Although cisplatin is the most widely used metal-based antitumor drug, its numerous side effects have prompted researchers to further investigate metallic agents [1], [2], [3], [4]. This has also driven the development of non‑platinum metal-based therapeutics [5], [6], [7]. Among them, ruthenium complexes are regarded as one of the most promising alternatives for anticancer drugs due to their unique chemical structural features [8], [9], [10]. Certain ruthenium complexes have demonstrated promising anticancer activities, with some exhibiting cytotoxicity comparable or even superior to that of cisplatin. These complexes are characterized by high selectivity, efficient uptake by tumor cells, and a degree of antimetastatic capability [11], [12]. As potential anticancer agents, a growing body of research has revealed that ruthenium complexes exert their effects through multiple anticancer mechanisms [13], [14], [15]. Liu et al. discovered that an indole-coordinated ruthenium(II) arene complex (InRu) can target tryptophan 2,3-dioxygenase expression to enhance tumor immunotherapy and prevent immune escape [16]. A selenium (Se)‑ruthenium (Ru) complex (RuSe) acts as a radiosensitizer to synergistically enhance the efficacy of radiotherapy in killing cancer cells [17]. Additionally, Ru(II) can trigger endoplasmic reticulum (ER) stress and apoptosis, and its incorporation into transferrin improves biosafety [18].Huang et al. reported a dinuclear ruthenium(II) complex exhibiting strong near-infrared (NIR) absorption properties, enabling efficient anticancer phototherapy. This Ru complex triggered intracellular redox imbalance and disrupted energy metabolism and biosynthesis in cancer cells [19]. In addition, a deep-red-light-triggered bis-tridentate ruthenium(II) photocatalyst was described, which combats multidrug resistance by inducing cellular metabolic disturbance [20].Samya Banerjee et al. have also contributed to the field by designing a class of photo-responsive ruthenium(II) complexes that effectively achieve photodynamic antitumor activity [21]. Furthermore, Johannes Karges et al. led to the design and synthesis of a polymer nanoreactor centered on a ruthenium catalyst. This system catalyzes the oxidation of glutathione (GSH) to glutathione disulfide (GSSG) within hypoxic cancer cells, thereby promoting the generation of reactive oxygen species (ROS) and lipid peroxidation, ultimately leading to cancer cell death [22]. Moreover, Gilles Gasser et al. reported a novel series of Ru(II) polypyridyl complexes capable of inducing potent phototoxicity against CT-26 colorectal carcinoma cells upon deep-red to near-infrared irradiation, even under hypoxic conditions [23].So far, four ruthenium-based complexes have entered clinical evaluation as anticancer agents, namely imidazolium (imidazole)(dimethylsulfoxide) tetrachlororuthenate(III) (NAMI-A) [24], indazolium trans-tetrachlorobis(1H-indazole)ruthenate(III) (KP1019) [25], its sodium salt analogue KP1339 (also known as IT-139 or NKP-1339) [26], and the Ru(II)-based phototherapeutic agent TLD1433 [27].

β-Carboline alkaloids represent a class of important natural organic compounds with notable pharmacological and biological activities. In recent years, synthetic compounds derived from the β-carboline scaffold have attracted extensive attention from researchers worldwide. Many of these compounds exhibit promising biological properties, including neurobiological effects, as well as a range of pharmacological activities such as antitumor, antimalarial, antithrombotic, antibacterial, anti-osteoporotic, antiparasitic, and antiviral actions [28], [29]. On the other hand, ruthenium complexes have garnered significant interest not only for their antitumor efficacy but also for their favorable selectivity showing low toxicity toward normal cells and high potency against cancer cells along with antimetastatic potential. To date, numerous studies have reported the integration of metal complexes with β-carboline pharmacophores. These hybrid agents have been shown to facilitate chemotherapy, photodynamic therapy, and combined photothermal-chemotherapy. Moreover, they can induce DNA damage and trigger autophagy, among other mechanisms [28]. For instance, our previous work employing proteomic profiling revealed that a Ru(II) complex bearing a β-carboline-derived ligand binds to mitochondrial ATPase, thereby promoting tumor cell death [30]. Additionally, Ru(II)–β-carboline complexes can interact with mitochondrial DNA, leading to the activation of the cGAS (cyclic GMP–AMP synthase)–STING (stimulator of interferon genes) pathway and potentiation of antitumor immunity [31].Furthermore, a complex incorporating both BODIPY-derived and β-carboline ligands was found to localize in the endoplasmic reticulum (ER) and block late-stage ER autophagy, thereby enhancing the ability of the complex (denoted as Re1) to induce immunogenic cell death (ICD) [32]. In a study by Tan et al., a series of Ru(II)–β-carboline complexes were shown to simultaneously induce both apoptosis and autophagy in tumor cells, with both processes being mediated by the accumulation of reactive oxygen species (ROS) [33].

The detailed mechanisms underlying the antitumor activity of ruthenium complexes remain an area of active investigation. Over the past few years, our research has focused extensively on elucidating the mechanisms of ruthenium-based antitumor agents, including their design, synthesis, structural modification, biological evaluation, and underlying molecular pathways [34], [35], [36], [37], [38]. We have observed that for β-carboline-derived ruthenium complexes, the substituents on the main ligand significantly influence their antitumor mechanisms. For example, a -NO₂ substituted Ru–β-carboline complex can induce tumor cell apoptosis through a reductive damage pathway. To further investigate the impact of substituents on the activity and mechanism of such complexes, in this work, we designed and synthesized two novel β-carboline-based ruthenium complexes: [Ru(phen)₂(1-(p-tolyl)-9H-pyrido[3,4-b]indole)]PF₆ (denoted as Ru1) and [Ru(phen)₂(1-(4-chlorophenyl)-9H-pyrido[3,4-b]indole)]PF₆ (denoted as Ru2). β-Carboline derivatives are known to target nuclear DNA and induce DNA damage, thereby exerting antitumor effects while also triggering autophagy. Our experimental results demonstrate that both Ru1 and Ru2 exhibit significant antitumor activity in vitro, with notable selectivity against HeLa cells. These complexes bind to nuclear DNA, induce ROS-mediated DNA damage, and subsequently cause S-phase cell cycle arrest. Furthermore, Ru1 effectively induces autophagy in tumor cells. Ultimately, both DNA damage and autophagy collaboratively contributed to the induction of cellular apoptosis. In summary, we report a DNA-targeting ruthenium complex that effectively damages DNA and promotes tumor cell autophagy, leading to potent antitumor effects. This work provides a new strategic direction for cancer therapy.