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.

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.

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.

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.

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.

Population Pharmacokinetics of Upadacitinib Using the Immediate-Release and Extended-Release Formulations in Healthy Subjects and Subjects with Rheumatoid Arthritis: Analyses of Phase I-III Clinical Trials.

BACKGROUND AND OBJECTIVES: Upadacitinib is a selective Janus kinase (JAK) 1 inhibitor being developed as an orally administered treatment for patients with moderate to severe rheumatoid arthritis (RA) and other autoimmune disorders. These analyses characterized the population pharmacokinetics of upadacitinib across phase I-III clinical trials using data for immediate-release (IR) and extended-release (ER) formulations. METHODS: Pharmacokinetic data from 4170 subjects taking IR doses of 1-48 mg and ER doses of 7.5-30 mg across 12 studies spanning phase I-III clinical trials, with a total of 29,372 upadacitinib plasma concentrations, were analyzed using non-linear mixed-effects modeling. The model was evaluated using bootstrap analyses and visual predictive checks. RESULTS: A two-compartment model with first-order absorption with lag time for the IR formulation, mixed zero- and first-order absorption with lag time for the ER formulation, and linear elimination, adequately described upadacitinib plasma concentration-time profiles. Population estimates of upadacitinib apparent oral clearance and steady-state volume of distribution in healthy volunteers for the ER formulation were 53.7 L/h and 294 L, respectively. The relative bioavailability of the ER formulation compared with the IR formulation was estimated to be 76.2%. Statistically significant covariates were patient population (RA subjects vs. healthy subjects), creatinine clearance, and baseline bodyweight on apparent clearance (CL/F) and bodyweight on volume of distribution of the central compartment (Vc/F). The intersubject variability for upadacitinib CL/F and Vc/F were estimated to be 21% and 24%, respectively, in the phase I studies, and 37% and 53%, respectively, in the phase II/III studies. Upadacitinib area under the concentration-time curve (AUC) was estimated to be only 5% higher or lower for RA patients who were < 60 or > 100 kg, respectively, relative to subjects with a bodyweight of 60-100 kg. RA subjects with mild or moderate renal impairment had 13% and 26% higher AUC, respectively, compared with RA subjects with normal renal function. Sex, race, concomitant use of pH-modifying drugs, moderate cytochrome P450 3A inhibitors, or methotrexate use had no effect on upadacitinib exposure. CONCLUSIONS: A robust population pharmacokinetic model was developed for upadacitinib using a large dataset from phase I-III clinical trials in healthy volunteers and subjects with RA. None of the identified covariates had a clinically meaningful effect on upadacitinib exposures. The model is appropriate to use for simulations and to evaluate the exposure-response relationship of upadacitinib.

An Integrated Population Pharmacokinetic Model Versus Individual Models of Depatuxizumab Mafodotin, an Anti-EGFR Antibody Drug Conjugate, in Patients With Solid Tumors Likely to Overexpress EGFR.

Depatuxizumab mafodotin (depatux-m) is an antibody-drug conjugate (ADC) designed for the treatment of tumors expressing epidermal growth factor receptor (EGFR), consisting of a veneered "humanized" recombinant IgG1κ antibody that has binding properties specific to a unique epitope of human EGFR with noncleavable maleimido-caproyl linkers each attached to a potent antimitotic cytotoxin, monomethyl auristatin F. We aimed to describe the development and comparison of 2 population pharmacokinetic modeling approaches. Data from 2 phase 1 studies enrolling patients with glioblastoma multiforme or advanced solid tumors were included in the analysis. Patients in these studies received doses of depatux-m ranging from 0.5 to 4.0 mg/kg as monotherapy, in combination with temozolomide, or radiation plus temozolomide depending on the study and/or arm. First, an integrated ADC model to simultaneously describe the concentration-time data for ADC, total antibody, and cys-mafodotin was built using a 2-compartment model for ADC for each drug-to-antibody ratio. Then, 3 individual models were developed for ADC, total antibody, and cys-mafodotin separately using 2-compartment models for ADC and total antibody and a 1-compartment model for cys-mafodotin. Visual predictive checks suggested accurate model fitting across a range of concentrations. The analysis showed that both an integrated complex ADC model and the individual models that have shorter computational time would result in similar outcomes.

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.

Smoking History Predicts Sensitivity to PARP Inhibitor Veliparib in Patients with Advanced Non-Small Cell Lung Cancer.

