Bioactivation and reactivity research advances - 2021 year in review.

This year's review on bioactivation and reactivity began as a part of the annual review on biotransformation and bioactivation led by Cyrus Khojasteh (see references). Increased contributions from experts in the field led to the development of a stand alone edition for the first time this year focused specifically on bioactivation and reactivity. Our objective for this review is to highlight and share articles which we deem influential and significant regarding the development of covalent inhibitors, mechanisms of reactive metabolite formation, enzyme inactivation, and drug safety. Based on the selected articles, we created two sections: (1) reactivity and enzyme inactivation, and (2) bioactivation mechanisms and safety (Table 1). Several biotransformation experts have contributed to this effort from academic and industry settings.[Table: see text].

Novel advances in biotransformation and bioactivation research - 2020 year in review.

This annual review is the sixth of its kind since 2016 (see references). Our objective is to explore and share articles which we deem influential and significant in the field of biotransformation and bioactivation. These fields are constantly evolving with new molecular structures and discoveries of corresponding pathways for metabolism that impact relevant drug development with respect to efficacy and safety. Based on the selected articles, we created three sections: (1) drug design, (2) metabolites and drug metabolizing enzymes, and (3) bioactivation and safety (Table 1). Unlike in years past, more biotransformation experts have joined and contributed to this effort while striving to maintain a balance of authors from academic and industry settings.[Table: see text].

Preclinical in vitro and in vivo pharmacokinetic properties of danicamtiv, a new targeted myosin activator for the treatment of dilated cardiomyopathy.

Dilated cardiomyopathy (DCM) is a disease of the myocardium defined by left ventricular enlargement and systolic dysfunction leading to heart failure. Danicamtiv, a new targeted myosin activator designed for the treatment of DCM, was characterised in in vitro and in vivo preclinical studies. Danicamtiv human hepatic clearance was predicted to be 0.5 mL/min/kg from in vitro metabolic stability studies in human hepatocytes. For human, plasma protein binding was moderate with a fraction unbound of 0.16, whole blood-to-plasma partitioning ratio was 0.8, and danicamtiv showed high permeability and no efflux in a Caco-2 cell line. Danicamtiv metabolism pathways in vitro included CYP-mediated amide-cleavage, N-demethylation, as well as isoxazole- and piperidine-ring-opening. Danicamtiv clearance in vivo was low across species with 15.5, 15.3, 1.6, and 5.7 mL/min/kg in mouse, rat, dog, and monkey, respectively. Volume of distribution ranged from 0.24 L/kg in mouse to 1.7 L/kg in rat. Oral bioavailability ranged from 26% in mouse to 108% in dog. Simple allometric scaling prediction of human plasma clearance, volume of distribution, and half-life was 0.64 mL/min/kg, 0.98 L/kg, and 17.7 h, respectively. Danicamtiv preclinical attributes and predicted human pharmacokinetics supported advancement toward clinical development.

A prospective, iterative, adaptive trial of carfilzomib-based desensitization.

Proteasome inhibitor-based strategies hold promise in transplant but have yielded varying results. Carfilzomib, a second-generation proteasome inhibitor, may possess advantages over bortezomib, the first-generation proteasome inhibitors. The purpose of this study was to evaluate the safety, toxicity, and preliminary efficacy of carfilzomib in highly HLA-sensitized kidney transplant candidates. Renal transplant candidates received escalating doses of carfilzomib followed by plasmapheresis (group A) or an identical regimen with additional plasmapheresis once weekly before carfilzomib dosing. Thirteen participants received carfilzomib, which was well tolerated with most adverse events classified as low grade. The safety profile was similar to bortezomib desensitization; however, neurotoxicity was not observed with carfilzomib. Toxicity resulted in permanent dose reduction in 1 participant but caused no withdrawals or deaths. HLA antibodies were substantially reduced with carfilzomib alone, and median maximal immunodominant antibody reduction was 72.8% (69.8% for group A, P = .031, 80.1% for group B, P = .938). After depletion, rebound occurred rapidly and antibody levels returned to baseline between days 81 and 141. Bone marrow studies revealed that approximately 69.2% of plasma cells were depleted after carfilzomib monotherapy. Carfilzomib monotherapy-based desensitization provides an acceptable safety and toxicity profile while leading to significant bone marrow plasma cell depletion and anti-HLA antibody reduction.

