Translation of nonclinical to clinical safety findings for 27 biotherapeutics.

Human adverse drug reactions (ADRs), and in vivo nonclinical adverse and nonadverse findings, were identified in 27 biotherapeutic programs and placed into organ categories to determine translation. The sensitivity of detecting human ADRs was 30.8% with a positive predictive value (PPV) of 53.3% for nonclinical adverse findings; sensitivity increased to 67.3% and PPV fell to 35.0% when including nonadverse findings. Nonclinical findings were associated with a greater likelihood of a human ADR in that organ category, especially for adverse findings [positive likelihood ratio (LR+) >10 (lower 95% confidence interval [CI] of >5)]. The specificity and negative predictive value (NPV) were very high (>85%). A lack of nonclinical findings in an organ category was associated with a lower likelihood of a human ADR in that organ category. About 40-50% of human ADRs and nonclinical adverse findings, and about 30% of nonclinical nonadverse findings, were attributed to pharmacology. Slightly more than half of the human ADRs with a translating nonclinical finding had findings in animals that could be considered very similar. Overall, 38% of nonclinical findings translated to a human ADR at the organ category level. When nonclinical findings did not translate to humans, the cause was usually higher exposures or longer dosing in animals. All programs with human ADRs attributed to immunogenicity also had nonclinical adverse or nonadverse findings related to immunogenicity. Overall, nonclinical adverse and nonadverse findings were useful in predicting human ADRs, especially at an organ category level, and the majority of human ADRs were predicted by nonclinical toxicity studies.

Assessment of the Utility of Physiologically-based Pharmacokinetic Model for prediction of Pharmacokinetics in Chinese and Japanese Populations.

The objective for the present analyses was to evaluate the utility of physiologically-based pharmacokinetic (PBPK) modeling for prediction of the pharmacokinetics (PK) in Chinese and Japanese populations with a panel of Pfizer internal compounds. Twelve compounds from Pfizer internal development pipeline with available Westerner PK data and available PK data in at least one of the subpopulations of Japanese and Chinese populations were identified and included in the current analysis. These selected compounds represent various elimination pathways across different therapeutic areas. The Simcyp® PBPK simulator was used to develop and verify the PBPK models of individual compounds. The developed models for these compounds were verified by using the clinical PK data in Westerners. The verified PBPK models were further used to predict the PK of these compounds in Chinese and Japanese populations and the predicted PK parameters were compared with the observed PK parameters. Ten of the 12 compounds had PK data in Chinese, and all the 12 compounds had PK data in Japanese. In general, the PBPK models performed well in predicting PK in Chinese and Japanese, with 8 of 10 drugs in Chinese and 7 of 12 drugs in Japanese has AAFE values less than 1.25-fold. PBPK-guided predictions of the relative PK difference were successful for 75% and 50%, respectively, between Chinese and Western and between Japanese and Western of the tested drugs using 0.8-1.25 as criteria. In conclusion, well verified PBPK models developed using data from Westerners can be used to predict the PK in Chinese and Japanese populations.

Efficacy and safety results of depatuxizumab mafodotin (ABT-414) in patients with advanced solid tumors likely to overexpress epidermal growth factor receptor.

BACKGROUND: Epidermal growth factor receptor (EGFR) alterations are associated with multiple cancers. Current EGFR-directed therapies have led to increased efficacy but are associated with specific side effects. The antibody-drug conjugate depatuxizumab mafodotin (depatux-m) targets EGFR with a monoclonal antibody linked to a cytotoxin, and is highly tumor-specific. METHODS: This phase 1/2 study evaluated the safety, pharmacokinetics, and efficacy of depatux-m in patients who had advanced solid tumors with known wild-type EGFR overexpression, amplification, or mutated EGFR variant III. A 3 + 3 dose escalation was used, and 2 dosing schedules were evaluated. Depatux-m also was manufactured under an alternate process to reduce the drug load and improve the safety profile, and it was tested at the maximum tolerated dose (MTD). In another cohort, prolonged infusion time of depatux-m was evaluated; and a cohort with confirmed EGFR amplification also was evaluated at the MTD. RESULTS: Fifty-six patients were treated. The MTD and the recommended phase 2 dose for depatux-m was 3.0 mg/kg. Common adverse events (AEs) were blurred vision (48%) and fatigue (41%). A majority of patients (66%) experienced 1 or more ocular AEs. Grade 3 or 4 AEs were observed in 43% of patients. One patient with EGFR-amplified, triple-negative breast cancer had a partial response. Stable disease was observed in 23% of patients. Pharmacokinetics revealed that depatux-m exposures were approximately dose-proportional. CONCLUSIONS: Depatux-m resulted in infrequent nonocular AEs but increased ocular AEs. Patient follow-up confirmed that ocular AEs were reversible. Lowering the drug-antibody ratio did not decrease the number of ocular AEs. A partial response in 1 patient with EGFR-amplified disease provides the opportunity to study depatux-m in diseases with a high incidence of EGFR amplification. Cancer 2018;124:2174-83. © 2018 The Authors. Cancer published by Wiley Periodicals, Inc. on behalf of American Cancer Society. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.

