A reactive oxygen species-generating, cancer stem cell-potent manganese(ii) complex and its encapsulation into polymeric nanoparticles.

Intracellular redox modulation offers a viable approach to effectively remove cancer stem cells (CSCs), a subpopulation of tumour cells thought to be responsible for cancer recurrence and metastasis. Here we report the breast CSC potency of reactive oxygen species (ROS)-generating manganese(ii)- and copper(ii)-4,7-diphenyl-1,10-phenanthroline complexes bearing diclofenac, a nonsteriodial anti-inflammatory drug (NSAID), 1 and 3. Notably, the manganese(ii) complex, 1, exhibits 9-fold, 31-fold, and 40-fold greater potency towards breast CSCs than 3, salinomycin (an established breast CSC-potent agent), and cisplatin (a clinically approved anticancer drug) respectively. Encouragingly, 1 displays 61-fold higher potency toward breast CSCs than normal skin fibroblast cells. Clinically relevant epithelial spheroid studies show that 1 is able to selectively inhibit breast CSC-enriched HMLER-shEcad mammosphere formation and viability (one order of magnitude) over non-tumorigenic breast MCF10A spheroids. Mechanistic studies show that 1 prompts breast CSC death by generating intracellular ROS and inhibiting cyclooxygenase-2 (COX-2) activity. The manganese(ii) complex, 1, induces a greater degree of intracellular ROS in CSCs than the corresponding copper(ii) complex, 3, highlighting the ROS-generating superiority of manganese(ii)- over copper(ii)-phenanthroline complexes. Encapsulation of 1 by biodegradable methoxy poly(ethylene glycol)-b-poly(d,l-lactic-co-glycolic) acid (PEG-PLGA) copolymers at the appropriate feed (5%, 1 NP5 ) enhances breast CSC uptake and greatly reduces overall toxicity. The nanoparticle formulation 1 NP5 indiscriminately kills breast CSCs and bulk breast cancer cells, and evokes a similar cellular response to the payload, 1. To the best of our knowledge, this is the first study to investigate the anti-CSC properties of managense complexes and to demonstrate that polymeric nanoparticles can be used to effectively deliver managense complexes into CSCs

Modulating the Chemical and Biological Properties of Cancer Stem Cell-Potent Copper(II)-Nonsteroidal Anti-Inflammatory Drug Complexes.

Copper(II) complexes bearing nonsteroidal anti-inflammatory drugs (NSAIDs) are known to potently kill cancer stem cells (CSCs), a subpopulation of tumour cells with high metastatic and relapse fidelity. One of the major disadvantages associated to these copper(II) complexes is their instability in the presence of strong cellular reductants (such as ascorbic acid). Here we present a biologically stable copper(II)-NSAID complex containing a bathocuproinedisulfonic acid disodium ligand and two indomethacin moieties, Cu(bathocuproinedisulfonic acid disodium)(indomethacin)2, 2. The copper(II) complex, 2 kills bulk breast cancer cells and breast CSC equally (in the sub-micromolar range) and displays very low toxicity against non-tumorigenic breast and kidney cells (IC50 value > 100 µM). Three-dimensional cell culture studies show that 2 can significantly reduce the number and size of breast CSC mammospheres formed (from single suspensions) to a similar level as salinomycin (an established anti-breast CSC agent). The copper(II) complex, 2 is taken up reasonably by breast CSCs and localises largely in the cytoplasm (>90%). Cytotoxicity studies in the presence of specific inhibitors suggest that 2 induces CSC death via a reactive oxygen species (ROS) and cyclooxygenase isoenzyme-2 (COX-2) dependent apoptosis pathway

A Cancer Stem Cell Potent Cobalt(III)-Cyclam Complex Bearing Two Tolfenamic Acid Moieties

Cancer stem cells (CSCs) are thought to be responsible for cancer relapse. CSCs are a subtype of cancer cells with the ability to differentiate, self-renew, and form secondary or tertiary tumors. Current cancer treatments—including chemotherapy, radiation, and surgery—effectively remove bulk cancer cells but are unable to eliminate CSCs. Here, we present the synthesis, characterization, and anti-CSC properties of a cobalt(III)–cyclam complex bearing two tolfenamic acid moieties, 3. Notably, 3 displays sub-micromolar potency towards breast CSCs and bulk breast cancer cells. Detailed mechanistic studies show that 3 is taken up readily by breast CSCs, enters the nucleus, causes DNA damage, and induces caspase-dependent apoptosis. Furthermore, 3 inhibits cyclooxygenase-2 (COX-2) expression in CSCs. The mechanism of action of 3 is similar to that of a naproxen-appended cobalt(III)–cyclam complex, 1 recently reported by our group. The advantage of 3 over 1 is that it has the potential to remove whole tumor populations (bulk cancer cells and CSCs) with a single dose

The bulk osteosarcoma and osteosarcoma stem cell activity of a necroptosis-inducing nickel(II)-phenanthroline complex.