Proteasomal adaptations underlying carfilzomib-resistance in human bone marrow plasma cells.

Donor-specific antibodies (DSAs) have a deleterious effect on allografts and remain a major immunologic barrier in transplantation. Current therapies to eliminate DSAs are ineffective in highly HLA-sensitized patients. Proteasome inhibitors have been employed as a strategy to target bone marrow plasma cells (BMPCs), the source of long-term antibody production; however, their efficacy has been limited by poorly defined drug-resistance mechanisms. Here, we performed transcriptomic profiling of CD138+ BMPCs that survived in vivo desensitization therapy with the proteasome inhibitor carfilzomib to identify mechanisms of drug resistance. The results revealed a genomic signature that included increased expression of the immunoproteasome, a highly specialized proteasomal variant. Western blotting and functional studies demonstrated that catalytically active immunoproteasomes and the immunoproteasome activator PA28 were upregulated in carfilzomib-resistant BMPCs. Carfilzomib-resistant BMPCs displayed reduced sensitivity to the proteasome inhibitors carfilzomib, bortezomib, and ixazomib, but enhanced sensitivity to an immunoproteasome-specific inhibitor ONX-0914. Finally, in vitro carfilzomib treatment of BMPCs from HLA-sensitized patients increased levels of the immunoproteasome ß5i (PSMB8) catalytic subunit suggesting that carfilzomib therapy directly induces an adaptive immunoproteasome response. Taken together, our results indicate that carfilzomib induces structural changes in proteasomes and immunoproteasome formation.

Novel advances in biotransformation and bioactivation research-2019 year in review.

Biotransformation is one of the main mechanisms used by the body to eliminate drugs. As drug molecules become more complicated, the involvement of drug metabolizing enzymes increases beyond those that are typically studied, such as the cytochrome P450 enzymes. In this review, we try to capture the many outstanding articles that were published in the past year in the field of biotransformation (see Table 1). We have divided the articles into two categories of (1) metabolites and drug metabolizing enzymes, and (2) bioactivation and safety. This annual review is the fifth of its kind since 2016 (Baillie et al. 2016; Khojasteh et al. 2017, 2018, 2019). This effort in itself also continues to evolve. We have followed the same format we used in previous years in terms of the selection of articles and the authoring of each section. I am pleased of the continued support of Rietjens, Miller, Zhang, Driscoll and Mitra to this review. We would like to welcome Klarissa D. Jackson as a new author for this year's issue. We strive to maintain a balance of authors from academic and industry settings. We would be pleased to hear your opinions of our commentary, and we extend an invitation to anyone who would like to contribute to a future edition of this review. Cyrus Khojasteh, on behalf of the authors.

Metabolite Profiling and Reaction Phenotyping for the in Vitro Assessment of the Bioactivation of Bromfenac †.

Bromfenac is a nonsteroidal anti-inflammatory drug that was approved and subsequently withdrawn from the market because of reported cases of acute hepatotoxicity. Recently, in vitro studies have revealed that bromfenac requires UDPGA and alamethicin supplemented human liver microsomes (HLM) to form a major metabolite, bromfenac indolinone (BI). Bromfenac and BI form thioether adducts through a bioactivation pathway in HLM and hepatocytes. [J. P. Driscoll et al., Chem. Res. Toxicol. 2018, 31, 223-230.] Here, Cytochrome P450 (CYP) and UDP-glucuronosyltransferase (UGT) reaction phenotyping experiments using recombinant enzymes were performed on bromfenac and BI to identify the CYP and UGT enzymes responsible for bromfenac's metabolism and bioactivation. It was determined that UGT2B7 converts bromfenac to BI, and that while CYP2C8, CYP2C9, and CYP2C19 catalyze the hydroxylation of bromfenac, only CYP2C9 forms thioether adducts when incubated with NAC or GSH as trapping agents. Although CYP2C9 was shown to form a reactive intermediate, no inhibition of CYP2C9 was observed when an IC50 shift assay was performed. Reaction phenotyping experiments with BI and recombinant CYP enzymes indicated that CYPs 1A2, 2B6, 2C8, 2C9, 2C19, 2D6, and 3A4 were responsible for the formation of an aliphatic hydroxylated metabolite. An aromatic hydroxylation on the indolinone moiety was also formed by CYP1A2 and CYP3A4. The aromatic hydroxylated BI is a precursor to the quinone methide and quinone imine intermediates in the proposed bioactivation pathway. Through time-dependent inhibition (TDI) experiments, it was revealed that BI can cause an IC50 shift in CYP1A2 and CYP3A4. However, BI does not inhibit the other isoforms that were also responsible for the formation of the aliphatic hydroxylation, an alternative biotransformation that does not undergo further downstream bioactivation. The results of these metabolism studies with bromfenac and BI add to our understanding of the relationship between biotransformation, reactive intermediate generation, and a potential mechanistic link to the hepatotoxicity of this compound.

