Toward "E-Ring-Free" Lamellarin Analogues: Synthesis and Preliminary Biological Evaluation.

Since the discovery of anticancer properties of a naturally occurring hexacyclic marine alkaloid Lamellarin D, the attempts have been made to prepare its synthetic analogues and elucidate the effects of each structural component on their activity profile. While F-ring-free, A-ring-free and B-ring-open lamellarins are known, E-ring-free analogues have never been investigated. In this work, we developed a facile and straightforward synthetic method toward E-ring-free lamellarin analogues based on the [3+2]-cycloaddition. For the first time, we prepared several pentacyclic lamellarin analogues without E-ring in their structure and assessed their cytotoxicity in a panel of cancer cell lines in comparison with several hexacyclic lamellarins. E-ring-free lamellarins were devoid of cytotoxicity due to their poor solubility in cellular environment.

Coordination of Ru(II)-Arene Fragments to Dipyridophenazine Ligands Leads to the Modulation of Their In Vitro and In Vivo Anticancer Activity.

Despite extensive research on the anticancer properties of Ru complexes with dipyrido[3,2-a:2',3'-c]phenazine (dppz) ligands, their in vivo efficacy is rarely investigated. Aiming to understand whether the coordination of certain half-sandwich Ru(II)-arene fragments might improve the therapeutic potential of dppz ligands, we prepared a series of Ru(II)-arene complexes with the general formula [(η6-arene)Ru(dppz-R)Cl]PF6, where the arene fragment was benzene, toluene, or p-cymene and R was -NO2, -Me, or -COOMe. All compounds were fully characterized by 1H and 13C NMR spectroscopy and high-resolution ESI mass-spectrometry, and their purity was verified by elemental analysis. The electrochemical activity was investigated using cyclic voltammetry. The anticancer activity of dppz ligands and their respective Ru complexes was assessed against several cancer cell lines, and their selectivity toward cancer cells was assessed using healthy MRC5 lung fibroblasts. The substitution of benzene with a p-cymene fragment resulted in a more than 17-fold increase of anticancer activity and selectivity of Ru complexes and significantly enhanced DNA degradation in HCT116 cells. All Ru complexes were electrochemically active in the biologically accessible redox window and were shown to markedly induce the production of ROS in mitochondria. The lead Ru-dppz complex significantly reduced tumor burden in mice with colorectal cancers without inducing liver and kidney toxicity.

Organoantimony Dihydroperoxides: Synthesis, Crystal Structures, and Hydrogen Bonding Networks.

Despite growing interest in the potential applications of p-block hydroperoxo complexes, the chemistry of inorganic hydroperoxides remains largely unexplored. For instance, single-crystal structures of antimony hydroperoxo complexes have not been reported to date. Herein, we present the synthesis of six triaryl and trialkylantimony dihydroperoxides [Me3Sb(OOH)2, Me3Sb(OOH)2·H2O, Ph3Sb(OOH)2·0.75(C4H8O), Ph3Sb(OOH)2·2CH3OH, pTol3Sb(OOH)2, pTol3Sb(OOH)2·2(C4H8O)], obtained by the reaction of the corresponding dibromide antimony(V) complexes with an excess of highly concentrated hydrogen peroxide in the presence of ammonia. The obtained compounds were characterized by single-crystal and powder X-ray diffraction, Fourier transform infrared and Raman spectroscopies, and thermal analysis. The crystal structures of all six compounds reveal hydrogen-bonded networks formed by hydroperoxo ligands. In addition to the previously reported double hydrogen bonding, new types of hydrogen-bonded motifs formed by hydroperoxo ligands were found, including infinite hydroperoxo chains. Solid-state density functional theory calculation of Me3Sb(OOH)2 revealed reasonably strong hydrogen bonding between OOH ligands with an energy of 35 kJ/mol. Additionally, the potential application of Ph3Sb(OOH)2·0.75(C4H8O) as a two-electron oxidant for the enantioselective epoxidation of olefins was investigated in comparison with Ph3SiOOH, Ph3PbOOH, t-BuOOH, and H2O2.

Effects of Bis(imino)acenaphthene (Bian)-Derived Ligands on the Cytotoxicity, DNA Interactions, and Redox Activity of Palladium(II) Bipyridine Complexes.