A phase 1 study of PARP-inhibitor ABT-767 in advanced solid tumors with BRCA1/2 mutations and high-grade serous ovarian, fallopian tube, or primary peritoneal cancer.

Purpose This phase 1 study examined safety, pharmacokinetics (PK), and efficacy of the poly(ADP-ribose) polymerase (PARP) inhibitor ABT-767 in patients with advanced solid tumors and BRCA1/2 mutations or with high-grade serous ovarian, fallopian tube, or primary peritoneal cancer. Methods Patients received ABT-767 monotherapy orally until disease progression or unacceptable toxicity. Dose was escalated from 20 mg once daily to 500 mg twice daily (BID). Dose-limiting toxicities, recommended phase 2 dose (RP2D), food effect, objective response rate, and biomarkers predicting response were determined. Results Ninety-three patients were treated with ABT-767; 80 had a primary diagnosis of ovarian cancer. ABT-767 demonstrated dose-proportional PK up to 500 mg BID and half-life of ~2 h. Food had no effect on ABT-767 bioavailability. Most common grade 3/4 treatment-related adverse events were nausea, fatigue, decreased appetite, and anemia. Anemia showed dose-dependent increase. RP2D was 400 mg BID. Objective response rate by RECIST 1.1 was 21% (17/80) in all evaluable patients and 20% (14/71) in evaluable patients with ovarian cancer. Response rate by RECIST 1.1 and/or CA-125 was 30% (24/80) in patients with ovarian cancer. Mutations in BRCA1 or BRCA2, homologous recombination deficiency (HRD), and platinum sensitivity were associated with tumor response. Median progression-free survival was longer for HRD positive (6.7 months) versus HRD negative patients (1.8 months) with ovarian cancer. Conclusions ABT-767 had an acceptable safety profile up to the established RP2D of 400 mg BID and dose-proportional PK. Patients with BRCA1 or BRCA2 mutation, HRD positivity, and platinum sensitivity were more sensitive to ABT-767.

Development of a Level A in Vitro-in Vivo Correlation for Veliparib (ABT-888) Extended Release Tablet Formulation.

PURPOSE: The aim of the current manuscript is to develop and validate a level A in vitro-in vivo correlation (IVIVC) for veliparib extended-release (ER) tablet formulations. METHODS: The in vitro release profiles of veliparib formulations were determined using USP Dissolution Apparatus 2 with 900 mL of 0.1 N HCl at 75 rpm. In a clinical study, 24 subjects with solid tumors received one of the ER formulations (200 mg): fast (Formulation A), intermediate (Formulation B), and slow (Formulation C), and two 100 mg immediate release capsules (Formulation D). Blood samples were collected over a period of 48 h and analyzed using LCMS/MS. A linear correlation model was developed using fraction absorbed and fraction dissolved data from formulations A and B. Besides assessing internal predictability, external predictability was evaluated using formation C. Prediction errors were estimated for maximum observed plasma concentration (Cmax) and area under the plasma-concentration time curve from zero to last measured time point (AUCt) to determine the predictive ability of the correlation. RESULTS: There was a significant linear relationship (r2 = 0.944) between the fraction of drug absorbed and the fraction of drug dissolved. The prediction error using the internal validation for Cmax and AUCt were below 15% for the individual formulations and below 10% for the average. The prediction error in AUCt and Cmax for formulation C was 5% and 11%, respectively. CONCLUSIONS: A level A IVIVC for the veliparib ER tablet formulation was established. The IVIVC may allow the associated dissolution data to be used as a surrogate for bioavailability.