We report the anti-osteosarcoma and anti-osteosarcoma stem cell (OSC) properties of a nickel(II) complex, 1. The nickel(II) complex, 1 displays similar potency towards bulk osteosarcoma cells and OSCs, in the micromolar range. Notably, 1 displays similar or better OSC potency than the clinically approved platinum(II) anticancer drugs, cisplatin and carboplatin, in two- and three-dimensional osteosarcoma cell cultures. Mechanistic studies revealed that 1 induces osteosarcoma cell death by necroptosis, an ordered form of necrosis. The nickel(II) complex, 1 triggers necrosome-dependent mitrochondrial membrane depolarisation and propidium iodide uptake. Interestingly, 1 does not evoke necroptosis by intracellular reactive oxygen species (ROS) elevation or poly ADP ribose polymerase (PARP-1) hyperactivation. ROS elevation and PARP-1 activity are traits that have been observed for established necroptosis-inducers such as shikinon, TRAIL, and glutamate. Thus the necroptosis pathway evoked by 1 is distinct. To the best of our awareness this is the first report into the anti-osteosarcoma and anti-OSC properties of a nickel complex

Breast cancer stem cell potency of nickel(II)-polypyridyl complexes containing non-steroidal anti-inflammatory drugs.

We report the breast cancer stem cell (CSC) potency of two nickel(II)-3,4,7,8-tetramethyl-1,10-phenanthroline complexes, 1 and 3, containing the non-steroidal anti-inflammatory drugs (NSAIDs), naproxen and indomethacin, respectively. The nickel(II) complexes, 1 and 3 kill breast CSCs and bulk breast cancer cells in the micromolar range. Notably, 1 and 3 display comparable or better potency towards breast CSCs than salinomycin, an established CSC-active agent. The complexes, 1 and 3 also display significantly lower toxicity towards non-cancerous epithelial breast cells than breast CSCs or bulk breast cancer cells (up to 4.6-fold). Mechanistic studies suggest that 1 and 3 downregulate cyclooxygenase-2 (COX-2) in breast CSCs and kill breast CSCs in a COX-2 dependent manner. Furthermore, the potency of 1 and 3 towards breast CSCs decreased upon co-treatment with necroptosis inhibitors (necrostatin-1 and dabrafenib), implying that 1 and 3 induce necroptosis, an ordered form of necrosis, in breast CSCs. As apoptosis resistance is a hallmark of CSCs, compounds like 1 and 3, which potentially provide access to alternative (non-apoptotic) cell death pathways could hold the key to overcoming hard-to-kill CSCs. To the best of our knowledge, 1 and 3 are the first compounds to be associated to COX-2 inhibition and necroptosis induction in CSCs

A Triangular Platinum(II) Multi-nuclear Complex with Impressive Cytotoxicity Towards Breast Cancer Stem Cells.

The preparation of multi-nuclear metal complexes offers a route to novel anticancer agents and delivery systems. The potency of a novel triangular multi-nuclear complex containing three platinum atoms, Pt-3, towards breast cancer stem cells (CSCs) is reported. The tri-nuclear platinum(II) complex, Pt-3 exhibits selectivity toxicity towards breast CSCs over bulk breast cancer cells and non-tumorigenic breast cells. Remarkably, Pt-3 inhibits the formation, size, and viability of mammospheres to a better extent than salinomycin, an established CSC-potent agent, and cisplatin and carboplatin, clinically used platinum drugs. Mechanism of action studies show that Pt-3 effectively enters breast CSCs, penetrates the nucleus, induces genomic DNA damage, and prompts caspase-dependent apoptosis. To the best of our knowledge, Pt-3 is the first multi-nuclear platinum complex to selectivity kill breast CSCs over other breast cell types

Polypyridyl Zinc(II)-Indomethacin Complexes with Potent Anti-Breast Cancer Stem Cell Activity.

