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

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.

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.