INTRODUCTION: Tobacco-related NSCLC is associated with reduced survival and greater genomic instability. Veliparib, a potent poly(adenosine diphosphate-ribose) polymerase inhibitor, augments platinum-induced DNA damage. A phase 2 trial of untreated advanced NSCLC showed a trend for improved outcomes (hazard ratio [HR] = 0.80, 95% confidence interval: 0.54-1.18, p = 0.27 for overall survival and HR = 0.72, 95% CI: 0.45-1.15, p = 0.17 for progression-free survival) when veliparib was added to carboplatin/paclitaxel. Here we report an exploratory analysis by smoking history. METHODS: Patients were randomized 2:1 to receive carboplatin/paclitaxel with veliparib, 120 mg (n = 105), or placebo (n = 53). Patients were stratified by histologic subtype and smoking history (recent smokers [n = 95], former smokers [n = 42], and never-smokers [n = 21]). Plasma cotinine level was measured as a chemical index of smoking. Mutation status was assessed by whole exome sequencing (n = 38). RESULTS: Smoking history, histologic subtype, age, Eastern Cooperative Oncology Group performance status, sex, and geographic region predicted veliparib benefit in univariate analyses. In multivariate analysis, history of recent smoking was most predictive for veliparib benefit. Recent smokers treated with veliparib derived significantly greater progression-free survival and overall survival benefits (HR = 0.38 [p < 0.01] and HR = 0.43 [p < 0.01]) than former smokers (HR = 2.098 [p = 0 0208] and HR = 1.62 [p = 0.236]) and never-smokers (HR = 1.025 [p = 0.971] and HR = 1.33 [p = 0.638]). Sequencing data revealed that mutational burden was not associated with veliparib benefit. The rate of grade 3 or 4 adverse events was higher in recent smokers with veliparib treatment; all-grade and serious adverse events were similar in both treatment arms. CONCLUSIONS: Smoking history predicted for efficacy with a veliparib-chemotherapy combination; toxicity was acceptable regardless of smoking history. A prespecified analysis of recent smokers is planned for ongoing phase 3 studies of veliparib in NSCLC.

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.

Safety and tolerability of veliparib combined with capecitabine plus radiotherapy in patients with locally advanced rectal cancer: a phase 1b study.

BACKGROUND: Further optimisation of present standard chemoradiation is needed in patients with locally advanced rectal cancer. Veliparib, an oral poly(ADP-ribose) polymerase inhibitor, has been shown to enhance the antitumour activity of chemotherapy and radiotherapy in preclinical models. We aimed to establish the maximum tolerated dose and establish the recommended phase 2 dose of veliparib combined with neoadjuvant capecitabine and radiotherapy. METHODS: This phase 1b, open-label, multicentre, dose-escalation study was done at six hospitals (one in Australia and five in the USA). Patients were eligible if they were aged 18 years or more and were newly diagnosed with stage II to III locally advanced, resectable adenocarcinoma of the rectum with a distal tumour border of less than 12 cm from anal verge. Patients were ineligible if they had received anticancer therapy or surgery (except colostomy or ileostomy) 28 days or less before the first dose of study drug, previous pelvic radiotherapy, or previous treatment with poly (ADP-ribose) polymerase inhibitors. Enrolled patients received capecitabine (825 mg/m2 orally twice daily) with radiotherapy (50·4 Gy in 1·8 Gy fractions daily, approximately 5 days consecutively per week for about 5·5 weeks). Veliparib (20-400 mg orally twice daily) was administered daily starting on day 2 of week 1 and continuing until 2 days after radiotherapy completion. Patients underwent total mesorectal excision 5-10 weeks after radiotherapy completion. The primary objectives were to establish the maximum tolerated dose and recommended phase 2 dose of veliparib plus capecitabine and radiotherapy, with an exposure-adjusted continual reassessment methodology. Efficacy and safety analyses were done per protocol. The reported study has completed accrual and all analyses are final. This trial is registered with ClinicalTrials.gov, number NCT01589419. FINDINGS: Between June 12, 2012, and Jan 13, 2015, 32 patients received veliparib (22 in the dose-escalation group; ten in the safety expansion group); 31 were assessable for efficacy (<400 mg, n=16; 400 mg, n=15). During dose escalation, grade 2 dose-limiting toxic effects occurred in two patients; no grade 3-4 dose-limiting toxic effects were noted. Therefore, the maximum tolerated dose was not reached; the recommended phase 2 dose was selected as 400 mg twice daily. The most common treatment-emergent adverse events in all 32 patients were nausea (17 [53%]), diarrhoea (16 [50%]), and fatigue (16 [50%]). Grade 3 diarrhoea was noted in three (9%) of 32 patients; no grade 4 events were reported. Veliparib pharmacokinetics were dose proportional, with no effect on capecitabine pharmacokinetics. Tumour downstaging after surgery was noted in 22 (71%) of 31 patients; nine (29%) of 31 patients achieved a pathological complete response. INTERPRETATION: Veliparib plus capecitabine and radiotherapy had an acceptable safety profile and showed a dose-proportional pharmacokinetic profile with no effect on the pharmacokinetics of capecitabine. Preliminary antitumour activity warrants further evaluation. FUNDING: AbbVie Inc.

