Chemical Constituents of Anneslea fragrans and Their Antiausterity Activity against the PANC-1 Human Pancreatic Cancer Cell Line

Structural variety and pharmacological potential of naphthylisoquinoline alkaloids

Naphthylisoquinoline alkaloids are a fascinating class of natural biaryl compounds. They show characteristic mono- and dimeric scaffolds, with chiral axes and stereogenic centers. Since the appearance of the last comprehensive overview on these secondary plant metabolites in this series in 1995, the number of discovered representatives has tremendously increased to more than 280 examples known today. Many novel-type compounds have meanwhile been discovered, among them naphthylisoquinoline-related follow-up products like e.g., the first seco-type (i.e., ring-opened) and ring-contracted analogues. As highlighted in this review, the knowledge on the broad structural chemodiversity of naphthylisoquinoline alkaloids has been decisively driven forward by extensive phytochemical studies on the metabolite pattern of Ancistrocladus abbreviatus from Coastal West Africa, which is a particularly "creative" plant. These investigations furnished a considerable number of more than 80-mostly new-natural products from this single species, with promising antiplasmodial activities and with pronounced cytotoxic effects against human leukemia, pancreatic, cervical, and breast cancer cells. Another unique feature of naphthylisoquinoline alkaloids is their unprecedented biosynthetic origin from polyketidic precursors and not, as usual for isoquinoline alkaloids, from aromatic amino acids-a striking example of biosynthetic convergence in nature. Furthermore, remarkable botanical results are presented on the natural producers of naphthylisoquinoline alkaloids, the paleotropical Dioncophyllaceae and Ancistrocladaceae lianas, including first investigations on the chemoecological role of these plant metabolites and their storage and accumulation in particular plant organs.

Discovery and Mechanistic Studies of Dual-Target Hits for Carbonic Anhydrase IX and VEGFR-2 as Potential Agents for Solid Tumors: X-ray, In Vitro, In Vivo, and In Silico Investigations of Coumarin-Based Thiazoles

A dual-targeting approach is predicted to yield better cancer therapy outcomes. Consequently, a series of coumarin-based thiazoles (5a-h, 6, and 7a-e) were designed and constructed as potential carbonic anhydrase (CA) and VEGFR-2 suppressors. The inhibitory actions of the target compounds were assessed against CA isoforms IX and VEGFR-2. The assay results showed that coumarin-based thiazoles 5a, 5d, and 5e can effectively inhibit both targets. 5a, 5d, and 5e cytotoxic effects were tested on pancreatic, breast, and prostate cancer cells (PANC1, MCF7, and PC3). Further mechanistic investigation disclosed the ability of 5e to interrupt the PANC1 cell progression in the S stage by triggering the apoptotic cascade, as seen by increased levels of caspases 3, 9, and BAX, alongside the Bcl-2 decline. Moreover, the in vivo efficacy of compound 5e as an antitumor agent was evaluated. Also, molecular docking and dynamics displayed distinctive interactions between 5e and CA IX and VEGFR-2 binding pockets.

Phytochemicals from Anneslea fragrans Wall. and Their Hepatoprotective and Anti-Inflammatory Activities

Anneslea fragrans Wall., popularly known as "Pangpo tea", is an edible, medicinal, and ornamental plant of the Family Theaceae. The leaves of A. fragrans were historically applied for the treatment of liver and intestinal inflammatory diseases in China. This study aimed to explore the hepatoprotective agents from A. fragrans leaves through hepatoprotective and anti-inflammatory assessment. The phytochemical investigation of the leaves of A. fragrans resulted in the isolation and identification of a total of 18 chemical compounds, including triterpenoids, aliphatic alcohol, dihydrochalcones, chalcones, flavanols, phenolic glycoside, and lignans. Compounds 1-2, 4-6, 11-12, and 16-18 were identified from A. fragrans for the first time. Compounds 7 and 14 could significantly alleviate hepatocellular damage by decreasing the contents of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and inhibit the hepatocellular apoptosis in the HepG2 cells induced by N-acetyl-p-aminophenol (APAP). In addition, compounds 7 and 14 inhibited reactive oxygen species (ROS) and malondialdehyde (MDA) contents and increased the catalase (CAT) superoxide dismutase (SOD), and glutathione (GSH) levels for suppressing APAP-induced oxidative stress. Additionally, compounds 7, 13, and 14 also had significant anti-inflammatory effects by inhibiting interleukin-6 (IL-6), interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) productions on LPS-induced RAW246.7 cells.

