Influence of reducing agents on the cytotoxic activity of platinum(IV) complexes: induction of G2/M arrest, apoptosis and oxidative stress in A2780 and cisplatin resistant A2780cis cell lines

Computational Exploration of the Synergistic Anticancer Effect of a Multi-Action Ru(II)-Pt(IV) Conjugate

An in-depth computational study of the ability of a recently proposed multi-action Ru(II)–Pt(IV) conjugate to act as a photosensitizer in photodynamic therapy (PDT) and chemotherapeutic drugs is presented here. The investigated complex is characterized by a polypyridyl Ru(II) chromophore linked to a Pt(IV) complex that, acting as a prodrug, should be activated by reduction releasing the Ru-based chromophore that can absorb light of proper wavelength to be used in PDT. The reaction mechanism for active species formation has been fully elucidated by means of density functional theory and its time-dependent extension. The reduction mechanism, assisted by ascorbate, of the Pt(IV) prodrug to the Pt(II) active species has been explored, taking into consideration all the possible modes of attack of the reductant for releasing the axial ligands and affording active cisplatin. Given the similarity in the photophysical properties of the chromophore linked or not to the Pt(IV) complex, both the Ru(II)–Pt(IV) conjugate precursor and the Ru(II) chromophore should be able to act as PDT photosensitizers according to type I and type II photoprocesses. In particular, they are able to generate singlet oxygen cytotoxic species as well as auto-ionize to form highly reactive O₂^–• species.

A computational study on the ability of a multi-action Ru(II)−Pt(IV) conjugate to act as a photosensitizer in photodynamic therapy (PDT) and chemotherapeutic drugs is presented here. The reduction mechanism of the Pt(IV) complex along with the photophysical properties of both the prodrug Ru(II)−Pt(IV) conjugate and Ru(II) complex is provided. The mechanism of action has been fully elucidated by means of density functional theory and its time-dependent extension.

Ascorbic acid ameliorates dysregulated folliculogenesis induced by mono-(2-ethylhexyl)phthalate in neonatal mouse ovaries via reducing ovarian oxidative stress

Phthalates, including di-(2-ethylhexyl)phthalate (DEHP), are common industrial chemicals in the environment. Recent evidence indicates that DEHP and its active metabolite mono-(2-ethylhexyl)phthalate (MEHP) negatively modulate reproductive functions and induce reactive oxygen species. Ascorbic acid (AA) is a dietary requirement for primates, and it acts as a potent free radical scavenger to protect tissues against oxidative stress. In this study, to investigate the toxic effects of MEHP on the follicle development and the beneficial role of AA, neonatal mouse ovaries were treated with different concentrations of MEHP with or without AA for 6 days. Then, the follicle constitution and oxidative status were compared in different groups. Results showed MEHP accelerated primordial follicle recruitment by increasing the percentage of primary and secondary follicles and decreasing the percentage of primordial follicles in the ovaries. Moreover, MEHP-induced ovarian oxidative stress by significantly increasing malondialdehyde (MDA) concentration and the expression of GSS and SOD1. When ovaries were co-administrated with MEHP and AA, follicle constitution was normalized, and the oxidative status was significantly decreased. These results suggested that AA ameliorated MEHP-induced ovarian oxidative stress and follicular dysregulation, which attested the clinical significance of AA for ovary protection in the case of MEHP exposure.

Novel Pt(IV) Prodrugs Displaying Antimitochondrial Effects

The design, synthesis, characterization, and biological activity of a series of platinum(IV) prodrugs containing the axial ligand 3-(4-phenylquinazoline-2-carboxamido)propanoate (L3) are reported. L3 is a derivative of the quinazolinecarboxamide class of ligands that binds to the translocator protein (TSPO) at the outer mitochondrial membrane. The cytotoxicities of cis,cis,trans-[Pt(NH₃)₂Cl₂(L3)(OH)] (C-Pt1), cis,cis,trans-[Pt(NH₃)₂Cl₂(L3)(BZ)] (C-Pt2), trans-[Pt(DACH)(OX)(L3)(OH)] (C-Pt3), and trans-[Pt(DACH)(OX)(L3)(BZ)] (C-Pt4) (DACH: R,R-diaminocyclohexane, BZ: benzoate, OX: oxalate) in MCF-7 breast cancer and noncancerous MCF-10A epithelial cells were assessed and compared with those of cisplatin, oxaliplatin, and the free ligand L3. Moreover, the cellular uptake, ROS generation, DNA damage, and the effect on the mitochondrial function, mitochondrial membrane potential, and morphology were investigated. Molecular interactions of L3 in the TSPO binding site were studied using molecular docking. The results showed that complex C-Pt1 is the most effective Pt(IV) complex and exerts a multimodal mechanism involving DNA damage, potent ROS production, loss of the mitochondrial membrane potential, and mitochondrial damage.

