An iridium(iii)-based photosensitizer disrupting the mitochondrial respiratory chain induces ferritinophagy-mediated immunogenic cell death

A Ruthenium(II) Complex Inhibits BRD4 for Synergistic Seno- and Chemo-Immunotherapy in Cisplatin-Resistant Tumor Cells

Drug resistance is a significant challenge for tumor therapy. Activating immunity is an effective method to combat drug-resistant tumors. Utilizing metallic chemotherapeutic agents to induce nonapoptotic programmed cell death is a practical approach to stimulate immunity. Besides, triggering tumor cell senescence, named senotherapy, is also an effective but often ignored method to induce immune responses. Despite some progress, reports on metallic immunotherapeutic stimuli are sparse and mainly delve into the level of organelle targeting, with vague drug-target mechanisms. Here, we report a Ru(II) complex (Ru2c) inhibits BRD4 with high affinity at a nanomolar constant. After encapsulation into biotin-DNA cage, Ru2c@biotin-DNA cage was demonstrated to kill drug-resistant cancer cells through a synergistic apoptosis-ferroptosis-senescence pathway, exhibiting 51-fold anticancer activity compared to the commercial inhibitor JQ-1. Ru2c effectively erased drug-resistant tumors and activated innate and acquired immunity in vivo. To the best of our knowledge, Ru2c is the first metal-based BRD4 inhibitor to achieve synergistic seno-immunotherapy and chemo-immunotherapy.

Nucleus-targeted ruthenium(II) complex triggers immunogenic cell death and sensitizes melanoma to anti-PD-1 therapy by activating cGAS-STING pathway

A significant challenge in the treatment of melanoma with immune checkpoint blockades (ICBs) is the limited T cells response often observed in immunologically "cold" tumors. By leveraging the immunogenicity of immunogenic cell death (ICD), which increases the susceptibility of tumor cells to ICBs, this study investigated the potential of a nucleus-targeted ruthenium(II) complex (Ru1) as an inducer of ICD. Treatment with Ru1 induced DNA damage in melanoma cells, activating the cyclic GMP-AMP synthase-stimulator of the interferon genes (cGAS-STING) pathway. This triggered endoplasmic reticulum (ER) stress, leading to ICD. Ru1-treated dying melanoma cells exhibited characteristics such as cell exposure of calreticulin (CRT) on the cell surface, release of adenosine triphosphate (ATP), and secretion of high-mobility group box 1 (HMGB1). Vaccination with Ru1-treated, dying melanoma cells elicited robust antitumor immune responses, as evidenced by CD8+ T cells activation, reduced Foxp3+ T cells count, and the development of a memory immune response that protected mice from subsequent melanoma challenges. Combining Ru1 with anti-PD-1 therapy significantly promoted T cells infiltration, enhanced dendritic cell activation, and reduced tumor-associated immunosuppressive factors, indicating a reprogramming of the tumor microenvironment. These findings suggest that Ru1 is a promising therapeutic agent for treating "cold" tumors in cancer chemoimmunotherapy.

Improved Orthogonality in Naphthalimide/Cyanine Dyad Boosts Superoxide Generation: a Tumor-Targeted Type-I Photosensitizer for Photodynamic Therapy of Tumor by Inducing Ferroptosis

It is highly desired to achieve Type-I photosensitizer (PS) to overcome the hypoxic limitation found in most clinically used PSs. Herein, a new heavy-atom-free Type-I PS T-BNCy5 is presented by incorporating a biotin-modified naphthalimide (NI) unit into the meso-position of a N-benzyl-functionalized, strongly photon-capturing pentamethine cyanine (Cy5) dye. Such molecular engineering induces a rigid orthogonal geometry between NI and Cy5 units by introducing an intramolecular sandwich-like π-π stacking assembly, which effectively promotes intersystem crossing (ISC) and greatly extends the triplet-state lifetime (τ = 389 µs), thereby markedly improving the superoxide (O2 •-)-generating ability. In vitro assays reveal that T-BNCy5 specifically accumulates in mitochondria, where it not only generates O2 •- under photoirradiation but also induces the burst of the most cytotoxic hydroxy radical (HO•) by a cascade of biochemical reactions, ultimately triggering cell ferroptosis with the IC50 value up to ≈0.45 µm whether under normoxia or hypoxia. In vivo assays manifest that, benefiting from its biotin unit, T-BNCy5 displays a strong tumor-targeting ability, and after a single PDT treatment, it can not only ablate the tumor almost completely but also be cleared from the body through biosafe urinary excretion, indicating its potential for future clinical translation.

