Comparative antibacterial activity of a novel semisynthetic antibiotic: etimicin sulphate and other aminoglycosides

Establishment of epidemiological cut-off values of etimicin: a new fourth-generation aminoglycoside, against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Acinetobacter baumannii and Staphylococcus aureus

OBJECTIVE

To determine the epidemiological cut-off (ECOFF) values of etimicin against Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Acinetobacter baumannii and Staphylococcus aureus.

METHODS

We selected 1500 isolates from five hospitals throughout five cities in China spanning from January 2018 to December 2021 in the study. Minimal inhibit concentrations (MICs) of etimicin were determined using the broth microdilution method. ECOFFs of etimicin against six species were calculated using ECOFFinder software and visual estimation following EUCAST principles.

RESULTS

MICs of etimicin were distributed from 0.064 to >128 mg/L for S. aureus, from 0.125 to >128 mg/L for P. aeruginosa, from 0.25 to >128 mg/L for K. pneumoniae, P. mirabilis and A. baumannii, and from 0.5 to >128 mg/L for E. coli. The MIC ECOFF of etimicin was 2 mg/L for K. pneumoniae, 8 mg/L for E. coli and P. mirabilis, 16 mg/L for P. aeruginosa and A. baumannii, and the tentative ECOFF (TECOFF) of etimicin was 2 mg/L for S. aureus.

CONCLUSIONS

(T)ECOFFs of etimicin against E. coli, K. pneumoniae, P. mirabilis, P. aeruginosa, A. baumannii and S. aureus were determined, which will be helpful to differentiate wild-type strains.

A phase I clinical study: Evaluation of safety, tolerability, and population pharmacokinetic-pharmacodynamic target attainment analysis of etimicin sulfate among healthy chinese participants

BACKGROUND

This phase I clinical study aimed to assess the safety, tolerability, and population pharmacokinetic-pharmacodynamics (PK-PD) target attainment analysis of etimicin sulfate in healthy participants, and to provide scientific reference for further development of clinical breakpoints.

METHODS

A total of 24 healthy Chinese subjects were enrolled in this study and received an etimicin sulfate infusion. A population PK model was constructed for the estimation of the PK profiles of etimicin sulfate. The area under the concentration-time curve divided by the minimum inhibitory concentration (AUC0-24h/MIC) and the peak concentration divided by the MIC (Cmax/MIC) were selected as the PK/PD indices. The probability of target attainment (PTA) was calculated for each designed dosing regimen using Monte Carlo simulations. The minimum MIC value with a PTA ≥ 90% for each regimen was considered as the PK/PD cutoff values.

RESULTS

Etimicin sulfate demonstrated safety, tolerability, and predictable PK characteristics. No deaths or serious adverse events were reported. Seven treatment-emergent adverse events (TEAEs) were reported by five participants; all TEAEs were minor and were rapidly relieved. A two-compartment model was developed and validated for describing the PK features of etimicin sulfate among Chinese healthy participants. The diagnostic goodness-of-fit plots and visual predictive check plots showed that this developed model could describe these data well.

CONCLUSIONS

The PTA results showed that etimicin sulfate provided clinical improvement against strains with an MIC of 0.5-1 mg/L and below, and antibacterial effect against strains with an MIC of 0.25 mg/L and below. However, etimicin sulfate had limited clinical efficacy for clinical isolates with MIC values > 1 mg/L.

Development and validation of two bioanalysis methods for the determination of etimicin in human serum and urine by liquid chromatography-tandem mass spectrometry: Applications to a human pharmacokinetic and breakpoint study

