Modeling the Drug delivery Lifecycle of PLG Nanoparticles Using Intravital Microscopy.

Polylactide-co-glycolide (PLG) nanoparticles hold immense promise for cancer therapy due to their enhanced efficacy and biodegradable matrix structure. Understanding their interactions with blood cells and subsequent biodistribution kinetics is crucial for optimizing their therapeutic potential. In this study, three doxorubicin-loaded PLG nanoparticle systems are synthesized and characterized, analyzing their size, zeta potential, morphology, and in vitro release behavior. Employing intravital microscopy in 4T1-tumor-bearing mice, real-time blood and tumor distribution kinetics are investigated. A mechanistic pharmacokinetic model is used to analyze biodistribution kinetics. Additionally, flow cytometry is utilized to identify cells involved in nanoparticle hitchhiking. Following intravenous injection, PLG nanoparticles exhibit an initial burst release (<1 min) and rapidly adsorb to blood cells (<5 min), hindering extravasation. Agglomeration leads to the clearance of one carrier species within 3 min. In stable dispersions, drug release rather than extravasation remains the dominant pathway for drug elimination from circulation. This comprehensive investigation provides valuable insights into the interplay between competing kinetics that influence the lifecycle of PLG nanoparticles post-injection. The findings advance the understanding of nanoparticle behavior and lay the foundation for improved cancer therapy strategies using nanoparticle-based drug delivery systems.

Future Nanotechnology-Based Strategies for Improved Management of Helicobacter pylori Infection.

Helicobacter pylori (H. pylori) is a recalcitrant pathogen, which can cause gastric disorders. During the past decades, polypharmacy-based regimens, such as triple and quadruple therapies have been widely used against H. pylori. However, polyantibiotic therapies can disturb the host gastric/gut microbiota and lead to antibiotic resistance. Thus, simpler but more effective approaches should be developed. Here, some recent advances in nanostructured drug delivery systems to treat H. pylori infection are summarized. Also, for the first time, a drug release paradigm is proposed to prevent H. pylori antibiotic resistance along with an IVIVC model in order to connect the drug release profile with a reduction in bacterial colony counts. Then, local delivery systems including mucoadhesive, mucopenetrating, and cytoadhesive nanobiomaterials are discussed in the battle against H. pylori infection. Afterward, engineered delivery platforms including polymer-coated nanoemulsions and polymer-coated nanoliposomes are poposed. These bioinspired platforms can contain an antimicrobial agent enclosed within smart multifunctional nanoformulations. These bioplatforms can prevent the development of antibiotic resistance, as well as specifically killing H. pylori with no or only slight negative effects on the host gastrointestinal microbiota. Finally, the essential checkpoints that should be passed to confirm the potential effectiveness of anti-H. pylori nanosystems are discussed.

Extracellular Vesicle (EV) biohybrid systems for cancer therapy: Recent advances and future perspectives.

Extracellular vesicles (EVs) are a class of cell-derived lipid-bilayer membrane vesicles secreted by almost all mammalian cells and involved in intercellular communication by shuttling various biological cargoes. Over the last decade, EVs - namely exosomes and microvesicles - have been extensively explored as next-generation nanoscale drug delivery systems (DDSs). This is in large due to their endogenous origin, which enables EVs to circumvent some of the limitations associated with existing cancer therapy approaches (i.e. by preventing recognition by the immune system and improving selectivity towards tumor tissue). However, successful translation of these cell-derived vesicles into clinical applications has been hindered by several factors, among which the loading of exogenous therapeutic molecules still represents a great challenge. In order to address this issue and to further advance these biologically-derived systems as drug carriers, EV-biohybrid nano-DDSs, obtained through the fusion of EVs with conventional synthetic nano-DDSs, have recently been proposed as a valuable alternative as DDSs. Building on the idea of "combining the best of both worlds", a combination of these two unique entities aims to harness the beneficial properties associated with both EVs and conventional nano-DDSs, while overcoming the flaws of the individual components. These biohybrid systems also provide a unique opportunity for exploitation of new synergisms, often leading to improved therapeutic outcomes, thus paving the way for advancements in cancer therapy. This review aims to describe the recent developments of EV-biohybrid nano-DDSs in cancer therapy, to highlight the most promising results and breakthroughs, as well as to provide a glimpse on the possible intrinsic targeting mechanisms of EVs that can be bequeathed to their hybrid systems. Finally, we also provide some insights in the future perspectives of EV-hybrid DDSs.

