Hemodynamic Effects of Late Sodium Current Inhibitors in a Swine Model of Heart Failure.

OBJECTIVES: To evaluate possible treatment-related hemodynamic changes, we administered ranolazine or mexiletine to swine with heart failure (HF) and to controls. BACKGROUND: Ranolazine and mexiletine potently inhibit depolarizing late Na+ current (INa,late) and Na+ entry into cardiomyocytes. Blocking Na+ entry may increase forward-mode Na/Ca exchange and reduce cellular Ca+2 load, further compromising systolic contraction during HF. METHODS AND RESULTS: Anesthetized tachypaced HF swine received ranolazine (n = 9) or mexiletine (n = 7) as boluses, then as infusions; the same experiments were performed in 10 nonpaced controls. The swine with HF had characteristic elevated left ventricular end-diastolic pressure (LVEDP) and reduced maximal left ventricular pressure rise (+dP/dtmax) and left ventricular peak systolic pressure (LVSP). No significant change occurred after ranolazine dosing for any parameter: LVEDP, +dP/dtmax, LVSP, heart rate, maximal LV pressure fall rate (-dP/dtmax), or time constant for isovolumic relaxation. Similar results seen in additional swine with HF: 7 were given mexiletine, and 7 others were given ranolazine after a 27% rate decrement to maximize INa,late. Patch-clamped HF cardiomyocytes confirmed drug-induced INa,late blockade. CONCLUSIONS: Ranolazine or mexiletine blocking INa,late neither worsened nor improved hemodynamics during advanced HF. Although results must be clinically confirmed, they suggest inhibition of INa,late by ranolazine or mexiletine may not exacerbate HF in patients.

Discovery and optimization of 1,7-disubstituted-2,2-dimethyl-2,3-dihydroquinazolin-4(1H)-ones as potent and selective PKCθ inhibitors.

A high-throughput screening campaign helped us to identify an initial lead compound (1) as a protein kinase C-θ (PKCθ) inhibitor. Using the docking model of compound 1 bound to PKCθ as a model, structure-based drug design was employed and two regions were identified that could be explored for further optimization, i.e., (a) a hydrophilic region around Thr442, unique to PKC family, in the inner part of the hinge region, and (b) a lipophilic region at the forefront of the ethyl moiety. Optimization of the hinge binder led us to find 1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one as a potent and selective hinge binder, which resulted in the discovery of compound 5. Filling the lipophilic region with a suitable lipophilic substituent boosted PKCθ inhibitory activity and led to the identification of compound 10. The co-crystal structure of compound 10 bound to PKCθ confirmed that both the hydrophilic and lipophilic regions were fully utilized. Further optimization of compound 10 led us to compound 14, which demonstrated an improved pharmacokinetic profile and inhibition of IL-2 production in a mouse.

Mating Disruption or Mass Trapping, Compared With Chemical Insecticides, for Suppression of Chilo suppressalis (Lepidoptera: Crambidae) in Northeastern China.

Asiatic rice borer, Chilo suppressalis (Walker), larvae cause extensive crop losses worldwide. Because chemical control is problematic, and sex pheromone applications are a valuable management tactic in China, judicious timing of a minimal density of pheromone dispensers is important in developing a cost-effective C. suppressalis IPM program. During June-October in 2011, 20, 30, 40, and 50 dispensers per hectare for mass trapping, and 200, 300, 400, and 500 dispensers per hectare for mating disruption were placed in northeastern China rice fields. Based on those results, only the two highest mass trapping densities were used in 2012-2013. The 40, 50, and 500 dispenser densities reduced egg masses to <2.0 per 100 tillers, compared with >9.5 in the insecticide-treated plots in 2011-2013. The reduced oviposition resulted in >85% reduction of larval damage, which was comparable with the currently used insecticides, dimethoate and deltamethrin (0.35 kg/ha), which gave no egg reduction, but ≍80 and 89% reduction in larval damage. The 40 and 500 densities are recommended to Chinese rice farmers for mass trapping and mating disruption programs, respectively.

Sequencing by avidity enables high accuracy with low reagent consumption.

