Graduation Date

Summer 8-15-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Programs

Pharmaceutical Sciences

First Advisor

DJ Murry, PharmD

Second Advisor

Paul Trippier, PhD

Third Advisor

Aaron Mohs, PhD

Fourth Advisor

James B. Ford, DO

Abstract

The integration of translational drug metabolism and pharmacokinetics (DMPK) with model-informed pharmacokinetic (PK) strategies is reshaping the landscape of modern drug development. A comprehensive understanding of in vitro and in vivo preclinical PK characteristics paves the way for the successful progression of drug candidates into clinical development. The first part of this dissertation focuses on the absorption, distribution, metabolism, and excretion (ADME) properties of JNJ-64619178 (JNJ) as a potential therapeutic for medulloblastoma. Overexpression of protein arginine methyltransferase 5 (PRMT5) is pivotal in MYC-driven primary medulloblastoma tumors, suggesting a potential therapeutic target for the treatment of medulloblastoma. JNJ is a potent inhibitor of PRMT5 and is currently under clinical trials, notably for non-Hodgkin lymphoma and lung cancer. In our study, we determined the potential of JNJ for treating Group 3 medulloblastoma. We developed a sensitive LC-MS/MS bioanalytical method to accurately quantify JNJ in the biological matrix. The developed method demonstrated appropriate sensitivity, selectivity, and robustness, meeting regulatory guideline requirements. Applying the validated method, we identified JNJ as having acceptable drug-like PK properties in terms of in vitro and in vivo studies. JNJ represented excellent stability in plasma and brain matrices, indicating resistance to enzymatic degradation. The metabolic stability result showed no significant phase I metabolism. Following IV dosing, the volume of distribution (Vd) was 1.16 L/kg, which is approximately 1.65 times of total body water in mice, indicating a considerable tissue distribution. The systemic clearance was slow, with a value of 0.23 L/h/kg. After oral dosing, the maximum plasma concentration (Cmax) reached was ~3.5 times higher than the IC50 of JNJ in the HD-MB cell line. JNJ was well-retained in the target brain environment after 24 hours with a mean concentration of 23.49 ng/g. However, as the achieved brain concentration was significantly below the in vitro IC50 value (1.7 µM or 821.71 ng/mL), alternate dosing strategies or improved drug delivery of an oral dosage form designed for medulloblastoma would be required.

Model-informed drug dosing approaches, including the incorporation of population pharmacokinetic (PopPK) and physiologically-based pharmacokinetic (PBPK) modeling, have become indispensable tools in translational clinical pharmacology to speed drug development. For an established drug, these approaches enhance therapeutic precision and clinical utility, explicitly in underserved populations such as pediatrics. In this context, by leveraging existing clinical and experimental data, we wanted to address knowledge gaps related to the variability of drug exposure across pediatric populations with obesity. We prospectively evaluated the PK variability of midazolam (CYP3A substrate) and its CYP3A-mediated major metabolite 1-hydroxy midazolam in obese children and adolescents using PopPK and subsequently a PBPK model. CYP3A metabolizes over 50 percent of marketed drugs, and substantial variability exists in functional activity, resulting in significant variability in drug effect when patients are given fixed doses of CYP3A metabolized drugs. We used midazolam as a probe drug to assess in vivo CYP3A activity in children with obesity. First, a PopPK model was developed for the drug and metabolite and validated with a nonlinear mixed-effects modeling approach (Phoenix NLME 8.3.5). In the final model, an increase in total body weight (TBW) was associated with a significant decrease in midazolam clearance via CYP3A metabolism. Midazolam clearance decreased 29.71 – 41.76 and 49.43 – 50.15 % in obese and morbidly obese patients, respectively, compared to normal weight individuals (p< 0.05), with a fixed dosing of 2 mg. We observed a correlation between serum IL-6 and midazolam exposure; however, with limited samples and incomplete IL-6 data, body weight remained the predominant factor in PopPK analysis. Thus, with this result, we anticipated that a further investigation through a PBPK modeling strategy may help elucidate the likely multi-factorial underpinnings of altered PK in obesity and potentially identify tipping points for what burden of inflammatory cytokines may result in clinically relevant alterations in PK. Using literature published data and clinical samples, we developed whole-body PBPK models of midazolam and 1-hydroxy midazolam using GastroPlus™ (V9.9). Our developed model had good predictive performance, confirmed through mean fold error metrics and diagnostic goodness-of-fit plots. An inhibitory IL-6 PBPK model predicted that obesity-driven IL-6 elevation leads to up to 40% reduction in CYP3A4 activity and increased the systemic exposure of midazolam by up to 30% in obese populations. Overall, our findings provide a mechanistic basis for obesity-related changes in CYP3A mediated drug pharmacokinetics, emphasizing the need for development of dosing guidelines in this critical population.

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