Mechanism of anti-inflammatory effects of rifampicin in an ex vivo culture system of hidradenitis suppurativa.

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease of the hair follicles leading to painful lesions, associated with increased levels of pro-inflammatory cytokines. Numerous guidelines recommend antibiotics like clindamycin and rifampicin in combination, as first-line systemic therapy in moderate-to-severe forms of inflammation. HS has been proposed to be mainly an auto-inflammatory disease associated with but not initially provoked by bacteria. Therefore, it has to be assumed that the pro-inflammatory milieu previously observed in HS skin is not solely dampened by the bacteriostatic inhibition of DNA-dependent RNA polymerase. To further clarify the mechanism of anti-inflammatory effects of rifampicin, ex vivo explants of lesional HS from 8 HS patients were treated with rifampicin, and its effect on cytokine production, immune cells as well as the expression of Toll-like receptor 2 (TLR2) were investigated. Analysis of cell culture medium of rifampicin-treated HS explants revealed an anti-inflammatory effect of rifampicin that significantly inhibiting interleukin (IL)-1ß, IL-6, IL-8, IL-10 and tumour necrosis factor (TNF)-α production. Immunohistochemistry of the rifampicin-treated explants suggested a tendency for it to reduce the expression of TLR2 while not affecting the number of immune cells.

Pharmaceutical Development of Nanostructured Vesicular Hydrogel Formulations of Rifampicin for Wound Healing.

Chronic wounds exhibit elevated levels of inflammatory cytokines, resulting in the release of proteolytic enzymes which delay wound-healing processes. In recent years, rifampicin has gained significant attention in the treatment of chronic wounds due to an interesting combination of antibacterial and anti-inflammatory effects. Unfortunately, rifampicin is sensitive to hydrolysis and oxidation. As a result, no topical drug product for wound-healing applications has been approved. To address this medical need two nanostructured hydrogel formulations of rifampicin were developed. The liposomal vesicles were embedded into hydroxypropyl methylcellulose (HPMC) gel or a combination of hyaluronic acid and marine collagen. To protect rifampicin from degradation in aqueous environments, a freeze-drying method was developed. Before freeze-drying, two well-defined hydrogel preparations were obtained. After freeze-drying, the visual appearance, chemical stability, residual moisture content, and redispersion time of both preparations were within acceptable limits. However, the morphological characterization revealed an increase in the vesicle size for collagen-hyaluronic acid hydrogel. This was confirmed by subsequent release studies. Interactions of marine collagen with phosphatidylcholine were held responsible for this effect. The HPMC hydrogel formulation remained stable over 6 months of storage. Moving forward, this product fulfills all criteria to be evaluated in preclinical and clinical studies.

Temporal Changes in Extracellular Vesicle Hemostatic Protein Composition Predict Favourable Left Ventricular Remodeling after Acute Myocardial Infarction.

