Three-dimensional and co-culture models for preclinical evaluation of metal-based anticancer drugs

Synthesis and preclinical evaluation of BOLD-100 radiolabeled with ruthenium-97 and ruthenium-103

BOLD-100 (formerly IT-139, KP1339), a well-established chemotherapeutic agent, is currently being investigated in clinical trials for the treatment of gastric, pancreatic, colorectal, and bile duct cancer. Despite numerous studies, the exact mode of action is still the subject of discussions. Radiolabeled BOLD-100 could be a powerful tool to clarify pharmacokinetic pathways of the compound and to predict therapy responses in patients using nuclear molecular imaging prior to the therapy. In this study, the radiosyntheses of carrier-added (c.a.) [97/103Ru]BOLD-100 were performed with the two ruthenium isotopes ruthenium-103 (103Ru; β-, γ) and ruthenium-97 (97Ru; EC, γ), of which in particular the latter isotope is suitable for imaging by single-photon emission computed tomography (SPECT). To identify the best tumor-to-background ratio for diagnostic imaging, biodistribution studies were performed with two different injected doses of c.a. [103Ru]BOLD-100 (3 and 30 mg kg-1) in Balb/c mice bearing CT26 allografts over a time period of 72 h. Additionally, ex vivo autoradiography of the tumors (24 h p.i.) was conducted. Our results indicate that the higher injected dose (30 mg kg-1) leads to more unspecific accumulation of the compound in non-targeted tissue, which is likely due to an overload of the albumin transport system. It was also shown that lower amounts of injected c.a. [103Ru]BOLD-100 resulted in a relatively higher tumor uptake and, therefore, a better tumor-to-background ratio, which are encouraging results for future imaging studies using c.a. [97Ru]BOLD-100.

Anti-Migratory and Cytotoxic Activities of [Ga(8-hydroxyquinolinato)3 ]: Roles of Endogenous Cu(II) and Drug-Induced Phenotypic Changes

As shown by IncuCyte Zoom imaging proliferation assays, invasive triple-negative human breast MDA-MB-231 cancer cells treated with sub-toxic doses (5.0-20 μM, 72 h) of [GaQ3 ] (Q=8-hydroxyquinolinato) caused profound morphological changes and inhibition of cell migration, which were likely due to terminal cell differentiation or similar phenotypical change. This is the first demonstration of potential use of a metal complex in differentiation anti-cancer therapy. Additionally, a trace amount of Cu(II) (0.20 μM) added to the medium dramatically increased [GaQ3 ] cytotoxicity (IC50 ~2 μM, 72 h) due to its partial dissociation and the action of the HQ ligand as a Cu(II) ionophore, as shown with electrospray mass spectrometry and fluorescence spectroscopy assays in the medium. Hence, cytotoxicity of [GaQ3 ] is strongly linked to ligand binding of essential metal ions in the medium, for example, Cu(II). Appropriate delivery mechanisms of such complexes and their ligands could enable a powerful new triple therapeutic approach for cancer chemotherapy, including cytotoxicity against primary tumour, arrest of metastases, and activation of innate and adaptive immune responses.

Application of three-dimensional cell culture technology in screening anticancer drugs

The drug development process involves a variety of drug activity evaluations, which can determine drug efficacy, strictly analyze the biological indicators after the drug action, and use these indicators as the preclinical drug evaluation criteria. At present, most of the screening of preclinical anticancer drugs mainly relies on traditional 2D cell culture. However, this traditional technology cannot simulate the tumor microenvironment in vivo, let alone reflect the characteristics of solid tumors in vivo, and has a relatively poor ability to predict drug activity. 3D cell culture is a technology between 2D cell culture and animal experiments, which can better reflect the biological state in vivo and reduce the consumption of animal experiments. 3D cell culture can link the individual study of cells with the study of the whole organism, reproduce in vitro the biological phenotype of cells in vivo more greatly, and thus predict the activity and resistance of anti-tumor drugs more accurately. In this paper, the common techniques of 3D cell culture are discussed, with emphasis on its main advantages and application in the evaluation of anti-tumor resistance, which can provide strategies for the screening of anti-tumor drugs.

Enriching Chemical Space of Bioactive Scaffolds by New Ring Systems: Benzazocines and Their Metal Complexes as Potential Anticancer Drugs

The search for new scaffolds of medicinal significance combined with molecular shape enhances their innovative potential and continues to attract the attention of researchers. Herein, we report the synthesis, spectroscopic characterization (¹H and ¹³C NMR, UV-vis, IR), ESI-mass spectrometry, and single-crystal X-ray diffraction analysis of a new ring system of medicinal significance, 5,6,7,9-tetrahydro-8H-indolo[3,2-e]benzazocin-8-one, and a series of derived potential ligands (HL¹-HL⁵), as well as ruthenium(II), osmium(II), and copper(II) complexes (1a, 1b, and 2-5). The stability of compounds in 1% DMSO aqueous solutions has been confirmed by ¹H NMR and UV-vis spectroscopy measurements. The antiproliferative activity of HL¹-HL⁵ and 1a, 1b, and 2-5 was evaluated by in vitro cytotoxicity tests against four cancer cell lines (LS-174, HCT116, MDA-MB-361, and A549) and one non-cancer cell line (MRC-5). The lead compounds HL⁵ and its copper(II) complex 5 were 15× and 17×, respectively, more cytotoxic than cisplatin against human colon cancer cell line HCT116. Annexin V-FITC apoptosis assay showed dominant apoptosis inducing potential of both compounds after prolonged treatment (48 h) in HCT116 cells. HL⁵ and 5 were found to induce a concentration- and time-dependent arrest of cell cycle in colon cancer cell lines. Antiproliferative activity of 5 in 3D multicellular tumor spheroid model of cancer cells (HCT116, LS-174) superior to that of cisplatin was found. Moreover, HL⁵ and 5 showed notable inhibition potency against glycogen synthase kinases (GSK-3α and GSK-3β), tyrosine-protein kinase (Src), lymphocyte-specific protein-tyrosine kinase (Lck), and cyclin-dependent kinases (Cdk2 and Cdk5) (IC₅₀ = 1.4-6.1 μM), suggesting their multitargeted mode of action as potential anticancer drugs.

