Recoding the Cancer Epigenome by Intervening in Metabolism and Iron Homeostasis with Mitochondria‐Targeted Rhenium(I) Complexes

Pt(II) Bis(pyrrole-imine) complexes: Luminescent probes and cytotoxicity in MCF-7 cells†

Four Pt(II) bis(pyrrole-imine) Schiff base chelates (1-4) were synthesised by previously reported methods, through a condensation reaction, and the novel crystal structure of 2,2'-{propane-1,3-diylbis[nitrilo(E)methylylidene]}bis(pyrrol-1-ido)platinum(II) (1) was obtained. Pt(II) complexes 1-4 exhibited phosphorescence, with increased luminescence in anaerobic solvents or when bound to human serum albumin (HSA). One of the complexes shows a 15.6-fold increase in quantum yield when bound to HSA and could be used to detect HSA concentrations as low as 5 nM. Pt(II) complexes 1-3 was investigated as potential theranostic agents in MCF-7 breast cancer cells, but only complex 3 exhibited cytotoxicity when irradiated with UV light (λ355nmExcitation). Interestingly, the cytotoxicity of complex 1 was unresponsive to UV light irradiation. This indicates that only complex 3 can be considered a potential photosensitising agent.

Metal-based anticancer agents as immunogenic cell death inducers: the past, present, and future

Cancer is the deadliest disease in the world behind heart disease. Sadly, this remains true even as we suffer the ravages of the Covid-19 pandemic. Whilst current chemo- and radiotherapeutic treatment strategies have significantly improved the patient survival rate, disease reoccurrence continues to pose a deadly risk for all too many patients. Incomplete removal of tumour cells from the body increases the chances of metastasis and developing resistance against current treatments. Immunotherapy represents a therapeutic modality that has helped to overcome these limitations in recent decades. However, further progress is needed. So-called immunogenic cell death (ICD) is a recently discovered and unique mode of cell death that could trigger this necessary further progress. ICD involves stimulation of a tumour-specific immune response as a downstream effect. Facilitated by certain treatment modalities, cells undergoing ICD can trigger the IFN-γ mediated immune response involving cytotoxic T cells (CTLs) and γδ T cells that eradicate residual tumour cells. In recent years, there has been a significant increase in the number of small-molecules being tested as potential ICD inducers. A large number of these ICD inducers are metal-based complexes. In fact, anticancer metal drugs based on Pt, Ru, Ir, Cu, and Au are now known to give rise to an immune response against tumour cells as the result of ICD. Advances have also been made in terms of exploiting combinatorial and delivery strategies. In favourable cases, these approaches have been shown to increase the efficacy of otherwise ICD "silent" metal complexes. Taken in concert, rationally designed novel anticancer metal complexes that can act as ICD inducers show promise as potential new immunotherapies for neoplastic disease. This Tutorial Review will allow the readers to assess the progress in this fast-evolving field thus setting the stage for future advances.

Sulfur-Coordinated Organoiridium(III) Complexes Exert Breast Anticancer Activity via Inhibition of Wnt/β-Catenin Signaling

The sulfur-coordinated organoiridium(III) complexes pbtIrSS and ppyIrSS, which contain C,N and S,S (dithione) chelating ligands, were found to inhibit breast cancer tumorigenesis and metastasis by targeting Wnt/β-catenin signaling for the first time. Treatment with pbtIrSS and ppyIrSS induces the degradation of LRP6, thereby decreasing the protein levels of DVL2, β-catenin and activated β-catenin, resulting in downregulation of Wnt target genes CD44 and survivin. Additionally, pbtIrSS and ppyIrSS can suppress cell migration and invasion of breast cancer cells. Furthermore, both complexes show the ability to inhibit sphere formation and mediate the stemness properties of breast cancer cells. Importantly, pbtIrSS exerts potent anti-tumor and anti-metastasis effects in mouse xenograft models through the blockage of Wnt/β-catenin signaling. Taken together, our results indicate that pbtIrSS has great potential to be developed as a breast cancer therapeutic agent with a novel mechanism.