Development of In Vitro-In Vivo Correlation for Potassium Chloride Extended Release Tablet Formulation Using Urinary Pharmacokinetic Data.

PURPOSE: To develop and validate a Level A in vitro-in vivo correlation (IVIVC) for potassium chloride extended-release (ER) formulations. METHODS: Three prototype ER formulations of potassium chloride with different in vitro release rates were developed and their urinary pharmacokinetic profiles were evaluated in healthy subjects. A mathematical model between in vitro dissolution and in vivo urinary excretion, a surrogate for measuring in vivo absorption, was developed using time-scale and time-shift parameters. The IVIVC model was then validated based on internal and external predictability. RESULTS: With the established IVIVC model, there was a good correlation between the observed fraction of dose excreted in urine and the time-scaled and time-shifted fraction of the drug dissolved, and between the in vitro dissolution time and the in vivo urinary excretion time for the ER formulations. The percent prediction error (%PE) on cumulative urinary excretion over the 24 h interval (Ae0-24h) and maximum urinary excretion rate (Rmax) was less than 15% for the individual formulations and less than 10% for the average of the two formulations used to develop the model. Further, the %PE values using external predictability were below 10%. CONCLUSIONS: A novel Level A IVIVC was successfully developed and validated for the new potassium chloride ER formulations using urinary pharmacokinetic data. This successful IVIVC may facilitate future development or manufacturing changes to the potassium chloride ER formulation.

Factors Influencing the Central Nervous System Distribution of a Novel Phosphoinositide 3-Kinase/Mammalian Target of Rapamycin Inhibitor GSK2126458: Implications for Overcoming Resistance with Combination Therapy for Melanoma Brain Metastases.

Small molecule inhibitors targeting the mitogen-activated protein kinase pathway (Braf/mitogen-activated protein kinase kinase/extracellular signal-regulated kinase) have had success in extending survival for patients with metastatic melanoma. Unfortunately, resistance may occur via cross-activation of alternate signaling pathways. One approach to overcome resistance is to simultaneously target the phosphoinositide 3-kinase/mammalian target of rapamycin signaling pathway. Recent reports have shown that GSK2126458 [2,4-difluoro-N-(2-methoxy-5-(4-(pyridazin-4-yl)quinolin-6-yl)pyridin-3-yl) benzenesulfonamide], a dual phosphoinositide 3-kinase/mammalian target of rapamycin inhibitor, can overcome acquired resistance to Braf and mitogen-activated protein kinase kinase inhibitors in vitro. These resistance mechanisms may be especially important in melanoma brain metastases because of limited drug delivery across the blood-brain barrier. The purpose of this study was to investigate factors that influence the brain distribution of GSK2126458 and to examine the efficacy of GSK2126458 in a novel patient-derived melanoma xenograft (PDX) model. Both in vitro and in vivo studies indicate that GSK2126458 is a substrate for P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp), two dominant active efflux transporters in the blood-brain barrier. The steady-state brain distribution of GSK2126458 was 8-fold higher in the P-gp/Bcrp knockout mice compared with the wild type. We also observed that when simultaneously infused to steady state, GSK212658, dabrafenib, and trametinib, a rational combination to overcome mitogen-activated protein kinase inhibitor resistance, all had limited brain distribution. Coadministration of elacridar, a P-gp/Bcrp inhibitor, increased the brain distribution of GSK2126458 by approximately 7-fold in wild-type mice. In the PDX model, GSK2126458 showed efficacy in flank tumors but was ineffective in intracranial melanoma. These results show that P-gp and Bcrp are involved in limiting the brain distribution of GSK2126458 and provide a rationale for the lack of efficacy of GSK2126458 in the orthotopic PDX model.

Efflux transporters at the blood-brain barrier limit delivery and efficacy of cyclin-dependent kinase 4/6 inhibitor palbociclib (PD-0332991) in an orthotopic brain tumor model.

