Absorption, Metabolism, Excretion, and the Contribution of Intestinal Metabolism to the Oral Disposition of [14C]Cobimetinib, a MEK Inhibitor, in Humans

Human absorption, distribution, metabolism, and excretion studies: Conventional or microtracer?

A human absorption, distribution, metabolism, and excretion (hADME) study is an essential clinical pharmacology study for small-molecule drugs. The study provides insights into circulating drug-related materials and the drug's elimination pathways in humans, which can guide future studies on safety and drug-drug interaction of metabolites as well as organ impairment and drug-drug interaction of the parent drug. The 2 hADME study types, namely conventional and microtracer, are comprehensively compared in this manuscript. A review of literature found that conventional hADME studies were approximately 7 times that of microtracer hADME studies for small molecule and peptide drugs based on publications in 3 peer-reviewed journals from 2010 to 2024. Each study type has advantages and disadvantages. The advantages of conventional hADME studies primarily include the ease, low cost, and flexibility of radiometric sample analysis. In contrast, the advantages of microtracer hADME studies primarily include exemption from prerequisite studies and use of non-good manufacturing practice 14C-labeled materials. The disadvantages of each study type are essentially the advantages of the other. The manuscript also discusses scenarios where a microtracer hADME study may be preferable. Finally, recommendations are provided on selecting the appropriate hADME study type for an investigational drug. SIGNIFICANCE STATEMENT: The manuscript discusses 2 primary human absorption, distribution, metabolism, and excretion study types: conventional and microtracer. It covers published literature studies, the pros and cons of each type, scenarios for conducting microtracer studies, and a recommended decision tree for selecting the appropriate human absorption, distribution, metabolism, and excretion study type.

Advances in Understanding and Management of Erdheim-Chester Disease

Erdheim Chester Disease (ECD) is a rare histiocytic disorder marked by infiltration of organs with CD68+ histiocytes. ECD stems from mutations of BRAF and MAP2K1 in hematopoietic stem and progenitor cells (HSPCs), which further differentiate into monocytes and histiocytes. Histopathology reveals lipid-containing histiocytes, which test positive for CD68 and CD133 in immunohistochemistry. Signs and symptoms vary and depend on the organ/s of manifestation. Definitive radiological results associated with ECD include hairy kidney, coated aorta, and cardiac pseudotumor. Treatment options primarily include anti-cytokine therapy and inhibitors of BRAF and MEK signaling.

Beyond Rule of Five and PROTACs in Modern Drug Discovery: Polarity Reducers, Chameleonicity, and the Evolving Physicochemical Landscape

Developing orally bioavailable drugs demands an understanding of absorption in early drug development. Traditional methods and physicochemical properties optimize absorption for rule of five (Ro5) compounds; beyond rule of five (bRo5) drugs necessitate advanced tools like the experimental measure of exposed polarity (EPSA) and the AbbVie multiparametric score (AB-MPS). Analyzing AB-MPS and EPSA against ∼1000 compounds with human absorption data and ∼10,000 AbbVie tool compounds (∼1000 proteolysis targeting chimeras or PROTACs, ∼7000 Ro5s, and ∼2000 bRo5s) revealed new patterns of physicochemical trends. We introduced a high-throughput "polarity reduction" descriptor: ETR, the EPSA-to-topological polar surface area (TPSA) ratio, highlights unique bRo5 and PROTAC subsets for specialized drug design strategies for effective absorption. Our methods and guidelines refine drug design by providing innovative in vitro approaches, enhancing physicochemical property optimization, and enabling accurate predictions of intestinal absorption in the complex bRo5 domain.

Application of physiologically based pharmacokinetics modeling in the research of small-molecule targeted anti-cancer drugs

INTRODUCTION

Physiologically based pharmacokinetics (PBPK) models are increasingly used in the drug research and development, especially in anti-cancer drugs. Between 2001 and 2020, a total of 89 small-molecule targeted antitumor drugs were approved in China and the United States, some of which already included PBPK modeling in their application or approval packages. This article intended to review the prevalence and application of PBPK model in these drugs.

METHOD

Article search was performed in the PubMed to collect English research articles on small-molecule targeted anti-cancer drugs using PBPK modeling. The selected articles were classified into nine categorizes according to the application areas and further analyzed.

RESULT

From 2001 to 2020, more than 60% of small-molecule targeted anti-cancer drugs (54/89) were studied using PBPK model with a wide range of application. Ninety research articles were included, of which 48 involved enzyme-mediated drug-drug interaction (DDI). Of these retrieved articles, Simcyp, GastroPlus, and PK-Sim were the most widely model building platforms, which account for 63.8%, 15.2%, and 8.6%, respectively.

