Polymeric in situ forming depots for long-acting drug delivery systems

Long-acting injectable delivery system comprising ordered mixed drug aggregates with deaggregating and uniformly embeddable viscoelastic -polysaccharide solutions

This study aimed to construct a ready-to-use, two-syringe mixing (TM) system comprising free-flowing drug aggregates with deaggregating and uniformly embeddable polysaccharide solutions as a new approach for long-acting parenteral delivery. Rotigotine (RG) and donepezil (DP), approved for the treatment of Parkinson's and Alzheimer's diseases, respectively, were employed as model compounds. For syringe filling, free-flowing drug aggregates were engineered using ordered mixing, adhering pulverized RG (1.1 ± 0.3 μm) or DP particles (0.8 ± 0.2 μm) to hydrophilic polyvinylpyrrolidone K17 particles (120 to 150 μm). Drug aggregates were effectively deaggregated and distributed as individual fine drug particles in hyaluronate (HA) or carboxymethyl cellulose (CMC) matrices via electrostatic interactions during TM process. TM systems of RG with HA or CMC and DP with HA provided extended drug release with decreased in vivo spread following subcutaneous injection. TM systems of RG and DP provided protracted pharmacokinetic profiles over 4 weeks with decreased initial exposure compared to drug suspensions and even profiles comparable to those of biodegradable polymer-based in situ forming implants (ISFI). Moreover, RG-loaded HA- or CMC-TM systems alleviated the local inflammation compared to the ISFI. Therefore, this polysaccharide-based TM system is expected to serve as a simple and effective long-acting delivery system for water-insoluble therapeutic agents.

Cannabidiol-loaded-injectable depot formulation for the treatment of triple-negative breast cancer: design, development, in-vitro and in-ovo evaluation of its anticancer activity

Triple-negative breast cancer (TNBC) is an invasive and difficult-to-treat carcinoma that represents 15-20 % of breast malignancies and is frequently diagnosed in younger women. Chemotherapy is the mainstay treatment approach. Cannabidiol (CBD), the main non-psychoactive cannabinoid, has shown a potential anticancer activity in TNBC, enhancing the effect of conventional antineoplastics. This research aims to develop in situ forming implants (ISFIs) as a long-acting depot formulation of CBD with potential application in TNBC. This formulation is intended to be administered in the tumor site during neoadjuvant chemotherapeutic regimens, allowing a controlled CBD release. ISFIs were elaborated with 100 mg of polycaprolactone (PCL) and 2.5 mg (2.5-CB-ISFI), 5 mg (5-CB-ISFI) or 10 mg (10-CB-ISFI) of CBD dissolved in 400 µL of NMP. All the formulations exhibited a controlled drug release for around two months. 10-CB-ISFI formulation with the highest CBD content and the most suitable CBD release profile was selected for biological studies. This formulation inhibited the proliferation and migration of MDA-MB-231 and 4T1 cells and exerted an antiangiogenic effect in ovo. Interestingly, the antiangiogenic activity of 10-CB-ISFI was higher compared with CBD in solution administered at the same concentration, showing vascular inhibition percentages of around 80 % and 60 %, respectively. Finally, this formulation reduced the growth of MDA-MB-231-derived tumors developed in the chorioallantoic membrane (CAM) model. The single administration of 10-CB-ISFI exhibited a similar antitumor efficacy to the daily administration of CBD in solution (≈60 % tumor growth inhibition). Therefore, the injectable depot formulation of CBD developed in this work showed a promising utility in TNBC treatment.

A novel long-acting phospholipid phase transition gel with progesterone effectively promoted uterine development

Progesterone (PRG), a steroidal hormone, is commonly utilized in the clinical practice of obstetrics and gynecology. The high frequency of PRG injections, however, has brought significant pain and inconvenience to patients. In this study, we developed a long-acting injection leveraging the phase transition mechanism for the long-term treatment in Assisted Reproductive Technology (ART). The components we selected all possess excellent biocompatibility. Pharmacokinetic studies revealed that the PRG-loaded phospholipid phase transition gels (PRG-PPTGs) released the PRG continuously for over 7 days. Notably, pharmacological investigation demonstrated that PRG-PPTGs, when administered weekly, effectively promoted uterine development. Our findings suggested that PRG-PPTGs successfully achieve both the prevention of burst release and the reduction of dosing frequency, highlighting the potential of PPTGs as promising long-acting composite system for hydrophobic drugs.