6-Acetyl-8-cyclopentyl-5-methyl-2-([5-(piperazin-1-yl)pyridin-2-yl]amino)pyrido(2,3-d)pyrimidin-7(8H)-one [palbociclib (PD-0332991)] is a cyclin-dependent kinase 4/6 inhibitor approved for the treatment of metastatic breast cancer and is currently undergoing clinical trials for many solid tumors. Glioblastoma (GBM) is the most common primary brain tumor in adults and has limited treatment options. The cyclin-dependent kinase 4/6 pathway is commonly dysregulated in GBM and is a promising target in treating this devastating disease. The blood-brain barrier (BBB) limits the delivery of drugs to invasive regions of GBM, where the efflux transporters P-glycoprotein and breast cancer resistance protein can prevent treatments from reaching the tumor. The purpose of this study was to examine the mechanisms limiting the effectiveness of palbociclib therapy in an orthotopic xenograft model. The in vitro intracellular accumulation results demonstrated that palbociclib is a substrate for both P-glycoprotein and breast cancer resistance protein. In vivo studies in transgenic mice confirmed that efflux transport is responsible for the limited brain distribution of palbociclib. There was an ∼115-fold increase in brain exposure at steady state in the transporter deficient mice when compared with wild-type mice, and the efflux inhibitor elacridar significantly increased palbociclib brain distribution. Efficacy studies demonstrated that palbociclib is an effective therapy when GBM22 tumor cells are implanted in the flank, but ineffective in an orthotopic (intracranial) model. Moreover, doses designed to mimic brain exposure were ineffective in treating flank tumors. These results demonstrate that efflux transport in the BBB is involved in limiting the brain distribution of palbociclib and this has critical implications in determining effective dosing regimens of palbociclib therapy in the treatment of brain tumors.

Factors influencing the CNS distribution of a novel MEK-1/2 inhibitor: implications for combination therapy for melanoma brain metastases.

Brain metastases are a major cause of mortality in patients with advanced melanoma. Adequate brain distribution of targeted agents for melanoma will be critical for treatment success. Recently, improvement in overall survival led to US Food and Drug Administration (FDA) approval of the v-raf murine sarcoma viral oncogene homolog B (BRAF) inhibitors, vemurafenib and dabrafenib, and the mitogen-activated protein kinase kinase-1 (MEK)-1/2 inhibitor, trametinib. However, brain metastases and emergence of resistance remain a significant problem. MEK-1/2 is downstream of BRAF in the mitogen-activated protein kinase (MAPK) signaling pathway, making it an attractive target to combat resistance. The recently approved combination of dabrafenib and trametinib has shown improvement in progression-free survival; however, adequate brain distribution of both compounds is required to effectively treat brain metastases. In previous studies, we found limited brain distribution of dabrafenib. The purpose of the current study was to investigate factors influencing the brain distribution of trametinib. In vitro studies indicated that trametinib is a substrate for both P-glycoprotein (P-gp) and Bcrp, efflux transporters found at the blood-brain barrier. In vivo studies in transgenic mouse models confirmed that P-gp plays an important role in restricting brain distribution of trametinib. The brain-to-plasma partition coefficient (AUCbrain/AUCplasma) was approximately 5-fold higher in Mdr1a/b((-/-)) (P-gp knockout) and Mdr1a/b((-/-))Bcrp1((-/-)) (triple knockout) mice when compared with wild-type and Bcrp1((-/-)) (Bcrp knockout) mice. The brain distribution of trametinib was similar between the wild-type and Bcrp knockout mice. These results show that P-gp plays an important role in limiting brain distribution of trametinib and may have important implications for use of trametinib as single agent or in combination therapy for treatment of melanoma brain metastases.

Oncology Combination Dose-Finding Study Design for Targeted and Immuno-Oncology Therapies.

Combination therapies are often evaluated during the clinical development of oncology investigational agents. A new investigational agent may be combined with one or more approved agent(s) or investigational agent(s). As the initial step to test combination therapies, combination dose escalation of an investigational agent and an approved drug is generally conducted using one of the following designs: sequential design, parallel (staggered) design, healthy participant first-in-human prior to first-in-patient combination escalation, monotherapy lead-in (intra-patient "crossover"), and potentially combination escalation (no monotherapy component). Dose-finding studies for the combinations of two investigational agents may follow similar principles and considerations, and a more conservative approach may be required. A comparison of the characteristics of these designs indicates an efficient design should consider factors including the predicted difference in dose/exposure-response relationships between monotherapy and combination therapy, any potential for pharmacokinetic and pharmacodynamic interactions between the combinatory agents, and the benefit/risk to study participants, etc. In this report, we propose application scenarios for each trial design based on the above considerations and a review of the internal database and published external studies. Generation of robust exposure-response data via an appropriate design will assist the selection of appropriate doses for further assessment to support optimal dose selection as encouraged by the US Food and Drug Administration based on Project Optimus.