Advances in the application of 3D tumor models in precision oncology and drug screening

Traditional tumor models cannot perfectly simulate the real state of tumors in vivo, resulting in the termination of many clinical trials. 3D tumor models’ technology provides new in vitro models that bridge the gap between in vitro and in vivo findings, and organoids maintain the properties of the original tissue over a long period of culture, which enables extensive research in this area. In addition, they can be used as a substitute for animal and in vitro models, and organoids can be established from patients’ normal and malignant tissues, with unique advantages in clinical drug development and in guiding individualized therapies. 3D tumor models also provide a promising platform for high-throughput research, drug and toxicity testing, disease modeling, and regenerative medicine. This report summarizes the 3D tumor model, including evidence regarding the 3D tumor cell culture model, 3D tumor slice model, and organoid culture model. In addition, it provides evidence regarding the application of 3D tumor organoid models in precision oncology and drug screening. The aim of this report is to elucidate the value of 3D tumor models in cancer research and provide a preclinical reference for the precise treatment of cancer patients.

Evaluation of the Anti-Histoplasma capsulatum Activity of Indole and Nitrofuran Derivatives and Their Pharmacological Safety in Three-Dimensional Cell Cultures

Histoplasma capsulatum is a fungus that causes histoplasmosis. The increased evolution of microbial resistance and the adverse effects of current antifungals help new drugs to emerge. In this work, fifty-four nitrofurans and indoles were tested against the H. capsulatum EH-315 strain. Compounds with a minimum inhibitory concentration (MIC₉₀) equal to or lower than 7.81 µg/mL were selected to evaluate their MIC₉₀ on ATCC G217-B strain and their minimum fungicide concentration (MFC) on both strains. The quantification of membrane ergosterol, cell wall integrity, the production of reactive oxygen species, and the induction of death by necrosis–apoptosis was performed to investigate the mechanism of action of compounds 7, 11, and 32. These compounds could reduce the extracted sterol and induce necrotic cell death, similarly to itraconazole. Moreover, 7 and 11 damaged the cell wall, causing flaws in the contour (11), or changing the size and shape of the fungal cell wall (7). Furthermore, 7 and 32 induced reactive oxygen species (ROS) formation higher than 11 and control. Finally, the cytotoxicity was measured in two models of cell culture, i.e., monolayers (cells are flat) and a three-dimensional (3D) model, where they present a spheroidal conformation. Cytotoxicity assays in the 3D model showed a lower toxicity in the compounds than those performed on cell monolayers. Overall, these results suggest that derivatives of nitrofurans and indoles are promising compounds for the treatment of histoplasmosis.

Ruthenium(ii)-arene complexes as anti-metastatic agents, and related techniques

With the discovery of cisplatin, a vast area of applications of metallodrugs in cancer treatment was opened but due to the side effects caused by the cisplatin complexes, researchers began to look for alternatives with similar anticancer properties but fewer side effects. Ruthenium was found to be a promising candidate, considering its significant anticancer properties and low side effects. Several ruthenium complexes, viz. NAMI-A, KP1019, KP1339, and TLD1433, have entered clinical trials. Some other arene ruthenium complexes such as RM175 and RAPTA-C have also entered clinical trials but very few of them have shown anti-metastatic properties. Herein, we provide information and probable mechanistic pathways for ruthenium(ii)-arene complexes that have been studied, so far, for their anti-metastatic activities. Also, we discuss the techniques and their significance for determining the anti-metastatic effects of the complexes.

KP772 overcomes multiple drug resistance in malignant lymphoma and leukemia cells in vitro by inducing Bcl-2-independent apoptosis and upregulation of Harakiri

Despite high cure rates in pediatric patients with acute leukemia, development of resistance limits the efficacy of antileukemic therapy. Tris(1,10-phenanthroline)tris(thiocyanato-κN)lanthanum(III) (KP772) is an experimental antineoplastic agent to which multidrug-resistant cell models have shown hypersensitivity. Antiproliferative and apoptotic activities of KP772 were tested in leukemia, lymphoma and solid tumor cell lines as well as primary leukemia cells (isolated from the bone marrow of a child with acute myeloid leukemia (AML). The ability to overcome drug resistances was investigated in doxorubicin- and vincristine-resistant cell lines. Real-time PCR was used to gain insight into the mechanism of apoptosis induction. KP772 inhibited proliferation and induced apoptosis in various leukemia and lymphoma cell lines in a concentration-dependent manner (LC₅₀ = 1-2.5 µM). Primary AML cells were also sensitive to KP772, whereas daunorubicin showed no significant effect. KP772 induces apoptosis independently of Bcl-2, Smac, and the CD95 receptor and is also effective in caspase 3-deficient MCF7 cells, indicating that apoptosis is partly triggered independently of caspase 3. mRNA expression profiling revealed an upregulation of the BH3-only Bcl-2 protein Harakiri in the course of KP772-induced apoptosis. Remarkably, KP772 overcame drug resistance to doxorubicin and vincristine in vitro, and the apoptotic effect in resistant cells was even superior to that in non-resistant parental cells. In combination with vincristine, doxorubicin and cytarabine, synergistic effects were observed in BJAB cells. The cytotoxic potency in vitro/ex vivo and the remarkable ability to overcome multidrug resistance propose KP772 as a promising candidate drug for antileukemic therapy, especially of drug-refractory malignancies.Graphic abstract.

