Relative Bioavailability of Cenobamate Administered as a Crushed Tablet, Either Orally or via Nasogastric Tube, versus an Intact Whole Tablet.

Cenobamate is approved for the treatment of focal seizures in adults and is currently available as an oral tablet. Alternative methods of drug administration are needed for patients who are unable to swallow whole intact tablets. This phase 1, open-label, randomized, single-dose, three-way crossover (3-period, 3-treatment, 6-sequence) study (NCT05572255), conducted in healthy volunteers, assessed the relative bioavailability of a crushed 200-mg cenobamate tablet administered orally or via nasogastric (NG) tube compared with an intact 200-mg tablet. Each treatment was separated by a 13-day washout period. Plasma samples for cenobamate concentration analysis were collected pre-dose and at multiple time points up to 264 h post-dose. Standard bioequivalence study criteria were applied to the relative bioavailability assessments. All 90% confidence intervals of test-to-reference geometric mean ratios for cenobamate pharmacokinetic parameters (Cmax, AUClast, and AUCinf) were within 85-110% (predefined limit, 80-125%), suggesting no difference in cenobamate exposures following administration of an intact tablet orally or a crushed tablet orally or via NG tube. All treatment-emergent adverse events (TEAEs) were classified as mild and resolved. There were no deaths or other serious AEs (SAEs), and no TEAEs led to discontinuation. Our results indicate that the administration of cenobamate as a crushed tablet taken orally or via an NG tube can provide additional flexibility when patients cannot swallow intact tablets. Based on the results of this study, cenobamate is now approved by FDA to be taken whole or the tablets can be crushed. The crushed tablet can be mixed with water and either administered by mouth as an oral suspension or administered via a nasogastric tube.

Factors Influencing Luciferase-Based Bioluminescent Imaging in Preclinical Models of Brain Tumor.

Bioluminescent imaging (BLI) is a powerful tool in biomedical research to measure gene expression and tumor growth. The current study examined factors that influence the BLI signal, specifically focusing on the tissue distribution of two luciferase substrates, D-luciferin and CycLuc1. D-luciferin, a natural substrate of firefly luciferase, has been reported to have limited brain distribution, possibly due to the efflux transporter, breast cancer resistance protein (Bcrp), at the blood-brain barrier. CycLuc1, a synthetic analog of D-luciferin, has a greater BLI signal at lower doses than D-luciferin, especially in the brain. Our results indicate that limited brain distribution of D-luciferin and CycLuc1 is predominantly dictated by their low intrinsic permeability across the cell membrane, where the efflux transporter, Bcrp, plays a relatively minor role. Both genetic ablation and pharmacological inhibition of Bcrp decreased the systemic clearance of both luciferase substrates, significantly increasing exposure in the blood and, hence, in organs and tissues. These data also indicate that the biodistribution of luciferase substrates can be differentially influenced in luciferase-bearing tissues, leading to a "tissue-dependent" BLI signal. The results of this study point to the need to consider multiple mechanisms that influence the distribution of luciferase substrates. SIGNIFICANCE STATEMENT: Bioluminescence is used to monitor many biological processes, including tumor growth. This study examined the pharmacokinetics, brain distribution, and the role of active efflux transporters on the luciferase substrates D-luciferin and CycLuc1. CycLuc1 has a more sustained systemic circulation time (longer half-life) that can provide an advantage for the superior imaging outcome of CycLuc1 over D-luciferin. The disparity in imaging intensities between brain and peripheral sites is due to low intrinsic permeability of these luciferase substrates across the blood-brain barrier.

In Vivo Efficacy of Tesevatinib in EGFR-Amplified Patient-Derived Xenograft Glioblastoma Models May Be Limited by Tissue Binding and Compensatory Signaling.