Pharmacokinetic assessment of efflux transport in sunitinib distribution to the brain.

This study quantitatively assessed transport mechanisms that limit the brain distribution of sunitinib and investigated adjuvant strategies to improve its brain delivery for the treatment of glioblastoma multiforme (GBM). Sunitinib has not shown significant activity in GBM clinical trials, despite positive results seen in preclinical xenograft studies. We performed in vivo studies in transgenic Friend leukemia virus strain B mice: wild-type, Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) genotypes were examined. The brain-to-plasma area under the curve ratio after an oral dose (20 mg/kg) was similar to the steady-state tissue distribution coefficient, indicating linear distribution kinetics in mice over this concentration range. Furthermore, the distribution of sunitinib to the brain increased after administration of selective P-glycoprotein (P-gp) or breast cancer resistance protein (Bcrp) pharmacological inhibitors and a dual inhibitor, elacridar, comparable to that of the corresponding transgenic genotype. The brain-to-plasma ratio after coadministration of elacridar in wild-type mice was ≈ 12 compared with ≈ 17.3 in Mdr1a/b(-/-)Bcrp1(-/-) mice. Overall, these findings indicate that there is a cooperation at the blood-brain barrier (BBB) in restricting the brain penetration of sunitinib, and brain delivery can be enhanced by administration of a dual inhibitor. These data indicate that the presence of cooperative efflux transporters, P-gp and Bcrp, in an intact BBB can protect invasive glioma cells from chemotherapy. Thus, one may consider the use of transporter inhibition as a powerful adjuvant in the design of future clinical trials for the targeted delivery of sunitinib in GBM.

Saturable active efflux by p-glycoprotein and breast cancer resistance protein at the blood-brain barrier leads to nonlinear distribution of elacridar to the central nervous system.

The study objective was to investigate factors that affect the central nervous system (CNS) distribution of elacridar. Elacridar inhibits transport mediated by P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) and has been used to study the influence of transporters on brain distribution of chemotherapeutics. Adequate distribution of elacridar across the blood-brain barrier (BBB) and into the brain parenchyma is necessary to target tumor cells in the brain that overexpress transporters and reside behind an intact BBB. We examined the role of P-gp and Bcrp on brain penetration of elacridar using Friend leukemia virus strain B wild-type, Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice. Initially, the mice were administered 2.5 mg/kg of elacridar intravenously, and the plasma and brain concentrations were determined. The brain-to-plasma partition coefficient of elacridar in the wild-type mice was 0.82, as compared with 3.5 in Mdr1a/b(-/-) mice, 6.6 in Bcrp1(-/-) mice, and 15 in Mdr1a/b(-/-)Bcrp1(-/-) mice, indicating that both P-gp and Bcrp limit the brain distribution of elacridar. The four genotypes were then administered increasing doses of elacridar, and the CNS distribution of elacridar was determined. The observed and model predicted maximum brain-to-plasma ratios (Emax) at the highest dose were not significantly different in all genotypes. However, the ED50 was lower for Mdr1a/b(-/-) mice compared with Bcrp1(-/-) mice. These findings correlate with the relative expression of P-gp and Bcrp at the BBB in these mice and demonstrate the quantitative enhancement in elacridar CNS distribution as a function of its dose. Overall, this study provides useful concepts for future applications of elacridar as an adjuvant therapy to improve targeting of chemotherapeutic agents to tumor cells in the brain parenchyma.

Mechanisms limiting distribution of the threonine-protein kinase B-RaF(V600E) inhibitor dabrafenib to the brain: implications for the treatment of melanoma brain metastases.