Serum electrolyte dynamics in multiple myeloma patients undergoing autologous haematopoietic stem cell transplantation.

AIM: High-dose melphalan followed by autologous haematopoietic cell transplantation remains the standard-of-care therapy for multiple myeloma (MM). Gastrointestinal toxicity concomitant with electrolyte derangement is a primary cause of morbidity from transplant. Here, we assessed the dynamics of electrolyte imbalances and its role in hematologic counts and engraftment. Ω Patients and Methods One hundred and eighteen MM patients that received transplant were studied. RESULTS: Engraftment speed (ES) was calculated as the period between the first rise in the absolute neutrophil count (ANC) and full engraftment defined as the first of three consecutive days with ANC > 500 × 106 /L. The defined median ES was 2 days (range 0-5 days) and 40 patients had ES ≤2 days. Engraftment occurred at a median of 10 days. The median time-to-nadir for phosphorus and potassium was 10 and 4.28 days, respectively. The drop in phosphorus and potassium serum level was statistically greater in patients with an ES ≤2 days compared to patients with ES ≥2 days. Magnesium level were not significantly affected and there was no significant difference between the drop in serum phosphorus and potassium based on severity of nausea or oral mucositis. CONCLUSION: Our results indicate that there is a significant correlation between the magnitude of drop in potassium and phosphorous levels and a steep rise in neutrophil counts around the engraftment period following stem cell transplant. These events indicate a "genesis syndrome" characterized by a rapid, massive transfer of electrolytes into proliferating cells as has been previously described after HCT for certain high-grade lymphomas and leukemias.

Biotransformation and bioactivation reactions - 2018 literature highlights.

In the past three decades, ADME sciences have become an integral component of the drug discovery and development process. At the same time, the field has continued to evolve, thus, requiring ADME scientists to be knowledgeable of and engage with diverse aspects of drug assessment: from pharmacology to toxicology, and from in silico modeling to in vitro models and finally in vivo models. Progress in this field requires deliberate exposure to different aspects of ADME; however, this task can seem daunting in the current age of mass information. We hope this review provides a focused and brief summary of a wide array of critical advances over the past year and explains the relevance of this research ( Table 1 ). We divided the articles into categories of (1) drug optimization, (2) metabolites and drug metabolizing enzymes, and (3) bioactivation. This annual review is the fourth of its kind (Baillie et al. 2016 ; Khojasteh et al. 2017 , 2018 ). We have followed the same format we used in previous years in terms of the selection of articles and the authoring of each section. This effort in itself also continues to evolve. I am pleased that Rietjens, Miller, and Mitra have again contributed to this annual review. We would like to welcome Namandjé N. Bumpus, James P. Driscoll, and Donglu Zhang as authors for this year's issue. We strive to maintain a balance of authors from academic and industry settings. We would be pleased to hear your opinions of our commentary, and we extend an invitation to anyone who would like to contribute to a future edition of this review. Cyrus Khojasteh, on behalf of the authors.

In vitro and in vivo pharmacokinetic characterization of mavacamten, a first-in-class small molecule allosteric modulator of beta cardiac myosin.

