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Sotatercept is a breakthrough, first-in-class biologic, that is FDA-approved for the treatment of pulmonary arterial hypertension (PAH). A population pharmacokinetic (PopPK) model was developed using data from two phase 1 studies in healthy participants, and two phase 2 studies and one phase 3 study in participants with PAH. The pooled sotatercept PK data encompassed single intravenous (IV) or subcutaneous (SC) doses ranging from 0.01 to 3.0 mg/kg, as well as multiple SC doses ranging from 0.03 to 1.0 mg/kg, with PK samples collected up to a maximum of ~150 weeks following Q3W and Q4W dosing regimens. The final PopPK analysis included 350 participants, with 30 and 320 participants receiving sotatercept IV and SC, respectively. A two-compartment model with a first-order absorption rate constant and a linear disposition from central compartment well-described sotatercept PK. The estimated bioavailability is ~66%; bioavailability, clearance (CL), and central volume (VC) have low to moderate inter-individual variability. Time-varying body weight and baseline albumin concentration were statistically significant predictors of PK; CL and VC were predicted to increase with increasing body weight, while CL was predicted to decrease with increasing baseline albumin concentration. However, the magnitude of covariate effects is not predicted to meaningfully alter the disposition of sotatercept. Altogether, the PopPK modeling results demonstrate favorable PK characteristics (low to moderate variability and typical bioavailability), supporting sotatercept as a SC biological agent for the treatment of patients with PAH., (© 2024 The Author(s). CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Homozygous familial hypercholesterolemia (HoFH) is a rare and serious genetic condition characterized by premature cardiovascular disease due to severely elevated low-density lipoprotein cholesterol (LDL-C). HoFH primarily results from loss-of-function (LOF) mutations in the LDL receptor (LDLR), reducing LDL-C clearance such that patients experience severe hypercholesterolemia, exacerbating the risk of developing cardiovascular events. Treatment options such as statins, lomitapide, ezetimibe, proprotein convertase subtilisin/kexin type 9 inhibitors, and apheresis help lower LDL-C; however, many patients with HoFH still fail to reach their target LDL-C levels and many of these lipid-lowering therapies are not indicated for pediatric use. Angiopoietin-like protein 3 (ANGPTL3) has been identified as a target to treat elevated LDL-C by acting as a natural inhibitor of lipoprotein lipase (LPL) and endothelial lipase (EL), enzymes involved in the hydrolysis of the triglyceride and phospholipid content of very low-density lipoproteins. Persons heterozygous for LOF mutations in ANGPTL3 were reported to have lower LDL-C than non-carriers and lower risk of coronary artery disease. Evinacumab is a first-in-class human monoclonal antibody that specifically binds to ANGPTL3 to prevent its inhibition of LPL and EL. In clinical trials, a 15 mg/kg intravenous dose every 4 weeks has shown a mean percent change from baseline in LDL-C of ~50% in adult, adolescent, and pediatric patients with HoFH. This mini review article describes the mechanism of action of evinacumab, evinacumab population PK and PD modeling, and clinical development history of evinacumab for the treatment of HoFH., (© 2024 Regeneron Pharmaceuticals, Inc. Clinical and Translational Science published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