CONCLUSION

PBPK modeling is commonly and widely used to research small-molecule targeted anti-cancer drugs.

Harnessing systematic protein-ligand interaction fingerprints for drug discovery

Determining protein-ligand interaction characteristics and mechanisms is crucial to the drug discovery process. Here, we review recent progress and successful applications of a systematic protein-ligand interaction fingerprint (IFP) approach for investigating proteome-wide protein-ligand interactions for drug development. Specifically, we review the use of this IFP approach for revealing polypharmacology across the kinome, predicting promising targets from which to design allosteric inhibitors and covalent kinase inhibitors, uncovering the binding mechanisms of drugs of interest, and demonstrating resistant mechanisms of specific drugs. Together, we demonstrate that the IFP strategy is efficient and practical for drug design research for protein kinases as targets and is extensible to other protein families.

Switch Pocket Kinase: An Emerging Therapeutic Target for the Design of Anticancer Agents

Protein kinases are amongst the most focused enzymes in current century to design, synthesize and formulate drugs ought to be effective in the treatment of various disordered and diseased states involving either overexpression or deficiency situations. The ATP pocket on the kinases is the binding active site for most of the kinase inhibitors. However, the kinase mutations prevent the binding of kinase inhibitors to ATP pocket. The switch pocket site on this enzyme when occupied by switch pocket inhibitors, the enzyme become inactive even in the mutated state. This review comprises the detailed information on various classical protein kinases and switch pocket kinase inhibitors with their mechanism of action so that new molecules can be designed to encounter mutations in the kinase enzyme.

MetaClass, a Comprehensive Classification System for Predicting the Occurrence of Metabolic Reactions Based on the MetaQSAR Database

(1) Background: Machine learning algorithms are finding fruitful applications in predicting the ADME profile of new molecules, with a particular focus on metabolism predictions. However, the development of comprehensive metabolism predictors is hampered by the lack of highly accurate metabolic resources. Hence, we recently proposed a manually curated metabolic database (MetaQSAR), the level of accuracy of which is well suited to the development of predictive models. (2) Methods: MetaQSAR was used to extract datasets to predict the metabolic reactions subdivided into major classes, classes and subclasses. The collected datasets comprised a total of 3788 first-generation metabolic reactions. Predictive models were developed by using standard random forest algorithms and sets of physicochemical, stereo-electronic and constitutional descriptors. (3) Results: The developed models showed satisfactory performance, especially for hydrolyses and conjugations, while redox reactions were predicted with greater difficulty, which was reasonable as they depend on many complex features that are not properly encoded by the included descriptors. (4) Conclusions: The generated models allowed a precise comparison of the propensity of each metabolic reaction to be predicted and the factors affecting their predictability were discussed in detail. Overall, the study led to the development of a freely downloadable global predictor, MetaClass, which correctly predicts 80% of the reported reactions, as assessed by an explorative validation analysis on an external dataset, with an overall MCC = 0.44.

Drug Exposure to Establish Pharmacokinetic-Response Relationships in Oncology

In the oncology field, understanding the relationship between the dose administered and the exerted effect is particularly important because of the narrow therapeutic index associated with anti-cancer drugs and the high interpatient variability. Therefore, in this review, we provide a critical perspective of the different methods of characterising treatment exposure in the oncology setting. The increasing number of modelling applications in oncology reflects the applicability and the impact of pharmacometrics on all phases of the drug development process and patient management as well. Pharmacometric modelling is a worthy component within the current paradigm of model-based drug development, but pharmacometric modelling techniques are also accessible for the clinician in the optimisation of current oncology therapies. Consequently, the application of population models in a hospital setting by generating close collaborations between physicians and pharmacometricians is highly recommended, providing a systematic means of developing and assessing model-based metrics as 'drivers' for various responses to treatments, which can then be evaluated as predictors for treatment success. Characterising the key determinants of variability in exposure is of particular importance for anticancer agents, as efficacy and toxicity are associated with exposure. We present the different strategies to describe and predict drug exposure that can be applied depending on the data available, with the objective of obtaining the most useful information in the patients' favour throughout the full drug cycle. Therefore, the objective of the present article is to review the different approaches used to characterise a patient's exposure to oncology drugs, which will result in a better understanding of the time course of the response and the magnitude of interpatient variability.

