Patient preferences in the treatment of stage III/IV classic Hodgkin lymphoma: Results from the CONNECT cross-sectional survey.

We explored patient front-line treatment preferences in newly diagnosed stage III/IV classic Hodgkin lymphoma (cHL). The CONNECT patient survey, administered online from 30 December 2020 to 1 March 2021, examined preferences overall and by age at diagnosis in 182 adult patients diagnosed with stage III/IV cHL within the past 10 years in the United States. At diagnosis, patients' median age was 36 years; 66% of patients were younger (aged 16-41 years) and 34% older (aged 42-85 years). When asked about initial treatment goals, 74% of patients ranked cure as their first or second goal (86% younger vs. 52% older patients; p < 0.001). At diagnosis, 72% of patients preferred aggressive treatment, and 85% were willing to accept more short-term risks in exchange for a better-working therapy long term. For long-term risks, younger versus older patients were significantly more concerned about second cancers (p < 0.001) and fertility issues (p = 0.007), whereas older patients were more concerned about lung damage (p = 0.028) and infections (p < 0.001). Most patients (94%) reported having a caregiver at some point, but 99% of these patients retained some control of treatment decisions. Collectively, these survey results highlight patient treatment preferences and differences in treatment goals and long-term side effect concerns based on patient age.

Physician frontline treatment preferences for stage III/IV classic Hodgkin lymphoma: the real-world US CONNECT study.

Aim: To understand US physicians' frontline (1L) treatment preferences/decision-making for stage III/IV classic Hodgkin lymphoma (cHL). Materials & methods: Medical oncologists and/or hematologists (≥2 years' practice experience) who treat adults with stage III/IV cHL were surveyed online (October-November 2020). Results: Participants (n = 301) most commonly considered trial efficacy/safety data and national guidelines when selecting 1L cHL treatments. Most physicians (91%) rated overall survival (OS) as the most essential attribute when selecting 1L treatment. Variability was seen among regimen selection for hypothetical newly diagnosed patients, with OS cited as the most common reason for regimen selection. Conclusion: While treatment selection varied based on patient characteristics, US physicians consistently cited OS as the top factor considered when selecting a 1L treatment for cHL.

Classic Hodgkin lymphoma (cHL) is a type of cancer that grows in lymph nodes. The researchers created a survey to assess how doctors in the USA choose medicine to treat patients who are newly diagnosed with an advanced stage of cHL (stage 3 or 4 out of 4 stages). We surveyed 301 doctors who treat patients with cHL. When choosing a medicine to treat cHL, most doctors said they consider results from research studies, how well the medicine works, information on the medicine's safety and recommendations in official guidelines. Most doctors said that overall survival (how long the patient survives after being diagnosed with cHL) is the most important outcome they consider when choosing a medicine to treat cHL. During the survey, doctors saw four unique patient profiles. These profiles differed in age, disease stage (how far along the cHL is) and other illnesses the patient has. While medicine choice was different across profiles, overall survival was still the reason for choosing each individual patient's medicine. These survey results show that doctors in the USA highly consider overall survival when choosing medicine for patients newly diagnosed with an advanced stage of cHL.

The impact of classic Hodgkin lymphoma on informal caregivers: results from the CONNECT cross-sectional survey.

PURPOSE: As part of the CONNECT study, we evaluated the caregiver role in treatment decision-making when caring for patients with classic Hodgkin lymphoma (cHL) in the USA. METHODS: The CONNECT caregiver survey was administered online December 2020-March 2021 to self-identified adult caregivers of cHL patients recruited from patient referrals and online panels. The caregiver's role in treatment decision-making, health-related quality of life (HRQoL, PROMIS-Global), and work impacts (WPAI:CG) were assessed. RESULTS: We surveyed 209 caregivers (58% women; median age 47 years; 54% employed; 53% spouse/partner); 69% of patients cared for were diagnosed with cHL in the past 1-2 years, with 48% having stage III/IV cHL and 29% in remission. More spouse/partner than other caregivers were involved in caregiving at symptom onset (61% vs 27%), whereas more other than spouse/partner caregivers began after first treatment (34% vs 5%). Cure, caregivers' top treatment goal (49%), was rated higher by spouse/partner than other caregivers (56% vs 42%). More spouse/partner than other caregivers were involved in treatment option discussions with physicians (52% vs 28%), were involved in patients' treatment decisions (54% vs 23%), and were aligned with patients' treatment goals (93% vs 79%). While caregivers reported HRQoL similar to that of the general population, nearly 30% of employed caregivers reported work impairment. CONCLUSION: Cure was caregivers' top treatment goal. Spouse/partner vs other caregivers were more involved, were involved earlier, and reported greater alignment with patient treatment goals and decision-making. Caregivers reported good HRQoL; however, caregiving impacted work productivity regardless of patient relationship.

