Studies of antibacterial activity (in vitro and in vivo) and mode of action for des-acyl tridecaptins (DATs).

Tridecaptins comprise a class of linear cationic lipopeptides with an N-terminal fatty acyl moiety. These 13-mer antimicrobial peptides consist of a combination of d- and l-amino acids, conferring increased proteolytic stability. Intriguingly, they are biosynthesized by non-ribosomal peptide synthetases in the same bacterial species that also produce the cyclic polymyxins displaying similar fatty acid tails. Previously, the des-acyl analog of TriA1 (termed H-TriA1) was found to possess very weak antibacterial activity, albeit it potentiated the effect of several antibiotics. In the present study, two series of des-acyl tridecaptins were explored with the aim of improving the direct antibacterial effect. At the same time, overall physico-chemical properties were modulated by amino acid substitution(s) to diminish the risk of undesired levels of hemolysis and to avoid an impairment of mammalian cell viability, since these properties are typically associated with highly hydrophobic cationic peptides. Microbiology and biophysics tools were used to determine bacterial uptake, while circular dichroism and isothermal calorimetry were used to probe the mode of action. Several analogs had improved antibacterial activity (as compared to that of H-TriA1) against Enterobacteriaceae. Optimization enabled identification of the lead compound 29 that showed a good ADMET profile as well as in vivo efficacy in a variety of mouse models of infection.

Optimization of the Antibacterial Spectrum and the Developability Profile of the Novel-Class Natural Product Corramycin.

Corramycin 1 is a novel zwitterionic antibacterial peptide isolated from a culture of the myxobacterium Corallococcus coralloides. Though Corramycin displayed a narrow spectrum and modest MICs against sensitive bacteria, its ADMET and physchem profile as well as its high tolerability in mice along with an outstanding in vivo efficacy in an Escherichia coli septicemia mouse model were promising and prompted us to embark on an optimization program aiming at enlarging the spectrum and at increasing the antibacterial activities by modulating membrane permeability. Scanning the peptidic moiety by the Ala-scan strategy followed by key stabilization and introduction of groups such as a primary amine or siderophore allowed us to enlarge the spectrum and increase the overall developability profile. The optimized Corramycin 28 showed an improved mouse IV PK and a broader spectrum with high potency against key Gram-negative bacteria that translated into excellent efficacy in several in vivo mouse infection models.

Expert workshop summary: Advancing toward a standardized murine model to evaluate treatments for antimicrobial resistance lung infections.

The rise in antimicrobial resistance (AMR), and increase in treatment-refractory AMR infections, generates an urgent need to accelerate the discovery and development of novel anti-infectives. Preclinical animal models play a crucial role in assessing the efficacy of novel drugs, informing human dosing regimens and progressing drug candidates into the clinic. The Innovative Medicines Initiative-funded "Collaboration for prevention and treatment of MDR bacterial infections" (COMBINE) consortium is establishing a validated and globally harmonized preclinical model to increase reproducibility and more reliably translate results from animals to humans. Toward this goal, in April 2021, COMBINE organized the expert workshop "Advancing toward a standardized murine model to evaluate treatments for AMR lung infections". This workshop explored the conduct and interpretation of mouse infection models, with presentations on PK/PD and efficacy studies of small molecule antibiotics, combination treatments (ß-lactam/ß-lactamase inhibitor), bacteriophage therapy, monoclonal antibodies and iron sequestering molecules, with a focus on the major Gram-negative AMR respiratory pathogens Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii. Here we summarize the factors of variability that we identified in murine lung infection models used for antimicrobial efficacy testing, as well as the workshop presentations, panel discussions and the survey results for the harmonization of key experimental parameters. The resulting recommendations for standard design parameters are presented in this document and will provide the basis for the development of a harmonized and bench-marked efficacy studies in preclinical murine pneumonia model.

Variability of murine bacterial pneumonia models used to evaluate antimicrobial agents.

