Combination of amino acid/dipeptide with ligustrazine-betulinic acid as antitumor agents

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.

A series of ligustrazine platinum(IV) complexes with potent anti-proliferative and anti-metastatic properties that exert chemotherapeutic and immunotherapeutic effects

The development of novel anticancer drugs with antiproliferative and antimetastatic activities is of great importance in the pharmaceutical field. Herein, a series of ligustrazine (LSZ) platinum(IV) complexes with chemotherapeutic and immunotherapeutic effects were designed, prepared and evaluated as antitumor agents for the first time. Complex 4 with potent antitumor activities both in vitro and in vivo was screened out as a candidate. Notably, it displays significantly more effective anti-metastatic activities than the platinum(II) drugs cisplatin and oxaliplatin. Mechanism detection discloses that it causes serious DNA damage and increases the expression of γ-H2AX and P53. Then, the apoptosis of tumor cells is promoted by activating the mitochondrial apoptotic pathway Bcl-2/Bax/caspase-3 and causing autophagy via modulating LC3-I/II and P62 expression. Furthermore, the immune therapeutic responses are significantly elevated by blocking HIF-1α, ERK 1/2 and COX-2 pathways to reduce PD-L1 expression, and further increasing CD3+ and CD8+ T cells to elevate T cell immunity in tumors. Tumor metastasis is blocked by the synergistic functions of DNA damage, hypoxia modulation and immune activation.

Anti-tumor effects of novel alkannin derivatives with potent selectivity on comprehensive analysis

BACKGROUND

Therapeutic approaches based on glycolysis and energy metabolism of tumor cells are new promising strategies for the treatment of cancer. Currently, researches on the inhibition of pyruvate kinase M2, a key rate limiting enzyme in glycolysis, have been corroborated as an effective cancer therapy. Alkannin is a potent pyruvate kinase M2 inhibitor. However, its non-selective cytotoxicity has affected its subsequent clinical application. Thus, it needs to be structurally modified to develop novel derivatives with high selectivity.

PURPOSE

Our study aimed to ameliorate the toxicity of alkannin through structural modification and elucidate the mechanism of the superior derivative 23 in lung cancer therapy.

METHODS

On the basis of the principle of collocation, different amino acids and oxygen-containing heterocycles were introduced into the hydroxyl group of the alkannin side chain. We examined the cell viability of all derivatives on three tumor cells (HepG2, A549 and HCT116) and two normal cells (L02 and MDCK) by MTT assay. Besides, the effect of derivative 23 on the morphology of A549 cells as observed by Giemsa and DAPI staining, respectively. Flow cytometry was performed to assess the effects of derivative 23 on apoptosis and cell cycle arrest. To further assess the effect of derivative 23 on the Pyruvate kinase M2 in glycolysis, an enzyme activity assay and western blot assay were performed. Finally, in vivo the antitumor activity and safety of the derivative 23 were evaluated by using Lewis mouse lung cancer xenograft model.

RESULTS

Twenty-three novel alkannin derivatives were designed and synthesized to improve the cytotoxicity selectivity. Among these derivatives, derivative 23 showed the highest cytotoxicity selectivity between cancer and normal cells. The anti-proliferative activity of derivative 23 on A549 cells (IC₅₀ = 1.67 ± 0.34 μM) was 10-fold higher than L02 cells (IC₅₀ = 16.77 ± 1.44 μM) and 5-fold higher than MDCK cells (IC₅₀ = 9.23 ± 0.29 μM) respectively. Subsequently, fluorescent staining and flow cytometric analysis showed that derivative 23 was able to induce apoptosis of A549 cells and arrest the cell cycle in the G0/G1 phase. In addition, the mechanistic studies suggested derivative 23 was an inhibitor of pyruvate kinase; it could regulate glycolysis by inhibiting the activation of the phosphorylation of PKM2/STAT3 signaling pathway. Furthermore, studies in vivo demonstrated derivative 23 significantly inhibited the growth of xenograft tumor.

CONCLUSION

In this study, alkannin selectivity is reported to be significantly improved following structural modification, and derivative 23 is first shown to be able to inhibit lung cancer growth via the PKM2/STAT3 phosphorylation signaling pathway in vitro, indicating the potential value of derivative 23 in treating lung cancer.

