Correction to "Shifting the Antibody-Drug Conjugate Paradigm: A Trastuzumab-Gold-Based Conjugate Demonstrates High Efficacy against Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer Mouse Model".

[This corrects the article DOI: 10.1021/acsptsci.3c00270.].

From Chemotherapy to Phototherapy - Changing the Therapeutic Action of a Metallo-Intercalating RuII -ReI Luminescent System by Switching its Sub-Cellular Location.

The synthesis of a new heterodinuclear ReI RuII metallointercalator containing RuII (dppz) and ReI (dppn) moieties is reported. Cell-free studies reveal that the complex has similar photophysical properties to its homoleptic M(dppz) analogue and it also binds to DNA with a similar affinity. However, the newly reported complex has very different in-cell properties to its parent. In complete contrast to the homoleptic system, the RuII (dppz)/ReI (dppn) complex is not intrinsically cytotoxic but displays appreciable phototoxic, despite both complexes displaying very similar quantum yields for singlet oxygen sensitization. Optical microscopy suggests that the reason for these contrasting biological effects is that whereas the homoleptic complex localises in the nuclei of cells, the RuII (dppz)/ReI (dppn) complex preferentially accumulates in mitochondria. These observations illustrate how even small structural changes in metal based therapeutic leads can modulate their mechanism of action.

Synthesis and Characterization of Lipophilic Salts of Metformin to Improve Its Repurposing for Cancer Therapy.

Epidemiological evidence has accentuated the repurposing of metformin hydrochloride for cancer treatment. However, the extreme hydrophilicity and poor permeability of metformin hydrochloride are responsible for its poor anticancer activity in vitro and in vivo. Here, we report the synthesis and characterization of several lipophilic metformin salts containing bulky anionic permeation enhancers such as caprate, laurate, oleate, cholate, and docusate as counterions. Of various counterions tested, only docusate was able to significantly improve the lipophilicity and lipid solubility of metformin. To evaluate the impact of the association of anionic permeation enhancers with metformin, we checked the in vitro anticancer activity of various lipophilic salts of metformin using drug-sensitive (MYCN-2) and drug-resistant (SK-N-Be2c) neuroblastoma cells as model cancer cells. Metformin hydrochloride showed a very low potency (IC50 ≈ >100 mM) against MYCN-2 and SK-N-Be2c cells. Anionic permeation enhancers showed a considerably higher activity (IC50 ≈ 125 µM to 1.6 mM) against MYCN-2 and SK-N-Be2c cells than metformin. The association of metformin with most of the bulky anionic agents negatively impacted the anticancer activity against MYCN-2 and SK-N-Be2c cells. However, metformin docusate showed 700- to 4300-fold improvement in anticancer potency compared to metformin hydrochloride and four- to five-fold higher in vitro anticancer activity compared to sodium docusate, indicating a synergistic association between metformin and docusate. A similar trend was observed when we tested the in vitro activity of metformin docusate, sodium docusate, and metformin hydrochloride against hepatocellular carcinoma (HepG2) and triple-negative breast cancer (MDA-MB-231) cells.

Photoactive metal complexes that bind DNA and other biomolecules as cell probes, therapeutics, and theranostics.

This review discusses the advantages of using luminescent d6-transition-metal complexes as cell probes for optical microscopy. In particular it focusses on the Thomas group's use of specific complexes as "building blocks" toward the construction of biomolecular binding substrates, with DNA being a particular target. Using this approach, a range of new imaging probes for conventional optical microscopy, nanoscopy and transmission electron microscopy have been identified. Through selection of specific metal centres and by substitution of coordinated ligands we illustrate how new chemotherapeutics, photo-therapeutics, and theranostics have been identified and developed from the original architectures.

Making the Right Link to Theranostics: The Photophysical and Biological Properties of Dinuclear RuII-ReI dppz Complexes Depend on Their Tether.