Pt(IV) pro-drugs with an axial HDAC inhibitor demonstrate multimodal mechanisms involving DNA damage and apoptosis independent of cisplatin resistance in A2780/A2780cis cells

Epigenetic agents such as histone deacetylase (HDAC) inhibitors are widely investigated for use in combined anticancer therapy and the co-administration of Pt drugs with HDAC inhibitors has shown promise for the treatment of resistant cancers. Coordination of an HDAC inhibitor to an axial position of a Pt(IV) derivative of cisplatin allows the combination of the epigenetic drug and the Pt chemotherapeutic into a single molecule. In this work we carry out mechanistic studies on the known Pt(IV) complex cis,cis,trans-[Pt(NH₃)₂Cl₂(PBA)₂] (B) with the HDAC inhibitor 4-phenylbutyrate (PBA) and its derivatives cis,cis,trans-[Pt(NH₃)₂Cl₂(PBA)(OH)] (A), cis,cis,trans-[Pt(NH₃)₂Cl₂(PBA)(Bz)] (C), and cis,cis,trans-[Pt(NH₃)₂Cl₂(PBA)(Suc)] (D) (Bz = benzoate, Suc = succinate). The comparison of the cytotoxicity, effect on HDAC activity, reactive oxygen species (ROS) generation, γ-H2AX (histone 2A-family member X) foci generation and induction of apoptosis in cisplatin-sensitive and cisplatin-resistant ovarian cancer cells shows that A - C exhibit multimodal mechanisms involving DNA damage and apoptosis independent of cisplatin resistance.

Exploring six-coordinate germanium(IV)-diketonate complexes as anticancer agents

Cancer remains one of the leading causes of death worldwide and despite several attempts using chemotherapy to combat the deadly disease, toxic side effects and drug resistance temper efficacy [1]. Thus, drugs with potentially new mechanisms and lower toxicity to normal cells are needed. Metalloids such as arsenic compounds have been clinically beneficial in fighting cancer, but germanium is yet to gain such prominence [2,3]. We report the synthesis of four octahedral germanium(IV) complexes bearing acetylacetonato ligand, [GeIV(acac)3)]+, with different anions (3 - 6) using a streamlined synthetic approach. The compounds were structurally and electrochemically characterized using NMR, MS, X-ray crystallography, and cyclic voltammetry. The cyclic voltammogram of 3-5 revealed distinct irreversible peaks in the range of -0.9 to -1.9 V, corresponding to Ge(IV)/ Ge(II) or Ge(II)/Ge(0) couple in DMSO. We explored the anticancer activity of the complexes against a panel of cancer cell lines with IC50 values in the sub-micromolar range (9-15 μM). The compounds display ~3-fold selectivity in cancer cells over normal epithelial cells. In addition to the promising anticancer activity, the compounds display high complex stability in biological media, induces G1 arrest, reactive oxygen stress (ROS) accumulation, and mitochondria membrane depolarization in cancer cells. Furthermore, the compounds induce significant apoptosis.

Investigations of the Kinetics and Mechanism of Reduction of a Carboplatin Pt(IV) Prodrug by the Major Small-Molecule Reductants in Human Plasma