Conjugation as a Tool in Therapeutics: Role of Amino Acids/Peptides-Bioactive (Including Heterocycles) Hybrid Molecules in Treating Infectious Diseases

Peptide-based drugs are gaining significant momentum in the modern drug discovery, which is witnessed by the approval of new drugs by the FDA in recent years. On the other hand, small molecules-based drugs are an integral part of drug development since the past several decades. Peptide-containing drugs are placed between small molecules and the biologics. Both the peptides as well as the small molecules (mainly heterocycles) pose several drawbacks as therapeutics despite their success in curing many diseases. This gap may be bridged by utilising the so called 'conjugation chemistry', in which both the partners are linked to one another through a stable chemical bond, and the resulting conjugates are found to possess attracting benefits, thus eliminating the stigma associated with the individual partners. Over the past decades, the field of molecular hybridisation has emerged to afford us new and efficient molecular architectures that have shown high promise in medicinal chemistry. Taking advantage of this and also considering our experience in this field, we present herein a review concerning the molecules obtained by the conjugation of peptides (amino acids) to small molecules (heterocycles as well as bioactive compounds). More than 125 examples of the conjugates citing nearly 100 references published during the period 2000 to 2022 having therapeutic applications in curing infectious diseases have been covered.

Design and synthesis of novel anti-multidrug-resistant staphylococcus aureus derivatives of glycyrrhetinic acid by blocking arginine biosynthesis, metabolic and H2S biogenesis

With the soaring number of multidrug-resistant bacteria, it is imperative to develop novel efficient antibacterial agents and discovery new antibacterial pathways. Herein, we designed and synthesized a series of structurally novel glycyrrhetinic acid (GA) derivatives against multidrug-resistant Staphylococcus aureus (MRSA). The in vitro antibacterial activity of these compounds was evaluated using the microbroth dilution method, agar plate coating experiments and real-time growth curves, respectively. Most of the target derivatives showed moderate antibacterial activity against Staphylococcus aureus (S. aureus) and MRSA (MIC = 3.125-25 μM), but inactivity against Escherichia coli (E. Coli) and Pseudomonas aeruginosa (P. aeruginosa) (MIC > 200 μM). Among them, compound 11 had the strongest antibacterial activity against MRSA, with an MIC value of 3.125 μM, which was 32 times and 64 times than the first-line antibiotics penicillin and norfloxacin, respectively. Additionally, transcriptomic (RNA-seq) and quantitative polymerase chain reaction (qPCR) analysis revealed that the antibacterial mechanism of compound 11 was through blocking the arginine biosynthesis and metabolic and the H₂S biogenesis. Importantly, compound 11 was confirmed to have good biocompatibility through the in vitro hemolysis tests, cytotoxicity assays and the in vivo quail chicken chorioallantoic membrane (qCAM) experiments. Current study provided new potential antibacterial candidates from glycyrrhetinic acid derivatives for clinical treatment of MRSA infections.

Design, synthesis and cytotoxic evaluation of novel betulonic acid-diazine derivatives as potential antitumor agents

With the purpose to improve antiproliferative activity, 26 new betulonic acid-diazine derivatives were designed and synthesized from betulinic acid. The anticancer activity of these semi-synthetic compounds was evaluated by MTT assay in both tumor cell lines and normal cell line. The results indicated that majority of new compounds exhibited improved antitumor activity compared with the parent compound betulonic acid. Compound BoA2C, in particular, had the most significant action with IC50 value of 3.39 μM against MCF-7 cells, while it showed lower cytotoxicity on MDCK cell line than cisplatin. Furthermore, we discovered that BoA2C strongly increased MCF-7 cell damage mostly by influencing arginine and fatty acid metabolism. In addition, the structure-activity relationships were briefly discussed. The results of this study suggested that the introduction of different diazines at C-28 could selectively inhibit different kinds of cancer cells and might be an effective way to synthesize potent anticancer lead compound from betulonic acid.

