Interaction with Ribosomal Proteins Accompanies Stress Induction of the Anticancer Metallodrug BOLD-100/KP1339 in the Endoplasmic Reticulum

The ruthenium-based anticancer agent BOLD-100/KP1339 has shown promising results in several in vitro and in vivo tumour models as well as in early clinical trials. However, its mode of action remains to be fully elucidated. Recent evidence identified stress induction in the endoplasmic reticulum (ER) and concomitant down-modulation of HSPA5 (GRP78) as key drug effects. By exploiting the naturally formed adduct between BOLD-100 and human serum albumin as an immobilization strategy, we were able to perform target-profiling experiments that revealed the ribosomal proteins RPL10, RPL24, and the transcription factor GTF2I as potential interactors of this ruthenium(III) anticancer agent. Integrating these findings with proteomic profiling and transcriptomic experiments supported ribosomal disturbance and concomitant induction of ER stress. The formation of polyribosomes and ER swelling of treated cancer cells revealed by TEM validated this finding. Thus, the direct interaction of BOLD-100 with ribosomal proteins seems to accompany ER stress-induction and modulation of GRP78 in cancer cells.

An Organometallic Gold(I) Bis-N-Heterocyclic Carbene Complex with Multimodal Activity in Ovarian Cancer Cells

The organometallic AuI bis-N-heterocyclic carbene complex [Au(9-methylcaffeine-8-ylidene)2 ]+ (AuTMX2 ) was previously shown to selectively and potently stabilise telomeric DNA G-quadruplex (G4) structures. This study sheds light on the molecular reactivity and mode of action of AuTMX2 in the cellular context using mass spectrometry-based methods, including shotgun proteomics in A2780 ovarian cancer cells. In contrast to other metal-based anticancer agents, this organogold compound is less prone to form coordinative bonds with biological nucleophiles and is expected to exert its drug effects mainly by non-covalent interactions. Global protein expression changes of treated cancer cells revealed a multimodal mode of action of AuTMX2 by alterations in the nucleolus, telomeres, actin stress-fibres and stress-responses, which were further supported by pharmacological assays, fluorescence microscopy and cellular accumulation experiments. Proteomic data are available via ProteomeXchange with identifier PXD020560.

Exploring the Chemoselectivity towards Cysteine Arylation by Cyclometallated AuIII Compounds: New Mechanistic Insights

To gain more insight into the factors controlling efficient cysteine arylation by cyclometallated AuIII complexes, the reaction between selected gold compounds and different peptides was investigated by high-resolution liquid chromatography electrospray ionization mass spectrometry (HR-LC-ESI-MS). The deduced mechanisms of C-S cross-coupling, also supported by density functional theory (DFT) and quantum mechanics/molecular mechanics (QM/MM) calculations, evidenced the key role of secondary peptidic gold binding sites in favouring the process of reductive elimination.

An Anticancer Rhenium Tricarbonyl Targets Fe-S Cluster Biogenesis in Ovarian Cancer Cells

Target identification remains a critical challenge in inorganic drug discovery to deconvolute potential polypharmacology. Herein, we describe an improved approach to prioritize candidate protein targets based on a combination of dose-dependent chemoproteomics and treatment effects in living cancer cells for the rhenium tricarbonyl compound TRIP. Chemoproteomics revealed 89 distinct dose-dependent targets with concentrations of competitive saturation between 0.1 and 32 μM despite the broad proteotoxic effects of TRIP. Target-response networks revealed two highly probable targets of which the Fe-S cluster biogenesis factor NUBP2 was competitively saturated by free TRIP at nanomolar concentrations. Importantly, TRIP treatment led to a down-regulation of Fe-S cluster containing proteins and upregulated ferritin. Fe-S cluster depletion was further verified by assessing mitochondrial bioenergetics. Consequently, TRIP emerges as a first-in-class modulator of the scaffold protein NUBP2, which disturbs Fe-S cluster biogenesis at sub-cytotoxic concentrations in ovarian cancer cells.

