Chiral platinum(II) metallointercalators with potent in vitro cytotoxic activity

Kinetically Inert Platinum (II) Complexes for Improving Anticancer Therapy: Recent Developments and Road Ahead

The search for better chemotherapeutic drugs to alleviate the deficiencies of existing platinum (Pt) drugs has picked up the pace in the millennium. There has been a disparate effort to design better and safer Pt drugs to deal with the problems of deactivation, Pt resistance and toxic side effects of clinical Pt drugs. In this review, we have discussed the potential of kinetically inert Pt complexes as an emerging class of next-generation Pt drugs. The introduction gives an overview about the development, use, mechanism of action and side effects of clinical Pt drugs as well as the various approaches to improve some of their pharmacological properties. We then describe the impact of kinetic lability on the pharmacology of functional Pt drugs including deactivation, antitumor efficacy, toxicity and resistance. Following a brief overview of numerous pharmacological advantages that a non-functional kinetically inert Pt complex can offer; we discussed structurally different classes of kinetically inert Pt (II) complexes highlighting their unique pharmacological features.

Platinum(IV) Prodrugs Incorporating an Indole-Based Derivative, 5-Benzyloxyindole-3-Acetic Acid in the Axial Position Exhibit Prominent Anticancer Activity

Kinetically inert platinum(IV) complexes are a chemical strategy to overcome the impediments of standard platinum(II) antineoplastic drugs like cisplatin, oxaliplatin and carboplatin. In this study, we reported the syntheses and structural characterisation of three platinum(IV) complexes that incorporate 5-benzyloxyindole-3-acetic acid, a bioactive ligand that integrates an indole pharmacophore. The purity and chemical structures of the resultant complexes, P-5B3A, 5-5B3A and 56-5B3A were confirmed via spectroscopic means. The complexes were evaluated for anticancer activity against multiple human cell lines. All complexes proved to be considerably more active than cisplatin, oxaliplatin and carboplatin in most cell lines tested. Remarkably, 56-5B3A demonstrated the greatest anticancer activity, displaying GI50 values between 1.2 and 150 nM. Enhanced production of reactive oxygen species paired with the decline in mitochondrial activity as well as inhibition of histone deacetylase were also demonstrated by the complexes in HT29 colon cells.

Synthesis and Characterisation of Fluorescent Novel Pt(II) Cyclometallated Complexes with Anticancer Activity

Cancer poses a significant threat to global health and new treatments are required to improve the prognosis for patients. Previously, unconventional platinum complexes designed to incorporate polypyridyl ligands paired with diaminocyclohexane have demonstrated anticancer activity in KRAS mutated cells, previously thought to be undruggable and have cytotoxicity values up to 100 times better than cisplatin. In this work, these complexes were used as inspiration to design six novel cyclometallated examples, whose fluorescence could be exploited to better understand the mechanism of action of these kinds of platinum drugs. The cytotoxicity results revealed that these cyclometallated complexes (CMCs) have significantly different activity compared to the complexes that inspired them; they are as cytotoxic as cisplatin and have much higher selectivity indices in breast cancer cell lines (MCF10A/MCF-7). Complexes 1b, 2a, and 3b all had very high selectivity indexes compared to previous Pt(II) complexes. This prompted further investigation into their DNA binding properties, which revealed that they had good affinity to ctDNA, especially CMCs 1a and 3b. Their inherent fluorescence was successfully utilised in the calculation of their DNA binding affinity and could be useful in future work.

Versatile Platinum(IV) Prodrugs of Naproxen and Acemetacin as Chemo-Anti-Inflammatory Agents

Developing new and versatile platinum(IV) complexes that incorporate bioactive moieties is a rapidly evolving research strategy for cancer drug discovery. In this study, six platinum(IV) complexes (1-6) that are mono-substituted in the axial position with a non-steroidal anti-inflammatory molecule, naproxen or acemetacin, were synthesised. A combination of spectroscopic and spectrometric techniques confirmed the composition and homogeneity of 1-6. The antitumour potential of the resultant complexes was assessed on multiple cell lines and proved to be significantly improved compared with cisplatin, oxaliplatin and carboplatin. The platinum(IV) derivatives conjugated with acemetacin (5 and 6) were determined to be the most biologically potent, demonstrating GI₅₀ values ranging between 0.22 and 250 nM. Remarkably, in the Du145 prostate cell line, 6 elicited a GI₅₀ value of 0.22 nM, which is 5450-fold more potent than cisplatin. A progressive decrease in reactive oxygen species and mitochondrial activity was observed for 1-6 in the HT29 colon cell line, up to 72 h. The inhibition of the cyclooxygenase-2 enzyme was also demonstrated by the complexes, confirming that these platinum(IV) complexes may reduce COX-2-dependent inflammation and cancer cell resistance to chemotherapy.