In-situ forming solvent-induced phase inversion implants for controlled drug delivery: Role of hydrophilic polymers

In recent years, there has been a surge of research focused on in situ-forming implants as a method of localized drug delivery. Despite advancements, the predominant challenge in situ-forming solvent-induced phase inversion (SIPI) implants is significant burst release which typically occurs within the first 24 h post-administration. Another notable challenge is the real-time characterization of these implants, which is crucial for understanding their in situ formation and degradation mechanism. This study explores the impact of various hydrophilic polymers-hydroxypropyl methylcellulose (HPMC), hydroxypropyl cellulose (HPC), Carbopol, and carboxymethylcellulose (CMC) - on implant formation and drug release. SIPI systems, which are commonly composed of poly(lactic-co-glycolic acid) (PLGA) and N-methyl pyrrolidone (NMP), offer localized, controlled drug release but suffer from an initial burst within 24 h post-administration. The incorporation of hydrophilic polymers aims to modulate this release and improve implant properties. For first-time, optical coherence tomography (OCT) imaging was employed for non-invasive assessment of the rate of in situ phase inversion and the resulting implant morphology, whereas scanning electron microscopy (SEM) and digital microscopy provided further insights into the internal structure of the implants. The results demonstrated that the inclusion of polymers such as HPMC and Carbopol effectively reduced burst release, whereas polymers such as HPC and CMC exhibited faster phase inversion, resulting in a more porous implant morphology and greater burst release. Additionally, the mechanical properties and mucoadhesive capabilities of the formulations were tested, suggesting that Carbopol-enhanced implants are particularly suitable for applications requiring prolonged retention at mucosal sites. This investigation provides critical insights into the design and optimization of SIPI systems for drug delivery.

Current research and future potential of thermogels for sustained drug delivery

INTRODUCTION

Drug administration is ubiquitous in the healthcare field, and it is crucial to optimize drug delivery methods to improve drug efficacy, reduce systemic toxicity, and enhance patient compliance Thermogels have shown immense potential in drug delivery due to their injectability, biocompatibility, and ability to provide localized and sustained drug release.

AREA COVERED

This paper discusses the unique properties of thermogel in relation to drug kinetics and their suitability as a carrier. Different considerations and applications of thermogel drug delivery systems (DDS) were highlighted and their challenges to enter the market discussed. A comprehensive literature search was conducted using major databases such as PubMed, Scopus, and Web of Science. The search employed relevant keywords to identify studies on thermogel DDS. Clinicaltrials.gov was also utilized to determine the current state of clinical studies.

EXPERT OPINION

Nonetheless, thermogel holds great promise for the future in DDS with research achieving greater heights in terms of complexity and clinical pursuits. Their flexibility in fabrication and modularity manner makes it a great material to tailor to different drug delivery applications and to be integrated into various biomedical disciplinaries.

Long-term controlled release with reduced initial burst release utilizing calcium ion-triggering nanoaggregates of pasireotide-loaded fattigated albumin nanoparticles

The aim of this study was to investigate the long-term controlled release of peptide-loaded fattigated albumin nanoparticles via calcium ion-triggering nanoaggregation with minimal initial burst release. Fattigated albumin nanoparticles were prepared via sonication by the self-assembly of human serum albumin (HSA)-oleic acid conjugates (AOC) with three different substitution ratios of oleic acid (OA) to modulate hydrophobicity. Then, pasireotide pamoate (PAS) as a model peptide was encapsulated into the hydrophobic core of HSA-OA nanoparticles (PAS-AONs). The critical micelle concentration of AOC decreased as OA substitution ratio increased. The loading efficiency of PAS increased owing to the strong hydrophobic-hydrophobic interactions between PAS and the hydrophobic block in the AONs. The release rate was also delayed, whereas the initial burst release was minimized, as the hydrophobicity of AOC increased. Interestingly, calcium ions triggered the formation of nanoaggregates of negatively charged PAS-AONs via electrostatic interactions, resulting in a further decrease in the release rate for one month via a reduced surface area while minimizing the initial burst release in a calcium ion concentration-dependent manner. The modulation of OA substitutions and calcium ion concentration of AONs could provide the potential for long-term delivery of peptide drugs while minimizing the initial huge burst release and controlling the release rate.

Self-aggregating long-acting injectable microcrystals

Injectable drug depots have transformed our capacity to enhance medication adherence through dose simplification. Central to patient adoption of injectables is the acceptability of needle injections, with needle gauge as a key factor informing patient discomfort. Maximizing drug loading in injectables supports longer drug release while reducing injection volume and discomfort. Here, to address these requirements, we developed self-aggregating long-acting injectable microcrystals (SLIM), an injectable formulation containing drug microcrystals that self-aggregate in the subcutaneous space to form a monolithic implant with a low ratio of polymer excipient to drug (0.0625:1 w/w). By minimizing polymer content, SLIM supports injection through low-profile needles (<25 G) with high drug loading (293 mg ml-1). We demonstrate in vitro and in vivo that self-aggregation is driven by solvent exchange at the injection site and that slower-exchanging solvents result in increased microcrystal compaction and reduced implant porosity. We further show that self-aggregation enhances long-term drug release in rodents. We anticipate that SLIM could enable low-cost interventions for contraceptives.

Amorphous Roxithromycin Loaded in-situ Gel for the Treatment of Staphylococcus aureus Induced Upper Respiratory Tract Infection

Objective

Upper respiratory tract infections are among the most prevalent respiratory diseases, imposing both financial and physical burdens on affected individuals. Roxithromycin (ROX), a primary drug for treating bacterial-induced respiratory tract infections, is typically administered orally due to its hydrophobic nature. However, the non-specific distribution resulting from oral administration reduces bioavailability and can cause side effects such as diarrhea.