Introducing N-, P-, and S-donor leaving groups: an investigation of the chemical and biological properties of ruthenium, rhodium and iridium thiopyridone piano stool complexes

A series of 15 piano-stool complexes featuring either a RuII, RhIII or IrIII metal center, a bidentate thiopyridone ligand, and different leaving groups was synthesized. The leaving groups were selected in order to cover a broad range of different donor atoms. Thus, 1-methylimidazole served as a N-donor, 1,3,5-triaza-7-phosphaadamantane (pta) as a P-donor, and thiourea as a S-donor. Additionally, three complexes featuring different halido leaving groups (Cl, Br, I) were added. Leaving group alterations were carried out with respect to a possible influence on pharmacokinetic and pharmacodynamic parameters, as well as the cytotoxicity of the respective compounds. The complexes were characterized via NMR spectroscopy, X-ray diffraction (where possible), mass spectrometry, and elemental analysis. Cytotoxicity was assessed in 2D cultures of human cancer cell lines by microculture and clonogenic assays as well as in multicellular tumor spheroids. Furthermore, cellular accumulation studies, flow-cytometric apoptosis and ROS assays, DNA plasmid assays, and laser ablation ICP-MS studies for analyzing the distribution in sections of multicellular tumor spheroids were conducted. This work demonstrates the importance of investigating each piano-stool complexes' properties, as the most promising candidates showed advantages over each other in certain tests/assays. Thus, it was not possible to single out one lead compound, but rather a group of complexes with enhanced cytotoxicity and activity.

The Anticancer Activity of Indazole Compounds: A Mini Review

The incidence and mortality of cancer continue to grow since the current medical treatments often fail to produce a complete and durable tumor response and ultimately give rise to therapy resistance and tumor relapse. Heterocycles with potential therapeutic values are of great pharmacological importance, and among them, indazole moiety is a privileged structure in medicinal chemistry. Indazole compounds possess potential anticancer activity, and indazole-based agents such as, axitinib, lonidamine and pazopanib have already been employed for cancer therapy, demonstrating indazole compounds as useful templates for the development of novel anticancer agents. The aim of this review is to present the main aspects of exploring anticancer properties, such as the structural modifications, the structure-activity relationship and mechanisms of action, making an effort to highlight the importance and therapeutic potential of the indazole compounds in the present anticancer agents.

Targeting the NAD Salvage Synthesis Pathway as a Novel Therapeutic Strategy for Osteosarcomas with Low NAPRT Expression

For osteosarcoma (OS), the most common primary malignant bone tumor, overall survival has hardly improved over the last four decades. Especially for metastatic OS, novel therapeutic targets are urgently needed. A hallmark of cancer is aberrant metabolism, which justifies targeting metabolic pathways as a promising therapeutic strategy. One of these metabolic pathways, the NAD+ synthesis pathway, can be considered as a potential target for OS treatment. Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme in the classical salvage pathway for NAD+ synthesis, and NAMPT is overexpressed in OS. In this study, five OS cell lines were treated with the NAMPT inhibitor FK866, which was shown to decrease nuclei count in a 2D in vitro model without inducing caspase-driven apoptosis. The reduction in cell viability by FK866 was confirmed in a 3D model of OS cell lines (n = 3). Interestingly, only OS cells with low nicotinic acid phosphoribosyltransferase domain containing 1 (NAPRT1) RNA expression were sensitive to NAMPT inhibition. Using a publicly available (Therapeutically Applicable Research to Generate Effective Treatments (TARGET)) and a previously published dataset, it was shown that in OS cell lines and primary tumors, low NAPRT1 RNA expression correlated with NAPRT1 methylation around the transcription start site. These results suggest that targeting NAMPT in osteosarcoma could be considered as a novel therapeutic strategy, where low NAPRT expression can serve as a biomarker for the selection of eligible patients.

Multifunctional Pt(iv) prodrug candidates featuring the carboplatin core and deferoxamine

The synergistic combination of the anticancer drug carboplatin and the iron chelator deferoxamine (DFO) served as a foundation for the development of novel multifunctional prodrugs. Hence, five platinum(iv) complexes, featuring the equatorial coordination sphere of carboplatin, and one or two DFO units incorporated at axial positions, were synthesized and characterized using ESI-HRMS, multinuclear (¹H, ¹³C, ¹⁵N, ¹⁹⁵Pt) NMR spectroscopy and elemental analysis. Analytical studies demonstrated that the chelating properties of the DFO moiety were not compromised after coupling to the platinum(iv) core. The cytotoxic activity of the compounds was evaluated in monolayer (2D) and spheroid (3D) cancer cell models, derived from ovarian teratocarcinoma (CH1/PA-1), colon carcinoma (SW480) and non-small cell lung cancer (A549). The platinum(iv)-DFO prodrugs demonstrated moderate in vitro cytotoxicity (a consequence of their slow activation kinetics) but with less pronounced differences between intrinsically chemoresistant and chemosensitive cell lines as well as between 2D and 3D models than the clinically used platinum(ii) drug carboplatin.

