Synthesis and evaluation of panaxatriol derivatives as Na+, K+-ATPase inhibitors

20(R)-Panaxatriol enhances METTL3-mediated m6A modification of STUB1 to inhibit autophagy and exert antitumor effects in Triple-Negative Breast Cancer cells

BACKGROUND

Aberrant activation of autophagy in triple-negative breast cancer (TNBC) has led researchers to investigate potential therapeutic strategies targeting this process. The regulation of autophagy is significantly influenced by METTL3. Our previous research has shown that the Panax ginseng-derived compound, 20(R)-panaxatriol (PT), has potential as an anti-tumor agent. However, it remains unclear whether PT can modulate autophagy through METTL3 to exert its anti-tumor effects.

OBJECTIVE

Our objective is to investigate whether PT can regulate autophagy in TNBC cells and elucidate the molecular mechanisms.

STUDY DESIGN

For in vitro experiments, we employed SUM-159-PT and MDA-MB-231 cells. While in vivo experiments involved BALB/c nude mice and NOD/SCID mice.

METHODS

In vitro, TNBC cells were treated with PT, and cell lines with varying expression levels of METTL3 were established. We assessed the impact on tumor cell activity and autophagy by analyzing autophagic flux, Western Blot (WB), and methylation levels. In vivo, subcutaneous transplantation models were established in BALB/c nude and NOD/SCID mice to observe the effect of PT on TNBC growth. HE staining and immunofluorescence were employed to analyze histopathological changes in tumor tissues. MeRIP-seq and dual-luciferase reporter gene assays were used to identify key downstream targets. Additionally, the silencing of STIP1 Homology And U-Box Containing Protein 1 (STUB1) explored PT's effects. The mechanism of PT's action on STUB1 via METTL3 was elucidated through mRNA stability assays, mRNA alternative splicing analysis, and nuclear-cytoplasmic mRNA separation.

RESULTS

In both in vivo and in vitro experiments, it was discovered that PT significantly upregulates the expression of METTL3, leading to autophagy inhibition and therapeutic effects in TNBC. Simultaneously, through MeRIP-seq analysis and dual-luciferase reporter gene assays, we have demonstrated that PT modulates STUB1 via METTL3, influencing autophagy in TNBC cells. Furthermore, intriguingly, PT extends the half-life of STUB1 mRNA by enhancing its methylation modification, thereby enhancing its stability.

CONCLUSION

In summary, our research reveals that PT increases STUB1 m6A modification through a METTL3-mediated mechanism in TNBC cells, inhibiting autophagy and further accentuating its anti-tumor properties. Our study provides novel mechanistic insights into TNBC pathogenesis and potential drug targets for TNBC.

Asymmetric Domino Heck/Dearomatization Reaction of β-Naphthols to Construct Indole-Terpenoid Frameworks

A palladium-catalyzed enantioselective Heck cyclization/dearomatization cascade via capturing the cyclized Heck π-allylpalladium intermediate by β-naphthols is reported, which provides a new strategy for the construction of chiral indole-terpenoid frameworks. This method affords indole-functionalized β-naphthalenone compounds bearing an all-carbon-substituted quaternary chiral center in excellent yields (up to 92%) and enantioselectivities (up to 94% ee). In addition, the utility of this method is showcased by the gram-scale syntheses and diverse transformations of the dearomatized products.

Na+/K+-ATPase Revisited: On Its Mechanism of Action, Role in Cancer, and Activity Modulation

Maintenance of Na⁺ and K⁺ gradients across the cell plasma membrane is an essential process for mammalian cell survival. An enzyme responsible for this process, sodium-potassium ATPase (NKA), has been currently extensively studied as a potential anticancer target, especially in lung cancer and glioblastoma. To date, many NKA inhibitors, mainly of natural origin from the family of cardiac steroids (CSs), have been reported and extensively studied. Interestingly, upon CS binding to NKA at nontoxic doses, the role of NKA as a receptor is activated and intracellular signaling is triggered, upon which cancer cell death occurs, which lies in the expression of different NKA isoforms than in healthy cells. Two major CSs, digoxin and digitoxin, originally used for the treatment of cardiac arrhythmias, are also being tested for another indication—cancer. Such drug repositioning has a big advantage in smoother approval processes. Besides this, novel CS derivatives with improved performance are being developed and evaluated in combination therapy. This article deals with the NKA structure, mechanism of action, activity modulation, and its most important inhibitors, some of which could serve not only as a powerful tool to combat cancer, but also help to decipher the so-far poorly understood NKA regulation.