Assessment of Bone Health Awareness and Education in Breast Cancer Patients with Bone Metastasis in the USA.

Bone metastases are common in advanced breast cancer (BC) patients and increase the risk for skeletal-related events (SREs), which present a significant health and economic burden. Bone targeting agents (BTAs) can improve health-related quality of life by delaying or preventing SREs; nevertheless, a significant portion of eligible BC patients are not receiving this therapy. A bone health education needs assessment survey was conducted to examine cancer-related bone health awareness and to identify opportunities to improve bone health education. Direct-to-patient outreach was used to recruit adult BC patients in the USA self-reporting a diagnosis of bone metastasis within the past 3 years. Of the 200 patients, 59% experienced at least one SRE prior to survey participation (44% radiation to bone, 29% bone fracture, 17% spinal cord compression, 15% surgery to bone), and 83% were currently receiving a BTA. Awareness of general cancer bone health, protection strategies against SREs, and screening tests were low to moderate. Patients currently not receiving a BTA were least knowledgeable about cancer bone health, with only 40% aware of BTAs as a protective strategy, and only 26% were very or extremely satisfied with the information received from healthcare providers. Sixty-two percent of patients wanted to receive information by more than one mode of communication. Notable gaps in bone health education were observed in bone metastatic BC patients at risk for SREs, suggesting the need for earlier and more effective communication and education strategies to promote appropriate BTA use and better health outcomes.

Observations of Oncologists on Treatment Selection With Interim Positron Emission Tomography-Adapted Approaches in Classic Hodgkin Lymphoma: The Real-World CONNECT Study.

PURPOSE: We surveyed oncologists who treat classic Hodgkin lymphoma (cHL) as part of the CONNECT study to understand the treatment decision-making process, including the impact of positron emission tomography/computed tomography (PET/CT) imaging. METHODS: US physicians self-identifying as oncologists, hematologists, or hematologists/oncologists with ≥2 years of practice experience who treated ≥1 adult with stage III/IV cHL in the frontline setting in the last year were surveyed (October 19-November 16, 2020). Physician demographics, guideline adherence, and PET/CT utilization, interpretation, and access barriers were assessed. RESULTS: In total, 301 physicians participated in the survey. Eighty-eight percent of physicians gave somewhat-to-significant consideration to NCCN guidelines. Most physicians (94%; n = 284) reported obtaining a PET/CT scan at diagnosis; of these physicians, 97% reported obtaining an interim PET/CT scan for stage III/IV cHL, with 65% typically obtaining an interim PET/CT scan after cycle 2. The Deauville 5-point scale (5PS) was the primary scoring system used to review PET/CT results by 62% of physicians, with a positive score defined as ≥3 by 44%, ≥4 by 37%, and ≥2 by 12% of physicians. Fifty-five percent of physicians reported difficulty in obtaining PET/CT scans. CONCLUSION: Although most physicians considered NCCN guidelines when treating patients with stage III/IV cHL, interim PET/CT scans after cycle 2 were not universally obtained. When PET/CT scans were obtained, Deauville 5PS scores were not always provided, and variability existed on what defined a positive score. These findings suggest that opportunities exist for education and improved PET-adapted treatment approaches.