Exploring the Potential of Metallodrugs as Chemotherapeutics for Triple Negative Breast Cancer

This review focuses on studies of coordination and organometallic compounds as potential chemotherapeutics against triple negative breast cancer (TNBC) which has one of the poorest prognoses and worst survival rates from all breast cancer types. At present, chemotherapy is still the standard of care for TNBC since only one type of targeted therapy has been recently developed. References for metal-based compounds studied in TNBC cell lines will be listed, and those of metal-specific reviews, but a detailed overview will also be provided on compounds studied in vivo (mostly in mice models) and those compounds for which some preliminary mechanistic data was obtained (in TNBC cell lines and tumors) and/or for which bioactive ligands have been used. The main goal of this review is to highlight the most promising metal-based compounds with potential as chemotherapeutic agents in TNBC.

Characterization of cachexia in the human fibrosarcoma HT-1080 mouse tumour model

BACKGROUND

Cancer cachexia is a complex metabolic disease with unmet medical need. Although many rodent models are available, none are identical to the human disease. Therefore, the development of new preclinical models that simulate some of the physiological, biochemical, and clinical characteristics of the human disease is valuable. The HT-1080 human fibrosarcoma tumour cell line was reported to induce cachexia in mice. Therefore, the purpose of this work was to determine how well the HT-1080 tumour model could recapitulate human cachexia and to examine its technical performance. Furthermore, the efficacy of ghrelin receptor activation via anamorelin treatment was evaluated, because it is one of few clinically validated mechanisms.

METHODS

Female severe combined immunodeficient mice were implanted subcutaneously or heterotopically (renal capsule) with HT-1080 tumour cells. The cachectic phenotype was evaluated during tumour development, including body weight, body composition, food intake, muscle function (force and fatigue), grip strength, and physical activity measurements. Heterotopic and subcutaneous tumour histology was also compared. Energy balance was evaluated at standard and thermoneutral housing temperatures in the subcutaneous model. The effect of anamorelin (ghrelin analogue) treatment was also examined.

RESULTS

The HT-1080 tumour model had excellent technical performance and was reproducible across multiple experimental conditions. Heterotopic and subcutaneous tumour cell implantation resulted in similar cachexia phenotypes independent of housing temperature. Tumour weight and histology was comparable between both routes of administration with minimal inflammation. Subcutaneous HT-1080 tumour-bearing mice presented with weight loss (decreased fat mass and skeletal muscle mass/fibre cross-sectional area), reduced food intake, impaired muscle function (reduced force and grip strength), and decreased spontaneous activity and voluntary wheel running. Key circulating inflammatory biomarkers were produced by the tumour, including growth differentiation factor 15, Activin A, interleukin 6, and TNF alpha. Anamorelin prevented but did not reverse anorexia and weight loss in the subcutaneous model.

CONCLUSIONS

The subcutaneous HT-1080 tumour model displays many of the perturbations of energy balance and physical performance described in human cachexia, consistent with the production of key inflammatory factors. Anamorelin was most effective when administered early in disease progression. The HT-1080 tumour model is valuable for studying potential therapeutic targets for the treatment of cachexia.

Metallodrugs are unique: opportunities and challenges of discovery and development

Metals play vital roles in nutrients and medicines and provide chemical functionalities that are not accessible to purely organic compounds. At least 10 metals are essential for human life and about 46 other non-essential metals (including radionuclides) are also used in drug therapies and diagnostic agents. These include platinum drugs (in 50% of cancer chemotherapies), lithium (bipolar disorders), silver (antimicrobials), and bismuth (broad-spectrum antibiotics). While the quest for novel and better drugs is now as urgent as ever, drug discovery and development pipelines established for organic drugs and based on target identification and high-throughput screening of compound libraries are less effective when applied to metallodrugs. Metallodrugs are often prodrugs which undergo activation by ligand substitution or redox reactions, and are multi-targeting, all of which need to be considered when establishing structure-activity relationships. We focus on early-stage in vitro drug discovery, highlighting the challenges of evaluating anticancer, antimicrobial and antiviral metallo-pharmacophores in cultured cells, and identifying their targets. We highlight advances in the application of metal-specific techniques that can assist the preclinical development, including synchrotron X-ray spectro(micro)scopy, luminescence, and mass spectrometry-based methods, combined with proteomic and genomic (metallomic) approaches. A deeper understanding of the behavior of metals and metallodrugs in biological systems is not only key to the design of novel agents with unique mechanisms of action, but also to new understanding of clinically-established drugs.

Novel phthiocol-based organometallics with tridentate coordination motif and their unexpected cytotoxic behaviour

Novel phthiocol-based organometallics with in situ formed tridentate N,O,O-coordination motif were established via three-component microwave assisted one-pot reaction. These complexes exhibited enhanced stability in aqueous solution compared to the parental compound KP2048 and showed unexpected cytotoxic behaviour and selectivity in 2D and 3D cell cultures.

Comparative antitumor studies of organoruthenium complexes with 8-hydroxyquinolines on 2D and 3D cell models of bone, lung and breast cancer

The purpose of this work was to screen the antitumor actions of two metal organoruthenium-8-hydroxyquinolinato (Ru-hq) complexes to find a potential novel agent for bone, lung and breast chemotherapies. We showed that ruthenium compounds (1 and 2) impaired the cell viability of human bone (MG-63), lung (A549) and breast (MCF7) cancer cells with greater selectivity and specificity than cisplatin. Besides, complexes 1 and 2 decreased proliferation, migration and invasion on cell monolayers at lower concentrations (2.5-10 μM). In addition, both compounds induced genotoxicity revealed by the micronucleus test, which led to G2/M cell cycle arrest and induced the tumor cells to undergo apoptosis. On the other hand, in multicellular 3D models (multicellular spheroids; MCS), 1 and 2 overcame CDDP presenting lower IC50 values only in MCS of lung origin. Moreover, 1 outperformed 2 in MCS of bone and breast origin. Finally, our findings revealed that both compounds inhibited the cell invasion of multicellular spheroids, showing that complex 1 exhibited the most important antimetastatic action. Taken together, these results indicate that compound 1 is an interesting candidate to be tested on in vivo models as a novel strategy for anticancer therapy.