Background: Homozygous familial hypercholesterolemia (HoFH) is a rare genetic disorder characterized by severely elevated low-density lipoprotein cholesterol (LDL-C) levels due to profoundly defective LDL receptor (LDLR) function. Given that severely elevated LDL-C starts in utero, atherosclerosis often presents during childhood or adolescence, creating a largely unmet need for aggressive LDLR-independent lipid-lowering therapies in young patients with HoFH. Here we present the first evaluation of the efficacy and safety of evinacumab, a novel LDLR-independent lipid-lowering therapy, in pediatric patients with HoFH from parts A and B of a 3-part study., Methods: The phase 3, part B, open-label study treated 14 patients 5 to 11 years of age with genetically proven HoFH (true homozygotes and compound heterozygotes) with LDL-C >130 mg/dL, despite optimized lipid-lowering therapy (including LDLR-independent apheresis and lomitapide), with intravenous evinacumab 15 mg/kg every 4 weeks., Results: Evinacumab treatment rapidly and durably (through week 24) decreased LDL-C with profound reduction in the first week, with a mean (SE) LDL-C reduction of -48.3% (10.4%) from baseline to week 24. ApoB (mean [SE], -41.3% [9.0%]), non-high-density lipoprotein cholesterol (-48.9% [9.8%]), and total cholesterol (-49.1% [8.1%]) were similarly decreased. Treatment-emergent adverse events were reported in 10 (71.4%) patients; however, only 2 (14.3%) reported events that were considered to be treatment-related (nausea and abdominal pain). One serious treatment-emergent adverse event of tonsillitis occurred (n=1), but this was not considered treatment-related., Conclusions: Evinacumab constitutes a new treatment for pediatric patients with HoFH and inadequately controlled LDL-C despite optimized lipid-lowering therapy, lowering LDL-C levels by nearly half in these extremely high-risk and difficult-to-treat individuals., Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04233918., Competing Interests: Disclosures A.W. reports payment or honoraria for lectures, presentations, speakers’ bureaus, article writing, or educational events from Novartis and Algorithm; participation in a data safety monitoring board or advisory board for Amryt Pharma; leadership or fiduciary role in other board, society, committee, or advocacy group, paid or unpaid, for Novartis; and research support for pharmaceutical trials from Amgen, Regeneron Pharmaceuticals, Inc, Novartis, Silence Therapeutics, Esperion, and Ultragenyx. S.G.-P. reports receiving research support from Amgen. S.A., J.M., S.B., P.B., R.T.G., B.H., and R.P. are employees of and stockholders in Regeneron Pharmaceuticals, Inc. E.A.B. is a steering committee member for the REDUCE-IT (Amarin) and PROMINENT (Kowa) trials, and receives research support from Regeneron Pharmaceuticals, Inc. He has received speaking or consulting honoraria from 89Bio, Amarin, Amgen, Amryt, Dalcor, Esperion, Immunovant, Ionis, Merck, New Amsterdam, and Pfizer. M.-J.C. reports honoraria from AstraZeneca, Merck Sharp & Dohme, Pfizer, Amgen, and Sanofi. C.B.-S. reports honoraria for presentations from the National Association of Continuing Medical Education and the Cardiometabolic Health Congress. S.B. reports funding or consulting fees from Amgen, Altimmune, Axcella, Regeneron Pharmaceuticals, Inc, Ionis Pharmaceuticals, Boehringer Ingelheim, Esperion, Lilly, Madrigal, Merck, and Novartis. J.B. reports funding or consulting fees from Regeneron Pharmaceuticals, Inc. P.M.M. reports receipt of research grants to his institution for the participation in the ODYSSEY OUTCOMES trial, as well as financial fees for serving as a medical monitor for the trial and associated support for travel related to trial meetings from Sanofi; consulting fees from Regeneron Pharmaceuticals, Inc, Amgen, Esperion, Kaneka, and Stage II Innovations; advisor fees from Novartis for serving on their advisory committee; and research grants to his institution from Ionis, FH Foundation, GB Life Sciences, Aegerion, Amgen, Kowa, Novartis, and Regeneron Pharmaceuticals, Inc. The other authors report no conflicts.

Effective antiviral treatments for coronavirus disease 2019 (COVID-19) are needed to reduce the morbidity and mortality associated with severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2) infection, particularly in patients with risk factors for severe disease. Molnupiravir (MK-4482, EIDD-2801) is an orally administered, ribonucleoside prodrug of β-D-N4-hydroxycytidine (NHC) with submicromolar potency against SARS-CoV-2. A population pharmacokinetic (PopPK) analysis for molnupiravir exposure was conducted using 4202 NHC plasma concentrations collected in 1207 individuals from a phase I trial in healthy participants, a phase IIa trial in non-hospitalized participants with COVID-19, a phase II trial in hospitalized participants with COVID-19, and a phase II/III trial in non-hospitalized participants with COVID-19. Molnupiravir pharmacokinetics (PK) was best described by a two-compartment model with a transit-compartment absorption model and linear elimination. Molnupiravir apparent elimination clearance increased with body weight less-than-proportionally (power 0.412) and was estimated as 70.6 L/h in 80-kg individuals with a moderate interindividual variability (43.4% coefficient of variation). Additionally, effects of sex and body mass index on apparent central volume and food status and formulation on the absorption mean transit time were identified as statistically significant descriptors of variability in these PK parameters. However, none of the identified covariate effects caused clinically relevant changes in the area under the NHC concentration versus time curve between doses, the exposure metric most closely related to clinical response. Overall, the PopPK model indicates that molnupiravir can be administered in adults without dose adjustment based on age, sex, body size, food, and mild-to-moderate renal or mild hepatic impairment., (© 2023 Merck Sharp & Dohme LLC. Ridgeback Biotherapeutics. Jill Fiedler-Kelly and The Authors. CPT: Pharmacometrics & Systems Pharmacology published by Wiley Periodicals LLC on behalf of American Society for Clinical Pharmacology and Therapeutics.)