A Physiological-Based Pharmacokinetic Model Embedded with a Target-Mediated Drug Disposition Mechanism Can Characterize Single-Dose Warfarin Pharmacokinetic Profiles in Subjects with Various CYP2C9 Genotypes under Different Cotreatments.

Warfarin, a commonly prescribed oral anticoagulant medication, is highly effective in treating deep vein thrombosis and pulmonary embolism. However, the clinical dosing of warfarin is complicated by high interindividual variability in drug exposure and response and its narrow therapeutic index. CYP2C9 genetic polymorphism and drug-drug interactions (DDIs) are substantial contributors to this high variability of warfarin pharmacokinetics (PK), among numerous factors. Building a physiology-based pharmacokinetic (PBPK) model for warfarin is not only critical for a mechanistic characterization of warfarin PK but also useful for investigating the complicated dose-exposure relationship of warfarin. Thus, the objective of this study was to develop a PBPK model for warfarin that integrates information regarding CYP2C9 genetic polymorphisms and their impact on DDIs. Generic PBPK models for both S- and R-warfarin, the two enantiomers of warfarin, were constructed in R with the mrgsolve package. As expected, a generic PBPK model structure did not adequately characterize the warfarin PK profile collected up to 15 days following the administration of a single oral dose of warfarin, especially for S-warfarin. However, following the integration of an empirical target-mediated drug disposition (TMDD) component, the PBPK-TMDD model well characterized the PK profiles collected for both S- and R-warfarin in subjects with different CYP2C9 genotypes. Following the integration of enzyme inhibition and induction effects, the PBPK-TMDD model also characterized the PK profiles of both S- and R-warfarin in various DDI settings. The developed mathematic framework may be useful in building algorithms to better inform the clinical dosing of warfarin. SIGNIFICANCE STATEMENT: The present study found that a traditional physiology-based pharmacokinetic (PBPK) model cannot sufficiently characterize the pharmacokinetic profiles of warfarin enantiomers when warfarin is administered as a single dose, but a PBPK model with a target-mediated drug disposition mechanism can. After incorporating CYP2C9 genotypes and drug-drug interaction information, the developed model is anticipated to facilitate the understanding of warfarin disposition in subjects with different CYP2C9 genotypes in the absence and presence of both cytochrome P450 inhibitors and cytochrome P450 inducers.

Pharmacokinetic Modeling of Warfarin ІI - Model-based Analysis of Warfarin Metabolites following Warfarin Administered either Alone or Together with Fluconazole or Rifampin.

The objective of this study is to conduct a population pharmacokinetic (PK) model-based analysis on 10 warfarin metabolites (4'-, 6-, 7-, 8- and 10-hydroxylated (OH)-S- and R- warfarin), when warfarin is administered alone or together with either fluconazole or rifampin. One or two compartment PK models expanded from target mediated drug disposition (TMDD) models developed previously for warfarin enantiomers were able to sufficiently characterize the PK profiles of 10 warfarin metabolites in plasma and urine under different conditions. Model-based analysis shows CYP2C9 mediated metabolic elimination pathways are more inhibitable by fluconazole (% formation CL (CLf) of 6- and 7-OH-S-warfarin decrease: 73.2% and 74.8%) but less inducible by rifampin (% CLf of 6- and 7-OH-S-warfarin increase: 85% and 75%), compared with non-CYP2C9 mediated elimination pathways (% CLf of 10-OH-S-warfarin and CLR of S-warfarin decrease in the presence of fluconazole: 65.0% and 15.3%; % CLf of 4'- 8- and 10-OH-S-warfarin increase in the presence of rifampin: 260%, 127% and 355%), which potentially explains the CYP2C9 genotype-dependent DDIs exhibited by S-warfarin, when warfarin is administrated together with fluconazole or rifampin. Additionally, for subjects with CYP2C9 *2 and *3 variants, a model-based analysis of warfarin metabolite profiles in subjects with various CYP2C9 genotypes demonstrates CYP2C9 mediated elimination is less important and non-CYP2C9 mediated elimination is more important, compared with subjects without these variants. To our knowledge, this is so far one of the most comprehensive population-based PK analyses of warfarin metabolites in subjects with various CYP2C9 genotypes under different co-medications. Significance Statement The studies we wish to publish are potentially impactful. The need for a TMDD pharmacokinetic model and the demonstration of genotyped-dependent drug interactions may explain the extensive variability in dose-response relationships that are seen in the clinical dose adjustments of warfarin.