Influence of Ultra-High-Pressure Pretreatment Method on Chemical Constituents, Antioxidant and Cytoprotective Activities of Free, Esterified, and Bound Phenolics from Anneslea Fragrans Wall. Leaves

Anneslea fragrans Wall., an edible and medicinal plant, is traditionally used to treat liver and gastrointestinal diseases. This paper aimed to investigate the influence of ultra-high pressure (UHP) pretreatment on the phenolics profiling, antioxidant, and cytoprotective activities of free (FP), esterified (EP), and bound (BP) phenolics from A. fragrans leaves. A total of 32 compounds were characterized and quantified. The davidigenin (44.46 and 113.37 mg/g extract) was the highest in A. fragrans leaves. The vitexin (9), afzelin (10), coreopsin (15), and davidigenin (28) were analyzed with MS² fragment pathways. Results showed that UHP treated A. fragrans leaves had higher total phenolic (TPC) and total flavonoid (TFC) contents of FP, EP, and BP fractions than those in the raw leaves. Moreover, UHP pretreated A. fragrans leaves had higher scavenging activities on DPPH⁺• and ABTS⁺•, and inhibitory effects on the intracellular ROS generation in H₂O₂-induced HepG2 cells. UFP showed the highest inhibition of ROS production among the samples. Therefore, UHP pretreatment method might be used as an effective strategy for elevating the availabilities of A. fragrans leaves to develop functional foods.

Targeting Pancreatic Cancer with Novel Plumbagin Derivatives: Design, Synthesis, Molecular Mechanism, In Vitro and In Vivo Evaluation

Pancreatic tumors grow in an "austerity" tumor microenvironment characterized by nutrient deprivation and hypoxia. This leads to the activation of adaptive pathways in pancreatic cancer cells, promoting tolerance to nutrition starvation and aggressive malignancy. Conventional anticancer drugs are often ineffective against tumors that grow in such austerity condition. Plumbagin, a plant-derived naphthoquinone, has shown potent preferential cytotoxicity against pancreatic cancer cells under nutrient-deprived conditions. Therefore, we synthesized a series of plumbagin derivatives and found that 2-(cyclohexylmethyl)-plumbagin (3f) was the most promising compound with a PC₅₀ value of 0.11 μM. Mechanistically, 3f was found to inhibit the PI3K/Akt/mTOR signaling pathways, leading to cancer cell death under nutrient-deprived conditions. In vivo studies using pancreatic cancer xenograft mouse models confirmed the efficacy of 3f, demonstrating significant inhibition of tumor growth in a dose-dependent manner. Compound 3f represents a highly promising lead for anticancer drug development based on an antiausterity strategy.

Antiproliferative potential of Physalis peruviana-derived magnolin against pancreatic cancer: a comprehensive in vitro and in silico study

Physalis peruviana L. is a common edible fruit in Egypt and other regional countries.