In the 10-week, phase 2 CLARITY study of patients with major depressive disorder, adjunctive therapy to antidepressants with pimavanserin 34 mg once daily statistically significantly improved the Hamilton Depression Rating Scale (HAMD-17) total score (primary endpoint) and Sheehan Disability Scale (SDS) score (secondary endpoint) versus placebo. This analysis characterized the exposure-response (E-R) relationships of pimavanserin in this CLARITY patient population. Exposure measures were estimated for each patient based on population-pharmacokinetic empirical Bayesian estimates. E-R models were developed to describe exposure-efficacy (HAMD-17, SDS, and Clinical Global Impression-Improvement [CGI-I] scale) and exposure-safety relationships (Karolinska Sleepiness Scale [KSS], Massachusetts General Hospital Sexual Functioning Inventory [MGH-SFI], and adverse events [AEs] of headache, sedation, and somnolence) relationships. For the primary efficacy endpoint (HAMD-17 scores), a sigmoid maximum-effect model described the time course of response, and a linear function of pimavanserin exposure was statistically significant. HAMD-17 scores decreased steadily over time following placebo and pimavanserin treatment; separation from placebo increased as peak pimavanserin plasma concentration (C max ) increased. At median pimavanserin C max (34-mg dose), the reduction from baseline in HAMD-17 scores was -11.1 and -13.5 at weeks 5 and 10, respectively. Relative to placebo, the model predicted comparable reductions in HAMD-17 scores at weeks 5 and 10. Similar improvements in favor of pimavanserin were detected with SDS, CGI-I, MGH-SFI, and KSS scores. No E-R relationship was found for AEs. E-R modeling predicted a relationship between higher pimavanserin exposure and improvement in HAMD-17 score and improvement across multiple secondary efficacy endpoints., (© 2023 The Authors. Clinical Pharmacology in Drug Development published by Wiley Periodicals LLC on behalf of American College of Clinical Pharmacology.)

An intramuscular formulation of aripiprazole monohydrate dosed once monthly (AOM) was developed to address nonadherence with the approved oral tablets. A 3-compartment linear population pharmacokinetic model for oral and AOM doses was developed; relative bioavailability was estimated for AOM relative to oral dosing and body mass index and sex were significant predictors of AOM absorption rate constant (longer absorption half-life for women and absorption half-life increases with increasing body mass index). Aripiprazole apparent oral clearance for subjects with cytochrome P450 (CYP) 2D6 poor metabolizer status and in the presence of strong CYP2D6 inhibitors was approximately half that of subjects with CYP2D6 extensive metabolizer status and 24% lower in the presence of strong CYP3A4 inhibitors. Simulations of the population pharmacokinetics were conducted to evaluate the effect of different dose initiation strategies for AOM, the effects of CYP2D6 metabolizer status, coadministration of CYP2D6 and CYP3A4 inhibitors, and missed doses. An exposure-response model with an exponential hazard function of the model-predicted minimum concentration (C min ) described the time to relapse. The hazard ratio (95% confidence interval) was 4.41 (2.89-6.75). Thus, a subject with a diagnosis of schizophrenia and C min  ≥ 95 ng/mL is 4.41 times less likely to relapse relative to a subject with C min  < 95 ng/mL., (© 2022 The Authors. Clinical Pharmacology in Drug Development published by Wiley Periodicals LLC on behalf of American College of Clinical Pharmacology.)

Sphingosine-1-phosphate (S1P) binding to the S1P-1 receptor (S1P1R) controls the egress of lymphocytes from lymphoid organs and targets modulation of immune responses in autoimmune diseases. Pharmacologic modulation of S1P receptors has been linked to heart rate reduction. BMS-986166, a prodrug of the active phosphorylated metabolite BMS-986166-P, presents an improved cardiac safety profile in preclinical studies compared to other S1P1R modulators. The pharmacokinetics, safety, and pharmacodynamics of BMS-986166 versus placebo after single (0.75-5.0 mg) and repeated (0.25-1.5 mg/day) oral administration were assessed in healthy participants after a 1-day lead-in placebo period. A population model was developed to jointly describe BMS-986166 and BMS-986166-P pharmacokinetics and predict individual exposures. Inhibitory sigmoid models described the relationships between average daily BMS-986166-P concentrations and nadir of time-matched (day -1) placebo-corrected heart rate on day 1 (nDDHR, where DD represents ∆∆) and nadir of absolute lymphocyte count (nALC). Predicted decreases in nDDHR and nALC were 9 bpm and 20% following placebo, with maximum decreases of 10 bpm in nDDHR due to drug effect, and approximately 80% in nALC due to drug and placebo. A 0.5-mg/day dose regimen achieves the target 65% reduction in nALC associated with a 2-bpm decrease in nDDHR over placebo., (© 2020 Bristol Myers Squibb. Clinical Pharmacology in Drug Development published by Wiley Periodicals LLC on behalf of American College of Clinical Pharmacology.)