Pharmacokinetic Modeling of Warfarin І - Model-based Analysis of Warfarin Enantiomers with a Target Mediated Drug Disposition Model Reveals CYP2C9 Genotype-dependent Drug-drug Interactions of S-Warfarin.

The objective of this study is to characterize the impact of CYP2C9 genotype on warfarin drug-drug interactions when warfarin is taken together with fluconazole, a cytochrome P450 (CYP) inhibitor, or rifampin, a CYP inducer with a nonlinear mixed effect modeling approach. A target mediated drug disposition model with a urine compartment was necessary to characterize both S-warfarin and R-warfarin plasma and urine pharmacokinetic profiles sufficiently. Following the administration of fluconazole, our study found subjects with CYP2C9 *2 or *3 alleles experience smaller changes in S-warfarin CL compared with subjects without these alleles (69.5%, 64.8%, 59.7% and 47.8% decrease in subjects with CYP2C9 *1/*1, *1/*3, *2/*3 and *3/*3 respectively). Whereas, following the administration of rifampin, subjects with CYP2C9 *2/*3 or CYP2C9 *3/*3 experience larger changes in S-warfarin CL compared with subjects with at least one copy of CYP2C9 *1 or *1B (115%, 111%, 119%, 198% and 193% increase in subjects with CYP2C9 *1/*1, *1B/*1B, *1/*3, *2/*3 and *3/*3 respectively). The results suggest different dose adjustments are potentially required for patients with different CYP2C9 genotypes if warfarin is administered together with CYP inhibitors or inducers. Significance Statement The present study found a target mediated drug disposition model is needed to sufficiently characterize the clinical pharmacokinetic profiles of warfarin racemates under different co-treatments in subjects with various CYP2C9 genotypes, following a single dose of warfarin administration. The study also found S-warfarin, the pharmacologically more active ingredient in warfarin, exhibits CYP2C9 genotype-dependent drug-drug interactions, which indicates the dose of warfarin may need to be adjusted differently in subjects with different CYP2C9 genotypes in the presence of drug-drug interactions.

Assessment of Bone Health Education in US Multiple Myeloma and Solid Tumor Patients at Risk for Skeletal-Related Events.

PURPOSE: Cancer patients with bone metastasis (BM) from solid tumors or multiple myeloma (MM) have an increased risk of painful skeletal-related events (SREs), which can decrease quality of life and increase mortality. Bone targeting agents (BTAs) can help delay or prevent SREs; however, a significant portion of eligible patients are not receiving BTA therapy. This study was conducted to understand patient awareness of cancer-related bone health and to identify opportunities to improve bone health education in cancer patients at risk of SREs. METHODS: The online BonE heAlth eduCatiOn Needs assessment (BEACON) survey included questions about patient demographics, cancer diagnosis and treatments (including BTA usage), and extent and satisfaction with bone health education received. Direct-to-patient outreach was used to recruit patients. Eligible patients were US adults with a diagnosis of self-reported MM or BM from a solid tumor (breast, lung, or prostate cancer) within the past three years. RESULTS: Of 125 patients, 71% were diagnosed with solid tumors with BM and 29% with MM. At least one prior SRE was experienced by 57% of patients (38% radiation to bone, 32% bone fracture, 22% spinal cord compression, and 19% surgery to bone), and 74% were currently receiving BTA therapy. Awareness of cancer bone health, protection strategies, and screening tests was low to moderate; patients were least informed of the impact of lifestyle changes (38%) and specific cancer treatments (≤35%) on bone health. Sixty-two percent of patients were not completely satisfied with the bone health education received. Patients generally wanted more information (58%) and to receive information by more than one mode of communication. CONCLUSION: Notable gaps in bone health education were observed in cancer patients at risk for SREs indicating an important need for improved communication and education strategies to promote better health outcomes.