Preparation, cytotoxic activity and DNA interaction studies of new platinum(II) complexes with 1,10-phenanthroline and 5-alkyl-1,3,4-oxadiazol-2(3H)-thione derivatives

This work describes the synthesis, characterization and in vitro anticancer activity of two platinum(II) complexes of the type [Pt(L1)₂(1,10-phen)] 1 and [Pt(L2)₂(1,10-phen)] 2, where L1 = 5-heptyl-1,3,4-oxadiazole-2-(3H)-thione, L2 = 5-nonyl-1,3,4-oxadiazole-2-(3H)-thione and 1,10-phen = 1,10-phenanthroline. As to the structure of these complexes, the X-ray structural analysis of 1 indicates that the geometry around the platinum(II) ion is distorted square-planar, where two 5-alkyl-1,3,4-oxadiazol-2-thione derivatives coordinate a platinum(II) ion through the sulfur atom. A chelating bidentate phenanthroline molecule completes the coordination sphere. We tested these complexes in two breast cancer cell lines, namely, MCF-7 (a hormone responsive cancer cell) and MDA-MB-231 (triple negative breast cancer cell). In both cells, the most lipophilic platinum compound, complex 2, was more active than cisplatin, one of the most widely used anticancer drugs nowadays. DNA binding studies indicated that such complexes are able to bind to ct-DNA with K_b values of 10⁴ M^-1. According to data from dichroism circular and fluorescence spectroscopy, these complexes appear to bind to the DNA in a non-intercalative, probably via minor groove. Molecular docking followed by semiempirical simulations indicated that these complexes showed favorable interactions with the minor groove of the double helix of ct-DNA in an A-T rich region. Thereafter, flow cytometry analysis showed that complex 2 induced apoptosis and necrosis in MCF-7 cells.

Bioactive Platinum(IV) Complexes Incorporating Halogenated Phenylacetates

A new series of cytotoxic platinum(IV) complexes (1-8) incorporating halogenated phenylacetic acid derivatives (4-chlorophenylacetic acid, 4-fluorophenylacetic acid, 4-bromophenylacetic acid and 4-iodophenylacetic acid) were synthesised and characterised using spectroscopic and spectrometric techniques. Complexes 1-8 were assessed on a panel of cell lines including HT29 colon, U87 glioblastoma, MCF-7 breast, A2780 ovarian, H460 lung, A431 skin, Du145 prostate, BE2-C neuroblastoma, SJ-G2 glioblastoma, MIA pancreas, the ADDP-resistant ovarian variant, and the non-tumour-derived MCF10A breast line. The in vitro cytotoxicity results confirmed the superior biological activity of the studied complexes, especially those containing 4-fluorophenylacetic acid and 4-bromophenylacetic acid ligands, namely 4 and 6, eliciting an average GI₅₀ value of 20 nM over the range of cell lines tested. In the Du145 prostate cell line, 4 exhibited the highest degree of potency amongst the derivatives, displaying a GI₅₀ value of 0.7 nM, which makes it 1700-fold more potent than cisplatin (1200 nM) and nearly 7-fold more potent than our lead complex, 56MESS (4.6 nM) in this cell line. Notably, in the ADDP-resistant ovarian variant cell line, 4 (6 nM) was found to be almost 4700-fold more potent than cisplatin. Reduction reaction experiments were also undertaken, along with studies aimed at determining the complexes' solubility, stability, lipophilicity, and reactive oxygen species production.

Potent Chlorambucil-Platinum(IV) Prodrugs

The DNA-alkylating derivative chlorambucil was coordinated in the axial position to atypical cytotoxic, heterocyclic, and non-DNA coordinating platinum(IV) complexes of type, [Pt^IV(H_L)(A_L)(OH)₂](NO₃)₂ (where H_L is 1,10-phenanthroline, 5-methyl-1,10-phenanthroline or 5,6-dimethyl-1,10-phenanthroline, A_L is 1S,2S-diaminocyclohexane). The resultant platinum(IV)-chlorambucil prodrugs, PCLB, 5CLB, and 56CLB, were characterized using high-performance liquid chromatography, nuclear magnetic resonance, ultraviolet-visible, circular dichroism spectroscopy, and electrospray ionization mass spectrometry. The prodrugs displayed remarkable antitumor potential across multiple human cancer cell lines compared to chlorambucil, cisplatin, oxaliplatin, and carboplatin, as well as their platinum(II) precursors, PHENSS, 5MESS, and 56MESS. Notably, 56CLB was exceptionally potent in HT29 colon, Du145 prostate, MCF10A breast, MIA pancreas, H460 lung, A2780, and ADDP ovarian cell lines, with GI₅₀ values ranging between 2.7 and 21 nM. Moreover, significant production of reactive oxygen species was detected in HT29 cells after treatment with PCLB, 5CLB, and 56CLB up to 72 h compared to chlorambucil and the platinum(II) and (IV) precursors.