A series of heteroleptic bipyridine Pd(II) complexes based on 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-Bian) or 1,2-bis[(2,4,6-trimethylphenyl)imino]acenaphthene (tmp-Bian) were prepared. All complexes were fully characterized by spectrochemical methods, and their crystal structures were confirmed by X-ray diffraction analysis. The 72 h stability of heteroleptic bipyridine Pd(II) complexes with Bian ligands under physiological conditions was investigated using 1H NMR spectroscopy. The anticancer activity of all complexes was assessed in a panel of cancer cell lines in comparison with uncoordinated ligands and clinically used drugs cisplatin and doxorubicin. The ability of the complexes to bind DNA was investigated using several methods, including EtBr replacement assay, density functional theory calculations, circular dichroism spectroscopy, DNA gel electrophoresis, and TUNEL assay. The electrochemical activity of all complexes and the uncoordinated ligands was studied using cyclic voltammetry, and reactive oxygen species production in cancer cells was investigated using confocal microscopy. Heteroleptic bipyridine PdII-Bian complexes were cytotoxic in a low micromolar concentration range and showed some selectivity toward cancer cells in comparison with noncancerous MRC-5 lung fibroblasts.

Deletion of Annexin A1 in Mice Upregulates the Expression of Its Receptor, Fpr2/3, and Reactivity to the AnxA1 Mimetic Peptide in Platelets.

Annexin A1 (ANXA1) is an endogenous protein, which plays a central function in the modulation of inflammation. While the functions of ANXA1 and its exogenous peptidomimetics, N-Acetyl 2-26 ANXA1-derived peptide (ANXA1Ac2-26), in the modulation of immunological responses of neutrophils and monocytes have been investigated in detail, their effects on the modulation of platelet reactivity, haemostasis, thrombosis, and platelet-mediated inflammation remain largely unknown. Here, we demonstrate that the deletion of Anxa1 in mice upregulates the expression of its receptor, formyl peptide receptor 2/3 (Fpr2/3, orthologue of human FPR2/ALX). As a result, the addition of ANXA1Ac2-26 to platelets exerts an activatory role in platelets, as characterised by its ability to increase the levels of fibrinogen binding and the exposure of P-selectin on the surface. Moreover, ANXA1Ac2-26 increased the development of platelet-leukocyte aggregates in whole blood. The experiments carried out using a pharmacological inhibitor (WRW4) for FPR2/ALX, and platelets isolated from Fpr2/3-deficient mice ascertained that the actions of ANXA1Ac2-26 are largely mediated through Fpr2/3 in platelets. Together, this study demonstrates that in addition to its ability to modulate inflammatory responses via leukocytes, ANXA1 modulates platelet function, which may influence thrombosis, haemostasis, and platelet-mediated inflammation under various pathophysiological settings.

Elucidation of Structure-Activity Relationships in Indolobenzazepine-Derived Ligands and Their Copper(II) Complexes: the Role of Key Structural Components and Insight into the Mechanism of Action.

Indolo[3,2-d][1]benzazepines (paullones), indolo[3,2-d][2]benzazepines, and indolo[2,3-d][2]benzazepines (latonduines) are isomeric scaffolds of current medicinal interest. Herein, we prepared a small library of novel indolo[3,2-d][2]benzazepine-derived ligands HL1-HL4 and copper(II) complexes 1-4. All compounds were characterized by spectroscopic methods (1H and 13C NMR, UV-vis, IR) and electrospray ionization (ESI) mass spectrometry, while complexes 2 and 3, in addition, by X-ray crystallography. Their purity was confirmed by HPLC coupled with high-resolution ESI mass spectrometry and/or elemental analysis. The stability of compounds in aqueous solutions in the presence of DMSO was confirmed by 1H NMR and UV-vis spectroscopy measurements. The compounds revealed high antiproliferative activity in vitro in the breast cancer cell line MDA-MB-231 and hepatocellular carcinoma cell line LM3 in the low micromolar to nanomolar concentration range. Important structure-activity relationships were deduced from the comparison of anticancer activities of HL1-HL4 and 1-4 with those of structurally similar paullone-derived (HL5-HL7 and 5-7) and latonduine-derived scaffolds (HL8-HL11 and 8-11). The high anticancer activity of the lead drug candidate 4 was linked to reactive oxygen species and endoplasmic reticulum stress induction, which were confirmed by fluorescent microscopy and Western blot analysis.