CYP2C9 Genotype-Dependent Warfarin Pharmacokinetics: Impact of CYP2C9 Genotype on R- and S-Warfarin and Their Oxidative Metabolites.

Multiple factors can impact warfarin therapy, including genetic variations in the drug-metabolizing enzyme cytochrome P450 2C9 (CYP2C9). Compared with individuals with the wild-type allele, CYP2C9*1, carriers of the common *3 variant have significantly impaired CYP2C9 metabolism. Genetic variations in CYP2C9, the primary enzyme governing the metabolic clearance of the more potent S-enantiomer of the racemic anticoagulant warfarin, may impact warfarin-drug interactions. To establish a baseline for such studies, plasma and urine concentrations of R- and S-warfarin and 10 warfarin metabolites were monitored for up to 360 hours following a 10-mg warfarin dose in healthy subjects with 4 different CYP2C9 genotypes: CYP2C9*1/*1 (n = 8), CYP2C9*1/*3 (n = 9), CYP2C9*2/*3 (n = 3), and CYP2C9*3/*3 (n = 4). Plasma clearance of S-warfarin, but not R-warfarin, decreased multiexponentially and in a CYP2C9 gene-dependent manner: 56%, 70%, and 75% for CYP2C9*1/*3, CYP2C9*2/*3, and CYP2C9*3/*3 genotypes, respectively, compared with CYP2C9*1/*1, resulting in pronounced differences in the S:R ratio that identified warfarin-sensitive genotypes. CYP2C9 was the primary P450 enzyme contributing to S-warfarin metabolism and a minor contributor to R-warfarin metabolism. In the presence of a defective CYP2C9 allele, switching of warfarin metabolism to other oxidative pathways and P450 enzymes for the metabolic elimination of S-warfarin was not observed. The 10-hydroxywarfarin metabolites, whose detailed pharmacokinetics are reported for the first time, exhibited a prolonged half-life with no evidence of renal excretion and displayed elimination rate-limited kinetics. Understanding the impact of CYP2C9 genetics on warfarin pharmacokinetics lays the foundation for future genotype-dependent warfarin-drug interaction studies.

Immobilized Cytochrome P450 for Monitoring of P450-P450 Interactions and Metabolism.

Cytochrome P450 (P450) protein-protein interactions have been shown to alter their catalytic activity. Furthermore, these interactions are isoform specific and can elicit activation, inhibition, or no effect on enzymatic activity. Studies show that these effects are also dependent on the protein partner cytochrome P450 reductase (CPR) and the order of protein addition to purified reconstituted enzyme systems. In this study, we use controlled immobilization of P450s to a gold surface to gain a better understanding of P450-P450 interactions between three key drug-metabolizing isoforms (CYP2C9, CYP3A4, and CYP2D6). Molecular modeling was used to assess the favorability of homomeric/heteromeric P450 complex formation. P450 complex formation in vitro was analyzed in real time utilizing surface plasmon resonance. Finally, the effects of P450 complex formation were investigated utilizing our immobilized platform and reconstituted enzyme systems. Molecular modeling shows favorable binding of CYP2C9-CPR, CYP2C9-CYP2D6, CYP2C9-CYP2C9, and CYP2C9-CYP3A4, in rank order.KDvalues obtained via surface plasmon resonance show strong binding, in the nanomolar range, for the above pairs, with CYP2C9-CYP2D6 yielding the lowestKD, followed by CYP2C9-CYP2C9, CYP2C9-CPR, and CYP2C9-CYP3A4. Metabolic incubations show that immobilized CYP2C9 metabolism was activated by homomeric complex formation. CYP2C9 metabolism was not affected by the presence of CYP3A4 with saturating CPR concentrations. CYP2C9 metabolism was activated by CYP2D6 at saturating CPR concentrations in solution but was inhibited when CYP2C9 was immobilized. The order of addition of proteins (CYP2C9, CYP2D6, CYP3A4, and CPR) influenced the magnitude of inhibition for CYP3A4 and CYP2D6. These results indicate isoform-specific P450 interactions and effects on P450-mediated metabolism.

