-liquid phase transfer conditions. The ability to inhibit HCV RNA replication was assessed in a cell based subgenomic replicon assay. None of the described compounds displayed significant anti-HCV activity.

Characterization of resistance to non-obligate chain-terminating ribonucleoside analogs that inhibit hepatitis C virus replication in vitro.

The urgent need for efficacious drugs to treat chronic hepatitis C virus (HCV) infection requires a concerted effort to develop inhibitors specific for virally encoded enzymes. We demonstrate that 2'-C-methyl ribonucleosides are efficient chain-terminating inhibitors of HCV genome replication. Characterization of drug-resistant HCV replicons defined a single S282T mutation within the active site of the viral polymerase that conferred loss of sensitivity to structurally related compounds in both replicon and isolated polymerase assays. Biochemical analyses demonstrated that resistance at the level of the enzyme results from a combination of reduced affinity of the mutant polymerase for the drug and an increased ability to extend the incorporated nucleoside analog. Importantly, the combination of these agents with interferon-alpha results in synergistic inhibition of HCV genome replication in cell culture. Furthermore, 2'-C-methyl-substituted ribonucleosides also inhibited replication of genetically related viruses such as bovine diarrhea virus, yellow fever, and West African Nile viruses. These observations, together with the finding that 2'-C-methyl-guanosine in particular has a favorable pharmacological profile, suggest that this class of compounds may have broad utility in the treatment of HCV and other flavivirus infections.

Inhibition of hepatitis C virus RNA replication by 2'-modified nucleoside analogs.

The RNA-dependent RNA polymerase (NS5B) of hepatitis C virus (HCV) is essential for the replication of viral RNA and thus constitutes a valid target for the chemotherapeutic intervention of HCV infection. In this report, we describe the identification of 2'-substituted nucleosides as inhibitors of HCV replication. The 5'-triphosphates of 2'-C-methyladenosine and 2'-O-methylcytidine are found to inhibit NS5B-catalyzed RNA synthesis in vitro, in a manner that is competitive with substrate nucleoside triphosphate. NS5B is able to incorporate either nucleotide analog into RNA as determined with gel-based incorporation assays but is impaired in its ability to extend the incorporated analog by addition of the next nucleotide. In a subgenomic replicon cell line, 2-C-methyladenosine and 2'-O-methylcytidine inhibit HCV RNA replication. The 5'-triphosphates of both nucleosides are detected intracellularly following addition of the nucleosides to the media. However, significantly higher concentrations of 2'-C-methyladenosine triphosphate than 2'-O-methylcytidine triphosphate are detected, consistent with the greater potency of 2'-C-methyladenosine in the replicon assay, despite similar inhibition of NS5B by the triphosphates in the in vitro enzyme assays. Thus, the 2'-modifications of natural substrate nucleosides transform these molecules into potent inhibitors of HCV replication.

1,8-Naphthyridin-2,7-(1,8H)-dione is an effective mimic of protonated cytosine in peptide nucleic acid triplex recognition systems.

A novel bicyclic mimic of protonated cytosine [1,8-naphthyridin-2,7-(1,8H)-dione, (K)] for Hoogsteen type triplex recognition of guanine has been designed for incorporation into peptide nucleic acids. Bis-PNA clamps with the K base incorporated in the Hoogsteen strand showed a significant stabilization of the triplexes at pH 7 as compared to similar triplexes with PNA oligomers containing either cytosine (6.7 degrees C per unit) or pseudoisocytosine (1.5 degrees C per unit). Cooperative stabilization was observed when the K units were placed in adjacent positions ( approximately 3 degrees C per unit).

Substituted 1,8-naphthyridin-2(1H)-ones are superior to thymine in the recognition of adenine in duplex as well as triplex structures.

The synthesis and evaluation of a series of novel nucleobases based on substituted 1,8-naphthyridin-2(1H)-ones are reported. The nucleobases were designed to meet the requirements for incorporation into peptide nucleic acids (PNAs) and were evaluated as part of PNA duplex and triplex nucleic acid recognition systems. Of the various nucleobases tested, only the 7-chloro-1,8-naphthyridin-2(1H)-one (7-Cl-bT) nucleobase led to consistently increased affinity in all recognition systems, duplex (Watson-Crick) as well as triplex (Hoogsteen). For multiply modified systems, the increase in thermal stability per modification was dependent on the sequence context, ranging from 2.0 degrees C (in separate positions) to 3.5 degrees C (in adjacent positions) in PNA-DNA duplexes and from 1.2 degrees C (in separate positions) to 3.2 degrees C (in adjacent positions) in PNA-RNA duplexes. Singly mismatched oligonucleotide targets were employed to demonstrate uncompromised sequence discrimination. When part of multiply modified triplex (Hoogsteen) recognition systems, the 7-Cl-bT unit gave rise to increases in the thermal stability ranging from 2.7 to 3.5 degrees C when incorporated into separated and adjacent positions, respectively. Our results furthermore indicate that the duplex stabilization is predominantly enthalpic and therefore most likely not a consequence of single-strand preorganization. Finally, and most surprisingly, we find no direct correlation between the end-stacking efficiency of this type of nucleobase and its helix stabilization when involved in Watson-Crick base pairing within a helix.