Brain metastases are a common cause of death in stage IV metastatic melanoma. Dabrafenib is a BRAF (gene encoding serine/threonine-protein kinase B-Raf) inhibitor that has been developed to selectively target the valine 600 to glutamic acid substitution (BRAF(V600E)), which is commonly found in metastatic melanoma. Clinical trials with dabrafenib have shown encouraging results; however, the central nervous system distribution of dabrafenib remains unknown. Thus, the objective of the current study was to evaluate the brain distribution of dabrafenib in mice, and to see whether active efflux by P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) restricts its delivery across the blood-brain barrier (BBB). In vitro accumulation studies conducted in Madin-Darby canine kidney II cells indicate that dabrafenib is an avid substrate for both P-gp and BCRP. Directional flux studies revealed greater transport in the basolateral to apical direction with corrected efflux ratios greater than 2 for both P-gp and Bcrp1 transfected cell lines. In vivo, the ratio of area under the concentration-time curve (AUC)(brain) to AUC(plasma) (K(p)) of dabrafenib after an i.v. dose (2.5 mg/kg) was 0.023, which increased by 18-fold in Mdr1 a/b(-/-)Bcrp1(-/-) mice to 0.42. Dabrafenib plasma exposure was ∼2-fold greater in Mdr1 a/b(-/-)Bcrp1(-/-) mice as compared with wild-type with an oral dose (25 mg/kg); however, the brain distribution was increased by ~10-fold with a resulting K(p) of 0.25. Further, compared with vemurafenib, another BRAF(V600E) inhibitor, dabrafenib showed greater brain penetration with a similar dose. In conclusion, the dabrafenib brain distribution is limited in an intact BBB model, and the data presented herein may have clinical implications in the prevention and treatment of melanoma brain metastases.

Sunitinib LC-MS/MS Assay in Mouse Plasma and Brain Tissue: Application in CNS Distribution Studies.

Sunitinib malate is a multi-targeted tyrosine-kinase inhibitor, currently in clinical trials for glioma. Previously developed methods for preclinical studies in species such as mice have either employed high-performance liquid chromatography (HPLC) or did not describe a detailed analytical method, which could be employed by other preclinical laboratories. In this paper, we have developed and validated a simple, sensitive high-performance liquid chromatography tandem mass-spectrometric method (LC-MS/MS) for the determination of sunitinib concentration in mouse plasma and brain tissue homogenate using dasatinib-free base as the internal standard. A single step liquid-liquid extraction method was used for both the matrices. Since sunitinib exhibits light-induced E/Z isomerism, all sample preparation was done in light-protected conditions. Separation was performed on a ZORBAX Eclipse XDB C18 column 4.6 × 50 mm, 1.8 µm. The mobile phase consisted of 20 mM ammonium formate (with 0.1 % formic acid): acetonitrile (70:30, v/v) pumped isocratically at a flow rate of 0.25 mL min-1 with a total run-time of 13 min. The retention times of sunitinib and dasatinib were 7.8 and 5.5 min, respectively. The calibration curve was linear over the range from 1.95 to 500 ng mL-1 in both plasma and brain tissue homogenate with 1.95 ng mL-1 as the lower limit of quantification (LLOQ) for both the matrices. Inter- and intra-day accuracy and precision was <15 % for low QC, med QC and high QC and <20 % for LLOQ. The method was applied to a pharmacokinetic study in FVB wild-type mice to determine the plasma and brain concentrations after a single oral sunitinib malate dose of 20 mg kg-1.

Impact of P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) on the brain distribution of a novel BRAF inhibitor: vemurafenib (PLX4032).