This analysis developed a population pharmacokinetic (PK) model for odanacatib, characterized demographic and concomitant medication covariates effect, and provided odanacatib exposure estimates for subjects in phase 2/3 studies. Data from multiple phase 1 (P005, P025, and P014), phase 2b (P004 and P022), and phase 3 (Long-Term Odanacatib Fracture Trial; P018) studies were pooled to create a data set of 1280 postmenopausal women aged 45 to 91 years (102 from phase 1, 514 from phase 2b, and 664 from phase 3) who received weekly oral odanacatib doses ranging from 3 to 100 mg. A 1-compartment model with first-order absorption, dose-dependent relative bioavailability (F1), and first-order elimination best described odanacatib PK. F1 decreased from the 100% reference bioavailability for a 3-mg oral dose to 24.5% for a 100-mg dose. Eight statistically significant covariates were included in the final PK model: body weight, age, race, and concomitant cytochrome P450 (CYP)3A inhibitors on apparent clearance; body weight on apparent central volume of distribution; and concomitant hydrochlorothiazide, high-fat breakfast, and a study effect on F1. All fixed- and random-effects parameters were estimated with good precision (%standard error of the mean ≤29.5%). This population PK analysis provides insights into intrinsic- and extrinsic-factor effects on odanacatib exposure in postmenopausal and elderly women with osteoporosis. The magnitude of the intrinsic-factor effects was generally modest (odanacatib exposure geometric mean ratios, 0.80-1.21) even in subjects aged >80 years, or in subsets with multiple combinations of factors., (© 2020, The American College of Clinical Pharmacology.)

Congenital amegakaryocytic thrombocytopaenia (CAMT) is a disorder caused by c-MPL mutations that impair thrombopoietin (TPO) signalling, resulting in a near absence of megakaryocytes (MKs). While this phenotype is consistent in adults, neonates with CAMT can present with severe thrombocytopaenia despite normal MK numbers. To investigate this, we characterized MKs and platelets in newborn c-MPL –/– mice. Liver MKs in c-MPL –/– neonates were reduced in number and size compared with wild-type (WT) age-matched MKs, and exhibited ultrastructural abnormalities not found in adult c-MPL –/– MKs. Platelet counts were lower in c-MPL –/– compared with WT mice at birth and did not increase over the first 2 weeks of life. In vivo biotinylation revealed a significant reduction in the platelet half-life of c-MPL –/– newborn mice (P2) compared with age-matched WT pups, which was not associated with ultrastructural abnormalities. Genetic deletion of the pro-apoptotic Bak did not rescue the severely reduced platelet half-life of c-MPL –/– newborn mice, suggesting that it was due to factors other than platelets entering apoptosis early. Indeed, adult GFP+ (green fluorescent protein transgenic) platelets transfused into thrombocytopenic c-MPL –/– P2 pups also had a shortened lifespan, indicating the importance of cell-extrinsic factors. In addition, neonatal platelets from WT and c-MPL –/– mice exhibited reduced P-selectin surface expression following stimulation compared with adult platelets of either genotype, and platelets from c-MPL –/– neonates exhibited reduced glycoprotein IIb/IIIa (GPIIb/IIIa) activation in response to thrombin compared with age-matched WT platelets. Taken together, our findings indicate that c-MPL deficiency is associated with abnormal maturation of neonatal MKs and developmental stage-specific defects in platelet function., Competing Interests: Conflict of Interest: The authors declare no competing financial interests.