Use of Half-Generation PAMAM Dendrimers (G0.5–G3.5) with Carboxylate End-Groups to Improve the DACHPtCl2 and 5-FU Efficacy as Anticancer Drugs

The DACHPtCl2 compound (trans-(R,R)-1,2-diaminocyclohexanedichloroplatinum(II)) is a potent anticancer drug with a broad spectrum of activity and is less toxic than oxaliplatin (trans-l-diaminocyclohexane oxalate platinum II), with which it shares the active metal fragment DACHPt. Nevertheless, due to poor water solubility, its use as a chemotherapeutic drug is limited. Here, DACHPtCl2 was conjugated, in a bidentate form, with half-generation PAMAM dendrimers (G0.5–G3.5) with carboxylate end-groups, and the resulting conjugates were evaluated against various types of cancer cell lines. In this way, we aimed at increasing the solubility and availability at the target site of DACHPt while potentially reducing the adverse side effects. DNA binding assays showed a hyperchromic effect compatible with DNA helix’s disruption upon the interaction of the metallodendrimers and/or the released active metallic fragments with DNA. Furthermore, the prepared DACHPt metallodendrimers presented cytotoxicity in a wide set of cancer cell lines used (the relative potency regarding oxaliplatin was in general high) and were not hemotoxic. Importantly, their selectivity for A2780 and CACO-2 cancer cells with respect to non-cancer cells was particularly high. Subsequently, the anticancer drug 5-FU was loaded in a selected metallodendrimer (the G2.5COO(DACHPt)16) to investigate a possible synergistic effect between the two drugs carried by the same dendrimer scaffold and tested for cytotoxicity in A2780cisR and CACO-2 cancer cell lines. This combination resulted in IC50 values much lower than the IC50 for 5-FU but higher than those found for the metallodendrimers without 5-FU. It seems, thus, that the metallic fragment-induced cytotoxicity dominates over the cytotoxicity of 5-FU in the set of considered cell lines.

Use of Half-Generation PAMAM Dendrimers (G0.5-G3.5) with Carboxylate End-Groups to Improve the DACHPtCl2 and 5-FU Efficacy as Anticancer Drugs

The DACHPtCl2 compound (trans-(R,R)-1,2-diaminocyclohexanedichloroplatinum(II)) is a potent anticancer drug with a broad spectrum of activity and is less toxic than oxaliplatin (trans-l-diaminocyclohexane oxalate platinum II), with which it shares the active metal fragment DACHPt. Nevertheless, due to poor water solubility, its use as a chemotherapeutic drug is limited. Here, DACHPtCl2 was conjugated, in a bidentate form, with half-generation PAMAM dendrimers (G0.5-G3.5) with carboxylate end-groups, and the resulting conjugates were evaluated against various types of cancer cell lines. In this way, we aimed at increasing the solubility and availability at the target site of DACHPt while potentially reducing the adverse side effects. DNA binding assays showed a hyperchromic effect compatible with DNA helix's disruption upon the interaction of the metallodendrimers and/or the released active metallic fragments with DNA. Furthermore, the prepared DACHPt metallodendrimers presented cytotoxicity in a wide set of cancer cell lines used (the relative potency regarding oxaliplatin was in general high) and were not hemotoxic. Importantly, their selectivity for A2780 and CACO-2 cancer cells with respect to non-cancer cells was particularly high. Subsequently, the anticancer drug 5-FU was loaded in a selected metallodendrimer (the G2.5COO(DACHPt)16) to investigate a possible synergistic effect between the two drugs carried by the same dendrimer scaffold and tested for cytotoxicity in A2780cisR and CACO-2 cancer cell lines. This combination resulted in IC50 values much lower than the IC50 for 5-FU but higher than those found for the metallodendrimers without 5-FU. It seems, thus, that the metallic fragment-induced cytotoxicity dominates over the cytotoxicity of 5-FU in the set of considered cell lines.

Transition Metal-Based Prodrugs for Anticancer Drug Delivery

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Transition metal complexes, of which the platinum(II) complex cisplatin is an example, have been used in medicine to treat cancer for more than 40 years. Although many successes have been achieved, there are problems associated with the use of these drugs, such as side effects and drug resistance. Converting them into prodrugs, to make them more inert, so that they can travel to the tumour site unchanged and release the drug in its active form only there, is a strategy which is the subject of much research nowadays. The new prodrugs may be activated and release the cytotoxic agent by differences in oxygen concentration or in pH, by the action of overexpressed enzymes, by differences in metabolic rates, etc., which characteristically distinguish cancer cells from normal ones, or even by the input of radiation, which can be visible light. Converting a metal complex into a prodrug may also be used to improve its pharmacological properties. In some cases, the metal complex is a carrier which transports the active drug as a ligand. Some platinum prodrugs have reached clinical trials. So far platinum, ruthenium and cobalt have been the most studied metals. This review presents the recent developments in this area, including the types of complexes used, the mechanisms of drug action and in some cases the techniques applied to monitor drug delivery to cells.

