Antibody–drug conjugates: Recent advances in linker chemistry

Antibody–drug conjugates (ADCs) are gradually revolutionizing clinical cancer therapy. The antibody–drug conjugate linker molecule determines both the efficacy and the adverse effects, and so has a major influence on the fate of ADCs. An ideal linker should be stable in the circulatory system and release the cytotoxic payload specifically in the tumor. However, existing linkers often release payloads nonspecifically and inevitably lead to off-target toxicity. This defect is becoming an increasingly important factor that restricts the development of ADCs. The pursuit of ADCs with optimal therapeutic windows has resulted in remarkable progress in the discovery and development of novel linkers. The present review summarizes the advance of the chemical trigger, linker‒antibody attachment and linker‒payload attachment over the last 5 years, and describes the ADMET properties of ADCs. This work also helps clarify future developmental directions for the linkers.     

Synthesis and in vitro biological activities of ferrocenyl–chalcone amides

A series of aminoferrocenyl–chalcone amides 11–19 were synthesized through condensation of a carboxylic acid-functionalized chalcone 10 with ferrocenylamines, using 1,1′-carbonyldiimidazole as the coupling agent. The compounds were screened for their antiplasmodial activities against CQS 3D7 and CQR FCR3 strains of Plasmodium falciparum. All compounds were found to be active, with IC₅₀ values ranging between 0.5–4.5 and 2.1–6.6 µM against 3D7 and FCR3, respectively. Amide 11, featuring a 2-aminoethylene linker, was the most active of all, with IC₅₀ values of 2.6 and 2.1 µM against the 3D7 and FCR3 strains, respectively. In screens against a panel of three cancer cell lines, i.e., TK-10, UACC-62, and MCF-7, amide 19, with a piperazinyl linker, showed increased activity against all three cell lines, compared to the reference drug, parthenolide. Antimicrobial assays that had been performed on six different microorganisms revealed that most of the synthesized amides were inactive against all of these microorganisms. Compound 17, however, with an aminodi(ethyleneoxy) linker, displayed moderate bactericidal activity against the gram-negative microorganisms, with a MIC₁₀₀ value of 128 µM. The outcomes of this study may hence significantly contribute toward malaria and cancer chemotherapy research, and more generally to the growing body of research that aims at illustrating the potential of employing organometallic compounds in medicinal chemistry programs.     

Boron’s journey: advances in the study and application of pharmacokinetics

Introduction: Boron-containing compounds (BCCs) are attractive chemical entities in drug development. Some of these compounds have been used in the treatment of human disease, and studies on their pharmacodynamics suggest that they employ multiple forms of activity. However, less is known about the pharmacokinetic profile of these molecules.

Areas covered: The herein compiled reported data is presented in accordance with the classical ‘ADME’ system for identifying the scope of BCCs in the respective fields. Our analysis suggests that these compounds have several distinct ways to move within the human body, and that the specific structural features of each molecule account for its distinct pharmacokinetic profile. These insights should be useful for designing BCCs with a desired effect.

Expert opinion: Increasing knowledge about the pharmacokinetics of BCCs is providing a broader understanding about the design of new release systems and potential drugs, as well as probable protein transporters that could be related to key roles in physiological processes. These transporters may be involved in sodium transport, hormone release and regulation of the cell cycle. The shared features among groups of BCCs are being identified in order to apply these insights to the design of advantageous compounds.     

Recent advances in pharmacologic prevention and treat ment of osteoporosis

１ＩｎｔｒｏｄｕｃｔｉｏｎＯｓｔｅｏｐｏｒｏｓｉｓｉｓａｒｅｄｕｃｔｉｏｎｉｎｂｏｎｅｍａｓｓａｎｄａｃｈａｎｇｅｉｎｍｉｃｒｏａｒｃｈｉｔｅｃｔｕｒｅ，ｗｈｉｃｈｉｎｃｒｅａｓｅｓｔｈｅｓｕｓｃｅｐｔｉｂｉｌｉｔｙｏｆｆｒａｃｔｕｒｅｓ．Ｏｓｔｅｏｐｏｒｏｓｉｓｉｓｔｈｅｍｏｓｔｃｏｍｍｏｎｍｅｔａｂｏｌｉｃｂｏｎｅｄｉｓｅａｓｅｉｎｔｈｅｄｅｖｅｌｏｐｅｄｗｏｒｌｄａｎｄｉｓｉｎｃｒｅａｓｉｎｇｌｙｒｅｃｏｇｎｉｓｅｄａｓａｎｉｍｐｏｒｔａｎｔｐｕｂｌｉｃｈｅａｌｔｈｐｒｏｂｌｅｍ．Ｏｓｔｅ…     