Synthesis and Discovery of Ligustrazine–Heterocycle Derivatives as Antitumor Agents

Ligustrazine (TMP) is a natural pyrazine alkaloid extracted from the roots of Ligusticum Chuanxiong Hort, which has the potential as an antitumor agent. A series of 33 ligustrazine–heterocycle (TMPH) derivatives were designed, synthesized, and investigated via antitumor screening assays, molecular docking analysis, and prediction of drug-like properties. TMP was attached to other heterocyclic derivatives by an 8–12 methylene alkyl chain as a linker to obtain 33 TMPH derivatives. The structures were confirmed by ¹H-NMR, ¹³C-NMR, and high-resolution mass spectroscopy spectral (HR-MS) data. The antiproliferative activity against human breast cancer MCF-7, MDA-MB-231, mouse breast cancer 4T1, mouse fibroblast L929, and human umbilical vein endothelial HUVEC cell lines was evaluated by MTT assay. Compound 12–9 displayed significant inhibitory activity with IC₅₀ values in the low micromolar range (0.84 ± 0.02 µM against the MDA-MB-231 cell line). The antitumor effects of compound 12–9 were further evaluated by plate cloning, Hoechst 33 342 staining, and annexin V-FITC/PI staining. The results indicated that compound 12–9 inhibited the proliferation and apoptosis of breast cancer cells. Furthermore, molecular docking of compound 12–9 into the active site of the Bcl-2, CASP-3, and PSMB5 target proteins was performed to explore the probable binding mode. The 33 newly synthesized compounds were predicted to have good drug-like properties in a theoretical study. Overall, these results indicated that compound 12–9 inhibited cell proliferation through PSMB5 and apoptosis through Bcl-2/CASP-3 apoptotic signaling pathways and had good drug-like properties. These results provided more information, and key precursor lead derivatives, in the search for effective bioactive components from Chinese natural medicines.

Natural inspired ligustrazine-based SLC-0111 analogues as novel carbonic anhydrase inhibitors

Ligustrazine is the principle bioactive alkaloid in the widely-used Chinese herb Chuan Xiong rhizome. Herein, a series of novel derivatives has been designed as human carbonic anhydrases inhibitors (hCAIs) starting from the natural product Ligustrazine inserted as a tail instead of the 4-fluorophenyl tail of SLC-0111, a front-runner selective hCA IX inhibitor currently in clinical trials as antitumor/antimetastatic agent. Other derivatives were designed via incorporation of different linkers, of amide and ester type, or incorporation of different zinc anchoring groups such as secondary sulfamoyl and carboxylic acid functionalities. The newly designed molecules were prepared following different synthetic pathways, and were assessed for their inhibitory actions against four isoforms: the widespread cytosolic (hCA I and II), and the transmembrane tumor-related (hCA IX and XII). The primary sulfonamides efficiently inhibited the target hCA IX and hCA XII in the nanomolar range (K_Is: 6.2-951.5 nM and 3.3-869.3 nM, respectively). The most selective hCA IX inhibitors 6c and 18 were assessed for their potential anticancer effects, and displayed anti-proliferative activity against MCF-7 cancer cell line with IC₅₀s of 11.9 and 36.7 μM, respectively. Molecular modelling studies unveiled the relationship between structural features and inhibitory profiles against the off-target hCA II and the target, tumor-related isoforms hCA IX and XII.

Tetramethylpyrazine: A Review of Its Antitumor Potential and Mechanisms

Cancer remains a major public health threat. The mitigation of the associated morbidity and mortality remains a major research focus. From a molecular biological perspective, cancer is defined as uncontrolled cell division and abnormal cell growth caused by various gene mutations. Therefore, there remains an urgent need to develop safe and effective antitumor drugs. The antitumor effect of plant extracts, which are characterized by relatively low toxicity and adverse effect, has attracted significant attention. For example, increasing attention has been paid to the antitumor effects of tetramethylpyrazine (TMP), the active component of the Chinese medicine Chuanqiong, which can affect tumor cell proliferation, apoptosis, invasion, metastasis, and angiogenesis, as well as reverse chemotherapeutic resistance in neoplasms, thereby triggering antitumor effects. Moreover, TMP can be used in combination with chemotherapeutic agents to enhance their effects and reduce the side effect associated with chemotherapy. Herein, we review the antitumor effects of TMP to provide a theoretical basis and foundation for the further exploration of its underlying antitumor mechanisms and promoting its clinical application.