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.

Population pharmacokinetics of ABT-767 in BRCA1 or BRCA2 mutation carriers with advanced solid tumors or in subjects with high grade serous ovarian, primary peritoneal or fallopian tube cancer.

PURPOSE: The objective of the manuscript is to describe the development of a population pharmacokinetic model for ABT-767, a potent and orally bioavailable inhibitor of poly (ADP-ribose) polymerase enzyme, and to evaluate the potential influence of patient demographics and baseline covariates on the pharmacokinetics of ABT-767. METHODS: A total of 1809 plasma ABT-767 concentrations from 90 subjects were used for population pharmacokinetic modeling. Covariates screened for influence on pharmacokinetic parameters were body weight, lean body weight, body surface area, albumin, creatinine clearance, serum creatinine, liver function tests, and age. The effect of food on absorption and bioavailability were also evaluated. Model validation was performed using bootstrap analysis and visual predictive check. RESULTS: A two-compartment model with firstorder absorption adequately described the pharmacokinetics of ABT-767. The population estimates of apparent clearance from central compartment (CL/F), volume of central compartment (V c/F), and absorption rate constant (k a) were 7.34 L/h, 25.8 L, 1.45 h-1, respectively. The estimates of interindividual variabilities (%CV) in CL/F, V c/F, and k a were 40.4, 40.5, and 53.8%, respectively. The k a was influenced by food. Albumin on CL/F was a statistically significant covariate; however, it explained only 8% of the variability in the pharmacokinetics of ABT-767. CONCLUSIONS: Albumin on CL/F was the only statistically significant baseline covariate affecting ABT-767 pharmacokinetics, but it only explained a fraction of the pharmacokinetic variability. Dosage adjustments based on body size, age, or mild renal impairment are not needed for ABT-767. The developed model will be used to evaluate ABT-767 exposure-response analyses and to perform simulations for different dose and dosing regimens.

Evaluation of the effect of the EGFR antibody-drug conjugate ABT-414 on QT interval prolongation in patients with advanced solid tumors likely to over-express EGFR.

PURPOSE: ABT-414 is an antibody-drug conjugate (ADC) being developed for the treatment of tumors harboring amplification of the epidermal growth factor receptor (EGFR). This study evaluated the potential of ABT-414 to prolong the QT interval as part of the initial phase 1 study (NCT01741727). METHODS: Data from patients who received ABT-414 monotherapy at a dose of 1-4 mg/kg once every 3 weeks or 1 or 1.5 mg/kg weekly for 2 out of every 3 weeks (alternate schedule) by intravenous infusion were included in the analysis of triplicate 12-lead ECGs obtained before dosing and through 168 h after dosing. Data from time-matched pharmacokinetic samples and QT interval assessments were evaluated using linear mixed-effects modeling to determine the effects of ABT-414, total ABT-806, and cysteine-maleimidocaproyl monomethyl auristatin F (Cys-mcMMAF) on the QT interval corrected using Fridericia's formula (QTcF). RESULTS: Fifty-one patients were included in the analyses. ABT-414 had no clinically meaningful effect on QTcF. Using pooled data from doses ≥2 mg/kg, the estimated mean ∆QTcF reached a maximum of 4.30 ms after dosing, with a one-sided 95% upper confidence bound of 8.32 ms. The exposure-response analysis showed no statistically significant relationship between ΔQTcF and the concentration of any analyte (P > 0.05). No patient had a QTcF value >480 ms or a ∆QTcF value >30 ms. CONCLUSIONS: ABT-414 had no clinically meaningful effect on the QTcF interval at doses being evaluated for treatment of patients with solid tumors.

Quantitative Fluorescence Microscopy Measures Vascular Pore Size in Primary and Metastatic Brain Tumors.

Tumors residing in the central nervous system (CNS) compromise the blood-brain barrier (BBB) via increased vascular permeability, with the magnitude of changes dependent on the tumor type and location. Current studies determine penetrability of a cancer therapeutic by administering progressively larger molecules until cutoff is observed where little to no tumor accumulation occurs. However, decades-old experimental work and mathematical modeling document methods to calculate both the size of the vascular opening (pore) with solute permeability values. In this study, we updated this classic mathematical modeling approach with quantitative fluorescence microscopy in two preclinical tumor models, allowing simultaneous administration of multiple sized tracers to determine vascular permeability at a resolution of nearly one micron. We observed that three molecules ranging from 100 Da to 70 kDa permeated into a preclinical glioblastoma model at rates proportional to their diffusion in water. This suggests the solutes freely diffused from blood to glioma across vascular pores without steric restriction, which calculates to a pore size of >140 nm in diameter. In contrast, the calculated pore size of a brain metastasis of breast cancer was approximately 10-fold smaller than glioma vasculature. This difference explains why antibodies are effective against glioblastoma but generally fail in brain metastases of breast cancer. On the basis of our observations, we hypothesize that trastuzumab most likely fails in the treatment of brain metastases of breast cancer because of poor CNS penetration, while the similar sized antibody bevacizumab is effective in the same tumor type not because it penetrates the CNS degree better, but because it scavenges VEGF in the vascular compartment, which reduces edema and permeation. Cancer Res; 77(2); 238-46. ©2016 AACR.