Inhibition of Microtubule Dynamics in Cancer Cells by Indole-Modified Latonduine Derivatives and Their Metal Complexes.

Indolo[2,3-d]benzazepines (indololatonduines) are rarely discussed in the literature. In this project, we prepared a series of novel indololatonduine derivatives and their RuII and OsII complexes and investigated their microtubule-targeting properties in comparison with paclitaxel and colchicine. Compounds were fully characterized by spectroscopic techniques (1H NMR and UV-vis), ESI mass-spectrometry, and X-ray crystallography, and their purity was confirmed by elemental analysis. The stabilities of the compounds in DMSO and water were confirmed by 1H and 13C NMR and UV-vis spectroscopy. Novel indololatonduines demonstrated anticancer activity in vitro in a low micromolar concentration range, while their coordination to metal centers resulted in a decrease of cytotoxicity. The preliminary in vivo activity of the RuII complex was investigated. Fluorescence staining and in vitro tubulin polymerization assays revealed the prepared compounds to have excellent microtubule-destabilizing activities, even more potent than the well-known microtubule-destabilizing agent colchicine.

Heteroleptic Pd(II) and Pt(II) Complexes with Redox-Active Ligands: Synthesis, Structure, and Multimodal Anticancer Mechanism.

A series of heteroleptic square-planar Pt and Pd complexes with bis(diisopropylphenyl) iminoacenaphtene (dpp-Bian) and Cl, 1,3-dithia-2-thione-4,5-dithiolate (dmit), or 1,3-dithia-2-thione-4,5-diselenolate (dsit) ligands have been prepared and characterized by spectroscopic techniques, elemental analysis, X-ray diffraction analysis, and cyclic voltammetry (CV). The intermolecular noncovalent interactions in the crystal structures were assessed by density functional theory (DFT) calculations. The anticancer activity of Pd complexes in breast cancer cell lines was limited by their solubility. Pd(dpp-Bian) complexes with dmit and dsit ligands as well as an uncoordinated dpp-Bian ligand were devoid of cytotoxicity, while the [Pd(dpp-Bian)Cl2] complex was cytotoxic. On the contrary, all Pt(dpp-Bian) complexes demonstrated anticancer activity in a low micromolar concentration range, which was 8-20 times higher than the activity of cisplatin, and up to 2.5-fold selectivity toward cancer cells over healthy fibroblasts. The presence of a redox-active dpp-Bian ligand in Pt and Pd complexes resulted in the induction of reactive oxygen species (ROS) in cancer cells. In addition, these complexes were able to intercalate into DNA, indicating the dual mechanism of action.

Interfering with Metabolic Profile of Triple-Negative Breast Cancers Using Rationally Designed Metformin Prodrugs.

Triple-negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, characterized by an aberrant metabolic phenotype with high metastatic capacity, resulting in poor patient prognoses and low survival rates. We designed a series of novel AuIII cyclometalated prodrugs of energy-disrupting Type II antidiabetic drugs namely, metformin and phenformin. Prodrug activation and release of the metformin ligand was achieved by tuning the cyclometalated AuIII fragment. The lead complex 3met was 6000-fold more cytotoxic compared to uncoordinated metformin and significantly reduced tumor burden in mice with aggressive breast cancers with lymphocytic infiltration into tumor tissues. These effects was ascribed to 3met interfering with energy production in TNBCs and inhibiting associated pro-survival responses to induce deadly metabolic catastrophe.

Heteroleptic Ruthenium(II) Complexes with Bathophenanthroline and Bathophenanthroline Disulfonate Disodium Salt as Fluorescent Dyes for In-Gel Protein Staining.

The in-gel detection of proteins for various proteomic experiments is commonly done with the fluorescent RuII tris(bathophenanthroline disulfonate) complex (Ru(BPS)3), which is more cost-effective compared to commercial Ru-based formulations but requires tedious procedures for its preparation and strongly acidic staining conditions. Herein, we report the synthesis and characterization of heteroleptic RuII complexes Ru(BPS)2(BP) and Ru(BPS)(BP)2 containing bathophenanthroline (BP) and bathophenanthroline disulfonate disodium salt (BPS) in comparison with Ru(BPS)3. It was shown by fluorescent and UV-vis measurements that novel RuII complexes were excitable in both UV and visible light, close to emission bands of classical lasers, which is important for successful in-gel protein detection. Novel fluorescent dyes demonstrated improved protein detection in comparison with commercially available SYPRO Ruby staining solution. In addition, unlike commonly used staining protocols, staining with Ru(BPS)(BP)2 can be performed at nearly neutral pH, thereby reducing artificial post-translational modifications (PTMs).