We present avidity sequencing, a sequencing chemistry that separately optimizes the processes of stepping along a DNA template and that of identifying each nucleotide within the template. Nucleotide identification uses multivalent nucleotide ligands on dye-labeled cores to form polymerase-polymer-nucleotide complexes bound to clonal copies of DNA targets. These polymer-nucleotide substrates, termed avidites, decrease the required concentration of reporting nucleotides from micromolar to nanomolar and yield negligible dissociation rates. Avidity sequencing achieves high accuracy, with 96.2% and 85.4% of base calls having an average of one error per 1,000 and 10,000 base pairs, respectively. We show that the average error rate of avidity sequencing remained stable following a long homopolymer.

The APOBEC-2 crystal structure and functional implications for the deaminase AID.

APOBEC-2 (APO2) belongs to the family of apolipoprotein B messenger RNA-editing enzyme catalytic (APOBEC) polypeptides, which deaminates mRNA and single-stranded DNA. Different APOBEC members use the same deamination activity to achieve diverse human biological functions. Deamination by an APOBEC protein called activation-induced cytidine deaminase (AID) is critical for generating high-affinity antibodies, and deamination by APOBEC-3 proteins can inhibit retrotransposons and the replication of retroviruses such as human immunodeficiency virus and hepatitis B virus. Here we report the crystal structure of APO2. APO2 forms a rod-shaped tetramer that differs markedly from the square-shaped tetramer of the free nucleotide cytidine deaminase, with which APOBEC proteins share considerable sequence homology. In APO2, two long alpha-helices of a monomer structure prevent the formation of a square-shaped tetramer and facilitate formation of the rod-shaped tetramer via head-to-head interactions of two APO2 dimers. Extensive sequence homology among APOBEC family members allows us to test APO2 structure-based predictions using AID. We show that AID deamination activity is impaired by mutations predicted to interfere with oligomerization and substrate access. The structure suggests how mutations in patients with hyper-IgM-2 syndrome inactivate AID, resulting in defective antibody maturation.

XENOFOOD-An Autoclaved Feed Supplement Containing Autoclavable Antimicrobial Peptides-Exerts Anticoccidial GI Activity, and Causes Bursa Enlargement, but Has No Detectable Harmful Effects in Broiler Cockerels despite In Vitro Detectable Cytotoxicity on LHM Cells.

Entomopathogenic bacteria are obligate symbionts of entomopathogenic nematode (EPN) species. These bacteria biosynthesize and release non-ribosomal-templated hybrid peptides (NR-AMPs), with strong, and large-spectral antimicrobial potential, capable of inactivating pathogens belonging to different prokaryote, and eukaryote taxa. The cell-free conditioned culture media (CFCM) of Xenorhabdus budapestensis and X. szentirmaii efficiently inactivate poultry pathogens like Clostridium, Histomonas, and Eimeria. To learn whether a bio-preparation containing antimicrobial peptides of Xenorhabdus origin with accompanying (in vitro detectable) cytotoxic effects could be considered a safely applicable preventive feed supplement, we conducted a 42-day feeding experiment on freshly hatched broiler cockerels. XENOFOOD (containing autoclaved X. budapestensis, and X. szentirmaii cultures developed on chicken food) were consumed by the birds. The XENOFOOD exerted detectable gastrointestinal (GI) activity (reducing the numbers of the colony-forming Clostridium perfringens units in the lower jejunum. No animal was lost in the experiment. Neither the body weight, growth rate, feed-conversion ratio, nor organ-weight data differed between the control (C) and treated (T) groups, indicating that the XENOFOOD diet did not result in any detectable adverse effects. We suppose that the parameters indicating a moderate enlargement of bursas of Fabricius (average weight, size, and individual bursa/spleen weight-ratios) in the XENOFOOD-fed group must be an indirect indication that the bursa-controlled humoral immune system neutralized the cytotoxic ingredients of the XENOFOOD in the blood, not allowing to reach their critical cytotoxic concentration in the sensitive tissues.

Antimicrobial Peptides (AMP) in the Cell-Free Culture Media of Xenorhabdus budapestensis and X. szentirmaii Exert Anti-Protist Activity against Eukaryotic Vertebrate Pathogens including Histomonas meleagridis and Leishmania donovani Species.