Antimicrobial resistance has become one of the greatest threats to human health, and new antibacterial treatments are urgently needed. As a tool to develop novel therapies, animal models are essential to bridge the gap between preclinical and clinical research. However, despite common usage of in vivo models that mimic clinical infection, translational challenges remain high. Standardization of in vivo models is deemed necessary to improve the robustness and reproducibility of preclinical studies and thus translational research. The European Innovative Medicines Initiative (IMI)-funded "Collaboration for prevention and treatment of MDR bacterial infections" (COMBINE) consortium, aims to develop a standardized, quality-controlled murine pneumonia model for preclinical efficacy testing of novel anti-infective candidates and to improve tools for the translation of preclinical data to the clinic. In this review of murine pneumonia model data published in the last 10 years, we present our findings of considerable variability in the protocols employed for testing the efficacy of antimicrobial compounds using this in vivo model. Based on specific inclusion criteria, fifty-three studies focusing on antimicrobial assessment against Pseudomonas aeruginosa, Klebsiella pneumoniae and Acinetobacter baumannii were reviewed in detail. The data revealed marked differences in the experimental design of the murine pneumonia models employed in the literature. Notably, several differences were observed in variables that are expected to impact the obtained results, such as the immune status of the animals, the age, infection route and sample processing, highlighting the necessity of a standardized model.

Pharmacokinetics-Pharmacodynamics of Enmetazobactam Combined with Cefepime in a Neutropenic Murine Thigh Infection Model.

Third-generation cephalosporin (3GC)-resistant Enterobacteriaceae are classified as critical priority pathogens, with extended-spectrum ß-lactamases (ESBLs) as principal resistance determinants. Enmetazobactam (formerly AAI101) is a novel ESBL inhibitor developed in combination with cefepime for empirical treatment of serious Gram-negative infections in settings where ESBLs are prevalent. Cefepime-enmetazobactam has been investigated in a phase 3 trial in patients with complicated urinary tract infections or acute pyelonephritis. This study examined pharmacokinetic-pharmacodynamic (PK-PD) relationships of enmetazobactam, in combination with cefepime, for ESBL-producing isolates of Klebsiella pneumoniae in 26-h murine neutropenic thigh infection models. Enmetazobactam dose fractionation identified the time above a free threshold concentration (fT > CT ) as the PK-PD index predictive of efficacy. Nine ESBL-producing isolates of K. pneumoniae, resistant to cefepime and piperacillin-tazobactam, were included in enmetazobactam dose-ranging studies. The isolates encoded CTX-M-type, SHV-12, DHA-1, and OXA-48 ß-lactamases and covered a cefepime-enmetazobactam MIC range from 0.06 to 2 µg/ml. Enmetazobactam restored the efficacy of cefepime against all isolates tested. Sigmoid curve fitting across the combined set of isolates identified enmetazobactam PK-PD targets for stasis and for a 1-log10 bioburden reduction of 8% and 44% fT > 2 µg/ml, respectively, with a concomitant cefepime PK-PD target of 40 to 60% fT > cefepime-enmetazobactam MIC. These findings support clinical dose selection and breakpoint setting for cefepime-enmetazobactam.

Synthetic studies of cystobactamids as antibiotics and bacterial imaging carriers lead to compounds with high in vivo efficacy.