Cabozantinib and dasatinib synergize to induce tumor regression in non-clear cell renal cell carcinoma

The lack of effective treatment options for advanced non-clear cell renal cell carcinoma (NCCRCC) is a critical unmet clinical need. Applying a high-throughput drug screen to multiple human kidney cancer cells, we identify the combination of the VEGFR-MET inhibitor cabozantinib and the SRC inhibitor dasatinib acts synergistically in cells to markedly reduce cell viability. Importantly, the combination is well tolerated and causes tumor regression in vivo. Transcriptional and phosphoproteomic profiling reveals that the combination converges to downregulate the MAPK-ERK signaling pathway, a result not predicted by single-agent analysis alone. Correspondingly, the addition of a MEK inhibitor synergizes with either dasatinib or cabozantinib to increase its efficacy. This study, by using approved, clinically relevant drugs, provides the rationale for the design of effective combination treatments in NCCRCC that can be rapidly translated to the clinic.

Mass balance, metabolic disposition, and pharmacokinetics of [14C]ensartinib, a novel potent anaplastic lymphoma kinase (ALK) inhibitor, in healthy subjects following oral administration

PURPOSE

Ensartinib is a novel, potent and highly selective inhibitor of anaplastic lymphoma kinase (ALK) that has promising clinical activity and low toxicity in patients with ALK-positive non-small cell lung cancer. This study was conducted to investigate the pharmacokinetics, metabolism and excretion of ensartinib following a single 200 mg/100 μCi oral dose of radiolabeled ensartinib to healthy subjects.

METHODS

Six healthy male subjects were enrolled and administrated an oral suspension in a fasted state. Blood, urine and feces were collected. Radioactivity concentrations were measured by liquid scintillation counting and plasma concentrations of ensartinib by liquid chromatography-tandem mass spectrometry. Both techniques were applied for metabolite profiling and characterization.

RESULTS

The mean total recovery was 101.21% of the radiolabeled dose with 91.00% and 10.21% excreted in feces and urine, respectively. Unchanged ensartinib was the predominant drug-related component in urine and feces, representing 4.39% and 38.12% of the administered dose, respectively. Unchanged ensartinib and its metabolite M465 were the major circulating components, accounting for the same 27.45% of the plasma total radioactivity (AUC_0-24h pool), while other circulating metabolites were minor, accounting for less than 10%. Mean C_max, AUC_0-∞, T_1/2 and T_max values for ensartinib in plasma were 185 ng/mL, 3827 h ng/mL, 18.3 h and 3.25 h, respectively. The total radioactivity in plasma was cleared with terminal half-life of 27.2 h. Treatment with ensartinib was well tolerated, and no serious adverse events were reported.

CONCLUSION

It was well tolerated in the six healthy male subjects following a single oral administration of 200 mg/100 μCi dose of ensartinib. Besides unchanged ensartinib, metabolite of M465 was the predominant circulating drug-related component. The drug was primarily eliminated in feces.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT03804541.

RAS/MAPK Pathway Driver Alterations Are Significantly Associated With Oncogenic KIT Mutations in Germ-cell Tumors

OBJECTIVE

To report the mutational profile and clinical outcomes of a cohort of patients with KIT-mutant seminomas and nonseminomatous germ-cell tumors (SGCT/NSGCTs).

PATIENTS AND METHODS

Retrospective cohort study of all patients with KIT-mutant GCTs sequenced at Memorial Sloan Kettering between March 2014 and March 2020. Tumors were assessed with MSK-IMPACT, a DNA next-generation sequencing assay for targeted sequencing of up to 468 key cancer genes.

RESULTS

Among 568 patients with GCTs, 8.1% had somatic KIT mutations, including 28 seminomas and 18 mixed/NSGCTs. Exons 17 (67.3%), 11 (22.4%), and 13 (6.1%) were most commonly affected. KIT-mutant cases were enriched for oncogenic RAS/MAPK pathway alterations compared to KIT-wildtype cases (34.8% vs 19.2%, P = .02). Among KIT-mutant cases, concurrent mutations were noted in KRAS (21.7%), RRAS2 (11.8%), CBL (6.5%), NRAS (4.3%), MAP2K1 (2.2%), and RAC1 (2.2%). Mutations in KRAS, RRAS2, and NRAS were mutually exclusive. In all, 73.9% of patients developed metastases and 95.7% received chemotherapy. No patients received KIT-directed tyrosine kinase inhibitors (TKIs). Classification as a NSGCT rather than a SGCT was associated with an increased risk of death (hazard ratio 9.1, 95% confidence interval 1.1-78.4, P = .04) while the presence of a concurrent RAS/MAPK pathway alteration was not (hazard ratio 0.8, 95% confidence interval 0.1-4.3, P = .76).