Manipulating exciton dynamics of thermally activated delayed fluorescence materials for tuning two-photon nanotheranostics

Rational manipulation of energy utilization from excited-state radiation of theranostic agents with a donor–acceptor structure is relatively unexplored. Herein, we present an effective strategy to tune the exciton dynamics of radiative excited state decay for augmenting two-photon nanotheranostics. As a proof of concept, two thermally activated delayed fluorescence (TADF) molecules with different electron-donating segments are engineered, which possess donor–acceptor structures and strong emissions in the deep-red region with aggregation-induced emission characteristics. Molecular simulations demonstrate that change of the electron-donating sections could effectively regulate the singlet–triplet energy gap and oscillator strength, which promises efficient energy flow. A two-photon laser with great permeability is used to excite TADF NPs to perform as theranostic agents with singlet oxygen generation and fluorescence imaging. These unique performances enable the proposed TADF emitters to exhibit tailored balances between two-photon singlet oxygen generation and fluorescence emission. This result demonstrates that TADF emitters can be rationally designed as superior candidates for nanotheranostic agents by the custom controlling exciton dynamics.

Exciton dynamics can be manipulated rationally in the design of TADF materials for nanotheranostics. Regulating the ΔE_ST and f promises efficient energy flow for tailoring balances between singlet oxygen generation and fluorescence emission.

A Subset of New Platinum Antitumor Agents Kills Cells by a Multimodal Mechanism of Action Also Involving Changes in the Organization of the Microtubule Cytoskeleton

The substitution inert platinum agent [Pt(1 S,2 S-diaminocyclohexane)(5,6-dimethyl-1,10-phenanthroline)]²⁺ (56MeSS, 5) is a potent cytotoxic metallodrug. In contrast to conventional cisplatin or oxaliplatin, the mechanism of action (MoA) of 5 is fundamentally different. However, details of the mechanism by which the 5,6-dimethyl-1,10-phenanthroline ligand contributes to the cytotoxicity of 5 and its derivatives have not been sufficiently clarified so far. Here, we show that 5 and its Pt(IV) derivatives exhibit an intriguing potency in the triple-negative breast cancer cells MDA-MB-231. Moreover, we show that the Pt(IV) derivatives of 5 act by multimodal MoA resulting in the global biological effects, that is, they damage nuclear DNA, reduce the mitochondrial membrane potential, induce the epigenetic processes, and last but not least, the data provide evidence that changes in the organization of cytoskeleton networks are functionally important for 5 and its derivatives, in contrast to clinically used platinum cytostatics, to kill cancer cells.

Multi-action Pt(IV) anticancer agents; do we understand how they work?

Pt(IV) complexes act as prodrugs that are activated inside cancer cells releasing cytotoxic Pt(II) drugs such as cisplatin as well as two axial ligands. These ligands can be used to confer favorable pharmacological properties to the prodrug. They can be innocent spectators, targeting agents or bioactive moieties. When the ligands are bioactive moieties such as enzyme inhibitors or antiproliferative agents, the prodrug attacks several cellular targets at the same time acting as a multi-action prodrug. These compounds are very potent and often overcome resistance to cisplatin. Despite solid rationalization and careful design, often there is no correlation between the ability of the bioactive ligand to inhibit the target enzyme and the cytotoxicity. This might be because most bioactive ligands affect several cellular functions and not only the ones they were designed to inhibit. Thus, even "dual action" prodrugs might in reality be multi-action prodrugs. This class of multi-action Pt(IV) prodrugs seems to have great potential in the attempts to overcome resistance.

Metal-plant frameworks in nanotechnology: An overview

BACKGROUND

Since ancient times, potential of plants in research and medicine have found pronounced applications, due to better therapeutic value. To meet the mounting demands for commercial nanoparticles, novel eco-friendly methods of synthesis has led to a remarkable progress via unfolding a green synthesis protocol towards metallic nanoparticles synthesis.

HYPOTHESIS/PURPOSE

This review highlights the biological synthesis of various metallic nanoparticles as safe, cost effective process, where the phytochemicals present in extract such as flavonoid, phenols, terpenoids act as capping, reducing and stabilizing agents. Moreover, due to their nano size, the nanoparticles directly bind to bacterial strains leading to higher antimicrobial activity.

CONCLUSION

Nano-sized dosage systems have a potential for enhancing the activity and overcoming problems associated with phyto medicines. Hence, synthesis of metallic nanoparticles using various plant extracts, emerge as safe alternative to conventional methods for biomedical applications.

