The Important Role of Transporter Structures in Drug Disposition, Efficacy, and Toxicity

Drug Transporters and Metabolizing Enzymes in Antimicrobial Drug Pharmacokinetics: Mechanisms, Drug-Drug Interactions, and Clinical Implications

Drug transporters and metabolizing enzymes are integral components of drug disposition, governing the absorption, distribution, metabolism, and excretion (ADME) of pharmaceuticals. Their activities critically determine therapeutic efficacy and toxicity profiles, particularly for antimicrobial agents, one of the most widely prescribed drug classes frequently co-administered with other medications. Emerging evidence highlights the clinical significance of the drug-drug interactions (DDIs) mediated by these systems, which may alter antimicrobial pharmacokinetics, compromise treatment outcomes, or precipitate adverse events. With the continuous introduction of novel antimicrobial agents into clinical practice, the role of drug transporters and metabolizing enzymes in the pharmacokinetics of antibiotics and the DDIs between antibiotics and other drugs mediated by these transporters and enzymes are important to determine in order to provide a theoretical basis for the safe and effective use of antimicrobial drugs in clinical use.

Structural and functional implications of ABCC1 variants on clinical statin response

ATP-binding cassette (ABC) proteins are membrane transporters responsible for metabolites and active substances removal from cells. Their genes' variations have been associated with protein function and expression defects. Familial Hypercholesterolemia (FH) patients hosting those alterations might compromise the efficacy of high-dose statin treatment, a primary therapeutic strategy. ABCC1 is a member of the ABC-transporter superfamily, potentially relevant to pharmacological therapy responses and toxicity risks in hypercholesterolemic patients. Here, we evaluated specific non-synonymous (SNV) missense variants in the ABCC1 gene from a FH patient cohort, assessing potential impacts on protein structure, molecular dynamics and interactions with rosuvastatin, atorvastatin, pravastatin, pitavastatin, and lovastatin. Molecular docking, complemented by motion, visual and binding affinity analysis using the PLANNET model, suggested that these mutations had minimal impact on drug interactions. These findings prompted further analysis of two other efflux pumps, ABCG2 and P-gp, and their statin interactions. Interestingly, diminished binding affinities hinted at a compensatory mechanism wherein other transporters might mitigate potential ABCC1 mutation effects, ensuring effective drug efflux. Clinical profiles from the patient cohort did not show a correlation between these variants and clinical outcomes, potentially pointing to the role of alternate drug transporters in statin interaction.

Obesity-related drug transporter expression alterations in human liver and kidneys

BACKGROUND

Pathophysiological changes associated with obesity might impact various drug pharmacokinetics (PK) parameters. The liver and kidneys are the primary organs involved in drug clearance, and the function of hepatic and renal transporters is critical to efficient drug elimination (or reabsorption). Considering the impact of an increased BMI on the drug's PK is crucial in directing dosing decisions. Given the critical role of transporters in drug biodisposition, this study investigated how overweight and obesity affect the gene expression of renal and hepatic drug transporters.

METHODS

Human liver and kidney samples were collected post-mortem from 32 to 28 individuals, respectively, which were divided into the control group (lean subjects; 18.5 ≤ BMI < 25 kg/m2) and the study group (overweight/obese subjects; BMI ≥ 25 kg/m2). Real-time quantitative PCR was performed for the analysis of 84 drug transporters.

RESULTS

Our results show significant changes in the expression of genes involved in human transporters, both renal and hepatic. In liver tissue, we found that ABCC4 was up-regulated in overweight/obese subjects. In kidney tissue, up-regulation was only observed for ABCC10, while the other differentially expressed genes were down-regulated: ABCA1, ABCC3, and SLC15A1.

CONCLUSIONS

The observed alterations may be reflected by the differences in drug PK between lean and obese populations. However, these findings need further evaluation through the proteomic and functional study of these transporters in this patient population.

