Throughout history, natural products (NPs) have provided a rich source of compounds that have wide applications in the fields of medicine, health sciences, pharmacy and biology. Although naturally active substances are good lead compounds for the discovery of new drugs, most of them suffer from various deficiencies or shortcomings, such as complex structures, poor stability and solubility. Therefore, structural modification of NPs is needed to develop novel compounds with specific properties. Areas covered: This article presents an overview on the structural modifications of NPs in drug development. The application of multiple classes of NPs to the treatment of conditions such as cancers, infection, Alzheimer's and diabetes are discussed. This article also reveals that modification of NPs is a versatile approach to explore their mode of actions, which may lead to the discovery of novel drugs. Expert opinion: NPs are usually described by structural diversity and complexity. The use of isolated NPs as scaffolds for modification is a good approach to drug discovery and development. Despite many limitations associated with NPs, the total synthesis, semisynthetic modification, SAR-based modification, sometimes even a single atom alteration, may lead to the discovery of a novel drug.

Alzheimer's disease (AD) is a multifactorial syndrome resulting in profound misery and poses a substantial burden on human health, economy, and society throughout the world. Based on the numerous AD-related targets in the disease network, multi-target design strategy is a crucial direction to seek for enhanced therapy, and multi-target drugs have the ability to regulate more targets than single-target drugs, affecting the disease network with more potency. Herein, we highlight nine major targets associated with AD, which are acetylcholine esterase (AChE), beta-site amyloid precursor protein cleaving enzyme 1 (β-secretase, BACE-1), glycogen synthase kinase 3 beta (GSK-3β), monoamine oxidases (MAOs), metal ions in the brain, N-methyl-D-aspartate (NMDA) receptor, 5-hydroxytryptamine (5-HT) receptors, the third subtype of histamine receptor (H3 receptor), and phosphodiesterases (PDEs), and their respective relationship to the disease network. Furthermore, eleven multi-target design strategies classified by the involvement of AChE and related promising compounds for improved therapy of AD in recent years are described based on the nine major targets.

The vital roles of microtubule in mitosis and cell division make it an attractive target for antitumor therapy. Colchicine binding site of tubulin is one of the most important pockets that have been focused on to design tubulin-destabilizing agents. Over the past few years, a large number of colchicine binding site inhibitors (CBSIs) have been developed inspired by natural products or synthetic origins, and many moieties frequently used in these CBSIs are structurally in common. In this review, we will classify the CBSIs into classical CBSIs and nonclassical CBSIs according to their spatial conformations and binding modes with tubulin, and highlight the privileged structures from these CBSIs in the development of tubulin inhibitors targeting the colchicine binding site.

BackgroundHuman skin has the capacity to metabolise foreign chemicals (xenobiotics), but knowledge of the various enzymes involved is incomplete. A broad-based unbiased proteomics approach was used to describe the profile of xenobiotic metabolising enzymes present in human skin and hence indicate principal routes of metabolism of xenobiotic compounds. Several in vitro models of human skin have been developed for the purpose of safety assessment of chemicals. The suitability of these epidermal models for studies involving biotransformation was assessed by comparing their profiles of xenobiotic metabolising enzymes with those of human skin.Methodology/Principal FindingsLabel-free proteomic analysis of whole human skin (10 donors) was applied and analysed using custom-built PROTSIFT software. The results showed the presence of enzymes with a capacity for the metabolism of alcohols through dehydrogenation, aldehydes through dehydrogenation and oxidation, amines through oxidation, carbonyls through reduction, epoxides and carboxylesters through hydrolysis and, of many compounds, by conjugation to glutathione. Whereas protein levels of these enzymes in skin were mostly just 4–10 fold lower than those in liver and sufficient to support metabolism, the levels of cytochrome P450 enzymes were at least 300-fold lower indicating they play no significant role. Four epidermal models of human skin had profiles very similar to one another and these overlapped substantially with that of whole skin.Conclusions/SignificanceThe proteomics profiling approach was successful in producing a comprehensive analysis of the biotransformation characteristics of whole human skin and various in vitro skin models. The results show that skin contains a range of defined enzymes capable of metabolising different classes of chemicals. The degree of similarity of the profiles of the in vitro models indicates their suitability for epidermal toxicity testing. Overall, these results provide a rational basis for explaining the fate of xenobiotics in skin and will aid chemical safety testing programmes.

There have been many efforts to improve oral drug bioavailability and therapeutic efficacy and patient compliance. A variety of controlled-release oral delivery systems have been developed to meet these needs. Gastroretentive drug delivery technologies have the potential to achieve retention of the dosage form in the upper gastrointestinal tract (GIT) that can be sufficient to ensure complete solubilisation of the drugs in the stomach fluids, followed by subsequent absorption in the stomach or proximal small intestine. This can be beneficial for drugs that have an “absorption window” or are absorbed to a different extent in various segments of the GIT. Therefore, gastroretentive technologies in tandem with controlled-release strategies could enhance both the therapeutic efficacy of many drugs and improve patient compliance through a reduction in dosing frequency. The paper reviews different gastroretentive drug delivery technologies and controlled-release strategies that can be combined and summarises examples of formulations currently in clinical development and commercially available gastroretentive controlled-release products. The different parameters that need to be considered and monitored during formulation development for these pharmaceutical applications are highlighted.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) plays an important role in regulating lipoprotein metabolism by binding to low-density lipoprotein receptors (LDLRs), leading to their degradation. LDL cholesterol (LDL-C) lowering drugs that operate through the inhibition of PCSK9 are being pursued for the management of hypercholesterolemia and reducing its associated atherosclerotic cardiovascular disease (CVD) risk. Two PCSK9-blocking monoclonal antibodies (mAbs), alirocumab and evolocumab, were approved in 2015. However, the high costs of PCSK9 antibody drugs impede their prior authorization practices and reduce their long-term adherence. Given the potential of small-molecule drugs, the development of small-molecule PCSK9 inhibitors has attracted considerable attention. This article provides an overview of the recent development of small-molecule PCSK9 inhibitors disclosed in the literature and patent applications, and different approaches that have been pursued to modulate the functional activity of PCSK9 using small molecules are described. Challenges and potential strategies in developing small-molecule PCSK9 inhibitors are also discussed.

A series of novel quinoline-chalcone derivatives were designed, synthesized and evaluated for their antiproliferative activity. Among them, compound 24d exhibited the most potent activity with IC50 values ranging from 0.009 to 0.016 μM in a panel of cancer cell lines. Compound 24d also displayed a good safety profile with LD50 value of 665.62 mg/kg by intravenous injection, and its hydrochloride salt 24d-HCl significantly inhibited tumor growth in H22 xenograft models without observable toxic effects, which was more potent than that of CA-4. Mechanism studies demonstrated that 24d bound to the colchicine site of tubulin, arrested cell cycle at the G2/M phase, induced apoptosis, depolarized mitochondria and induced reactive oxidative stress (ROS) generation in K562 cells. Moreover, 24d has potent in vitro anti-metastasis, in vitro and in vivo anti-vascular activities. Collectively, our findings suggest that 24d deserves to be further investigated as a potent and safe anti-tumor agent for cancer therapy.

Design, synthesis and biological evaluation of quinoline-indole derivatives as anti-tubulin agents targeting the colchicine binding site,