Recent progress on betulinic acid and its derivatives as antitumor agents: a mini review

Natural products are one of the important sources for the discovery of new drugs. Betulinic acid (BA), a pentacyclic triterpenoid widely distributed in the plant kingdom, exhibits powerful biological effects, including antitumor activity against various types of cancer cells. A considerable number of BA derivatives have been designed and prepared to remove their disadvantages, such as poor water solubility and low bioavailability. This review summarizes the current studies of the structural diversity of antitumor BA derivatives within the last five years, which provides prospects for further research on the structural modification of betulinic acid.

Novel Anthraquinone Compounds Inhibit Colon Cancer Cell Proliferation via the Reactive Oxygen Species/JNK Pathway

A series of amide anthraquinone derivatives, an important component of some traditional Chinese medicines, were structurally modified and the resulting antitumor activities were evaluated. The compounds showed potent anti-proliferative activities against eight human cancer cell lines, with no noticeable cytotoxicity towards normal cells. Among the candidate compounds, 1-nitro-2-acyl anthraquinone-leucine (8a) showed the greatest inhibition of HCT116 cell activity with an IC₅₀ of 17.80 μg/mL. In addition, a correlation model was established in a three-dimensional quantitative structure-activity relationship (3D-QSAR) study using Comparative Molecular Field Analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA). Moreover, compound 8a effectively killed tumor cells by reactive oxygen species (ROS)-JNK activation, causing an increase in ROS levels, JNK phosphorylation, and mitochondrial stress. Cytochrome c was then released into cytoplasm, which, in turn activated the cysteine protease pathway and ultimately induced tumor cell apoptosis, suggesting a potential use of this compound for colon cancer treatment.

High-pressure studies on l,l-dileucine crystals by Raman spectroscopy and synchrotron X-ray diffraction combined with DFT calculations

The vibrational properties of the dipeptide l-leucyl-l-leucine hydrate were investigated through Raman and infrared spectroscopy. With the aid of first principle calculations using the density functional theory, the assignment of the vibrational modes from the material was furnished. In addition, the behavior of the crystal under high pressure was investigated using Raman spectroscopy (~8 GPa) and synchrotron X-ray diffraction (~26 GPa). The results show significant changes in both the X-ray diffractogram and the Raman spectra, suggesting that l-leucyl-l-leucine hydrate undergoes a phase transition between 2.3 and 2.9 GPa. Finally, for pressures above 16 GPa the broadening of X-ray peaks suggests a disorder in the crystal lattice induced by high-pressure effects.

Design, Synthesis and Biological Evaluation of New HDAC1 and HDAC2 Inhibitors Endowed with Ligustrazine as a Novel Cap Moiety

Introduction

Histone deacetylases (HDACs) represent one of the most validated cancer targets. The inhibition of HDACs has been proven to be a successful strategy for the development of novel anticancer candidates.

Methods

This work describes design and synthesis of a new set of HDAC inhibitors (7a-c and 8a, b) utilizing ligustrazine as a novel cap moiety, and achieving the pharmacophoric features required to induce the desired inhibition.

Results

The newly synthesized derivatives were evaluated for their potential inhibitory activity toward two class I histone deacetylases, namely HDAC1 and HDAC2. The tested ligustrazine-based compounds were more potent toward HDAC2 (IC₅₀ range: 53.7–205.4 nM) than HDAC1 (IC₅₀ range: 114.3–2434.7 nM). Furthermore, the antiproliferative activities against two HDAC-expressing cancer cell lines; HT-29 and SH-SY5Y were examined by the MTT assay. Moreover, a molecular docking study of the designed HDAC inhibitors (7a-c and 8a,b) was carried out to investigate their binding pattern within their prospective targets; HDAC1 (PDB-ID: 4BKX) and HDAC2 (PDB-ID: 6G3O).

Discussion

Compound 7a was found to be the most potent analog in this study toward HDAC1 and HDAC2 with IC₅₀ values equal 114.3 and 53.7 nM, respectively. Moreover, it was the most effective counterpart (IC₅₀ = 1.60 µM), with 4.7-fold enhanced efficiency than reference drug Gefitinib (IC₅₀ = 7.63 µM) against SH-SY5Y cells. Whereas, compound 8a (IC₅₀ = 1.96 µM) was the most active member toward HT-29 cells, being 2.5-times more potent than Gefitinib (IC₅₀ = 4.99 µM). Collectively, these results suggest that 7a merits further optimization and development as an effective new HDACI lead compound.

