MK-4815, a potential new oral agent for treatment of malaria.

Malaria continues to have a significant impact on the health of the developing world. Efforts to combat this disease now focus on combination therapy in order to stem the emergence of resistant parasites. Continued efforts are needed to discover and develop new agents for use in combination antimalarial regimens. MK-4815 is a small molecule with antimalarial activity that was identified from a large pharmaceutical compound collection using a semiautomated version of a well-established in vitro assay for the erythrocytic stages of Plasmodium falciparum. In vitro studies indicate that the compound selectively accumulates in infected red blood cells and is most effective against the metabolically active late trophozoite/early schizont stages. A variety of drug-resistant field isolates of P. falciparum were found to be as sensitive to MK-4815 as the wild-type lines. MK-4815 is orally active in a P. berghei mouse model of acute malaria. In this model, where untreated animals succumb to infection 10 to 12 days postinfection, MK-4815 was completely curative when given as a single dose of 50 mg/kg, 2 doses of 25 mg/kg, or 4.5 doses of 12.5 mg/kg. In pharmacokinetic studies with mice and rhesus monkeys, MK-4815 demonstrated oral bioavailability and low clearance. In addition, MK-4815 is inexpensive to synthesize, an important characteristic for providing affordable antimalaria therapy to the developing world. The attractive biological and pharmaceutical profile of MK-4815 demonstrates its potential for use in combination with other agents in the fight against malaria.

Kibdelomycin A, a congener of kibdelomycin, derivatives and their antibacterial activities.

Emergence of bacterial resistance has eroded the effectiveness of many life saving antibiotics leading to an urgent need for new chemical classes of antibacterial agents. We have applied a Staphylococcus aureus fitness test strategy to natural products screening to meet this challenge. In this paper we report the discovery of kibdelomycin A, a demethylated congener of kibdelomycin, the representative of a novel class of antibiotics produced by a new strain of Kibdelosporangium. Kibdelomycin A is a potent inhibitor of DNA gyrase and topoisomerase IV, inhibits DNA synthesis and shows whole cell antibiotic activity, albeit, less potently than kibdelomycin. Kibdelomycin C-33 acetate and tetrahydro-bisdechloro derivatives of kibdelomycin were prepared which helped define a basic SAR of the family.

Platensimycin is a selective FabF inhibitor with potent antibiotic properties.

Bacterial infection remains a serious threat to human lives because of emerging resistance to existing antibiotics. Although the scientific community has avidly pursued the discovery of new antibiotics that interact with new targets, these efforts have met with limited success since the early 1960s. Here we report the discovery of platensimycin, a previously unknown class of antibiotics produced by Streptomyces platensis. Platensimycin demonstrates strong, broad-spectrum Gram-positive antibacterial activity by selectively inhibiting cellular lipid biosynthesis. We show that this anti-bacterial effect is exerted through the selective targeting of beta-ketoacyl-(acyl-carrier-protein (ACP)) synthase I/II (FabF/B) in the synthetic pathway of fatty acids. Direct binding assays show that platensimycin interacts specifically with the acyl-enzyme intermediate of the target protein, and X-ray crystallographic studies reveal that a specific conformational change that occurs on acylation must take place before the inhibitor can bind. Treatment with platensimycin eradicates Staphylococcus aureus infection in mice. Because of its unique mode of action, platensimycin shows no cross-resistance to other key antibiotic-resistant strains tested, including methicillin-resistant S. aureus, vancomycin-intermediate S. aureus and vancomycin-resistant enterococci. Platensimycin is the most potent inhibitor reported for the FabF/B condensing enzymes, and is the only inhibitor of these targets that shows broad-spectrum activity, in vivo efficacy and no observed toxicity.

Selective FPR2 Agonism Promotes a Proresolution Macrophage Phenotype and Improves Cardiac Structure-Function Post Myocardial Infarction.