Nanoscale electron transport measurements of immobilized cytochrome P450 proteins.

Gold nanopillars, functionalized with an organic self-assembled monolayer, can be used to measure the electrical conductance properties of immobilized proteins without aggregation. Measurements of the conductance of nanopillars with cytochrome P450 2C9 (CYP2C9) proteins using conducting probe atomic force microscopy demonstrate that a correlation exists between the energy barrier height between hopping sites and CYP2C9 metabolic activity. Measurements performed as a function of tip force indicate that, when subjected to a large force, the protein is more stable in the presence of a substrate. This agrees with the hypothesis that substrate entry into the active site helps to stabilize the enzyme. The relative distance between hopping sites also increases with increasing force, possibly because protein functional groups responsible for electron transport (ETp) depend on the structure of the protein. The inhibitor sulfaphenazole, in addition to the previously studied aniline, increased the barrier height for electron transfer and thereby makes CYP2C9 reduction more difficult and inhibits metabolism. This suggests that P450 Type II binders may decrease the ease of ETp processes in the enzyme, in addition to occupying the active site.

Case study 1. Practical considerations with experimental design and interpretation.

At some point, anyone with knowledge of drug metabolism and enzyme kinetics started out knowing little about these topics. This chapter was specifically written with the novice in mind. Regardless of the enzyme one is working with or the goal of the experiment itself, there are fundamental components and concepts of every experiment using drug metabolism enzymes. The following case studies provide practical tips, techniques, and answers to questions that may arise in the course of conducting such experiments. Issues ranging from assay design and development to data interpretation are addressed. The goal of this section is to act as a starting point to provide the reader with key questions and guidance while attempting his/her own work.

The use of immobilized cytochrome P4502C9 in PMMA-based plug flow bioreactors for the production of drug metabolites.

Cytochrome P450 enzymes play a key role in the metabolism of pharmaceutical agents. To determine metabolite toxicity, it is necessary to obtain P450 metabolites from various pharmaceutical agents. Here, we describe a bioreactor that is made by immobilizing cytochrome P450 2C9 (CYP2C9) to a poly(methyl methacrylate) surface and, as an alternative to traditional chemical synthesis, can be used to biosynthesize P450 metabolites in a plug flow bioreactor. As part of the development of the CYP2C9 bioreactor, we have studied two different methods of attachment: (1) coupling via the N-terminus using N-hydroxysulfosuccinimide 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide and (2) using the Ni(II) chelator 1-acetato-4-benzyl-triazacyclononane to coordinate the enzyme to the surface using a C-terminal histidine tag. Additionally, the propensity for metabolite production of the CYP2C9 proof-of-concept bioreactors as a function of enzyme attachment conditions (e.g., time and enzyme concentration) was examined. Our results show that the immobilization of CYP2C9 enzymes to a PMMA surface represents a viable and alternative approach to the preparation of CYP2C9 metabolites for toxicity testing. Furthermore, the basic approach can be adapted to any cytochrome P450 enzyme and in a high-throughput, automated process.

Measurement of electron transfer through cytochrome P450 protein on nanopillars and the effect of bound substrates.

Electron transfer in cytochrome P450 enzymes is a fundamental process for activity. It is difficult to measure electron transfer in these enzymes because under the conditions typically used they exist in a variety of states. Using nanotechnology-based techniques, gold conducting nanopillars were constructed in an indexed array. The P450 enzyme CYP2C9 was attached to each of these nanopillars, and conductivity measurements made using conducting probe atomic force microscopy under constant force conditions. The conductivity measurements were made on CYP2C9 alone and with bound substrates, a bound substrate-effector pair, and a bound inhibitor. Fitting of the data with the Poole-Frenkel model indicates a correlation between the barrier height for electron transfer and the ease of CYP2C9-mediated metabolism of the bound substrates, though the spin state of iron is not well correlated. The approach described here should have broad application to the measurement of electron transfer in P450 enzymes and other metalloenzymes.

Selective filling of nanowells in nanowell arrays fabricated using polystyrene nanosphere lithography with cytochrome P450 enzymes.