PlatinER: A Highly Potent Anticancer Platinum(II) Complex that Induces Endoplasmic Reticulum Stress Driven Immunogenic Cell Death.

Immunogenic cell death (ICD) is a rare immunostimulatory form of cell death that can improve the clinical outcomes of chemo-immunotherapeutic combination regimens through the establishment of a long-term cancer immunity. None of the clinically used DNA-binding PtII complexes is considered a Type II ICD inducer. We generated a series of PtII -carbene complexes by applying minor structural alterations to the scaffold of a Type II ICD inducer Pt-NHC and compared their efficiency in triggering ICD-related cellular responses and phagocytosis. We successfully identified PlatinER, a novel highly potent PtII candidate with superior ICD properties. Crucially, the magnitude of ICD-associated phagocytosis induced upon exposure of cancer cells to Pt complexes was dependent on the levels of ER-localized reactive oxygen species (ROS) generation, which underpins their mechanisms of action and provides a feasible approach for the design of more effective Type II ICD inducers.

Design, Synthesis and Evaluation of New Indolylpyrimidylpiperazines for Gastrointestinal Cancer Therapy.

Human A3 adenosine receptor hA3AR has been implicated in gastrointestinal cancer, where its cellular expression has been found increased, thus suggesting its potential as a molecular target for novel anticancer compounds. Observation made in our previous work indicated the importance of the carbonyl group of amide in the indolylpyrimidylpiperazine (IPP) for its human A2A adenosine receptor (hA2AAR) subtype binding selectivity over the other AR subtypes. Taking this observation into account, we structurally modified an indolylpyrimidylpiperazine (IPP) scaffold, 1 (a non-selective adenosine receptors' ligand) into a modified IPP (mIPP) scaffold by switching the position of the carbonyl group, resulting in the formation of both ketone and tertiary amine groups in the new scaffold. Results showed that such modification diminished the A2A activity and instead conferred hA3AR agonistic activity. Among the new mIPP derivatives (3-6), compound 4 showed potential as a hA3AR partial agonist, with an Emax of 30% and EC50 of 2.89 ± 0.55 µM. In the cytotoxicity assays, compound 4 also exhibited higher cytotoxicity against both colorectal and liver cancer cells as compared to normal cells. Overall, this new series of compounds provide a promising starting point for further development of potent and selective hA3AR partial agonists for the treatment of gastrointestinal cancers.

Dual-Targeting Dual-Action Platinum(IV) Platform for Enhanced Anticancer Activity and Reduced Nephrotoxicity.

A novel and highly efficient dual-targeting platform was designed to ensure targeted in vivo delivery of dual-action PtIV prodrugs. The dual targeting was established by liposomal encapsulation of PtIV complexes, thereby utilizing the enhanced permeability and retention (EPR) effect as the first stage of targeting to attain a high accumulation of the drug-loaded liposomes in the tumor. After the release of the PtIV prodrug inside cancer cells, a second stage of targeting directed a portion of the PtIV prodrugs to the mitochondria. Upon intracellular reduction, these PtIV prodrugs released two bioactive molecules, acting both on the mitochondrial and on the nuclear DNA. Our PtIV system showed excellent activity in vitro and in vivo, characterized by a cytotoxicity in a low micromolar range and complete tumor remission, respectively. Notably, marked in vivo activity was accompanied by reduced kidney toxicity, highlighting the unique therapeutic potential of our novel dual-targeting dual-action platform.

Induction of the Endoplasmic Reticulum Stress Pathway by Highly Cytotoxic Organoruthenium Schiff-Base Complexes.

Current anticancer drug discovery efforts focus on the identification of first-in-class compounds with a mode-of-action distinct from conventional DNA-targeting agents for chemotherapy. An emerging trend is the identification of endoplasmic reticulum (ER) targeting compounds that induce ER stress in cancer cells, leading to cell death. However, a limited pool of such compounds has been identified to date, and there are limited studies done on such compounds to allow for the rational design of ER stress-inducing agents. In our present study, we present a series of highly cytotoxic, ER stress-inducing Ru(II)-arene Schiff-Base (RAS) complexes, bearing iminoquinoline chelate ligands. We demonstrate that by structural modification to the iminoquinoline ligand, we could tune its π-acidity and influence reactive oxygen species (ROS) induction, switching between a ROS-mediated ER stress pathway activation and one that is not mediated by ROS induction. Our current study adds to the available ER stress inducers and shows how structural tuning could be used as a means to modulate the mode-of-action of such compounds.