Dysregulated inflammation following myocardial infarction (MI) leads to maladaptive healing and remodeling. The study characterized and evaluated a selective formyl peptide receptor 2 (FPR2) agonist BMS-986235 in cellular assays and in rodents undergoing MI. BMS-986235 activated G proteins and promoted ß-arrestin recruitment, enhanced phagocytosis and neutrophil apoptosis, regulated chemotaxis, and stimulated interleukin-10 and monocyte chemoattractant protein-1 gene expression. Treatment with BMS-986235 improved mouse survival, reduced left ventricular area, reduced scar area, and preserved wall thickness. Treatment increased macrophage arginase-1 messenger RNA and CD206 receptor levels indicating a proresolution phenotype. In rats following MI, BMS-986235 preserved viable myocardium, attenuated left ventricular remodeling, and increased ejection fraction relative to control animals. Therefore, FPR2 agonism improves post-MI healing, limits remodeling and preserves function, and may offer an innovative therapeutic option to improve outcomes.

Experimental model of congestive heart failure induced by transverse aortic constriction in BALB/c mice.

INTRODUCTION: Murine transverse aortic constriction (TAC) is a frequently used model of pressure overload-induced left ventricular (LV) remodeling. However, there is considerable variability in disease progression to overt heart failure (HF) development in the most commonly used strain of mice (i.e., C57BL/6J). Studies have shown that C57BL/6J mice are more resistant than BALB/c mice to congestive HF development following myocardial infarction or angiotensin II-induced hypertension. Therefore, we tested the hypothesis that BALB/c mice may be a better research model to study TAC-induced progressive HF. METHODS: Following sham or TAC surgery in both C57BL/6J (n = 29) and BALB/c (n = 32) mice, we evaluated cardiac dimensions and function by echocardiography at 2, 4, 8, and 12 weeks and monitored survival throughout the study. In a separate cohort of BALB/c mice, we repeated the study in the presence of the angiotensin converting enzyme inhibitor enalapril or a vehicle initiated 2 weeks post-TAC and administered for 6 weeks. At the end of the studies, we assessed the heart weight, lung weight, and plasma brain natriuretic peptide (BNP) concentration. RESULTS: Following comparable TAC, both C57BL/6J and BALB/c mice showed significant LV remodeling compared with the sham control mice. BALB/c mice progressively developed systolic dysfunction, LV dilation, lung congestion, and significant mortality, whereas C57BL/6J mice did not. In the separate cohort of BALB/c TAC mice, enalapril significantly reduced the heart weight, lung weight, and plasma BNP concentration and improved survival compared with the vehicle control. DISCUSSION: BALB/c mice uniformly developed congestive HF post-TAC. Enalapril was effective in improving survival and reducing lung congestion in this model. The data suggest that BALB/c mice may be a better research tool than C57BL/6J mice to study TAC-induced disease progression to HF and to evaluate novel therapies for the treatment of chronic HF with reduced ejection fraction.

PAP inhibitor with in vivo efficacy identified by Candida albicans genetic profiling of natural products.

Natural products provide an unparalleled source of chemical scaffolds with diverse biological activities and have profoundly impacted antimicrobial drug discovery. To further explore the full potential of their chemical diversity, we survey natural products for antifungal, target-specific inhibitors by using a chemical-genetic approach adapted to the human fungal pathogen Candida albicans and demonstrate that natural-product fermentation extracts can be mechanistically annotated according to heterozygote strain responses. Applying this approach, we report the discovery and characterization of a natural product, parnafungin, which we demonstrate, by both biochemical and genetic means, to inhibit poly(A) polymerase. Parnafungin displays potent and broad spectrum activity against diverse, clinically relevant fungal pathogens and reduces fungal burden in a murine model of disseminated candidiasis. Thus, mechanism-of-action determination of crude fermentation extracts by chemical-genetic profiling brings a powerful strategy to natural-product-based drug discovery.

A mouse model of heart failure exhibiting pulmonary edema and pleural effusion: Useful for testing new drugs.