Mavacamten is a small molecule modulator of cardiac myosin designed as an orally administered drug for the treatment of patients with hypertrophic cardiomyopathy. The current study objectives were to assess the preclinical pharmacokinetics of mavacamten for the prediction of human dosing and to establish the potential need for clinical pharmacokinetic studies characterizing drug-drug interaction potential. Mavacamten does not inhibit CYP enzymes, but at high concentrations relative to anticipated therapeutic concentrations induces CYP2B6 and CYP3A4 enzymes in vitro. Mavacamten showed high permeability and low efflux transport across Caco-2 cell membranes. In human hepatocytes, mavacamten was not a substrate for drug transporters OATP, OCT and NTCP. Mavacamten was determined to have minimal drug-drug interaction risk. In vitro mavacamten metabolite profiles included phase I- and phase II-mediated metabolism cross-species. Major pathways included aromatic hydroxylation (M1), aliphatic hydroxylation (M2); N-dealkylation (M6), and glucuronidation of the M1-metabolite (M4). Reaction phenotyping revealed CYPs 2C19 and 3A4/3A5 predominating. Mavacamten demonstrated low clearance, high volume of distribution, long terminal elimination half-life and excellent oral bioavailability cross-species. Simple four-species allometric scaling led to predicted plasma clearance, volume of distribution and half-life of 0.51 mL/min/kg, 9.5 L/kg and 9 days, respectively, in human.

Emerging small molecule approaches to enhance the antimyeloma benefit of proteasome inhibitors.

Multiple myeloma (MM) is a clonal plasma cell malignancy which, despite recent treatment advances, remains incurable in the vast majority of the over 118,000 patients in the USA afflicted with this disease. Treatment of MM has dramatically improved in the past decade with the introduction of new drugs into therapeutic strategies in both the frontline and relapse settings that has led to a significant improvement in the median overall survival (OS). These drugs have been incorporated into clinical guidelines and transformed the treatment approach to MM. Numerous classes of antimyeloma agents, i.e., alkylators, steroids, proteasome inhibitors, immunomodulatory agents, deactylase inhibitors, and monoclonal antibodies, are now FDA-approved and can be combined in doublet or triplet regimens. Moreover, many patients do not respond to therapy and those that do eventually relapse. Emerging therapies that may overcome drug resistance and improve MM treatment include that inhibit regulatory and Ub-processing components of the proteasome, a specialized variant of the proteasome known as the immunoproteasome, proteolysis-targeting chimeric molecules (PROTACS and Degronomids). Emerging strategies also include accessory plasmacytoid dendritic cells (pDCs), vaccines, checkpoint inhibitors, and chimeric antigen receptor-engineered T (CAR-T) cells. Advances in understanding proteasome and plasma cell biology may allow for earlier treatment of MM patients using rationally informed combination therapies with curative potential.

Role of Glucuronidation and P450 Oxidation in the Bioactivation of Bromfenac.

Bromfenac is a nonsteroidal anti-inflammatory drug that was approved in the United States in 1997. It was withdrawn from clinical use less than one year later, in 1998, due to hepatotoxicity. We investigate the potential of bromfenac to be metabolized to reactive intermediates to further the current understanding of bromfenac bioactivation. Incubations were conducted with hepatocytes and human, rat, and cynomolgus liver microsomes fortified with cofactors and N-acetylcysteine. One thioether adduct of hydroxylated bromfenac and three thioether adducts of hydroxylated bromfenac indolinone were detected in extracts following incubations in liver microsomes fortified with NADPH and UDPGA. These findings demonstrate a bioactivation pathway for bromfenac and contribute to the body of evidence that could advance the understanding of the toxicity associated with bromfenac.

Inhibitory Effects of Trapping Agents of Sulfur Drug Reactive Intermediates against Major Human Cytochrome P450 Isoforms.

In some cases, the formation of reactive species from the metabolism of xenobiotics has been linked to toxicity and therefore it is imperative to detect potential bioactivation for candidate drugs during drug discovery. Reactive species can covalently bind to trapping agents in in vitro incubations of compound with human liver microsomes (HLM) fortified with ß-nicotinamide adenine dinucleotide phosphate (NADPH), resulting in a stable conjugate of trapping agent and reactive species, thereby facilitating analytical detection and providing evidence of short-lived reactive metabolites. Since reactive metabolites are typically generated by cytochrome P450 (CYP) oxidation, it is important to ensure high concentrations of trapping agents are not inhibiting the activities of CYP isoforms. Here we assessed the inhibitory properties of fourteen trapping agents against the major human CYP isoforms (CYP1A2, 2C9, 2C19, 2D6 and 3A). Based on our findings, eleven trapping agents displayed inhibition, three of which had IC50 values less than 1 mM (2-mercaptoethanol, N-methylmaleimide and N-ethylmaleimide (NEM)). Three trapping agents (dimedone, N-acetyl-lysine and arsenite) did not inhibit CYP isoforms at concentrations tested. To illustrate effects of CYP inhibition by trapping agents on reactive intermediate trapping, an example drug (ticlopidine) and trapping agent (NEM) were chosen for further studies. For the same amount of ticlopidine (1 µM), increasing concentrations of the trapping agent NEM (0.007-40 mM) resulted in a bell-shaped response curve of NEM-trapped ticlopidine S-oxide (TSO-NEM), due to CYP inhibition by NEM. Thus, trapping studies should be designed to include several concentrations of trapping agent to ensure optimal trapping of reactive metabolites.