Vemurafenib [N-(3-{[5-(4-chlorophenyl)-1H-pyrrolo[2,3-b]pyridin-3-yl]carbonyl}-2,4-difluorophenyl)propane-1-sulfonamide(PLX4032)] is a novel small-molecule BRAF inhibitor, recently approved by the Food and Drug Administration for the treatment of patients with metastatic melanoma with a BRAF(V600E) mutation. The objective of this study was to investigate the role of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in the distribution of vemurafenib to the central nervous system. In vitro studies conducted in transfected Madin-Darby canine kidney II cells show that the intracellular accumulation of vemurafenib is significantly restricted because of active efflux by P-gp and BCRP. Bidirectional flux studies indicated greater transport in the basolateral-to-apical direction than the apical-to-basolateral direction because of active efflux by P-gp and BCRP. The selective P-gp and BCRP inhibitors zosuquidar and (3S,6S,12aS)-1,2,3,4,6,7,12,12a-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-dioxopyrazino(1',2':1,6)pyrido(3,4-b)indole-3-propanoic acid-1,1-dimethylethyl ester (Ko143) were able to restore the intracellular accumulation and bidirectional net flux of vemurafenib. The in vivo studies revealed that the brain distribution coefficient (area under the concentration time profile of brain/area under the concentration time profile of plasma) of vemurafenib was 0.004 in wild-type mice. The steady-state brain-to-plasma ratio of vemurafenib was 0.035 ± 0.009 in Mdr1a/b(-/-) mice, 0.009 ± 0.006 in Bcrp1(-/-) mice, and 1.00 ± 0.19 in Mdr1a/b(-/-)Bcrp1(-/-) mice compared with 0.012 ± 0.004 in wild-type mice. These data indicate that the brain distribution of vemurafenib is severely restricted at the blood-brain barrier because of active efflux by both P-gp and BCRP. This finding has important clinical significance given the ongoing trials examining the efficacy of vemurafenib in brain metastases of melanoma.

Quantitative proteomics of transporter expression in brain capillary endothelial cells isolated from P-glycoprotein (P-gp), breast cancer resistance protein (Bcrp), and P-gp/Bcrp knockout mice.

The objective of this study was to quantitatively examine the protein expression of relevant transporters and other proteins in the brain capillary endothelial cells isolated from wild-type mice and P-glycoprotein (P-gp), breast cancer resistance protein (Bcrp), and P-gp/Bcrp knockout mice. After the isolation of brain capillary endothelial cells, a highly sensitive liquid chromatography-tandem mass spectrometry method with multiple reaction monitoring was used to determine the quantitative expression of membrane transporters at the blood-brain barrier (BBB) of the various mouse genotypes. Quantitative expression of 29 protein molecules, including 12 ATP-binding cassette transporters, 10 solute carrier transporters, five receptors, and two housekeeping proteins, was examined by quantitative proteomics in the four mouse genotypes. There was no significant difference in the expression of P-gp between the wild-type and Bcrp1(-/-) mice. Likewise, Bcrp expression was not significantly different between the wild-type and Mdr1a/b(-/-) mice. There was no significant difference in the expression of any of the measured proteins in the brain capillary endothelial cells across the genotypes, except for the lack of expression of the corresponding protein in the mice that had a genetic deletion of P-gp or Bcrp. In conclusion, using a quantitative proteomic approach, we have shown that there are no changes in the expression of several relevant transporters in brain capillary endothelial cells isolated from single and combination knockout mice. These data suggest that the mechanism behind the functional compensation between P-gp and Bcrp at the BBB is not related to compensatory changes in transporter expression.

Lapatinib distribution in HER2 overexpressing experimental brain metastases of breast cancer.

PURPOSE: Lapatinib, a small molecule EGFR/HER2 inhibitor, partially inhibits the outgrowth of HER2+ brain metastases in preclinical models and in a subset of CNS lesions in clinical trials of HER2+ breast cancer. We investigated the ability of lapatinib to reach therapeutic concentrations in the CNS following (14)C-lapatinib administration (100 mg/kg p.o. or 10 mg/kg, i.v.) to mice with MDA-MD-231-BR-HER2 brain metastases of breast cancer. METHODS: Drug concentrations were determined at differing times after administration by quantitative autoradiography and chromatography. RESULTS: (14)C-Lapatinib concentration varied among brain metastases and correlated with altered blood-tumor barrier permeability. On average, brain metastasis concentration was 7-9-fold greater than surrounding brain tissue at 2 and 12 h after oral administration. However, average lapatinib concentration in brain metastases was still only 10-20% of those in peripheral metastases. Only in a subset of brain lesions (17%) did lapatinib concentration approach that of systemic metastases. No evidence was found of lapatinib resistance in tumor cells cultured ex vivo from treated brains. CONCLUSIONS: Results show that lapatinib distribution to brain metastases of breast cancer is partially restricted and blood-tumor barrier permeability is a key component of lapatinib therapeutic efficacy which varies between tumors.

Oncology dose optimization paradigms: knowledge gained and extrapolated from approved oncology therapeutics.