Recent advances (2010–2015) in studies of cerium oxide nanoparticles’ health effects

Cerium oxide nanoparticles, widespread applied in our life, have attracted much concern for their human health effects. However, most of the works addressing cerium oxide nanoparticles toxicity have only used in vitro models or in vivo intratracheal instillation methods. The toxicity studies have varied results and not all are conclusive. The information about risk assessments derived from epidemiology studies is severely lacking. The knowledge of occupational safety and health (OSH) for exposed workers is very little. Thus this review focuses on recent advances in studies of toxicokinetics, antioxidant activity and toxicity. Additionally, aim to extend previous health effects assessments of cerium oxide nanoparticles, we summarize the epidemiology studies of engineered cerium oxide nanoparticles used as automotive diesel fuel additive, aerosol particulate matter in air pollution, other industrial ultrafine and nanoparticles (e.g., fumes particles generated in welding and flame cutting processes).     

Racemic total synthesis and evaluation of the biological activities of the isoquinoline–benzylisoquinoline alkaloid muraricine

The first racemic total synthesis of the isoquinoline–benzylisoquinoline alkaloid muraricine is reported herein. Pharmacological characterization identified muraricine as a moderate inhibitor of P-glycoprotein, a crucial factor of multidrug resistance in cancer. When combined with vincristine, muraricine partly reversed the chemoresistance of vincristine-resistant leukemia cells at a nontoxic concentration. Furthermore, no cytotoxic effects on noncancerous human cells in therapeutically relevant concentrations were observed.     

Synthesis and biological activities of Schiff bases of gabapentin with different aldehydes and ketones: a structure–activity relationship study

A series of novel gabapentin derivatives 6a–k and 7a–f were synthesized, and their biological activities were determined. The chemical structures were confirmed by elemental analyses, UV–visible, FT-IR, and ¹H NMR spectral studies. The structure–activity relationships (SAR) for anticonvulsant and antioxidant activities were discussed. Compounds 7a–f were evaluated for their possible anticonvulsant activity by Maximal Electroshock Seizure (MES) test, and their neurotoxic effects were determined by rotorod test. Majority of the compounds were active in MES tests. Compounds 7b and 7e showed good protective effect from seizure when compared to standard drug, phenytoin (100 mg/kg). The same compounds showed no neurotoxicity at the maximum dose administered (100 mg/kg). Most of the novel compounds showed DPPH radical scavenging activity, where compounds 6f, 6j, and 7a were the best radical scavengers (IC₅₀ was about 60 μg/ml).     

Recent progress in understanding of structure, ligand interactions and the mechanism of activation of the β₂-adrenergic receptor

The understanding of β?-adrenergic receptor (β?AR) interactions with ligands as well as the mechanism of receptor activation changed radically from 2007, when the first crystallographic structure of the receptor was reported. Since then numerous crystallographic studies described interactions with all main classes of β?AR ligands and with G proteins, which provided a great insight into the molecular structure of the receptor. However, molecular mechanisms of receptor activations remain to be determined. Functional research supported the concept of ligand-directed signaling at β-adrenoceptors. Agonist can activate alternative signaling pathways with different capacities and trigger cellular effects. It indicates that agonists nominally belonging to the same class may bind to and/or stabilize different active conformations of the receptor which are selectively recognized by signaling proteins in the allosteric manner.     

Tricyclic antidepressants and fibromyalgia: what is the mechanism of action?

Fibromyalgia is a chronic pain disorder of which other clinical features, such as persistent fatigue and disordered sleep, may be a secondary consequence. The initial pharmacological approach to treating the disorder is the management of the pain. Tricyclic antidepressants are the most effective drugs in use so far, especially when administered in combination with other therapies (e.g., selective serotonin re-uptake inhibitors), which suggests modulation of the neurotransmitters serotonin and noradrenaline. The effectiveness of amitriptyline and related tricyclic antidepressants, however, is consistent with the involvement of mechanisms, such as potassium channel modulation and NMDA receptor antagonism, in addition to or in place of the modulation of monoamine neurotransmitters. Investigation of the importance of each of the pharmacological properties of amitriptyline and related molecules in the management of fibromyalgia could provide clues for the rational design of new drugs.     

