Photoactivatable nanoagonists chemically programmed for pharmacokinetic tuning and in situ cancer vaccination.

Immunotherapy holds great promise for the treatment of aggressive and metastatic cancers; however, currently available immunotherapeutics, such as immune checkpoint blockade, benefit only a small subset of patients. A photoactivatable toll-like receptor 7/8 (TLR7/8) nanoagonist (PNA) system that imparts near-infrared (NIR) light-induced immunogenic cell death (ICD) in dying tumor cells in synchrony with the spontaneous release of a potent immunoadjuvant is developed here. The PNA consists of polymer-derived proimmunoadjuvants ligated via a reactive oxygen species (ROS)-cleavable linker and polymer-derived photosensitizers, which are further encapsulated in amphiphilic matrices for systemic injection. In particular, conjugation of the TLR7/8 agonist resiquimod to biodegradable macromolecular moieties with different molecular weights enabled pharmacokinetic tuning of small-molecule agonists and optimized delivery efficiency in mice. Upon NIR photoirradiation, PNA effectively generated ROS not only to ablate tumors and induce the ICD cascade but also to trigger the on-demand release of TLR agonists. In several preclinical cancer models, intravenous PNA administration followed by NIR tumor irradiation resulted in remarkable tumor regression and suppressed postsurgical tumor recurrence and metastasis. Furthermore, this treatment profoundly shifted the tumor immune landscape to a tumoricidal one, eliciting robust tumor-specific T cell priming in vivo. This work highlights a simple and cost-effective approach to generate in situ cancer vaccines for synergistic photodynamic immunotherapy of metastatic cancers.

Clinical Pharmacology and Interplay of Immune Checkpoint Agents: A Yin-Yang Balance.

T cells have a central role in immune system balance. When activated, they may lead to autoimmune diseases. When too anergic, they contribute to infection spread and cancer proliferation. Immune checkpoint proteins regulate T cell function, including cytotoxic T lymphocyte antigen-4 (CTLA-4) and programmed cell death-1 (PD-1) and its ligand (PD-L1). These nodes of self-tolerance may be exploited pharmacologically to downregulate (CTLA-4 agonists) and activate [CTLA-4 and PD-1/PD-L1 antagonists, also called immune checkpoint inhibitors (ICIs)] the immune system.CTLA-4 agonists are used to treat rheumatologic immune disorders and graft rejection. CTLA-4, PD-1, and PD-L1 antagonists are approved for multiple cancer types and are being investigated for chronic viral infections. Notably, ICIs may be associated with immune-related adverse events (irAEs), which can be highly morbid or fatal. CTLA-4 agonism has been a promising method to reverse such life-threatening irAEs. Herein, we review the clinical pharmacology of these immune checkpoint agents with a focus on their interplay in human diseases.

Model-Informed Precision Dosing: Background, Requirements, Validation, Implementation, and Forward Trajectory of Individualizing Drug Therapy.

Model-informed precision dosing (MIPD) has become synonymous with modern approaches for individualizing drug therapy, in which the characteristics of each patient are considered as opposed to applying a one-size-fits-all alternative. This review provides a brief account of the current knowledge, practices, and opinions on MIPD while defining an achievable vision for MIPD in clinical care based on available evidence. We begin with a historical perspective on variability in dose requirements and then discuss technical aspects of MIPD, including the need for clinical decision support tools, practical validation, and implementation of MIPD in health care. We also discuss novel ways to characterize patient variability beyond the common perceptions of genetic control. Finally, we address current debates on MIPD from the perspectives of the new drug development, health economics, and drug regulations.

Population pharmacokinetic modeling of dolutegravir/lamivudine to support a once-daily fixed-dose combination regimen in virologically suppressed adults living with HIV-1.