Tesevatinib is a potent oral brain penetrant EGFR inhibitor currently being evaluated for glioblastoma therapy. Tesevatinib distribution was assessed in wild-type (WT) and Mdr1a/b(-/-)Bcrp(-/-) triple knockout (TKO) FVB mice after dosing orally or via osmotic minipump; drug-tissue binding was assessed by rapid equilibrium dialysis. Two hours after tesevatinib dosing, brain concentrations in WT and TKO mice were 0.72 and 10.03 µg/g, respectively. Brain-to-plasma ratios (Kp) were 0.53 and 5.73, respectively. With intraperitoneal infusion, brain concentrations were 1.46 and 30.6 µg/g (Kp 1.16 and 25.10), respectively. The brain-to-plasma unbound drug concentration ratios were substantially lower (WT mice, 0.03-0.08; TKO mice, 0.40-1.75). Unbound drug concentrations in brains of WT mice were 0.78 to 1.59 ng/g. In vitro cytotoxicity and EGFR pathway signaling were evaluated using EGFR-amplified patient-derived glioblastoma xenograft models (GBM12, GBM6). In vivo pharmacodynamics and efficacy were assessed using athymic nude mice bearing either intracranial or flank tumors treated by oral gavage. Tesevatinib potently reduced cell viability [IC50 GBM12 = 11 nmol/L (5.5 ng/mL), GBM6 = 102 nmol/L] and suppressed EGFR signaling in vitro However, tesevatinib efficacy compared with vehicle in intracranial (GBM12, median survival: 23 vs. 18 days, P = 0.003) and flank models (GBM12, median time to outcome: 41 vs. 33 days, P = 0.007; GBM6, 44 vs. 33 days, P = 0.007) was modest and associated with partial inhibition of EGFR signaling. Overall, tesevatinib efficacy in EGFR-amplified PDX GBM models is robust in vitro but relatively modest in vivo, despite a high brain-to-plasma ratio. This discrepancy may be explained by drug-tissue binding and compensatory signaling.

Brain Distributional Kinetics of a Novel MDM2 Inhibitor SAR405838: Implications for Use in Brain Tumor Therapy.

Achieving an effective drug concentration in the brain is as important as targeting the right pathway when developing targeted agents for brain tumors. SAR405838 is a novel molecularly targeted agent that is in clinical trials for various solid tumors. Its application for tumors in the brain has not yet been examined, even though the target, the MDM2-p53 interaction, is attractive for tumors that could occur in the brain, including glioblastoma and brain metastases. In vitro and in vivo studies indicate that SAR405838 is a substrate of P-glycoprotein (P-gp). P-gp mediated active efflux at the blood-brain barrier plays a dominant role in limiting SAR405838 brain distribution. Even though the absence of P-gp significantly increases the drug exposure in the brain, the systemic exposure, including absorption and clearance processes, were unaffected by P-gp deletion. Model-based parameters of SAR405838 distribution across the blood-brain barrier indicate the CLout of the brain was approximately 40-fold greater than the CLin The free fraction of SAR405838 in plasma and brain were found to be low, and subsequent Kpuu values were less than unity, even in P-gp/Bcrp knockout mice. These results indicate additional efflux transporters other than P-gp and Bcrp may be limiting distribution of SAR405838 to the brain. Concomitant administration of elacridar significantly increased brain exposure, also without affecting the systemic exposure. This study characterized the brain distributional kinetics of SAR405838, a novel MDM2 inhibitor, to evaluate its potential in the treatment of primary and metastatic brain tumors. SIGNIFICANCE STATEMENT: This paper examined the brain distributional kinetics of a novel MDM2-p53 targeted agent, SAR405838, to see its possible application for brain tumors by using in vitro, in vivo, and in silico approaches. SAR405838 is found to be a substrate of P-glycoprotein (P-gp), which limits its distribution to the brain. Based on the findings in the paper, manipulation of the function of P-gp can significantly increase the brain exposure of SAR405838, which may give an insight on its potential benefit as a treatment for primary and metastatic brain cancer.

Brain Distribution of a Panel of Epidermal Growth Factor Receptor Inhibitors Using Cassette Dosing in Wild-Type and Abcb1/Abcg2-Deficient Mice.