The development of Pt(IV) anticancer prodrugs to overcome the detrimental side effects of Pt(II)-based anticancer drugs is of current interest. The kinetics and reaction mechanisms of the reductive activation of the carboplatin Pt(IV) prodrug cis,trans-[Pt(cbdca)(NH₃)₂Cl₂] (cbdca = cyclobutane-1,1-dicarboxylate) by the major small-molecule reductants in human plasma were analyzed in this work. The reductants included ascorbate (Asc), the thiol-containing molecules L-cysteine (Cys), DL-homocysteine (Hcy), and glutathione (GSH), and the dipeptide Cys–Gly. Overall second-order kinetics were established in all cases. At the physiological pH of 7.4, the observed second-order rate constants k′ followed the order Asc << Cys–Gly ~ Hcy < GSH < Cys. This reactivity order together with the abundances of the reductants in human plasma indicated Cys as the major small-molecule reductant in vivo, followed by GSH and ascorbate, whereas Hcy is much less important. In the cases of Cys and GSH, detailed reaction mechanisms and the reactivity of the various protolytic species at physiological pH were derived. The rate constants of the rate-determining steps were evaluated, allowing the construction of reactivity-versus-pH distribution diagrams for Cys and GSH. The diagrams unraveled that species III of Cys (⁻SCH₂CH(NH₃⁺)COO⁻) and species IV of GSH (⁻OOCCH(NH₃⁺)CH₂CH₂CONHCH(CH₂S⁻)- CONHCH₂COO⁻) were exclusively dominant in the reduction process. These two species are anticipated to be of pivotal importance in the reduction of other types of Pt(IV) prodrugs as well.

Cytotoxic RuII-p-cymene complexes of an anthraimidazoledione: halide dependent solution stability, reactivity and resistance to hypoxia deactivation

RuII-(η6-p-cymene) complexes of anthraimidazoldione (PAIDH) based ligand bearing the formula [RuII(η6-p-cymene)(PAIDH)(X)]+ (where, X = Cl, Br and I) showed excellent in vitro antiproliferative activity (IC50 range 1-2 μM) against hepatocellular carcinoma (HepG2), human pancreatic carcinoma (MIA PaCa-2) and triple negative human metastatic breast adenocarcinoma (MDA-MB-231). The ESI-MS and 1H NMR data show that the complexes are stable in aqueous solution at pH 7.4 (4 mM NaCl) with less than 10% hydrolysis in 24 h. However, when the coordinated halide is bromo (2) or iodo (3), the complex exchanges the halide with chloride in solution. The exchange is dependent on chloride concentration. Fastest chloride exchange was observed for the bromo complex 2 and slowest for the iodo complex 3 showing the higher kinetic inertness of the latter. Complex 3 exhibits the weakest interaction with glutathione (GSH) and 9-ethylguanine (9-EtG) in the series. ESI-MS studies of a 20% methanolic solution of 3 in 4 mM aqueous NaCl showed 80% intact complex even after 24 h of incubation with 9-EtG or GSH. 1-3 show similar in vitro cytotoxicity profile, but based on combined results from solution stability and cytotoxicity, the iodo complex 3 seems to be the best one in the series. There is no deterioration of toxicity under hypoxia or by induction of GSH in HepG2 cells. The low cytotoxicity of the complexes against difficult to treat triple negative breast carcinoma viz. MDA-MB-231 in vitro (IC50 = 1.5 ± 0.1 μM) is very encouraging, compared with cytotoxicity of clinical drug cisplatin (IC50 = 37.2 ± 2.5 μM). The complexes can alter mitochondrial membrane potential, arrest the cell cycle in G0/G1 phase and kill cells via apoptosis. They inhibit migration of the metastatic MDA-MB-231 cells at IC20 dose.

A Dogma in Doubt: Hydrolysis of Equatorial Ligands of PtIV Complexes under Physiological Conditions

Due to their high kinetic inertness and consequently reduced side reactions with biomolecules, PtIV complexes are considered to define the future of anticancer platinum drugs. The aqueous stability of a series of biscarboxylato PtIV complexes was studied under physiologically relevant conditions. Unexpectedly and in contrast to the current chemical understanding, especially oxaliplatin and satraplatin complexes underwent fast hydrolysis in equatorial position (even in cell culture medium and serum). Notably, the resulting hydrolysis products strongly differ in their reduction kinetics, a crucial parameter for the activation of PtIV drugs, which also changes the anticancer potential of the compounds in cell culture. The discovery that intact PtIV complexes can hydrolyze at equatorial position contradicts the dogma on the general kinetic inertness of PtIV compounds and needs to be considered in the screening and design for novel platinum-based anticancer drugs.