Interleukin-1 beta (IL-1β) is an inflammatory mediator which may contribute to the pathophysiology of rheumatoid arthritis (RA) and type 2 diabetes mellitus (T2DM). Population pharmacokinetics (PK) of LY2189102, a high affinity anti-IL-1β humanized monoclonal immunoglobulin G4 evaluated for efficacy in RA and T2DM, were characterized using data from 79 T2DM subjects (Study H9C-MC-BBDK) who received 13 weekly subcutaneous (SC) doses of LY2189102 (0.6, 18, and 180 mg) and 96 RA subjects (Study H9C-MC-BBDE) who received five weekly intravenous (IV) doses (0.02-2.5 mg/kg). Frequency of anti-drug antibody (ADA) development appears dose-dependent and is different between studies (36.7% in Study H9C-MC-BBDK vs. 2.1% in Study H9C-MC-BBDE), likely due to several factors, including differences in patient population and background medications, administration routes, and assays. A two-compartment model with dose-dependent bioavailability best characterizes LY2189102 PK following IV and SC administration. Typical elimination and distribution clearances, central and peripheral volumes of distribution are 0.222 L/day, 0.518 L/day, 3.08 L, and 1.94 L, resulting in a terminal half-life of 16.8 days. Elimination clearance increased linearly, yet modestly, with baseline creatinine clearance and appears 37.6% higher in subjects who developed ADA. Bioavailability (0.432-0.721) and absorption half-life (94.3-157 h) after SC administration are smaller with larger doses. Overall, LY2189102 PK is consistent with other therapeutic humanized monoclonal antibodies and is likely to support convenient SC dosing.

The dynamics of aging and type 2 diabetes (T2D) disease progression were investigated in normal [Wistar-Kyoto (WKY)] and diabetic [Goto-Kakizaki (GK)] rats and a mechanistic disease progression model was developed for glucose, insulin, and glycosylated hemoglobin (HbA1c) changes over time. The study included 30 WKY and 30 GK rats. Plasma glucose and insulin, blood glucose and HbA1c concentrations and hematological measurements were taken at ages 4, 8, 12, 16 and 20 weeks. A mathematical model described the development of insulin resistance (IR) and β-cell function with age/growth and diabetes progression. The model utilized transit compartments and an indirect response model to quantitate biomarker changes over time. Glucose, insulin and HbA1c concentrations in WKY rats increased to a steady-state at 8 weeks due to developmental changes. Glucose concentrations at 4 weeks in GK rats were almost twice those of controls, and increased to a steady-state after 8 weeks. Insulin concentrations at 4 weeks in GK rats were similar to controls, and then hyperinsulinemia occurred until 12-16 weeks of age indicating IR. Subsequently, insulin concentrations in GK rats declined to slightly below WKY controls due to β-cell failure. HbA1c showed a delayed increase relative to glucose. Modeling of HbA1c was complicated by age-related changes in hematology in rats. The diabetes model quantitatively described the glucose/insulin inter-regulation and HbA1c production and reflected the underlying pathogenic factors of T2D--IR and β-cell dysfunction. The model could be extended to incorporate other biomarkers and effects of various anti-diabetic drugs.

Imatinib (Glivec, Gleevec, STI571) is a small tyrosine kinase inhibitor that is currently in phase II clinical trials in patients with recurrent glioblastoma. Its therapeutic benefit is minimal, although it is greater in some patients when combined with hydroxyurea. Imatinib is transported by human and rodent ATP-binding cassette (ABC) transporters like P-glycoprotein (Pgp) and the breast cancer resistance protein (BCRP). We have investigated whether ABC transporters determine the pharmacokinetics of imatinib and its pharmacological active metabolite CGP74588 in rat C6 glioma cells. ABC transporter expressions were measured by quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). C6 cells express high concentrations of the Pgp-encoding gene Mdr1b and a 10-fold smaller amount of the Pgp-encoding gene Mdr1a. The relative expression of ABC transporter genes are: Mdr1b>Mrp4>Mrp1>Mrp5>Mdr1a>Mrp3>Mrp2>Bcrp. The accumulation of imatinib into C6 cells increased linearly with the extracellular concentration of imatinib (0.5-50microM) and was not increased by zosuquidar (selective Pgp inhibitor) or elacridar (inhibitor of both Pgp and Bcrp). In contrast, there was less CGP74588 than imatinib in C6 cells and its concentration increased with the extracellular concentration in a sigmoid fashion. Lastly, 10microM valspodar (selective Pgp inhibitor), elacridar and zosuquidar all increased the accumulation of CGP74588 by 2.5-fold. Thus CGP74588 is readily transported by the Pgp in rat C6 gliomas cells, which raises the question of the role of Pgp in the resistance of recurrent glioblastomas to imatinib.