Semi-automated rapid quantification of brain vessel density utilizing fluorescent microscopy.

BACKGROUND: Measurement of vascular density has significant value in characterizing healthy and diseased tissue, particularly in brain where vascular density varies among regions. Further, an understanding of brain vessel size helps distinguish between capillaries and larger vessels like arterioles and venules. Unfortunately, few cutting edge methodologies are available to laboratories to rapidly quantify vessel density. NEW METHOD: We developed a rapid microscopic method, which quantifies the numbers and diameters of blood vessels in brain. Utilizing this method we characterized vascular density of five brain regions in both mice and rats, in two tumor models, using three tracers. RESULTS: We observed the number of sections/mm(2) in various brain regions: genu of corpus callosum 161±7, hippocampus 266±18, superior colliculus 300±24, frontal cortex 391±55, and inferior colliculus 692±18 (n=5 animals). Regional brain data were not significantly different between species (p>0.05) or when using different tracers (70kDa and 2000kDa Texas Red; p>0.05). Vascular density decreased (62-79%) in preclinical brain metastases but increased (62%) a rat glioma model. COMPARISON WITH EXISTING METHODS: Our values were similar (p>0.05) to published literature. We applied this method to brain-tumors and observed brain metastases of breast cancer to have a ∼2.5-fold reduction (p>0.05) in vessels/mm(2) compared to normal cortical regions. In contrast, vascular density in a glioma model was significantly higher (sections/mm(2) 736±84; p<0.05). CONCLUSIONS: In summary, we present a vascular density counting method that is rapid, sensitive, and uses fluorescence microscopy without antibodies.

ABCG2 and ABCB1 Limit the Efficacy of Dasatinib in a PDGF-B-Driven Brainstem Glioma Model.

Dasatinib is a multikinase inhibitor in clinical trials for glioma, and thus far has failed to demonstrate significant efficacy. We investigated whether the ABC efflux transporters ABCG2 and ABCB1 expressed in the blood-brain barrier (BBB), are limiting the efficacy of dasatinib in the treatment of glioma using genetic and pharmacologic approaches. We utilized a genetic brainstem glioma mouse model driven by platelet-derived growth factor-B and p53 loss using abcg2/abcb1 wild-type (ABC WT) or abcg2/abcb1 knockout mice (ABC KO). First, we observed that brainstem glioma tumor latency is significantly prolonged in ABC KO versus ABC WT mice (median survival of 47 vs. 34 days). Dasatinib treatment nearly doubles the survival of brainstem glioma-bearing ABC KO mice (44 vs. 80 days). Elacridar, an ABCG2 and ABCB1 inhibitor, significantly increases the efficacy of dasatinib in brainstem glioma-bearing ABC WT mice (42 vs. 59 days). Pharmacokinetic analysis demonstrates that dasatinib delivery into the normal brain, but not into the tumor core, is significantly increased in ABC KO mice compared with ABC WT mice. Surprisingly, elacridar did not significantly increase dasatinib delivery into the normal brain or the tumor core of ABC WT mice. Next, we demonstrate that the tight junctions of the BBB of this model are compromised as assessed by tissue permeability to Texas Red dextran. Finally, elacridar increases the cytotoxicity of dasatinib independent of ABCG2 and ABCB1 expression in vitro In conclusion, elacridar improves the efficacy of dasatinib in a brainstem glioma model without significantly increasing its delivery to the tumor core. Mol Cancer Ther; 15(5); 819-29. ©2016 AACR.

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.

Strategies to improve delivery of anticancer drugs across the blood-brain barrier to treat glioblastoma.

Glioblastoma (GBM) is a lethal and aggressive brain tumor that is resistant to conventional radiation and cytotoxic chemotherapies. Molecularly targeted agents hold great promise in treating these genetically heterogeneous tumors, yet have produced disappointing results. One reason for the clinical failure of these novel therapies can be the inability of the drugs to achieve effective concentrations in the invasive regions beyond the bulk tumor. In this review, we describe the influence of the blood-brain barrier on the distribution of anticancer drugs to both the tumor core and infiltrative regions of GBM. We further describe potential strategies to overcome these drug delivery limitations. Understanding the key factors that limit drug delivery into brain tumors will guide future development of approaches for enhanced delivery of effective drugs to GBM.