Saquinavir Inhibits the malaria parasite's chloroquine resistance transporter

The antiretroviral protease inhibitors (APIs) ritonavir, saquinavir, and lopinavir, used to treat HIV infection, inhibit the growth of Plasmodium falciparum at clinically relevant concentrations. Moreover, it has been reported that these APIs potentiate the activity of chloroquine (CQ) against this parasite in vitro. The mechanism underlying this effect is not understood, but the degree of chemosensitization varies between the different APIs and, with the exception of ritonavir, appears to be dependent on the parasite exhibiting a CQ-resistant phenotype. Here we report a study of the role of the P. falciparum chloroquine resistance transporter (PfCRT) in the interaction between CQ and APIs, using transgenic parasites expressing different PfCRT alleles and using the Xenopus laevis oocyte system for the heterologous expression of PfCRT. Our data demonstrate that saquinavir behaves as a CQ resistance reverser and that this explains, at least in part, its ability to enhance the effects of CQ in CQ-resistant P. falciparum parasites. Copyrigh

The Frequency of Malaria Is Similar among Women Receiving either Lopinavir/Ritonavir or Nevirapine-based Antiretroviral Treatment

HIV protease inhibitors (PIs) show antimalarial activity in vitro and in animals. Whether this translates into a clinical benefit in HIV-infected patients residing in malaria-endemic regions is unknown. We studied the incidence of malaria, as defined by blood smear positivity or a positive Plasmodium falciparum histidine-rich protein 2 antigen test, among 444 HIV-infected women initiating antiretroviral treatment (ART) in the OCTANE trial (A5208; ClinicalTrials.gov: NCT00089505). Participants were randomized to treatment with PI-containing vs. PI-sparing ART, and were followed prospectively for ≥48 weeks; 73% also received cotrimoxazole prophylaxis. PI-containing treatment was not associated with protection against malaria in this study population

The aminopeptidase inhibitor CHR-2863 is an orally bioavailable inhibitor of murine malaria

Malaria remains a significant risk in many areas of the world, with resistance to the current antimalarial pharmacopeia an everincreasing problem. The M1 alanine aminopeptidase (PfM1AAP) and M17 leucine aminopeptidase (PfM17LAP) are believed to play a role in the terminal stages of digestion of host hemoglobin and thereby generate a pool of free amino acids that are essential for parasite growth and development. Here, we show that an orally bioavailable aminopeptidase inhibitor, CHR-2863, is efficacious against murine malaria

Fingerprinting the Substrate Specificity of M1 and M17 Aminopeptidases of Human Malaria, Plasmodium falciparum

Plasmodium falciparum, the causative agent of human malaria, expresses two aminopeptidases, PfM1AAP and PfM17LAP, critical to generating a free amino acid pool used by the intraerythrocytic stage of the parasite for proteins synthesis, growth and development. These exopeptidases are potential targets for the development of a new class of anti-malaria drugs.To define the substrate specificity of recombinant forms of these two malaria aminopeptidases we used a new library consisting of 61 fluorogenic substrates derived both from natural and unnatural amino acids. We obtained a detailed substrate fingerprint for recombinant forms of the enzymes revealing that PfM1AAP exhibits a very broad substrate tolerance, capable of efficiently hydrolyzing neutral and basic amino acids, while PfM17LAP has narrower substrate specificity and preferentially cleaves bulky, hydrophobic amino acids. The substrate library was also exploited to profile the activity of the native aminopeptidases in soluble cell lysates of P. falciparum malaria.This data showed that PfM1AAP and PfM17LAP are responsible for majority of the aminopeptidase activity in these extracts. These studies provide specific substrate and mechanistic information important for understanding the function of these aminopeptidases and could be exploited in the design of new inhibitors to specifically target these for anti-malaria treatment

A Plasmodium falciparum S33 proline aminopeptidase is associated with changes in erythrocyte deformability

Infection with the apicomplexan parasite Plasmodium falciparum is a major cause of morbidity and mortality worldwide. One of the Striking features of this parasite is its ability to remodel and decrease the deformability of host red blood cells, a process that contributes to disease. To further understand the virulence of Pf we investigated the biochemistry and function of a putative Pf S33 proline aminopeptidase (PJPAP). Unlike other P. falciparum aminopeptidases, PJPAP contains a predicted protein export element that is non-syntenic with other human infecting Plasmodium species. Characterization of PJPAP demonstrated that it is exported into the host red blood cell and that it is a prolyl aminopeptidase with a preference for N-terminal proline substrates. In addition genetic deletion of this exopeptidase was shown to lead to an increase in the deformability of parasite-infected red cells and in reduced adherence to the endothelial cell receptor CD36 under flow conditions. Our studies suggest that PJPAP plays a role in the rigidification and adhesion of infected red blood cells to endothelial surface receptors, a role that may make this protein a novel target for anti-disease interventions strategies. (C) 2016 Elsevier Inc. All rights reserved