The Lipid Metabolism as Target and Modulator of BOLD-100 Anticancer Activity: Crosstalk with Histone Acetylation

The leading first-in-class ruthenium-complex BOLD-100 currently undergoes clinical phase-II anticancer evaluation. Recently, BOLD-100 is identified as anti-Warburg compound. The present study shows that also deregulated lipid metabolism parameters characterize acquired BOLD-100-resistant colon and pancreatic carcinoma cells. Acute BOLD-100 treatment reduces lipid droplet contents of BOLD-100-sensitive but not -resistant cells. Despite enhanced glycolysis fueling lipid accumulation, BOLD-100-resistant cells reveal diminished lactate secretion based on monocarboxylate transporter 1 (MCT1) loss mediated by a frame-shift mutation in the MCT1 chaperone basigin. Glycolysis and lipid catabolism converge in the production of protein/histone acetylation substrate acetyl-coenzymeA (CoA). Mass spectrometric and nuclear magnetic resonance analyses uncover spontaneous cell-free BOLD-100-CoA adduct formation suggesting acetyl-CoA depletion as mechanism bridging BOLD-100-induced lipid metabolism alterations and histone acetylation-mediated gene expression deregulation. Indeed, BOLD-100 treatment decreases histone acetylation selectively in sensitive cells. Pharmacological targeting confirms histone de-acetylation as central mode-of-action of BOLD-100 and metabolic programs stabilizing histone acetylation as relevant Achilles' heel of acquired BOLD-100-resistant cell and xenograft models. Accordingly, histone gene expression changes also predict intrinsic BOLD-100 responsiveness. Summarizing, BOLD-100 is identified as epigenetically active substance acting via targeting several onco-metabolic pathways. Identification of the lipid metabolism as driver of acquired BOLD-100 resistance opens novel strategies to tackle therapy failure.

Exploring the Potential of Metal-Based Candidate Drugs as Modulators of the Cytoskeleton

During recent years, accumulating evidence suggested that metal-based candidate drugs are promising modulators of cytoskeletal and cytoskeleton-associated proteins. This was substantiated by the identification and validation of actin, vimentin and plectin as targets of distinct ruthenium(II)- and platinum(II)-based modulators. Despite this, structural information about molecular interaction is scarcely available. Here, we compile the scattered reports about metal-based candidate molecules that influence the cytoskeleton, its associated proteins and explore their potential to interfere in cancer-related processes, including proliferation, invasion and the epithelial-to-mesenchymal transition. Advances in this field depend crucially on determining binding sites and on gaining comprehensive insight into molecular drug-target interactions. These are key steps towards establishing yet elusive structure-activity relationships.

Die Wechselwirkung mit ribosomalen Proteinen begleitet die Stressinduktion des Wirkstoffkandidaten BOLD-100/KP1339 im endoplasmatischen Retikulum

Der metallhaltige Wirkstoff BOLD‐100/KP1339 zeigte bereits vielversprechende Resultate in verschiedenen In vitro‐ und In vivo‐Tumormodellen sowie in klinischen Studien. Der detaillierte Wirkmechanismus wurde jedoch noch nicht komplett aufgeklärt. Als entscheidende Wirkstoffeffekte kristallisierten sich kürzlich die Stressinduktion im endoplasmatischen Retikulum (ER) und die damit einhergehende Modulierung von HSPA5 (GRP78) heraus. Das spontane und stabile Addukt zwischen BOLD‐100 und menschlichem Serumalbumin wurde als Immobilisierungsstrategie ausgewählt, um einen chemoproteomischen Ansatz auszuführen, der die ribosomalen Proteine RPL10, RPL24 und den Transkriptionsfaktor GTF2I als potentielle Interaktoren dieser Ru(III)‐Verbindung identifizierten. Dieses Ergebnis wurde mit proteomischen und transkriptomischen Profiling‐Experimenten kombiniert, was die Interpretation einer ribosomalen Beeinträchtigung sowie der Induktion von ER‐Stress unterstützte. Die Bildung von Polyribosomen und begleitende ER‐Schwellungen in behandelten Krebszellen wurden zudem durch TEM‐Messungen bestätigt. Somit scheint eine direkte Wechselwirkung von BOLD‐100 mit ribosomalen Proteinen die ER‐Stressinduktion und die Modulierung von GRP78 in Krebszellen zu begleiten.

Highly Cytotoxic Molybdenocenes with Strong Metabolic Effects Inhibit Tumour Growth in Mice

A series of six highly lipophilic Cp-substituted molybdenocenes bearing different bioactive chelating ligands was synthesized and characterized by NMR spectroscopy, mass spectrometry and X-ray crystallography. In vitro experiments showed a greatly increased cytotoxic potency when compared to the non-Cp-substituted counterparts. In vivo experiments performed with the dichlorido precursor, (Ph2 C-Cp)2 MoCl2 and the in vitro most active complex, containing the thioflavone ligand, showed an inhibition of tumour growth. Proteomic studies on the same two compounds demonstrated a significant regulation of tubulin-associated and mitochondrial inner membrane proteins for both compounds and a strong metabolic effect of the thioflavone containing complex.