Synthesis, Modification, and Biological Evaluation of a Library of Novel Water-Soluble Thiopyridone-Based Organometallic Complexes and Their Unexpected (Biological) Behavior

A series of 16 dinuclear thiopyridone-based organometallics with excellent water solubility, increased stability and remarkable cytotoxicity were synthesized and characterized. The complexes of this work formed dimeric species featuring a double positive charge in polar protic solvents, accounting for their outstanding solubility in aqueous solution. Most of them displayed higher antiproliferative activity than their parental thiomaltol complex, with unexpected cytotoxicity trends depending on the employed metal center, ligand modification, and cell line. Insights into their behavior in biological systems were gathered by means of amino-acid interaction studies, cytotoxicity tests in 3D spheroid models, laser ablation, cellular accumulation measurements, as well as cell cycle experiments.

Low-dimensional compounds containing bioactive ligands. Part XIV: High selective antiproliferative activity of tris(5-chloro-8-quinolinolato)gallium(III) complex against human cancer cell lines

Four gallium(III) complexes, [Ga(ClQ)₃]⋅MeOH (1 - MeOH), [Ga(ClQ)₃] (1), [Ga(BrQ)₃] (2), [Ga(dIQ)₃] (3) and [Ga(CQ)₃] (4), were prepared (H-ClQ = 5-chloro-8-quinolinol, H-BrQ = 7-bromo-8-quinolinol, H-dIQ = 5,7-diiodo-8-quinolinol, H-CQ = 5-chloro-7-iodo-8-quinolinol) and characterised by elemental analysis, IR and NMR spectroscopy. Single crystal structure analysis of 1 - MeOH confirmed that the complex has a molecular structure with gallium(III) metal ion coordinated in mer-fashion by N- and O-donor atoms of three ClQ ligands. Stability of all complexes in DMSO was proved by ¹H NMR spectroscopy. The in vitro antiproliferative activity of 1 was evaluated against the A2780, MBA-MB-231 and HCT116 cell lines. Complex 1 displays higher antiproliferative activity (IC₅₀ values in the range 2.1-6 μm) compared to the ClQ ligand and cisplatin; and a significant selective antiproliferative potency (IC₅₀ = 136 μm, for normal MRC5pd30 cell line). Radical scavenging experiments revealed that complex 1 exhibits the highest antioxidant activity of the prepared complexes as well as the ligands.

Ruthenium(II)-Arene Thiocarboxylates: Identification of a Stable Dimer Selectively Cytotoxic to Invasive Breast Cancer Cells

Ru^II -arene complexes provide a versatile scaffold for novel anticancer drugs. Seven new Ru^II -arene-thiocarboxylato dimers were synthesized and characterized. Three of the complexes (2 a, b and 5) showed promising antiproliferative activities in MDA-MB-231 (human invasive breast cancer) cells, and were further tested in a panel of fifteen cancerous and noncancerous cell lines. Complex 5 showed moderate but remarkably selective activity in MDA-MB-231 cells (IC₅₀ =39±4 μm Ru). Real-time proliferation studies showed that 5 induced apoptosis in MDA-MB-231 cells but had no effect in A549 (human lung cancer, epithelial) cells. By contrast, 2 a and b showed moderate antiproliferative activity, but no apoptosis, in either cell line. Selective cytotoxicity of 5 in aggressive, mesenchymal-like MDA-MB-231 cells over many common epithelial cancer cell lines (including noninvasive breast cancer MCF-7) makes it an attractive lead compound for the development of specifically antimetastatic Ru complexes with low systemic toxicity.

High-Throughput, Temporal and Dose Dependent, Effect of Vitamins and Minerals on Chondrogenesis

Tissue engineered hyaline cartilage is plagued by poor mechanical properties largely due to inadequate type II collagen expression. Of note, commonly used defined chondrogenic media lack 14 vitamins and minerals, some of which are implicated in chondrogenesis. Type II collagen promoter-driven Gaussia luciferase was transfected into ATDC5 cells to create a chondrogenic cell with a secreted-reporter. The reporter cells were used in an aggregate-based chondrogenic culture model to develop a high-throughput analytic platform. This high-throughput platform was used to assess the effect of vitamins and minerals, alone and in combination with TGFβ1, on COL2A1 promoter-driven expression. Significant combinatorial effects between vitamins, minerals, and TGFβ1 in terms of COL2A1 promoter-driven expression and metabolism were discovered. An “optimal” continual supplement of copper and vitamin K in the presence of TGFβ1 gave a 2.5-fold increase in COL2A1 promoter-driven expression over TGFβ1 supplemented media alone in ATDC5 cells.

Anticancer and antimetastatic activity of copper(II)-tropolone complex against human breast cancer cells, breast multicellular spheroids and mammospheres

The goal of this work was to display the anticancer and antimetastatic activity of a copper(II) with tropolone (trp), complex [Cu(trp)₂] toward human breast cancer cells in monolayer (2D) and spheroids (3D). Cytotoxicity assays against MCF7 (IC_50(complex) = 5.2 ± 1.8 μM, IC_50(CDDP) = 19.3 ± 2.1 μM) and MDA-MB-231 (IC_50(complex) = 4.0 ± 0.2 μM, IC_50(CDDP) = 27.0 ± 1.9 μM) demonstrate that [Cu(trp)₂] exert greater antitumor potency than cisplatin (CDDP) on 2D and 3D human breast cancer cell models. Besides, [Cu(trp)₂] inhibits cell migration by reducing the metalloproteinases activities and the compound undergoes the breast cancer cells to apoptosis at lower concentrations (2.5-10 μM). Moreover, [Cu(trp)₂] overcame CDDP presenting an IC₅₀ value 26-fold more lower against breast multicellular spheroids ((IC_50(complex) = 4.9 μM, IC_50(CDDP) = 130 μM)). Also, our results showed that [Cu(trp)₂] inhibited the cell migration and cell invasion of breast multicellular spheroids, showing that [Cu(trp)₂] exhibited antimetastatic properties. On the other hand, [Cu(trp)₂] reduced mammosphere forming capacity affecting the size and number of mammospheres. Taken together, [Cu(trp)₂] exhibited anticancer and antimetastatic properties on monolayer (2D) and spheroids (3D) derived from human breast cancer cells.

