Biocatalysis using Thermostable Cytochrome P450 Enzymes in Bacterial Membranes - Comparison of Metabolic Pathways with Human Liver Microsomes and Recombinant Human Enzymes.

Detailed structural characterization of small molecule metabolites is desirable during all stages of drug development, and often relies on the synthesis of metabolite standards. However, introducing structural changes into already complex, highly functionalized small molecules both regio- and stereo-selectively can be challenging using purely chemical approaches, introducing delays into the drug pipeline. An alternative is to use the cytochrome P450 enzymes (P450s) that produce the metabolites in vivo, taking advantage of the enzyme's inherently chiral active site to achieve regio- and stereoselectivity. Importantly, biotransformations are more sustainable: they proceed under mild conditions and avoid environmentally damaging solvents and transition metal catalysts. Recombinant enzymes avoid the need to use animal liver microsomes. However, native enzymes must be stabilized to work for extended periods or at elevated temperatures, and stabilizing mutations can alter catalytic activity. Here we assessed a set of novel, thermostable P450s in bacterial membranes, a format analogous to liver microsomes, for their ability to metabolize drugs through various pathways and compared them to human liver microsomes. Collectively, the thermostable P450s could replicate the metabolic pathways seen with human liver microsomes, including bioactivation to protein-reactive intermediates. Novel metabolites were found, suggesting the possibility of obtaining metabolites not produced by human or rodent liver microsomes. Importantly, no alteration in assay conditions from standard protocols for microsomal incubations was necessary. Thus, such bacterial membranes represent an analogous metabolite generation system to liver microsomes in terms of metabolites produced and ease of use, but which provides access to more diversity of metabolite structures. SIGNIFICANCE STATEMENT: In drug development it is often chemically challenging, to synthesize authentic metabolites of drug candidates for structural identification and evaluation of activity and safety. Biosynthesis using microsomes or recombinant human enzymes is confounded by the instability of the enzymes. Here we show that thermostable ancestral cytochrome P450 enzymes derived from P450 families responsible for human drug metabolism offer advantages over the native human forms in being more robust and over microbial enzymes in faithfully reflecting human drug metabolism.

Ancestral Sequence Reconstruction of a Cytochrome P450 Family Involved in Chemical Defense Reveals the Functional Evolution of a Promiscuous, Xenobiotic-Metabolizing Enzyme in Vertebrates.

The cytochrome P450 family 1 enzymes (CYP1s) are a diverse family of hemoprotein monooxygenases, which metabolize many xenobiotics including numerous environmental carcinogens. However, their historical function and evolution remain largely unstudied. Here we investigate CYP1 evolution via the reconstruction and characterization of the vertebrate CYP1 ancestors. Younger ancestors and extant forms generally demonstrated higher activity toward typical CYP1 xenobiotic and steroid substrates than older ancestors, suggesting significant diversification away from the original CYP1 function. Caffeine metabolism appears to be a recently evolved trait of the CYP1A subfamily, observed in the mammalian CYP1A lineage, and may parallel the recent evolution of caffeine synthesis in multiple separate plant species. Likewise, the aryl hydrocarbon receptor agonist, 6-formylindolo[3,2-b]carbazole (FICZ) was metabolized to a greater extent by certain younger ancestors and extant forms, suggesting that activity toward FICZ increased in specific CYP1 evolutionary branches, a process that may have occurred in parallel to the exploitation of land where UV-exposure was higher than in aquatic environments. As observed with previous reconstructions of P450 enzymes, thermostability correlated with evolutionary age; the oldest ancestor was up to 35 °C more thermostable than the extant forms, with a 10T50 (temperature at which 50% of the hemoprotein remains intact after 10 min) of 71 °C. This robustness may have facilitated evolutionary diversification of the CYP1s by buffering the destabilizing effects of mutations that conferred novel functions, a phenomenon which may also be useful in exploiting the catalytic versatility of these ancestral enzymes for commercial application as biocatalysts.