INTRODUCTION: Mouse models of chronic heart failure (HF) have been widely used in HF research. However, the current HF models most often use the C57BL/6 mouse strain and do not show the clinically relevant characteristics of pulmonary congestion. In this study, we developed a robust mouse model of HF in the BALB/c mouse strain, exhibiting pulmonary edema and pleural effusion, and we validated the model using the standard pharmacological therapies in patients with chronic HF and reduced ejection fraction (HFrEF) or acute decompensated HF. METHODS: After induction of myocardial infarction (MI) by permanent ligation of the left coronary artery in BALB/c mice, the cardiac function, pulmonary congestion, disease biomarkers, and survival were evaluated using the angiotensin converting enzyme inhibitor enalapril or the loop diuretic furosemide. Enalapril was administered 4 weeks post-MI for 6 weeks or furosemide was given 10 weeks post-MI for 4 days, when pulmonary congestion was evident. RESULTS: Compared to sham controls, MI mice developed systolic dysfunction, exhibited lung weight increase at 4 weeks, and progressively developed pleural effusion (60% of the animals) at 10 weeks. Compared to the vehicle, enalapril significantly reduced the lung weight and pleural effusion, preserved systolic function, and improved survival. Furthermore, furosemide completely abolished the pleural effusion. Enalapril or furosemide also reduced the plasma brain natriuretic peptide concentration. DISCUSSION: The post-MI HF in BALB/c mice shows reproducible and robust pulmonary congestion and may be a clinically relevant model for novel drug testing for treatment in patients with HFrEF or acute decompensated HF.

Anticoccidial kinase inhibitors: identification of protein kinase targets secondary to cGMP-dependent protein kinase.

Trisubstituted pyrrole inhibitors of the essential coccidian parasite cGMP dependent protein kinase (PKG) block parasite invasion and show in vivo efficacy against Eimeria in chickens and Toxoplasma in mice. An imidazopyridine inhibitor of PKG activity with greater potency in both parasite invasion assays and in vivo activity has recently been identified. Susceptibility experiments with a Toxoplasma knock-out strain expressing a complementing compound-refractory PKG allele ('T761Q-KO'), suggest a role for additional secondary protein kinase targets. Using extracts from this engineered T. gondii strain and a radiolabeled imidazopyridine ligand, a single peak of binding activity associated with calmodulin-like domain protein kinase (CDPK1) has been identified. Like PKG, CDPK1 has been implicated in host cell invasion and exhibits sub-nanomolar sensitivity to the compound. Amino acid sequence comparisons of coccidian CDPKs and a mutational analysis reveal that the binding of the ligand to PKG and CDPK1 (but not other CDPK isoforms) is mediated by similar contacts in a catalytic site hydrophobic binding pocket, and can be blocked by analogous amino acid substitutions. Transgenic strains over-expressing a biochemically active but compound-refractory CDPK1 mutant ('G128Q') fail to show reduced susceptibility to the compound in vivo, suggesting that selective inhibition of this enzyme is not responsible for the enhanced anti-parasitic potency of the imidazopyridine analog. An alternative secondary target candidate, the alpha-isoform of casein kinase 1 (CK1alpha), shows sensitivity to the compound in the low nanomolar range. These results provide an example of the utility of the Toxoplasma model system for investigating the mechanism of action of novel anticoccidial agents.

Characterization of Plasmodium falciparum cGMP-dependent protein kinase (PfPKG): antiparasitic activity of a PKG inhibitor.

