Crown ethers reverse P-glycoprotein-mediated multidrug resistance in cancer cells

Recent developments of P-glycoprotein inhibitors and its structure-activity relationship (SAR) studies

P-glycoprotein (P-gp) over-expression is a key factor in multi-drug resistance (MDR), which is a major factor in the failure of cancer treatment. P-gp inhibitors have been demonstrated to have powerful pharmacological properties and may be used as a therapeutic approach to overcome the MDR in cancer cells. Combining clinical investigations with biochemical and computational research may potentially lead to a clearer understanding of the pharmacological properties and the mechanisms of action of these P-gp inhibitors. The task of turning these discoveries into effective therapeutic candidates for a variety of malignancies, including resistant and metastatic kinds, falls on medicinal chemists. A variety of P-gp inhibitors with great potency, high selectivity, and minimal toxicity have been identified in recent years. The latest advances in drug design, characterization, structure-activity relationship (SAR) research, and modes of action of newly synthesized, powerful small molecules P-gp inhibitors over the previous ten years are highlighted in this review. P-gp transporter over-expression has been linked to MDR, therefore the development of P-gp inhibitors will expand our understanding of the processes and functions of P-gp-mediated drug efflux, which will be helpful for drug discovery and clinical cancer therapies.

Cellular resistance mechanisms in cancer and the new approaches to overcome resistance mechanisms chemotherapy

Despite major advancements in cancer healing approaches over the last few decades, chemotherapy remains the most popular malignancy treatment. Chemotherapeutic drugs are classified into many kinds based on their mechanism of action. Multidrug resistance (MDR) is responsible for approximately 90% of fatalities in malignancy cases treated with standard chemotherapeutics or innovative targeted medicines. Many innovative prospective anti-cancer medicines displayed high anti-cancer efficacy in a single application. However, combining them with other medications improves cancer treatment efficacy. This supports the belief that a combination of drugs is significantly more effective than a single medicine. Due to the intricacy of MDR processes and the diversity of tumor illnesses, there will rarely be a single medicine that can be utilized to treat all types of cancer. Finding new medications that can reverse MDR in malignancy cells will augment efficacy of chemotherapeutic agents and allow us to treat cancers that are now incurable.

Interaction of crown ethers with the ABCG2 transporter and their implication for multidrug resistance reversal

Overexpression of ABC transporters, such as ABCB1 and ABCG2, plays an important role in mediating multidrug resistance (MDR) in cancer. This feature is also attributed to a subpopulation of cancer stem cells (CSCs), having enhanced tumourigenic potential. ABCG2 is specifically associated with the CSC phenotype, making it a valuable target for eliminating aggressive and resistant cells. Several natural and synthetic ionophores have been discovered as CSC-selective drugs that may also have MDR-reversing ability, whereas their interaction with ABCG2 has not yet been explored. We previously reported the biological activities, including ABCB1 inhibition, of a group of adamantane-substituted diaza-18-crown-6 (DAC) compounds that possess ionophore capabilities. In this study, we investigated the mechanism of ABCG2-inhibitory activity of DAC compounds and the natural ionophores salinomycin, monensin and nigericin. We used a series of functional assays, including real-time microscopic analysis of ABCG2-mediated fluorescent substrate transport in cells, and docking studies to provide comparative aspects for the transporter-compound interactions and their role in restoring chemosensitivity. We found that natural ionophores did not inhibit ABCG2, suggesting that their CSC selectivity is likely mediated by other mechanisms. In contrast, DACs with amide linkage in the side arms demonstrated noteworthy ABCG2-inhibitory activity, with DAC-3Amide proving to be the most potent. This compound induced conformational changes of the transporter and likely binds to both Cavity 1 and the NBD-TMD interface. DAC-3Amide reversed ABCG2-mediated MDR in model cells, without affecting ABCG2 expression or localization. These results pave the way for the development of new crown ether compounds with improved ABCG2-inhibitory properties.

Recent Updates on Supramolecular-Based Drug Delivery - Macrocycles and Supramolecular Gels

Supramolecules-based drug delivery has attracted significant recent research attention as it could enhance drug solubility, retention time, targeting, and stimuli responsiveness. Among the different supramolecules and assemblies, the macrocycles and the supramolecular hydrogels are the two important categories investigated to a greater extent. Here, we provide the most recent advancements in these categories. Under macrocycles, reports on drug delivery by cyclodextrins, cucurbiturils, calixarenes/pillararenes, crown ethers and porphyrins are detailed. The second category discusses the supramolecular hydrogels of macrocycles/polymers and low molecular weight gelators. The updated information provided could be helpful to advance R & D in this vital area.