The subset of plasma extracellular vesicles (EVs) that coprecipitate with low-density lipoprotein (LDL-EVs) carry coagulation and fibrinolysis pathway proteins as cargo. We investigated the association between LDL-EV hemostatic/fibrinolysis protein ratios and post-acute myocardial infarction (post-AMI) left ventricular (LV) remodeling which precedes heart failure. Protein concentrations of von Willebrand factor (VWF), SerpinC1 and plasminogen were determined in LDL-EVs extracted from plasma samples obtained at baseline (within 72 h post-AMI), 1 month and 6 months post-AMI from 198 patients. Patients were categorized as exhibiting adverse (n = 98) or reverse (n = 100) LV remodeling based on changes in LV end-systolic volume (increased or decreased ≥15) over a 6-month period. Multiple level longitudinal data analysis with structural equation (ML-SEM) model was used to assess predictive value for LV remodeling independent of baseline differences. At baseline, protein levels of VWF, SerpinC1 and plasminogen in LDL-EVs did not differ between patients with adverse versus reverse LV remodeling. At 1 month post-AMI, protein levels of VWF and SerpinC1 decreased whilst plasminogen increased in patients with adverse LV remodeling. In contrast, VWF and plasminogen decreased whilst SerpinC1 remained unchanged in patients with reverse LV remodeling. Overall, compared with patients with adverse LV remodeling, higher levels of SerpinC1 and VWF but lower levels of plasminogen resulted in higher ratios of VWF:Plasminogen and SerpinC1:Plasminogen at both 1 month and 6 months post-AMI in patients with reverse LV remodeling. More importantly, ratios VWF:Plasminogen (AUC = 0.674) and SerpinC1:Plasminogen (AUC = 0.712) displayed markedly better prognostic power than NT-proBNP (AUC = 0.384), troponin-I (AUC = 0.467) or troponin-T (AUC = 0.389) (p < 0.001) to predict reverse LV remodeling post-AMI. Temporal changes in the ratios of coagulation to fibrinolysis pathway proteins in LDL-EVs outperform current standard plasma biomarkers in predicting post-AMI reverse LV remodeling. Our findings may provide clinical cues to uncover the cellular mechanisms underpinning post-AMI reverse LV remodeling.

Predicting the environmental emissions arising from conventional and nanotechnology-related pharmaceutical drug products.

Today, environmental pollution with pharmaceutical drugs and their metabolites poses a major threat to the aquatic ecosystems. Active substances such as fenofibrate, are processed to pharmaceutical drug formulations before they are degraded by the human body and released into the wastewater. Compared to the conventional product Lipidil® 200, the pharmaceutical product Lipidil 145 One® and Ecocaps take advantage of nanotechnology to improve uptake and bioavailability of the drug in humans. In the present approach, a combination of in vitro drug release studies and physiologically-based biopharmaceutics modeling was applied to calculate the emission of three formulations of fenofibrate (Lipidil® 200, Lipidil 145 One®, Ecocaps) into the environment. Special attention was paid to the metabolized and non-metabolized fractions and their individual toxicity, as well as to the emission of nanomaterials. The fish embryo toxicity test revealed a lower aquatic toxicity for the metabolite fenofibric acid and therefore an improved toxicity profile. When using the microparticle formulation Lipidil® 200, an amount of 126 mg of non-metabolized fenofibrate was emitted to the environment. Less than 0.05% of the particles were in the lower nanosize range. For the nanotechnology-related product Lipidil 145 One®, the total drug emission was reduced by 27.5% with a nanomaterial fraction of approximately 0.5%. In comparison, the formulation prototype Ecocaps reduced the emission of fenofibrate by 42.5% without any nanomaterials entering the environment. In a streamlined life cycle assessment, the lowered dose in combination with a lowered drug-to-metabolite ratio observed for Ecocaps led to a reduction of the full life cycle impacts of fenofibrate with a reduction of 18% reduction in the global warming potential, 61% in ecotoxicity, and 15% in human toxicity. The integrated environmental assessment framework highlights the outstanding potential of advanced modeling technologies to determine environmental impacts of pharmaceuticals during early drug development using preclinical in vitro data.

Sustainable Stabilizer-Free Nanoparticle Formulations of Valsartan Using Eudragit® RLPO.