Methods

In this study, we prepared a thermo-sensitive in-situ gel using a facile and highly reproducible method by simply mixing two types of poloxamers with ROX.

Results

The ROX can be well dissolved in the poloxamer matrix in amorphous state to give solution. Upon intranasal administration, the ROX solution undergoes a phase transition to form in-situ gel under body temperature. This gel remains in the nasal cavity for an extended period, releasing the drug directly to the site of infection and minimizing non-specific distribution. Pharmacokinetic experiments revealed that, compared to oral administration, the bioavailability of local nasal administration increased by 1.5 times, and the drug concentration in the local nasal cavity increased by 8 times. In contrast, concentrations in the liver and small intestine did not significantly differ from those following oral administration. In vivo antibacterial experiments also showed that the ROX in-situ gel has superior antibacterial efficacy and excellent biocompatibility.

Conclusion

These results suggest that the thermo-sensitive ROX in-situ gel is a promising formulation for treating bacterial upper respiratory tract infections.

Long-acting injectable in situ forming implants: Impact of polymer attributes and API

Poly(DL-lactide-co-glycolide) (PLGA) and N-methyl-2-pyrrolidone (NMP)-based in situ forming implants are liquid formulations that solidify through phase separation following injection into the body. Drug is dissolved or suspended in the final formulation liquid prior to injection. Depending on the polymers used, the depots formed can deliver drug over different periods of time. Accordingly, it is important to understand the impact of PLGA properties on implant drug release. However, currently available publications only investigate such impacts based on a single drug, which is insufficient to determine the potential interplay between drug and PLGA properties affecting drug release, or to draw any solid conclusions concerning the general impact of PLGA on drug release. The current work explores in situ forming implants with different active pharmaceutical ingredients (APIs) to determine whether any interplay between the APIs and the polymer attributes might affect drug release. In particular, the drug state (solution or suspension form) may impact polymer interaction and drug release. Naproxen and meloxicam were chosen as model drugs and were loaded into in situ forming implants. The final implants of naproxen and meloxicam were solutions and suspensions, respectively. The impact of PLGA properties (slight changes in molecular weight (MW), slight/major changes in lactic/glycolic acid (L/G) ratio, as well as changes in polymer blockiness in end-cap (acid vs ester)) on drug release was investigated. The slight changes in PLGA MW (18-31 KDa), L/G ratio (75/15-85/15) and blockiness had similar impacts on the release of naproxen and meloxicam from the formulations. These impacts were consistent with a previous report on risperidone implants. However, the impact of end-cap and significant change in the L/G ratio (from 75/15-85/15 to 50/50) was determined to be drug dependent. For meloxicam and for risperidone (previous report), the ester end-cap (compared to the acid end-cap) and much higher L/G ratio (75/15-85/15 versus 50/50) resulted in significantly longer overall drug release durations. In contrast, the naproxen implants had shorter release durations when prepared with the ester end-caped polymer (compared to acid end-cap), and when prepared with significantly higher L/G ratio polymers (75/15-85/15 versus 50/50). In addition, using the same PLGA polymer, implants loading different APIs demonstrated different release durations. This work highlights the complexity of PLGA attributes in determining the performance of implant drug formulations and the critical role of the interplay with the API properties. This study provides valuable knowledge for the future development of in situ forming implant drug products.

Bottlebrush Pastes as a Platform for Solvent-Free, Injectable, and Shape-Persistent Materials with Tissue-Mimetic Viscoelasticity

Architecturally hindered crystallization of bottlebrush graft copolymers offers a reaction- and solvent-free pathway for creating injectable elastomers with tissue-mimetic softness. Currently, injectable materials involve solvents and chemical reactions, leading to uncontrolled swelling, leaching of unreacted moieties, and side reactions with tissue. To address this issue, bottlebrush copolymers with a poly(ethylene glycol) (PEG) amorphous block and crystallizable poly(lactic acid) (PLA) grafted chains (A-g-B) were synthesized, with grafted chains of controlled length arranged along the backbone at controlled spacing. The densely grafted PEG brush is leveraged to architecturally control both the rate and degree of crystallization of PLA grafts, offering tunability of mechanical properties as a function of architecture and time in a single-component solvent-free system covering a broad range of aggregation states comprising fluid-, paste-, and elastomer-like behaviors with modulus ranging from 1 to 50 kPa. The PLA-g-PEG pastes are particularly interesting, as they combine solvent-free injectability and time-controlled formation of shape-persistent elastomers at constant temperature. This molecular paste platform may advance reconstructive surgery, drug depots, and tissue engineering.

Dual release scaffolds as a promising strategy for enhancing bone regeneration: an updated review

Advancements in tissue regeneration, particularly bone regeneration is key area of research due to potential of novel therapeutic approaches. Efforts to reduce reliance on autologous and allogeneic bone grafts have led to the development of biomaterials that promote synchronized and controlled bone healing. However, the use of growth factors is limited by their short half-life, slow tissue penetration, large molecular size and potential toxicity. These factors suggest that traditional delivery methods may be inadequate hence, to address these challenges, new strategies are being explored. These novel approaches include the use of bioactive substances within advanced delivery systems that enable precise spatiotemporal control. Dual-release composite scaffolds offer a promising solution by reducing the need for multiple surgical interventions and simplifying the treatment process. These scaffolds allow for sustained and controlled drug release, enhancing bone repair while minimizing the drawbacks of conventional methods. This review explores various dual-drug release systems, discussing their modes of action, types of drugs used and release mechanisms to improve bone regeneration.