Advancing understanding of human variability through toxicokinetic modeling, in vitro-in vivo extrapolation, and new approach methodologies

The merging of physiology and toxicokinetics, or pharmacokinetics, with computational modeling to characterize dosimetry has led to major advances for both the chemical and pharmaceutical research arenas. Driven by the mutual need to estimate internal exposures where in vivo data generation was simply not possible, the application of toxicokinetic modeling has grown exponentially in the past 30 years. In toxicology the need has been the derivation of quantitative estimates of toxicokinetic and toxicodynamic variability to evaluate the suitability of the tenfold uncertainty factor employed in risk assessment decision-making. Consideration of a host of physiologic, ontogenetic, genetic, and exposure factors are all required for comprehensive characterization. Fortunately, the underlying framework of physiologically based toxicokinetic models can accommodate these inputs, in addition to being amenable to capturing time-varying dynamics. Meanwhile, international interest in advancing new approach methodologies has fueled the generation of in vitro toxicity and toxicokinetic data that can be applied in in vitro-in vivo extrapolation approaches to provide human-specific risk-based information for historically data-poor chemicals. This review will provide a brief introduction to the structure and evolution of toxicokinetic and physiologically based toxicokinetic models as they advanced to incorporate variability and a wide range of complex exposure scenarios. This will be followed by a state of the science update describing current and emerging experimental and modeling strategies for population and life-stage variability, including the increasing application of in vitro-in vivo extrapolation with physiologically based toxicokinetic models in pharmaceutical and chemical safety research. The review will conclude with case study examples demonstrating novel applications of physiologically based toxicokinetic modeling and an update on its applications for regulatory decision-making. Physiologically based toxicokinetic modeling provides a sound framework for variability evaluation in chemical risk assessment.

Hair follicle sulfotransferase activity and effectiveness of oral minoxidil in androgenetic alopecia

BACKGROUND

Androgenetic alopecia (AGA) is common. While topical minoxidil remains the only FDA-approved therapeutic for AGA, its efficacy is limited in stimulating clinically significant hair regrowth over the longer term. Oral minoxidil, which is used off-label, is a promising alternative; however, its effectiveness and underlying mechanisms warrant further investigation.

AIMS

To elucidate the site of action and infer the physiological mechanisms underlying therapeutic responses to oral minoxidil in patients with AGA.

METHODS

Forty-one patients with AGA underwent 6 months of low-dose oral minoxidil treatment. Minoxidil sulfotransferase (SULT) activity was assayed in plucked scalp hair follicles. The primary outcome was hair growth after low-dose oral minoxidil treatment for a minimum of 6 months, and the secondary outcome was SULT activity in hair follicles.

RESULTS

After 6 months of treatment, 26 (63.4%) patients experienced a clinical improvement in alopecia symptoms. The response rate was higher in men (19/26 [73.1%]) than in women (6/15 [40.0%]). Patients with low hair follicle SULT activity demonstrated a higher minoxidil response rate than those with high enzyme activity (85% vs. 43%, p = 0.009).

CONCLUSIONS

Our findings indicate that low SULT activity within the hair follicles is associated with a favorable response to oral minoxidil therapy in patients with AGA. Further elucidation of the underlying mechanisms could significantly improve personalized therapeutic approaches through improved patient selection and the rational design of adjuvant treatments.

Precision Medicine in Childhood Cancer: The Influence of Genetic Polymorphisms on Vincristine-Induced Peripheral Neuropathy

Cancer is the leading cause of disease-related death among children. Vincristine (VCR), a key component of childhood cancer treatment protocols, is associated with the risk of peripheral neuropathy (PN), a condition that may be reversible upon drug discontinuation but can also leave lasting sequelae. Single nucleotide polymorphism (SNP) in genes involved in VCR pharmacokinetics and pharmacodynamics have been investigated in relation to an increased risk of PN. However, the results of these studies have been inconsistent. A retrospective cohort study was conducted to investigate the potential association of drug transporter genes from the ATP-binding cassette (ABC) family and the centrosomal protein 72 (CEP72) gene with the development of PN in 88 Caucasian children diagnosed with cancer and treated with VCR. Genotyping was performed using real-time PCR techniques for the following SNPs: ABCB1 rs1128503, ABCC1 rs246240, ABCC2 rs717620, and CEP72 rs924607. The results indicated that age at diagnosis (OR = 1.33; 95% CI = 1.07-1.75) and the ABCC1 rs246240 G allele (OR = 12.48; 95% CI = 2.26-100.42) were associated with vincristine-induced peripheral neuropathy (VIPN). No association was found between this toxicity and CEP72 rs924607. Our study provides insights that may contribute to optimizing childhood cancer therapy in the future by predicting the risk of VIPN.