A Quadruple-Action Platinum(IV) Prodrug with Anticancer Activity Against KRAS Mutated Cancer Cell Lines

We developed a novel Pt^IV prodrug that simultaneously releases four different bioactive moieties inside the cancer cell. Its cytotoxicity against monolayer cultures (2D) and spheroid (3D) cancer cells is significantly better than cisplatin. It is 200-450-fold more potent than cisplatin against KRAS mutated pancreatic and colon cancers and is 40-fold more selective towards KRAS mutated cells compared to non-cancerous. This is important since RAS proteins play a role in regulating cell differentiation, proliferation, and survival and KRAS is mutated in 90 % of pancreatic adenocarcinomas, 45 % of colorectal cancers, and 35 % of lung adenocarcinomas. The selectivity index, determined by dividing the IC₅₀ value in non-cancerous cells by that of a cancerous cell line, is two-fold better than cisplatin, attesting to preferential cytotoxicity towards neoplastic cells.

Probing the Interactions of Cytotoxic [Pt(1S,2S-DACH)(5,6-dimethyl-1,10-phenanthroline)] and Its PtIV Derivatives with Human Serum

The discrepancy between the in vitro cytotoxic results and the in vivo performance of Pt56MeSS prompted us to look into its interactions and those of its Pt^IV derivatives with human serum (HS), human serum albumin (HSA), lipoproteins, and serum-supplemented cell culture media. The Pt^II complex, Pt56MeSS, binds noncovalently and reversibly to slow-tumbling proteins in HS and in cell culture media and interacts through the phenanthroline group with HSA, with a K_d value of ∼1.5×10^-6  m. All Pt^IV complexes were found to be stable toward reduction in HS, but those with axial carboxylate ligands, cct-[Pt(1S,2S-DACH)(5,6-dimethyl-1,10-phenantroline)(acetato)₂ ](TFA)₂ (Pt56MeSS(OAc)₂ ) and cct-[Pt(1S,2S-DACH)(5,6-dimehtyl-1,10-phenantroline)(phenylbutyrato)₂ ](TFA)₂ (Pt56MeSS(PhB)₂ ), were spontaneously reduced at pH 7 or higher in phosphate buffer, but not in Tris buffer (pH 8). HS also decreased the rate of reduction by ascorbate of the Pt^IV complexes relative to the reduction rates in phosphate buffer, suggesting that for this compound class, phosphate buffer is not a good model for HS.

The Next Generation of Platinum Drugs: Targeted Pt(II) Agents, Nanoparticle Delivery, and Pt(IV) Prodrugs

The platinum drugs, cisplatin, carboplatin, and oxaliplatin, prevail in the treatment of cancer, but new platinum agents have been very slow to enter the clinic. Recently, however, there has been a surge of activity, based on a great deal of mechanistic information, aimed at developing nonclassical platinum complexes that operate via mechanisms of action distinct from those of the approved drugs. The use of nanodelivery devices has also grown, and many different strategies have been explored to incorporate platinum warheads into nanomedicine constructs. In this Review, we discuss these efforts to create the next generation of platinum anticancer drugs. The introduction provides the reader with a brief overview of the use, development, and mechanism of action of the approved platinum drugs to provide the context in which more recent research has flourished. We then describe approaches that explore nonclassical platinum(II) complexes with trans geometry or with a monofunctional coordination mode, polynuclear platinum(II) compounds, platinum(IV) prodrugs, dual-threat agents, and photoactivatable platinum(IV) complexes. Nanoparticles designed to deliver platinum(IV) complexes will also be discussed, including carbon nanotubes, carbon nanoparticles, gold nanoparticles, quantum dots, upconversion nanoparticles, and polymeric micelles. Additional nanoformulations, including supramolecular self-assembled structures, proteins, peptides, metal-organic frameworks, and coordination polymers, will then be described. Finally, the significant clinical progress made by nanoparticle formulations of platinum(II) agents will be reviewed. We anticipate that such a synthesis of disparate research efforts will not only help to generate new drug development ideas and strategies, but also will reflect our optimism that the next generation of approved platinum cancer drugs is about to arrive.

Synthesis and Analysis of the Structure, Diffusion and Cytotoxicity of Heterocyclic Platinum(IV) Complexes

We have developed six dihydroxidoplatinum(IV) compounds with cytotoxic potential. Each derived from active platinum(II) species, these complexes consist of a heterocyclic ligand (HL) and ancillary ligand (AL) in the form [Pt(HL)(AL)(OH)2](2+), where HL is a methyl-functionalised variant of 1,10-phenanthroline and AL is the S,S or R,R isomer of 1,2-diaminocyclohexane. NMR characterisation and X-ray diffraction studies clearly confirmed the coordination geometry of the octahedral platinum(IV) complexes. The self-stacking of these complexes was determined using pulsed gradient stimulated echo nuclear magnetic resonance. The self-association behaviour of square planar platinum(II) complexes is largely dependent on concentration, whereas platinum(IV) complexes do not aggregate under the same conditions, possibly due to the presence of axial ligands. The cytotoxicity of the most active complex, exhibited in several cell lines, has been retained in the platinum(IV) form.