A fixed-dose combination (FDC) of 50 mg dolutegravir and 300 mg lamivudine is indicated for the treatment of HIV-1 infection. This analysis aimed to characterize the population pharmacokinetics (PK) of dolutegravir and lamivudine based on data from a phase 3 study (TANGO) in virologically suppressed adults living with HIV-1 switching to dolutegravir/lamivudine FDC. These analyses included 362 participants who contributed 2,629 dolutegravir and 2,611 lamivudine samples collected over 48 weeks. A one-compartment model with first-order absorption and elimination parameterized by apparent oral clearance (CL/F), apparent volume of distribution (V/F), and absorption rate constant (Ka) described dolutegravir PK. Covariate search yielded body weight, bilirubin, and ethnicity as predictors of CL/F, and weight was predictive for V/F. The estimates of CL/F, V/F, and Ka were 0.858 L/h, 16.7 L, and 2.15 h-1, respectively. A two-compartment model with first-order absorption and elimination parameterized by CL/F, apparent intercompartmental clearance (Q/F), apparent central volume of distribution (V2/F), apparent peripheral volume of distribution (V3/F), and Ka described lamivudine PK. Covariate search yielded eGFR and race as predictors of CL/F, and weight was predictive for V2/F. The estimated parameter values were CL/F = 19.6 L/h, Q/F = 2.97 L/h, V2/F = V3/F = 105 L, and Ka = 2.30 h-1. The steady-state prediction suggested that the effect of covariates dolutegravir and lamivudine exposures was small (<20%) and not clinically relevant. Therefore, no dose adjustments are recommended based on these analyses. The results support the use of dolutegravir/lamivudine FDC in the treatment of HIV-1 infection in adults.CLINICAL TRIALSThis study is registered with ClinicalTrials.gov as NCT03446573.

First-in-human, randomized, double-blind, placebo-controlled, single and multiple ascending doses clinical study to assess the safety, tolerability, and pharmacokinetics of cipargamin administered intravenously in healthy adults.

This first-in-human study assessed safety, tolerability, and pharmacokinetics (PK) of cipargamin (intravenous) in healthy adults. It included part 1, single ascending dose [SAD: 10.5 mg-210 mg; n = 8 (active: 6, placebo: 2)], and part 2, multiple ascending dose [MAD: 60 and 120 mg daily for 5 days; n = 9 (active: 6, placebo: 3)]. Last dose follow-ups were on days 3, 4, and 6 for SAD and 7, 8, and 10 for MAD. Safety and PK review was done at completion of each cohort. We explored the cipargamin use for clinical development in patients with severe malaria. In SAD part, systemic exposure (maximum measured concentration and area under the curve) increased with increasing dose (10.5 mg-210 mg) following single intravenous dose. Cipargamin was eliminated with a mean T1/2 of 21.9-38.9 h. Volume of distribution (92.9 L-154 L) and clearance (2.43 L/h-4.33 L/h) was moderate and low, respectively, across the dose range. In MAD part, the mean accumulation ratio was 1.51 (60 mg) and 2.43 (120 mg) after once-daily cipargamin administration for 5 days. After day 5, the mean T1/2 was 35.5 (60 mg) and 31.9 h (120 mg) with twofold dose increase (60-120 mg) resulting in ~2-fold increased exposure. Cipargamin was well tolerated with commonly reported mild gastrointestinal, neurological, and genitourinary events. Increasing exposure to cipargamin showed higher baseline-corrected QTcF, and model-predicted ΔΔQTcF indicated that an effect on ΔΔQTcF ≥10 ms can be excluded up to 6470 ng/mL. However, these results should be interpreted with caution due to inadequate Fridericia's QT correction. CLINICAL TRIALS: This study is registered with ClinicalTrials.gov as NCT04321252.

Determining tissue distribution of the oral antileishmanial agent miltefosine: a physiologically-based pharmacokinetic modeling approach.