CONCLUSION

Mitogenic driver alterations can co-occur with activating KIT mutations, which may explain the lack of efficacy of KIT-directed TKIs in prior trials. Novel KIT-directed TKIs that target exon 17 mutations may benefit chemotherapy-refractory patients with KIT-mutant GCTs without RAS/MAPK alterations. Dual MEK/KIT inhibitor therapy in KIT-mutant GCTs with concurrent RAS/MAPK alterations could also be a plausible therapeutic strategy.

Effect of Hepatic Impairment on Cobimetinib Pharmacokinetics: The Complex Interplay Between Physiological Changes and Drug Characteristics

Cobimetinib is a kinase inhibitor indicated for use in combination with vemurafenib for treatment of unresectable/metastatic melanoma with specific BRAF mutations. Cobimetinib is extensively metabolized in liver; thus, patients with hepatic impairment (HI) might have increased cobimetinib exposure. In this study, we investigated the impact of HI on the pharmacokinetics (PK) and safety of cobimetinib. Subjects with normal hepatic function and mild to severe HI were enrolled. All subjects received a single oral dose of 10 mg cobimetinib, and serial blood samples were collected at specified times. Cobimetinib PK in subjects with mild and moderate HI was similar to that in those with normal liver function. However, subjects with severe HI, on average, showed ∼30% lower total AUC_0-∞ and ∼2-fold higher unbound AUC_0-∞ compared with those with normal hepatic function. These exposure differences can be explained by lower albumin levels observed in subjects with severe HI, the strong correlation between albumin level and the unbound fraction and the general PK variability of cobimetinib. In addition, previous studies with cobimetinib showed a lack of an exposure-response relationship for efficacy and safety. Therefore, collectively, our results suggest that the starting dose for patients with hepatic impairment can be the same as that for those with normal hepatic function.

Regional Proteomic Quantification of Clinically Relevant Non-Cytochrome P450 Enzymes along the Human Small Intestine

Current challenges in accurately predicting intestinal metabolism arise from the complex nature of the intestine, leading to limited applicability of available in vitro tools as well as knowledge deficits in intestinal physiology, including enzyme abundance. In particular, information on regional enzyme abundance along the small intestine is lacking, especially for non-cytochrome P450 enzymes such as carboxylesterases (CESs), UDP-glucuronosyltransferases (UGTs), and sulfotransferases (SULTs). We used cryopreserved human intestinal mucosa samples from nine donors as an in vitro surrogate model for the small intestine and performed liquid chromatography tandem mass spectrometry-based quantitative proteomics for 17 non-cytochrome P450 enzymes using stable isotope-labeled peptides. Relative protein quantification was done by normalization with enterocyte marker proteins, i.e., villin-1, sucrase isomaltase, and fatty acid binding protein 2, and absolute protein quantification is reported as picomoles per milligram of protein. Activity assays in glucuronidations and sequential metabolisms were conducted to validate the proteomics findings. Relative or absolute quantifications are reported for CES1, CES2, five UGTs, and four SULTs along the small intestine: duodenum, jejunum, and ileum for six donors and in 10 segments along the entire small intestine (A-J) for three donors. Relative quantification using marker proteins may be beneficial in further controlling for technical variabilities. Absolute quantification data will allow for scaling factor generation and in vivo extrapolation of intestinal clearance using physiologically based pharmacokinetic modeling. SIGNIFICANCE STATEMENT: Current knowledge gaps exist in intestinal protein abundance of non-cytochrome P450 enzymes. Here, we employ quantitative proteomics to measure non-cytochrome P450 enzymes along the human small intestine in nine donors using cryopreserved human intestinal mucosa samples. Absolute and relative abundances reported here will allow better scaling of intestinal clearance.

Is there enough evidence to classify cycloalkyl amine substituents as structural alerts?

Basic amine substituents provide several pharmacokinetic benefits relative to acidic and neutral functional groups, and have been extensively utilized as substituents of choice in drug design. On occasions, basic amines have been associated with off-target pharmacology via interactions with aminergic G-protein coupled receptors, ion-channels, kinases, etc. Structural features associated with the promiscuous nature of basic amines have been well-studied, and can be mitigated in a preclinical drug discovery environment. In addition to the undesirable secondary pharmacology, α-carbon oxidation of certain secondary or tertiary cycloalkyl amines can generate electrophilic iminium and aldehyde metabolites, potentially capable of covalent adduction to proteins or DNA. Consequently, cycloalkyl amines have been viewed as structural alerts (SAs), analogous to functional groups such as anilines, furans, thiophenes, etc., which are oxidized to reactive metabolites that generate immunogenic haptens by covalently binding to host proteins. Detailed survey of the literature, however, suggests that cases where preclinical or clinical toxicity has been explicitly linked to the metabolic activation of a cycloalkyl amine group are extremely rare. Moreover, there is a distinct possibility for the formation of electrophilic iminium/amino-aldehyde metabolites with numerous cycloalkyl amine-containing marketed drugs, since stable ring cleavage products have been characterized as metabolites in human mass balance studies. In the present work, a critical analysis of the evidence for and against the role of iminium ions/aldehydes as mediators of toxicity is discussed with a special emphasis on often time overlooked detoxication pathways of these reactive species to innocuous metabolites.

