Solubility and Stability Enhanced Oral Formulations for the Anti-Infective Corallopyronin A

A laboratory-based predictive pathway for the development of Neisseria gonorrhoeae high-level resistance to corallopyronin A, an inhibitor of bacterial RNA polymerase

The continued emergence of Neisseria gonorrhoeae strains that express resistance to multiple antibiotics, including the last drug for empiric monotherapy (ceftriaxone), necessitates the development of new treatment options to cure gonorrheal infections. Toward this goal, we recently reported that corallopyronin A (CorA), which targets the switch region of the β' subunit (RpoC) of bacterial DNA-dependent RNA polymerase (RNAP), has potent anti-gonococcal activity against a panel of multidrug-resistant clinical strains. Moreover, in that study, CorA could eliminate gonococcal infection of primary human epithelial cells and gonococci in a biofilm state. To determine if N. gonorrhoeae could develop high-level resistance to CorA in a single step, we sought to isolate spontaneous mutants expressing any CorA resistance phenotypes. However, no single-step mutants with high-level CorA resistance were isolated. High-level CorA resistance could only be achieved in this study through a multi-step pathway involving over-expression of the MtrCDE drug efflux pump and single amino acid changes in the β and β' subunits (RpoB and RpoC, respectively) of RNAP. Molecular modeling of RpoB and RpoC interacting with CorA was used to deduce how the amino acid changes in RpoB and RpoC could influence gonococcal resistance to CorA. Bioinformatic analyses of whole genome sequences of clinical gonococcal isolates indicated that the CorA resistance determining mutations in RpoB/C, identified herein, are very rare (≤ 0.0029%), suggesting that the proposed pathway for resistance is predictive of how this phenotype could potentially evolve if CorA is used therapeutically to treat gonorrhea in the future.

IMPORTANCE

The continued emergence of multi-antibiotic-resistant strains of Neisseria gonorrhoeae necessitates the development of new antibiotics that are effective against this human pathogen. We previously described that the RNA polymerase-targeting antibiotic corallopyronin A (CorA) has potent activity against a large collection of clinical strains that express different antibiotic resistance phenotypes including when such gonococci are in a biofilm state. Herein, we tested whether a CorA-sensitive gonococcal strain could develop spontaneous resistance. Our finding that CorA resistance could only be achieved by a multi-step process involving over-expression of the MtrCDE efflux pump and single amino acid changes in RpoB and RpoC suggests that such resistance may be difficult for gonococci to evolve if this antibiotic is used in the future to treat gonorrheal infections that are refractory to cure by other antibiotics.

ASDs of PROTACs: Spray-dried solid dispersions as enabling formulations

Proteolysis targeting chimeras (PROTACs) are a promising class of pharmaceutical agents with a unique mode of action. PROTACs enable the targeting of a broad variety of structures including transcription factors and other "undruggable" targets. The poor solubility and slow dissolution of PROTACs currently limit the extensive use of their potential. Up to date, only very limited drug delivery options have been examined to address this challenge. Therefore, we explored the potential of amorphous solid dispersions (ASDs) by spray drying a model PROTAC with different polymers. The resulting formulations were assessed in terms of purity, solid state, dissolution performance, and stability. A strong increase in supersaturation compared to the physical mixture was provided, although in both systems the PROTAC molecule itself was already in the amorphous state. Evaluation of the reasons for the superiority of the ASD formulations revealed that the major factor was the homogeneous, molecular distribution of the active pharmaceutical ingredient (API) in the polymer matrix, as well as improved wettability of the formulation containing Soluplus compared to the physical mixture. The manufactured formulations were stable over a minimum of 8 weeks when protected from light and humidity.

Solubility Enhanced Formulation Approaches to Overcome Oral Delivery Obstacles of PROTACs

PROteolysis TArgeting Chimaeras (PROTACs) offer new opportunities in modern medicine by targeting proteins that are undruggable to classic inhibitors. However, due to their hydrophobic structure, PROTACs typically suffer from low solubility, and oral bioavailability remains challenging. At the same time, due to their investigative state, the drug supply is meager, leading to limited possibilities in terms of formulation development. Therefore, we investigated the solubility enhancement employing mini-scale formulations of amorphous solid dispersions (ASDs) and liquisolid formulations of the prototypic PROTAC ARCC-4. Based on preliminary supersaturation testing, HPMCAS (L Grade) and Eudragit^® L 100-55 (EL 100-55) were demonstrated to be suitable polymers for supersaturation stabilization of ARCC-4. These two polymers were selected for preparing ASDs via vacuum compression molding (VCM), using drug loads of 10 and 20%, respectively. The ASDs were subsequently characterized with respect to their solid state via differential scanning calorimetry (DSC). Non-sink dissolution testing revealed that the physical mixtures (PMs) did not improve dissolution. At the same time, all ASDs enabled pronounced supersaturation of ARCC-4 without precipitation for the entire dissolution period. In contrast, liquisolid formulations failed in increasing ARCC-4 solubility. Hence, we demonstrated that ASD formation is a promising principle to overcome the low solubility of PROTACs.