Going Beyond Common Drug Metabolizing Enzymes: Case Studies of Biotransformation Involving Aldehyde Oxidase, γ-Glutamyl Transpeptidase, Cathepsin B, Flavin-Containing Monooxygenase, and ADP-Ribosyltransferase.

The significant roles that cytochrome P450 (P450) and UDP-glucuronosyl transferase (UGT) enzymes play in drug discovery cannot be ignored, and these enzyme systems are commonly examined during drug optimization using liver microsomes or hepatocytes. At the same time, other drug-metabolizing enzymes have a role in the metabolism of drugs and can lead to challenges in drug optimization that could be mitigated if the contributions of these enzymes were better understood. We present examples (mostly from Genentech) of five different non-P450 and non-UGT enzymes that contribute to the metabolic clearance or bioactivation of drugs and drug candidates. Aldehyde oxidase mediates a unique amide hydrolysis of GDC-0834 (N-[3-[6-[4-[(2R)-1,4-dimethyl-3-oxopiperazin-2-yl]anilino]-4-methyl-5-oxopyrazin-2-yl]-2-methylphenyl]-4,5,6,7-tetrahydro-1-benzothiophene-2-carboxamide), leading to high clearance of the drug. Likewise, the rodent-specific ribose conjugation by ADP-ribosyltransferase leads to high clearance of an interleukin-2-inducible T-cell kinase inhibitor. Metabolic reactions by flavin-containing monooxygenases (FMO) are easily mistaken for P450-mediated metabolism such as oxidative defluorination of 4-fluoro-N-methylaniline by FMO. Gamma-glutamyl transpeptidase is involved in the initial hydrolysis of glutathione metabolites, leading to formation of proximate toxins and nephrotoxicity, as is observed with cisplatin in the clinic, or renal toxicity, as is observed with efavirenz in rodents. Finally, cathepsin B is a lysosomal enzyme that is highly expressed in human tumors and has been targeted to release potent cytotoxins, as in the case of brentuximab vedotin. These examples of non-P450- and non-UGT-mediated metabolism show that a more complete understanding of drug metabolizing enzymes allows for better insight into the fate of drugs and improved design strategies of molecules in drug discovery.

The Ask Me to Explain Campaign: A 90-Day Intervention to Promote Patient and Family Involvement in Care in a Pediatric Emergency Department.

BACKGROUND: Patient satisfaction is a central outcome measure of patient-centered care and is associated with improved patient safety, but the effect of specific interventions in pediatric emergency medicine on patient satisfaction is not well studied. In 2013 the University of Chicago Medicine Comer Children's Hospital's Pediatric Emergency Department identified substantial room for improvement in communication both among physicians and nurses and between hospital staff and patients. A pilot study was conducted to quantify the impact of a specific package of improvement activities on patient satisfaction in the Pediatric Emergency Department. METHODS: Using a 90-day action plan (December 2013- February 2014), the Ask Me to Explain campaign included visual signage to remind clinicians and staff to focus on addressing the concerns of their patients. Providers were educated on the campaign tools, their purpose, and how to use them to initiate discussion and provide answers to patient concerns. Education was then spread to support staff throughout the department. The primary outcome measure was the response to questions on a patient satisfaction survey delivered by a third-party vendor, specifically, "Likelihood of your recommending our Emergency Department to others." RESULTS: "Top Box" scores increased for all questions during the 90-day intervention period. Specifically, staff sensitivity to patient concerns increased from 44.0% to 59.2% (p = 0.041), and patient satisfaction with being informed about delays increased from 34.7% to 51.1% (p = 0.024). Interestingly, patient satisfaction either remained above baseline or continued to improve for all questions after the campaign had concluded. CONCLUSION: A 90-day action plan may provide a successful template for improving communication between providers and patients in a pediatric emergency department or in other health care settings.