Structure-activity relationship and mechanistic study on guggulsterone derivatives; Discovery of new anti-pancreatic cancer candidate

Pancreatic cancer is one of the deadliest types of malignancies. A new intervention aiming to combat pancreatic cancer is targeting its extra-ordinary ability to tolerate nutrition starvation, a phenomenon known as "Austerity". As a part of a research program aiming to develop a new-generation of anticancer agents, known as "anti-austerity agents", guggulsterone derivatives (GSDs) were identified as unique anti-austerity agents in terms of potency and selectivity. These agents are able to exert preferential cytotoxic activity only under nutrient-deprived conditions with little or no toxicity under normal conditions. In the present study, a library of 14 GSDs was synthesized and screened against PANC-1 human pancreatic cells. Among tested compounds, GSD-11 showed the most potent activity with PC₅₀ a value of 0.72 μM. It also inhibited pancreatic cancer cell migration and colony formation in a concentration-dependent manner. A mechanistic study revealed that this compound can inhibit the activation of the Akt/mTOR signaling pathway. Therefore, GSD-11 could be a promising lead compound for the anticancer drug discovery against pancreatic cancer.

A pharmacognostic approach for mitigating pancreatic cancer: emphasis on herbal extracts and phytoconstituents

Background

Pancreatic cancer is studied as one of the most lethal cancers with currently no control of its lethality, mainly due to its late diagnosis and lack of foolproof treatment processes. Despite continuous efforts being made in looking for therapies to deal with cancer, it keeps on being a labyrinth for the researchers. Efforts like discovering new treatment options, repurposing existing drugs, are continuously made to deal with this cancer.

Main body

With the urge to get answers and the fact that nature has all roots of therapeutics, efforts are made in the direction of finding those answers for providing ministrations for pancreatic cancer from plant products. Plant products are used as treatment options either directly in the form of extracts or an alternative to them is individual phytochemicals that are either isolated from the plants or are commercially synthesized for various purposes. In this review, we put forward such pharmacognostic initiatives made in combating pancreatic cancer, focusing mainly on plant extracts and various phytochemicals; along with the mechanisms which they triggered to fulfill the need for cytotoxicity to pancreatic cancer cells (in vitro and in vivo).

Conclusion

This study will thus provide insights into new combination therapy that can be used and also give a clue on which plant product and phytoconstituent can be used in dealing with pancreatic cancer.

Graphical abstract

Anneslea fragrans Wall. ameliorates ulcerative colitis via inhibiting NF-κB and MAPK activation and mediating intestinal barrier integrity

ETHNOPHARMACOLOGICAL RELEVANCE

Anneslea fragrans Wall. is traditionally used as a folk medicine in treating indigestion, fever, dysentery, diarrhea, and liver inflammation in China, Vietnam and Cambodia. However, its anti-inflammatory activity and mechanism under a safety therapeutic dose as well as the main chemical components have not yet been fully investigated.

AIM OF THE STUDY

This study aimed to explore the therapeutic effect and possible molecular mechanisms of aqueous-methanol extract (AFE) of A. fragrans leaves on dextran sodium sulfate (DSS)-induced ulcerative colitis (UC) mice and illustrate its potent anti-inflammatory chemical compounds.

MATERIALS AND METHODS

The AFE was obtained and then analyzed by high performance liquid chromatography (HPLC). Phytochemical investigation on the AFE was carried out to isolate and characterize its major components. The acute toxicity test was performed to provide the safety information of AFE. Subsequently, the protective effect of AFE on DSS-induced UC was evaluated by physiological changes, histopathological and immunohistochemical analysis, and the expressions of antioxidant enzyme, pro-inflammatory cytokines and anti-inflammatory cytokines. The expressions of target proteins in nuclear factor-kappa B (NF-κB) and mitogen-activated protein kinase (MAPK) were determined by western blot analysis. The tight junction (TJ) proteins in colon tissue were performed by immunohistochemical technique for evaluating the intestinal barrier integrity.

RESULTS

HPLC guided isolation of AFE resulted into two dihydrochalcones, which were elucidated as vacciniifolin (1) and confusoside (2). Acute toxicity evaluation revealed that median lethal dose (LD₅₀) of AFE was greater than 5000 mg/kg. Furthermore, AFE significantly attenuated ulcerative colitis symptoms, suppressed myeloperoxidase activity, and increased the expression of superoxide dismutase and glutathione. AFE treatment could also reduce the levels of tumor necrosis factor-α, interleukin-1β, and interleukin-6 and increase the levels of interleukin-4 and interleukin-10 in colon tissues and serum of DSS-induced UC mice. In addition, AFE significantly increased the expression of zonula occludens-1, occludin and claudin-1, and inhibited the phosphorylation of target protein of the NF-κB and MAPK signaling pathways in colon tissue.