Cancer stem cells (CSCs) are thought of as a clinically pertinent subpopulation of tumors, partly responsible for cancer relapse and metastasis. Research programs aimed at discovering anti-CSC agents have largely focused on biologics and purely organic molecules. Recently, we showed that a family of redox-active copper(II) complexes with phenanthroline-based ligands and nonsteroidal anti-inflammatory drugs (NSAIDs) such as indomethacin, are capable of potently and selectively killing breast CSCs. Herein we present analogous redox-inactive, zinc(II)-phenanthroline-indomethacin complexes with the ability to kill breast CSCs and bulk breast cancer cells with equal potency (in the submicro- or micromolar range). A single dose of the zinc(II) complexes could theoretically be administered to eliminate whole tumor populations. Excitingly, some of the zinc(II) complexes decrease the growth and viability of mammospheres to a comparable or higher degree than salinomycin, a compound known to effectively kill breast CSCs. As far as we are aware this is the first report to examine the anti-breast CSC activity of zinc(II)-containing compounds

Immunogenic Cell Death of Breast Cancer Stem Cells by an Endoplasmic Reticulum-Targeting Copper(II) Complex.

Immunogenic cell death (ICD) offers a method of stimulating the immune system to attack and remove cancer cells. We report a copper(II) complex containing a Schiff base ligand and a polypyridyl ligand, 4 capable of inducing ICD in breast cancer stem cells (CSCs). The complex, 4 kills both bulk breast cancer cells and breast CSCs in the sub-micromolar range. Notably, 4 exhibits greater potency (one order of magnitude) towards breast CSCs than salinomycin (an established breast CSC-potent agent) and cisplatin (a clinically approved anticancer drug). Epithelial spheroid studies show that 4 is able to selectively inhibit breast CSC-enriched HMLER-shEcad spheroid formation and viability over non-tumorigenic breast MCF10A spheroids. Mechanistic studies show that 4 operates as a Type II ICD inducer. Specifically, 4 readily enters the endoplasmic reticulum (ER) of breast CSCs, elevates intracellular reactive oxygen species (ROS) levels, induces ER stress, evokes damage-associated molecular patterns (DAMPs), and promotes breast CSC phagocytosis by macrophages. As far as we are aware, 4 is the first metal complex to induce ICD in breast CSCs and promote their engulfment by immune cells

The Cancer Stem Cell Potency of Group 10-Azadiphosphine Metal Complexes

The cancer stem cell (CSC) potency of a series of structurally analogous Group 10-azadiphosphine metal complexes is reported. The complexes comprise a Group 10 metal (Ni for 1, Pd for 2, or Pt for 3), an azadiphosphine ligand, and two chloride ligands. The complexes exhibit micromolar potency towards bulk breast cancer cells and breast CSCs cultured in monolayer systems. The cytotoxicity of the complexes is comparable to or better than clinically used metallopharmaceuticals, cisplatin and carboplatin, and the gold-standard anti-breast CSC agent, salinomycin. Notably, the breast CSC mammosphere inhibitory effect and potency of the complexes is dependent on the Group 10 metal present, increasing in the following order: 3<2<1. This study highlights the importance of the metal within a given series of structurally related compounds to their breast CSC mammosphere activity and reinforces the therapeutic potential of Group 10 coordination complexes as anti-CSC agents

Synthesis and Characterization of Pt(IV) Fluorescein Conjugates to Investigate Pt(IV) Intracellular Transformations

Pt­(IV) anticancer compounds typically operate as prodrugs that are reduced in the hypoxic environment of cancer cells, losing two axial ligands in the process to generate active Pt­(II) species. Here we report the synthesis of two fluorescent Pt­(IV) prodrugs of cisplatin in order to image and evaluate the Pt­(IV) reduction process in simulated and real biological environments. Treatment of the complexes dissolved in PBS buffer with reducing agents typically encountered in cells, glutathione or ascorbate, afforded a 3- to 5-fold fluorescence turn-on owing to reduction and loss of their fluorescein-based axial ligands, which are quenched when bound to platinum. Both Pt­(IV) conjugates displayed moderate cytotoxicity against human cancer cell lines, with IC₅₀ values higher than that of cisplatin. Immunoblotting and DNA flow cytometry analyses of one of the complexes, Pt­(IV)­FL₂, revealed that it damages DNA, causes cell cycle arrest in S or G2/M depending on exposure time, and ultimately triggers apoptotic cell death. Fluorescence microscopic studies prove that Pt­(IV)­FL₂ enters cells intact and undergoes reduction intracellularly. The results are best interpreted in terms of a model in which the axial fluorescein ligands are expelled through lysosomes, with the platinum­(II) moiety generated in the process binding to genomic DNA, which results in cell death