Search

Invasive fungal infections have become an important healthcare issue due in large part to high mortality rates under standard of care (SOC) therapies creating an urgent need for new and effective anti-fungal agents. We have developed a series of non-peptide, structurally-constrained analogs of host defence proteins that have distinct advantages over peptides for pharmaceutical uses. Here we report the chemical optimization of bis-guanidine analogs focused on alterations of the central aryl core and the connection of it to the terminal guanidines. This effort resulted in the production of highly potent, broadly active compounds with low mammalian cell cytotoxicity that have comparable or improved antifungal activities over SOC agents. One optimal compound was also found to possess favourable in vitro pharmaceutical and off-target properties suitable for further development.

Disseminated infection by Candida species represents a common, often life-threatening condition. Increased resistance to current antifungal drugs has led to an urgent need to develop new antifungal drugs to treat this pathogen. However, in vivo screening of candidate antifungal compounds requires large numbers of animals and using immunosuppressive agents to allow for fungal dissemination. To increase the efficiency of screening, to use fewer mice, and to remove the need for immunosuppressive agents, which may interfere with the drug candidates, we tested the potential for a novel approach using in vivo imaging of a fluorescent strain of Candida albicans, in a mouse strain deficient in the host defense peptide, murine &beta, defensin 1 (mBD-1). We developed a strain of C. albicans that expresses red fluorescent protein (RFP), which exhibits similar infectivity to the non-fluorescent parent strain. When this strain was injected into immunocompetent mBD-1-deficient mice, we observed a non-lethal disseminated infection. Further, we could quantify its dissemination in real time, and observe the activity of an antifungal peptide mimetic drug by in vivo imaging. This novel method will allow for the rapid in vivo screening of antifungal drugs, using fewer mice, and increase the efficiency of testing new antifungal agents.

Host-defense peptides (HDPs) have an important therapeutic potential against microbial infections but their metabolic instability and cellular cytotoxicity have limited their utility. To overcome these limitations, we utilized five small-molecule, nonpeptide HDP mimetics (smHDPMs) and tested their effects on cytotoxicity, antimicrobial activity, and mast cell (MC) degranulation. None of the smHDPMs displayed cytotoxicity against mouse 3T3 fibroblasts or human transformed liver HepG2 cells. However, one compound had both antifungal and antibacterial activity. Surprisingly, all five compounds induced degranulation in a human MC line, LAD2, and this response was substantially reduced in Mas-related G protein-coupled receptor (GPCR)-X2 (MRGPRX2)-silenced cells. Furthermore, all five compounds induced degranulation in RBL-2H3 cells expressing MRGPRX2 but this response was abolished in cells expressing naturally occurring loss-of-function missense variants G165E (rs141744602) and D184H (rs372988289). Mrgprb2 is the likely mouse ortholog of human MRGPRX2, which is expressed in connective tissue MCs (CTMCs) such as cutaneous and peritoneal MCs (PMCs). All five smHDPMs induced degranulation in wild-type PMCs but not in cells derived from Mrgprb2-/- mice. These findings suggest that smHDPMs could serve as novel targets for the treatment of drug-resistant fungal and bacterial infections because of their ability to harness CTMCs&rsquo, host defense functions.