Novel Homo-Bivalent and Polyvalent Compounds Based on Ligustrazine and Heterocyclic Ring as Anticancer Agents

Bivalent and polyvalent inhibitors can be used as antitumor agents. In this experiment, eight ligustrazine dimers and seven ligustrazine tetramers linked by alkane diamine with different lengths of carbon chain lengths were synthesized. After screening their antiproliferation activities against five cancer cell lines, most ligustrazine derivatives showed better cytotoxicity than the ligustrazine monomer. In particular, ligustrazine dimer 8e linked with decane-1,10-diamine exhibited the highest cytotoxicity in FaDu cells with an IC50 (50% inhibiting concentration) value of 1.36 nM. Further mechanism studies suggested that 8e could induce apoptosis of FaDu cells through the depolarization of mitochondrial membrane potential and S-phase cell cycle arrest. Inspired by these results, twenty-seven additional small molecule heterocyclic dimers linked with decane-1,10-diamine and nine cinnamic acid dimers bearing ether chain were synthesized and screened. Most monocyclic and bicyclic aromatic systems showed highly selective anti-proliferation activity to FaDu cells and low toxicity to normal MCF 10A cells. The structure-activity relationship revealed that the two terminal amide bonds and the alkyl linker with a chain length of 8-12 carbon were two important factors to maintain its antitumor activity. In addition, the ADMET calculation predicted that most of the potent compounds had good oral bioavailability.

Conjugation of Ginsenoside with Dietary Amino Acids: A Promising Strategy To Suppress Cell Proliferation and Induce Apoptosis in Activated Hepatic Stellate Cells

Ginseng has been widely used as a functional food in the world because of its well-defined health benefits. Previous studies have confirmed that AD-1, a new ginsenoside derived from ginseng, can ameliorate thioacetamide-induced liver injury and fibrosis in mice. Simultaneously, amino acid supplementation is getting more attention as an important adjuvant therapy in the improvement of hepatopathy. The aim of this study was to conjugate AD-1 with several selected amino acids and investigate the cytotoxicity of the obtained conjugates in activated t-HSC/Cl-6 cells and normal human liver cells (LO2). Structure-activity relationships of conjugates and underlying mechanisms of the effect are also explored. The results indicated that conjugate 7c remarkably inhibited cell proliferation in activated t-HSC/Cl-6 cells (IC₅₀ = 3.8 ± 0.4 μM) and appeared to be nontoxic to LO2. Besides, conjugate 7c had a relatively good plasma stability. Further study demonstrated that inducing S-phase arrest and activation of mitochondrial-mediated apoptosis were included in the mechanisms underlying the efficiency of conjugate 7c. These findings provided further insight into designing functional foods (ginsenoside and amino acid) for the application in prevention or improvement of liver fibrosis.

BA-12 Inhibits Angiogenesis via Glutathione Metabolism Activation

There is a need for an efficient and low-cost leading compound discovery mode. However, drug development remains slow, expensive, and risky. Here, this manuscript proposes a leading compound discovery strategy based on a combination of traditional Chinese medicine (TCM) formulae and pharmacochemistry, using a ligustrazine-betulinic acid derivative (BA-12) in the treatment of angiogenesis as an example. Blocking angiogenesis to inhibit the growth and metastasis of solid tumors is currently one recognized therapy for cancer in the clinic. Firstly, based on a traditional Prunella vulgaris plaster, BA-12 was synthesized according to our previous study, as it exhibited better antitumor activities than other derivatives on human bladder carcinoma cells (T24); it was then uploaded for target prediction. Secondly, the efficacy and biotoxicity of BA-12 on angiogenesis were evaluated using human umbilical vein endothelial cells (HUVECs), a quail chick chorioallantoic membrane, and Caenorhabditis elegans. According to the prediction results, the main mechanisms of BA-12 were metabolic pathways. Thus, multiple metabolomics approaches were applied to reveal the mechanisms of BA-12. Finally, the predictive mechanisms of BA-12 on glutathione metabolism and glycerophospholipid metabolism activation were validated using targeted metabolomics and pharmacological assays. This strategy may provide a reference for highly efficient drug discovery, with the aim of sharing TCM wisdom for unmet clinical needs.