Purpose: The selective protein tyrosine kinase inhibitor, imatinib, inhibits the growth of glioma cells in preclinical models, but its poor brain distribution limits its efficacy in patients. P-glycoprotein (P-gp, rodent Mdr1a/1b or Abcb1a/1b) and Breast cancer resistance protein (rodent Bcrp1 or Abcg2) were suggested to restrict the delivery of imatinib to the brain. This study evaluates the effect of administering selective inhibitors of these transporters together with imatinib on the systemic and cerebral disposition of imatinib in mice., Materials and Methods: Wild-type, Mdr1a/1b(-/-) and Bcrp1(-/-) mice were given imatinib intravenously, either alone, or with valspodar, zosuquidar (P-gp inhibitors), or elacridar (a P-gp and Bcrp1 inhibitor). The blood and brain concentrations of [(14)C]imatinib and its radioactive metabolites were determined., Results: The blockade of P-gp by valspodar or zosuquidar (>3 mg/kg) enhanced the brain uptake of imatinib ( approximately 4-fold) in wild-type mice, but not that of its metabolites. Blockade of both P-gp and Bcrp1 by elacridar (>3 mg/kg) produced significantly greater brain penetration of imatinib (9.3-fold) and its metabolites (2.8-fold). In contrast, only the lack of P-gp enhanced imatinib brain penetration (6.4-fold) in knockout mice. These results of brain uptake correlated reasonably well with those obtained previously by our group using in situ brain perfusion., Conclusions: Imatinib and its metabolites penetrate into the brain poorly and their penetration is limited by P-gp and (probably) Bcrp1. Administering imatinib together with P-gp (and Bcrp1) transporter inhibitors such as elacridar may improve the delivery of imatinib to the brain, making it potentially more effective against malignant gliomas.

Imatinib, a protein tyrosine kinase inhibitor, may prevent the growth of glioblastoma cells. Unfortunately, its brain distribution is restricted by p-glycoprotein (p-gp or multidrug resistance protein Mdr1a), and probably by breast cancer resistance protein (Bcrp1), two efflux pumps expressed at the blood-brain barrier (BBB). We have used in situ brain perfusion to investigate the mechanisms of imatinib transport across the mouse BBB. The brain uptake of imatinib in wild-type mice was limited by saturable efflux processes. The inhibition of p-gp, by valspodar and zosuquidar, increased imatinib uptake (2.5-fold), as did the deficiency of p-gp in Mdr1a/1b(-/-) mice (5.5-fold). Perfusing imatinib with the p-gp/Bcrp1 inhibitor, elacridar, enhanced the brain uptake of imatinib in wild-type (4.1-fold) and Mdr1a/1b(-/-) mice (1.2-fold). However, the brain uptake of imatinib was similar in wild-type and Bcrp1(-/-) mice when it was perfused at a non-saturating concentration. The brain uptake of CGP74588, an active metabolite of imatinib, was low. It was increased by perfusion with elacridar (twofold), but not with valspodar and zosuquidar. CGP74588 uptake was 1.5 times greater in Bcrp1(-/-) mice than in wild-type mice. These data suggest that imatinib transport at the mouse BBB is limited by p-gp and probably by Bcrp1, and that CGP74588 transport is restricted by Bcrp1.

The combination of imatinib mesylate and hydroxyurea provides a therapeutic benefit in patients with glioblastoma, although each drug is not effective when used alone. The increase of brain delivery of one or both drugs has been suggested to be a potential cause of this therapeutic benefit. The cross-influence of hydroxyurea and imatinib on their respective brain distribution was examined in mice and rats. We used in situ brain perfusion in mice to determine whether these two drugs have an influence on their respective initial transport across the blood-brain barrier. The brain penetration of hydroxyurea, assessed by its brain uptake clearance, Knet, was low in mice (approximately 0.10 microl/g/s) and not modified by coperfusion of imatinib (0.5-500 microM). Likewise, the brain penetration of imatinib was low (Knet, 1.39 +/- 0.17 microl/g/s) and not modified by direct coperfusion of hydroxyurea (0.2-1000 microM) or by intravenous pretreatment with 15 or 1000 mg/kg hydroxyurea. We also examined a potential time-dependent influence of hydroxyurea on imatinib brain distribution after sustained subcutaneous administration in rats using an implantable osmotic pump. The brain penetration of imatinib in rats increased with time, approximately 1.6-fold (p < 0.01) after 7 and 14 days' infusion of imatinib (3 mg/day) with or without hydroxyurea (15 mg/day), and was not influenced by hydroxyurea. The results of these two sets of experiments indicate that hydroxyurea has no significant influence on the brain distribution of imatinib in mice and rats.