Biotransformation of the Novel Myeloperoxidase Inhibitor AZD4831 in Preclinical Species and Humans.

We report herein an in-depth analysis of the metabolism of the novel myeloperoxidase inhibitor AZD4831 ((R)-1-(2-(1-aminoethyl)-4-chlorobenzyl)-2-thioxo-2,3-dihydro-1H-pyrrolo[3,2-d]pyrimidin-4(5H)-one) in animals and human. Quantitative and qualitative metabolite profiling were performed on samples collected from mass balance studies in rats and humans. Exposure of circulating human metabolites with comparable levels in animal species used in safety assessment were also included. Structural characterization of 20 metabolites was performed by liquid chromatography high-resolution mass spectrometry, and quantification was performed by either 14C analysis using solid phase scintillation counting or accelerator mass spectrometry and, where available, authentication with synthesized metabolite standards. A complete mass balance study in rats is presented, while data from dogs and human are limited to metabolite profiling and characterization. The metabolism of AZD4831 is mainly comprised of reactions at the primary amine nitrogen and the thiourea sulfur, resulting in several conjugated metabolites with or without desulfurization. A carbamoyl glucuronide metabolite of AZD4831 (M7) was the most abundant plasma metabolite in both human healthy volunteers and heart failure patients after single and repeated dose administration of AZD4831, accounting for 75%-80% of the total drug-related exposure. Exposures to M7 and other human circulating metabolites were covered in rats and/or dogs, the two models most frequently used in the toxicology studies, and were also highly abundant in the mouse, the second model other than rat used in carcinogenicity studies. The carbamoyl glucuronide M7 was the main metabolite in rat bile, while a desulfurized and cyclized metabolite (M5) was abundant in rat plasma and excreta. SIGNIFICANCE STATEMENT: The biotransformation of AZD4831, a novel myeloperoxidase inhibitor inhibiting xanthine derivative bearing thiourea and primary aliphatic amine functions, is described. Twenty characterized metabolites demonstrate the involvement of carbamoylation with glucuronidation, desulfurization, and cyclization as main biotransformation reactions. The carbamoyl glucuronide was the main metabolite in human plasma, likely governed by a significant species difference in plasma protein binding for this metabolite, but this and other human plasma metabolites were covered in animals used in the toxicity studies.

Application of Accelerator Mass Spectrometry to Characterize the Mass Balance Recovery and Disposition of AZD4831, a Novel Myeloperoxidase Inhibitor, following Administration of an Oral Radiolabeled Microtracer Dose in Humans.

This study evaluated the mass balance and disposition of AZD4831, a novel myeloperoxidase inhibitor, in six healthy participants using a 14C-labeled microtracer coupled with analysis by accelerator mass spectrometry (AMS). A single oral dose of 10 mg 14C-AZD4831 (14.8 kBq) was administered as a solution, and 14C levels were quantified by AMS in blood, urine, and feces over 336 hours postdose. AZD4831 was rapidly absorbed, and AZD4831 plasma concentrations declined in a biphasic manner, with a long half-life of 52 hours. AZD4831 was eliminated via metabolism and renal excretion. An N-carbamoyl glucuronide metabolite of AZD4831 (M7), formed primarily via UGT1A1, was the predominant circulating metabolite. Presumably, M7 contributed to the long half-life of AZD4831 via biliary elimination and hydrolysis/enterohepatic recirculation of AZD4831. On average, ∼84% of administered 14C-AZD4831 was recovered by 336 hours postdose (urine, 51.2%; feces, 32.4%). Between 32%-44% of the dose was excreted as unchanged AZD4831 in urine, indicating renal elimination as the major excretory route. Only 9.7% of overall fecal recovery was recorded in the first 48 hours, with the remainder excreted over 48%-336 hours, suggesting that most fecal recovery was due to biliary elimination. Furthermore, only 6% of unchanged AZD4831 was recovered in feces. Overall, the fraction of the administered AZD4831 dose absorbed was high. 14C-AZD4831 was well tolerated. These findings contribute to increasing evidence that human absorption, distribution, metabolism, and excretion studies can be performed with acceptable mass balance recovery at therapeutically relevant doses and low radiolabel-specific activity using an AMS-14C microtracer approach. SIGNIFICANCE STATEMENT: In this study, the human absorption, distribution, metabolism, and excretion (hADME) of the novel myeloperoxidase inhibitor AZD4831 was assessed following oral administration. This included investigation of the disposition of M7, the N-carbamoyl glucuronide metabolite. Resolution of challenges highlighted in this study contributes to increasing evidence that hADME objectives can be achieved in a single study for compounds with therapeutically relevant doses and low radiolabel-specific activity by using an AMS-14C microtracer approach, thus reducing the need for preclinical radiolabeled studies.

