Phospholipidic Colchicinoids as Promising Prodrugs Incorporated into Enzyme-Responsive Liposomes: Chemical, Biophysical, and Enzymological Aspects

Design and preparation of pH-sensitive cytotoxic liposomal formulations containing antitumor colchicine analogues for target release

Herein, we describe the synthesis of pH-sensitive lipophilic colchicine prodrugs for liposomal bilayer inclusion, as well as preparation and characterization of presumably stealth PEGylated liposomes with above-mentioned prodrugs. These formulations liberate strongly cytotoxic colchicinoid derivatives selectively under slightly acidic tumor-associated conditions, ensuring tumor-targeted delivery of the compounds. The design of the prodrugs is addressed to pH-triggered release of active compounds in the slight acidic media, that corresponds to tumor microenvironment, while keeping sufficient stability of the whole formulation at physiological pH. Correlations between the structure of the conjugates, their hydrolytic stability, colloidal stability, ability of the prodrug retention in the lipid bilayer are described. Several formulations were found promising for further development and in vivo investigations.

Enzyme-responsive liposomes for controlled drug release

Compared to other nanovectors, liposomes exhibit unique advantages, such as good biosafety and high drug-loading capacity. However, slow drug release from conventional liposomes makes most payloads unavailable, restricting the therapeutic efficacy. Therefore, in the last ∼20 years, enzyme-responsive liposomes have been extensively investigated, which liberate drugs under the stimulation of enzymes overexpressed at disease sites. In this review, we elaborate on the research progress on enzyme-responsive liposomes. The involved enzymes mainly include phospholipases, particularly phospholipase A2, matrix metalloproteinases, cathepsins, and esterases. These enzymes can cleave ester bonds or specific peptide sequences incorporated in the liposomes for controlled drug release by disrupting the primary structure of liposomes, detaching protective polyethylene glycol shells, or activating liposome-associated prodrugs. Despite decades of efforts, there are still a lack marketed products of enzyme-responsive liposomes. Therefore, more efforts should be made to improve the safety and effectiveness of enzyme-responsive liposomes and address the issues associated with production scale-up.

Unravelling the in vivo dynamics of liposomes: Insights into biodistribution and cellular membrane interactions

Liposomes, as a colloidal drug delivery system dating back to the 1960s, remain a focal point of extensive research and stand as a highly efficient drug delivery method. The amalgamation of technological and biological advancements has propelled their evolution, elevating them to their current status. The key attributes of biodegradability and biocompatibility have been instrumental in driving substantial progress in liposome development. Demonstrating a remarkable ability to surmount barriers in drug absorption, enhance stability, and achieve targeted distribution within the body, liposomes have become pivotal in pharmaceutical research. In this comprehensive review, we delve into the intricate details of liposomal drug delivery systems, focusing specifically on their pharmacokinetics and cell membrane interactions via fusion, lipid exchange, endocytosis etc. Emphasizing the nuanced impact of various liposomal characteristics, we explore factors such as lipid composition, particle size, surface modifications, charge, dosage, and administration routes. By dissecting the multifaceted interactions between liposomes and biological barriers, including the reticuloendothelial system (RES), opsonization, enhanced permeability and retention (EPR) effect, ATP-binding cassette (ABC) phenomenon, and Complement Activation-Related Pseudoallergy (CARPA) effect, we provide a deeper understanding of liposomal behaviour in vivo. Furthermore, this review addresses the intricate challenges associated with translating liposomal technology into practical applications, offering insights into overcoming these hurdles. Additionally, we provide a comprehensive analysis of the clinical adoption and patent landscape of liposomes across diverse biomedical domains, shedding light on their potential implications for future research and therapeutic developments.

Gout therapeutics and drug delivery

Gout is a common inflammatory arthritis caused by persistently elevated uric acid levels. With the improvement of people's living standards, the consumption of processed food and the widespread use of drugs that induce elevated uric acid, gout rates are increasing, seriously affecting the human quality of life, and becoming a burden to health systems worldwide. Since the pathological mechanism of gout has been elucidated, there are relatively effective drug treatments in clinical practice. However, due to (bio)pharmaceutical shortcomings of these drugs, such as poor chemical stability and limited ability to target the pathophysiological pathways, traditional drug treatment strategies show low efficacy and safety. In this scenario, drug delivery systems (DDS) design that overcome these drawbacks is urgently called for. In this review, we initially describe the pathological features, the therapeutic targets, and the drugs currently in clinical use and under investigation to treat gout. We also comprehensively summarize recent research efforts utilizing lipid, polymeric and inorganic carriers to develop advanced DDS for improved gout management and therapy.