Palladium Complexes of N,N'-Bis(2-aminoethyl)oxamide (H2L): Structural (PdIIL, PdII2L2, and PdIVLCl2), Electrochemical, Dynamic 1H NMR, and Cytotoxicity Studies.

The monomeric (PdL·2H2O) and dimeric (Pd2L2·7H2O) palladium(II) complexes of N,N'-bis(2-aminoethyl)oxamide (H2L) were isolated, and their structures were established by single-crystal X-ray diffraction. Both compounds display identical cis-(2Namide + 2Namine) coordination environments of the metal ion. The dimer, representing a combination of two PdL species with an open lateral chelate ring, has an "open clamshell"-like structure. The intramolecular metal-metal separation in Pd2L2 (3.215 Å) is slightly shorter than the sum of the van der Waals radii of the palladium(II) atoms. The dimeric complex is relatively stable to dissociation, and its spectral features in aqueous solutions have been compared to those of the monomeric complex. A 1H NMR spectroscopic study revealed the presence of the dynamic conformational exchange process assigned to a turning of the dimeric molecule "inside out" with an activation energy of 65 kJ/mol. Cyclic voltammetry of PdL in perchlorate-, chloride-, and sulfate-containing electrolytes revealed two-electron oxidation of the palladium center. For the dimeric complex similar, though irreversible, oxidation to the palladium(IV) state was observed in NaCl electrolyte. At the same time, in NaClO4 or Na2SO4 solutions oxidation of Pd2L2 occurs in two distinct steps. The first step is quasi-reversible and can be assigned to the formation of species in an intermediate PdIIIPdIII state. Monomeric palladium(IV) complex PdIVLCl2 was generated via chemical oxidation of PdIIL by peroxodisulfate in the presence of chloride ions and structurally characterized. The related MIIL complexes (M = Pd, Ni, Cu) showed low cytotoxicity in human cancer cell lines AGS (gastric adenocarcinoma) and HCT116 (colorectal carcinoma) with IC50 values from 204 to 525 µM, while the proligand H2L was devoid of antiproliferative activity (IC50 > 1000 µM).

From Catalysis to Cancer: Toward Structure-Activity Relationships for Benzimidazol-2-ylidene-Derived N-Heterocyclic-Carbene Complexes as Anticancer Agents.

The promise of the metal(arene) structure as an anticancer pharmacophore has prompted intensive exploration of this chemical space. While N-heterocyclic carbene (NHC) ligands are widely used in catalysis, they have only recently been considered in metal complexes for medicinal applications. Surprisingly, a comparatively small number of studies have been reported in which the NHC ligand was coordinated to the RuII(arene) pharmacophore and even less with an OsII(arene) pharmacophore. Here, we present a systematic study in which we compared symmetrically substituted methyl and benzyl derivatives with the nonsymmetric methyl/benzyl analogues. Through variation of the metal center and the halido ligands, an in-depth study was conducted on ligand exchange properties of these complexes and their biomolecule binding, noting in particular the stability of the M-CNHC bond. In addition, we demonstrated the ability of the complexes to inhibit the selenoenzyme thioredoxin reductase (TrxR), suggested as an important target for anticancer metal-NHC complexes, and their cytotoxicity in human tumor cells. It was found that the most potent TrxR inhibitor diiodido(1,3-dibenzylbenzimidazol-2-ylidene)(η6-p-cymene)ruthenium(II) 1bI was also the most cytotoxic compound of the series, with the antiproliferative effects in general in the low to middle micromolar range. However, since there was no clear correlation between TrxR inhibition and antiproliferative potency across the compounds, TrxR inhibition is unlikely to be the main mode of action for the compound type and other target interactions must be considered in future.

Rollover Cyclometalated Bipyridine Platinum Complexes as Potent Anticancer Agents: Impact of the Ancillary Ligands on the Mode of Action.