Background We are developing a series of small nonpeptide mimics of host defense proteins (smHDPs) for antifungal applications. MICs < 0.1 µg/ ml have been demonstrated against multiple yeast and mold species. Their potential therapeutic utility has been evaluated in animal models of disseminated fungal infections. Methods Susceptibility testing against clinical isolates of Candida albicans (CA) and Aspergillus fumigatus (AF) was done according to CLSI guidelines. Cytotoxicity (CC50) in mouse 3T3 and human HepG2 cells was determined in an MTS assay (Promega Cell Titer 96). For candidiasis, neutropenic CD-1 mice were infected IV with 3.5 x 104 CFU CA and test agents were administered subcutaneously (SC) once (QD) or twice (BID) daily beginning 2 hrs post-infection (PI). The positive control was fluconazole (20 mg/kg PO QD). Kidney burdens were measured at 24 hrs PI (n = 5/grp) and survival was measured at 2 weeks after 5 days of treatment (n = 8/grp). For aspergillosis, neutropenic CD-1 mice were infected IV with 4.5 log10 spores AF and test agents were administered SC BID for 5 days beginning 24 hrs PI. The positive control was posaconazole (20 mg/kg PO QD). Liver and kidney fungal burdens were measured 24 hrs after the last dose (n = 10/grp). Results The lead smHDP, FC-5096, has MICs of 0.08 and 0.024 ug/ml, respectively, against the CA and AF clinical isolate strains used in the mouse efficacy studies. Selectivity for antifungal vs. mammalian cell cytotoxicity (MIC/CC50) was >1,000 fold. In the disseminated candidiasis model, FC-5096 significantly reduced fungal kidney burdens relative to untreated mice to levels found at treatment onset (P < 0.0001). Full survival over 2 weeks was observed after 5 days of BID treatment with FC-5096. All untreated mice succumbed between days 3 – 6 PI. Efficacy was comparable to fluconazole. In the disseminated aspergillosis model, FC-5096 produced up to 2.5 log10 reductions in fungal liver burdens and efficacy was significantly better than posaconazole (P = 0.0251). In kidney, both FC-5096 and posaconazole caused > 1.6 log10 reductions in fungal burdens that exceeded the limit of detection. Conclusion The high antifungal potency, low cytotoxicity and robust in vivo efficacy support further study of FC-5096 for clinical development. Disclosures Richard W. Scott, PhD, Fox Chase Chemical Diversity Center (Employee) Simon DP Baugh, PhD, Fox Chase Chemical Diversity Center (Employee) Mark E Pulse, MS, Fox Chase Chemical Diversity Center (Independent Contractor)

Systemic fungal infections are increasingly common, especially in immune compromised patients. Even with newly developed drugs, there remain issues of limited spectrum, side effects, and the development of resistance. Host defense peptides (HDPs) have been examined recently for their utility as therapeutic antifungals, especially due to the low levels of resistance that develop. Unfortunately, the peptides exhibit poor pharmacologic properties in vivo. We have demonstrated the potent activity of nonpeptidic compounds that mimic HDPs in both structure and function against clinical strains of Candida albicans associated with oral and invasive candidiasis in mouse models. However, to test numerous compounds in vivo requires large numbers of mice, with multiple time points, and requires immunosuppression of the mice using cyclophosphamide, which can influence pharmacological parameters. We have identified a strain of mouse that develops invasive candidiasis without the need for immunosuppressive drugs. When we infect these mice with a strain of C. albicans that constitutively expresses Red Fluorescent Protein, we can quantify the infection in real time by in vivo imaging. We can further observe the reduction in fluorescence in infected mice after treatment with an HDP mimetic. Together our results demonstrate a novel in vivo method for screening new antifungal drugs.

Invasive candidiasis caused by Candida albicans and non-albicans Candida (NAC) present a serious disease threat. Although the echinocandins are recommended as the first line of antifungal drug class, resistance to these agents is beginning to emerge, demonstrating the need for new antifungal agents. Host defense peptides (HDP) exhibit potent antifungal activity, but as drugs they are difficult to manufacture efficiently, and they are often inactivated by serum proteins. HDP mimetics are low molecular weight non-peptide compounds that can alleviate these problems and were shown to be membrane-active against C. albicans and NAC. Here, we expand upon our previous works to describe the in vitro and in vivo activity of 11 new HDP mimetics that are active against C. albicans and NAC that are both sensitive and resistant to standard antifungal drugs. These compounds exhibit minimum inhibitory/fungicidal concentration (MIC/MFC) in the µg/mL range in the presence of serum and are inhibited by divalent cations. Rapid propidium iodide influx into the yeast cells following in vitro exposure suggested that these HDP mimetics were also membrane active. The lead compounds were able to kill C. albicans in an invasive candidiasis CD-1 mouse model with some mimetic candidates decreasing kidney burden by 3–4 logs after 24 h in a dose-dependent manner. The data encouraged further development of this new anti-fungal drug class for invasive candidiasis.

There is a strong need for new broadly active antifungal agents for the treatment of oral candidiasis that not only are active against many species of Candida , including drug-resistant strains, but also evade microbial countermeasures which may lead to resistance. Host defense peptides (HDPs) can provide a foundation for the development of such agents. Toward this end, we have developed fully synthetic, small-molecule, nonpeptide mimetics of the HDPs that improve safety and other pharmaceutical properties. Here we describe the identification of several HDP mimetics that are broadly active against C. albicans and other species of Candida , rapidly fungicidal, and active against yeast and hyphal cultures and that exhibit low cytotoxicity for mammalian cells. Importantly, specificity for Candida over commensal bacteria was also evident, thereby minimizing potential damage to the endogenous microbiome which otherwise could favor fungal overgrowth. Three compounds were tested as topical agents in two different mouse models of oral candidiasis and were found to be highly active. Following single-dose administrations, total Candida burdens in tongues of infected animals were reduced up to three logs. These studies highlight the potential of HDP mimetics as a new tool in the antifungal arsenal for the treatment of oral candidiasis.