Miltefosine (MTS) is the only approved oral drug for treating leishmaniasis caused by intracellular Leishmania parasites that localize in macrophages of the liver, spleen, skin, bone marrow, and lymph nodes. MTS is extensively distributed in tissues and has prolonged elimination half-lives due to its high plasma protein binding, slow metabolic clearance, and minimal urinary excretion. Thus, understanding and predicting the tissue distribution of MTS help assess therapeutic and toxicologic outcomes of MTS, especially in special populations, e.g., pediatrics. In this study, a whole-body physiologically-based pharmacokinetic (PBPK) model of MTS was built on mice and extrapolated to rats and humans. MTS plasma and tissue concentration data obtained by intravenous and oral administration to mice were fitted simultaneously to estimate model parameters. The resulting high tissue-to-plasma partition coefficient values corroborate extensive distribution in all major organs except the bone marrow. Sensitivity analysis suggests that plasma exposure is most susceptible to changes in fraction unbound in plasma. The murine oral-PBPK model was further validated by assessing overlay of simulations with plasma and tissue profiles obtained from an independent study. Subsequently, the murine PBPK model was extrapolated to rats and humans based on species-specific physiological and drug-related parameters, as well as allometrically scaled parameters. Fold errors for pharmacokinetic parameters were within acceptable range in both extrapolated models, except for a slight underprediction in the human plasma exposure. These animal and human PBPK models are expected to provide reliable estimates of MTS tissue distribution and assist dose regimen optimization in special populations.

Assessing the degree of hepatic ischemia-reperfusion injury using PBPK modeling of sodium fluorescein disposition in ex vivo machine-perfused livers.

Ischemia-reperfusion injury (IRI) is an intrinsic risk associated with liver transplantation. Ex vivo hepatic machine perfusion (MP) is an emerging organ preservation technique that can mitigate IRI, especially in livers subjected to prolonged warm ischemia time (WIT). However, a method to quantify the biological response to WIT during MP has not been established. Previous studies used physiologically-based pharmacokinetic (PBPK) modeling to demonstrate that a decrease in hepatic transport and biliary excretion of the tracer molecule sodium fluorescein (SF) could correlate with increasing WIT in situ. Furthermore, these studies proposed intracellular sequestration of the hepatocyte canalicular membrane transporter multi-drug resistance-associated protein 2 (MRP2) leading to decreased MRP2 activity (maximal transport velocity; Vmax) as the potential mechanism for decreased biliary SF excretion. We adapted an extant PBPK model to account for ex vivo hepatic MP and fit a 6-parameter version of this model to control time course measurements of SF in MP perfusate and bile. We then identified parameters whose values were likely insensitive to changes in WIT and fixed them to generate a reduced model with only 3 unknown parameters. Finally, we fit the reduced model to each individual biological replicate SF time course with differing WIT and found the mean estimated value for each parameter and compared them using a one-way ANOVA. We demonstrated that there was a significant decrease in the estimated value of Vmax for MRP2 at 30 min WIT. These studies provide the foundation for future studies investigating real-time assessment of liver viability during ex vivo MP.

High-dose methotrexate pharmacokinetics and its impact on prognosis of paediatric acute lymphoblastic leukaemia patients: A population pharmacokinetic study.

This study delivers a comprehensive evaluation of the efficacy and pharmacokinetics of high-dose methotrexate (HDMTX) in a large cohort of Chinese paediatric acute lymphoblastic leukaemia patients. A total of 533 patients were included in the prognostic analysis. An association was observed between lower steady-state MTX concentrations (<56 µmol/L) and poorer outcomes in intermediate-/high-risk (IR/HR) patients. Subgroup analysis further revealed that this relationship between concentrations and prognosis was even more pronounced in patients with MLL rearrangements. In contrast, such an association did not emerge within the low-risk patient group. Additionally, utilizing population pharmacokinetic modelling (6051 concentrations from 815 patients), we identified the significant impact of physiological maturation, estimated glomerular filtration rate, sex and concurrent dasatinib administration on MTX pharmacokinetics. Simulation-based recommendations include a reduced dosage regimen for those with renal insufficiency and a specific 200 mg/kg dosage for infants under 1 year. The findings underscore the critical role of HDMTX in treating IR/HR populations and call for a reassessment of its application in lower-risk groups. An individualized pharmacokinetic dosage regimen could achieve the most optimal results, ensuring the largest proportion of steady-state concentrations within the optimal range.

Enzyme-mediated drug-drug interactions: a review of in vivo and in vitro methodologies, regulatory guidance, and translation to the clinic.