Inhibiting Glycolysis and Disrupting the Mitochondrial HK2-VDAC1 Protein-Protein Interaction Using a Bifunctional Lonidamine-Conjugated Metal Probe for Combating Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) relies primarily on aerobic glycolysis for energy and rapid cancer cell proliferation. Hexokinase 2 (HK2), a key enzyme regulating glycolysis, is overexpressed in TNBC, promoting tumor cell proliferation and apoptosis resistance by interacting with the mitochondrial membrane's voltage-dependent anion channel 1 (VDAC1). However, the development of bioactive molecules for effectively disrupting the HK2-VDAC1 interaction remains challenging. Herein, we have modified londamine (LND) with an iridium(III) complex to create bifunctional far-red probe 1. This complex not only has the ability to distinguish TNBC cells from normal cells by probing HK2 in mitochondria, but also significantly enhances antitumor activity by inhibiting mitochondrial glycolysis and effectively disrupting the HK2-VDAC1 interaction. This led to increased Bax-VDAC1 interaction, opening of the mitochondrial permeability transition pores (MPTPs), and generation of ROS, ultimately leading to mitochondrial dysfunction and enhanced cancer cell apoptosis. Probe 1 also demonstrated stronger antiproliferative activity than LND alone in a TNBC mouse model by targeting the HK2-VDAC1 interaction without causing overt toxicity. This work showcases the potential of probe 1 as an effective therapeutic agent for TNBC by inhibiting the mitochondrial HK2-VDAC1 interaction.

Photo-Activated Ferrocene-Iridium(III) Prodrug Induces Immunogenic Cell Death in Melanoma Stem Cells

Cancer stem cells (CSCs) are key contributors to tumor resistance, recurrence, and metastasis. Conventional chemotherapy often fails to target and eradicate CSCs, significantly impairing their therapeutic efficacy. Herein, we design and synthesize a photoactivated ferrocene-iridium(III) complex (Ir-3) to achieve immunotherapy against melanoma cells (including stem cells). In short, Ir-3 effectively targets mitochondria and dissociates under light irradiation to produce a cytotoxic Ir(III) photosensitizer and Fe2+ ions. They can generate reactive oxygen species by the Fenton reaction, robustly induce ferroptosis and autophagy, and eventually trigger immunogenic cell death in melanoma cells (including stem cells). Furthermore, under light exposure, Ir-3 effectively inhibits stem cell-related properties and promotes macrophage-mediated phagocytosis of melanoma stem cells. For in vivo studies, Ir-3 is encapsulated in DSPE-PEG 2000 to form tumor-targeting Ir-3@PEG nanoparticles. After photoactivation, Ir-3@PEG can significantly inhibit primary and distant tumors, effectively inhibit the stemness of melanoma stem cells, and induce innate and adaptive immune responses.

Ruthenium(II) Polypyridyl Complexes Containing COUBPY Ligands as Potent Photosensitizers for the Efficient Phototherapy of Hypoxic Tumors

Hypoxia, a hallmark of many solid tumors, is linked to increased cancer aggressiveness, metastasis, and resistance to conventional therapies, leading to poor patient outcomes. This challenges the efficiency of photodynamic therapy (PDT), which relies on the generation of cytotoxic reactive oxygen species (ROS) through the irradiation of a photosensitizer (PS), a process partially dependent on oxygen levels. In this work, we introduce a novel family of potent PSs based on ruthenium(II) polypyridyl complexes with 2,2'-bipyridyl ligands derived from COUPY coumarins, termed COUBPYs. Ru-COUBPY complexes exhibit outstanding in vitro cytotoxicity against CT-26 cancer cells when irradiated with light within the phototherapeutic window, achieving nanomolar potency in both normoxic and hypoxic conditions while remaining nontoxic in the dark, leading to impressive phototoxic indices (>30,000). Their ability to generate both Type I and Type II ROS underpins their exceptional PDT efficiency. The lead compound of this study, SCV49, shows a favorable in vivo pharmacokinetic profile, excellent toxicological tolerability, and potent tumor growth inhibition in mice bearing subcutaneous CT-26 tumors at doses as low as 3 mg/kg upon irradiation with deep-red light (660 nm). These results allow us to propose SCV49 as a strong candidate for further preclinical development, particularly for treating large hypoxic solid tumors.

Induction of ferroptosis of iridium(III) complexes localizing at the mitochondria and lysosome by photodynamic therapy

In this study, [Ir(ppy)2(DMHBT)](PF6) (ppy = deprotonated 1-phenylpyridine, DMHBT = 10,12-dimethylpteridino[6,7-f][1,10]phenanthroline-11,13-(10,12H)-dione, 8a), [Ir(bzq)2(DMHBT)](PF6) (bzq = deprotonated benzo[h]quinoline, 8b) and [Ir(piq)2(DMHBT)](PF6) (piq = deprotonated 1-phenylisoquinoline, 8c) were synthesized and characterized by HRMS, 13C NMR and 1H NMR. In vitro cytotoxicity experiments showed that 8a, 8b, 8c show moderate cytotoxicity against B16 cells, while the cytotoxicity of the complexes 8a, 8b and 8c toward B16 cells was greatly improved upon light irradiation, which can be used as photosensitizers to exert anticancer efficacy in photodynamic therapy (PDT). After being taken up by cells, 8a, 8b, 8c were localized in the mitochondria, resulting in a large amount of Ca2+ in-flux, a burst release of ROS, a sustained opening of mitochondrial permeability transition pore, and a decrease of the mitochondrial membrane potential, which led to mitochondrial dysfunction and further activation of caspase 3 and Bcl-2 family proteins to induce apoptosis. Overloaded ROS reacted with polyunsaturated fatty acids on the cell membrane, and initiated lipid peroxidation, inhibited the xc--system-glutathione (GSH)-glutathione peroxidase 4 (GPX4) antioxidant defense system, and upregulated the expression of the damage-associated molecules, HMGB1, CRT, and HSP70. The presence of Fer-1 was effective on increasing the cell survival, which demonstrates that the complexes possess the potential to induce ferroptosis and immunogenic cell death. In addition, 8a, 8b and 8c induced autophagy by inhibiting the AKT/PI3K/mTOR signaling pathway, downregulating p62 and promoting Beclin-1 expression upon light irradiation.