CONCLUSION

Dihydrochalcone glycosides are the major chemical constituents in AFE. AFE ameliorated DSS-induced UC in mice by inhibiting the inflammatory response via modulation of NF-κB and MAPK pathways and maintaining the intestinal barrier function, indicating that the plant A. fragrans could be used as a therapeutic candidate for ulcerative colitis.

GDP Induces PANC-1 Human Pancreatic Cancer Cell Death Preferentially under Nutrient Starvation by Inhibiting PI3K/Akt/mTOR/Autophagy Signaling Pathway

Pancreatic tumors are hypovascular, which leads to a poor nutrient supply to support the aggressively proliferating tumor cells. However, human pancreatic cancer cells have extreme resistance to nutrition starvation, which enables them to survive under severe metabolic stress conditions within the tumor microenvironment, a phenomenon known as "austerity" in cancer biology. Discovering agents which can preferentially inhibit the cancer cells' ability to tolerate starvation conditions represents a new generation of anticancer agents. In this study, geranyl 2,4-dihydroxy-6-phenethylbenzoate (GDP), isolated from Boesenbergia pandurata rhizomes, exhibited potent preferential cytotoxicity against PANC-1 human pancreatic cancer cells under nutrition starvation conditions. GDP also possessed PANC-1 cell migration and colony formation inhibitory activities under normal nutrient-rich conditions. Mechanistically, GDP inhibited PI3K/Akt/mTOR/autophagy survival signaling pathway, leading to selective PANC-1 cancer cell death under the nutrition starvation condition. Therefore, GDP is a promising anti-austerity agent for drug development against pancreatic cancer.

Activity Guided Isolation of Phenolic Compositions from Anneslea fragrans Wall. and Their Cytoprotective Effect against Hydrogen Peroxide Induced Oxidative Stress in HepG2 Cells

Anneslea fragrans Wall., commonly known as “Pangpo Tea”, is traditionally used as a folk medicine and healthy tea for the treatment of liver and intestine diseases. The aim of this study was to purify the antioxidative and cytoprotective polyphenols from A. fragrans leaves. After fractionation with polar and nonpolar organic solvents, the fractions of aqueous ethanol extract were evaluated for their total phenolic (TPC) and flavonoid contents (TFC) and antioxidant activities (DPPH, ABTS, and FRAP assays). The n-butanol fraction (BF) showed the highest TPC and TFC with the strongest antioxidant activity. The bio-guided chromatography of BF led to the purification of six flavonoids (1–6) and one benzoquinolethanoid (7). The structures of these compounds were determined by NMR and MS techniques. Compound 6 had the strongest antioxidant capacity, which was followed by 5 and 2. The protective effect of the isolated compounds on hydrogen peroxide (H₂O₂)-induced oxidative stress in HepG2 cells revealed that the compounds 5 and 6 exhibited better protective effects by inhibiting ROS productions, having no significant difference with vitamin C (p > 0.05), whereas 6 showed the best anti-apoptosis activity. The results suggest that A. fragrans could serve as a valuable antioxidant phytochemical source for developing functional food and health nutraceutical products.