Cytotoxicity profile of novel sterically hindered platinum(II) complexes with (1R,2R)-N(1),N(2)-dibutyl-1,2-diaminocyclohexane

Four Pt(II) complexes of (1R,2R)-N(1),N(2)-dibutyl-1,2-diaminocyclohexane with two alkyl branches as steric hindrance have been designed and synthesized. In vitro cytotoxicity of these compounds indicated complex 4 is a cytotoxic agent more potent than its parent molecule, oxaliplatin, against almost all the tested cell lines. Agarose gel electrophoresis study showed that the kinetic reactivity of complex 4 with DNA is slow down due to the sterically hindered effect, demonstrating that it may possess a different mechanism of action from cisplatin. Flow cytometry results revealed that complex 4 induced apoptosis of tumor cells by blocking the cell-cycle progression in the G2/M phase. Western blot analysis showed it had a similar apoptotic mechanism to cisplatin which could induce apoptosis via a mitochondrial-dependent pathway.

Mononuclear Cu(ii) and Zn(ii) complexes with a simple diamine ligand: synthesis, structure, phosphodiester binding and DNA cleavage studies

Mononuclear Cu(ii) and Zn(ii) complexes with simple 1,2-diaminocylohexane were synthesized. They interact with phosphodiesters and CT-DNA. Cu(ii) complex with ascorbate efficiently cleaves supercoiled DNA up to Form III at 25 µM under oxidative pathway.

A Systems Biology Approach to Understanding the Mechanisms of Action of an Alternative Anticancer Compound in Comparison to Cisplatin

Many clinically available anticancer compounds are designed to target DNA. This commonality of action often yields overlapping cellular response mechanisms and can thus detract from drug efficacy. New compounds are required to overcome resistance mechanisms that effectively neutralise compounds like cisplatin and those with similar chemical structures. Studies have shown that 56MESS is a novel compound which, unlike cisplatin, does not covalently bind to DNA, but is more toxic to many cell lines and active against cisplatin-resistant cells. Furthermore, a transcriptional study of 56MESS in yeast has implicated iron and copper metabolism as well as the general yeast stress response following challenge with 56MESS. Beyond this, the cytotoxicity of 56MESS remains largely uncharacterised. Here, yeast was used as a model system to facilitate a systems-level comparison between 56MESS and cisplatin. Preliminary experiments indicated that higher concentrations than seen in similar studies be used. Although a DNA interaction with 56MESS had been theorized, this work indicated that an effect on protein synthesis/ degradation was also implicated in the mechanism(s) of action of this novel anticancer compound. In contrast to cisplatin, the different mechanisms of action that are indicated for 56MESS suggest that this compound could overcome cisplatin resistance either as a stand-alone treatment or a synergistic component of therapeutics.

A dual-targeting, p53-independent, apoptosis-inducing platinum(II) anticancer complex, [Pt(BDI(QQ))]Cl

The therapeutic index and cellular mechanism of action of [Pt(BDI(QQ))]Cl, a monocationic, square-planar platinum(II) complex, are reported. [Pt(BDI(QQ))]Cl was used to treat several cell lines, including wild type and cisplatin-resistant ovarian carcinoma cells (A2780 and A2780CP70) and non-proliferating lung carcinoma cells (A549). [Pt(BDI(QQ))]Cl selectively kills cancer cells over healthy cells and exhibits no cross-resistance with cisplatin. The mechanism of cell killing was established through detailed cell-based assays. [Pt(BDI(QQ))]Cl exhibits dual-threat capabilities, targeting nuclear DNA and mitochondria simultaneously. [Pt(BDI(QQ))]Cl induces DNA damage, leading to p53 enrichment, mitochondrial membrane potential depolarisation, and caspase-mediated apoptosis. [Pt(BDI(QQ))]Cl also accumulates in the mitochondria, resulting in direct mitochondrial damage. Flow cytometric studies demonstrated that [Pt(BDI(QQ))]Cl has no significant effect on cell cycle progression. Remarkably, p53-status is a not a determinant of [Pt(BDI(QQ))]Cl activity. In p53-null cells, [Pt(BDI(QQ))]Cl induces cell death through mitochondrial dysfunction. Cancers with p53-null status could therefore be targeted using [Pt(BDI(QQ))]Cl.

The effects of 56MESS on mitochondrial and cytoskeletal proteins and the cell cycle in MDCK cells

BACKGROUND

56MESS has been shown to be cytotoxic but the mode of this action is unclear. In order to probe the mechanism of action for 56MESS, MDCK cells were utilised to investigate the effect on treated cells.