Heterocyclic Crown Ethers with Potential Biological and Pharmacological Properties: From Synthesis to Applications

Cyclic organic compounds with several ether linkages in their structure are of much concern in our daily life applications. Crown ethers (CEs) are generally heterocyclic and extremely versatile compounds exhibiting higher binding affinity. In recent years, due to their unique structure, crown ethers are widely used in drug delivery, solvent extraction, cosmetics manufacturing, material studies, catalysis, separation, and organic synthesis. Beyond their conventional place in chemistry, this review article summarizes the synthesis, biological, and potential pharmacological activities of CEs. We have emphasized the prospects of CEs as anticancer, anti-inflammatory, antibacterial, and antifungal agents and have explored their amyloid genesis inhibitory activity, electrochemical, and potential metric sensing properties. The central feature of these compounds is their ability to form selective and stable complexes with various organic and inorganic cations. Therefore, CEs can be used in gas chromatography as the stationary phase and are also valuable for cation chromatographic to determine and separate alkali and alkaline-earth cations.

A metal-carbene template approach enables efficient synthesis of a functionalized cage-annulated crown ether

A facile synthetic method to form cage-annulated crown ether with anchored imidazolium units was developed. The present work verified the potential application of the metal-carbene template approach (MCTA) in the preparation of novel flexible polyimidazolium cages by photochemical [2+2] cycloaddition reactions and may provide a new method for the preparation of flexible pure organic cages with incorporation of a variety of functional sites.

Structure activity relationships and the binding mode of quinolinone-pyrimidine hybrids as reversal agents of multidrug resistance mediated by P-gp

P-gp-associated multidrug resistance is a major impediment to the success of chemotherapy. With the aim of finding non-toxic and effective P-gp inhibitors, we investigated a panel of quinolin-2-one-pyrimidine hybrids. Among the active compounds, two of them significantly increased intracellular doxorubicin and rhodamine 123 accumulation by inhibiting the efflux mediated by P-gp and restored doxorubicin toxicity at nanomolar range. Structure-activity relationships showed that the number of methoxy groups, an optimal length of the molecule in its extended conformation, and at least one flexible methylene group bridging the quinolinone to the moiety bearing the pyrimidine favored the inhibitory potency of P-gp. The best compounds showed a similar binding pattern and interactions to those of doxorubicin and tariquidar, as revealed by MD and hybrid QM/MM simulations performed with the recent experimental structure of P-gp co-crystallized with paclitaxel. Analysis of the molecular interactions stabilizing the different molecular complexes determined by MD and QTAIM showed that binding to key residues from TMH 4-7 and 12 is required for inhibition.

Lipid nanocapsules co-encapsulating paclitaxel and salinomycin for eradicating breast cancer and cancer stem cells

Cancer stem cells (CSCs) comprise a diminutive population of the tumor but pose major obstacles in cancer treatment, often their presence being correlated with poor prognosis, therapeutic resistance and relapse. Nanocarriers of combined drugs regimes demonstrate improved pharmacokinetics and decreased systemic toxicity by targeting the bulk tumor cells along with CSCs, holding the key to future successful chemotherapy. Herein, we developed lipid nanocapsules (LNCs) with co-encapsulated paclitaxel (PTX) and salinomycin (SAL) to eliminate breast cancer cells (MCF-7; non-bCSCs) and cancer stem cells (bCSCs) respectively. LNCs loaded with either PTX or SAL alone or in combination were fabricated by the phase inversion temperature (PIT) method. Physicochemical properties such as nano-size (90 ± 5 nm) and spherical morphology of LNCs were confirmed by dynamic light scattering (DLS) and scanning electron microscopy (SEM) respectively. More than 98 % encapsulation efficiency of drug, alone or in combination, and their controlled drug release was obtained. Drug loaded LNCs were efficiently internalized and exhibited cytotoxicity in non-bCSCs and bCSCs, with dual drug loaded LNCs offering superior cytotoxicity and anti-bCSCs property. Drug loaded nanocapsules induced apoptosis in bCSCs, potentiated with the co-delivery of paclitaxel and salinomycin. Synergistic cytotoxic effect on both cells, non-bCSCs and bCSCs and effective reduction of the tumor mammospheres growth by co-encapsulated paclitaxel and salinomycin suggest LNCs to be promising for treatment of breast cancer.