Elucidating the mechanism of action of pregabalin: α(2)δ as a therapeutic target in anxiety

This review provides a brief summary of what is known about the anxiolytic mechanism of action of pregabalin, a highly selective, high-affinity ligand of the P/Q type of voltage-gated calcium channel (CaV). Evidence from in vivo models of neuronal hyperexcitability suggests that pregabalin reduces synaptic release of neurotransmitters in selected CNS regions including the cortex, olfactory bulb, hypothalamus, amygdala, hippocampus, cerebellum and dorsal horn of the spinal cord. Release of neurotransmitters from the synaptic vesicle, and propagation of neurotransmission, requires the vesicle to fuse with the presynaptic membrane. Pregabalin binding to the α(2)δ type 1 protein of the P/Q type CaV reduces the availability of Ca2+ required for membrane fusion and exocytosis of neurotransmitters. Evidence that the anxiolytic mechanism of action of pregabalin is mediated by binding to the α(2)δ type 1 protein comes from animal models, which have demonstrated a structure-activity relationship between the affinity of ligands for the α(2)δ type 1 protein and their potency in models of anxiety such as the Vogel conflict test. Furthermore, the anxiolytic activity of pregabalin is lost in transgenic mice with specific point mutations in the CaV α(2)δ type 1 protein. Pregabalin-mediated reduction in calcium currents has also been shown to result in a significant inhibition of the release of neurotransmitters implicated in pathological anxiety such as glutamate and monoamine neurotransmitters. However, further research is needed to confirm that these effects contribute to the anxiolytic mechanism of action of pregabalin. Finally, pregabalin may also act by inhibiting synaptogenesis of excitatory neurons formed in response to chronic stress or anxiety, or more acutely inhibit the trafficking of CaV to the plasma membrane.     

Prediction of drug–ABC-transporter interaction — Recent advances and future challenges

With the discovery of P-glycoprotein (P-gp), it became evident that ABC-transporters play a vital role in bioavailability and toxicity of drugs. They prevent intracellular accumulation of toxic compounds, which renders them a major defense mechanism against xenotoxic compounds. Their expression in cells of all major barriers (intestine, blood–brain barrier, blood–placenta barrier) as well as in metabolic organs (liver, kidney) also explains their influence on the ADMET properties of drugs and drug candidates. Thus, in silico models for the prediction of the probability of a compound to interact with P-gp or analogous transporters are of high value in the early phase of the drug discovery process. Within this review, we highlight recent developments in the area, with a special focus on the molecular basis of drug–transporter interaction. In addition, with the recent availability of X-ray structures of several ABC-transporters, also structure-based design methods have been applied and will be addressed.     

The role of immunotherapy in Guillain-Barré syndrome: understanding the mechanism of action

INTRODUCTION: Guillain-Barré syndrome (GBS) is the most frequent cause of acute flaccid paralysis and, despite treatment, there continues to be an associated mortality and severe disability ranging from 9 to 17%. This article reviews the rationale behind the existing immunotherapy in GBS and discusses the future direction that work in this area should follow. AREAS COVERED: The pathogenesis of GBS and the current evidence for the different forms of immunotherapy in GBS are reviewed. The proposed mechanism of action of each treatment--(steroids, plasma exchange and intravenous immunoglobulin (IVIG))--in GBS are discussed. EXPERT OPINION: Both plasma exchange and IVIG are equally effective in GBS although the latter is preferred in view of its ease of access and lower rates of complications. Although not clinically established, there may be a role for the concomitant use of steroids with IVIG and, in patients with severe disease and poor prognostic scores, plasma exchange followed by IVIG or two successive IVIG may prove beneficial.     

Opioids and the immune system: what is their mechanism of action?