There is an alarming scarcity of novel chemical matter with bioactivity against multidrug-resistant Gram-negative bacterial pathogens. Cystobactamids, recently discovered natural products from myxobacteria, are an exception to this trend. Their unusual chemical structure, composed of oligomeric para-aminobenzoic acid moieties, is associated with a high antibiotic activity through the inhibition of gyrase. In this study, structural determinants of cystobactamid's antibacterial potency were defined at five positions, which were varied using three different synthetic routes to the cystobactamid scaffold. The potency against Acinetobacter baumannii could be increased ten-fold to an MIC (minimum inhibitory concentration) of 0.06 µg mL-1, and the previously identified spectrum gap of Klebsiella pneumoniae could be closed compared to the natural products (MIC of 0.5 µg mL-1). Proteolytic degradation of cystobactamids by the resistance factor AlbD was prevented by an amide-triazole replacement. Conjugation of cystobactamid's N-terminal tetrapeptide to a Bodipy moiety induced the selective localization of the fluorophore for bacterial imaging purposes. Finally, a first in vivo proof of concept was obtained in an E. coli infection mouse model, where derivative 22 led to the reduction of bacterial loads (cfu, colony-forming units) in muscle, lung and kidneys by five orders of magnitude compared to vehicle-treated mice. These findings qualify cystobactamids as highly promising lead structures against infections caused by Gram-positive and Gram-negative bacterial pathogens.

Antibiotics. Targeting DnaN for tuberculosis therapy using novel griselimycins.

The discovery of Streptomyces-produced streptomycin founded the age of tuberculosis therapy. Despite the subsequent development of a curative regimen for this disease, tuberculosis remains a worldwide problem, and the emergence of multidrug-resistant Mycobacterium tuberculosis has prioritized the need for new drugs. Here we show that new optimized derivatives from Streptomyces-derived griselimycin are highly active against M. tuberculosis, both in vitro and in vivo, by inhibiting the DNA polymerase sliding clamp DnaN. We discovered that resistance to griselimycins, occurring at very low frequency, is associated with amplification of a chromosomal segment containing dnaN, as well as the ori site. Our results demonstrate that griselimycins have high translational potential for tuberculosis treatment, validate DnaN as an antimicrobial target, and capture the process of antibiotic pressure-induced gene amplification.

Raising HDL with CETP inhibitor torcetrapib improves glucose homeostasis in dyslipidemic and insulin resistant hamsters.

We investigated whether raising HDL-cholesterol levels with cholesteryl ester transfer protein (CETP) inhibition improves glucose homeostasis in dyslipidemic and insulin resistant hamsters. Compared with vehicle, torcetrapib 30 mg/kg/day (TOR) administered for 10 days significantly increased by ∼40% both HDL-cholesterol levels and 3H-tracer appearance in HDL after 3H-cholesterol labeled macrophages i.p. injection. TOR significantly reduced fasting plasma triglycerides, glycerol and free fatty acids levels by 65%, 31% and 23%, respectively. TOR also reduced blood glucose levels and plasma insulin by 20% and 49% respectively, which led to a 60% reduction in HOMA-IR index (all p<0.01). After 3H-2-deoxyglucose and insulin injection, TOR significantly increased glucose uptake in oxidative soleus muscle, liver and heart by 26, 33 and 70%, respectively. Raising HDL levels with the CETP inhibitor torcetrapib improves glucose homeostasis in dyslipidemic and insulin resistant hamsters. Whether similar effect would be observed with other CETP inhibitors should be investigated.

Human FGF-1 gene transfer promotes the formation of collateral vessels and arterioles in ischemic muscles of hypercholesterolemic hamsters.

BACKGROUND: Acidic fibroblast growth factor (FGF-1) has been identified as a potent mitogen for vascular cells, inducing formation of mature blood vessels in vitro and in vivo and represents one of the most promising approaches for the treatment of ischemic cardiovascular diseases by gene therapy. Nevertheless, and most probably due to the few experimental models able to address the issue, no study has described the therapeutic effects of FGF-1 gene transfer in subjects with peripheral arterial disease (PAD) exhibiting a clinically relevant cardiovascular pathology. METHODS: In order to assess the potency of FGF-1 gene transfer for therapeutic angiogenesis in ischemic skeletal muscles displaying decreased gene expression levels and sustained impaired formation of collateral vessels and arterioles, we developed a model of PAD in hamsters with a background of hypercholesterolemia. Hamsters fed a cholesterol-rich diet and subjected to hindlimb ischemia exhibit a sustained impaired angiogenic response, as evidenced by decreased angiographic score and histological quantification of arterioles in the ischemic muscles. RESULTS: In this model, we demonstrate that NV1FGF (a human FGF-1 expression plasmid), given intramuscularly 14 days after induction of hindlimb ischemia, promoted the formation of both collateral vessels and arterioles 14 days after treatment (i.e. 28 days post-ischemia). CONCLUSIONS: Our data provide evidence that NV1FGF can reverse the cholesterol-induced impairment of revascularization in a hamster model of hindlimb ischemia by promoting the growth of both collateral vessels and arterioles in ischemic muscles exhibiting significantly decreased levels of gene expression compared with control muscles. Therefore, this study underscores the relevance of NV1FGF gene therapy to overcome perfusion defects in patients with PAD.