Tyrosine kinase inhibitors that target the epidermal growth factor receptor (EGFR) have had success in treating EGFR-positive tumors, including non-small-cell lung cancer (NSCLC). However, developing EGFR inhibitors that can be delivered to the brain remains a challenge. To identify optimal compounds for brain delivery, eight EGFR inhibitors [afatinib, 6-[4-[(4-ethylpiperazin-1-yl)methyl]phenyl]-N-(1-phenylethyl)-7H-pyrrolo[2,3-day]pyrimidin-4-amine (AEE788), [4-(3-chloro-2-fluoroanilino)-7-methoxyquinazolin-6-yl] (2R)-2,4-dimethylpiperazine-1-carboxylate (AZD3759), erlotinib, dacomitinib, gefitinib, osimertinib, and vandetanib] were evaluated for distributional kinetics using cassette dosing with the ultimate goal of understanding the brain penetrability of compounds that share the same molecular target in an important oncogenic signaling pathway for both primary brain tumors (glioblastoma) and brain metastases (e.g., NSCLC). Cassette dosing was validated by comparing the brain-to-plasma ratios obtained from cassette-dosing to discrete-dosing studies. The brain-to-blood partition coefficients (Kp,brain) were calculated following cassette dosing of the eight EGFR inhibitors. The comparison of Kp,brain in wild-type and transporter-deficient mice confirmed that two major efflux transporters at the blood-brain barrier (BBB), P-glycoprotein and breast cancer resistance protein, play a crucial role in the brain distribution of seven out of eight EGFR inhibitors. Results show that the prediction of brain distribution based on physicochemical properties of a drug can be misleading, especially for compounds subject to extensive efflux transport. Moreover, this study informs the choice of EGFR inhibitors, i.e., determining BBB permeability combined with a known target potency, that may be effective in future clinical trials for brain tumors.

Integrated mapping of pharmacokinetics and pharmacodynamics in a patient-derived xenograft model of glioblastoma.

Therapeutic options for the treatment of glioblastoma remain inadequate despite concerted research efforts in drug development. Therapeutic failure can result from poor permeability of the blood-brain barrier, heterogeneous drug distribution, and development of resistance. Elucidation of relationships among such parameters could enable the development of predictive models of drug response in patients and inform drug development. Complementary analyses were applied to a glioblastoma patient-derived xenograft model in order to quantitatively map distribution and resulting cellular response to the EGFR inhibitor erlotinib. Mass spectrometry images of erlotinib were registered to histology and magnetic resonance images in order to correlate drug distribution with tumor characteristics. Phosphoproteomics and immunohistochemistry were used to assess protein signaling in response to drug, and integrated with transcriptional response using mRNA sequencing. This comprehensive dataset provides simultaneous insight into pharmacokinetics and pharmacodynamics and indicates that erlotinib delivery to intracranial tumors is insufficient to inhibit EGFR tyrosine kinase signaling.

Barriers to Effective Drug Treatment for Brain Metastases: A Multifactorial Problem in the Delivery of Precision Medicine.

The treatment of metastatic lesions in the brain represents a serious unmet medical need in the field of neuro-oncology. Even though many effective compounds have demonstrated success in treating peripheral (non-CNS) tumors with targeted agents, one aspect of this lack of success in the brain may be related to poor delivery of otherwise effective compounds. Many factors can influence the brain delivery of these agents, but one key barrier is a heterogeneously "leaky" BBB that expresses efflux transporters that limit the BBB permeability for many targeted agents. Future success in therapeutics for brain metastases must take into account the adequate delivery of "active, free drug" to the target, and may include combinations of targeted drugs that are appropriate to address each individual patient's tumor type. This review discusses some issues that are pertinent to precision medicine for brain metastases, using specific examples of tumor types that have a high incidence of brain metastases.

Pharmacokinetic Assessment of Cooperative Efflux of the Multitargeted Kinase Inhibitor Ponatinib Across the Blood-Brain Barrier.

A compartmental blood-brain barrier (BBB) model describing drug transport across the BBB was implemented to evaluate the influence of efflux transporters on the rate and extent of the multikinase inhibitor ponatinib penetration across the BBB. In vivo pharmacokinetic studies in wild-type and transporter knockout mice showed that two major BBB efflux transporters, P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp), cooperate to modulate the brain exposure of ponatinib. The total and unbound (free) brain-to-plasma ratios were approximately 15-fold higher in the triple knockout mice lacking both P-gp and Bcrp [Mdr1a/b(-/-)Bcrp1(-/-)] compared with the wild-type mice. The triple knockout mice had a greater than an additive increase in the brain exposure of ponatinib when compared with single knockout mice [Bcrp1(-/-) or Mdr1a/b(-/-)], suggesting functional compensation of transporter-mediated drug efflux. Based on the BBB model characterizing the observed brain and plasma concentration-time profiles, the brain exit rate constant and clearance out of the brain were approximately 15-fold higher in the wild-type compared with Mdr1a/b(-/-)Bcrp1(-/-) mice, resulting in a significant increase in the mean transit time (the average time spent by ponatinib in the brain in a single passage) in the absence of efflux transporters (P-gp and Bcrp). This study characterized transporter-mediated drug efflux from the brain, a process that reduces the duration and extent of ponatinib exposure in the brain and has critical implications for the use of targeted drug delivery for brain tumors.