Platinum-based anticancer coordination compounds are widely used in the treatment of many tumor types, where they are very effective but also cause severe side effects. Organoplatinum compounds are significantly less investigated than the analogous coordination compounds. We report here rollover cyclometalated Pt compounds based on 2,2'-bipyridine which are demonstrated to be potent antitumor agents both in vitro and in vivo. Variation of the co-ligands on the Pt(2,2'-bipyridine) backbone resulted in the establishment of structure-activity relationships. They showed that the biological activity was in general inversely correlated with the reaction kinetics to biomolecules as shown for amino acids, proteins, and DNA. The less stable compounds caused higher reactivity with biomolecules and were shown to induce p53-dependent DNA damage. In contrast, the presence of bulky PTA and PPh3 ligands was demonstrated to cause lower reactivity and increased antineoplastic activity. Such compounds were devoid of DNA-damaging activity and induced ATF4, a component of the endoplasmic reticulum (ER) stress pathway. The lead complex inhibited tumor growth similar to oxaliplatin while showing no signs of toxicity in test mice. Therefore, we demonstrated that it is possible to fine-tune rollover-cyclometalated Pt(II) compounds to target different cancer pathways and be a means to overcome the side effects associated with cisplatin and analogous compounds in cancer chemotherapy.

NO Releasing and Anticancer Properties of Octahedral Ruthenium-Nitrosyl Complexes with Equatorial 1 H-Indazole Ligands.

With the aim of enhancing the biological activity of ruthenium-nitrosyl complexes, new compounds with four equatorially bound indazole ligands, namely, trans-[RuCl(Hind)4(NO)]Cl2·H2O ([3]Cl2·H2O) and trans-[RuOH(Hind)4(NO)]Cl2·H2O ([4]Cl2·H2O), have been prepared from trans-[Ru(NO2)2(Hind)4] ([2]). When the pH-dependent solution behavior of [3]Cl2·H2O and [4]Cl2·H2O was studied, two new complexes with two deprotonated indazole ligands were isolated, namely [RuCl(ind)2(Hind)2(NO)] ([5]) and [RuOH(ind)2(Hind)2(NO)] ([6]). All prepared compounds were comprehensively characterized by spectroscopic (IR, UV-vis, 1H NMR) techniques. Compound [2], as well as [3]Cl2·2(CH3)2CO, [4]Cl2·2(CH3)2CO, and [5]·0.8CH2Cl2, the latter three obtained by recrystallization of the first isolated compounds (hydrates or anhydrous species) from acetone and dichloromethane, respectively, were studied by X-ray diffraction methods. The photoinduced release of NO in [3]Cl2 and [4]Cl2 was investigated by cyclic voltammetry and resulting paramagnetic NO species were detected by EPR spectroscopy. The quantum yields of NO release were calculated and found to be low (3-6%), which could be explained by NO dissociation and recombination dynamics, assessed by femtosecond pump-probe spectroscopy. The geometry and electronic parameters of Ru species formed upon NO release were identified by DFT calculations. The complexes [3]Cl2 and [4]Cl2 showed considerable antiproliferative activity in human cancer cell lines with IC50 values in low micromolar or submicromolar concentration range and are suitable for further development as potential anticancer drugs. p53-dependence of Ru-NO complexes [3]Cl2 and [4]Cl2 was studied and p53-independent mode of action was confirmed. The effects of NO release on the cytotoxicity of the complexes with or without light irradiation were investigated using NO scavenger carboxy-PTIO.

Structural Determinants of p53-Independence in Anticancer Ruthenium-Arene Schiff-Base Complexes.

p53 is a key tumor suppressor gene involved in key cellular processes and implicated in cancer therapy. However, it is inactivated in more than 50% of all cancers due to mutation or overexpression of its negative regulators. This leads to drug resistance and poor chemotherapeutic outcome as most clinical drugs act via a p53-dependent mechanism of action. An attractive strategy to circumvent this resistance would be to identify new anticancer drugs that act via p53-independent mode of action. In the present study, we identified 9 Ru (II)-Arene Schiff-base (RAS) complexes able to induce p53-independent cytotoxicity and discuss structural features that are required for their p53-independent activity. Increasing hydrophobicity led to an increase in cellular accumulation in cells with a corresponding increase in efficacy. We further showed that all nine complexes demonstrated p53-independent activity. This was despite significant differences in their physicochemical properties, suggesting that the iminoquinoline ligand, a common structural feature for all the complexes, is required for the p53-independent activity.