Advanced liposome and polymersome-based drug delivery systems: Considerations for physicochemical properties, targeting strategies and stimuli-sensitive approaches

Liposomes and polymersomes are colloidal vesicles that are self-assembled from lipids and amphiphilic polymers, respectively. Because of their ability to encapsulate both hydrophilic and hydrophobic therapeutics, they are of great interest in drug delivery research. Today, the applications of liposomes and polymersomes have expanded to a wide variety of complex therapeutic molecules, including nucleic acids, proteins and enzymes. Thanks to their chemical versatility, they can be tailored to different drug delivery applications to achieve maximum therapeutic index. This review article evaluates liposomes and polymersomes from a perspective that takes into account the physical and biological barriers that reduce the efficiency of the drug delivery process. In this context, the design approaches of liposomes and polymersomes are discussed with representative examples in terms of their physicochemical properties (size, shape, charge, mechanical), targeting strategies (passive and active) and response to different stimuli (pH, redox, enzyme, temperature, light, magnetic field, ultrasound). Finally, the challenges limiting the transition from laboratory to practice, recent clinical developments, and future perspectives are addressed.

Optical Switches for Lipid Membranes: Computed Molecular Projection Area as a Switch Selection Criterion

Optical switches in lipid membranes are an emerging tool to tune the properties of the bilayer or membrane protein integrated therein. Here, we use simple geometry and physics considerations to deduce structural criteria to design efficient photoactivated switches for lipid membranes. We compare how the area of projection on the bilayer of various classes of photoswitches changes upon the trans/cis or open/closed transition and show that azobenzene and stilbene should distort the bilayer structure the most. We also conclude that planar-elongated molecules, in which atoms of isomerizable double bond have no additional substituents, while substituents of the fragments adjacent to the double bond prevent formation of the planar molecule in cis configuration, are to be the best photoswitches for lipid membranes.

Regioselective approach to colchiceine tropolone ring functionalization at C(9) and C(10) yielding new anticancer hybrid derivatives containing heterocyclic structural motifs

The influence of base type, temperature, and solvent on regioselective C(9)/C(10) “click” modifications within the tropolone ring of colchiceine (2) is investigated. New ether derivatives of 2, bearing alkyne, azide, vinyl, or halide aryl groups enable assembly of the alkaloid part with heterocycles or important biomolecules such as saccharides, geldanamycin or AZT into hybrid scaffolds by dipolar cycloaddition (CuAAC) or Heck reaction. Compared to colchicine (1) or colchiceine (2), ether congeners, as e.g. 3e [IC₅₀s_(3e) ∼ 0.9 nM], show improved or similar anticancer effects, whereby the bulkiness of the substituents and the substitution pattern of the tropolone proved to be essential. Biological studies reveal that expanding the ether arms by terminal basic heterocycles as quinoline or pyridine, decreases the toxicity in HDF cells at high anticancer potency (IC₅₀s ∼ 1–2 nM). Docking of ether and hybrid derivatives into the colchicine pocket of α_GTP/β tubulin dimers reveals a relationship between the favourable binding mode and the attractive anticancer potency.

Liposomal Formulation of a PLA2-Sensitive Phospholipid-Allocolchicinoid Conjugate: Stability and Activity Studies In Vitro

To assess the stability and efficiency of liposomes carrying a phospholipase A2-sensitive phospholipid-allocolchicinoid conjugate (aC-PC) in the bilayer, egg phosphatidylcholine and 1-palmitoyl-2-oleoylphosphatidylglycerol-based formulations were tested in plasma protein binding, tubulin polymerization inhibition, and cytotoxicity assays. Liposomes L-aC-PC10 containing 10 mol. % aC-PC in the bilayer bound less plasma proteins and were more stable in 50% plasma within 4 h incubation, according to calcein release and FRET-based assays. Liposomes with 25 mol. % of the prodrug (L-aC-PC25) were characterized by higher storage stability judged by their hydrodynamic radius evolution yet enhanced deposition of blood plasma opsonins on their surface according to SDS-PAGE and immunoblotting. Notably, inhibition of tubulin polymerization was found to require that the prodrug should be hydrolyzed to the parent allocolchicinoid. The L-aC-PC10 and L-aC-PC25 formulations demonstrated similar tubulin polymerization inhibition and cytotoxic activities. The L-aC-PC10 formulation should be beneficial for applications requiring liposome accumulation at tumor or inflammation sites.

Design, synthesis, and biological evaluation of biotinylated colchicine derivatives as potential antitumor agents

Chemical drug design based on the biochemical characteristics of cancer cells has become an important strategy for discovering new anti-tumour drugs to improve tumour targeting effects and reduce off-target toxicities. Colchicine is one of the most prominent and historically microtubule-targeting drugs, but its clinical applications are hindered by notorious adverse effects. In this study, we presented a novel tumour-specific conjugate 9 that consists of deacetylcolchicine (Deac), biotin, and a cleavable disulphide linker. 9 was found to exhibit potent anti-tumour activity and exerted higher selectivity between tumour and nontarget cells than Deac. The targeting moiety biotin might enhance the transport capability and selectivity of 9 to tumour cells via biotin receptor-mediated endocytosis. The tubulin polymerisation activity of 9 (with DTT) was close to the parent drug Deac. These preliminary results suggested that 9 is a high potency and reduced toxicity antitumor agent and worthy of further investigation.