Anti-microbial peptides provide a powerful toolkit for combating multidrug resistance. Combating eukaryotic pathogens is complicated because the intracellular drug targets in the eukaryotic pathogen are frequently homologs of cellular structures of vital importance in the host organism. The entomopathogenic bacteria (EPB), symbionts of entomopathogenic-nematode species, release a series of non-ribosomal templated anti-microbial peptides. Some may be potential drug candidates. The ability of an entomopathogenic-nematode/entomopathogenic bacterium symbiotic complex to survive in a given polyxenic milieu is a coevolutionary product. This explains that those gene complexes that are responsible for the biosynthesis of different non-ribosomal templated anti-microbial protective peptides (including those that are potently capable of inactivating the protist mammalian pathogen Leishmania donovanii and the gallinaceous bird pathogen Histomonas meleagridis) are co-regulated. Our approach is based on comparative anti-microbial bioassays of the culture media of the wild-type and regulatory mutant strains. We concluded that Xenorhabdus budapestensis and X. szentirmaii are excellent sources of non-ribosomal templated anti-microbial peptides that are efficient antagonists of the mentioned pathogens. Data on selective cytotoxicity of different cell-free culture media encourage us to forecast that the recently discovered "easy-PACId" research strategy is suitable for constructing entomopathogenic-bacterium (EPB) strains producing and releasing single, harmless, non-ribosomal templated anti-microbial peptides with considerable drug, (probiotic)-candidate potential.

COVID-19 Models for Hospital Surge Capacity Planning: A Systematic Review.

OBJECTIVE: Health system preparedness for coronavirus disease (COVID-19) includes projecting the number and timing of cases requiring various types of treatment. Several tools were developed to assist in this planning process. This review highlights models that project both caseload and hospital capacity requirements over time. METHODS: We systematically reviewed the medical and engineering literature according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We completed searches using PubMed, EMBASE, ISI Web of Science, Google Scholar, and the Google search engine. RESULTS: The search strategy identified 690 articles. For a detailed review, we selected 6 models that met our predefined criteria. Half of the models did not include age-stratified parameters, and only 1 included the option to represent a second wave. Hospital patient flow was simplified in all models; however, some considered more complex patient pathways. One model included fatality ratios with length of stay (LOS) adjustments for survivors versus those who die, and accommodated different LOS for critical care patients with or without a ventilator. CONCLUSION: The results of our study provide information to physicians, hospital administrators, emergency response personnel, and governmental agencies on available models for preparing scenario-based plans for responding to the COVID-19 or similar type of outbreak.

Methadone Blockade of Cardiac Inward Rectifier K+ Current Augments Membrane Instability and Amplifies U Waves on Surface ECGs: A Translational Study.

Background Methadone is associated with a disproportionate risk of sudden death and ventricular tachyarrhythmia despite only modest inhibition of delayed rectifier K+ current (IKr), the principal mechanism of drug-associated arrhythmia. Congenital defects of inward rectifier K+ current (IK1) have been linked to increased U-wave amplitude on ECG and fatal arrhythmia. We hypothesized that methadone may also be a potent inhibitor of IK1, contributing to delayed repolarization and manifesting on surface ECGs as augmented U-wave integrals. Methods and Results Using a whole-cell voltage clamp, methadone inhibited both recombinant and native IK1 with a half-maximal inhibitory concentration IC50) of 1.5 µmol/L, similar to that observed for IKr block (half-maximal inhibitory concentration of 2.9 µmol/L). Methadone modestly increased the action potential duration at 90% repolarization and slowed terminal repolarization at low concentrations. At higher concentrations, action potential duration at 90% repolarization lengthening was abolished, but its effect on terminal repolarization rose steadily and correlated with increased fluctuations of diastolic membrane potential. In parallel, patient ECGs were analyzed before and after methadone initiation, with 68% of patients having a markedly increased U-wave integral compared with premethadone (lead V3; mean +38%±15%, P=0.016), along with increased QT and TPeak to TEnd intervals, likely reflective of IKr block. Conclusions Methadone is a potent IK1 inhibitor that causes augmentation of U waves on surface ECG. We propose that increased membrane instability resulting from IK1 block may better explain methadone's arrhythmia risk beyond IKr inhibition alone. Drug-induced augmentation of U waves may represent evidence of blockade of multiple repolarizing ion channels, and evaluation of the effect of that agent on IK1 may be warranted.

Type Strains of Entomopathogenic Nematode-Symbiotic Bacterium Species, Xenorhabdus szentirmaii (EMC) and X. budapestensis (EMA), Are Exceptional Sources of Non-Ribosomal Templated, Large-Target-Spectral, Thermotolerant-Antimicrobial Peptides (by Both), and Iodinin (by EMC).