Unraveling Neurological Drug Delivery: Polymeric Nanocarriers for Enhanced Blood-Brain Barrier Penetration

Treating neurological illnesses is challenging because the blood-brain barrier hinders therapeutic medications from reaching the brain. Recent advances in polymeric nanocarriers (PNCs), which improve medication permeability across the blood-brain barrier, may influence therapy strategies for neurological diseases. PNCs have several ways to deliver medications to the nervous system. This review article provides a summary of the parts and manufacturing methods involved in making PNCs. Additionally, it highlights the elements that result in PNCs having enhanced blood-brain barrier penetration. A combination of passive and active targeting strategies is used by PNCs intended to overcome the blood-brain barrier. Among these are micellar structures, nanogels, nanoparticles, cubosomes, and dendrimers. These nanocarriers, which are functionalized with certain ligands that target BBB transporters, enable the direct delivery of drugs to the brain. Mainly, the BBB prevents medications from entering the brain. Understanding the BBB's physiological and anatomical characteristics is necessary to get over this obstacle. Preclinical and clinical research demonstrates the safety and effectiveness of these PNCs, and their potential use in the treatment of neurological illnesses, including brain tumors, Parkinson's disease, and Alzheimer's disease, is discussed. Concerns that PNCs may have about their biocompatibility and possible toxicity are also covered in this review article. This study examines the revolutionary potential of PNCs in CNS drug delivery, potential roadblocks, ongoing research, and future opportunities for PNC design progress. PNCs open the door to more focused and efficient treatment for neurological illnesses by comprehending the subtleties of BBB penetration.

Physicochemical Properties, Drug Release and In Situ Depot-Forming Behaviors of Alginate Hydrogel Containing Poorly Water-Soluble Aripiprazole

The objective of this study was to investigate the physicochemical properties, drug release and in situ depot-forming behavior of alginate hydrogel containing poorly water-soluble aripiprazole (ARP) for achieving free-flowing injectability, clinically accessible gelation time and sustained drug release. The balanced ratio of pyridoxal phosphate (PLP) and glucono-delta-lactone (GDL) was crucial to modulate gelation time of the alginate solution in the presence of calcium carbonate. Our results demonstrated that the sol state alginate hydrogel before gelation was free-flowing, stable and readily injectable using a small 23 G needle. In addition, the ratio (w/w) of PLP and GDL altered the gelation time, which was longer as the PLP content increased but shorter as the GDL content increased. The alginate hydrogel with a ratio of PLP to GDL of 15:9 had the optimal physicochemical properties in terms of a clinically acceptable gelation time (9.1 min), in situ-depot formation with muscle-mimicking stiffness (3.55 kPa) and sustained release over a two-week period. The alginate hydrogel, which is tunable by varying the ratio of PLP and GDL, could provide a controllable pharmaceutical preparation to meet the need for long-acting performance of antipsychotic drugs like ARP.

Schiff-Base Cross-Linked Hydrogels Based on Properly Synthesized Poly(ether urethane)s as Potential Drug Delivery Vehicles in the Biomedical Field: Design and Characterization

In situ-forming hydrogels based on the Schiff-base chemistry are promising for drug delivery applications, thanks to their stability under physiological conditions, injectability, self-healing properties, and pH-responsiveness. In this work, two water-soluble poly(ethylene glycol)-based poly(ether urethane)s (PEUs) were engineered. A high-molecular-weight PEU (SHE3350, M̅ n 24 kDa, D 1.7), bearing primary amino groups along each polymeric chain, was synthesized using N-Boc serinol and subjected to an acidic treatment to expose primary amines (ca. 1020 units/gSHE3350). In parallel, a low-molecular-weight PEU (AHE1500, M̅ n 4 kDa, D 1.5) with aldehyde end groups was synthesized by end-capping an isocyanate-terminated prepolymer with 4-hydroxybenzaldehyde, and the aldehyde groups were quantified to be around 1020 units/gAHE1500. Hydrogels were prepared by simply mixing SHE3350 and AHE1500 aqueous solutions and characterized to assess their physico-chemical and rheological properties. Schiff-base bond formation was proved through carbon-13 and proton solid-state NMR spectroscopies. Rheological characterization confirmed the formation of gels with high resistance to applied strain (ca. 1000%). Hydrogels exhibited high absorption ability (ca. 270% increase in wet weight) in physiological-like conditions (i.e., 37 °C and pH 7.4) up to 27 days. In contact with buffer at pH 5, enhanced fluid absorption was observed until dissolution occurred starting from 13 days due to Schiff-base hydrolysis in acidic conditions. Conversely, gels showed a reduced absorption ability at pH 9 due to shrinkage phenomena. Furthermore, they exhibited high permeability and controlled, sustained, and pH-triggered release of a model molecule (i.e., fluorescein isothiocyanate dextran) for up to 17 days. Lastly, the hydrogels showed easy injectability and self-healing ability.