Pharmacokinetics and Pharmacodynamics (PK/PD) of Corallopyronin A against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a World Health Organization’s high priority pathogen organism, with an estimated > 100,000 deaths worldwide in 2019. Thus, there is an unmet medical need for novel and resistance-breaking anti-infectives. The natural product Co-rallopyronin A (CorA), currently in preclinical development for filariasis, is efficacious against MRSA in vitro. In this study, we evaluated the pharmacokinetics of CorA after dosing in mice. Furthermore, we determined compound concentrations in target compartments, such as lung, kidney and thigh tissue, using LC-MS/MS. Based on the pharmacokinetic results, we evaluated the pharmacodynamic profile of CorA using the standard neutropenic thigh and lung infection models. We demonstrate that CorA is effective in both standard pharmacodynamic models. In addition to reaching effective levels in the lung and muscle, CorA was detected at high levels in the thigh bone. The data presented herein encourage the further exploration of the additional CorA indications treatment of MRSA- and methicillin-sensitive S. aureus- (MSSA) related infections.

Potent In Vitro and Ex Vivo Anti-Gonococcal Activity of the RpoB Inhibitor Corallopyronin A

Gonorrhea remains a major global public health problem because of the high incidence of infection (estimated 82 million cases in 2020) and the emergence and spread of Neisseria gonorrhoeae strains resistant to previous and current antibiotics used to treat infections. Given the dearth of new antibiotics that are likely to enter clinical practice in the near future, there is concern that cases of untreatable gonorrhea might emerge. In response to this crisis, the World Health Organization (WHO), in partnership with the Global Antibiotic Research and Development Partnership (GARDP), has made the search for and development of new antibiotics against N. gonorrhoeae a priority. Ideally, these antibiotics should also be active against other sexually transmitted organisms, such as Chlamydia trachomatis and/or Mycoplasma genitalium, which are often found with N. gonorrhoeae as co-infections. Corallopyronin A is a potent antimicrobial that exhibits activity against Chlamydia spp. and inhibits transcription by binding to the RpoB switch region. Accordingly, we tested the effectiveness of corallopyronin A against N. gonorrhoeae. We also examined the mutation frequency and modes of potential resistance against corallopyronin A. We report that corallopyronin A has potent antimicrobial action against antibiotic-susceptible and antibiotic-resistant N. gonorrhoeae strains and could eradicate gonococcal infection of cultured, primary human cervical epithelial cells. Critically, we found that spontaneous corallopyronin A-resistant mutants of N. gonorrhoeae are exceedingly rare (≤10^-10) when selected at 4× the MIC. Our results support pre-clinical studies aimed at developing corallopyronin A for gonorrheal treatment regimens. IMPORTANCE The high global incidence of gonorrhea, the lack of a protective vaccine, and the emergence of N. gonorrhoeae strains expressing resistance to currently used antibiotics demand that new treatment options be developed. Accordingly, we investigated whether corallopyronin A, an antibiotic which is effective against other pathogens, including C. trachomatis, which together with gonococci frequently cause co-infections in humans, could exert anti-gonococcal action in vitro and ex vivo, and potential resistance emergence. We propose that corallopyronin A be considered a potential future treatment option for gonorrhea because of its potent activity, low resistance development, and recent advances in scalable production.

Pharmacology and early ADMET data of corallopyronin A, a natural product with macrofilaricidal anti-wolbachial activity in filarial nematodes