Enzyme-mediated pharmacokinetic drug-drug interactions can be caused by altered activity of drug metabolizing enzymes in the presence of a perpetrator drug, mostly via inhibition or induction. We identified a gap in the literature for a state-of-the art detailed overview assessing this type of DDI risk in the context of drug development. This manuscript discusses in vitro and in vivo methodologies employed during the drug discovery and development process to predict clinical enzyme-mediated DDIs, including the determination of clearance pathways, metabolic enzyme contribution, and the mechanisms and kinetics of enzyme inhibition and induction. We discuss regulatory guidance and highlight the utility of in silico physiologically-based pharmacokinetic modeling, an approach that continues to gain application and traction in support of regulatory filings. Looking to the future, we consider DDI risk assessment for targeted protein degraders, an emerging small molecule modality, which does not have recommended guidelines for DDI evaluation. Our goal in writing this report was to provide early-career researchers with a comprehensive view of the enzyme-mediated pharmacokinetic DDI landscape to aid their drug development efforts.

Transporter-mediated drug-drug interactions: regulatory guidelines, in vitro and in vivo methodologies and translation, special populations, and the blood-brain barrier.

This review, part of a special issue on drug-drug interactions (DDIs) spearheaded by the International Society for the Study of Xenobiotics (ISSX) New Investigators, explores the critical role of drug transporters in absorption, disposition, and clearance in the context of DDIs. Over the past two decades, significant advances have been made in understanding the clinical relevance of these transporters. Current knowledge on key uptake and efflux transporters that affect drug disposition and development is summarized. Regulatory guidelines from the FDA, EMA, and PMDA that inform the evaluation of potential transporter-mediated DDIs are discussed in detail. Methodologies for preclinical and clinical testing to assess potential DDIs are reviewed, with an emphasis on the utility of physiologically based pharmacokinetic (PBPK) modeling. This includes the application of relative abundance and expression factors to predict human pharmacokinetics (PK) using preclinical data, integrating the latest regulatory guidelines. Considerations for assessing transporter-mediated DDIs in special populations, including pediatric, hepatic, and renal impairment groups, are provided. Additionally, the impact of transporters at the blood-brain barrier (BBB) on the disposition of CNS-related drugs is explored. Enhancing the understanding of drug transporters and their role in drug disposition and toxicity can improve efficacy and reduce adverse effects. Continued research is essential to bridge remaining gaps in knowledge, particularly in comparison with cytochrome P450 (CYP) enzymes.

Perceived barriers and facilitators for model-informed dosing in pregnancy: a qualitative study across healthcare practitioners and pregnant women.

BACKGROUND: Most women use medication during pregnancy. Pregnancy-induced changes in physiology may require antenatal dose alterations. Yet, evidence-based doses in pregnancy are missing. Given historically limited data, pharmacokinetic models may inform pregnancy-adjusted doses. However, implementing model-informed doses in clinical practice requires support from relevant stakeholders. PURPOSE: To explore the perceived barriers and facilitators for model-informed antenatal doses among healthcare practitioners (HCPs) and pregnant women. METHODS: Online focus groups and interviews were held among healthcare practitioners (HCPs) and pregnant women from eight countries across Europe, Africa and Asia. Purposive sampling was used to identify pregnant women plus HCPs across various specialties prescribing or providing advice on medication to pregnant women. Perceived barriers and facilitators for implementing model-informed doses in pregnancy were identified and categorised using a hybrid thematic analysis. RESULTS: Fifty HCPs and 11 pregnant women participated in 12 focus groups and 16 interviews between January 2022 and March 2023. HCPs worked in the Netherlands (n = 32), the UK (n = 7), South Africa (n = 5), Uganda (n = 4), Kenya, Cameroon, India and Vietnam (n = 1 each). All pregnant women resided in the Netherlands. Barriers and facilitators identified by HCPs spanned 14 categories across four domains whereas pregnant women described barriers and facilitators spanning nine categories within the same domains. Most participants found current antenatal dosing information inadequate and regarded model-informed doses in pregnancy as a valuable and for some, much-needed addition to antenatal care. Although willingness-to-follow model-informed antenatal doses was high across both groups, several barriers for implementation were identified. HCPs underlined the need for transparent model validation and endorsement of the methodology by recognised institutions. Foetal safety was deemed a critical knowledge gap by both groups. HCPs' information needs and preferred features for model-informed doses in pregnancy varied. Several pregnant women expressed a desire to access information and partake in decisions on antenatal dosing. CONCLUSIONS: Given the perceived limitations of current pharmacotherapy for pregnant women and foetuses, model-informed dosing in pregnancy was seen as a promising means to enhance antenatal care by pregnant women and healthcare practitioners.