Benzophenones from Betula alnoides with Antiausterity Activities against the PANC-1 Human Pancreatic Cancer Cell Line

The antiausterity strategy is a promising approach for the discovery of lead compounds with unprecedented anticancer activities by targeting the tolerance of cancer cells to nutrition starvation. These agents are selectively cytotoxic under the tumor microenvironment-mimicking condition of nutrition starvation, without apparent toxicity in the normal nutrient-rich condition. In this study, an ethanol extract of Betula alnoides showed antiausterity activity against PANC-1 human pancreatic cancer cells under nutrient-deprived conditions, with a PC₅₀ value of 13.2 μg/mL. Phytochemical investigation of this active extract led to the isolation of eight benzophenones (1-8), including six new compounds, named betuphenones A-F (2-7), and three known xanthones (9-11). The structure elucidation of the new compounds was achieved by HRFABMS, NMR, and ECD spectroscopic analyses. A plausible biogenetic pathway of the new compounds was proposed. Compounds 1-7 displayed antiausterity activity with PC₅₀ values of 4.9-8.4 μM. Moreover, compounds 2 and 7 induced alterations in PANC-1 cell morphology under nutrient-deprived conditions and also inhibited PANC-1 colony formation under nutrient-rich conditions.

Benzylisoquinoline alkaloids from Nelumbo nucifera Gaertn. petals with antiausterity activities against the HeLa human cervical cancer cell line

Ethanolic extract of Nelumbo nucifera petals showed preferential cytotoxic activity against HeLa human cervical cancer cell line with a PC₅₀ value of 10.4 μg/mL. This active extract was subjected to a phytochemical investigation study which led to the isolation of nine benzylisoquinoline alkaloids (1-9). The isolated compounds exhibited potent antiausterity activities. Moreover, under nutrient-deprived conditions, (-)-lirinidine (8) induced remarkable alterations in HeLa cell morphology including cell shrinkage and plasma blebbing leading to total cell death within 10 h. Mechanistically, 8 was found to inhibit Akt/mTOR signaling pathway. It also induced apoptosis by promoting caspase-3 activation and inhibiting Bcl-2 expression. Therefore, benzylisoquinoline alkaloids skeleton can be considered as a promising scaffold for the anticancer drug development against cervical cancer.

A new anti-austerity agent, 4'-O-methylgrynullarin from Derris scandens induces PANC-1 human pancreatic cancer cell death under nutrition starvation via inhibition of Akt/mTOR pathway

An ethanolic extract of Derris scandens flowers showed potent preferential cytotoxicity against PANC-1 human pancreatic cancer cells under nutrient-deprived condition, with a PC₅₀ value of 0.7 μg/mL. Phytochemical investigation of this active extract led to the isolation of four prenylated isoflavones (1-4) including a new compound named 4'-O-methylgrynullarin (1). The structure elucidation of the new compound was achieved by HRFABMS and NMR spectroscopic analysis. The isolated compounds exhibited potent anti-austerity activity against four different human pancreatic cancer cell lines under nutrient-deprived conditions. The new compound 4'-O-methylgrynullarin (1) was also found to inhibit PANC-1 cell migration and colony formation under nutrient-rich condition. Mechanistically, compound 1 inhibited key survival proteins in the Akt/mTOR signaling pathway. Therefore, 4'-O-methylgrynullarin (1) can be considered as a potential lead compound for the anticancer drug development based on the anti-austerity strategy.

Chemical constituents of Thai Piper ribesoides and their antiausterity activities against the PANC-1 human pancreatic cancer cell line

A methanolic extract of Thai Piper ribesoides showed preferential cytotoxicity against PANC-1 human pancreatic cancer cells under a nutrient-deprived condition, with a PC₅₀ value of 24 μg/mL. Phytochemical investigation of this bio-active extract led to the isolation of six compounds (1-6), including two new polyoxygenated cyclohexane derivatives, named ribesoidones A and B (1 and 2). The structural elucidation of the new compounds was achieved by a combination of HREIMS, NMR, and circular dichroism spectroscopic analyses. Isolated compounds were tested for their antiausterity activity against PANC-1 human pancreatic cancer cell line. Among these, compounds 1, 3, and 4 displayed potent preferential cytotoxic activity with PC₅₀ values of 5.5-7.2 μM. Ribesoidone A (1) was also found to inhibit PANC-1 colony formation under normal nutrient-rich conditions.