Antimicrobial multidrug resistance (MDR) is a global challenge, not only for public health, but also for sustainable agriculture. Antibiotics used in humans should be ruled out for use in veterinary or agricultural settings. Applying antimicrobial peptide (AMP) molecules, produced by soil-born organisms for protecting (soil-born) plants, seems a preferable alternative. The natural role of peptide-antimicrobials, produced by the prokaryotic partner of entomopathogenic-nematode/bacterium (EPN/EPB) symbiotic associations, is to sustain monoxenic conditions for the EPB in the gut of the semi-anabiotic infective dauer juvenile (IJ) EPN. They keep pathobiome conditions balanced for the EPN/EPB complex in polyxenic (soil, vanquished insect cadaver) niches. Xenorhabdus szentirmaii DSM16338(T) (EMC), and X. budapestensis DSM16342(T) (EMA), are the respective natural symbionts of EPN species Steinernema rarum and S. bicornutum. We identified and characterized both of these 15 years ago. The functional annotation of the draft genome of EMC revealed 71 genes encoding non-ribosomal peptide synthases, and polyketide synthases. The large spatial Xenorhabdus AMP (fabclavine), was discovered in EMA, and its biosynthetic pathway in EMC. The AMPs produced by EMA and EMC are promising candidates for controlling MDR prokaryotic and eukaryotic pathogens (bacteria, oomycetes, fungi, protozoa). EMC releases large quantity of iodinin (1,6-dihydroxyphenazine 5,10-dioxide) in a water-soluble form into the media, where it condenses to form spectacular water-insoluble, macroscopic crystals. This review evaluates the scientific impact of international research on EMA and EMC.

Structural determinants underlying photoprotection in the photoactive orange carotenoid protein of cyanobacteria.

The photoprotective processes of photosynthetic organisms involve the dissipation of excess absorbed light energy as heat. Photoprotection in cyanobacteria is mechanistically distinct from that in plants; it involves the orange carotenoid protein (OCP), a water-soluble protein containing a single carotenoid. The OCP is a new member of the family of blue light-photoactive proteins; blue-green light triggers the OCP-mediated photoprotective response. Here we report structural and functional characterization of the wild type and two mutant forms of the OCP, from the model organism Synechocystis PCC6803. The structural analysis provides high resolution detail of the carotenoid-protein interactions that underlie the optical properties of the OCP, unique among carotenoid-proteins in binding a single pigment per polypeptide chain. Collectively, these data implicate several key amino acids in the function of the OCP and reveal that the photoconversion and photoprotective responses of the OCP to blue-green light can be decoupled.

Structure of the Epstein-Barr virus major envelope glycoprotein.

Epstein-Barr virus (EBV) infection of B cells is associated with lymphoma and other human cancers. EBV infection is initiated by the binding of the viral envelope glycoprotein (gp350) to the cell surface receptor CR2. We determined the X-ray structure of the highly glycosylated gp350 and defined the CR2 binding site on gp350. Polyglycans shield all but one surface of the gp350 polypeptide, and we demonstrate that this glycan-free surface is the receptor-binding site. Deglycosylated gp350 bound CR2 similarly to the glycosylated form, suggesting that glycosylation is not important for receptor binding. Structure-guided mutagenesis of the glycan-free surface disrupted receptor binding as well as binding by a gp350 monoclonal antibody, a known inhibitor of virus-receptor interactions. These results provide structural information for developing drugs and vaccines to prevent infection by EBV and related viruses.

Crystal structure of a near-full-length archaeal MCM: functional insights for an AAA+ hexameric helicase.

The minichromosome maintenance protein (MCM) complex is an essential replicative helicase for DNA replication in Archaea and Eukaryotes. Whereas the eukaryotic complex consists of 6 homologous proteins (MCM2-7), the archaeon Sulfolobus solfataricus has only 1 MCM protein (ssoMCM), 6 subunits of which form a homohexamer. Here, we report a 4.35-A crystal structure of the near-full-length ssoMCM. The structure shows an elongated fold, with 5 subdomains that are organized into 2 large N- and C-terminal domains. A near-full-length ssoMCM hexamer generated based on the 6-fold symmetry of the N-terminal Methanothermobacter thermautotrophicus (mtMCM) hexamer shows intersubunit distances suitable for bonding contacts, including the interface around the ATP pocket. Four unusual beta-hairpins of each subunit are located inside the central channel or around the side channels in the hexamer. Additionally, the hexamer fits well into the double-hexamer EM map of mtMCM. Our mutational analysis of residues at the intersubunit interfaces and around the side channels demonstrates their critical roles for hexamerization and helicase function. These structural and biochemical results provide a basis for future study of the helicase mechanisms of the archaeal and eukaryotic MCM complexes in DNA replication.