NAMI-A and KP1019/1339, Two Iconic Ruthenium Anticancer Drug Candidates Face-to-Face: A Case Story in Medicinal Inorganic Chemistry

NAMI-A ((ImH)[trans-RuCl₄(dmso-S)(Im)], Im = imidazole) and KP1019/1339 (KP1019 = (IndH)[trans-RuCl₄(Ind)₂], Ind = indazole; KP1339 = Na[trans-RuCl₄(Ind)₂]) are two structurally related ruthenium(III) coordination compounds that have attracted a lot of attention in the medicinal inorganic chemistry scientific community as promising anticancer drug candidates. This has led to a considerable amount of studies on their respective chemico-biological features and to the eventual admission of both to clinical trials. The encouraging pharmacological performances qualified KP1019 mainly as a cytotoxic agent for the treatment of platinum-resistant colorectal cancers, whereas the non-cytotoxic NAMI-A has gained the reputation of being a very effective antimetastatic drug. A critical and strictly comparative analysis of the studies conducted so far on NAMI-A and KP1019 allows us to define the state of the art of these experimental ruthenium drugs in terms of the respective pharmacological profiles and potential clinical applications, and to gain some insight into the inherent molecular mechanisms. Despite their evident structural relatedness, deeply distinct biological and pharmacological profiles do emerge. Overall, these two iconic ruthenium complexes form an exemplary and unique case in the field of medicinal inorganic chemistry.

Challenges and Chances in the Preclinical to Clinical Translation of Anticancer Metallodrugs

Despite being “sentenced to death” for quite some time, anticancer platinum compounds are still the most frequently prescribed cancer therapies in the oncological routine and recent exciting news from late-stage clinical studies on combinations of metallodrugs with immunotherapies suggest that this situation will not change soon. It is perhaps surprising that relatively simple molecules like cisplatin, discovered over 50 years ago, are still widely used clinically, while none of the highly sophisticated metal compounds developed over the last decade, including complexes with targeting ligands and multifunctional (nano)formulations, have managed to obtain clinical approval. In this book chapter, we summarize the current status of ongoing clinical trials for anticancer metal compounds and discuss the reasons for previous failures, as well as new opportunities for the clinical translation of metal complexes.

In vitro and in vivo anticancer effects of two quinoline-platinum(II) complexes on human osteosarcoma models

Platinum-based drugs, mainly cisplatin, are used for the treatment of several solid tumors such as OS. However, cisplatin treatment often results in the development of chemoresistance, leading therapeutic failure. We have previously reported that platinum complexes containing 8-hydroxyquinoline ligands have good antitumor activity against different cancer cell lines and with a different and better cytotoxic profile than cisplatin. Here, the anticancer properties of two different quinoline-platinum complexes [Pt(Cl)₂(quinoline)(dmso)] (1) [PtCl(8-O-quinoline)(dmso)] (2) on in vitro (2D and 3D) and in vivo models (xenograft tumor of human osteosarcoma in mice) are presented. In this order, [PtCl(8-O-quinoline)(dmso)] (2) impaired cell viability to have a more pronounced antitumor effect than cisplatin on MG-63 osteosarcoma cells (IC₅₀ 4 µM vs. 39 µM). Besides, [PtCl(8-O-quinoline)(dmso)] (2) increased ROS production in a dose-manner response and this compound induced early and late apoptotic fractions of human osteosarcoma cells. Finally, [PtCl(8-O-quinoline)(dmso)] (2) decreased the cell viability of multicellular spheroids and reduced the tumor volume on athymic nude mice N:NIH(S) Fox1^nu without inducing side effects. In this way, [PtCl(8-O-quinoline)(dmso)] (2) did not alter the normal cytoarchitecture of liver and kidney and the blood biomarkers (GPT, GOT, uremia, and creatinine) did not suffer modifications. Taken together, our data indicate that these compounds showed a better anticancer performance than cisplatin on in vitro and in vivo studies. These results showed the importance of chelation in the antitumor properties, suggesting that the [PtCl(8-O-quinoline)(dmso)] (2) might be a promising agent for the treatment of human osteosarcoma tumors resistant to cisplatin.

Structure-activity relationships for ruthenium and osmium anticancer agents - towards clinical development

Anticancer metallodrugs based on ruthenium and osmium are among the most investigated and advanced non-platinum metallodrugs. Inorganic drug discovery with these agents has undergone considerable advances over the past two decades and has currently two representatives in active clinical trials. As many ruthenium and osmium metallodrugs are prodrugs, a key question to be addressed is how the molecular reactivity of such metal-based therapeutics dictates the selectivity and the type of interaction with molecular targets. Within this frame, this review introduces the field by the examples of the most advanced ruthenium lead structures. Then, global structure-activity relationships are discussed for ruthenium and osmium metallodrugs with respect to in vitro antiproliferative/cytotoxic activity and in vivo tumor-inhibiting properties, as well as pharmacokinetics. Determining and validating global mechanisms of action and molecular targets are still major current challenges. Moreover, significant efforts must be invested in screening in vivo tumor models that mimic human pathophysiology to increase the predictability for successful preclinical and clinical development of ruthenium and osmium metallodrugs.