Intestinal absorption mechanism and nutritional synergy promotion strategy of dietary flavonoids: transintestinal epithelial pathway mediated by intestinal transport proteins

Dietary flavonoids exhibit a variety of physiological functions in regulating glucose and lipid metabolism, improving cardiovascular function, and enhancing stress resistance. However, poor intestinal absorption limits their health benefits. Previous studies on improving the absorption efficiency of flavonoids have focused on targeted release, enhanced gastrointestinal stability and prolonged retention time in digestive tract. But less attention has been paid to promoting the uptake and transport of flavonoids by intestinal epithelial cells through modulation of transporter protein-mediated pathways. Interestingly, some dietary nutrients have been found to modulate the expression or function of transporter proteins, thereby synergistically or antagonistically affecting flavonoid absorption. Therefore, this paper proposed an innovative regulatory strategy known as the "intestinal transport protein-mediated pathway" to promote intestinal absorption of dietary flavonoids. The flavonoid absorption mechanism in the intestinal epithelium, mediated by intestinal transport proteins, was summarized. The functional differences between the uptake transporter and efflux transporters during flavonoid trans-intestinal cellular transport were discussed. Finally, from the perspective of nutritional synergy promotion of absorption, the feasibility of promoting flavonoid intestinal absorption by regulating the expression/function of transport proteins through dietary nutrients was emphasized. This review provides a new perspective and developing precise dietary nutrient combinations for efficient dietary flavonoid absorption.

Computational Chemistry in Structure-Based Solute Carrier Transporter Drug Design: Recent Advances and Future Perspectives

Solute carrier transporters (SLCs) are a class of important transmembrane proteins that are involved in the transportation of diverse solute ions and small molecules into cells. There are approximately 450 SLCs within the human body, and more than a quarter of them are emerging as attractive therapeutic targets for multiple complex diseases, e.g., depression, cancer, and diabetes. However, only 44 unique transporters (∼9.8% of the SLC superfamily) with 3D structures and specific binding sites have been reported. To design innovative and effective drugs targeting diverse SLCs, there are a number of obstacles that need to be overcome. However, computational chemistry, including physics-based molecular modeling and machine learning- and deep learning-based artificial intelligence (AI), provides an alternative and complementary way to the classical drug discovery approach. Here, we present a comprehensive overview on recent advances and existing challenges of the computational techniques in structure-based drug design of SLCs from three main aspects: (i) characterizing multiple conformations of the proteins during the functional process of transportation, (ii) identifying druggability sites especially the cryptic allosteric ones on the transporters for substrates and drugs binding, and (iii) discovering diverse small molecules or synthetic protein binders targeting the binding sites. This work is expected to provide guidelines for a deep understanding of the structure and function of the SLC superfamily to facilitate rational design of novel modulators of the transporters with the aid of state-of-the-art computational chemistry technologies including artificial intelligence.

Utilizing non-coding RNA-mediated regulation of ATP binding cassette (ABC) transporters to overcome multidrug resistance to cancer chemotherapy

Multidrug resistance (MDR) is one of the primary factors that produces treatment failure in patients receiving cancer chemotherapy. MDR is a complex multifactorial phenomenon, characterized by a decrease or abrogation of the efficacy of a wide spectrum of anticancer drugs that are structurally and mechanistically distinct. The overexpression of the ATP-binding cassette (ABC) transporters, notably ABCG2 and ABCB1, are one of the primary mediators of MDR in cancer cells, which promotes the efflux of certain chemotherapeutic drugs from cancer cells, thereby decreasing or abolishing their therapeutic efficacy. A number of studies have suggested that non-coding RNAs (ncRNAs), particularly microRNAs (miRNAs), long non-coding RNAs (lncRNAs) and circular RNAs (circRNAs), play a pivotal role in mediating the upregulation of ABC transporters in certain MDR cancer cells. This review will provide updated information about the induction of ABC transporters due to the aberrant regulation of ncRNAs in cancer cells. We will also discuss the measurement and biological profile of circulating ncRNAs in various body fluids as potential biomarkers for predicting the response of cancer patients to chemotherapy. Sequence variations, such as alternative polyadenylation of mRNA and single nucleotide polymorphism (SNPs) at miRNA target sites, which may indicate the interaction of miRNA-mediated gene regulation with genetic variations to modulate the MDR phenotype, will be reviewed. Finally, we will highlight novel strategies that could be used to modulate ncRNAs and circumvent ABC transporter-mediated MDR.