An artesunate-modified half-sandwich iridium(iii) complex inhibits colon cancer cell proliferation and metastasis through the STAT3 pathway

Colon cancer is one of the most commonly diagnosed cancers and is recognized as the most aggressive tumor of the digestive system. Aberrant activation of signal transducer and activator of transcription 3 (STAT3) is associated with proliferation, metastasis and immunosuppression of the tumor cells. Here, to inhibit the STAT3 pathway and suppress metastasis in colon cancer cells, the half-sandwich iridium complex Ir-ART containing an artesunate-derived ligand was synthesized. The complex showed remarkable antiproliferative activity against human colon cancer HCT-116 cells and exhibited a concentration-dependent reduction in STAT3 protein expression. Mechanism study demonstrates that Ir-ART is located mainly in the nucleus and mitochondria, causing γ-H2AX and cyclin B1 reduction and reactive oxygen species accumulation and mitochondrial membrane potential loss, ultimately leading to autophagic cell death. The migration of cancer cells was also inhibited via metalloproteinase 9 downregulation. Furthermore, Ir-ART could initiate antitumor immune responses by eliciting immunogenic cell death and downregulating immunosuppressive cytokine cyclooxygenase-2. Taken together, Ir-ART is expected to be further applied to chemotherapy and immunotherapy for colon cancer.

Leveraging the Photofunctions of Transition Metal Complexes for the Design of Innovative Phototherapeutics

Despite the advent of various medical interventions for cancer treatment, the disease continues to pose a formidable global health challenge, necessitating the development of new therapeutic approaches for more effective treatment outcomes. Photodynamic therapy (PDT), which utilizes light to activate a photosensitizer to produce cytotoxic reactive oxygen species (ROS) for eradicating cancer cells, has emerged as a promising approach for cancer treatment due to its high spatiotemporal precision and minimal invasiveness. However, the widespread clinical use of PDT faces several challenges, including the inefficient production of ROS in the hypoxic tumor microenvironment, the limited penetration depth of light in biological tissues, and the inadequate accumulation of photosensitizers at the tumor site. Over the past decade, there has been increasing interest in the utilization of photofunctional transition metal complexes as photosensitizers for PDT applications due to their intriguing photophysical and photochemical properties. This review provides an overview of the current design strategies used in the development of transition metal complexes as innovative phototherapeutics, aiming to address the limitations associated with PDT and achieve more effective treatment outcomes. The current challenges and future perspectives on the clinical translation of transition metal complexes are also discussed.

Four cyclometalated Ir(iii) complexes and insights into their luminescence, cytotoxicity and DNA/BSA binding performance

Four cyclometalated Ir(iii) complexes based on 4'-p-N,N-bis(2-hydroxyethyl)benzyl-2,2':6',2''-terpyridine (TPYOH) and 4'-p-N,N-bis(2-hydroxyethyl)benzyl-6'-benzyl-2,2'-bipyridine (PhbpyOH) were synthesized and characterized. All the Ir(iii) complexes exhibited strong MLCT absorption peaks at about 450 nm, broad emission bands in the range of 500-700 nm. Z-scan results revealed that only complex Ir1A could exhibit certain two-photon absorption with maximal cross section values of 215 GM at 890 nm. When excited by 700-850 nm femtosecond laser, complex Ir1A gave a TPEF peak around 567 nm. All four complexes exhibited enhanced cell growth inhibitory activity against MCF-7 tumour cells under light irradiation comparing to their dark toxicity, with Ir1B showing the highest PI value (>50). The pathways and efficiencies of ROS generation by Ir(iii) complexes varied, with Ir2A being more effective in producing 1O2 while Ir1A mainly generating O2˙-. The Ir(iii) complexes undergo hydrogen bonding with DNA bases/phosphodiester through two O-H bonds on the bis(hydroxyethyl)amino group. The free pyridine-N atom in Ir1A forms additional hydrogen bond with DNA base, while the ligand TPYOH in Ir2A has better molecular planarity due to adopting {N, N, N} coordination mode, thus these two complexes show better DNA affinity. The complexes demonstrated weak interactions with BSA, through hydrogen bonding with amino acid residues at different regions of BSA molecule.