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 Pt^IV prodrugs. The dual targeting was established by liposomal encapsulation of Pt^IV 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 Pt^IV prodrug inside cancer cells, a second stage of targeting directed a portion of the Pt^IV prodrugs to the mitochondria. Upon intracellular reduction, these Pt^IV prodrugs released two bioactive molecules, acting both on the mitochondrial and on the nuclear DNA. Our Pt^IV 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.

Shenqi Fuzheng Injection Reverses Cisplatin Resistance through Mitofusin-2-Mediated Cell Cycle Arrest and Apoptosis in A549/DDP Cells

The goal of this evaluation was to examine the mechanisms of Shenqi Fuzheng injection (SFI), an extract made from the plants Radix Astragali and Radix Codonopsis, in the process of chemotherapy sensitivity in non-small-cell lung cancer (NSCLC) cells. We investigated the expression of mitofusin-2 (Mfn2), a mitochondrial GTPase that may be related to chemoresistance, and found that Mfn2 expression was lower in human cisplatin-resistant lung carcinoma A549/DDP cells than in cisplatin-susceptible A549 cells. Chemosensitivity to cisplatin was restored in A549/DDP cells following supplementation in conjunction with SFI treatment, the effect of which we evaluated via cell cycle, apoptosis, and cell signaling analysis. We found that the combined use of A549/DDP cells with SFI and cisplatin enhanced cell cycle arrested in the G₂/M phase, which was accompanied by upregulation of p53 and p21 protein expression and induced mitochondrial apoptosis in conjunction with the upregulation of Bax and the downregulation of Bcl-2 protein expression. Moreover, cell cycle arrest and mitochondrial apoptosis coincided with the upregulation of Mfn2 expression, which, in turn, was related to the increased mitochondrial membrane permeabilization and elevated reactive oxygen species. In summary, our findings suggest that the effect of SFI in increasing chemotherapy sensitivity in cisplatin resistance of NSCLCs occurs through cell cycle arrest and the initiation of mitochondrial apoptosis involved in the upregulation of Mfn2 expression.

Synthesis, characterization and biological activity of new cyclometallated platinum(iv) iodido complexes

The synthesis of six novel cyclometallated platinum(iv) iodido complexes is accomplished by intermolecular oxidative addition of methyl iodide (compounds 2a-2c) or iodine (compounds 3a-3c) upon cyclometallated platinum(ii) compounds [PtX{(CH₃)₂N(CH₂)₃NCH(4-ClC₆H₃)}] (1a-1c: X = Cl, CH₃ or I). The X-ray molecular structures of platinum(ii) compound 1c and platinum(iv) compounds 3b and 3a' (an isomer of 3a) are reported. The cytotoxic activity against a panel of human adenocarcinoma cell lines (A-549 lung, MDA-MB-231 and MCF-7 breast, and HCT-116 colon), DNA interaction, topoisomerase I, IIα, and cathepsin B inhibition, and cell cycle arrest, apoptosis and ROS generation of the investigated complexes are presented. Remarkable antiproliferative activity was observed for most of the synthesized cycloplatinated compounds (series 1-3) in all the selected carcinoma cell lines. The best inhibition was provided for the octahedral platinum(iv) compounds 2a-2c exhibiting a methyl and an iodido axial ligand. Preliminary biological results point to a different mechanism of action for the investigated compounds. Cyclometallated platinum(ii) compounds 1a-1c modify the DNA migration as cisplatin. In contrast, cyclometallated platinum(iv) compounds 2a-2c and 3a-3c did not modify the DNA tertiary structure neither in the absence nor in the presence of ascorbic acid, which made them incapable of reducing platinum(iv) compounds 2b and 2c in a buffered aqueous medium (pH 7.40) according to ¹H NMR experiments. Remarkable topoisomerase IIα inhibitory activity is reported for platinum(iv) complexes 2b and 3a and in addition, for the last one, a moderate cathepsin B inhibition is reported. Cell cycle arrest (decrease in G0/G1 and G2 phases and arrest in the S phase), induction of apoptosis and ROS generation are related to the antiproliferative activity of some representative octahedral cyclometallated platinum(iv) compounds (2b and 2c).