The bioavailability of the antihypertensive drug valsartan can be enhanced by various microencapsulation methods. In the present investigation, valsartan-loaded polymeric nanoparticles were manufactured from Eudragit® RLPO using an emulsion-solvent evaporation method. Polyvinyl alcohol (PVA) was found to be a suitable stabilizer for the nanoparticles, resulting in a monodisperse colloid system ranging in size between 148 nm and 162 nm. Additionally, a high encapsulation efficiency (96.4%) was observed. However, due to the quaternary ammonium groups of Eudragit® RLPO, the stabilization of the dispersion could be achieved in the absence of PVA as well. The nanoparticles were reduced in size (by 22%) and exhibited similar encapsulation efficiencies (96.4%). This more cost-effective and sustainable production method reduces the use of excipients and their expected emission into the environment. The drug release from valsartan-loaded nanoparticles was evaluated in a two-stage biorelevant dissolution set-up, leading to the rapid dissolution of valsartan in a simulated intestinal medium. In silico simulations using a model validated previously indicate a potential dose reduction of 60-70% compared to existing drug products. This further reduces the expected emission of the ecotoxic compound into the environment.

Exploring the Interplay between Drug Release and Targeting of Lipid-Like Polymer Nanoparticles Loaded with Doxorubicin.

Targeted delivery of doxorubicin still poses a challenge with regards to the quantities reaching the target site as well as the specificity of the uptake. In the present approach, two colloidal nanocarrier systems, NanoCore-6.4 and NanoCore-7.4, loaded with doxorubicin and characterized by different drug release behaviors were evaluated in vitro and in vivo. The nanoparticles utilize a specific surface design to modulate the lipid corona by attracting blood-borne apolipoproteins involved in the endogenous transport of chylomicrons across the blood-brain barrier. When applying this strategy, the fine balance between drug release and carrier accumulation is responsible for targeted delivery. Drug release experiments in an aqueous medium resulted in a difference in drug release of approximately 20%, while a 10% difference was found in human serum. This difference affected the partitioning of doxorubicin in human blood and was reflected by the outcome of the pharmacokinetic study in rats. For the fast-releasing formulation NanoCore-6.4, the AUC0→1h was significantly lower (2999.1 ng × h/mL) than the one of NanoCore-7.4 (3589.5 ng × h/mL). A compartmental analysis using the physiologically-based nanocarrier biopharmaceutics model indicated a significant difference in the release behavior and targeting capability. A fraction of approximately 7.310-7.615% of NanoCore-7.4 was available for drug targeting, while for NanoCore-6.4 only 5.740-6.057% of the injected doxorubicin was accumulated. Although the targeting capabilities indicate bioequivalent behavior, they provide evidence for the quality-by-design approach followed in formulation development.

The role of recent nanotechnology in enhancing the efficacy of radiation therapy.

Radiation therapy is one of the most commonly used non-surgical interventions in tumor treatment and is often combined with other modalities to enhance its efficacy. Despite recent advances in radiation oncology, treatment responses, however, vary considerably between individual patients. A variety of approaches have been developed to enhance radiation response or to counteract resistance to ionizing radiation. Among them, a relatively novel class of radiation sensitizers comprises nanoparticles (NPs) which are highly efficient and selective systems in the nanometer range. NPs can either encapsulate radiation sensitizing agents, thereby protecting them from degradation, or sensitize cancer cells to ionizing radiation via their physicochemical properties, e.g. high Z number. Moreover, they can be chemically modified for active molecular targeting and the imaging of tumors. In this review we will focus on recent developments in nanotechnology, different classes and modifications of NPs and their radiation sensitizing properties.

Drug Release and Targeting: the Versatility of Polymethacrylate Nanoparticles for Peroral Administration Revealed by Using an Optimized In Vitro-Toolbox.