Panduratins Q-Y, dimeric metabolites from Boesenbergia rotunda and their antiausterity activities against the PANC-1 human pancreatic cancer cell line

A methanolic extract of the rhizomes of Boesenbergia rotunda showed potent preferential cytotoxicity against PANC-1 human pancreatic cancer cells under nutrient deficiency conditions with a PC₅₀ value of 6.6 μg/mL. Bioactivity-guided phytochemical investigation of the rhizomes of B. rotunda led to the isolation of nine undescribed dimeric metabolites, panduratins Q-Y. Their structures were elucidated based on NMR, MS, and ECD spectroscopic data interpretation. Panduratins Q-S and U-W exhibited potent cytotoxicity towards PANC-1 cell line with the PC₅₀ values ranging from 0.8 to 6.3 μM. Panduratin W, which possessed a cyclohexenylchalcone-linked flavanone skeleton, showed the most cytotoxicity with a PC₅₀ value of 0.8 μM under nutrient-deprived medium.

Ancistrobrevidines A-C and related naphthylisoquinoline alkaloids with cytotoxic activities against HeLa and pancreatic cancer cells, from the liana Ancistrocladus abbreviatus

From the leaves of Ancistrocladus abbreviatus (Ancistrocladaceae), six 5,1'-coupled naphthyldihydroisoquinoline alkaloids were isolated, ancistrobrevidines A-C (5-7), 5-epi-dioncophyllidine C₂ (10), 6-O-methylhamatinine (8), and 6-O-methylancistectorine A₃ (9); the two latter compounds were already known from related plants. Most strikingly, this series comprises alkaloids belonging to three different subclasses of naphthylisoquinolines. Ancistrobrevidine C (7) and the alkaloids 8 and 9, displaying the S-configuration at C-3 and an oxygen function at C-6, are three further representatives of the large subgroup of 5,1'-coupled Ancistrocladaceae-type compounds found in nature. 5-epi-Dioncophyllidine C₂ (10), lacking an oxygen function at C-6 and having the R-configuration at C-3, is only the third representative of a 5,1'-linked Dioncophyllaceae-type naphthylisoquinoline. Likewise rare are 5,1'-coupled hybrid-type alkaloids, which are 6-oxygenated and 3R-configured. The ancistrobrevidines A (5) and B (6) are the only second and third examples of such 5,1'-linked naphthylisoquinolines in Ancistrocladus species showing the landmarks of both, Ancistrocladaceae- and Dioncophyllaceae-type naphthylisoquinolines. In the roots of A. abbreviatus, two further unprecedented 5,1'-coupled alkaloids were discovered, ancistrobreviquinones A (11) and B (12), consisting of a 3,4-naphthoquinone portion coupled to a tetrahydroisoquinoline subunit. They are the very first quinoid naphthylisoquinolines possessing an ortho-diketone entity. Ancistrobrevidine C (7) exerted pronounced antiproliferative activities against HeLa cervical cancer cells and preferential cytotoxicity towards PANC-1 human pancreatic cancer cells under nutrient-deprived conditions following the antiausterity approach. Moreover, 7 suppressed the migration of PANC-1 cells and significantly inhibited colony formation under nutrient-rich conditions in a concentration-dependent manner, and induced dramatic alteration in cell morphology, leading to cell death.

Survey of natural products reported by Asian research groups in 2019

The new natural products reported in 2019 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2019 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Chemical constituents and absolute configuration of megastigmanes' isolated from Sedum sarmentosum Bunge

Phytochemical investigation of a methanolic extract of Sedum sarmentosum collected from Vietnam resulted in the isolation of a new megastigmane glucoside, named sedumoside K (1), together with 17 previously reported compounds (2-18). Structural elucidation of the new compound was achieved by HRFABMS, NMR spectroscopic analysis, acid hydrolysis and quantum ECD calculations. The absolute configuration of compounds 2-6 has been revised. The major isolates were tested for cytotoxic activity against HeLa human cervical cancer cells, and all showed moderate activities.