This work describes an original and simple technique for protein immobilization into nanowells, fabricated using nanopatterned array fabrication methods, while ensuring the protein retains normal biological activity. Nanosphere lithography was used to fabricate a nanowell array with nanowells 100 nm in diameter with a periodicity of 500 nm. The base of the nanowells was gold and the surrounding material was silicon dioxide. The different surface chemistries of these materials were used to attach two different self-assembled monolayers (SAM) with different affinities for the protein used here, cytochrome P450 (P450). The nanowell SAM, a methyl terminated thiol, had high affinity for the P450. The surrounding SAM, a polyethylene glycol silane, displayed very little affinity toward the P450 isozyme CYP2C9, as demonstrated by x-ray photoelectron spectroscopy and surface plasmon resonance. The regularity of the nanopatterned array was examined by scanning electron microscopy and atomic force microscopy. P450-mediated metabolism experiments of known substrates demonstrated that the nanowell bound P450 enzyme exceeded its normal activity, as compared to P450 solutions, when bound to the methyl terminated self-assembled monolayer. The nanopatterned array chips bearing P450 display long term stability and give reproducible results making them potentially useful for high-throughput screening assays or as nanoelectrode arrays.

Development of an in vitro system with human liver microsomes for phenotyping of CYP2C9 genetic polymorphisms with a mechanism-based inactivator.

Polymorphisms in cytochrome P450 enzymes can significantly alter the rate of drug metabolism, as well as the extent of drug-drug interactions. Individuals who homozygotically express the CYP2C9*3 allele (I359L) of CYP2C9 exhibit ∼70 to 80% reductions in the oral clearance of drugs metabolized through this pathway; the reduction in clearance is ∼40 to 50% for heterozygotic individuals. Although these polymorphisms result in a decrease in the activity of individual enzyme molecules, we hypothesized that decreasing the total number of active enzyme molecules in an in vitro system (CYP2C9*1/*1 human liver microsomes) by an equivalent percentage could produce the same net change in overall metabolic capacity. To this end, the selective CYP2C9 mechanism-based inactivator tienilic acid was used to reduce irreversibly the total CYP2C9 activity in human liver microsomes. Tienilic acid concentrations were effectively titrated to produce microsomal preparations with 43 and 73% less activity, mimicking the CYP2C9*1/*3 and CYP2C9*3/*3 genotypes, respectively. With probe substrates specific for other major cytochrome P450 enzymes (CYP1A2, CYP2B6, CYP2C8, CYP2C19, CYP2D6, CYP2E1, and CYP3A4), no apparent changes in the rate of metabolism were noted for these enzymes after the addition of tienilic acid, which suggests that this model is selective for CYP2C9. In lieu of using rare human liver microsomes from CYP2C9*1/*3 and CYP2C9*3/*3 individuals, a tienilic acid-created knockdown in human liver microsomes may be an appropriate in vitro model to determine CYP2C9-mediated metabolism of a given substrate, to determine whether other drug-metabolizing enzymes may compensate for reduced CYP2C9 activity, and to predict the extent of genotype-dependent drug-drug interactions.

Antibody tracking demonstrates cell type-specific and ligand-independent internalization of guanylyl cyclase a and natriuretic peptide receptor C.