Computational Prediction of the Site(s) of Metabolism and Binding Modes of Protein Kinase Inhibitors Metabolized by CYP3A4

Protein kinase inhibitors (KIs), which are mainly biotransformed by CYP3A4-catalyzed oxidation, represent a rapidly expanding class of drugs used primarily for the treatment of cancer. Ligand- and structure-based methods were applied here to investigate whether computational approaches may be used to predict the site(s) of metabolism (SOM) of KIs and to identify amino acids within the CYP3A4 active site involved in KI binding. A data set of the experimentally determined SOMs of 31 KIs known to undergo biotransformation by CYP3A4 was collated. The structure-based (molecular docking) approach employed three CYP3A4 X-ray crystal structures to account for structural plasticity of this enzyme. Docking pose and SOM predictivity were influenced by the X-ray crystal template used for docking and the scoring function used for ranking binding poses. The best prediction of SOM (77%) was achieved using the substrate (bromoergocryptine)-bound X-ray crystal template together with the potential of mean force score. Binding interactions of KIs with CYP3A4 active site residues were generally similar to those observed for other substrates of this enzyme. The ligand-based molecular superposition approach, using bromoergocryptine from the X-ray cocrystal structure as a template, poorly predicted (42%) the SOM of KIs, although predictivity improved to 71% when the docked conformation of sorafenib was used as the template. Among the web-based approaches examined, all web servers provided excellent predictivity, with one web server predicting the SOM of 87% of the data set molecules. Computational approaches may be used to predict the SOM of KIs, and presumably other classes of CYP3A4 substrates, but predictivity varies between methods.

Targeting the ERK Signaling Pathway in Melanoma

The discovery of the role of the RAS/RAF/MEK/ERK pathway in melanomagenesis and its progression have opened a new era in the treatment of this tumor. Vemurafenib was the first specific kinase inhibitor approved for therapy of advanced melanomas harboring BRAF-activating mutations, followed by dabrafenib and encorafenib. However, despite the excellent results of first-generation kinase inhibitors in terms of response rate, the average duration of the response was short, due to the onset of genetic and epigenetic resistance mechanisms. The combination therapy with MEK inhibitors is an excellent strategy to circumvent drug resistance, with the additional advantage of reducing side effects due to the paradoxical reactivation of the MAPK pathway. The recent development of RAS and extracellular signal-related kinases (ERK) inhibitors promises to add new players for the ultimate suppression of this signaling pathway and the control of pathway-related drug resistance. In this review, we analyze the pharmacological, preclinical, and clinical trial data of the various MAPK pathway inhibitors, with a keen interest for their clinical applicability in the management of advanced melanoma.

Reviewing the role of healthy volunteer studies in drug development

BACKGROUND

With the exception of genotoxic oncology drugs, first-in-human, Phase 1 clinical studies of investigational drugs have traditionally been conducted in healthy volunteers (HVs). The primary goal of these studies is to investigate the pharmacokinetics and pharmacodynamics of a novel drug candidate, determine appropriate dosing, and document safety and tolerability.

MAIN BODY

When tailored to specific study objectives, HV studies are beneficial to manufacturers and patients alike and can be applied to both non-oncology and oncology drug development. Enrollment of HVs not only increases study accrual rates for dose-escalation studies but also alleviates the ethical concern of enrolling patients with disease in a short-term study at subtherapeutic doses when other studies (e.g. Phase 2 or Phase 3 studies) may be more appropriate for the patient. The use of HVs in non-oncology Phase 1 clinical trials is relatively safe but nonetheless poses ethical challenges because of the potential risks to which HVs are exposed. In general, most adverse events associated with non-oncology drugs are mild in severity, and serious adverse events are rare, but examples of severe toxicity have been reported. The use of HVs in the clinical development of oncology drugs is more limited but is nonetheless useful for evaluating clinical pharmacology and establishing an appropriate starting dose for studies in cancer patients. During the development of oncology drugs, clinical pharmacology studies in HVs have been used to assess pharmacokinetics, drug metabolism, food effects, potential drug-drug interactions, effects of hepatic and renal impairment, and other pharmacologic parameters vital for clinical decision-making in oncology. Studies in HVs are also being used to evaluate biosimilars versus established anticancer biologic agents.