PURPOSE: The contribution of permeability and drug release to drug targeting were investigated in the course of development of a nanosized formulation of the anti-inflammatory compound TMP-001, for the local treatment in the gastrointestinal tract. METHODS: TMP-001 was encapsulated by nanoprecipitation into Eudragit® RS 100. The permeability of these carriers was investigated in an Ussing chamber model and the release rate was determined under biorelevant conditions. Formulation toxicity and particle-cell-interaction were investigated by flow cytometry, fluorescence and electron microscopy. Furthermore, spray drying was performed. RESULTS: Effective internalization of Eudragit®-nanoparticles into cancer cells was demonstrated. A burst release of the nanoparticles implied poor interaction of TMP-001 with Eudragit®. A sustained release (70.5% release after 30 min compared to 98.0% for the API) was accomplished after spray drying yielded an increased particle size. Recovery rate of TMP-001 after spray drying was 94.2 ± 5.9%. CONCLUSION: The release of API from polymeric nanoparticles contributes profoundly to the in vivo-performance of drug delivery devices in the gastrointestinal tract. The impact of drug-polymer interaction and particle size was analyzed. Sustained release of TMP-001 could only be achieved by increasing particle size. Therefore, biorelevant release testing has been demonstrated to be a valid tool for nanoformulation design.

Bridging laboratory and large scale production: preparation and in vitro-evaluation of photosensitizer-loaded nanocarrier devices for targeted drug delivery.

PURPOSE: Industrial production of nanosized drug delivery devices is still an obstacle to the commercialization of nanomedicines. This study encompasses the development of nanoparticles for peroral application in photodynamic therapy, optimization according to the selected product specifications, and the translation into a continuous flow process. METHODS: Polymeric nanoparticles were prepared by nanoprecipitation of Eudragit® RS 100 in presence and in absence of glycofurol. The photosensitizer temoporfin has been encapsulated into these carrier devices. Process parameters were optimized by means of a Design of Experiments approach and nanoparticles with optimal characteristics were manufactured by using microreactor technology. The efficacy was determined by means of cell culture models in A-253 cells. RESULTS: Physicochemical properties of nanoparticles achieved by nanoprecipitation from ethanolic solutions were superior to those obtained from a method based upon glycofurol. Nanoencapsulation of temoporfin into the matrix significantly reduced toxicity of this compound, while the efficacy was maintained. The release profiles assured a sustained release at the site of action. Finally, the transfer to continuous flow technology was achieved. CONCLUSION: By adjusting all process parameters, a potent formulation for application in the GI tract was obtained. The essential steps of process development and scale-up were part of this formulation development.

A bio-predictive release assay for liposomal prednisolone phosphate.

Predictive performance assays are crucial for the development and approval of nanomedicines and their bioequivalent successors. At present, there are no established compendial methods that provide a reliable standard for comparing and selecting these formulation prototypes, and our understanding of the in vivo release remains still incomplete. Consequently, extensive animal studies, with enhanced analytical resolution for both, released and encapsulated drug, are necessary to assess bioequivalence. This significantly raises the cost and duration of nanomedicine development. This work presents the development of a discriminatory and biopredictive release test method for liposomal prednisolone phosphate. Using model-informed deconvolution, we identified an in vivo target release. The experimental design employed a discrete L-optimal configuration to refine the analytical method and determine the impact of in vitro parameters on the dosage form. A three-point specification evaluated the key phases of in vivo release: early (T-5%), intermediate (T-20%), and late release behavior (T-40%), compared to the in vivo release profile of the reference product, NanoCort®. Various levels of shear responses and the influence of clinically relevant release media compositions were tested. This enabled an assessment of the effect of shear on the release, an essential aspect of their in vivo deformation and release behavior. The type and concentration of proteins in the medium influence liposome release. Fetal bovine serum strongly impacted the discriminatory performance at intermediate shear conditions. The method provided deep insights into the release response of liposomes and offers an interesting workflow for in vitro bioequivalence evaluation.

Breaking barriers: Innovative approaches for skin delivery of RNA therapeutics.

