Medizinische Klinik und Poliklinik III - Innere Medizin

Phytochemical combinations of lichen Evernia prunastri (L.) Ach. reduce drug resistance to temozolomide but not to paclitaxel in vitro

2025-12-29T10:48:33Z

Phytochemical combinations of lichen Evernia prunastri (L.) Ach. reduce drug resistance to temozolomide but not to paclitaxel in vitro Shcherbakova, A.; Nguyen, L.; Koptina, A.; Backlund, A.; Banerjee, S.; Romanov, E.; Ulrich-Merzenich, G. Introduction: Temozolomide (TMZ) and Paclitaxel (PXT), crucial anti-cancer drugs for glioblastoma (GBM) and primary breast cancer (BC), respectively, face drug resistance. Therefore, we investigated the adjuvant potential of characterized extracts of the lichens Evernia prunastri (L.) Ach. (Epr), Cladonia arbuscula (Wallr.) Flot (Car) and their metabolites, evernic acid (EA) and usnic acid (UA) alone or in combination with TMZ and PTX for their immunomodulatory and chemosensitivity increasing potential.
Methods: TMZ-resistant U-87 cells, MCF7 BC-cells, and normal human skin fibroblasts (HSKF) were treated with hexane (Hex), dichloromethane (DCM), and acetonitrile (ACN) extracts of Epr (EprDCM, EprACN), Car (CarHex, CarACN), and with EA and UA to measure cell metabolic activity. Molecular mechanisms were predicted using ChemGPS-NP and validated by Western blot, RNA sequencing, quantitative RT-PCR, and Wnt inhibitory factor 1 (WIF1) protein expression. Combinatory effects were calculated by Combination Index (CI) and Zero Interaction Potency methods (ZIP).
Results: Extracts and selected metabolites reduced concentration-dependent cellular metabolic activity in U-87 and MCF7 cells. EprACN and EA (U-87 cells: IC₅₀ 30 μg/mL), safe to HSKF, regulated key proteins in MAP kinases pathways, supporting predictions made by ChemGPS-NP. The combination EA-TMZ showed additive effects (TMZ-reduction: 3.4 fold), reduced transcription of Wnt pathway members, and increased in U-87 cells protein releases of WiF1, the central inhibitor of Wnt-signaling. Further gene expression data (GE) suggest involvement of IL-17 receptor and BDNF.
Discussion: The combination EA-TMZ interacts with the Wnt pathway regulation associated with sensitizing U-87 cells, without increasing GEs of pro-inflammatory cytokines. EA deserves further investigation as an adjuvant.

Cell Cycle Regulation of G-Quadruplex DNA Structures at Telomeres

2024-04-05T11:46:23Z

Cell Cycle Regulation of G-Quadruplex DNA Structures at Telomeres Stefan, A. Juranek; Katrin, Paeschke DNA and RNA regions containing tracts of guanines can form very stable secondary structures called G-quadruplex (G4). Genomic sequences with the potential to form G4 (G4-motifs) are abundant across species. In all analyzed genomes G4 motifs are found near promoter regions and double strand break sites and at telomeres. Telomeres are very G-rich and prone for G4 formation. Therefore they are routinely used in in vitro and in vivo experiments to elucidate the function of G4 structures in telomere metabolism. Recently various labs demonstrated that telomere length maintenance is mediated via G4 structures. Telomere-binding proteins specifically bind to G4 structure and regulate this structure throughout the cell cycle.

Detecting G4 unwinding

2024-04-05T11:33:58Z

Detecting G4 unwinding Stefan, Juranek; Katrin, Paeschke DNA can, in addition to the B-DNA conformation, fold into a variety of additional conformations. Among them are G-quadruplex structures that have gained a lot of attention in recent years. G-quadruplex structures (G4s) are highly stable nucleic acid structures that can fold within DNA and RNA molecules. They form in guanine-rich regions that harbor a specific G4 motif. The three-dimensional structure forms via Hoogsteen hydrogen bonding, where the guanines form hydrogen bonds to each other in order to generate G quartets, which stack in order to become G4 structures.
The existence and relevance of G4s was controversial as discussed in the past. However, accumulating data was published that supported the model that G4s form in living cells and importantly support biological processes. G4 formation and unfolding is tightly regulated in vivo. If G4s persist in the cell, they can lead to cellular defects such as genome instability. To avoid G4 accumulation in cells, and by this prevent cellular defect, cells has evolved a variety of proteins, mostly helicases, that efficiently unfold G4 DNA and RNA structures. Here, we describe a detailed protocol to monitor G4 struc- ture unfolding by helicases.

The DEAH helicase DHX36 and its role in G-quadruplex-dependent processes

2024-04-05T11:16:39Z

The DEAH helicase DHX36 and its role in G-quadruplex-dependent processes Schult, Philipp; Paeschke, Katrin DHX36 is a member of the DExD/H box helicasefamily, which comprises a large number of proteinsinvolved in various cellular functions. Recently, thefunction of DHX36 in the regulation of G-quadruplexes(G4s) was demonstrated. G4s are alternative nucleic acidstructures, which influence many cellular pathways on atranscriptional and post-transcriptional level. In thisreview we provide an overview of the current knowledgeabout DHX36 structure, substrate specificity, andmechanism of action based on the available models andcrystal structures. Moreover, we outline its multiplefunctions in cellular homeostasis, immunity, and disease.Finally, we discuss the open questions and providepotential directions for future research.