Dual-Targeting and Stimuli-Triggered Liposomal Drug Delivery in Cancer Treatment

The delivery of chemotherapeutics to solid tumors using smart drug delivery systems (SDDSs) takes advantage of the unique physiology of tumors (i.e., disordered structure, leaky vasculature, abnormal extracellular matrix (ECM), and limited lymphatic drainage) to deliver anticancer drugs with reduced systemic side effects. Liposomes are the most promising of such SDDSs and have been well investigated for cancer therapy. To improve the specificity, bioavailability, and anticancer efficacy of liposomes at the diseased sites, other strategies such as targeting ligands and stimulus-sensitive liposomes have been developed. This review highlights relevant surface functionalization techniques and stimuli-mediated drug release for enhanced delivery of anticancer agents at tumor sites, with a special focus on dual functionalization and design of multistimuli responsive liposomes.

Triggered Drug Release From Liposomes: Exploiting the Outer and Inner Tumor Environment

Since more than 40 years liposomes have being extensively studied for their potential as carriers of anticancer drugs. The basic principle behind their use for cancer treatment consists on the idea that they can take advantage of the leaky vasculature and poor lymphatic drainage present at the tumor tissue, passively accumulating in this region. Aiming to further improve their efficacy, different strategies have been employed such as PEGlation, which enables longer circulation times, or the attachment of ligands to liposomal surface for active targeting of cancer cells. A great challenge for drug delivery to cancer treatment now, is the possibility to trigger release from nanosystems at the tumor site, providing efficacious levels of drug in the tumor. Different strategies have been proposed to exploit the outer and inner tumor environment for triggering drug release from liposomes and are the focus of this review.

Stimuli-responsive phospholipid-drug conjugates (PDCs)-based nanovesicles for drug delivery and theranostics

Liposomes represent one of the most successful nano-drug delivery systems among enormous nano-carriers. Although great progress has been made in conventional liposomes, the emerging shortcomings still impair the therapeutic index. The proposal of stimuli-responsive phospholipid-drug conjugates (PDCs)-based nanovesicles solves the challenges that conventional liposomes are faced with, showing great potential for cancer diagnosis and therapy. Herein, we intend to overview the current progress and unique advantages of stimuli-responsive PDCs-based nanovesicles. First, the challenges of conventional liposomes and the development of PDCs-based nanovesicles are summarized. Next, the stimuli-responsive elements used in current stimuli-responsive PDCs-based nanovesicles are outlined. Then, the unique superiorities of stimuli-responsive PDCs-based nanovesicles for drug delivery and theranostics are highlighted in detail. Finally, the future opportunities and challenges of stimuli-responsive PDCs-based nanovesicles for clinical translation are put forward.

Stimulus-Responsive Nanomedicines for Disease Diagnosis and Treatment

Stimulus-responsive drug delivery systems generally aim to release the active pharmaceutical ingredient (API) in response to specific conditions and have recently been explored for disease treatments. These approaches can also be extended to molecular imaging to report on disease diagnosis and management. The stimuli used for activation are based on differences between the environment of the diseased or targeted sites, and normal tissues. Endogenous stimuli include pH, redox reactions, enzymatic activity, temperature and others. Exogenous site-specific stimuli include the use of magnetic fields, light, ultrasound and others. These endogenous or exogenous stimuli lead to structural changes or cleavage of the cargo carrier, leading to release of the API. A wide variety of stimulus-responsive systems have been developed-responsive to both a single stimulus or multiple stimuli-and represent a theranostic tool for disease treatment. In this review, stimuli commonly used in the development of theranostic nanoplatforms are enumerated. An emphasis on chemical structure and property relationships is provided, aiming to focus on insights for the design of stimulus-responsive delivery systems. Several examples of theranostic applications of these stimulus-responsive nanomedicines are discussed.

Colchicine Alkaloids and Synthetic Analogues: Current Progress and Perspectives

Colchicine, the main alkaloid of Colchicum autumnale, is one of the most famous natural molecules. Although colchicine belongs to the oldest drugs (in use since 1500 BC), its pharmacological potential as a lead structure is not yet fully exploited. This review is devoted to the synthesis and structure-activity relationships (SAR) of colchicine alkaloids and their analogues with modified A, B, and C rings, as well as hybrid compounds derived from colchicinoids including prodrugs, conjugates, and delivery systems. The systematization of a vast amount of information presented to date will create a paradigm for future studies of colchicinoids for neoplastic and various other diseases.