RNA therapeutics represent a rapidly expanding platform with game-changing prospects in personalized medicine. The disruptive potential of this technology will overhaul the standard of care with reference to both primary and specialty care. To date, RNA therapeutics have mostly been delivered parenterally via injection, but topical administration followed by intradermal or transdermal delivery represents an attractive method that is convenient to patients and minimally invasive. The skin barrier, particularly the lipid-rich stratum corneum, presents a significant hurdle to the uptake of large, charged oligonucleotide drugs. Therapeutic oligonucleotides need to be engineered for stability and specificity and formulated with state-of-the-art delivery strategies for efficient uptake. This review will cover various passive and active strategies deployed to enhance permeation through the stratum corneum and achieve effective delivery of RNA therapeutics to treat both local skin disorders and systemic diseases. Some strategies to achieve selectivity between local and systemic administration will also be discussed.

Blood-Nanoparticle Interactions Create a Brain Delivery Superhighway for Doxorubicin.

Purpose: This study investigated the brain targeting mechanism of doxorubicin-loaded polybutyl cyanoacrylate (PBCA) nanoparticles, particularly their interactions with the blood-brain barrier (BBB). The BBB protects the brain from drugs in the bloodstream and represents a crucial obstacle in the treatment of brain cancer. Methods: An advanced computer model analyzed the brain delivery of two distinct formulations, Doxil® and surfactant-coated PBCA nanoparticles. Computational learning was combined with in vitro release and cell interaction studies to comprehend the underlying brain delivery pathways. Results: Our analysis yielded a surprising discovery regarding the brain delivery mechanism of PBCA nanoparticles. While Doxil® exhibited the expected behavior, accumulating in the brain through extravasation in tumor tissue, PBCA nanoparticles employed a unique and previously uncharacterized mechanism. They underwent cell hitchhiking, resulting in a remarkable more than 1000-fold increase in brain permeation rate compared to Doxil® (2.59 × 10-4 vs 0.32 h-1). Conclusion: The nonspecific binding to blood cells facilitated and intensified interactions of surfactant-coated PBCA nanoparticles with the vascular endothelium, leading to enhanced transcytosis. Consequently, the significant increase in circulation time in the bloodstream, coupled with improved receptor interactions, contributes to this remarkable uptake of doxorubicin into the brain.

Understanding the In Vitro-In Vivo Nexus: Advanced correlation models predict clinical performance of liposomal doxorubicin.

In the century of precision medicine and predictive modeling, addressing quality-related issues in the medical supply chain is critical, with 62 % of the disruptions being attributable to quality challenges. This study centers on the development and safety of liposomal doxorubicin, where animal studies alone often do not adequately explain the complex interplay between critical quality attributes and in vivo performances. Anchored in our aim to elucidate this in vitro-in vivo nexus, we compared TLD-1, a novel liposomal doxorubicin delivery system, against the established formulations Doxil® and Lipodox®. Robust in vitro-in vivo correlations (IVIVCs) with excellent coefficients of determination (R2 > 0.98) were obtained in the presence of serum under dynamic high-shear conditions. They provided the foundation for an advanced characterization and benchmarking strategy. Despite the smaller vesicle size and reduced core crystallinity of TLD-1, its release behavior closely resembled that of Doxil®. Nevertheless, subtle differences between the dosage forms observed in the in vitro setting were reflected in the bioavailabilities observed in vivo. Data from a Phase-I clinical trial facilitated the development of patient-specific IVIVCs using the physiologically-based nanocarrier biopharmaceutics model, enabling a more accurate estimation of doxorubicin exposure. This advancement could impact clinical practice by allowing for more precise dose estimation and aiding in the assessment of the interchangeability of generic liposomal doxorubicin.

A Design-Conversed Strategy Establishes the Performance Safe Space for Doxorubicin Nanosimilars.