Synthesis, characterization and biological activity of new cyclometallated platinum(iv) complexes containing a para-tolyl ligand

The synthesis of three new cyclometallated platinum(ii) compounds containing a para-tolyl ligand and a tridentate [C,N,N'] (cm1) or a bidentate [C,N] ligand and an additional ligand such as SEt2 (cm2) or PPh3 (cm3) is reported. The X-ray molecular structure of platinum(ii) compound cm3 is also presented. Intermolecular oxidative addition of methyl iodide or iodine upon cm1, cm2 and cm3 produced six novel cyclometallated platinum(iv) compounds. The cytotoxic activity against a panel of human adenocarcinoma cell lines (A-549 lung, MDA-MB-231 and MCF-7 breast, and HCT-116 colon), DNA interaction, topoisomerase I, IIα, and cathepsin B inhibition, and cell cycle arrest, apoptosis and ROS generation of the investigated complexes are presented. The best results for antiproliferative activity were obtained for platinum(iv) compounds cm1MeI and cm1I2 arising from oxidative addition of methyl iodide and iodine, respectively, to cm1. Cyclometallated platinum(iv) compounds cm1MeI and cm3MeI induce significant changes in the mobility of DNA and, in addition, cm1MeI, cm3MeI and cm1I2, showed considerable topoisomerase IIα inhibitory activity. Moreover, the compounds exhibiting the higher antiproliferative activity (cm1MeI and cm1I2) were found to generate ROS and to supress HCT-116 colon cancer cell growth by a mixture of cell cycle arrest and apoptosis induction. 1H NMR experiments carried out in a buffered aqueous medium (pH 7.40) indicate that compound cm1MeI is not reduced by common biologically relevant reducing agents such as ascorbic acid, glutathione or cysteine.

Cisplatin resistance in cell models: evaluation of metallomic and biological predictive biomarkers to address early therapy failure

Cisplatin, one of the most extensively used metallodrugs in cancer treatment, presents the important drawback of patient resistance. This resistance is the consequence of different processes including those preventing the formation of DNA adducts and/or their quick removal. Thus, a tool for the accurate detection and quantitation of cisplatin-induced adducts might be valuable for predicting patient resistance. To prove the validity of such an assumption, highly sensitive plasma mass spectrometry (ICP-MS) strategies were applied to determine DNA adduct levels and intracellular Pt concentrations. These two metal-relative parameters were combined with an evaluation of biological responses in terms of genomic stability (with the Comet assay) and cell cycle progression (by flow cytometry) in four human cell lines of different origins and cisplatin sensitivities (A549, GM04312, A2780 and A2780cis), treated with low cisplatin doses (5, 10 and 20 μM for 3 hours). Cell viability and apoptosis were determined as resistance indicators. Univariate linear regression analyses indicated that quantitation of cisplatin-induced G-G intra-strand adducts, measured 1 h after treatment, was the best predictor for viability and apoptosis in all of the cell lines. Multivariate linear regression analyses revealed that the prediction improved when the intracellular Pt content or the Comet data were included in the analysis, for all sensitive cell lines and for the A2780 and A2780cis cell lines, respectively. Thus, a reliable cisplatin resistance predictive model, which combines the quantitation of adducts by HPLC-ICP-MS, and their repair, with the intracellular Pt content and induced genomic instability, might be essential to identify early therapy failure.

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.

Salidroside, a Chemopreventive Glycoside, Diminishes Cytotoxic Effect of Cisplatin in Vitro

Natural products represent the source or the inspiration for the majority of the active ingredients of medicines because of their structural diversity and a wide range of biological effects. Our aims in this study were (i) to synthesize enzymatically salidroside (SAL), the most effective phenylethanoid glycoside in Rhodiola species; (ii) to examine its antioxidant capacity using cell-free assays (reducing power, DPPH radicals scavenging and Fe²⁺ -chelating assays); (iii) to assess its DNA-protective potential on plasmid DNA (DNA topology assay) and in HepG2 cells (comet assay) damaged by Fe²⁺ ions and hydrogen peroxide, respectively; and (iv) to investigate the effects of SAL, cisplatin (CDDP) and combined treatments of SAL + CDDP on cell viability (MTT test), level of DNA damage (comet assay), proliferation, cell cycle (flow cytometry) and the expression of signalling molecules associated with cell growth and apoptotic pathways (Western immunoblotting). We found out that SAL manifested low antioxidant and DNA-protective capacity in all assays used. In both parental A2780 and CDDP-resistant A2780/CP human ovarian carcinoma cells, SAL itself exerted in fact no impact on the viability, while in combination with CDDP it showed antagonistic effect supporting the chemopreventive activity on the CDDP-induced cell damage. These results were confirmed by the partial reversal of the cell cycle alterations and the DNA damage level, as well as with partial restoration of cell survival/signalling pathways, when the expression of these molecules partially returned to their proper levels.