Structural basis for the association of PLEKHA7 with membrane-embedded phosphatidylinositol lipids.

PLEKHA7 (pleckstrin homology domain containing family A member 7) plays key roles in intracellular signaling, cytoskeletal organization, and cell adhesion, and is associated with multiple human cancers. The interactions of its pleckstrin homology (PH) domain with membrane phosphatidyl-inositol-phosphate (PIP) lipids are critical for proper cellular localization and function, but little is known about how PLEKHA7 and other PH domains interact with membrane-embedded PIPs. Here we describe the structural basis for recognition of membrane-bound PIPs by PLEHA7. Using X-ray crystallography, nuclear magnetic resonance, molecular dynamics simulations, and isothermal titration calorimetry, we show that the interaction of PLEKHA7 with PIPs is multivalent, distinct from a discrete one-to-one interaction, and induces PIP clustering. Our findings reveal a central role of the membrane assembly in mediating protein-PIP association and provide a roadmap for understanding how the PH domain contributes to the signaling, adhesion, and nanoclustering functions of PLEKHA7.

Phylogenetic relationships and biological features reveal that male Ostrinia furnacalis (Lepidoptera: Crambidae) in Northeast China can be categorized into postmedial line-based clades.

Ostrinia furnacalis (Guenée) (Lepidoptera: Crambidae), often called the Asian corn borer, is a complicated pest because of its complex biological features, such as its adult dynamics, host choice, and life span. This complexity has been causing difficulties in both pest forecasting and control for more than 60 years. One likely explanation for this complexity is that O. furnacalis has several varieties that vary based on some specific features. During 2015-2017, postmedial line-based varieties of male O. furnacalis were identified as distinct clades (I, II, and III), which were then compared based on COI gene sequences, male sacculus construction, life span, male dynamics, and host preference. The results showed that: (1) clades II and III were more closely related to each other than Clade I, because they both completed two generations per year, more were captured in 2016 or fewer were captured in 2015, and they were more closely related according to phylogenetic inference; (2) all three clades shared some features, such as life spans under various rearing conditions, similar dynamic trends, and three teeth on the male sacculus; and (3) all three clades were significantly different from O. nubilalis based on genetic sequences, postmedial line pattern of the forewing, and sacculus construction. Overall, if O. furnacalis is categorized into clades, the species' features are likely to be a combination or mixture of the features of each individual clade. Our findings help explain the biological complexity of O. furnacalis. Future investigations on each individual clade are essential for improving forecasting and control of this pest.

New Series of Potent Allosteric Inhibitors of Deoxyhypusine Synthase.

Deoxyhypusine synthase (DHPS) is the primary enzyme responsible for the hypusine modification and, thereby, activation of the eukaryotic translation initiation factor 5A (eIF5A), which is key in regulating the protein translation processes associated with tumor proliferation. Although DHPS inhibitors could be a promising therapeutic option for treating cancer, only a few studies reported druglike compounds with this inhibition property. Thus, in this work, we designed and synthesized a new chemical series possessing fused ring scaffolds designed from high-throughput screening hit compounds, discovering a 5,6-dihydrothieno[2,3-c]pyridine derivative (26d) with potent inhibitory activity; furthermore, the X-ray crystallographic analysis of the DHPS complex with 26d demonstrated a distinct allosteric binding mode compared to a previously reported inhibitor. These findings could be significantly useful in the functional analysis of conformational changes in DHPS as well as the structure-based design of allosteric inhibitors.

Discovery of Novel Allosteric Inhibitors of Deoxyhypusine Synthase.

Deoxyhypusine synthase (DHPS) utilizes spermidine and NAD as cofactors to incorporate a hypusine modification into the eukaryotic translation initiation factor 5A (eIF5A). Hypusine is essential for eIF5A activation, which, in turn, plays a key role in regulating protein translation of selected mRNA that are associated with the synthesis of oncoproteins, thereby enhancing tumor cell proliferation. Therefore, inhibition of DHPS is a promising therapeutic option for the treatment of cancer. To discover novel lead compounds that target DHPS, we conducted synthetic studies with a hit obtained via high-throughput screening. Optimization of the ring structures of the amide compound (2) led to bromobenzothiophene (11g) with potent inhibitory activity against DHPS. X-ray crystallographic analysis of 11g complexed with DHPS revealed a dramatic conformational change in DHPS, which suggests the presence of a novel allosteric site. These findings provide the basis for the development of novel therapy distinct from spermidine mimetic inhibitors.