Recent advances in nanoagents delivery system-based phototherapy for osteosarcoma treatment

Osteosarcoma (OS) is a prevalent and highly malignant bone tumor, characterized by its aggressive nature, invasiveness, and rapid progression, contributing to a high mortality rate, particularly among adolescents. Traditional treatment modalities, including surgical resection, radiotherapy, and chemotherapy, face significant challenges, especially in addressing chemotherapy resistance and managing postoperative recurrence and metastasis. Phototherapy (PT), encompassing photodynamic therapy (PDT) and photothermal therapy (PTT), offers unique advantages such as low toxicity, minimal drug resistance, selective destruction, and temporal control, making it a promising approach for the clinical treatment of various malignant tumors. Constructing multifunctional delivery systems presents an opportunity to effectively combine tumor PDT, PTT, and chemotherapy, creating a synergistic anti-tumor effect. This review aims to consolidate the progress in the application of novel delivery system-mediated phototherapy in osteosarcoma. By summarizing advancements in this field, the objective is to propose a rational combination therapy involving targeted delivery systems and phototherapy for tumors, thereby expanding treatment options and enhancing the prognosis for osteosarcoma patients. In conclusion, the integration of innovative delivery systems with phototherapy represents a promising avenue in osteosarcoma treatment, offering a comprehensive approach to overcome challenges associated with conventional treatments and improve patient outcomes.

Prostate cancer chemotherapy by intratumoral administration of Docetaxel-Mesoporous silica nanomedicines

Docetaxel (DTX) is a recommended treatment in patients with metastasic prostate cancer (PCa), despite its therapeutic efficacy is limited by strong systemic toxicity. However, in localized PCa, intratumoral (IT) administration of DTX could be an alternative to consider that may help to overcome the disadvantages of conventional intravenous (IV) therapy. In this context, we here present the first in vivo preclinical study of PCa therapy with nanomedicines of mesoporous silica nanoparticles (MSN) and DTX by IT injection over a xenograft mouse model bearing human prostate adenocarcinoma tumors. The efficacy and tolerability, the biodistribution and the histopathology after therapy have been investigated for the DTX nanomedicine and the free drug, and compared with the IV administration of DTX. The obtained results demonstrate that IT injection of DTX and DTX nanomedicines allows precise and selective therapy of non-metastatic PCa and minimize systemic diffusion of the drug, showing superior activity than IV route. This allows reducing the therapeutic dose by one order and widens substantially the therapeutic window for this drug. Furthermore, the use of DTX nanomedicines as IT injection promotes strong antitumor efficacy and drug accumulation at the tumor site, improving the results obtained with the free drug by the same route.

Fabrication and Optimization of a Silodosin In Situ-Forming PLGA Implants for the Treatment of Benign Prostatic Hyperplasia: In Vitro and In Vivo Study

Objectives: Lower urinary tract symptoms (LUTSs) related to benign prostatic hyperplasia (BPH) are common in older men, and alpha-adrenoceptor blockers continue to be a key part of managing these symptoms. This study aimed to formulate injectable poly (lactic-co-glycolic acid) (PLGA) in situ-forming implants (ISFIs) loaded with silodosin (SLD) to address symptoms associated with BPH. This method, which ensures prolonged therapeutic effects of SLD, is intended to decrease dosing frequency and improve treatment outcomes, leading to better patient adherence. Methods: An appropriate solvent with favorable PLGA solubility, viscosity, and in vitro release profile was selected. Additionally, an I-optimal design was employed as an optimization technique. An in vivo study in albino male rats was conducted to investigate prostate-specific antigens (PSAs), prostate weight and prostatic index, histopathology, and SLD pharmacokinetics. Results: The optimized formulation showed experimental values of 29.25% for the initial burst after 2 h and 58.23% for the cumulative release of SLD after 10 days. Pharmacokinetic data revealed that the SLD-ISFI formulation had lower Cmax and higher AUC values than subcutaneous (SC) pure SLD and oral commercial SLD capsule, indicating the controlled-release impact and improved bioavailability of the ISFI systems. SLD-ISFI produced a marked drop in the prostatic index by 2.09-fold compared to the positive control. Serum PSA level decreased significantly from 0.345 ± 0.007 to 0.145 ± 0.015 ng/mL after SLD-ISFI injection compared to the positive control. Conclusions: This study indicated that the optimized SLD-ISFI formulation proved its efficacy in managing BPH.