Biotransformation and bioactivation reactions of alicyclic amines in drug molecules.

Aliphatic nitrogen heterocycles such as piperazine, piperidine, pyrrolidine, morpholine, aziridine, azetidine, and azepane are well known building blocks in drug design and important core structures in approved drug therapies. These core units have been targets for metabolic attack by P450s and other drug metabolizing enzymes such as aldehyde oxidase and monoamine oxidase (MAOs). The electron rich nitrogen and/or α-carbons are often major sites of metabolism of alicyclic amines. The most common biotransformations include N-oxidation, N-conjugation, oxidative N-dealkylation, ring oxidation, and ring opening. In some instances, the metabolic pathways generate electrophilic reactive intermediates and cause bioactivation. However, potential bioactivation related adverse events can be attenuated by structural modifications. Hence it is important to understand the biotransformation pathways to design stable drug candidates that are devoid of metabolic liabilities early in the discovery stage. The current review provides a comprehensive summary of biotransformation and bioactivation pathways of aliphatic nitrogen containing heterocycles and strategies to mitigate metabolic liabilities.

MicroRNAs in brain metastases: potential role as diagnostics and therapeutics.

Brain metastases remain a daunting adversary that negatively impact patient survival. Metastatic brain tumors affect up to 45% of all cancer patients with systemic cancer and account for ~20% of all cancer-related deaths. A complex network of non-coding RNA molecules, microRNAs (miRNAs), regulate tumor metastasis. The brain micro-environment modulates metastatic tumor growth; however, defining the precise genetic events that promote metastasis in the brain niche represents an important, unresolved problem. Understanding these events will reveal disease-based targets and offer effective strategies to treat brain metastases. Effective therapeutic strategies based upon the biology of brain metastases represent an urgent, unmet need with immediate potential for clinical impact. Studies have demonstrated the ability of miRNAs to distinguish normal from cancerous cells, primary from secondary brain tumors, and correctly categorize metastatic brain tumor tissue of origin based solely on miRNA profiles. Interestingly, manipulation of miRNAs has proven effective in cancer treatment. With the promise of reduced toxicity, increased efficacy and individually directed personalized anti-cancer therapy, using miRNA in the treatment of metastatic brain tumors may prove very useful and improve patient outcome. In this review, we focus on the potential of miRNAs as diagnostic and therapeutic targets for the treatment of metastatic brain lesions.

HDAC6 Inhibition Releases HR23B to Activate Proteasomes, Expand the Tumor Immunopeptidome and Amplify T-cell Antimyeloma Activity.

Proteasomes degrade intracellular proteins to generate antigenic peptides that are recognized by the adaptive immune system and promote anticancer immunity. However, tumors subvert the antigen presentation machinery to escape immunosurveillance. We hypothesized that proteasome activation could concomitantly increase antigen abundance and diversity in multiple myeloma cells. High-throughput screens revealed that histone deacetylase 6 (HDAC6) inhibitors activated proteasomes to unmask neoantigens and amplify the tumor-specific antigenic landscape. Treatment of patient CD138+ cells with HDAC6 inhibitors significantly promoted the antimyeloma activity of autologous CD8+ T cells. Pharmacologic blockade and genetic ablation of the HDAC6 ubiquitin-binding domain released HR23B, which shuttles ubiquitinylated cargo to proteasomes, while silencing HDAC6 or HR23B in multiple myeloma cells abolished the effect of HDAC6 inhibitors on proteasomes, antigen presentation, and T-cell cytotoxicity. Taken together, our results demonstrate the paradigm-shifting translational impact of proteasome activators to expand the myeloma immunopeptidome and have revealed novel, actionable antigenic targets for T cell-directed immunotherapy. SIGNIFICANCE: The elimination of therapy-resistant tumor cells remains a major challenge in the treatment of multiple myeloma. Our study identifies and functionally validates agents that amplify MHC class I-presented antigens and pave the way for the development of proteasome activators as immune adjuvants to enhance immunotherapeutic responses in patients with multiple myeloma.