Synthesis, Biological Evaluation, and Molecular Modeling of Aza-Crown Ethers

Synthetic and natural ionophores have been developed to catalyze ion transport and have been shown to exhibit a variety of biological effects. We synthesized 24 aza- and diaza-crown ethers containing adamantyl, adamantylalkyl, aminomethylbenzoyl, and ε-aminocaproyl substituents and analyzed their biological effects in vitro. Ten of the compounds (8, 10–17, and 21) increased intracellular calcium ([Ca²⁺]_i) in human neutrophils, with the most potent being compound 15 (N,N’-bis[2-(1-adamantyl)acetyl]-4,10-diaza-15-crown-5), suggesting that these compounds could alter normal neutrophil [Ca²⁺]_i flux. Indeed, a number of these compounds (i.e., 8, 10–17, and 21) inhibited [Ca²⁺]_i flux in human neutrophils activated by N-formyl peptide (fMLF). Some of these compounds also inhibited chemotactic peptide-induced [Ca²⁺]_i flux in HL60 cells transfected with N-formyl peptide receptor 1 or 2 (FPR1 or FPR2). In addition, several of the active compounds inhibited neutrophil reactive oxygen species production induced by phorbol 12-myristate 13-acetate (PMA) and neutrophil chemotaxis toward fMLF, as both of these processes are highly dependent on regulated [Ca²⁺]_i flux. Quantum chemical calculations were performed on five structure-related diaza-crown ethers and their complexes with Ca²⁺, Na⁺, and K⁺ to obtain a set of molecular electronic properties and to correlate these properties with biological activity. According to density-functional theory (DFT) modeling, Ca²⁺ ions were more effectively bound by these compounds versus Na⁺ and K⁺. The DFT-optimized structures of the ligand-Ca²⁺ complexes and quantitative structure-activity relationship (QSAR) analysis showed that the carbonyl oxygen atoms of the N,N’-diacylated diaza-crown ethers participated in cation binding and could play an important role in Ca²⁺ transfer. Thus, our modeling experiments provide a molecular basis to explain at least part of the ionophore mechanism of biological action of aza-crown ethers.

Mechanisms of Multidrug Resistance in Cancer Chemotherapy

Cancer is one of the main causes of death worldwide. Despite the significant development of methods of cancer healing during the past decades, chemotherapy still remains the main method for cancer treatment. Depending on the mechanism of action, commonly used chemotherapeutic agents can be divided into several classes (antimetabolites, alkylating agents, mitotic spindle inhibitors, topoisomerase inhibitors, and others). Multidrug resistance (MDR) is responsible for over 90% of deaths in cancer patients receiving traditional chemotherapeutics or novel targeted drugs. The mechanisms of MDR include elevated metabolism of xenobiotics, enhanced efflux of drugs, growth factors, increased DNA repair capacity, and genetic factors (gene mutations, amplifications, and epigenetic alterations). Rapidly increasing numbers of biomedical studies are focused on designing chemotherapeutics that are able to evade or reverse MDR. The aim of this review is not only to demonstrate the latest data on the mechanisms of cellular resistance to anticancer agents currently used in clinical treatment but also to present the mechanisms of action of novel potential antitumor drugs which have been designed to overcome these resistance mechanisms. Better understanding of the mechanisms of MDR and targets of novel chemotherapy agents should provide guidance for future research concerning new effective strategies in cancer treatment.

Medicinal chemistry strategies to discover P-glycoprotein inhibitors: An update

The presence of multidrug resistance (MDR) in malignant tumors is one of the primary causes of treatment failure in cancer chemotherapy. The overexpression of the ATP binding cassette (ABC) transporter, P-glycoprotein (P-gp), which significantly increases the efflux of certain anticancer drugs from tumor cells, produces MDR. Therefore, inhibition of P-gp may represent a viable therapeutic strategy to overcome cancer MDR. Over the past 4 decades, many compounds with P-gp inhibitory efficacy (referred to as first- and second-generation P-gp inhibitors) have been identified or synthesized. However, these compounds were not successful in clinical trials due to a lack of efficacy and/or untoward toxicity. Subsequently, third- and fourth-generation P-gp inhibitors were developed but dedicated clinical trials did not indicate a significant therapeutic effect. In recent years, an extraordinary array of highly potent, selective, and low-toxicity P-gp inhibitors have been reported. Herein, we provide a comprehensive review of the synthetic and natural products that have specific inhibitory activity on P-gp drug efflux as well as promising chemosensitizing efficacy in MDR cancer cells. The present review focuses primarily on the structural features, design strategies, and structure-activity relationships (SAR) of these compounds.

Synthesis and supramolecular assembly of fluorinated biogenic amine recognition host polymers

Fluorine functionalized biogenic amine carrier polymers.