Nanomedicines exhibit multifaceted performances, yet their biopharmaceutics remain poorly understood and present several challenges in the translation from preclinical to clinical research. To address this issue and promote the production of high-quality nanomedicines, a systematic screening of the design space and in vivo performance is necessary. Establishing formulation performance specifications early on enables an informed selection of candidates and promotes the development of nanosimilars. The deconvolution of the pharmacokinetics enables the identification of key characteristics that influence their performances and disposition. Using an in vitro-in vivo rank-order relationship for doxorubicin nanoformulations, we defined in vitro release specifications for Doxil/Caelyx-like follow-on products. Additionally, our model predictions were used to establish the bioequivalence of Lipodox, a nanosimilar of Doxil/Caelyx. Furthermore, a virtual safe space was established, providing crucial insights into expected disposition kinetics and informing formulation development. By addressing bottlenecks in biopharmaceutics and formulation screening, our research advances the translation of nanomedicine from bench to bedside.

Unveiling the potential role of micro/nano biomaterials in the treatment of Helicobacter pylori infection.

INTRODUCTION: Helicobacter pylori causes stubborn infections and leads to a variety of stomach disorders, such as peptic ulcer, chronic atrophic gastritis, and gastric cancer. Although antibiotic-based approaches have been widely used against H. pylori, some challenges such as antibiotic resistance are increasing in severity. Therefore, simpler but more effective strategies are needed. AREAS COVERED: In this review, basic information on functionalized and non-functionalized micro/nano biomaterials and routes of administration for H. pylori inhibition are provided in an easy-to-understand format. Afterward, in vitro and in vivo studies of some promising bio-platforms including metal-based biomaterials, biopolymers, small-molecule saccharides, and vaccines for H. pylori inhibition are discussed in a holistic manner. EXPERT OPINION: Functionalized or non-functionalized micro/nano biomaterials loaded with anti-H. pylori agents can show efficient bactericidal activity with no/slight negative influence on the host gastrointestinal microbiota. However, this claim needs to be substantiated with hard data such as assessment of the biopharmaceutical parameters of anti-H. pylori systems and the measurement of diversity/abundance of bacterial genera in the host gastric/gut microbiota before and after H. pylori eradication.

Putting square pegs in round holes: Why traditional pharmacokinetic principles cannot universally be applied to iron-carbohydrate complexes.

Intravenous iron-carbohydrate complexes are nanomedicines that are commonly used to treat iron deficiency and iron deficiency anemia of various etiologies. Many challenges remain regarding these complex drugs in the context of fully understanding their pharmacokinetic parameters. Firstly, the measurement of the intact iron nanoparticles versus endogenous iron concentration fundamentally limits the availability of data for computational modeling. Secondly, the models need to include several parameters to describe the iron metabolism which is not completely defined and those identified (e.g. ferritin) exhibit considerable interpatient variability. Additionally, modeling is further complicated by the lack of traditional receptor/enzyme interactions. The known parameters of bioavailability, distribution, metabolism, and excretion for iron-carbohydrate nanomedicines will be reviewed and future challenges that currently prevent the direct application of physiologically-based pharmacokinetic or other computational modeling techniques will be discussed.

Simulate SubQ: The Methods and the Media.

For decades, there has been a growing interest in injectable subcutaneous formulations to improve the absorption of drugs into the systemic circulation and to prolong their release over a longer period. However, fluctuations in the blood plasma levels together with bioavailability issues often limit their clinical success. This warrants a closer look at the performance of long-acting depots, for example, and their dependence on the complex interplay between the dosage form and the physiological microenvironment. For this, biopredictive performance testing is used for a thorough understanding of the biophysical processes affecting the absorption of compounds from the injection site in vivo and their simulation in vitro. In the present work, we discuss in vitro methodologies including methods and media developed for the subcutaneous route of administration on the background of the most relevant absorption mechanisms. Also, we highlight some important knowledge gaps and shortcomings of the existing methodologies to provide the reader with a better understanding of the scientific evidence underlying these models.