Antimicrobial activity of Mimosa caesalpiniifolia Benth and its interaction with antibiotics against Staphylococcus aureus strains overexpressing efflux pump genes

This study aimed to evaluate the antimicrobial activity of the dichloromethane fraction (DCMF) from the stem bark of Mimosa caesalpiniifolia and its effect on the activity of conventional antibiotics against Staphylococcus aureus strains overexpressing specific efflux pump genes. DCMF showed activity against S. aureus, Staphylococcus epidermidis and Candida albicans. Addition of DCMF at subinhibitory concentrations to the growth media enhanced the activity of norfloxacin, ciprofloxacin and ethidium bromide against S. aureus strains overexpressing norA suggesting the presence of efflux pump inhibitors in its composition. Similar results were verified for tetracycline against S. aureus overexpressing tetK, as well as, for ethidium bromide against S. aureus overexpressing qacC. These results indicate that M. caesalpiniifolia is a source of molecules able to modulate the fluoroquinolone- and tetracycline-resistance in S. aureus probably by inhibition of NorA, TetK and QacC respectively. SIGNIFICANCE AND IMPACT OF THE STUDY: Drug resistance is a common problem in patients with infectious diseases. Dichloromethane fraction from the stem bark of Mimosa caesalpiniifolia showed antimicrobial activity against Gram-positive bacterium Staphylococcus aureus and against Candida albicans, but did not show activity against Gram-negative specie Escherichia coli. Moreover, this fraction was able to potentiate the action of norfloxacin, ciprofloxacin and tetracycline against S. aureus strains overexpressing different efflux pump genes. Thus, Mimosa caesalpiniifolia is a source of efflux pump inhibitors which could be used in combination with fluoroquinolones or tetracycline in the treatment of infectious diseases caused by S. aureus strains overexpressing efflux pump genes.

[Design and synthesis of imidazo-fused heterocycles derivatives and their anti-tumor activity against breast cancer in mice]

OBJECTIVE

To synthesize compounds based on imidazo-fused heterocycles and evaluate their anti-tumor activity against breast cancer.

METHODS

The compounds 1a-1e, 2a and 2b were synthesized by aerobic copper-catalyzed halocyclization of methyl N-heteroaromatics with aliphatic amines; 3a and 3b were generated by sonogashira reaction and Suzuki reaction, respectively; the compounds 4a-4c were obtained by Buchwald-Hartwig reaction of the corresponding amines and 1e. The effects of these compounds against breast cancer cells and their nephrotoxicity were determined using MTT assay. Annexin VFITC/PI apoptosis detection kit was used to assess the apoptosis-inducing effects of these compounds in breast cancer cells. With normal saline as the control, the safety and anti-tumor activity of the compound 2a (daily dose of 10 mg/kg for 14 days) was tested in a mouse model bearing human breast cancer xenografts.

RESULTS

The compounds 2a, 4a, 4b and 4c all showed obvious anti-tumor activities. Among these compounds, 2a showed the most potent anti-tumor effect against breast cancer cells with an IC₅₀ of 9.77 ± 2.32 μmol/L, similar to that of cisplatin (IC₅₀=8.96 ± 2.35 μmol/L); 2a also showed a slightly lower nephrotoxicity than cisplatin, and their CC₅₀ was 10.79±0.87 μmol/L and 8.45±0.68 μmol/L, respectively. 2a obviously promoted apoptosis of breast cancer cells in vitro and caused a moderate suppression of the breast cancer growth in the tumor-bearing mouse models without producing serious adverse effects.

CONCLUSIONS

Four compounds synthesized based on imidazo-fused heterocycles have anti-tumor activities against breast cancer. The compound 2a is capable of dose-dependently promoting apoptosis of breast cancer cells in vitro and has a good safety and a moderate efficacy for suppressing tumor growth in mouse models bearing human breast cancer xenografts.