Structural and functional characterization of a specific antidote for ticagrelor.

Ticagrelor is a direct-acting reversibly binding P2Y12 antagonist and is widely used as an antiplatelet therapy for the prevention of cardiovascular events in acute coronary syndrome patients. However, antiplatelet therapy can be associated with an increased risk of bleeding. Here, we present data on the identification and the in vitro and in vivo pharmacology of an antigen-binding fragment (Fab) antidote for ticagrelor. The Fab has a 20 pM affinity for ticagrelor, which is 100 times stronger than ticagrelor's affinity for its target, P2Y12. Despite ticagrelor's structural similarities to adenosine, the Fab is highly specific and does not bind to adenosine, adenosine triphosphate, adenosine 5'-diphosphate, or structurally related drugs. The antidote concentration-dependently neutralized the free fraction of ticagrelor and reversed its antiplatelet activity both in vitro in human platelet-rich plasma and in vivo in mice. Lastly, the antidote proved effective in normalizing ticagrelor-dependent bleeding in a mouse model of acute surgery. This specific antidote for ticagrelor may prove valuable as an agent for patients who require emergency procedures.

Inhibition of SGLT2 Preserves Function and Promotes Proliferation of Human Islets Cells In Vivo in Diabetic Mice.

Dapagliflozin is a sodium-glucose co-transporter 2 (SGLT2) inhibitor used for the treatment of diabetes. This study examines the effects of dapagliflozin on human islets, focusing on alpha and beta cell composition in relation to function in vivo, following treatment of xeno-transplanted diabetic mice. Mouse beta cells were ablated by alloxan, and dapagliflozin was provided in the drinking water while controls received tap water. Body weight, food and water intake, plasma glucose, and human C-peptide levels were monitored, and intravenous arginine/glucose tolerance tests (IVarg GTT) were performed to evaluate islet function. The grafted human islets were isolated at termination and stained for insulin, glucagon, Ki67, caspase 3, and PDX-1 immunoreactivity in dual and triple combinations. In addition, human islets were treated in vitro with dapagliflozin at different glucose concentrations, followed by insulin and glucagon secretion measurements. SGLT2 inhibition increased the animal survival rate and reduced plasma glucose, accompanied by sustained human C-peptide levels and improved islet response to glucose/arginine. SGLT2 inhibition increased both alpha and beta cell proliferation (Ki67+glucagon+ and Ki67+insulin+) while apoptosis was reduced (caspase3+glucagon+ and caspase3+insulin+). Alpha cells were fewer following inhibition of SGLT2 with increased glucagon/PDX-1 double-positive cells, a marker of alpha to beta cell transdifferentiation. In vitro treatment of human islets with dapagliflozin had no apparent impact on islet function. In summary, SGLT2 inhibition supported human islet function in vivo in the hyperglycemic milieu and potentially promoted alpha to beta cell transdifferentiation, most likely through an indirect mechanism.

Functionalized lipid nanoparticles for subcutaneous administration of mRNA to achieve systemic exposures of a therapeutic protein.

