Sempervirine inhibits RNA polymerase I transcription independently from p53 in tumor cells

Abstract

In the search of small molecules that can target MDM2/p53 pathway in testicular germ cell tumors (TGCTs), we identified sempervirine (2,3,4,13-tetrahydro-1H-benz[g]indolo[2,3-a]quinolizin-6-ium), an alkaloid of Gelsemium sempervirens, that has been previously proposed as an inhibitor of MDM2 that targets p53-wildtype (wt) tumor cells. We found that sempervirine not only affects cell growth of p53-wt cancer cells, but it is also active in p53-mutated and p53-null cells by triggering p53-dependent and independent pathways without affecting non-transformed cells. To understand which mechanism/s could be activated both in p53-wt and -null cells, we found that sempervirine induced nucleolar remodeling and nucleolar stress by reducing protein stability of RPA194, the catalytic subunit of RNA polymerase I, that led to rRNA synthesis inhibition and to MDM2 block. As shown for other cancer cell models, MDM2 inhibition by nucleolar stress downregulated E2F1 protein levels both in p53-wt and p53-null TGCT cells with the concomitant upregulation of unphosphorylated pRb. Finally, we show that sempervirine is able to enter the nucleus and accumulates within the nucleolus where it binds rRNA without causing DNA damage. Our results identify semperivirine as a novel rRNA synthesis inhibitor and indicate this drug as a non-genotoxic anticancer small molecule.

Sempervirine Inhibits Proliferation and Promotes Apoptosis by Regulating Wnt/β-Catenin Pathway in Human Hepatocellular Carcinoma

“…Previous reports indicated that G. elegans possessed ideal natural compounds for the treatment of cancer ( Liang et al, 2013 ; Que et al, 2021 ). Sempervirine, an alkaloid isolated from G. elegans , have shown anti-cancer activity ( Pan et al, 2016 ; Caggiano et al, 2020 ). Our data demonstrated that sempervirine inhibited HCC growth in a dose dependent manner.…”

Non-Coding RNAs and Splicing Activity in Testicular Germ Cell Tumors

“…Recently, two promising specific inhibitors of Pol I activity (CX-5461 and BHM-21) have been developed [ 85 , 86 ] and one of them (CX-5461) has passed phase I clinical trial (NCT02719977 and NCT04890613). To this end, we identified a natural molecule, sempervirine, extracted from Gelsemium sempervirens and previously thought to act as an MDM2 inhibitor [ 87 ] that specifically targets Pol I in TGCTs [ 88 ]. We found that this molecule binds and disassembles nucleoli of tumor cells after few hours of culture and induces PolI degradation, leading TGCT cells, but not non-tumor cells, to p53 dependent and independent cell death.…”

Synthesis of Fluorescent, DNA-Binding Benzo[b]indolonaphthyridinium Derivatives by a Misguided Westphal Condensation

“…The indoloquinolinium and indoloquinolizinium ions are promising structural motifs and lead structures in drug discovery. − These cationic azoniahetarenes are key structural features in various bioactive natural products such as javacarboline, flavopereirine, cryptolepine, and sempervirine, which have, for example, DNA-binding properties and antitumor activity. − In addition, the representatives of this class of compounds frequently exhibit a pronounced and characteristic fluorescence that changes significantly upon association with a biologically relevant host molecule, so that they may also be used for the fluorimetric detection of the latter. − As a result, the synthesis of indoloquinolinium and indoloquinolizinium derivatives is a topical research field in medicinal chemistry and pharmaceutical sciences, especially with the goal to identify highly bioactive and selective drug candidates. Among the synthetic approaches toward these target structures, cyclization reactions are often employed as essential key steps to assemble the azoniaheterocyclic framework. ,− For example, the conversion of benzenesulfonyl-protected 2-(pyridin-2-yl)­indoline derivatives, , the Stetter reaction, and the Sonogashira reaction in combination with the Larock indole synthesis have been successfully applied for this purpose.…”