Semisynthesis and Non-Small-Cell Lung Cancer Cytotoxicity Evaluation of Germacrane-Type Sesquiterpene Lactones from Elephantopus scaber

The specialized sesquiterpenoids produced by the genus Elephantopus L.: Chemistry, biological activities and structure-activity relationship exploration

The genus Elephantopus L. is a valuable resource rich in sesquiterpenoids with structural diversity and various bioactivities, showing great potential for applications in medicinal field and biological industry. Up to now, over 129 sesquiterpenoids have been isolated and identified from this plant genus, including 114 germacrane-type, 7 guaianolide-type, 5 eudesmane-type, 1 elemanolide-type, and 2 bis-sesquiterpenoids. These sesquiterpenoids were reported to show a diverse range of pharmacological properties, including cytotoxic, anti-tumor, anti-inflammatory, antimicrobial, and antiprotozoal. Consequently, some of them were identified as active scaffolds in the design and development of drugs. Considering that there is currently no overview available that covers the sesquiterpenoids and their biological activities in the Elephantopus genus, this article aims to comprehensively review the chemical structures, biosynthetic pathways, pharmacological properties, and structure-activity relationship of sesquiterpenoids found in the Elephantopus genus, which will establish a theoretical framework that can guide further research and exploration of sesquiterpenoids from Elephantopus plants as promising therapeutic agents.

Triphenylphosphonium-linked derivative of hecogenin with enhanced antiproliferative activity: Design, synthesis, and biological evaluation

Hecogenin (HCG), a steroidal sapogenin, possesses good antitumor properties. However, the application of HCG for cancer treatment has been hindered primarily by its moderate potency. In this study, we incorporated triphenylphosphonium cation (TPP+) at the C-3 and C-12 positions through different lengths of alkyl chains to target mitochondria and enhance the efficacy and selectivity of the parent compound. Cytotoxicity screening revealed that most of the target compounds exhibited potent antiproliferative activity against five human cancer cell lines (MKN45, A549, HCT-116, MCF-7, and HepG2). Structure-activity relationship studies indicated that the TPP+ group significantly enhanced the antiproliferative potency of HCG. Among these compounds, 3c demonstrated remarkable potency against MKN45 cells with an IC50 value of 0.48 μM, significantly more effective than its parent compound HCG (IC50 > 100 μM). Further investigations into the mechanism of action revealed that 3c induced apoptosis of MKN45 cells through the mitochondrial pathway. In a zebrafish xenograft model, 3c inhibited the proliferation of MKN45 cells. Overall, these results suggest that 3c, with potent antiproliferative activity, may serve as a valuable scaffold for developing new antitumor agents.

Structurally diverse rearranged sesquiterpenoids, including a pair of rare tautomers, from the aerial parts of Daphne penicillata

Eight structurally diverse rearranged sesquiterpenoids, including seven undescribed sesquiterpenoids (1a/1b and 3-8) were obtained from the aerial parts of Daphne penicillata. 1a/1b, 3, 5 and 6 possess rare rearranged guaiane skeletons and 4 represents the first example of rearranged carotene sesquiterpenoids. Their structures and absolute configurations were determined by extensive spectroscopic analyses, NMR and ECD calculations. Interestingly, 1a and 1b were a pair of magical interconverting epimers that may interconvert by retro-aldol condensation. The mechanism of interconversion has been demonstrated indirectly by 9-OH derivatization of 1a/1b and a hypothetical biogenetic pathway was proposed. All compounds were evaluated for anti-inflammatory and cytotoxic activities. Among them, 1a/1b and 2 exhibited potential inhibitory activities on the production of NO against LPS-induced BV2 microglial cells.

Structurally diverse terpenoids from Elephantopus scaber L. and their acetylcholinesterase inhibitory activities

Three undescribed compounds elephantopuscabers A-C, along with one previously reported compound spirowallichiione, were isolated from Elephantopus scaber L. Their structures were determined via extensive NMR spectroscopic analysis, quantum chemical calculations, and single-crystal X-ray diffraction crystallography. A plausible biosynthetic pathway for spirowallichiione was proposed. All the isolated compounds were tested for their acetylcholinesterase inhibitory activities. Among them, elephantopuscaber B and C displayed promising inhibitory activities against AChE, and the binding sites were predicted by molecular docking.