HIV-1 protease inhibitors and clinical malaria: A secondary analysis of the AIDS Clinical Trials Group A5208 study

HIV-1 protease inhibitors (PIs) have antimalarial activity in vitro and in murine models. The potential beneficial effect of HIV-1 PIs on malaria has not been studied in clinical settings. We used data from Adult AIDS Clinical Trials Group A5208 sites where malaria is endemic to compare the incidence of clinically diagnosed malaria among HIV-infected adult women randomized to either lopinavir/ritonavir (LPV/r)-based antiretroviral therapy (ART) or to nevirapine (NVP)-based ART. We calculated hazard ratios and 95% confidence intervals. We conducted a recurrent events analysis that included both first and second clinical malarial episodes and also conducted analyses to assess the sensitivity of results to outcome misclassification. Among the 445 women in this analysis, 137 (31%) received a clinical diagnosis of malaria at least once during follow-up. Of these 137, 72 (53%) were randomized to LPV/r-based ART. Assignment to the LPV/r treatment group (n = 226) was not consistent with a large decrease in the hazard of first clinical malarial episode (hazard ratio = 1.11 [0.79 to 1.56]). The results were similar in the recurrent events analysis. Sensitivity analyses indicated the results were robust to reasonable levels of outcome misclassification. In this study, the treatment with LPV/r compared to NVP had no apparent beneficial effect on the incidence of clinical malaria among HIV-infected adult women. Additional research concerning the effects of PI-based therapy on the incidence of malaria diagnosed by more specific criteria and among groups at a higher risk for severe disease is warranted. Copyrigh

The key glycolytic enzyme phosphofructokinase is involved in resistance to antiplasmodial glycosides

ABSTRACT Plasmodium parasites rely heavily on glycolysis for ATP production and for precursors for essential anabolic pathways, such as the methylerythritol phosphate (MEP) pathway. Here, we show that mutations in the Plasmodium falciparum glycolytic enzyme, phosphofructokinase (PfPFK9), are associated with in vitro resistance to a primary sulfonamide glycoside (PS-3). Flux through the upper glycolysis pathway was significantly reduced in PS-3-resistant parasites, which was associated with reduced ATP levels but increased flux into the pentose phosphate pathway. PS-3 may directly or indirectly target enzymes in these pathways, as PS-3-treated parasites had elevated levels of glycolytic and tricarboxylic acid (TCA) cycle intermediates. PS-3 resistance also led to reduced MEP pathway intermediates, and PS-3-resistant parasites were hypersensitive to the MEP pathway inhibitor, fosmidomycin. Overall, this study suggests that PS-3 disrupts core pathways in central carbon metabolism, which is compensated for by mutations in PfPFK9, highlighting a novel metabolic drug resistance mechanism in P. falciparum. IMPORTANCE Malaria, caused by Plasmodium parasites, continues to be a devastating global health issue, causing 405,000 deaths and 228 million cases in 2018. Understanding key metabolic processes in malaria parasites is critical to the development of new drugs to combat this major infectious disease. The Plasmodium glycolytic pathway is essential to the malaria parasite, providing energy for growth and replication and supplying important biomolecules for other essential Plasmodium anabolic pathways. Despite this overreliance on glycolysis, no current drugs target glycolysis, and there is a paucity of information on critical glycolysis targets. Our work addresses this unmet need, providing new mechanistic insights into this key pathway

Characterization of the Plasmodium falciparum M17 leucyl aminopeptidase. A protease involved in amino acid regulation with potential for antimalarial drug development

Amino acids generated from the catabolism of hemoglobin by intra-erythrocytic malaria parasites are not only essential for protein synthesis but also function in maintaining an osmotically stable environment, and creating a gradient by which amino acids that are rare or not present in hemoglobin are drawn into the parasite from host serum. We have proposed that a Plasmodium falciparum M17 leucyl aminopeptidase (PfLAP) generates and regulates the internal pool of free amino acids and therefore represents a target for novel antimalarial drugs. This enzyme has been expressed in insect cells as a functional 320-kDa homo-hexamer that is optimally active at neutral or alkaline pH, is dependent on metal ions for activity, and exhibits a substrate preference for N-terminally exposed hydrophobic amino acids, particularly leucine. PfLAP is produced by all stages in the intra-erythrocytic developmental cycle of malaria but was most highly expressed by trophozoites, a stage at which hemoglobin degradation and parasite protein synthesis are elevated. The enzyme was located by immunohistochemical methods and by transfecting malaria cells with a PfLAP-green fluorescent protein construct, to the cytosolic compartment of the cell at all developmental stages, including segregated merozoites. Amino acid dipeptide analogs, such as bestatin and its derivatives, are potent inhibitors of the protease and also block the growth of P. falciparum malaria parasites in culture. This study provides a biochemical basis for the antimalarial activity of aminopeptidase inhibitors. Availability of functionally active recombinant PfLAP, coupled with a simple enzymatic readout, will aid medicinal chemistry and/or high throughput approaches for the future design/discovery of new antimalarial drugs

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570