A Triterpene Lactone from Callistemon citrinus Inhibits the PANC-1 Human Pancreatic Cancer Cells Viability through Suppression of Unfolded Protein Response

Human pancreatic tumor cells such as PANC-1 are known for their ability to tolerate nutrient starvation and thrive under the hypovascular tumor microenvironment, a phenomenon termed as 'austerity'. A search of agents that preferentially inhibit the cancer cell viability under the starvation condition without toxicity in the nutrient-rich condition is a promising approach in anticancer drug discovery. In this study, a triterpene lactone, 3β-hydroxy-13,28-epoxyurs-11-en-28-one (ursenolide), isolated from a Callistemon citrinus extract has shown strong preferential cytotoxicity against PANC-1 cells under nutrient starvation with PC₅₀ value of 0.4 μm. Ursenolide-induced rounding of PANC-1 cell morphology followed by rupture of the cell membrane leading to cell death. In a real-time cell migration study, ursenolide was found to inhibit PANC-1 cell migration significantly. Mechanistically, it inhibited GRP78 and GRP94 under the starvation condition suggesting inhibition of unfolded protein response (UPR), an adaptive process of cell survival during starvation. It also inhibited the phosphorylation of the key survival protein Akt and mTOR. Overall results suggested that ursenolide is a potential anticancer agent against pancreatic cancer.

Chemical constituents of Callistemon citrinus from Egypt and their antiausterity activity against PANC-1 human pancreatic cancer cell line

Human pancreatic cancer is resistant to almost all conventional chemotherapeutic agents. It is known to proliferate aggressively within hypovascular tumor microenvironment by exhibiting remarkable tolerance to nutrition starvation,  a phenomenon termed as "austerity". Search for the new agents that eliminate the tolerance of cancer cells to nutrition starvation is a promising strategy in anticancer drug discovery. In this study, two new meroterpenoids named callistrilones O and P (1 and 2) together with eight known triterpenes (3-10) were isolated from the active dichloromethane extract of Callistemon citrinus leaves. The structure elucidation of the new compounds was achieved by HRFABMS, 1D, 2D NMR, and ECD quantum calculations. All isolated compounds were tested for their preferential cytotoxicity against PANC-1 human pancreatic cancer cells. Among these, callistrilone O (1) exhibited the most potent preferential cytotoxicity with a PC50 value of 0.3 nM, the strongest activity with over 2000 times potent than the positive control arctigenin. Callistrilone O (1) induced dramatic alterations in PANC-1 cell morphology leading to cell death under nutrient-deprived conditions. Compound 1 also inhibited PANC-1 cell migration and -PANC-1 colony formation under the nutrient-rich condition.

Highly Potent Antiausterity Agents from Callistemon citrinus and Their Mechanism of Action against the PANC-1 Human Pancreatic Cancer Cell Line

Human pancreatic cancer cells display remarkable tolerance to nutrition starvation that help them to survive in a hypovascular tumor microenvironment, a phenomenon known as "austerity". The elucidation of agents countering this tolerance is an established antiausterity strategy in anticancer drug discovery. In this study, a Callistemon citrinus leaf extract inhibited the viability of PANC-1 human pancreatic cancer cells preferentially under nutrient-deprived medium (NDM) with a PC₅₀ value of 7.4 μg/mL. Workup of this extract resulted in the isolation of three new meroterpenoids, callistrilones L-N (1-3), together with 14 known compounds (4-17). The structure elucidation of the new compounds was achieved by HRFABMS and by NMR and ECD spectroscopic analysis. The new compounds showed highly potent preferential cytotoxicity against PANC-1 cells with PC₅₀ values ranging from 10 to 65 nM in NDM. Of these, callistrilone L (1) inhibited PANC-1 cell migration and colony formation in a normal nutrient-rich condition. Callistrilone L (1) also strongly suppressed the migration of PANC-1 cells in real time. Mechanistically, 1 was found to inhibit the Akt/mTOR and autophagy activation pathway. Callistrilone L (1) and related meroterpenoids are promising leads for anticancer drug development based on the antiausterity strategy used in this work.