CONCLUSION

A thorough assessment of toxicity and pharmacology throughout the drug development process is critical to ensure the safety of HVs. With the appropriate safeguards, HVs will continue to play an important role in future drug development.

Cobimetinib (GDC-0973, XL518)

The mitogen-activated protein kinase cascade (MAPK/ERK pathway) is a signaling pathway activated as a cellular response to various stimuli and for regulating the proliferation and survival of several types of eukaryotic cells, among others a wide variety of tumor cells. Mutations of the proteins involved in this pathway have been discovered in several tumor entities, indicating their inhibition as a potential therapeutic target. BRAF inhibitors have been in the clinical use since 2011. Several MEK inhibitors have been studied for metastatic cancer treatment in the recent past. After trametinib, cobimetinib is another potent, selective oral MEK1/2 inhibitor that was approved by European Medicine Agency (EMA) and Food and Drug Administration (FDA) in 2015 for treatment of malignant melanoma in a combination with the BRAF inhibitor vemurafenib.

Cobimetinib and trametinib inhibit platelet MEK but do not cause platelet dysfunction

The MEK inhibitors cobimetinib and trametinib are used in combination with BRAF inhibitors to treat metastatic melanoma but increase rates of hemorrhage relative to BRAF inhibitors alone. Platelets express several members of the MAPK signalling cascade including MEK1 and MEK2 and ERK1 and ERK2 but their role in platelet function and haemostasis is ambiguous as previous reports have been contradictory. It is therefore unclear if MEK inhibitors might be causing platelet dysfunction and contributing to increased hemorrhage. In the present study we performed pharmacological characterisation of cobimetinib and trametinib in vitro to investigate potential for MEK inhibitors to cause platelet dysfunction.

We report that whilst both cobimetinib and trametinib are potent inhibitors of platelet MEK activity, treatment with trametinib did not alter platelet function. Treatment with cobimetinib results in inhibition of platelet aggregation, integrin activation, alpha-granule secretion and adhesion but only at suprapharmacological concentrations. We identified that the inhibitory effects of high concentrations of cobimetinib are associated with off-target inhibition on Akt and PKC. Neither inhibitor caused any alteration in thrombus formation on collagen under flow conditions in vitro.

Our findings demonstrate that platelets are able to function normally when MEK activity is fully inhibited, indicating MEK activity is dispensable for normal platelet function. We conclude that the MEK inhibitors cobimetinib and trametinib do not induce platelet dysfunction and are therefore unlikely to contribute to increased incidence of bleeding reported during MEK inhibitor therapy.

Utility of physiologically based pharmacokinetic (PBPK) modeling in oncology drug development and its accuracy: a systematic review

PURPOSE

Physiologically based pharmacokinetic (PBPK) modeling, a mathematical modeling approach which uses a pharmacokinetic model to mimick human physiology to predict drug concentration-time profiles, has been used for the discover and development of drugs in various fields, including oncology, since 2000. There have been a few general review articles on the utilization of PBPK in the development of oncology drugs, but these do not include an evaluation of model prediction accuracy. We therefore conducted a systematic review to define the accuracy of PBPK model prediction and its utility throughout all the developmental phases of oncology drugs.

METHODS

A systematic search was performed in the PubMed, PubMed Central and Cochrane Library databases from 1980 to February 2017 for articles (1) written in English, (2) focused on oncology or antineoplastic or anticancer drugs, tumor or cancer or anticancer drugs listed in the U.S. National Institutes of Health and (3) involving a PBPK model. The absolute-average-folding-errors (AAFEs) of the area under the curve (AUC) between predicted and observed values in each article were calculated to assess model prediction accuracy.

RESULTS

Of the 2341 articles initially identified by our search of the databases, 40 were included in the review analysis. These articles reported on six types of studies, i.e. in vivo (n = 4), first-in-human (n = 5), phase II/III clinical trials (n = 9), organ impairment (n = 3), pediatrics (n = 4) and drug-drug interactions (n = 15). AAFEs of the predicted AUC for all groups of studies were within 1.3-fold of each other despite variations in experimental methodologies.

CONCLUSION

PBPK modeling is a potential tool which can be effectively applied throughout all phases of oncology drug development. The number of experimental animals and human participants enrolled in the studies can be reduced using PBPK modeling and PBPK-population-PK modeling. The limited number of publications of unsuccessful model application to date may contribute to bias toward the usefulness of modeling.