The synthesis of new dinuclear complexes containing linked RuII(dppz) and ReI(dppz) moieties is reported. The photophysical and biological properties of the new complex, which incorporates a N,N'-bis(4-pyridylmethyl)-1,6-hexanediamine tether ligand, are compared to a previously reported RuII/ReI complex linked by a simple dipyridyl alkane ligand. Although both complexes bind to DNA with similar affinities, steady-state and time-resolved photophysical studies reveal that the nature of the linker affects the excited state dynamics of the complexes and their DNA photocleavage properties. Quantum-based DFT calculations on these systems offer insights into these effects. While both complexes are live cells permeant, their intracellular localizations are significantly affected by the nature of the linker. Notably, one of the complexes displayed concentration-dependent localization and possesses photophysical properties that are compatible with SIM and STED nanoscopy. This allowed the dynamics of its intracellular localization to be tracked at super resolutions.

Exploring the Cytotoxicity, Uptake, Cellular Response, and Proteomics of Mono- and Dinuclear DNA Light-Switch Complexes.

Drug resistance to platinum chemotherapeutics targeting DNA often involves abrogation of apoptosis and has emerged as a significant challenge in modern, non-targeted chemotherapy. Consequently, there is great interest in the anti-cancer properties of metal complexes-particularly those that interact with DNA-and mechanisms of consequent cell death. Herein we compare a parent cytotoxic complex, [Ru(phen)2(tpphz)]2+ [phen = 1,10-phenanthroline, tpphz = tetrapyridyl[3,2- a:2',3'- c:3″,2″- h:2‴,3‴- j]phenazine], with a mononuclear analogue with a modified intercalating ligand, [Ru(phen)2(taptp)]2+ [taptp = 4,5,9,18-tetraazaphenanthreno[9,10- b] triphenylene], and two structurally related dinuclear, tpphz-bridged, heterometallic complexes, RuRe and RuPt. All three of these structural changes result in a switch from intercalation to groove-binding DNA interaction and concomitant reduction in cytotoxic potency, but no significant change in relative cytotoxicity toward platinum-resistant A2780CIS cancer cells, indicating that the DNA interaction mode is not critical for the mechanism of platinum resistance. All variants exhibited a light-switch effect, which for the first time was exploited to investigate timing of cell death by live-cell microscopy. Surprisingly, cell death occurred rapidly as a consequence of oncosis, characterized by loss of cytoplasmic volume control, absence of significant mitochondrial membrane potential loss, and lack of activation of apoptotic cell death markers. Importantly, a novel, quantitative proteomic analysis of the A2780 cell genome following exposure of the cells to either mononuclear complex reveals changes in protein expression associated with global cell responses to oxidative stress and DNA replication/repair cellular pathways. This combination of multiple targeting modalities and induction of a non-apoptotic death mechanism makes these complexes highly promising chemotherapeutic cytotoxicity leads.

A three-in-one-bullet for oesophageal cancer: replication fork collapse, spindle attachment failure and enhanced radiosensitivity generated by a ruthenium(ii) metallo-intercalator.

Substitutionally inert ruthenium(ii) polypyridyl complexes have been developed as DNA intercalating agents yet cellular DNA damage responses to this binding modality are largely unexplored. Here, we show the nuclear-targeting complex [Ru(phen)2(tpphz)]2+ (phen = 1,10-phenanthroline, tpphz = tetrapyridophenazine) generates rapid and pronounced stalling of replication fork progression in p53-deficient human oesophageal cancer cells. In response, replication stress and double-strand break (DSB) DNA damage response (DDR) pathways are activated and cell proliferation is inhibited by growth arrest. Moreover, mitotic progression is compromised by [Ru(phen)2(tpphz)]2+, where the generation of metaphase chromosome spindle attachment failure results in spindle assembly checkpoint (SAC) activation. This dual mechanism of action results in preferential growth inhibition of rapidly-proliferating oesophageal cancer cells with elevated mitotic indices. In addition to these single-agent effects, [Ru(phen)2(tpphz)]2+ functions as a radiosensitizer with efficiency comparable to cisplatin, which occurs through a synergistic enhancement of DNA damage. These results establish that DNA replication is the target for [Ru(phen)2(tpphz)]2+ and provide the first experimental evidence that ruthenium-based intercalation targets multiple genome integrity pathways in cancer cells, thereby achieving enhanced selectivity compared to existing DNA-damaging agents such as cisplatin.