RESULTS

IC50 values for 56MESS and cisplatin in the MDCK cell line, determined by a SRB assay, were 0.25 ± 0.03 and 18 ± 1.2 μM respectively. In a preliminary study, cells treated with 56MESS displayed no caspase-3/7 activity, suggesting that the mechanism of action is caspase independent. Protein expression studies revealed an increase the expression in the MTC02 protein associated with mitochondria in cells treated with 56MESS and cisplatin. Non-synchronised 56MESS-treated cells caused an arrest in the G2/M phase of the cell cycle, in comparison to the S phase arrest of cisplatin. In G0/G1 synchronised cells, both 56MESS and cisplatin both appeared to arrest within the S phase.

CONCLUSIONS

these results suggest that 56MESS is capable of causing cell-cycle arrest, and that mitochondrial and cell cycle proteins may be involved in the mode of action of cytotoxicity of 56MESS.

Synthesis and analysis of the anticancer activity of platinum(ii) complexes incorporating dipyridoquinoxaline variants

Platinum complexes incorporating variants of dpq were synthesised. Their DNA affinity and cytotoxicity were compared to complexes containing phen variants, revealing unexpected trends in biological activity.

Cytotoxic platinum(II) intercalators that incorporate 1R,2R-diaminocyclopentane

Twelve metallointercalators of the type [Pt(I(L))(A(L))](2+), where A(L) is either the R,R or S,S enantiomer of 1,2-diaminocyclopentane (DACP) and I(L) is either 1,10-phenathroline, 4-methyl-1,10-phenanthroline, 5-methyl-1,10-phenanthroline, 4,7-dimethyl-1,10-phenanthroline, 5,6-dimethyl-1,10-phenanthroline or 3,4,7,8-tetramethyl-1,10-phenanthroline, were synthesised, characterised and the cytotoxicity to the L1210 cell line was determined. The crystal structures of PHENRRDACP and PHENSS were obtained as monoclinic with a space group of P2(1) (a/Å = 11.4966, b/Å = 6.6983, c/Å = 12.0235) and P2(1) (a/Å = 11.5777, b/Å = 7.0009, c/Å = 12.5079), respectively. The R,R enantiomer of 1,2-diaminocyclopentane (RRDACP) produced the most cytotoxic metallointercalators. The most cytotoxic metallointercalators were 56MERRDACP and 47MERRDACP with IC(50) values of 0.16 and 0.17 μM, respectively, in comparison to cisplatin (1 μM).

Does cytotoxicity of metallointercalators correlate with cellular uptake or DNA affinity?

The cytotoxicity of the metallointercalators, [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1R,2R-diaminocyclohexane)](2+) ([56MERR]) and [Pt(5,6-dimethyl-1,10-phenanthroline)(trans-1S,2S-diaminocyclohexane)](2+) ([56MESS]), towards A549 human lung cancer cells was examined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The IC(50) value obtained following exposure of A549 cells to [56MESS] for 4 h was approximately three times smaller than that obtained when [56MERR] was administered under the same conditions, indicating that the former complex displayed greater cytotoxicity. Both IC(50) values were greater than that obtained after exposure of A549 cells to cisplatin, demonstrating that the latter compound was the most cytotoxic of the three examined. Microprobe synchrotron radiation X-ray fluorescence (SR-XRF) analyses of metallointercalator-treated A549 cells showed that platinum became localised in DNA-rich regions of the nucleus. In contrast, when the same cells were treated with cisplatin the metal became distributed throughout the cell. Determination of the maximum concentration of platinum present inside the cells using graphite furnace atomic absorption spectrophotometry (GFAAS) of platinum-treated cells suggested that there was greater uptake of [56MERR] compared to [56MESS] by the A549 cells, and that platinum uptake did not account for the greater toxicity of [56MESS], as assessed by the MTT assay. Electrospray ionization mass spectrometric (ESI-MS) and circular dichroism (CD) spectroscopic studies of solutions containing either [56MERR] or [56MESS], and a duplex hexadecamer molecule, showed the two metallointercalators displayed very similar affinity towards the nucleic acid. Overall these results indicate that the difference in cytotoxicity of the two platinum metallointercalators is probably the result of variations in their interactions with other cellular components.