Stimuli-responsive drug delivery systems for inflammatory skin conditions

Inflammatory skin conditions highly influence the quality of life of the patients suffering from these disorders. Symptoms include red, itchy and painful skin lesions, which are visible to the rest of the world, causing stigmatization and a significantly lower mental health of the patients. Treatment options are often unsatisfactory, as they suffer from either low patient adherence or the risk of severe side effects. Considering this, there is a need for new treatments, and notably of new ways of delivering the drugs. Stimuli-responsive drug delivery systems are able to deliver their drug cargo in response to a given stimulus and are, thus, promising for the treatment of inflammatory skin conditions. For example, the use of external stimuli such as ultraviolet light, near infrared radiation, or alteration of magnetic field enables drug release to be precisely controlled in space and time. On the other hand, internal stimuli induced by the pathological condition, including pH alteration in the skin or upregulation of reactive oxygen species or enzymes, can be utilized to create drug delivery systems that specifically target the diseased skin to achieve a better efficacy and safety. In the latter context, however, it is of key importance to match the trigger mechanism of the drug delivery system to the actual pathological features of the specific skin condition. Hence, the focus of this article is placed not only on reviewing stimuli-responsive drug delivery systems developed to treat specific inflammatory skin conditions, but also on critically evaluating their efficacy in the context of specific skin diseases. STATEMENT OF SIGNIFICANCE: Skin diseases affect one-third of the world's population, significantly lowering the quality of life of the patients, who deal with symptoms such as painful and itchy skin lesions, as well as stigmatization due to the visibility of their symptoms. Current treatments for inflammatory skin conditions are often hampered by low patient adherence or serious drug side effects. Therefore, more emphasis should be placed on developing innovative formulations that provide better efficacy and safety for patients. Stimuli-responsive drug delivery systems hold considerable promise in this regard, as they can deliver their cargo precisely where and when it is needed, reducing adverse effects and potentially offering better treatment outcomes.

In vitro modelling of intramuscular injection site events

INTRODUCTION

Intramuscular (IM) injections deliver a plethora of drugs. The majority of IM-related literature details dissolution and/or pharmacokinetic (PK) studies, using methods with limited assessments of post-injection events that can impact drug fate, and absorption parameters. Food and Drug Association guidelines no longer require preclinical in vivo modeling in the U.S.A. Preclinical animal models fail to correlate with clinical outcomes, highlighting the need to study, and understand, IM drug fate in vitro using bespoke models emulating human IM sites. Post-IM injection events, i.e. underlying processes that influence PK outcomes, remain unacknowledged, complicating the application of in vitro methods in preclinical drug development. Understanding such events could guide approaches to predict and modulate IM drug fate in humans.

AREAS COVERED

This article reviews challenges in biorelevant IM site modeling (i.e. modeling drug fate outcomes), the value of technologies available for developing IM injectables, methods for studying drug fate, and technologies for training in performing IM administrations. PubMed, Web-of-Science, and Lens databases provided papers published between 2014 and 2024.

EXPERT OPINION

IM drug research is expanding what injectable therapeutics can achieve. However, post-injection events that influence PK outcomes remain poorly understood. Until addressed, advances in IM drug development will not realize their full potential.

Tricaprylin-based drug crystalline suspension for intramuscular long-acting delivery of entecavir with alleviated local inflammation

In order to ensure prolonged pharmacokinetic profile along with local tolerability at the injection site, tricaprylin-based drug crystalline suspension (TS) was designed and its local distribution, pharmacokinetics, and inflammatory response, were evaluated with conventional aqueous suspension (AS). As model drug particles, entecavir 3-palmitate (EV-P), an ester lipidic prodrug for entecavir (EV), was employed. The EV-P-loaded TS was prepared by ultra-sonication method. Prepared TS and conventional AS exhibited comparable morphology (rod or rectangular), median diameter (2.7 and 2.6 μm), crystallinity (melting point of 160-165°C), and in vitro dissolution profile. However, in vivo performances of drug microparticles were markedly different, depending on delivery vehicle. At AS-injected site, drug aggregates of up to 500 μm were formed upon intramuscular injection, and were surrounded with inflammatory cells and fibroblastic bands. In contrast, no distinct particle aggregation and adjacent granulation was observed at TS-injected site, with >4 weeks remaining of the oily vehicle in micro-computed tomographic observation. Surprisingly, TS exhibited markedly alleviated local inflammation compared to AS, endowing markedly lessened necrosis, fibrosis thickness, inflammatory area, and macrophage infiltration. The higher initial systemic exposure was observed with TS compared to AS, but TS provided prolonged delivery of EV for 3 weeks. Therefore, we suggest that the novel TS system can be a promising tool in designing parenteral long-acting delivery, with improved local tolerability.