Tracking HOCl concentrations across cellular organelles in real time using a super resolution microscopy probe.

BODIPY derivative, SF-1, exclusively shows a fluorescence ON response to HOCl and images endogenously generated HOCl in RAW 264.7 macrophages. Widefield and super resolution structured illumination microscopy images confirm localization in the Golgi complex and lysosomes, and hence specifically detects HOCl generated in these organelles. SF-1 is compatible with 3D-SIM imaging of individual cells.

Multimodal Super-resolution Optical Microscopy Using a Transition-Metal-Based Probe Provides Unprecedented Capabilities for Imaging Both Nuclear Chromatin and Mitochondria.

Detailed studies on the live cell uptake properties of a dinuclear membrane-permeable RuII cell probe show that, at low concentrations, the complex localizes and images mitochondria. At concentrations above ∼20 µM, the complex images nuclear DNA. Because the complex is extremely photostable, has a large Stokes shift, and displays intrinsic subcellular targeting, its compatibility with super-resolution techniques was investigated. It was found to be very well suited to image mitochondria and nuclear chromatin in two color, 2C-SIM, and STED and 3D-STED, both in fixed and live cells. In particular, due to its vastly improved photostability compared to that of conventional SR probes, it can provide images of nuclear DNA at unprecedented resolution.

A Super-Resolution Probe To Monitor HNO Levels in the Endoplasmic Reticulum of Cells.

Selective detection of nitroxyl (HNO), which has recently been identified as a reactive nitrogen species, is a challenging task. We report a BODIPY-based luminescence ON reagent for detection of HNO in aqueous solution and in live RAW 264.7 cells, based on the soft nucleophilicity of the phosphine oxide functionality toward HNO. The probe shows high selectivity to HNO over other reactive oxygen/nitrogen and sulfur species. Luminescence properties of the BODIPY-based chemodosimetric reagent make it an ideal candidate for use as a reagent for super-resolution structured illumination microscopy. The viability of the reagent for biological in vivo imaging application was also confirmed using Artemia as a model.

Homo- and Heteroleptic Phototoxic Dinuclear Metallo-Intercalators Based on RuII (dppn) Intercalating Moieties: Synthesis, Optical, and Biological Studies.

Using a new mononuclear "building block," for the first time, a dinuclear RuII (dppn) complex and a heteroleptic system containing both RuII (dppz) and RuII (dppn) moieties are reported. The complexes, including the mixed dppz/dppn system, are 1 O2 sensitizers. However, unlike the homoleptic dppn systems, the mixed dppz/dppn complex also displays a luminescence "switch on" DNA light-switch effect. In both cisplatin sensitive and resistant human ovarian carcinoma lines the dinuclear complexes show enhanced uptake compared to their mononuclear analogue. Thanks to a favorable combination of singlet oxygen generation and cellular uptake properties all three of the new complexes are phototoxic and display potent activity against chemotherapeutically resistant cells.

The Structure of Linkers Affects the DNA Binding Properties of Tethered Dinuclear Ruthenium(II) Metallo-Intercalators.

With the long-term aim of enhancing the binding properties of dinuclear RuII -based DNA light-switch complexes, a series of eight structurally related mono- and dinuclear systems are reported in which the linker of the bridging ligand has been modulated. These tethered systems have been designed to explore issues of steric demand at the binding site and the thermodynamic cost of entropy loss upon binding. Detailed spectroscopic and isothermal titration calorimetry (ITC) studies on the new complexes reveal that one of the linkers produces a dinuclear system that binds to duplex DNA with an affinity (Kb >107 m-1 ) that is higher than its corresponding monometallic complex and is the highest affinity for a non-threading bis-intercalating metal complex. These studies confirm that the tether has a major effect on the binding properties of dinuclear complexes containing intercalating units and establishes key design rules for the construction of dinuclear complexes with enhanced DNA binding characteristics.