Cellular and viral oncogenes: the key to unlocking unknowns of Kaposi's sarcoma-associated herpesvirus pathogenesis

Oncogenic viruses carry an extensive arsenal of oncogenes for hijacking cellular pathways. Notably, variations in oncogenes among tumor-producing viruses give rise to different mechanisms for cellular transformation. Specifically, Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic virus able to infect and transform a variety of cell types. The oncogenicity of KSHV disseminates from the virus' ability to induce and encode a wide variety of both cellular and viral oncogenes. Such an array of cellular and viral oncogenes enables KSHV to induce the malignant phenotype of a KSHV-associated cancer. Evolutionarily, KSHV has acquired many oncogenic homologues capable of inducing cell proliferation, cell differentiation, cell survival, and immune evasion. Integration between inducing and encoding oncogenes plays a vital role in KSHV pathogenicity. KSHV is alleged to harbor the highest number of potential oncogenes by which a virus promotes cellular transformation and malignancy. Many KSHV inducing/encoding oncogenes are mainly expressed during the latent phase of KSHV infection, a period required for virus establishment of malignant cellular transformation. Elucidation of the exact mechanism(s) by which oncogenes promote KSHV pathogenicity would not only give rise to potential novel therapeutic targets/drugs but would also add to our understanding of cancer biology. The scope of this review is to examine the roles of the most important cellular and viral oncogenes involved in KSHV pathogenicity.

Mitogen-activated protein kinase (MEK) inhibitors to treat melanoma alone or in combination with other kinase inhibitors

INTRODUCTION

Malignant melanoma (MM) is an aggressive disease with a rapidly rising incidence due to neoplasm of melanocytes. Molecular targeted therapies have demonstrated lower toxicity and improved overall survival versus conventional therapies of MM. The revealing of mutations in the BRAF/MEK/ERK pathway has led to the development of BRAF inhibitors such as vemurafenib and dabrafenib for the treatment of cutaneous MM. Though, progression of resistance to these agents has prompted attempts to target downstream proteins in this pathway. Trametinib, a MEK1/2 inhibitor, was approved in 2013 for the treatment of BRAF V600E/K mutation-positive unresectable or metastatic cutaneous melanoma patients. Areas covered: The aim of the current review is to present an update on the role of MEK in progressive melanomas and summarize latest results of clinical studies with innovative MEK inhibitors and/or combined approaches with other kinase inhibitors such as BRAF inhibitors in the treatment of MM. Expert opinion: Two combined treatments (i.e. trametinib plus dabrafenib and vemurafenib plus cobimetinib) target two different kinases in the BRAF/MEK/ERK pathway. The simultaneous prohibition of both MEK and BRAF is associated with more durable response rate than BRAF monotherapy and can overcome acquired resistance.

Evaluation of Cytochrome P450 3A4-Mediated Drug-Drug Interaction Potential for Cobimetinib Using Physiologically Based Pharmacokinetic Modeling and Simulation

BACKGROUND AND OBJECTIVES

Cobimetinib is eliminated mainly through cytochrome P450 (CYP) 3A4-mediated hepatic metabolism in humans. A clinical drug-drug interaction (DDI) study with the potent CYP3A4 inhibitor itraconazole resulted in an approximately sevenfold increase in cobimetinib exposure. The DDI risk for cobimetinib with other CYP3A4 inhibitors and inducers needs to be assessed in order to provide dosing instructions.

METHODS

A physiologically based pharmacokinetic (PBPK) model was developed for cobimetinib using in vitro data. It was then optimized and verified using clinical pharmacokinetic data and itraconazole-cobimetinib DDI data. The contribution of CYP3A4 to the clearance of cobimetinib in humans was confirmed using sensitivity analysis in a retrospective simulation of itraconazole-cobimetinib DDI data. The verified PBPK model was then used to predict the effect of other CYP3A4 inhibitors and inducers on cobimetinib pharmacokinetics.

RESULTS

The PBPK model described cobimetinib pharmacokinetic profiles after both intravenous and oral administration of cobimetinib well and accurately simulated the itraconazole-cobimetinib DDI. Sensitivity analysis suggested that CYP3A4 contributes ~78 % of the total clearance of cobimetinib. The PBPK model predicted no change in cobimetinib exposure (area under the plasma concentration-time curve, AUC) with the weak CYP3A inhibitor fluvoxamine and a three to fourfold increase with the moderate CYP3A inhibitors, erythromycin and diltiazem. Similarly, cobimetinib exposure in the presence of strong (rifampicin) and moderate (efavirenz) CYP3A inducers was predicted to decrease by 83 and 72 %, respectively.