Lenacapavir Exhibits Atropisomerism - Mechanistic Pharmacokinetics and Disposition Studies of Lenacapavir Reveal Intestinal Excretion as a Major Clearance Pathway.

Lenacapavir (LEN), a long-acting injectable, is the first approved human immunodeficiency virus type 1 capsid inhibitor and one of a few FDA-approved drugs that exhibit atropisomerism. LEN exists as a mixture of two class 2 atropisomers that interconvert at a fast rate (t1/2 <2 hours) with a ratio that is stable over time and unaffected by enzymes or binding to proteins in plasma. LEN exhibits low systemic clearance (CL) in nonclinical species and humans; however, in all species the observed CL was higher than the in vitro predicted CL. The volume of distribution was moderate in nonclinical species and consistent with the tissue distribution observed by whole body autoradiography in rats. LEN does not distribute to brain, consistent with being a P-glycoprotein (P-gp) substrate. Mechanistic drug disposition studies with [14C]LEN in IV-dosed BDC rats and dogs showed a substantial amount of unchanged LEN (31 - 60% of dose) excreted in feces, indicating that intestinal excretion (IE) was a major clearance pathway for LEN in both species. Coadministration of oral elacridar, a P-gp inhibitor, in rats decreased CL and IE of LEN. Renal excretion was <1% of dose in both species. In plasma, almost all radioactivity was unchanged LEN. Low levels of metabolites in excreta included LEN-conjugates with glutathione, pentose, and glucuronic acid, which were consistent with metabolites formed in vitro in Hµrel® hepatocyte co­cultures and those observed in human. Our studies highlight the importance of IE for efflux substrates that are highly metabolically stable compounds with slow elimination rates. Significance Statement LEN is a long-acting injectable that exists as conformationally stable atropisomers. Due to an atropisomeric interconversion rate that significantly exceeds the in vivo elimination rate, the atropisomer ratio of LEN remains constant in circulation. The disposition of LEN highlights that intestinal excretion has a substantial part in the elimination of compounds that are metabolically highly stable and efflux transporter substrates.

Evaluation of Systemic and Brain Pharmacokinetic Parameters for Repurposing Metformin Using Intravenous Bolus Administration.

Metformin's potential in treating ischemic stroke and neurodegenerative conditions is of growing interest. Yet, the absence of established systemic and brain pharmacokinetic (PK) parameters at relevant pre-clinical doses presents a significant knowledge gap. This study highlights these PK parameters and the importance of using pharmacologically relevant pre-clinical doses to study pharmacodynamics (PD) in stroke and related neurodegenerative diseases. An LC-MS/MS method to measure metformin levels in plasma, brain, and cerebrospinal fluid (CSF) was developed and validated. In vitro assays examined brain tissue binding and metabolic stability. Intravenous (IV) bolus administration of metformin to C57BL6 mice covered low to high dose range maintaining pharmacological relevance. Quantification of metformin in the brain was used to assess brain pharmacokinetic parameters, such as unidirectional blood-to-brain constant (Kin) and unbound brain-to-plasma ratio (Kp, uu, brain). Metformin exhibited no binding in the mouse plasma and brain and remained metabolically stable. It rapidly entered the brain, reaching detectable levels in as little as 5 minutes. A Kin value of 1.87 {plus minus} 0.27 µl/g/min was obtained. As the dose increased, Kp, uu, brain showed decreased value, implying saturation, but this did not affect an increase in absolute brain concentrations. Metformin was quantifiable in the CSF at 30 minutes but decreased over time, with concentrations lower than those in the brain across all doses. Our findings emphasize the importance of metformin dose selection based on pharmacokinetic parameters for pre-clinical pharmacological studies. We anticipate further investigations focusing on pharmacokinetics and pharmacodynamics (PKPD) in disease conditions, such as stroke. Significance Statement The study establishes crucial pharmacokinetic parameters of metformin for treating ischemic stroke and neurodegenerative diseases, addressing a significant knowledge gap. It further emphasizes the importance of selecting pharmacologically relevant pre-clinical doses. The findings highlight metformin's rapid brain entry, minimal binding, and metabolic stability. The necessity of considering pharmacokinetic parameters in pre-clinical studies provides a foundation for future investigations into metformin's efficacy for neurodegenerative disease (s).