Design, synthesis, and biological evaluation of artemyrianolide H derivatives as potential antihepatoma agents

Artemyrianolide H (AH) is a germacrene-type sesquiterpenolid isolated from Artemisia myriantha, and showed potent cytotoxicity against three human hepatocellular carcinoma cell lines HepG2, Huh7, and SK-Hep-1 with IC₅₀ values of 10.9, 7.2, and 11.9 µM, respectively. To reveal structure-activity relationship, 51 artemyrianolide H derivatives including 19 dimeric analogs were designed, synthesized, and assayed for their cytotoxicity against three human hepatoma cell lines. Among them, 34 compounds were more active than artemyrianolide H and sorafenib on the three cell lines. Especially, compound 25 exhibited the most promising activity with IC₅₀ values of 0.7 (HepG2), 0.6 (Huh7), and 1.3 µM (SK-Hep-1), which were 15.5, 12.0, and 9.2-fold higher than that of AH and 16.4, 16.3 and 17.5-fold higher than that of sorafenib. Cytotoxicity evaluation on normal human liver cell lines (THLE-2) demonstrated good safety profile of compound 25 with SI of 1.9 (HepG2), 2.2 (Huh 7) and 1.0 (SK-Hep1). Further studies revealed that compound 25 dose-dependently arrested cells at G2/M phase which was correlated with the up-regulation of both cyclin B1 and p-CDK1, and induced apoptosis through the activation of mitochondrial pathways in HepG2 cells. In addition, the migratory and invasive abilities in HepG2 cells after treatment with 1.5 μM of compound 25 were decreased by 89% and 86% with the increase of E-cadherin expression accompanied by the decrease of N-cadherin, vimentin expression. Bioinformatics analysis based on machine learning predicted that PDGFRA and MAP2K2 might be acting targets of compound 25, and SPR assays demonstrated compound 25 were bound with PDGFRA and MAP2K2 with K_D value of 0.168 nM, and 8.49 µM, respectively. This investigation proposed that compound 25 might be considered as a promising lead compound for the development of antihepatoma candidate.

Synthesis and Bioactivity Evaluation of Nepetaefolin F and Its Analogues

Nepetaefolin F (5), an abietane diterpenoid, showed significant inhibitory activity against human cancer cells in vitro with an IC₅₀ value of 6.3 μM. The syntheses of nepetaefolin F and its analogues are presented herein. The cytotoxicity against various cancer cell lines was evaluated; notably, the cyclopropanecarboxylate ester 42 displayed significant antitumor activity against MGC 803 cells with an IC₅₀ value of 20.9 μM. Further studies revealed that 42 could upregulate the expression of p62, microtubule-associated protein 1 light-chain 3 β (LC3 B-I), cleaved caspase-3, and cleaved caspase-9 and downregulate the expression of Beclin-1 and LC3B-II. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that 42 could modulate multiple signaling pathways, especially for peroxisome proliferator-activated receptor (PPAR) and AMP-activated protein kinase (AMPK), which are closely related to autophagy. These results suggested that compound 42 is a promising lead by inhibiting cell proliferation and autophagy, as inducing cell apoptosis in MGC 803 cells.

Identification of Crucial Polymethoxyflavones Tangeretin and 3,5,6,7,8,3′,4′-Heptamethoxyflavone and Evaluation of Their Contribution to Anticancer Effects of Pericarpium Citri Reticulatae ‘Chachi’ during Storage

Pericarpium Citri Reticulatae ‘Chachi’ (PCR-C), rich in polymethoxyflavones (PMFs), has potential anticancer bioactivity and its quality will be improved during storage. However, the main factors influencing the PCR-C quality during its storage remain unclear. In this study, multivariate analysis was performed to investigate free and bound PMFs of PCR-C during storage. The anticancer effects of purified PCR-C flavonoid extracts (PCR-CF) and the important PMFs were evaluated using A549 cells. The results showed that PCR-C samples exhibited remarkable differences in free PMFs during storage, which fell into three clusters: Cluster 1 included fresh (fresh peel) and PCR-C01 (year 1); Cluster 2 consisted of PCR-C03 (year 3) and PCR-C05 (year 5); and PCR-C10 (year 10) was Cluster 3. 3,5,6,7,8,3′,4′-heptamethoxyflavone, tangeretin, and isosinensetin were identified as the most important PMFs distinguishing the various types of PCR-C according to its storage periods. Moreover, PCR-CF inhibited A549 cell proliferation and induced cell cycle arrest at G2/M phase, cell apoptosis, and ROS accumulation, and all anticancer indices had an upward tendency during storage. Additionally, tangeretin and 3,5,6,7,8,3′,4′-heptamethoxyflavone exhibited anticancer effects on A549 cells, whereas isosinensetin displayed no anticancer effect, indicating that tangeretin and 3,5,6,7,8,3′,4′-heptamethoxyflavone jointly contributed to anticancer activity of PCR-C during storage. PCR-CF and the most important PMFs killed cancer cells (A549 cells) but had no cytotoxicity to normal lung fibroblast cells (MRC-5 cells). Overall, the high quality of long-term stored PCR-C might be due to the anticancer effects of tangeretin and 3,5,6,7,8,3′,4′-heptamethoxyflavone.