In-situ forming PLGA implants: Towards less toxic solvents

In-situ forming poly(lactic-co-glycolic acid) (PLGA) implants offer a great potential for controlled drug delivery for a variety of applications, e.g. periodontitis treatment. The polymer is dissolved in a water-miscible solvent. The drug is dissolved or dispersed in this solution. Upon contact with aqueous body fluids, the solvent diffuses into the surrounding tissue and water penetrates into the formulation. Consequently, PLGA precipitates, trapping the drug. Often, N-methyl-2-pyrrolidine (NMP) is used as a water-miscible solvent. However, parenteral administration of NMP raises toxicity concerns. The aim of this study was to identify less toxic alternative solvent systems for in-situ forming PLGA implants. Various blends of polyethylene glycol 400 (PEG 400), triethyl citrate (TEC) and ethanol were used to prepare liquid formulations containing PLGA, ibuprofen (as an anti-inflammatory drug) and/or chlorhexidine dihydrochloride (as an antiseptic agent). Implant formation and drug release kinetics were monitored upon exposure to phosphate buffer pH 6.8 at 37 °C. Furthermore, the syringeability of the liquids, antimicrobial activity of the implants, and dynamic changes in the latter's wet mass and pH of the release medium were studied. Importantly, 85:10:5 and 60:30:10 PEG 400:TEC:ethanol blends provided good syringeability and allowed for rapid implant formation. The latter controlled ibuprofen and chlorhexidine release over several weeks and assured efficient antimicrobial activity. Interestingly, fundamental differences were observed concerning the underlying release mechanisms of the two drugs: Ibuprofen was dissolved in the solvent mixtures and partially leached out together with the solvents during implant formation, resulting in relatively pronounced burst effects. In contrast, chlorhexidine dihydrochloride was dispersed in the liquids in the form of tiny particles, which were effectively trapped by precipitating PLGA during implant formation, leading to initial lag-phases for drug release.

Development and Evaluation of a Water-Free In Situ Depot Gel Formulation for Long-Acting and Stable Delivery of Peptide Drug ACTY116

In situ depot gel is a type of polymeric long-acting injectable (pLAI) drug delivery system; compared to microsphere technology, its preparation process is simpler and more conducive to industrialization. To ensure the chemical stability of peptide ACTY116, we avoided the use of harsh conditions such as high temperatures, high shear mixing, or homogenization; maintaining a water-free and oxygen-free environment was also critical to prevent hydrolysis and oxidation. Molecular dynamics (MDs) simulations were employed to assess the stability mechanism between ACTY116 and the pLAI system. The initial structure of ACTY116 with an alpha helix conformation was constructed using SYBYL-X, and the copolymer PLGA was generated by AMBER 16; results showed that PLGA-based in situ depot gel improved conformational stability of ACTY116 through hydrogen bonds formed between peptide ACTY116 and the components of the pLAI formulation, while PLGA (Poly(DL-lactide-co-glycolide)) also created steric hindrance and shielding effects to prevent conformational changes. As a result, the chemical and conformational stability and in vivo long-acting characteristics of ACTY116 ensure its enhanced efficacy. In summary, we successfully achieved our objective of developing a highly stable peptide-loaded long-acting injectable (LAI) in situ depot gel formulation that is stable for at least 3 months under harsh conditions (40 °C, above body temperature), elucidating the underlying stabilisation mechanism, and the high stability of the ACTY116 pLAI formulation creates favourable conditions for its in vivo pharmacological activity lasting for weeks or even months.

OnyxTMGel or Coil versus Hydrogel as Embolic Agents in Endovascular Applications: Review of the Literature and Case Series

This review focuses on the use of conventional gel or coil and "new" generation hydrogel used as an embolic agent in endovascular applications. In general, embolic agents have deep or multidistrict vascular penetration properties as they ensure complete occlusion of vessels by exploiting the patient's coagulation system, which recognises them as substances foreign to the body, thus triggering the coagulation cascade. This is why they are widely used in the treatment of endovascular corrections (EV repair), arteriovenous malformations (AVM), endoleaks (E), visceral aneurysms or pseudo-aneurysms, and embolisation of pre-surgical or post-surgical (iatrogenic) lesions. Conventional gels such as Onyx or coils are now commercially available, both of which are frequently used in endovascular interventional procedures, as they are minimally invasive and have numerous advantages over conventional open repair (OR) surgery. Recently, these agents have been modified and optimised to develop new embolic substances in the form of hydrogels based on alginate, chitosan, fibroin and other polymers to ensure embolisation through phase transition phenomena. The main aim of this work was to expand on the data already known in the literature concerning the application of these devices in the endovascular field, focusing on the advantages, disadvantages and safety profiles of conventional and innovative embolic agents and also through some clinical cases reported. The clinical case series concerns the correction and exclusion of endoleak type I or type II appeared after an endovascular procedure of exclusion of aneurysmal abdominal aortic (EVAR) with a coil (coil penumbra released by a LANTERN microcatheter), the exclusion of renal arterial malformation (MAV) with a coil (penumbra coil released by a LANTERN microcatheter) and the correction of endoleak through the application of Onyx 18 in the arteries where sealing by the endoprosthesis was not guaranteed.

Peptide Acylation in Aliphatic Polyesters: a Review of Mechanisms and Inhibition Strategies

Biodegradable polyesters are widely employed in the development of controlled release systems for peptide drugs. However, one of the challenges in developing a polyester-based delivery system for peptides is the acylation reaction between peptides and polymers. Peptide acylation is an important factor that affects formulation stability and can occur during storage, in vitro release, and after drug administration. This review focuses on the mechanisms and parameters that influence the rate of peptide acylation within polyesters. Furthermore, it discusses reported strategies to minimize the acylation reaction.