CONCLUSION

This study demonstrates the value of using PBPK simulation to assess the clinical DDI risk inorder to provide dosing instructions with other CYP3A4 perpetrators.

Cobimetinib and vemurafenib for the treatment of melanoma

INTRODUCTION

Cobimetinib combined with vemurafenib is a new approved MEK inhibitor for first line treatment of metastatic melanoma patients with BRAF V600 mutations. It improves tumor response rates and progression free survival compared to vemurafenib alone, while decreasing toxicities due to the paradoxical activation of the MAPK signaling pathway.

AREAS COVERED

This review covers the pharmacology, efficacy, and toxicity data derived from clinical and preclinical studies on cobimetinib. It also reports ongoing trials evaluating cobimetinib to better understand future developments for this drug.

EXPERT OPINION

The combination of cobimetinib and vemurafenib seems to be more toxic than the combination therapy dabrafenib and trametinib even if these four drugs have never been compared in a randomized trial. The future of this combination depends on its capacity to be combined simultaneously or sequentially with immune based therapies to improve the durability of responses.

Regulatory aspects of human radiolabeled mass balance studies in oncology: concise review

Human radiolabeled mass balance studies are performed to obtain information about the absorption, distribution, metabolism, and excretion of a drug in development. The main goals are to determine the route of elimination and major metabolic pathways. This review provides an overview of the current regulatory guidelines concerning human radiolabeled mass balance studies and discusses scientific trends seen in the last decade with a focus on mass balance studies of anticancer drugs. This paper also provides an overview of mass balance studies of anticancer agents that were executed in the last 10 years.

Absorption, metabolism and excretion of cobimetinib, an oral MEK inhibitor, in rats and dogs

1. The absorption, metabolism and excretion of cobimetinib, an allosteric inhibitor of MEK1/2, was characterized in mass balance studies following single oral administration of radiolabeled (¹⁴C) cobimetinib to Sprague-Dawley rats (30 mg/kg) and Beagle dogs (5 mg/kg). 2. The oral dose of cobimetinib was well absorbed (81% and 71% in rats and dogs, respectively). The maximal plasma concentrations for cobimetinib and total radioactivity were reached at 2-3 h post-dose. Drug-derived radioactivity was fully recovered (∼90% of the administered dose) with the majority eliminated in feces via biliary excretion (78% of the dose for rats and 65% for dogs). The recoveries were nearly complete after the first 48 h following dosing. 3. The metabolic profiles indicated extensive metabolism of cobimetinib prior to its elimination. For rats, the predominant metabolic pathway was hydroxylation at the aromatic core. Lower exposures for cobimetinib and total radioactivity were observed in male rats compared with female rats, which was consistent to in vitro higher clearance of cobimetinib for male rats. For dogs, sequential oxidative reactions occurred at the aliphatic portion of the molecule. Though rat metabolism was well-predicted in vitro with liver microsomes, dog metabolism was not. 4. Rats and dogs were exposed to the two major human circulating Phase II metabolites, which provided relevant metabolite safety assessment. In general, the extensive sequential oxidative metabolism in dogs, and not the aromatic hydroxylation in rats, was more indicative of the metabolism of cobimetinib in humans.

Safe handling of oral antineoplastic medications: Focus on targeted therapeutics in the home setting

Introduction With the growing number of oral targeted therapies being approved for use in cancer therapy, the potential for long-term administration of these drugs to cancer patients is expanding. The use of these drugs in the home setting has the potential to expose family members and caregivers to them either through direct contact with the drugs or indirectly by exposure to the parent compounds and/or their active metabolites in contaminated patients' waste. Methods A systematic literature review was performed and the known adverse health effect of 32 oral targeted therapeutics is summarized. In particular, the carcinogenicity, genotoxicity, and embryo-fetal toxicity, along with the route of excretion were evaluated. Results Carcinogenicity testing has not been performed on most of the oral targeted therapeutics and the genotoxicity data are mixed. However, the majority of these drugs exhibit adverse reproductive effects, some of which are severe. Currently, available data does not permit the possibility of a health hazard from inappropriate handling of drugs and contaminated patients waste to be ignored, especially in a long-term home setting. Further research is needed to understand these issues. Conclusions With the expanding use of targeted therapies in the home setting, family members and caregivers, especially those of reproductive risk age, are, potentially at risk. Overall basic education and related precautions should be taken to protect family members and caregivers from indirect or direct exposure from these drugs. Further investigations and discussion on this subject are warranted.