Hybrid of DNA-targeting Chlorambucil with Pt(IV) Species to Reverse Drug Resistance

Two hybrids of Pt(IV) species were designed and prepared by addition of a chlorambucil unit to the axial positions of the Pt(IV) complexes derived from DN603 and DN604. In vitro studies of two hybrids against two pairs of cisplatin sensitive and resistant cancer cell lines indicated that compound 5 had superior antitumor activity to cisplatin and chlorambucil via suppressing DNA damage repair to reverse drug resistance. Mechanistic investigation suggested that the potent antitumor activity of compound 5 arose from its major suppression of CK2-mediated MRE11-RAD50-NBS1(MRN) complex promotion of DNA double-strand break (DSB) repair. In nude mice with A549/CDDP xenografts, compound 5 exhibited higher anticancer efficacy than cisplatin and chlorambucil by reversing drug resistance, displayed improved effectiveness, and had no toxicity effects. Overall, compound 5 is a promising drug candidate, which could promote the anticancer activity and reverse drug resistance by attenuating CK2-induced MRN-dependent DSB repair.

Reversal of cisplatin resistance in human gastric cancer cells by a wogonin-conjugated Pt(IV) prodrug via attenuating Casein Kinase 2-mediated Nuclear Factor-κB pathways

Pt(IV) prodrugs, with two additional coordination sites in contrast to Pt(II) drugs, have been actively studied nowadays, for they can perform well in enhancing the accumulation and retention of the corresponding Pt(II) drugs in cancer cells. Our designed Pt(II) drug, DN604, was recently found to exhibit significant anticancer activity and low toxicity, while, wogonin, a naturally O-methylated flavones, has been widely investigated for its tumor therapeutic potential. Thus, two Pt(IV)-based prodrugs were derived by addition of a wogonin unit to the axial position of DN604 and its analogue DN603 via a linker group. In vitro cytotoxicity assay indicated that the resulting compound 8 not only inherited the genotoxicity of DN604 on gastric cancer cells, but also obtained the COX inhibitory property arising from wogonin. Further studies revealed that compound 8 caused the accumulation of ROS production and decreased the mitochondrial membrane potential (ΔΨm). The CK2α kinase activity assay, ChIP and luciferase assays showed that CK2 plays an important role in the blockade of compound 8 on activated NF-κB survival pathways, which were established for sensitivity of cancer cells to platinum drugs. Similarly in vivo, in nude mice with SGC-7901/cDDP xenografts, compound 8 improved the effectiveness of DN604 via reversing tumor resistance and maintaining low toxicity. Overall, compound 8 is a promising Pt(IV) prodrug, which could be used to promote the anticancer activity of its counterpart Pt(II) species and reverse drug resistance via attenuating CK2-mediated NF-κB pathways during platinum-based chemotherapies.

On the stability and biological behavior of cyclometallated Pt(IV) complexes with halido and aryl ligands in the axial positions

A series of cyclometallated platinum(IV) compounds (3a, 3a' and 3b') with a meridional [C,N,N'] terdentate ligand, featuring an halido and an aryl group in the axial positions has been evaluated for electrochemical reduction and preliminary biological behavior against a panel of human adenocarcinoma (A-549 lung, HCT-116 colon, and MCF-7 breast) cell lines and the normal bronquial epithelial BEAS-2B cells. Cathodic reduction potentials (shifting from -1.463 to -1.570V) reveal that the platinum(IV) compounds under study would be highly reluctant to be reduced in a biological environment. Actually ascorbic acid was not able to reduce complex 3a', the most prone to be reduced according its reduction potential, over a period of one week. These results suggest an intrinsic activity for the investigated platinum(IV) complexes (3a, 3a' and 3b'), which exhibit a remarkable cytotoxicity effectiveness (with IC₅₀ values in the low micromolar range), even greater than that of cisplatin. The IC₅₀ for A-549 lung cells and clog P values were found to follow the same trend: 3b'>3a'>3a. However, no correlation was observed between reduction potential and in vitro activity. As a representative example, cyclometallated platinum(IV) compound 3a', exercise its antiproliferative activity directly over non-microcytic A-549 lung cancer cells through a mixture of cell cycle arrest (13% arrest at G1 phase and 46% arrest at G2 phase) and apoptosis induction (increase of early apoptosis by 30 times with regard to control). To gain further insights into the mode of action of the investigated platinum(IV) complexes, drug uptake, cathepsin B inhibition and ROS generation were also evaluated. Interestingly an increased ROS generation could be related with the antiproliferative activity of the cyclometallated platinum(IV) series under study in the cisplatin-resistant A-549 lung and HCT-116 cancer cell lines.