Comparative studies of oxaliplatin-based platinum(iv) complexes in different in vitro and in vivo tumor models

Using platinum(iv) prodrugs of clinically established platinum(ii) compounds is a strategy to overcome side effects and acquired resistances. We studied four oxaliplatin-derived platinum(iv) complexes with varying axial ligands in various in vitro and in vivo settings. The ability to interfere with DNA (pUC19) in the presence and absence of a reducing agent (ascorbic acid) was investigated in cell-free experiments. Cytotoxicity was compared under normoxic and hypoxic conditions in monolayer cultures and multicellular spheroids of colon carcinoma cell lines. Effects on the cell cycle were investigated by flow cytometry, and the capacity of inducing apoptosis was confirmed by flow cytometry and Western blotting. The anti-cancer activity of one complex was studied in vivo in immunodeficient and immunocompetent mice, and the platinum levels in various organs and the tumor after treatment were quantified. The results demonstrate that modification of the axial ligands can improve the cytotoxic potency. The complexes are able to interfere with plasmid DNA, which is enhanced by co-incubation with a reducing agent, and cause cell cycle perturbations. At higher concentrations, they induce apoptosis, but generate only low levels of reactive oxygen species. Two of the complexes increase the life span of leukemia (L1210) bearing mice, and one showed effects similar to oxaliplatin in a CT26 solid tumor model, despite the low platinum levels in the tumor. As in the case of oxaliplatin, activity in the latter model depends on an intact immune system. These findings show new perspectives for the development of platinum(iv) prodrugs of the anticancer agent oxaliplatin, combining bioreductive properties and immunogenic aspects.

Drug delivery to solid tumors: the predictive value of the multicellular tumor spheroid model for nanomedicine screening

The increasing number of publications on the subject shows that nanomedicine is an attractive field for investigations aiming to considerably improve anticancer chemotherapy. Based on selective tumor targeting while sparing healthy tissue, carrier-mediated drug delivery has been expected to provide significant benefits to patients. However, despite reduced systemic toxicity, most nanodrugs approved for clinical use have been less effective than previously anticipated. The gap between experimental results and clinical outcomes demonstrates the necessity to perform comprehensive drug screening by using powerful preclinical models. In this context, in vitro three-dimensional models can provide key information on drug behavior inside the tumor tissue. The multicellular tumor spheroid (MCTS) model closely mimics a small avascular tumor with the presence of proliferative cells surrounding quiescent cells and a necrotic core. Oxygen, pH and nutrient gradients are similar to those of solid tumor. Furthermore, extracellular matrix (ECM) components and stromal cells can be embedded in the most sophisticated spheroid design. All these elements together with the physicochemical properties of nanoparticles (NPs) play a key role in drug transport, and therefore, the MCTS model is appropriate to assess the ability of NP to penetrate the tumor tissue. This review presents recent developments in MCTS models for a better comprehension of the interactions between NPs and tumor components that affect tumor drug delivery. MCTS is particularly suitable for the high-throughput screening of new nanodrugs.

Tumor cells and their crosstalk with endothelial cells in 3D spheroids

Recapitulating the tumor microenvironment is a central challenge in the development of experimental model for cancer. To provide a reliable tool for drug development and for personalized cancer therapy, it is critical to maintain key features that  exist in the original tumor. Along with this effort, 3-dimentional (3D) cellular models are being extensively studied. Spheroids are self-assembled cell aggregates that possess many important components of the physiological spatial growth and cell-cell interactions. In this study we aimed to investigate the interconnection between tumor and endothelial cells (EC) in hybrid spheroids containing either tumor cell (TC) lines or patient derived cancer cells. Preparation protocols of hybrid spheroids were optimized and their morphology and tissue-like features were analyzed. Our finding show that capillary-like structures are formed upon assembly and growth of TC:EC spheroids and that spheroids’ shape and surface texture may be an indication of spatial invasiveness of cells in the extra-cellular matrix (ECM). Establishing a model of hybrid tumor/stroma spheroids has a crucial importance in the experimental approach for personalized medicine, and may offer a reliable and low-cost method for the goal of predicting drug effects.

Response Profiling Using Shotgun Proteomics Enables Global Metallodrug Mechanisms of Action To Be Established

Response profiling using shotgun proteomics for establishing global metallodrug mechanisms of action in two colon carcinoma cell lines, HCT116 and SW480, has been applied and evaluated with the clinically approved arsenic trioxide. Surprisingly, the complete established mechanism of action of arsenic trioxide was observed by protein regulations in SW480, but not HCT116 cells. Comparing the basal protein expression in the two cell lines revealed an 80 % convergence of protein identification, but with significant expression differences, which in turn seem to affect the extent of protein regulation. A clear-cut redox response was observed in SW480 cells upon treatment with arsenic, but hardly in HCT116 cells. Response profiling was then used to investigate four anti-cancer metallodrugs (KP46, KP772, KP1339 and KP1537). Proteome alterations were mapped to selected functional groups, including DNA repair, endocytosis, protection from oxidative stress, protection from endoplasmatic reticulum (ER) stress, cell adhesion and mitochondrial function. The present data suggest that knowledge of the mechanism of action of anti-cancer metallodrugs and improved patient stratification strategies are imperative for the design of clinical studies.