Polysaccharide-based hydrogels for medical devices, implants and tissue engineering: A review

Hydrogels are highly biocompatible biomaterials composed of crosslinked three-dimensional networks of hydrophilic polymers. Owing to their natural origin, polysaccharide-based hydrogels (PBHs) possess low toxicity, high biocompatibility and demonstrate in vivo biodegradability, making them great candidates for use in various biomedical devices, implants, and tissue engineering. In addition, many polysaccharides also show additional biological activities such as antimicrobial, anticoagulant, antioxidant, immunomodulatory, hemostatic, and anti-inflammatory, which can provide additional therapeutic benefits. The porous nature of PBHs allows for the immobilization of antibodies, aptamers, enzymes and other molecules on their surface, or within their matrix, potentiating their use in biosensor devices. Specific polysaccharides can be used to produce transparent hydrogels, which have been used widely to fabricate ocular implants. The ability of PBHs to encapsulate drugs and other actives has been utilized for making neural implants and coatings for cardiovascular devices (stents, pacemakers and venous catheters) and urinary catheters. Their high water-absorption capacity has been exploited to make superabsorbent diapers and sanitary napkins. The barrier property and mechanical strength of PBHs has been used to develop gels and films as anti-adhesive formulations for the prevention of post-operative adhesion. Finally, by virtue of their ability to mimic various body tissues, they have been explored as scaffolds and bio-inks for tissue engineering of a wide variety of organs. These applications have been described in detail, in this review.

The cubosome-based nanoplatforms in cancer therapy: Seeking new paradigms for cancer theranostics

Lyotropic liquid crystals are self-assembled, non-lamellar, and mesophase nanostructured materials that have garnered significant attention as drug carriers. Cubosomes, a subtype of lyotropic liquid crystalline nanoparticles, possess three-dimensional structures that display bicontinuous cubic liquid-crystalline patterns. These patterns are formed through the self-organization of unsaturated monoglycerides (amphphilic lipids such as glyceryl monooleate or phytantriol), followed by stabilization using steric polymers (poloxamers). Owing to their bicontinuous structure and steric polymer-based stabilization, cubosomes have been demonstrated to possess greater entrapment efficiency for hydrophobic drugs compared to liposomes, while also exhibiting high stability. In the past decade, there has been significant interest in cubosomes due to their ability to deliver therapeutic and contrast agents for cancer treatment and imaging with minimal side effects, establishing them as a safe and effective approach. Concerning these advantages, the present review elaborates on the general aspects, composition, and preparation techniques of cubosomes, followed by explanations of their mechanisms of drug loading and release patterns. Furthermore, the review provides meticulous discussions on the use of cubosomes in the treatment and imaging of various types of cancer, culminating in the enumeration of patents related to cubosome-based drug delivery systems.

Optimizing formulation parameters for the development of carvedilol injectable in situ forming depots

In situ forming depots (ISFDs) represent attractive alternatives to the conventional sustained drug delivery systems. Carvedilol, a short half-life drug used on a daily basis to manage chronic conditions, could benefit from this technology. The aim of this work was to develop, for the first time, a new injectable long-acting carvedilol-ISFD. Accordingly, 4 different grades of polyesters with varying properties as i) lactide-to glycolide ratio (polylactide-co-glycolide (PLGA) vs. polylactide (PLA)), and ii) end functionality (acid- vs. ester-capped) were utilized for the preparation of ISFD formulations. In addition, 4 different organic solvents with varying properties (i.e. N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), ethyl acetate, and benzyl benzoate) were also investigated. It was found that NMP and DMSO were more suitable for the formation of depots. Furthermore, all ISFD formulations demonstrated excellent encapsulation efficiency (i.e. 96-98%). Interestingly, both PLGA-based ISFDs (acid-capped and ester-capped) exhibited similar release behaviors and were able to extend carvedilol release over 30 days. On the other hand, acid-capped and ester-capped PLA-based ISFDs exhibited slower release over the 30 days with an average release of only 36% and 60%, respectively. In conclusion, the developed carvedilol-ISFDs resulted in a tunable extended-release behavior, simply by choosing the appropriate grade of polymer. These results open the door toward a novel injectable carvedilol-ISFD formulation.

Long-acting microneedle formulations

The minimally-invasive and painless nature of microneedle (MN) application has enabled the technology to obviate many issues with injectable drug delivery. MNs not only administer therapeutics directly into the dermal and ocular space, but they can also control the release profile of the active compound over a desired period. To enable prolonged delivery of payloads, various MN types have been proposed and evaluated, including dissolving MNs, polymeric MNs loaded or coated with nanoparticles, fast-separable MNs hollow MNs, and hydrogel MNs. These intricate yet intelligent delivery platforms provide an attractive approach to decrease side effects and administration frequency, thus offer the potential to increase patient compliance. In this review, MN formulations that are loaded with various therapeutics for long-acting delivery to address the clinical needs of a myriad of diseases are discussed. We also highlight the design aspects, such as polymer selection and MN geometry, in addition to computational and mathematical modeling of MNs that are necessary to help streamline and develop MNs with high translational value and clinical impact. Finally, up-scale manufacturing and regulatory hurdles along with potential avenues that require further research to bring MN technology to the market are carefully considered. It is hoped that this review will provide insight to formulators and clinicians that the judicious selection of materials in tandem with refined design may offer an elegant approach to achieve sustained delivery of payloads through the simple and painless application of a MN patch.