Recent Developments in the Functionalization of Betulinic Acid and Its Natural Analogues: A Route to New Bioactive Compounds

Betulinic acid (BA) and its natural analogues betulin (BN), betulonic (BoA), and 23-hydroxybetulinic (HBA) acids are lupane-type pentacyclic triterpenoids. They are present in many plants and display important biological activities. This review focuses on the chemical transformations used to functionalize BA/BN/BoA/HBA in order to obtain new derivatives with improved biological activity, covering the period since 2013 to 2018. It is divided by the main chemical transformations reported in the literature, including amination, esterification, alkylation, sulfonation, copper(I)-catalyzed alkyne-azide cycloaddition, palladium-catalyzed cross-coupling, hydroxylation, and aldol condensation reactions. In addition, the synthesis of heterocycle-fused BA/HBA derivatives and polymer‒BA conjugates are also addressed. The new derivatives are mainly used as antitumor agents, but there are other biological applications such as antimalarial activity, drug delivery, bioimaging, among others.

Design, Synthesis, and Cytotoxic Analysis of Novel Hederagenin⁻Pyrazine Derivatives Based on Partial Least Squares Discriminant Analysis

Hederagenin (He) is a novel triterpene template for the development of new antitumor compounds. In this study, 26 new He–pyrazine derivatives were synthetized in an attempt to develop potent antitumor agents; they were screened for in vitro cytotoxicity against tumor and non-tumor cell lines. The majority of these derivatives showed much stronger cytotoxic activity than He. Remarkably, the most potent was compound 9 (half maximal inhibitory concentration (IC₅₀) was 3.45 ± 0.59 μM), which exhibited similar antitumor activities against A549 (human non-small-cell lung cancer) as the positive drug cisplatin (DDP; IC₅₀ was 3.85 ± 0.63 μM), while it showed lower cytotoxicity on H9c2 (murine heart myoblast; IC₅₀ was 16.69 ± 0.12 μM) cell lines. Compound 9 could induce the early apoptosis and evoke cell-cycle arrest at the synthesis (S) phase of A549 cells. Impressively, we innovatively introduced the method of cluster analysis modeled as partial least squares discriminant analysis (PLS-DA) into the structure–activity relationship (SAR) evaluation, and SAR confirmed that pyrazine had a profound effect on the antitumor activity of He. The present studies highlight the importance of pyrazine derivatives of He in the discovery and development of novel antitumor agents.

Recent progress in the structural modification and pharmacological activities of ligustrazine derivatives

Ligustrazine is a main active fraction of the traditional medicine known as Ligusticum chuanxiong hort, which has been used as clinical medication for cerebral thrombosis, coronary heart disease and stenocardia recently. The rapid metabolism and short half-life of ligustrazine seriously limits its application in clinical practice. Therefore, derivatives of ligustrazine are designed and synthesized in our and other labs, including piperazine, cinnamic acid, styrene, acylguanidine, amides, curcumin and triterpenes derivatives of ligustrazine. Most of these compounds present better pharmacodynamics activities and more favorable pharmacokinetic properties compared to the parent compound. Besides, some new biological activities of these compounds are discovered. Hence, this review continues the previous review of our group as well as aims to highlight recent prominent advances in this field in the past ten years.

Oleanolic Acid-amino Acids Derivatives: Design, Synthesis, and Hepatoprotective Evaluation In Vitro and In Vivo

Activated hepatic stellate cells (HSCs) are the main extracellular matrix (ECM)-producing cells in the injured liver and the key mediators of liver fibrosis; they also promote the progression of hepatocellular carcinoma (HCC). In the acidic extracellular microenvironment of HCC, HSCs are activated to promote the migration of HCC cells. It is worth attempting to alter the weak acidic microenvironment to promote activated HSC apoptosis to treat liver fibrosis and liver cancer. In the present study, a series of novel OA-amino acids analogues were designed and synthesized to introduce different amino acids in the 3-hydroxyl of OA using the ester condensation reaction to enhance hydrophilicity, alkalinity, and biological activity. We found that OA-lysine derivative (3g) could improve the hydrophilic of OA and induce HSCs apoptosis via inducing MMP depolarization and increasing intracellular Ca2+ levels. Additionally, 3g displayed a better hepatoprotective effect than OA (20 mg/kg, intragastric administration) against the acute liver injury induced by carbon tetrachloride (CCl₄) in mice. The results suggested that basic amino acids (lysine) could effectively enhance OA's hydrophilicity, alkalinity, and hepatoprotective activity in vitro and in vivo, which might be likely associated with increasing bioavailability and altering an extracellular weak acidic microenvironment with further verification. Therefore, the OA-lysine derivative (3g) has the potential to be developed as an agent with hepatoprotective activity.