There has been increasing attention to dose optimization in the development of targeted oncology therapeutics. The current report has analyzed the dose selection approaches for 116 new molecular entities (NMEs) approved for oncology indications by the US FDA from 2010 to August 2021, with the goal to extract learnings about the ways to select the optimal dose. The analysis showed that: (1) the initial label dose was lower than the maximum tolerated dose (MTD) or maximum studied dose (MSD) in Phase 1 for the majority of approved NMEs, and that the MTD approach is no longer the mainstay for dose selection; (2) there was no dose ranging or optimization beyond Phase 1 dose escalation for ~ 80% of the NMEs; (3) integrated dose/exposure-response analyses were commonly used to justify the dose selection; (4) lack of dose optimization led to dose-related PMRs/PMCs in 14% of cases, but 82% of these did not result in change of the initial label dose; and (5) depending on properties of the NME and specific benefit/risk considerations for the target patient population, there could be different dose selection paradigms leading to identification of the appropriate clinical dose. The analysis supports the need to incorporate more robust dose optimization during oncology clinical development, through comparative assessment of benefit/risk of multiple dose levels, over a wide exposure range using therapeutically relevant endpoints and adequate sample size. On the other hand, in certain cases, data from FIP dose escalation may be adequate to support the dose selection.

Starting dose selection and dose escalation for oncology small molecule first-in-patient trials: learnings from a survey of FDA-approved drugs.

The ideal starting dose for an oncology first-in-patient (FIP) trial should be low enough to be safe but not too far removed from therapeutically relevant doses. A low starting dose combined with small dose increments could lead to a lengthy dose escalation and could expose patients unnecessarily to sub-therapeutic dosing. In the current analyses, we reviewed 59 approved small molecule oncology drugs (SMOD) with the overarching goals to assess the current approaches of FIP starting dose selection and dose escalation, and to identify potential opportunities for improving trial efficiency and minimizing number of patients receiving sub-therapeutic dose levels. Of 59 SMODs, the majority (~ 66%) were kinase inhibitors and ~ 73% were approved for solid tumor indications. Most of the trials used a 3 + 3 design for dose escalation and had a median (range) of 4 cohorts (0-11) to reach MTD from the starting dose. The maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D) to starting dose ratio was highly variable with a median (range) of 8 (0.25-125). About 71% of the FIP trials had < 6 dose escalation steps to reach MTD or RP2D (with 15% ≤ 2 dose escalations), but the remaining 29% of trials had ≥ 6 dose escalation steps to reach MTD or RP2D suggesting that there is still room for increasing efficiency by reducing the number of dose escalation steps, reducing the variability in MTD to starting dose ratio, and consequently reducing significant number of patients exposed at sub-therapeutic doses in the dose escalation phase of FIP study.

Chronic exposure to nicotine and saquinavir decreases endothelial Notch-4 expression and disrupts blood-brain barrier integrity.

Since the advent of HAART, there have been substantial improvements in HIV patient survival; however, the prevalence of HIV associated dementia has increased. Importantly, HIV positive individuals who smoke progress to HIV associated neurological conditions faster than those who do not. Recent in vitro data have shown that pharmacological levels of saquinavir causes endothelial oxidative stress and significantly decreases Notch-4 expression, a primary protein involved in maintaining stability of blood-brain barrier (BBB) endothelium. This is concerning as nicotine can also generate reactive oxygen species in endothelium. It is largely unknown if pharmacological doses of these drugs can cause a similar in vivo down-regulation of Notch-4 and if there is a concurrent destabilization of the integrity of the BBB. The data herein show: (i) nicotine and protease inhibitors cause an additive oxidative stress burden in endothelium; (ii) that the integrity of the BBB is disrupted after concurrent chronic nicotine and protease inhibitor administration; and (iii) that BBB endothelial dysfunction is correlated with a decrease in Notch-4 and ZO-1 expression. Considering the high prevalence of smoking in the HIV infected population (3- to 4-fold higher than in the general population) this data must be followed up to determine if all protease inhibitors cause a similar BBB disruption or if there is a safer alternative. In addition, this data may suggest that the induced BBB disruption may allow foreign molecules to gain access to brain and be a contributing factor to the slow progression of HIV associated dementia.