Fluorescent Probes for Subcellular Localization during Osteclast Formation

Natural Products-Pyrazine Hybrids: A Review of Developments in Medicinal Chemistry

Pyrazine is a six-membered heterocyclic ring containing nitrogen, and many of its derivatives are biologically active compounds. References have been downloaded through Web of Science, PubMed, Science Direct, and SciFinder Scholar. The structure, biological activity, and mechanism of natural product derivatives containing pyrazine fragments reported from 2000 to September 2023 were reviewed. Publications reporting only the chemistry of pyrazine derivatives are beyond the scope of this review and have not been included. The results of research work show that pyrazine-modified natural product derivatives have a wide range of biological activities, including anti-inflammatory, anticancer, antibacterial, antiparasitic, and antioxidant activities. Many of these derivatives exhibit stronger pharmacodynamic activity and less toxicity than their parent compounds. This review has a certain reference value for the development of heterocyclic compounds, especially pyrazine natural product derivatives.

Recent advances in medicinal chemistry of oleanolic acid derivatives

Oleanolic acid (OA), a ubiquitous pentacyclic oleanane-type triterpene isolated from edible and medicinal plants, exhibits a wide spectrum of pharmacological activities and tremendous therapeutic potential. However, the undesirable pharmacokinetic properties limit its application and development. Numerous researches on structural modifications of OA have been carried out to overcome this limitation and improve its pharmacokinetic and therapeutic properties. This review aims to compile and summarize the recent progresses in the medicinal chemistry of OA derivatives, especially on structure-activity relationship in the last few years (2010-2021). It gives insights into the rational design of bioactive derivatives from OA scaffold as promising therapeutic agents.

HA-20 prevents hepatocyte steatosis in metabolic-associated fatty liver disease via regulating Ca2+ relative signalling pathways

Metabolic-associated fatty liver disease (MAFLD) is caused by hepatocyte steatosis and is associated with obesity, type II diabetes, and heart disease. There are currently no effective drugs to treat MAFLD. This study explored the effect of HA-20, an oleanolic acid derivative, on hepatocyte steatosis in MAFLD. HepG2, L02, and AML12 cells were developed using oleic acid for in vitro MAFLD cell assays, and a high-fat diet + high-fructose diet-induced (HFHF) MAFLD mouse model was established for in vivo studies. The results demonstrated that HA-20 prevented hepatocyte steatosis in cell assays and caused 26.3, 57.7 and 70.0% inhibition of triglyceride (TG) levels in the 5.0, 10.0 and 20.0 μM HA-20 groups, respectively. The EC₅₀ values of HA-20 treatment in HepG2, L02 and AML12 cells were 9.7 ± 0.6 μM, 42.4 ± 3.5 μM and 71.0 ± 14.7 μM, respectively. HA-20 also prevented hepatocyte steatosis in the MAFLD mouse model, the liver triglyceride contents were 2.3 ± 0.4 and 1.5 ± 0.2 mmol/L in the 2.5 and 5.0 mg/kg/day HA-20 groups, lower than 6.2 ± 0.7 mmol/L in the HFHF group and 3.3 ± 0.4 mmol/L in the metformin group. Further mechanistic investigation revealed that HA-20 increased the phosphorylation of calmodulin-dependent protein kinase kinase (p-CaMKK) and the phosphorylation of AMP-activated protein kinase (p-AMPK), at least partially by increasing intracellular Ca²⁺ concentration, which suppressed lipogenesis and enhanced β-oxidation. Our findings provide new insight into preventing MAFLD by increasing Ca²⁺ and suggest that HA-20 possesses therapeutic potential for MAFLD management.