Brain Distribution of a Novel MEK Inhibitor E6201: Implications in the Treatment of Melanoma Brain Metastases.

Clinically meaningful efficacy in the treatment of brain tumors, including melanoma brain metastases (MBM), requires selection of a potent inhibitor against a suitable target, and adequate drug distribution to target sites in the brain. Deregulated constitutive signaling of mitogen-activated protein kinase (MAPK) pathway has been frequently observed in melanoma, and mitogen-activated protein/extracellular signal-regulated kinase (MEK) has been identified to be an important target. E6201 is a potent synthetic small-molecule MEK inhibitor. The purpose of this study was to evaluate brain distribution of E6201, and examine the impact of active efflux transport at the blood-brain barrier on the central nervous system (CNS) exposure of E6201. In vitro studies utilizing transfected Madin-Darby canine kidney II (MDCKII) cells indicate that E6201 is not a substrate of P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp). In vivo studies also suggest a minimal involvement of P-gp and Bcrp in E6201's brain distribution. The total concentrations in brain were higher than in plasma, resulting in a brain-to-plasma AUC ratio (Kp) of 2.66 in wild-type mice. The brain distribution was modestly enhanced in Mdr1a/b-/-, Bcrp1-/-, and Mdr1a/b-/-Bcrp1-/- knockout mice. The nonspecific binding of E6201 was higher in brain compared with plasma. However, free-drug concentrations in brain following 40 mg/kg intravenous dose reach levels that exceed reported in vitro half-maximal inhibitory concentration (IC50) values, suggesting that E6201 may be efficacious in inhibiting MEK-driven brain tumors. The brain distribution characteristics of E6201 make it an attractive targeted agent for clinical testing in MBM, glioblastoma, and other CNS tumors that may be effectively targeted with inhibition of MEK signaling.

Is the blood-brain barrier really disrupted in all glioblastomas? A critical assessment of existing clinical data.

The blood-brain barrier (BBB) excludes the vast majority of cancer therapeutics from normal brain. However, the importance of the BBB in limiting drug delivery and efficacy is controversial in high-grade brain tumors, such as glioblastoma (GBM). The accumulation of normally brain impenetrant radiographic contrast material in essentially all GBM has popularized a belief that the BBB is uniformly disrupted in all GBM patients so that consideration of drug distribution across the BBB is not relevant in designing therapies for GBM. However, contrary to this view, overwhelming clinical evidence demonstrates that there is also a clinically significant tumor burden with an intact BBB in all GBM, and there is little doubt that drugs with poor BBB permeability do not provide therapeutically effective drug exposures to this fraction of tumor cells. This review provides an overview of the clinical literature to support a central hypothesis: that all GBM patients have tumor regions with an intact BBB, and cure for GBM will only be possible if these regions of tumor are adequately treated.

Heterogeneous Binding and Central Nervous System Distribution of the Multitargeted Kinase Inhibitor Ponatinib Restrict Orthotopic Efficacy in a Patient-Derived Xenograft Model of Glioblastoma.

This study investigated how differences in drug distribution and free fraction at different tumor and tissue sites influence the efficacy of the multikinase inhibitor ponatinib in a patient-derived xenograft model of glioblastoma (GBM). Efficacy studies in GBM6 flank (heterotopic) and intracranial (orthotopic) models showed that ponatinib is effective in the flank but not in the intracranial model, despite a relatively high brain-to-plasma ratio. In vitro binding studies indicated that flank tumor had a higher free (unbound) drug fraction than normal brain. The total and free drug concentrations, along with the tissue-to-plasma ratio (Kp) and its unbound derivative (Kp,uu), were consistently higher in the flank tumor than the normal brain at 1 and 6 hours after a single dose in GBM6 flank xenografts. In the orthotopic xenografts, the intracranial tumor core displayed higher Kp and Kp,uu values compared with the brain-around-tumor (BAT). The free fractions and the total drug concentrations, hence free drug concentrations, were consistently higher in the core than in the BAT at 1 and 6 hours postdose. The delivery disadvantages in the brain and BAT were further evidenced by the low total drug concentrations in these areas that did not consistently exceed the in vitro cytotoxic concentration (IC50). Taken together, the regional differences in free drug exposure across the intracranial tumor may be responsible for compromising efficacy of ponatinib in orthotopic GBM6.