Central Nervous System Distributional Kinetics of Selected Histone Deacetylase Inhibitors.

Histone deacetylase expression and activity are often dysregulated in central nervous system (CNS) tumors, providing a rationale for investigating histone deacetylase inhibitors (HDACIs) in selected brain tumor patients. Although many HDACIs have shown potential in in vitro studies, they have had modest efficacy in vivo This lack of activity could be due to insufficient CNS exposure to the unbound drug. In this study, we investigated the systemic pharmacokinetics and subsequent CNS distribution of two potent HDACIs, vorinostat and quisinostat, in the murine model. Both compounds undergo in vitro degradation in mouse plasma, requiring precautions during sample processing. They also have short half-lives in vivo, in both plasma and CNS, which may lead to diminished efficacy. Transgenic transporter-deficient mouse models show that the CNS delivery of vorinostat was not limited by the two major blood-brain barrier efflux transporters, p-glycoprotein and breast-cancer-resistance protein. Vorinostat had an unbound CNS tissue-to-plasma partition coefficient of 0.06 {plus minus} 0.02. Conversely, the exposure of unbound quisinostat in the brain was only 0.02 {plus minus} 0.001 of that in the plasma, and the CNS distribution of quisinostat was limited by the activity of p-glycoprotein. To gain further context for these findings, the CNS distributional kinetics for vorinostat and quisinostat were compared to another hydroxamic acid HDACI, panobinostat. A comprehensive understanding of the CNS target exposure to unbound HDACI, along with known potencies from in vitro testing, can inform the prediction of a therapeutic window for HDACIs that have limited CNS exposure to unbound drug and guide targeted dosing strategies. Significance Statement This study indicates that quisinostat and vorinostat are susceptible to enzymatic degradation in the plasma, and to a lesser degree, in the target CNS tissues. Employing techniques that minimize the post-sampling degradation in plasma, brain and spinal cord, accurate CNS distributional kinetic parameters for these potentially useful compounds were determined. A knowledge of CNS exposure (Kp,uu), time to peak, and duration can inform dosing strategies in preclinical and clinical trials in selected CNS tumors.

Translational pharmacokinetic-toxicodynamic model of myelosuppression for dose optimization in combination chemotherapy of capecitabine and oxaliplatin from rats to humans.

XELOX therapy, which comprises capecitabine and oxaliplatin, is the standard first-line chemotherapeutic regimen for colorectal cancer. However, its myelosuppressive effects pose challenges for its clinical management. Mathematical modeling combining pharmacokinetics (PK) and toxicodynamics (TD) is a promising approach for optimizing dosing strategies and reducing toxicity. This study aimed to develop a translational PK-TD model using rat data to inform dosing strategies and TD implications in humans. The rats were administered capecitabine, oxaliplatin, or XELOX combination regimen, and PK and TD data were collected. PK parameters were analyzed using sequential compartment analysis, whereas TD responses were assessed using Friberg's semi-physiological model. A toxicity intensity-based nomogram recommends optimal dosing strategies. Translational modeling techniques using the hybrid PK-TD model were employed to predict clinical responses. The PK-TD model successfully predicted the time-course profiles of hematological responses in rats following monotherapy and XELOX combination treatment. Interactive effects on lymphocytopenia were identified with the co-administration of capecitabine and oxaliplatin. A model-based recommended combination of the dose reduction rate for escaping severe lymphocytopenia was proposed as 40% and 60% doses of capecitabine and oxaliplatin, respectively. The current translational model techniques successfully simulated the time-course profiles of blood cell counts with confidence intervals in patients using rat data. Our study provides valuable insights into dose optimization strategies for each individual drug within the XELOX regimen and underscores the potential of translational modeling to improve patient outcomes. In addition to dose determination, these data will lay the groundwork for advancing drug development processes in oncology. Significance Statement This study introduced a novel translational modeling approach rooted in a rat PK-TD model to optimize dosing strategies for the XELOX regimen for colorectal cancer treatment. Our findings highlight the interactive effects on lymphocytopenia and suggest a toxicity intensity-based nomogram for dose reduction, thus advancing precision medicine. This translational modeling paradigm enhances our understanding of drug interactions, offering a tool to tailor dosing, minimize hematological toxicity, and improve therapeutic outcomes in patients undergoing XELOX therapy.