Oxidative Stress Induced by Pt(IV) Pro-drugs Based on the Cisplatin Scaffold and Indole Carboxylic Acids in Axial Position

The use of Pt(IV) complexes as pro-drugs that are activated by intracellular reduction is a widely investigated approach to overcome the limitations of Pt(II) anticancer agents. A series of ten mono- and bis-carboxylated Pt(IV) complexes with axial indole-3-acetic acid (IAA) and indole-3-propionic acid (IPA) ligands were synthesized and characterized by elemental analysis, ESI-MS, FT-IR, (1)H and (195)Pt NMR spectroscopy. Cellular uptake, DNA platination and cytotoxicity against a panel of human tumor cell lines were evaluated. All the complexes are able to overcome cisplatin-resistance and the most potent complex, cis,cis,trans-[Pt(NH3)2Cl2(IPA)(OH)] was on average three times more active than cisplatin. Mechanistic studies revealed that the trend in cytotoxicity of the Pt(IV) complexes is primarily consistent with their ability to accumulate into cancer cells and to increase intracellular basal reactive oxygen species levels, which in turn results in the loss of mitochondrial membrane potential and apoptosis induction. The role of the indole acid ligand as a redox modulator is discussed.

The role of the equatorial ligands for the redox behavior, mode of cellular accumulation and cytotoxicity of platinum(IV) prodrugs

The current study aims to elucidate the possible reasons for the significantly different pharmacological behavior of platinum(IV) complexes with cisplatin-, carboplatin- or nedaplatin-like cores and how this difference can be related to their main physicochemical properties. Chlorido-containing complexes are reduced fast (within hours) by ascorbate and are able to unwind plasmid DNA in the presence of ascorbate, while their tri- and tetracarboxylato analogs are generally inert under the same conditions. Comparison of the lipophilicity, cellular accumulation and cytotoxicity of the investigated platinum compounds revealed the necessity to define new structure-property/activity relationships (SPRs and SARs). The higher activity and improved accumulation of platinum(IV) complexes bearing Cl(-) in equatorial position cannot only be attributed to passive diffusion facilitated by their lipophilicity. Therefore, further platinum accumulation experiments under conditions where active/facilitated transport mechanisms are suppressed were performed. Under hypothermic conditions (4°C), accumulation of dichloridoplatinum(IV) complexes is reduced down to 10% of the amount determined at 37°C. These findings suggest the involvement of active and/or facilitated transport in cellular uptake of platinum(IV) complexes with a cisplatin-like core. Studies with ATP depletion mediated by oligomycin and low glucose partially confirmed these observations, but their feasibility was severely limited in the adherent cell culture setting.

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.

Reduction of ormaplatin and cis-diamminetetrachloroplatinum(iv) by ascorbic acid and dominant thiols in human plasma: kinetic and mechanistic analyses

The reductions of Pt(iv) anticancer prodrugs [Pt(dach)Cl₄] (ormaplatin/tetraplatin) and cis-[Pt(NH₃)₂Cl₄] by several dominant reductants in human plasma have been characterized and analyzed kinetically and mechanistically.

Studies on the structures, cytotoxicity and apoptosis mechanism of 8-hydroxylquinoline rhodium(iii) complexes in T-24 cells

Two rhodium(iii) complexes showed good cytotoxicity. The underlying investigation of the apoptosis mechanism suggested that the mitochondrial apoptotic pathway was involved.