Lipid nanoparticles (LNPs) are the most clinically advanced delivery system for RNA-based drugs but have predominantly been investigated for intravenous and intramuscular administration. Subcutaneous administration opens the possibility of patient self-administration and hence long-term chronic treatment that could enable messenger RNA (mRNA) to be used as a novel modality for protein replacement or regenerative therapies. In this study, we show that subcutaneous administration of mRNA formulated within LNPs can result in measurable plasma exposure of a secreted protein. However, subcutaneous administration of mRNA formulated within LNPs was observed to be associated with dose-limiting inflammatory responses. To overcome this limitation, we investigated the concept of incorporating aliphatic ester prodrugs of anti-inflammatory steroids within LNPs, i.e., functionalized LNPs to suppress the inflammatory response. We show that the effectiveness of this approach depends on the alkyl chain length of the ester prodrug, which determines its retention at the site of administration. An unexpected additional benefit to this approach is the prolongation observed in the duration of protein expression. Our results demonstrate that subcutaneous administration of mRNA formulated in functionalized LNPs is a viable approach to achieving systemic levels of therapeutic proteins, which has the added benefits of being amenable to self-administration when chronic treatment is required.

Developing an injectable co-formulation of two antidiabetic drugs: Excipient impact on peptide aggregation and pharmacokinetic properties.

Combination therapy in Type 2 Diabetes Mellitus is necessary to achieve tight glycaemic control and reduce complication risk. Current treatment plans require patients to take several drugs concomitantly leading to low therapy adherence. This study describes the development and characterisation of a stable parenteral co-formulation of a sodium glucose co-transporter 2 inhibitor (dapagliflozin) and a therapeutic lipidated peptide, using hydroxypropyl-ß-cyclodextrin as an enabling excipient. Using NMR, calorimetry, computational modelling and spectroscopic methods, we show that besides increasing the solubility of dapagliflozin, cyclodextrin prevents self-association of the peptide through interaction with the lipid chain and amino acids prone to aggregation including aromatic groups and ionisable residues. While those interactions cause a dramatic secondary structure change, no impact on potency was seen in vitro. A subcutaneous administration of the co-formulation in rat showed that both drugs reach exposure levels previously shown to be efficacious in clinical mono-therapy studies. Interestingly, a faster absorption rate was observed for the peptide formulated within the cyclodextrin vehicle with respect to the buffer vehicle, which could trigger an earlier onset of action. The cyclodextrin based co-formulation is therefore a promising approach to develop a fixed dose combination of a therapeutic peptide and a small molecule drug for increased patient adherence and better blood glucose control.

Quantification of unbound concentration of ticagrelor in plasma as a proof of mechanism biomarker of the reversal agent, MEDI2452.

Ticagrelor, a P2Y12 antagonist, is approved for prevention of thromboembolic events. MEDI2452 is a potential reversal agent for ticagrelor and ticagrelor active metabolite (TAM). The total plasma exposure of ticagrelor and TAM in patients are roughly 0.5-1 and 0.2-0.5 µmol/L, respectively. Both have similar high potency vs. P2Y12 (Ki 2 nmol/L) but are plasma protein-bound to 99.8% and only the 0.2% free fraction is able to inhibit the P2Y12 receptor. Thus, for unbound concentration measurements to be a proof of mechanism biomarker for MEDI2452 a very high sensitivity is required. Using established techniques as equilibrium dialysis and LC-MS/MS, made it possible to evaluate the efficacy of the reversal agent by measuring reduction of unbound concentration of ticagrelor in the presence of MEDI2452. With challenges such as ultra-low concentrations, small sample volumes, recovery issues and adsorption to plastic we managed to develop a highly sensitive assay for determining unbound concentration levels of ticagrelor and TAM in plasma with a quantification limit of 30 pmol/L and 45 pmol/L, respectively. With this method we were able to detect close to a 100-fold MEDI2452 mediated reduction in the unbound concentration of both ticagrelor and TAM. The assay provided proof of mechanism as MEDI2452 concentration- and dose-dependently eliminated unbound concentration of ticagrelor and reversed its antiplatelet activity in preclinical models and will support future development of MEDI2452.