A series of self-associating foldamers have been designed as heparin reversal agents, as antidotes to prevent bleeding due to this potent antithrombotic agent. The foldamers have a repeating sequence of Lys-Sal, in which Sal is 5-amino-2-methoxy-benzoic acid. These foldamers are designed to self-associate along one face of an extended chain in a β-sheet-like interaction. The methoxy groups were included to form intramolecular hydrogen bonds that preclude the formation of very large amyloid-like aggregates, while the positively charged Lys side chains were introduced to interact electrostatically with the highly anionic heparin polymer. The prototype compound (Lys-Sal)4 carboxamide weakly associates in aqueous solution at physiological salt concentration in a monomer-dimer-hexamer equilibrium. The association is greatly enhanced at either high ionic strength or in the presence of a heparin derivative, which is bound tightly. Variants of this foldamer are active in an antithrombin III-factor Xa assay, showing their potential as heparin reversal agents.

Lethal systemic fungal infections of Candida species are increasingly common, especially in immune compromised patients. By in vitro screening of small molecule mimics of naturally occurring host defense peptides (HDP), we have identified several active antifungal molecules, which also exhibited potent activity in two mouse models of oral candidiasis. Here we show that one such compound, C4, exhibits a mechanism of action that is similar to the parent HDP upon which it was designed. Specifically, its initial interaction with the anionic microbial membrane is electrostatic, as its fungicidal activity is inhibited by cations. We observed rapid membrane permeabilization to propidium iodide and ATP efflux in response to C4. Unlike the antifungal peptide histatin 5, it did not require energy-dependent transport across the membrane. Rapid membrane disruption was observed by both fluorescence and electron microscopy. The compound was highly active in vitro against numerous fluconazole-resistant clinical isolates of C. albicans and non-albicans species, and it exhibited potent, dose-dependent activity in a mouse model of invasive candidiasis, reducing kidney burden by three logs after 24 hours, and preventing mortality for up to 17 days. Together the results support the development of this class of antifungal drug to treat invasive candidiasis.

The Gram-negative bacterium Acinetobacter baumannii is an opportunistic pathogen in humans and infections are poorly treated by current therapy. Recent emergence of multi-drug resistant strains and the lack of new antibiotics demand an immediate action for development of new anti-Acinetobacter agents. To this end, oxidative phosphorylation (OxPhos) was identified as a novel target for drug discovery research. Consequently, a library of ∼10,000 compounds was screened using a membrane-based ATP synthesis assay. One hit identified was the 2-iminobenzimidazole 1 that inhibited the OxPhos of A. baumannii with a modestly high selectivity against mitochondrial OxPhos, and displayed an MIC of 25μM (17μg/mL) against the pathogen. The 2-iminobenzimidazole 1 was found to inhibit the type 1 NADH-quinone oxidoreductase (NDH-1) of A. baumannii OxPhos by a biochemical approach. Among various derivatives that were synthesized to date, des-hydroxy analog 5 is among the most active with a relatively tight SAR requirement for the N'-aminoalkyl side chain. Analog 5 also showed less cytotoxicity against NIH3T3 and HepG2 mammalian cell lines, demonstrating the potential for this series of compounds as anti-Acinetobacter agents. Additional SAR development and target validation is underway.

SummaryPlasmodium falciparum pathogenesis is affected by various cell types in the blood, including platelets, which can kill intraerythrocytic malaria parasites. Platelets could mediate these antimalarial effects through human defense peptides (HDPs), which exert antimicrobial effects by permeabilizing membranes. Therefore, we screened a panel of HDPs and determined that human platelet factor 4 (hPF4) kills malaria parasites inside erythrocytes by selectively lysing the parasite digestive vacuole (DV). PF4 rapidly accumulates only within infected erythrocytes and is required for parasite killing in infected erythrocyte-platelet cocultures. To exploit this antimalarial mechanism, we tested a library of small, nonpeptidic mimics of HDPs (smHDPs) and identified compounds that kill P. falciparum by rapidly lysing the parasite DV while sparing the erythrocyte plasma membrane. Lead smHDPs also reduced parasitemia in a murine malaria model. Thus, identifying host molecules that control parasite growth can further the development of related molecules with therapeutic potential.