A pharmacokinetic model for hyperpolarized 13C-pyruvate MRI when using metabolite-specific bSSFP sequences.

PURPOSE: Metabolite-specific balanced SSFP (MS-bSSFP) sequences are increasingly used in hyperpolarized [1-13C]Pyruvate (HP 13C) MRI studies as they improve SNR by refocusing the magnetization each TR. Currently, pharmacokinetic models used to fit conversion rate constants, kPL and kPB, and rate constant maps do not account for differences in the signal evolution of MS-bSSFP acquisitions. METHODS: In this work, a flexible MS-bSSFP model was built that can be used to fit conversion rate constants for these experiments. The model was validated in vivo using paired animal (healthy rat kidneys n = 8, transgenic adenocarcinoma of the mouse prostate n = 3) and human renal cell carcinoma (n = 3) datasets. Gradient echo (GRE) acquisitions were used with a previous GRE model to compare to the results of the proposed GRE-bSSFP model. RESULTS: Within simulations, the proposed GRE-bSSFP model fits the simulated data well, whereas a GRE model shows bias because of model mismatch. For the in vivo datasets, the estimated conversion rate constants using the proposed GRE-bSSFP model are consistent with a previous GRE model. Jointly fitting the lactate T2 with kPL resulted in less precise kPL estimates. CONCLUSION: The proposed GRE-bSSFP model provides a method to estimate conversion rate constants, kPL and kPB, for MS-bSSFP HP 13C experiments. This model may also be modified and used for other applications, for example, estimating rate constants with other hyperpolarized reagents or multi-echo bSSFP.

Efflux transporters in drug disposition during pregnancy.

Evidence-based dose selection of drugs in pregnant women has been lacking due to challenges in studying maternal-fetal pharmacokinetics. Hence, many drugs are administered off-label during pregnancy based on data obtained from non-pregnant women. During pregnancy, drug transporters play an important role in drug disposition along with known gestational age-dependent changes in physiology and drug-metabolizing enzymes. In this review, as Dr. Qingcheng Mao's former and current lab members, we summarize the collective contributions of Dr. Mao, who lost his life to cancer, focusing on the role of drug transporters in drug disposition during pregnancy. Dr. Mao and his team initiated their research by characterizing the structure of Breast Cancer Resistance Protein [BCRP, ATP-Binding Cassette (ABC) G2]. Subsequently, they have made significant contributions to the understanding of the role of BCRP and other transporters, particularly P-glycoprotein (P-gp/ABCB1), in the exposure of pregnant women and their fetuses to various drugs, including nitrofurantoin, glyburide, buprenorphine, bupropion, tetrahydrocannabinol, and their metabolites. This review also highlights the gestation- and pregnancy-dependent transporter expression at the blood-brain and blood-placenta barriers in mice. Significance Statement Dr. Qingcheng Mao and his team have made significant contributions to the investigation of the role of efflux transporters, especially P-glycoprotein and breast cancer resistance protein, in maternal-fetal exposure to many xenobiotics: nitrofurantoin, glyburide, buprenorphine, bupropion, tetrahydrocannabinol and their metabolites. Studies of individual compounds and the expression of transporters during gestation and pregnancy have improved the understanding of maternal-fetal pharmacokinetics.

The usefulness of determining plasma and tissue concentrations of phosphorodiamidate morpholino oligonucleotides to estimate their efficacy in Duchenne muscular dystrophy patients.