Corallopyronin A (CorA), a natural product antibiotic of Corallococcus coralloides, inhibits the bacterial DNA-dependent RNA polymerase. It is active against the essential Wolbachia endobacteria of filarial nematodes, preventing development, causing sterility and killing adult worms. CorA is being developed to treat the neglected tropical diseases onchocerciasis and lymphatic filariasis caused by Wolbachia-containing filariae. For this, we have completed standard Absorption, Distribution, Metabolism, Excretion and Toxicity (ADMET) studies. In Caco-2 assays, CorA had good adsorption values, predicting good transport from the intestines, but may be subject to active efflux. In fed-state simulated human intestinal fluid (pH 5.0), CorA half-life was >139 minutes, equivalent to the stability in buffer (pH 7.4). CorA plasma-stability was >240 minutes, with plasma protein binding >98% in human, mouse, rat, dog, mini-pig and monkey plasma. Clearance in human and dog liver microsomes was low (35.2 and 42 µl/min/mg, respectively). CorA was mainly metabolized via phase I reactions, i.e., oxidation, and to a minimal extent via phase II reactions. In contrast to rifampicin, CorA does not induce CYP3A4 resulting in a lower drug-drug-interaction potential. Apart from inhibition of CYP2C9, no impact of CorA on enzymes of the CYP450 system was detected. Off-target profiling resulted in three hits (inhibition/activation) for the A3 and PPARγ receptors and COX1 enzyme; thus, potential drug-drug interactions could occur with antidiabetic medications, COX2 inhibitors, angiotensin AT1 receptor antagonists, vitamin K-antagonists, and antidepressants. In vivo pharmacokinetic studies in Mongolian gerbils and rats demonstrated excellent intraperitoneal and oral bioavailability (100%) with fast absorption and high distribution in plasma. No significant hERG inhibition was detected and no phototoxicity was seen. CorA did not induce gene mutations in bacteria (Ames test) nor chromosomal damage in human lymphocytes (micronucleus test). Thus, CorA possesses an acceptable in vitro early ADMET profile; supported by previous in vivo experiments in mice, rats and Mongolian gerbils in which all animals tolerated CorA daily administration for 7-28 days. The non-GLP package will guide selection and planning of regulatory-conform GLP models prior to a first-into-human study.

In Vitro–In Vivo Relationship in Mini-Scale—Enabling Formulations of Corallopyronin A

In vivo studies in mice provide a valuable model to test novel active pharmaceutical ingredients due to their low material need and the fact that mice are frequently used as a species for early efficacy models. However, preclinical in vitro evaluations of formulation principles in mice are still lacking. The development of novel in vitro and in silico models supported the preclinical formulation evaluation for the anti-infective corallopyronin A (CorA). To this end, CorA and solubility-enhanced amorphous solid dispersion formulations, comprising povidone or copovidone, were evaluated regarding biorelevant solubilities and dissolution in mouse-specific media. As an acidic compound, CorA and CorA-ASD formulations showed decreased solubilities in mice when compared with human-specific media. In biorelevant biphasic dissolution experiments CorA-povidone showed a three-fold higher fraction partitioned into the organic phase of the biphasic dissolution, when compared with CorA-copovidone. Bioavailabilities determined by pharmacokinetic studies in BALB/c mice correlated with the biphasic dissolution prediction and resulted in a Level C in vitro–in vivo correlation. In vitro cell experiments excluded intestinal efflux by P-glycoprotein or breast cancer resistance protein. By incorporating in vitro results into a physiologically based pharmacokinetic model, the plasma concentrations of CorA-ASD formulations were predicted and identified dissolution as the limiting factor for bioavailability.

The RNA Polymerase Inhibitor Corallopyronin A Has a Lower Frequency of Resistance Than Rifampicin in Staphylococcus aureus

Corallopyronin A (CorA) is active against Gram-positive bacteria and targets the switch region of RNA polymerase. Because of the high frequency of mutation (FoM) leading to rifampicin resistance, we determined the CorA FoM in S. aureus using fluctuation analysis at 4 × minimum inhibitory concentration (MIC). Resistant mutants were characterized. S. aureus strains HG001, Mu50, N315, and USA300 had an MIC of 0.25 mg/L. The median FoM for CorA resistance was 1.5 × 10−8, 4.5-fold lower than the median FoM of 6.7 × 10−8 for rifampicin, and was reflected in a 4-fold lower mutation rate for CorA than rifampicin (6 × 10−9 for CorA vs. 2.5 × 10−8 for rifampicin). In CorA-resistant/rifampicin-sensitive strains, the majority of amino acid exchanges were S1127L in RpoB or K334N in RpoC. S. aureus Mu50, a rifampicin-resistant clinical isolate, yielded two further exchanges targeting amino acids L1131 and E1048 of the RpoB subunit. The plating of >1011 cells on agar containing a combination of 4 × MIC of rifampicin and 4 × MIC of CorA did not yield any growth. In conclusion, with proper usage, e.g., in combination therapy and good antibiotic stewardship, CorA is a potential antibiotic for treating S. aureus infections.