Multidrug Resistance (MDR) and Collateral Sensitivity in Bacteria, with Special Attention to Genetic and Evolutionary Aspects and to the Perspectives of Antimicrobial Peptides-A Review.

Antibiotic poly-resistance (multidrug-, extreme-, and pan-drug resistance) is controlled by adaptive evolution. Darwinian and Lamarckian interpretations of resistance evolution are discussed. Arguments for, and against, pessimistic forecasts on a fatal "post-antibiotic era" are evaluated. In commensal niches, the appearance of a new antibiotic resistance often reduces fitness, but compensatory mutations may counteract this tendency. The appearance of new antibiotic resistance is frequently accompanied by a collateral sensitivity to other resistances. Organisms with an expanding open pan-genome, such as Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae, can withstand an increased number of resistances by exploiting their evolutionary plasticity and disseminating clonally or poly-clonally. Multidrug-resistant pathogen clones can become predominant under antibiotic stress conditions but, under the influence of negative frequency-dependent selection, are prevented from rising to dominance in a population in a commensal niche. Antimicrobial peptides have a great potential to combat multidrug resistance, since antibiotic-resistant bacteria have shown a high frequency of collateral sensitivity to antimicrobial peptides. In addition, the mobility patterns of antibiotic resistance, and antimicrobial peptide resistance, genes are completely different. The integron trade in commensal niches is fortunately limited by the species-specificity of resistance genes. Hence, we theorize that the suggested post-antibiotic era has not yet come, and indeed might never come.

Activation of (Na+ + K+)-ATPase modulates cardiac L-type Ca2+ channel function.

Cellular Ca(2+) signaling underlies diverse vital biological processes, including muscle contractility, memory encoding, fertilization, cell survival, and cell death. Despite extensive studies, the fundamental control mechanisms that regulate intracellular Ca(2+) movement remain enigmatic. We have found recently that activation of the (Na(+)+K(+))-ATPase markedly potentiates intracellular Ca(2+) transients and contractility of rat heart cells. Little is known about the pathway responsible for the activation of the (Na(+)+K(+))-ATPase-initiated Ca(2+) signaling. Here, we demonstrate a novel mechanism in which activation of the (Na(+)+K(+))-ATPase is coupled to increased L-type Ca(2+) channel function through a signaling cascade involving Src and ERK1/2 but not well established regulators of the channel, such as adrenergic receptor system or activation of PKA or CaMKII. We have also identified Ser(1928), a phosphorylation site for the alpha1 subunit of the L-type Ca(2+) channel that may participate in the activation of the (Na(+)+K(+))-ATPase-mediated Ca(2+) signaling. The findings reported here uncover a novel molecular cross-talk between activation of the (Na(+)+K(+))-ATPase and L-type Ca(2+) channel and provide new insights into Ca(2+) signaling mechanisms for deeper understanding of the nature of cellular Ca(2+) handling in heart.

Select pyrimidinones inhibit the propagation of the malarial parasite, Plasmodium falciparum.

Plasmodium falciparum, the Apicomplexan parasite that is responsible for the most lethal forms of human malaria, is exposed to radically different environments and stress factors during its complex lifecycle. In any organism, Hsp70 chaperones are typically associated with tolerance to stress. We therefore reasoned that inhibition of P. falciparum Hsp70 chaperones would adversely affect parasite homeostasis. To test this hypothesis, we measured whether pyrimidinone-amides, a new class of Hsp70 modulators, could inhibit the replication of the pathogenic P. falciparum stages in human red blood cells. Nine compounds with IC(50) values from 30 nM to 1.6 micrOM were identified. Each compound also altered the ATPase activity of purified P. falciparum Hsp70 in single-turnover assays, although higher concentrations of agents were required than was necessary to inhibit P. falciparum replication. Varying effects of these compounds on Hsp70s from other organisms were also observed. Together, our data indicate that pyrimidinone-amides constitute a novel class of anti-malarial agents.