Fluorescence live cell imaging revealed wogonin targets mitochondria

Scutellaria baicalensis is one of the widely used Chinese traditional medicines, and wogonin is one of major active components in it. However, the mechanism of action of wogonin has largely remained unclear. In this work, we designed a fluorescent probe, namely ATTO565-WGN, by conjugating wogonin with the fluorophore ATTO565 based on Mannich reaction via a flexible chain linker. In vitro assays verified that the ATTO565-WGN conjugate has a similar anti-proliferative activity to wogonin against human A549 and HeLa cancer cell lines. Combining co-localization and competition studies, confocal fluorescence imaging clearly demonstrated that the fluorescent wogonin probe predominantly located in mitochondrial area of living cells, indicating that wogonin acts at mitochondrion to exert its pharmacological functions. Significantly, the conjugated ATTO565 fluorophore conferred the wogonin probe STED (Stimulated Emission Depletion) feature, enabling STED fluorescence living cell imaging with a 55 nm of ultrahigh spatial resolution. This will greatly beneficial for the in situ investigation of interactions between wogonin and biological targets at the finely organized and dynamic mitochondria of living cells. Moreover, this work also provides novel insights into rational design of mitochondrion targeting fluorescence probes for ultrahigh resolution living cell imaging.

Fluorescence-labeled neopeltolide derivatives for subcellular localization imaging

Design, synthesis and functional analysis of fluorescent derivatives of neopeltolide, an antiproliferative marine macrolide, are reported herein. Live cell imaging using the fluorescent derivatives showed rapid cellular uptake and localization within the endoplasmic reticulum as well as the mitochondria.

An oleanolic acid derivative reduces denervation-induced muscle atrophy via activation of CNTF-mediated JAK2/STAT3 signaling pathway

Denervation caused by sciatic nerve injury has brought great harm to the patients, especially denervation-induced muscle atrophy. The body stress produces a large number of Schwann cells when the sciatic nerve is injured, and the cells secrete some cytokines including ciliary neurotrophic factor (CNTF) that not only play a role in promoting the repair of sciatic nerve, but also maintain the normal physiological function of the muscles surrounding the damaged nerves. CNTF upregulates janus kinase 2 (JAK2) and signal transducers and activators of transcription 3 (STAT3) signals in myoblasts, and consequently accelerates the proliferation and differentiation of myoblasts. This effect on myoblasts is the most effective way to relieve muscle atrophy. Therefore, increasing CNTF is a promising direction to improve muscle atrophy. In the present study, an oleanolic acid derivative, HA-19, increased the proliferation of Schwann cells, and elevated CNTF production of the cells. HA-19 up-regulated the phosphorylation of JAK2 and STAT3 not only by directly acting on myoblasts, but also by increasing the secretion of CNTF of Schwann cells; and consequently, promoted the proliferation and differentiation of myoblasts. In denervation-induced muscle atrophy mice model, treatment with HA-19 significantly increased the weights of tibialis anterior (TA), gastrocnemius (Gastroc.), extensor digitorum longus (EDL), soleus and quadriceps (Quad.) under atrophied state. And, very interestingly, these muscles under normal condition were also strengthened by HA-19. Our finding demonstrated that HA-19 has a great potential as a lead compound for the drug discovery of anti-denervation-induced muscle atrophy.

A novel oleanolic acid derivative HA-19 ameliorates muscle atrophy via promoting protein synthesis and preventing protein degradation

Muscle atrophy refers to a decrease in the size of muscles in the body, occurs in certain muscles with inactivity in many diseases and lacks effective therapies up to date. Natural products still play an important role in drug discovery. In the present study, derivatives of a natural product, oleanolic acid, were screened with myoblast differentiation and myotube atrophy assays, respectively. Results revealed that one of the derivatives, HA-19 showed the most potent anti-muscle atrophy activity, and was used for further studies. We demonstrated that HA-19 led to the increase of the protein synthesis by activating mechanistic target of rapamycin complex 1 (mTORC1)/p70 S6K pathways, and also enhanced myoblast proliferation and terminal differentiation via up-regulating of the myogenic transcription factors Pax7, MyoD and Myogenin. The interesting thing was that HA-19 also suppressed protein degradation to prevent myotube atrophy by down-regulating negative growth factors, FoxO1, MuRF1 and Atrogin-1. The results were also supported by puromycin labelling and protein ubiquitination assays. These data revealed that HA-19 possessed a "dual effect" on inhibition of muscle atrophy. In disuse-induced muscle atrophy mice model, HA-19 treatment significantly increased the weights of bilateral tibialis anterior (TA), gastrocnemius (Gastroc.), quadriceps (Quad.), suggesting the effectiveness of HA-19 to remit disuse-induced muscle atrophy. Our finding demonstrated that HA-19 has a great potential as an inhibitor or lead compound for the anti-muscle atrophy drug discovery.