Corallopyronin A: antimicrobial discovery to preclinical development

Covering: August 1984 up to January 2022Worldwide, increasing morbidity and mortality due to antibiotic-resistant microbial infections has been observed. Therefore, better prevention and control of infectious diseases, as well as appropriate use of approved antibacterial drugs are crucial. There is also an urgent need for the continuous development and supply of novel antibiotics. Thus, identifying new antibiotics and their further development is once again a priority of natural product research. The antibiotic corallopyronin A was discovered in the 1980s in the culture broth of the Myxobacterium Corallococcus coralloides and serves, in the context of this review, as a show case for the development of a naturally occurring antibiotic compound. The review demonstrates how a hard to obtain, barely water soluble and unstable compound such as corallopyronin A can be developed making use of sophisticated production and formulation approaches. Corallopyronin A is a bacterial DNA-dependent RNA polymerase inhibitor with a new target site and one of the few representatives of this class currently in preclinical development. Efficacy against Gram-positive and Gram-negative pathogens, e.g., Chlamydia trachomatis, Orientia tsutsugamushi, Staphylococcus aureus, and Wolbachia has been demonstrated. Due to its highly effective in vivo depletion of Wolbachia, which are essential endobacteria of most filarial nematode species, and its robust macrofilaricidal efficacy, corallopyronin A was selected as a preclinical candidate for the treatment of human filarial infections. This review highlights the discovery and production optimization approaches for corallopyronin A, as well as, recent preclinical efficacy results demonstrating a robust macrofilaricidal effect of the anti-Wolbachia candidate, and the solid formulation strategy which enhances the stability as well as the bioavailability of corallopyronin A.

Beyond the approved: target sites and inhibitors of bacterial RNA polymerase from bacteria and fungi

Covering: 2016 to 2022RNA polymerase (RNAP) is the central enzyme in bacterial gene expression representing an attractive and validated target for antibiotics. Two well-known and clinically approved classes of natural product RNAP inhibitors are the rifamycins and the fidaxomycins. Rifampicin (Rif), a semi-synthetic derivative of rifamycin, plays a crucial role as a first line antibiotic in the treatment of tuberculosis and a broad range of bacterial infections. However, more and more pathogens such as Mycobacterium tuberculosis develop resistance, not only against Rif and other RNAP inhibitors. To overcome this problem, novel RNAP inhibitors exhibiting different target sites are urgently needed. This review includes recent developments published between 2016 and today. Particular focus is placed on novel findings concerning already known bacterial RNAP inhibitors, the characterization and development of new compounds isolated from bacteria and fungi, and providing brief insights into promising new synthetic compounds.

In vitro and in vivo assessment of hydroxypropyl cellulose as functional additive for enabling formulations containing itraconazole

Using polymers as additives to formulate ternary amorphous solid dispersions (ASDs) has successfully been established to increase the bioavailability of poorly soluble drugs, when one polymer is not able to provide both, stabilizing the drug in the matrix and the supersaturated solution. Therefore, we investigated the influence of low-viscosity hydroxypropyl cellulose (HPC) polymers as an additive in HPMC based ternary ASD formulations made by hot-melt extrusion (HME) on the bioavailability of itraconazole (ITZ). The partitioning potential of the different HPC grades was screened in biphasic supersaturation assays. Solid-state analytics were performed using differential scanning calorimetry (DSC), X-ray powder diffraction (XRPD). The addition of HPCs, especially HPC-UL, resulted in a superior partitioned amount of ITZ in biphasic supersaturation assays. Moreover, the approach in using HPCs as an additive in HPMC based ASDs led to an increase in partitioned ITZ compared to Sporanox® in biorelevant biphasic dissolution studies. The results from the biphasic dissolution experiments correlated well with the in vivo studies, which revealed the highest oral bioavailability for the ternary ASD comprising HPC-UL and HPMC.

•

Increased partitioning rate of itraconazole using low-viscosity HPC polymers.

•

Enhanced bioavailability of itraconazole using HPC-UL as functional additive.

•

Ternary amorphous solid dispersion with higher performance than Sporanox®.

Heterologous Expression of Pseudouridimycin and Description of the Corresponding Minimal Biosynthetic Gene Cluster

Pseudouridimycin (PUM) was recently discovered from Streptomyces sp. DSM26212 as a novel bacterial nucleoside analog that competes with UTP for access to the RNA polymerase (RNAP) active site, thereby inhibiting bacterial RNAP by blocking transcription. This represents a novel antibacterial mode of action and it is known that PUM inhibits bacterial RNAP in vitro, inhibits bacterial growth in vitro, and was active in vivo in a mouse infection model of Streptococcus pyogenes peritonitis. The biosynthetic gene cluster (BGC) was previously identified and characterized by knockout experiments. However, the minimal set of genes necessary for PUM production was not proposed. To identify the minimal BGC and to create a plug-and-play production platform for PUM and its biosynthetic precursors, several versions of a redesigned PUM BGC were generated and expressed in the heterologous host Streptomyces coelicolor M1146 under control of strong promotors. Heterologous expression allowed identification of the putative serine/threonine kinase PumF as an enzyme essential for heterologous PUM production and thus corroboration of the PUM minimal BGC.