Direct FGF receptor 1 activation through an anti-idiotypic strategy mimicks the biological activity of FGF-2 and inhibits the progression of the bladder carcinoma derived from NBT-II cells.

The hypothesis that tumor growth is angiogenesis-dependent has been documented by a considerable body of direct and indirect experimental data. Since the discovery of the vascular endothelial growth factor (VEGF), most attention has been focused on the VEGF system. Although fibroblast growth factors 1 and 2 (FGF-1 and FGF-2) can exert a strong angiogenic activity when they are supplied as a single pharmacological agent, their role in pathological angiogenesis in preclinical models remains controversial. To decipher the contribution of FGF receptors in various models of angiogenesis, we took advantage of the anti-idiotypic strategy to obtain circulating agonists specific for FGFR-1 and FGFR-2 (AIdF-1 and AIdF-2). They mimicked FGF-1 and FGF-2 for receptor binding, signal transduction, proliferation of endothelial cells and differentiation of the bladder carcinoma cell NBT-II which expresses FGFR-2b but not FGFR-1. The constitutive expression of FGFR-1 allowed binding of FGF-2 and AIdF-2 and inhibition of the proliferation of NBT-II cells. AIdF-1 and AIdF-2 induced angiogenesis in the corneal pocket assay. Although FGFR-1 dimerization achieved by AIdF-2 injection led to highly differentiated and smaller NBT-II tumors, no sign of reduction of tumor angiogenesis was observed, thus suggesting that endothelial cells are resistant to FGF.

A dynamic shift of VEGF isoforms with a transient and selective progesterone-induced expression of VEGF189 regulates angiogenesis and vascular permeability in human uterus.

A key mechanism underlying physiological angiogenesis of the human endometrium is its ability to regenerate the vascular capillary network and to perform vascular remodeling (i.e., development of spiral arteries). Vascular endothelial growth factor (VEGF) is associated with angiogenesis and capillary permeability in this tissue. VEGF is expressed as several spliced variants, its main human isoforms contain 121 and 165 aa; 17beta-estradiol (E(2)) increases endometrial VEGF, possibly in all isoforms. Here we show that progesterone (P) selectively increases the expression of the VEGF(189) (V(189)) isoform in the human uterus. V(189) is identified in the conditioned medium of stromal cells treated with E(2) + P; its presence in this in vitro model of decidual stromal cells is detected after 6-8 days, using ELISA, and after 8-10 days, using Western blot analysis with different antibodies, including one specific for V(189). The secretion pattern of V(189) parallels that of the decidual protein IGFBP-1. V(189) is secreted as a native isoform, as compared with the migration of recombinant V(189) by SDS/PAGE. In situ hybridization and immunocytochemistry(,) performed on the same biopsies, suggest that decidual cells express V(189) during the mid-late secretory phase of the menstrual cycle and early gestation. Finally, using an in vivo permeability assay, we show that native V(189) increases capillary permeability. These observations demonstrate that P regulates V(189) expression in decidual cells, which could have important implications for understanding uterine vascular remodeling and implantation, and may be relevant in a range of disease states such as edema and irregular bleeding.