Atrial natriuretic peptide (ANP) binds guanylyl cyclase-A (GC-A) and natriuretic peptide receptor-C (NPR-C). Internalization of GC-A and NPR-C is poorly understood, in part, because previous studies used (125)I-ANP binding to track these receptors, which are expressed in the same cell. Here, we evaluated GC-A and NPR-C internalization using traditional and novel approaches. Although HeLa cells endogenously express GC-A, (125)I-ANP binding and cross-linking studies only detected NPR-C, raising the possibility that past studies ascribed NPR-C-mediated processes to GC-A. To specifically measure internalization of a single receptor, we developed an (125)I-IgG-binding assay that tracks extracellular FLAG-tagged versions of GC-A and NPR-C independently of each other and ligand for the first time. FLAG-GC-A bound ANP identically with wild-type GC-A and was internalized slowly (0.5%/min), whereas FLAG-NPR-C was internalized rapidly (2.5%/min) in HeLa cells. In 293 cells, (125)I-ANP and (125)I-IgG uptake curves were superimposable because these cells only express a single ANP receptor. Basal internalization of both receptors was 8-fold higher in 293 compared with HeLa cells and ANP did not increase internalization of FLAG-GC-A. For FLAG-NPR-C, neither ANP, BNP, nor CNP increased its internalization in either cell line. Prolonged ANP exposure concomitantly reduced surface and total GC-A levels, consistent with rapid exchange of extracellular and intracellular receptor pools. We conclude that ligand binding does not stimulate natriuretic peptide receptor internalization and that cellular environment determines the rate of this process. We further deduce that NPR-C is internalized faster than GC-A and that increased internalization is not required for GC-A down-regulation.

Prolonged atrial natriuretic peptide exposure stimulates guanylyl cyclase-a degradation.

Natriuretic peptide receptor-A (NPR-A), also known as guanylyl cyclase-A, is a transmembrane receptor guanylyl cyclase that is activated by the cardiac hormones atrial natriuretic peptide and B-type natriuretic peptide. Although ligand-dependent NPR-A degradation (also known as down-regulation) is widely acknowledged in human and animal models of volume overload, down-regulation in cultured cells is controversial. Here, we examined the effect of ANP exposure on cellular NPR-A levels as a function of time. Relative receptor concentrations were estimated using guanylyl cyclase and immunoblot assays in a wide variety of cell lines that endogenously or exogenously expressed low or high numbers of receptors. ANP exposures of 1 h markedly reduced hormone-dependent but not detergent-dependent guanylyl cyclase activities in membranes from exposed cells. However, 1-h ANP exposures did not significantly reduce NPR-A concentrations in any cell line. In contrast, exposures of greater than 1 h reduced receptor concentrations in a time-dependent manner. The time required for half of the receptors to be degraded (t(1/2)) in primary bovine aortic endothelial and immortalized HeLa cells was approximately 8 h. In contrast, a 24-h exposure of ANP to 293T cells stably overexpressing NPR-A caused less than half of the receptors to be degraded. To our knowledge, this is the first report to directly measure NPR-A down-regulation in endogenously expressing cells. We conclude that down-regulation is a universal property of NPR-A but is relatively slow and varies with receptor expression levels and cell type.

Natriuretic peptides: their structures, receptors, physiologic functions and therapeutic applications.

Natriuretic peptides are a family of three structurally related hormone/ paracrine factors. Atrial natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) are secreted from the cardiac atria and ventricles, respectively. ANP signals in an endocrine and paracrine manner to decrease blood pressure and cardiac hypertrophy. BNP acts locally to reduce ventricular fibrosis. C-type natriuretic peptide (CNP) primarily stimulates long bone growth but likely serves unappreciated functions as well. ANP and BNP activate the transmembrane guanylyl cyclase, natriuretic peptide receptor-A (NPR-A). CNP activates a related cyclase, natriuretic peptide receptor-B (NPR-B). Both receptors catalyze the synthesis of cGMP, which mediates most known effects of natriuretic peptides. A third natriuretic peptide receptor, natriuretic peptide receptor-C (NPR-C), clears natriuretic peptides from the circulation through receptor-mediated internalization and degradation. However, a signaling function for the receptor has been suggested as well. Targeted disruptions of the genes encoding all natriuretic peptides and their receptors have been generated in mice, which display unique physiologies. A few mutations in these proteins have been reported in humans. Synthetic analogs of ANP (anaritide and carperitide) and BNP (nesiritide) have been investigated as potential therapies for the treatment of decompensated heart failure and other diseases. Anaritide and nesiritide are approved for use in acute decompensated heart failure, but recent studies have cast doubt on their safety and effectiveness. New clinical trials are examining the effect of nesiritide and novel peptides, like CD-NP, on these critical parameters. In this review, the history, structure, function, and clinical applications of natriuretic peptides and their receptors are discussed.