Cyclic GMP-dependent protein kinase (PKG) has been biochemically and genetically validated in Toxoplasma gondii as a primary target responsible for the antiparasitic activity of the trisubstituted pyrrole 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H pyrrol-3-yl] pyridine (Compound 1) [Biftu T, Feng D, Ponpipom M, et al. Synthesis and SAR of 2,3-diarylpyrrole inhibitors of parasite cGMP-dependent protein kinase as novel anticoccidial agents. Bioorg Med Chem Lett 2005;15:3296-301; Gurnett AM, Liberator PA, Dulski PM, et al. Purification and molecular characterization of cGMP-dependent protein kinase from Apicomplexan parasites. A novel chemotherapeutic target. J Biol Chem 2002;277:15913-22; Donald RGK, Allocco J, Singh SB, et al. Toxoplasma gondii cyclic GMP-dependent kinase: Chemotherapeutic targeting of an essential parasite protein kinase. Eukaryotic Cell 2002;1:317-28; Nare B, Allocco J, Liberator PA, Donald RGK. Evaluation of a cyclic GMP-dependent protein kinase inhibitor in treatment of murine Toxoplasmosis: Gamma interferon is required for efficacy. Antimicrob Agents Chemother 2002;46:300-7]. Compound 1 inhibits the growth of several related protozoan parasites of the subphylum Apicomplexa. Native PKG activity has been partially purified by cGMP-affinity and MonoQ ion exchange chromatography from Plasmodium falciparum (PfPKG). Biochemical fractions enriched for a 98kDa protein detected using anti-PKG antisera, contain cGMP-induced protein kinase activity that is sensitive to inhibition by Compound 1. To enable a more thorough characterization of PfPKG we expressed a synthetic cDNA incorporating T. gondii codon preference (Pf(Tg)PKG) in T. gondii parasites. The protein kinase activity of purified recombinant Pf(Tg)PKG is stimulated by cGMP, with significant cooperativity as demonstrated by a Hill coefficient of 2. Both substrate preference and inhibition of Pf(Tg)PKG kinase activity by Compound 1 are similar to that seen with native PfPKG, as well as PKG enzymes from Eimeria spp. and T. gondii. We conclude that PfPKG has biochemical and pharmacological properties that are similar to previously characterized apicomplexan PKG enzymes. Compound 1 is active against blood cell stages of P. falciparum cultured in vitro. In a Plasmodium berghei mouse model of infection, Compound 1 delays the onset of parasitemia but does not cure the parasite infection.

Inhibitors of casein kinase 1 block the growth of Leishmania major promastigotes in vitro.

Casein kinase 1 (CK1) is a family of multifunctional Ser/Thr protein kinases that are ubiquitous in eukaryotic cells. Recent studies have demonstrated the existence of, and role for, CK1 in protozoan parasites such as Leishmania, Plasmodium and Trypanosoma. The value of protein kinases as potential drug targets in protozoa is evidenced by the successful exploitation of cyclic guanosine monophosphate-dependent protein kinase (PKG) with selective tri-substituted pyrrole and imidazopyridine inhibitors. These compounds exhibit in vivo efficacy against Eimeria tenella in chickens and Toxoplasma gondii in mice. We now report that both of these protein kinase inhibitor classes inhibit the growth of Leishmania major promastigotes and Trypanosoma brucei bloodstream forms in vitro. Genome informatics predicts that neither of these trypanosomatids codes for a PKG orthologue. Biochemical studies have led to the unexpected discovery that an isoform of CK1 represents the primary target of the pyrrole and imidazopyridine kinase inhibitors in these organisms. CK1 from extracts of L. major promastigotes co-fractionated with [(3)H]imidazopyridine binding activity. Further purification of CK1 activity from L. major and characterization via liquid chromatography coupled tandem mass spectrometry identified CK1 isoform 2 as the specific parasite protein inhibited by imidazopyridines. L. major CK1 isoform 2 expressed as a recombinant protein in Escherichia coli displayed biochemical and inhibition characteristics similar to those of the purified native enzyme. The results described here warrant further evaluation of the activity of these kinase inhibitors against mammalian stage Leishmania parasites in vitro and in animal models of infection, as well as studies to genetically validate CK1 as a therapeutic target in trypanosomatid parasites.

Discovery of kibdelomycin, a potent new class of bacterial type II topoisomerase inhibitor by chemical-genetic profiling in Staphylococcus aureus.