Abstract 1096 Structural studies of the binding interaction between the negatively charged heparin pentasaccharide binding site and antithrombin III suggested that an amphiphilic structure resembling features designed into compounds prepared for antimicrobial activity might also provide an efficient design basis for the development of heparin antagonists. A key design element of our antimicrobial approach at PolyMedix involves compounds exhibiting polycationic arrays which are appended to a diverse set of rigid backbones. A broad screening of the antimicrobial compound library in an enoxaparin (ENX) anti-factor Xa assay, coupled with subsequent secondary testing, identified compounds with potent and broad neutralizing activity. A lead compound (PMX-60056) was identified in one structural series, the salicylamides, and this compound has successfully completed Phase 1 human clinical studies. Recently, a new series of antagonists identified in the initial screen, the arylamides, was investigated for heparin neutralizing activities. Compounds were first tested for their ability to neutralize the anticoagulant activity of ENX, tinzaparin (TZP) or fondaparinux (FPX) in an in vitro amidolytic assay for factor Xa activity. Activated partial thromboplastin time (aPTT) assays demonstrated that the compounds were also active against unfractionated heparin (UFH) in a plasma-based clotting assay. The lead compound PMX150 was comparable to or better than PMX-60056 versus all anticoagulants tested (EC50s: UFH 0.6 uM, ENX 0.1 uM, TZP 0.1 uM, FPX 0.7 uM). Early compounds have shown an interesting structure activity relationship (SAR) which has identified specific regions of the molecule that are important for activity. Additionally, rotation thromboelastometry (ROTEM) shows that compounds are able to neutralize heparin and ENX in human whole blood, restoring normal coagulation profiles. As an initial test for safety, compounds were evaluated in hemolysis and cytotoxicity assays using isolated human erythrocytes, a transformed human liver cell line (HepG2 cells) and a mouse fibroblast cell line (NIH3T3). PMX150 was not cytotoxic (or hemolytic) at concentrations 180 fold greater than the EC50 concentrations in the anti-coagulation assays, indicating a high selectivity index between toxicity and efficacy. Furthermore, the SAR has identified synthetic strategies that should further improve this safety margin. The in vivo efficacy of PMX150 was evaluated in a rat coagulation model using ENX (2 mg/kg) administered by IV injection followed 3 minutes later by saline, protamine or PMX150. Blood was collected before dosing with ENX, and at 1, 3, 10, and 60 min after dosing, for aPTT and factor Xa analysis. PMX150 was more efficacious than protamine; neutralizing 89–100% of the ENX anti-factor Xa activity over the entire 60 minute time course. The in vivo assays concur with the in vitro studies, showing that compounds have been identified with high efficacy versus low molecular weight heparin (LMWH). Protamine, the heparin antagonist currently used in the clinic, routinely causes a transient decrease in blood pressure upon dosing. Hemodynamic effects with PMX-60056 have also been observed in human subjects in the absence of heparin. As PMX150 represents a new chemical series, investigations into potential adverse hemodynamic effects were performed. Blood pressure and heart rate were measured via arterial catheters in rats administered protamine or PMX150 by a 10 minute IV infusion. As expected, protamine displayed transient and prolonged blood pressure reductions at 8 and 16 mg/kg dosages, respectively. However, PMX150 had little to no effect on blood pressure at 8 mg/kg and only a minor transient reduction at 16 mg/kg. In conclusion, we have identified a new series of fully synthetic small molecule antagonists that display potent in vitro activity against UFH, the LMWHs, and fondaparinux. The lead compound in this series, PMX150 is able to neutralize ENX in vivo with more efficacy than protamine and, furthermore, has an improved hemodynamic profile with respect to protamine. Disclosures: Scott: PolyMedix, Inc.: Employment, Equity Ownership. Costanzo:PolyMedix, Inc.: Employment, Equity Ownership. Freeman:PolyMedix, Inc.: Employment, Equity Ownership. Kavash:PolyMedix, Inc.: Employment, Equity Ownership. Young:PolyMedix, Inc.: Employment, Equity Ownership. DeGrado:PolyMedix, Inc.: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Jeske:PolyMedix, Inc.: Research Funding.