Spectroscopic investigations on the interactions of potent platinum(II) anticancer agents with bovine serum albumin

The interactions of three platinum(II)-based anticancer complexes [(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane)platinum(II)](2+), [(5,6-dimethyl-1,10-phenanthroline)(1R,2R-diaminocyclohexane)platinum(II)](2+), and [(5,6-dimethyl-1,10-phenanthroline)(1,2-diaminoethane)platinum(II)](2+) (56MEEN) with BSA have been examined by circular dichroism (CD), fluorescence and (1)H pulsed gradient spin-echo (PGSE) diffusion NMR spectroscopy. The number of association constants and sites differed depending upon the spectroscopic method. This may be because each technique monitors different types of interaction/s and/or as a consequence of the different concentration ranges required for each technique. The titration of BSA with the achiral 56MEEN as monitored by CD indicates a reduction in the α-helical nature of the albumin, with the association constant calculated to be ~5 × 10(6) M(-1) for one site. Due to the chiral nature of the other two complexes, their association with albumin was not monitored using CD but was examined using fluorescence and PGSE diffusion NMR. Titration of BSA with any of the three metal complexes resulted in quenching of fluorescence, with the number of association sites calculated to be ~1.1, with an association constant of ~2 × 10(5) M(-1). PGSE diffusion NMR provided insights into interactions occurring with the BSA in its entirety, rather than with individual regions. Metal complex binding sites were estimated (~10 equivalent) from the diffusion data, with the average association constant for all sites ~10(2)-10(3)M(-1). These experiments highlight the information that can be elucidated from complementary spectroscopic techniques and demonstrate the usefulness of PGSE diffusion NMR in monitoring multiple weak binding sites, which is of great importance in studying drug-biomolecule interactions.

Copper(II) and Palladium(II) Complexes with Cytotoxic and Antibacterial Activity

The synthesis of eight square pyramidal copper complexes with general structure [Cu(IL)(AL)H2O]2+, where IL represents various methylated 1,10-phenanthrolines, and AL represents either 1S,2S- or 1R,2R-diaminocyclohexane, is reported, with the complexes synthesised as both the perchlorate and chloride salts. The crystal structures of [Cu(1,10-phenanthroline)(1S,2S-diaminocyclohexane](ClO4)2·H2O and [Cu(5,6-dimethyl-1,10-phenanthroline)(1S,2S-diaminocyclohexane](ClO4)2·1.5H2O are reported. Four square planar palladium complexes with general structure [Pd(IL)(AL)]Cl2 have also been synthesised. These complexes were synthesised in order to investigate the structure–activity relationship against both cancer cell lines and bacterial cultures. The copper complexes display anticancer activity similar to cisplatin and 1,10-phenanthroline (phen) in the L1210 murine leukaemia cell line. Methylation of the phen increased the copper complex cytotoxicity by approximately four-fold, compared with the non-methylated complex. No significant difference in activity was observed by altering the chirality of the diaminocyclohexane ligand. The copper complexes demonstrated antibacterial activity against Bacillus subtilis, Staphylococcus aureus, and Escherichia coli; however, high levels of toxicity (30–60 % of death) were observed in the nematode Caenorhabditis elegans. The copper complexes have also been shown to act as DNA nucleases, with the ability to cleave plasmid DNA in the presence of hydrogen peroxide. The palladium complexes all have half maximal inhibitory concentration (IC50) values of ~10 μM in the L1210 cell line, with no significant difference in the cytotoxicity of any of the compounds tested. Minimal antibacterial activity of the palladium complexes was observed.

Identification of the molecular mechanisms underlying the cytotoxic action of a potent platinum metallointercalator

Platinum-based DNA metallointercalators are structurally different from the covalent DNA binders such as cisplatin and its derivatives but have potent in vitro activity in cancer cell lines. However, limited understanding of their molecular mechanisms of cytotoxic action greatly hinders their further development as anticancer agents. In this study, a lead platinum-based metallointercalator, [(5,6-dimethyl-1,10-phenanthroline) (1S,2S-diaminocyclohexane)platinum(II)](2+) (56MESS) was found to be 163-fold more active than cisplatin in a cisplatin-resistant cancer cell line. By using transcriptomics in a eukaryotic model organism, yeast Saccharomyces cerevisiae, we identified 93 genes that changed their expressions significantly upon exposure of 56MESS in comparison to untreated controls (p ≤ 0.05). Bioinformatic analysis of these genes demonstrated that iron and copper metabolism, sulfur-containing amino acids and stress response were involved in the cytotoxicity of 56MESS. Follow-up experiments showed that the iron and copper concentrations were much lower in 56MESS-treated cells compared to controls as measured by inductively coupled plasma optical emission spectrometry. Deletion mutants of the key genes in the iron and copper metabolism pathway and glutathione synthesis were sensitive to 56MESS. Taken together, the study demonstrated that the cytotoxic action of 56MESS is mediated by its ability to disrupt iron and copper metabolism, suppress the biosynthesis of sulfur-containing amino acids and attenuate cellular defence capacity. As these mechanisms are in clear contrast to the DNA binding mechanism for cisplatin and its derivative, 56MESS may be able to overcome cisplatin-resistant cancers. These findings have provided basis to further develop the platinum-based metallointercalators as anticancer agents.

ELECTRONIC SUPPLEMENTARY MATERIAL

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