Currently four kinds of phosphorodiamidate morpholino oligomers (PMOs) such as viltolarsen have been approved for the treatment of Duchenne muscular dystrophy (DMD); however, it is unclear whether human efficacy can be estimated using plasma concentrations. This study summarizes the tissue distribution of viltolarsen in mice and cynomolgus monkeys and evaluates the relationship between exposure and efficacy based on exon skipping. In the tissue distribution studies, all muscles in DMD model mice showed higher concentrations of viltolarsen than those in wild-type mice and cynomolgus monkeys, and the concentrations in skeletal muscle were correlated with the exon-skipping efficiency in mice and cynomolgus monkeys. In addition, a highly sensitive bioanalytical method using liquid chromatography with tandem mass spectrometry shows promise for determining plasma concentrations up to a later time point, and the tissue (muscle)/plasma concentration ratio (Kp) in DMD model mice was shown to be useful for predicting changes in pharmacodynamic (PD) markers in humans. Our results suggest that pharmacokinetic (PK)/PD analysis can be conducted by using the human PK profile or Kp values and skipping efficiency in DMD model mice. This information will be useful for the efficient and effective development of PMOs as therapeutic agents. Significance Statement We compare that plasma and tissue concentrations with the efficiency of exon skipping for viltolarsen as an example phosphorodiamidate morpholino oligomers in skeletal and cardiac muscle of mice and cynomolgus monkeys for pharmacokinetics/pharmacodynamics (PK/PD) analysis. Our results suggest that PK/PD analysis can be conducted by using the human PK profile or Kp values and skipping efficiency in DMD model mice.

Physiologically Based Pharmacokinetic (PBPK) Modeling of small molecules: How Much Progress Have We Made?

Physiologically based pharmacokinetic (PBPK) models of small molecules have become mainstream in drug development and academic research. The use of PBPK models is continuously expanding with the majority of work now focusing on predictions of drug-drug interactions, drug-disease interactions, and changes in drug disposition across lifespan. Recently, publications that use PBPK modeling to predict drug disposition during pregnancy and in organ impairment have increased reflecting the advances in incorporating diverse physiological changes into the models. Due to the expanding computational power and diversity of modeling platforms available, the complexity of PBPK models has also increased. Academic efforts have provided clear advances in better capturing human physiology in PBPK models and incorporating more complex mathematical concepts into PBPK models. Examples of such advances include the segregated gut model with a series gut compartments allowing modeling of physiological blood flow distribution within an organ and zonation of metabolic enzymes, and series compartment liver models allowing simulations of hepatic clearance for high extraction drugs. Despite these advances in academic research, the progress in assessing model quality and defining model acceptance criteria based on the intended use of the models has not kept pace. This review suggests that awareness of the need for predefined criteria for model acceptance has increased but many manuscripts still lack description of scientific justification and/or rationale for chosen acceptance criteria. As artificial intelligence and machine learning approaches become more broadly accepted, these tools offer promise for development of comprehensive assessment for existing observed data and analysis of model performance. Significance Statement PBPK modeling has become a mainstream application in academic literature and is broadly used for predictions, analysis and evaluation of pharmacokinetic data. Many significant advances have been made in developing advanced PBPK models that better capture human physiology but oftentimes sufficient justification for the chosen model acceptance criterion and model structure is still missing. This review provides a summary of the current landscape of PBPK applications used and highlights the needs for advancing PBPK modeling science and training in academia.

Quantitative Proteomics for Translational Pharmacology and Precision Medicine: State of The Art and Future Outlook.

Over the past 20 years, quantitative proteomics has contributed a wealth of protein expression data, which are currently used for a variety of systems pharmacology applications, as a complement or a surrogate for activity of the corresponding proteins. A symposium at the 25th North American ISSX meeting, in Boston, in September 2023, was held to explore current and emerging applications of quantitative proteomics in translational pharmacology and strategies for improved integration into model-informed drug development based on practical experience of each of the presenters. A summary of the talks and discussions is presented in this perspective alongside future outlooks that were outlined for future meetings. Significance Statement This perspective explores current and emerging applications of quantitative proteomics in translational pharmacology and precision medicine, and outlines outlooks for improved integration into model-informed drug development.