Drug screening in 3D in vitro tumor models: overcoming current pitfalls of efficacy read-outs

There is cumulating evidence that in vitro 3D tumor models with increased physiological relevance can improve the predictive value of pre-clinical research and ultimately contribute to achieve decisions earlier during the development of cancer-targeted therapies. Due to the role of tumor microenvironment in the response of tumor cells to therapeutics, the incorporation of different elements of the tumor niche on cell model design is expected to contribute to the establishment of more predictive in vitro tumor models. This review is focused on the several challenges and adjustments that the field of oncology research is facing to translate these advanced tumor cells models to drug discovery, taking advantage of the progress on culture technologies, imaging platforms, high throughput and automated systems. The choice of 3D cell model, the experimental design, choice of read-outs and interpretation of data obtained from 3D cell models are critical aspects when considering their implementation in drug discovery. In this review, we foresee some of these aspects and depict the potential directions of pre-clinical oncology drug discovery towards improved prediction of drug efficacy.

In vitro and in vivo antitumor effects of the VO-chrysin complex on a new three-dimensional osteosarcoma spheroids model and a xenograft tumor in mice

Osteosarcoma (OS) is the most common primary tumor of bone, occurring predominantly in the second decade of life. High-dose cytotoxic chemotherapy and surgical resection have improved prognosis, with long-term survival for patients with localized disease. Vanadium is an ultra-trace element that after being absorbed accumulates in bone. Besides, vanadium compounds have been studied during recent years to be considered as representative of a new class of non-platinum antitumor agents. Moreover, flavonoids are a wide family of polyphenolic compounds that display many interesting biological effects. Since coordination of ligands to metals can improve the pharmacological properties, we report herein, for the first time, the in vitro and in vivo effects of an oxidovanadium(IV) complex with the flavonoid chrysin on the new 3D human osteosarcoma and xenograft osteosarcoma mice models. The pharmacological results show that VOchrys inhibited the cell viability affecting the shape and volume of the spheroids and VOchrys suppressed MG-63 tumor growth in the nude mice without inducing toxicity and side effects. As a whole, the results presented herein demonstrate that the antitumor action of the complex was very promissory on human osteosarcoma models, whereby suggesting that VOchrys is a potentially good candidate for future use in alternative antitumor treatments.

Behavior of platinum(iv) complexes in models of tumor hypoxia: cytotoxicity, compound distribution and accumulation

Hypoxia in solid tumors remains a challenge for conventional cancer therapeutics. As a source for resistance, metastasis development and drug bioprocessing, it influences treatment results and disease outcome. Bioreductive platinum(iv) prodrugs might be advantageous over conventional metal-based therapeutics, as biotransformation in a reductive milieu, such as under hypoxia, is required for drug activation. This study deals with a two-step screening of experimental platinum(iv) prodrugs with different rates of reduction and lipophilicity with the aim of identifying the most appropriate compounds for further investigations. In the first step, the cytotoxicity of all compounds was compared in hypoxic multicellular spheroids and monolayer culture using a set of cancer cell lines with different sensitivities to platinum(ii) compounds. Secondly, two selected compounds were tested in hypoxic xenografts in SCID mouse models in comparison to satraplatin, and, additionally, (LA)-ICP-MS-based accumulation and distribution studies were performed for these compounds in hypoxic spheroids and xenografts. Our findings suggest that, while cellular uptake and cytotoxicity strongly correlate with lipophilicity, cytotoxicity under hypoxia compared to non-hypoxic conditions and antitumor activity of platinum(iv) prodrugs are dependent on their rate of reduction.

LA-ICP-MS imaging in multicellular tumor spheroids - a novel tool in the preclinical development of metal-based anticancer drugs

A novel application of advanced elemental imaging offers cutting edge in vitro assays with more predictive power on the efficacy of anticancer drugs in preclinical development compared to two dimensional cell culture models. We propose LA-ICP-MS analysis of multicellular spheroids, which are increasingly being used as three dimensional (3D) models of tumors, for improving the in vitro evaluation of anticancer metallodrugs. The presented strategy is very well suited for screening drug-tumor penetration, a key issue for drug efficacy. A major advantage of tumor spheroid models is that they enable us to create a tissue-like structure and function. With respect to 2D culture on the one hand and in vivo models on the other, multicellular spheroids thus show intermediate complexity, still allowing high repeatability and adequate through-put for drug research. This strongly argues for the use of spheroids as bridging models in preclinical anticancer drug development. Probing the lateral platinum distribution within these tumor models allows visualizing the penetration depth and targeting of platinum-based complexes. In the present study, we show for the first time that spatially-resolved metal accumulation in tumor spheroids upon treatment with platinum compounds can be appropriately assessed. The optimized LA-ICP-MS setup allowed discerning the platinum localization in different regions of the tumor spheroids upon compound treatment at biologically relevant (low micromolar) concentrations. Predominant platinum accumulation was observed at the periphery as well as in the center of the spheroids. This corresponds to the proliferating outermost layers of cells and the necrotic core, respectively, indicating enhanced platinum sequestration in these regions.

Remodeling Components of the Tumor Microenvironment to Enhance Cancer Therapy

Solid tumor pathophysiology is characterized by an abnormal microenvironment that guides tumor progression and poses barriers to the efficacy of cancer therapies. Most common among tumor types are abnormalities in the structure of the tumor vasculature and stroma. Remodeling the tumor microenvironment with the aim to normalize any aberrant properties has the potential to improve therapy. In this review, we discuss structural abnormalities of the tumor microenvironment and summarize the therapeutic strategies that have been developed to normalize tumors as well as their potential to enhance therapy. Finally, we present different in vitro models that have been developed to analyze and better understand the effects of the tumor microenvironment on cancer cell behavior.