Design and synthesis of fluorescently labeled steroidal antiestrogens

A set of derivatives of 11β-(4-oxyphenyl)estradiol were prepared as potential fluorescent imaging agents for the evaluation of the estrogen receptor. The compounds were designed based on the established affinity and selectivity of 11β-[4-(dimethylethoxy)phenyl]estradiol (RU39411) as an estrogen receptor (ER) antagonist. The 5-(dimethylamino) naphathalene-1-sulfonyl (dansyl) and 7-nitrobenzo[c][1,2,5] oxadiaol-4-yl (NBD) moieties were selected based on their fluorescent and physicochemical properties. A convergent synthesis was developed that culminated in the [3 + 2] copper (I) assisted alkyne-azide cycloaddition coupling of the steroidal and fluorescent components. Good yields were obtained for the intermediates and final products, and the structural variations in the steroid component will permit evaluation of ER affinity and selectivity.

Review of fluorescent steroidal ligands for the estrogen receptor 1995-2018

The development of fluorescent ligands for the estrogen receptor (ER) continues to be of interest. Over the past 20 years, most efforts have focused on appending an expanding variety of fluorophores to the B-, C- and D-rings of the steroidal scaffold. This review highlights the synthesis and evaluation of derivatives substituted primarily at the 6-, 7α- and 17α-positions, culminating with our recent work on 11β-substituted estradiols, and proposes an approach to new fluorescent imaging agents that retain high ER affinity.

Novel fluorescent probes of 10-hydroxyevodiamine: autophagy and apoptosis-inducing anticancer mechanisms

Natural product evodiamine and its derivatives represent a promising class of multi-target antitumor agents. However, the clinical development of these compounds has been hampered by a poor understanding of their antitumor mechanisms. To tackle this obstacle, herein, novel fluorescent probes were designed to elucidate the antitumor mode of action of 10-hydroxyevodiamine. This compound was proven to be distributed in the mitochondria and lysosomes and to act by autophagy and apoptosis mechanisms.

Synthesis, Biological Evaluation of Fluorescent 23-Hydroxybetulinic Acid Probes, and Their Cellular Localization Studies

23-Hydroxybetulinic acid (23-HBA) is a complex lupane triterpenoid, which has attracted increasing attention as an anticancer agent. However, its detailed mechanism of anticancer action remains elusive so far. To reveal its anticancer mode of action, a series of fluorescent 23-HBA derivatives conjugated with coumarin dyes were designed, synthesized, and evaluated for their antiproliferative activities. Subcellular localization and uptake profile studies of representative fluorescent 23-HBA probe 26c were performed in B16F10 cells, and the results suggested that probe 26c was rapidly taken up into B10F10 cells in a dose-dependent manner and mitochondrion was the main site of its accumulation. Further mode of action studies implied that the mitochondrial pathway was involved in 23-HBA-mediated apoptosis. Together, our results provided new clues for revealing the molecular mechanism of natural product 23-HBA for its further development into an antitumor agent.

Probing the Anticancer Action of Oridonin with Fluorescent Analogues: Visualizing Subcellular Localization to Mitochondria

Oridonin (1) is a complex ent-kaurane diterpenoid exhibiting remarkable antitumor activity. However, the detailed mechanism or cellular target that underlies this activity has not yet been identified. Herein, we report an efficient approach for exploring the anticancer mechanism of oridonin through development of the potent fluorescent analogues. A series of novel fluorescent oridonin probes linked with coumarin moieties were designed, synthesized, and characterized. Fluorescence microscopy and confocal imaging studies suggested that fluorescent oridonin probe 17d was rapidly taken up into tumor cells and the mitochondrion was the main site of its accumulation. Moreover, we confirmed that cytochrome c played an important role in oridonin induced mitochondrion-mediated apoptosis and α,β-unsaturated ketone is the active moiety of oridonin, which is crucial to its uptake, localization, and cytotoxicity. Our results provide new insights on the molecular mechanism of oridonin and would be useful for its further development into an antitumor agent.