Etimicin is a fourth-generation aminoglycoside antibiotic. It has potent activity and low toxicity when employed for the treatment of Gram-negative and Gram-positive bacterial infections. The pharmacokinetics of etimicin in humans have not been elucidated completely. Two liquid chromatography-tandem mass spectrometry (LC-MS/MS) bioanalytical methods, without the use of any ion-pairing reagents, were developed and validated for the quantification of etimicin in human samples of serum and urine. Using a deuterated reagent as the internal standard, analytes in serum and urine samples were extracted by protein precipitation and dilution before LC-MS/MS analysis, respectively. For the two methods, chromatographic separations were undertaken under isocratic elution of water-ammonia solution-acetic acid (96:3.6:0.2, v/v/v) and methanol at 50%:50% and a flow rate of 0.35 ml/min within 5 min. A Waters XTerra MS C18 column (2.1 × 150 mm, 3.5 μm) and a column temperature of 40°C were chosen. A Sciex Qtrap 5500 mass spectrometer equipped with an electrospray ion source was used in both methods under multiple-reaction monitoring in positive-ion mode. The two methods showed good linearity, accuracy, and precision with high recovery and a minimal matrix effect in the range of 50.0-20000 ng/ml for serum samples and 50.0-10000 ng/ml for urine samples, respectively. Carry-over effects were not observed. Etimicin remained stable in human samples of serum or urine under the storage, preparation, and analytical conditions of the two methods. These two simple and reliable methods were applied successfully to a dose-escalation, phase I clinical trial of etimicin in Chinese healthy volunteers after intravenous administration of single and multiple doses. Based on these two methods we ascertained, for the first time, the comprehensive pharmacokinetics of etimicin in humans, which will be used for the exploration of the breakpoint research further.

A new aminoglycoside etimicin shows low nephrotoxicity and ototoxicity in zebrafish embryos

Aminoglycoside antibiotics are widely used for many life-threatening infections. The use of aminoglycosides is often comprised by their deleterious side effects to the kidney and inner ear. A novel semisynthetic antibiotic, etimicin, has good antimicrobial activity against both gram-positive and gram-negative bacteria. But its toxicity profile analysis is still lacking. In the present study, we compared the in vivo toxic effects of three aminoglycosides, gentamicin, amikacin, and etimicin, in zebrafish embryos. We examined the embryotoxicity, nephrotoxicity, and the damage to the neuromast hair cells. Our results revealed that etimicin and amikacin exhibit more developmental toxicities to the young embryos than gentamicin. But at subtoxic doses, etimicin and amikacin show significantly reduced toxicities towards kidney and neuromast hair cells. We further demonstrated that fluorescently conjugated aminoglycosides (gentamicin-Texas red [GTTR], amikacin-Texas red [AMTR], and etimicin-Texas red [ETTR]) all enter the hair cells properly. Inside the hair cells, gentamicin, not etimicin and amikacin, displays robust reactive oxygen species generation and induces apoptosis. Our data support that the different intracellular cytotoxicity underlies the different ototoxicity of the three aminoglycosides and that etimicin is a new aminoglycoside with reduced risk of nephrotoxicity and ototoxicity.

Exploration of Antibiotic Activity of Aminoglycosides, in Particular Ribostamycin Alone and in Combination With Ethylenediaminetetraacetic Acid Against Pathogenic Bacteria

The emergence of infections caused by bacterial pathogens that are resistant to current antibiotic therapy is a critical healthcare challenge. Aminoglycosides are natural antibiotics with broad spectrum of activity; however, their clinical use is limited due to considerable nephrotoxicity. Moreover, drug-resistant bacteria that cause infections in human as well as livestock are less responsive to conventional antibiotics. Herein, we report the in vitro antibacterial evaluation of five different aminoglycosides, including ribostamycin, against a panel of Gram-positive and Gram-negative pathogens. Eight of the tested bacterial strains are linked to gastrointestinal (GI) infections. The minimum inhibitory concentration (MIC) of ribostamycin against three different Escherichia coli strains is in the range of 0.9–7.2 μM and against a strain of Haemophilus influenzae is 0.5 μM. We also found that the MIC of ribostamycin was considerably enhanced from 57.2 to 7.2 μM, an 8-fold improvement, when bacteria were treated with a combination of ribostamycin and ethylenediaminetetraacetic acid (EDTA). These findings demonstrate a promising approach to enhance the clinical potential of ribostamycin and provide a rational for its antibiotic reclassification from special level to non-restricted level.