Bacterial resistance to known therapeutics has led to an urgent need for new chemical classes of antibacterial agents. To address this we have applied a Staphylococcus aureus fitness test strategy to natural products screening. Here we report the discovery of kibdelomycin, a novel class of antibiotics produced by a new member of the genus Kibdelosporangium. Kibdelomycin exhibits broad-spectrum, gram-positive antibacterial activity and is a potent inhibitor of DNA synthesis. We demonstrate through chemical genetic fitness test profiling and biochemical enzyme assays that kibdelomycin is a structurally new class of bacterial type II topoisomerase inhibitor preferentially inhibiting the ATPase activity of DNA gyrase and topoisomerase IV. Kibdelomycin is thus the first truly novel bacterial type II topoisomerase inhibitor with potent antibacterial activity discovered from natural product sources in more than six decades.

Evaluation of a cyclic GMP-dependent protein kinase inhibitor in treatment of murine toxoplasmosis: gamma interferon is required for efficacy.

The trisubstituted pyrrole 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H-pyrrol-3-yl]pyridine (compound 1) is a potent inhibitor of cyclic GMP-dependent protein kinases from Apicomplexan protozoa and displays cytostatic activity against Toxoplasma gondii in vitro. Compound 1 has now been evaluated against T. gondii infections in the mouse and appeared to protect the animals when given intraperitoneally at 50 mg/kg twice daily for 10 days. However, samples from brain, spleen, and lung taken from infected treated mice revealed the presence of parasites after cessation of administration of compound 1, indicating that a transient asymptomatic parasite recrudescence occurs in all survivors. The ability of mice to control Toxoplasma infection after compound 1 treatment has been terminated suggested that the mouse immune system plays a synergistic role with chemotherapy in controlling the infection. To explore this possibility, gamma interferon (IFN-gamma)-knockout mice were infected with parasites and treated with compound 1, and survival was compared to that of normal mice. IFN-gamma-knockout mice were protected against T. gondii throughout the treatment phase but died during the posttreatment phase in which peak recrudescence was observed in treated immunocompetent mice. These data suggest that an IFN-gamma-dependent immune response was essential for controlling and resolving parasite recrudescence in mice treated with compound 1. In addition, when compound 1-cured immunocompetent mice were rechallenged with a lethal dose of T. gondii, all survived (n = 32). It appears that the cytostatic nature of compound 1 provides an "immunization" phase during chemotherapy which allows the mice to survive the recrudescence and any subsequent challenge with a lethal dose of T. gondii.

Toxoplasma gondii cyclic GMP-dependent kinase: chemotherapeutic targeting of an essential parasite protein kinase.

The trisubstituted pyrrole 4-[2-(4-fluorophenyl)-5-(1-methylpiperidine-4-yl)-1H-pyrrol-3-yl]pyridine (compound 1) has in vivo activity against the apicomplexan parasites Toxoplasma gondii and Eimeria tenella in animal models. The presumptive molecular target of this compound in E. tenella is cyclic GMP-dependent protein kinase (PKG). Native PKG purified from T. gondii has kinetic and pharmacologic properties similar to those of the E. tenella homologue, and both have been functionally expressed as recombinant proteins in T. gondii. Computer modeling of parasite PKG was used to predict catalytic site amino acid residues that interact with compound 1. The recombinant laboratory-generated mutants T. gondii PKG T761Q or T761M and the analogous E. tenella T770 alleles have reduced binding affinity for, and are not inhibited by, compound 1. By all other criteria, PKG with this class of catalytic site substitution is indistinguishable from wild-type enzyme. A genetic disruption of T. gondii PKG can only be achieved if a complementing copy of PKG is provided in trans, arguing that PKG is an essential protein. Strains of T. gondii, disrupted at the genomic PKG locus and dependent upon the T. gondii T761-substituted PKGs, are as virulent as wild type in mice. However, unlike mice infected with wild-type T. gondii that are cured by compound 1, mice infected with the laboratory-generated strains of T. gondii do not respond to treatment. We conclude that PKG represents the primary molecular target responsible for the antiparasitic efficacy of compound 1.