There is a significant amount of literature showing that morphine and other opioids modulate immune responses. The findings support many mechanisms by which this may occur. In vitro experiments provide evidence for direct actions of opioids on immune cells using a variety of functional end points. When these drugs are given in vivo, a plethora of immune parameters are also altered. The paper in this issue of the journal by Zhang et al. provides new information on morphine alteration of immune cell subsets in the spleen and thymus of mice and the potential role of glucocorticoids in these observed phenomena. This Commentary reviews the in vitro activities of morphine on leucocytes, as well as other documented mechanisms by which morphine can alter immune function in vivo.     

Does nitric oxide participate in the mechanism of action of dotarizine?

Behavioral and nociceptive effects of dotarizine (DOT) and other substances acting on migrainous attacks and nitric oxide (NO) metabolism were studied in comparative experiments on rats. Behavioral effects were evaluated by the changes induced in ambulations and rearings of rats in the Opto-Varimex apparatus; effects on nociception were determined by the changes of pain threshold in growing mechanical pressure on one of the rat paw. The data showed that (1) NO did not participate directly in the mechanism of the behavioral actions of DOT. A role could be ascribed to the modulating influence of DOT on the changes in NO formation induced by other agents; (2) the NO system did not participate in the mechanisms of the responses to the painful mechanical pressure on the rat paw; (3) the behavioral effects of the substances with facilitating or inhibitory action on the migrainous process (m-CPP and ergotamine) and the influence of substances proved to affect NO formation (L-arginine, histamine, L-NAME) on these effects suggest a role for NO as a modulating but not a basic factor in the mechanisms of action of these pro- and antimigrainous substances; and (4) the behavioral effects of DOT were similar to the effects of the antimigrainous drug ergotamine and different from the promigrainous drug meta-chlorophenyl-piperazine (m-CPP)--which suggest an antimigrainous activity of dotarizine.     

Alzheimer’s disease: Recent advances in diagnosis and overview of clinical research in newer treatments

Alzheimer’s disease (AD) is a progressive and fatal neurodegenerative disorder manifested by cognitive and memory deterioration, progressive impairment of activities of daily living, and a variety of neuropsychiatric symptoms and behavioral disturbances. This article discusses worldwide prevalence patterns, history, and summarizes hypotheses about the causes of AD. Currently available diagnostic methods, their effectiveness of, and problems with, different methods and recent advances are thoroughly discussed. Finally, current treatment strategies are discussed in light of the benefits and drawbacks of different therapeutic approaches along with ongoing drugs under development.     

Synthesis,characterization, molecular docking,and biological activities of coumarin–1,2,3-triazole-acetamide hybrid derivatives

Coumarins and their derivatives are receiving increasing attention due to numerous biochemical and pharmacological applications. In this study, a series of novel coumarin–1,2,3-triazole-acetamide hybrids was tested against some metabolic enzymes including α-glycosidase (α-Gly), α-amylase (α-Amy), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), human carbonic anhydrase I (hCA I), and hCA II. The new coumarin–1,2,3-triazole-acetamide hybrids showed K_i values in the range of 483.50–1,243.04 nM against hCA I, 508.55–1,284.36 nM against hCA II, 24.85–132.85 nM against AChE, 27.17–1,104.36 nM against BChE, 590.42–1,104.36 nM against α-Gly, and 55.38–128.63 nM against α-Amy. The novel coumarin–1,2,3-triazole-acetamide hybrids had effective inhibition profiles against all tested metabolic enzymes. Also, due to the enzyme inhibitory effects of the new hybrids, they are potential drug candidates to treat diseases such as epilepsy, glaucoma, type-2 diabetes mellitus (T2DM), Alzheimer's disease (AD), and leukemia. Additionally, these inhibition effects were compared with standard enzyme inhibitors like acetazolamide (for hCA I and II), tacrine (for AChE and BChE), and acarbose (for α-Gly and α-Amy). Also, those coumarin–1,2,3-triazole-acetamide hybrids with the best inhibition score were docked into the active site of the indicated metabolic enzymes.     

Artemisinin and chloroquine: do mode of action and mechanism of resistance involve the same protagonists?

Considerable progress has been made in antimalarial research; however, further studies are required to improve the efficacy of clinically available drugs, to develop new agents with superior activity and to avoid the emergence of resistance. In particular, efforts must focus on understanding the mode of action of antimalarial agents and on the mechanism by which the parasite Plasmodium falciparum impedes the action of these drugs. In this review, the current status of the antimalarial agents chloroquine and artemisinin is discussed, and the link between mechanism of action and resistance highlighted.