Mechanisms and pharmacokinetic/pharmacodynamic profiles underlying the low nephrotoxicity and ototoxicity of etimicin

Etimicin (ETM), a fourth-generation aminoglycosides (AGs), is now widely clinically used in China due to its high efficacy and low toxicity. However, the mechanisms underlying its low nephrotoxicity and ototoxicity remain unclear. In the present study we compared the antibacterial and toxicity profiles of etimicin, gentamicin (GM, a second-generation AG), and amikacin (AMK, a third-generation AG), and investigated their pharmacokinetic properties in the toxicity target organs (kidney and inner ear) and subcellular compartments. We first demonstrated that ETM exhibited superior antibacterial activities against clinical isolates to GM and AMK, and it exerted minimal nephrotoxicity and ototoxicity in rats following multi-dose administration. Then, we conducted pharmacokinetic studies in rats, showed that the three AGs accumulated in the kidney and inner ear with ETM being distributed to a lesser degree in the two toxicity target organs as compared with GM and AMK high-dose groups. Furthermore, we conducted in vitro experiments in NRK-52E rat renal tubular epithelial cells and HEI-OC1 cochlear hair cells, and revealed that all the three AGs were distributed predominantly in the mitochondria with ETM showing minimal accumulation; they not only directly inhibited the activity of mitochondrial complexes IV and V but also inhibited mitochondrial function and its related PGC-1α-NRF1-TFAM pathway; ETM caused minimal damage to the mitochondrial complex and mitochondrial biogenesis. Our results demonstrate that the minimal otonephrotoxicity of ETM results from its lesser accumulation in mitochondria of target cells and subsequently lesser inhibition of mitochondrial function. These results provide a new strategy for discovering novel AGs with high efficacy and low toxicity.

Exclusive Production of Gentamicin C1a from Micromonospora purpurea by Metabolic Engineering

Gentamicin C1a is an important precursor to the synthesis of etimicin, a potent antibiotic. Wild type Micromonospora purpurea Gb1008 produces gentamicin C1a, besides four other gentamicin C components: C1, C2, C2a, and C2b. While the previously reported engineered strain M. purpurea GK1101 can produce relatively high titers of C1a by blocking the genK pathway, a small amount of undesirable C2b is still being synthesized in cells. Gene genL (orf6255) is reported to be responsible for converting C1a to C2b and C2 to C1 in Micromonospora echinospora ATCC15835. In this work, we identify the genL that is also responsible for the same methylation in Micromonospora purpurea. Based on M. purpurea GK1101, we construct a new strain with genL inactivated and show that no C2b is produced in this strain. Therefore, we successfully engineer a strain of M. purpurea that solely produces gentamicin C1a. This strain can potentially be used in the industrial production of C1a for the synthesis of etimicin.

Development and validation of a sensitive LC-MS/MS method without derivatization/ion-pairing agents for etimicin quantification in rat plasma, internal ear and kidney

Etimicin (ETM), which belongs to the newest generation of aminoglycosides (AGs), has been proven to not only maintain but also strengthen the advantages of former AGs with relatively less toxicity. Now, it is widely applied for the treatment of bacterial infections in the clinic. Nevertheless, nephrotoxicity and ototoxicity are unavoidable issues for AGs, and while ETM is no exception, the seriousness of these issues is different. To explore the reason why ETM exhibits less toxicity and to better direct the optimization and development of new AGs, it is of great necessity and importance to monitor the pharmacokinetic behaviors of ETM in its potential toxicity target organs, the kidney and internal ear, as well as in plasma. Therefore, a novel, sensitive and efficient LC-MS/MS method without derivatization or ion-pairing agents had been developed and validated for quantification of ETM in rat plasma, kidney and internal ear for the first time. This method showed good linearity over the range of 50-2000ng/mL for rat plasma/internal ear and 100-5000ng/mL for rat kidney. The precision was less than 4.4% and the accuracy was below 4.8%. Recovery and matrix effects were 71.3%-82.8% and 97.6%-108.5%, respectively. After intravenous administration of a single dose of ETM, plasma drug concentrations fit well with a two-compartmental model, and the AUC_0-∞, t_1/2α, t_1/2β, MRT and CL were 127.96±5.52μg*h/mL, 0.53±0.03h, 3.32±1.11h, 1.01±0.03h and 234.80±10.05mL/h/kg, respectively. Particularly, ETM showed a considerably long half-life in kidney and internal ear, up to 155.96±19.95h and 83.11±26.60h, respectively, which might contribute greatly to its toxicity.