An ethanolic extract of Anneslea f ragrans leaves showed potent preferential cytotoxicity against PANC-1 human pancreatic cancer cells under a nutrient-deprived condition, with a PC 50 value of 9.6 μg/mL. Phytochemical investigation of this active extract led to the isolation of two new secondary metabolites, fragranones A (1) and B (2), along with 15 previously reported compounds. The structure elucidation of the new compounds was achieved by HRFABMS, acid hydrolysis, NMR, and ECD spectroscopic analysis. Fragranone A (1) is the first example of a rare natural product bearing an acetonide glucose moiety. Fragranone B ( 2) is representative of a rare class of natural products with a threonolactone unit linked to a chalcone through an ether linkage. The isolated compounds exhibited antiausterity activity against PANC-1 cells under nutrient-deprived conditions, and betulin ( 14) was found to be the most potent compound tested, with a PC 50 value of 8.4 μM. In addition, fragranone A (1) was found to suppress PANC-1 cancer cell migration in real time.

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.

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 PC 50 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 PC 50 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.

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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 nutrientrich condition is a promising approach in anticancer drug discovery. In this study, a triterpene lactone, 3βhydroxy-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 PC 50 value of 0.4 μM. Ursenolideinduced 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.