Versatile Route to trans-Platinum(II) Complexes via Manipulation of a Coordinated 3-(Pyridin-3-yl)propanoic Acid Ligand.

We describe the direct coupling of alcohols and amines to a 3-(pyridin-3-yl)propanoic acid ligand coordinated to a Pt(II) to afford ester and amide derivatives. Using this approach, a family of trans-Pt(II) compounds with amine ligands bearing long perfluorinated chains was prepared, as these chains potentially endow the complexes with thermoactivatable properties. Related compounds with alkyl chains in place of the perfluorinated chains were also prepared as controls using the same direct coupling method. The stability of the complexes in solution, their reactivity with DNA and proteins, and their antiproliferative activity evaluated in tumorigenic (A2780 and A2780cisR) and nontumorigenic (HEK293) cells at 37 °C and following exposure to elevated temperatures (that mimic the temperatures employed in thermotherapy) were also studied to assess their utility as putative (thermoactivated) anticancer agents.

Vascular-targeted low dose photodynamic therapy stabilizes tumor vessels by modulating pericyte contractility.

Vascular-targeted low-dose photodynamic therapy (L-PDT) was shown to improve chemotherapy distribution in malignant pleural tumors such as malignant pleural mesothelioma (MPM). However, the mechanisms triggered by L-PDT on the tumor vasculature are still debated. In pericyte and endothelial cell co-cultures, we show that pericytes exhibit enhanced sensitivity towards L-PDT compared to endothelial cells, displaying actin stress fibers and cellular contraction via Rho/ROCK kinase signaling myosin light chain and focal adhesion kinase phosphorylation (MLC-P, FAK-P). We then confirm, in two separate MPM models, in mice the phosphorylation of the MLC in pericytes specifically following L-PDT. Furthermore, while L-PDT does not affect tumor vascular density or diameter, we show that it enhances tumor vascular pericyte coverage, leads to a drop in tumor interstitial fluid pressure and enhances the transport of FITC-dextran throughout tumors. In conclusion, L-PDT has the potential to stabilize the tumor vascular bed which improves vascular transport. The mechanism described in the present study may help translate and optimize this approach in patients. Lasers Surg. Med. 51:550-561, 2019. © 2019 Wiley Periodicals, Inc.

Chemo-manipulation of tumor blood vessels by a metal-based anticancer complex enhances antitumor therapy.

Human pleural mesothelioma is an incurable and chemoresistant cancer. Using a nude mouse xenograft model of human pleural mesothelioma, we show that RAPTA-T, a compound undergoing preclinical evaluation, enhances tumor vascular function by decreasing blood vessel tortuosity and dilation, while increasing the coverage of endothelial cells by pericytes and vessel perfusion within tumors. This in turn significantly reduces the interstitial fluid pressure and increases oxygenation in the tumor. Consequently, RAPTA-T pre-treatment followed by the application of cisplatin or liposomal cisplatin (Lipoplatin) leads to increased levels of the cytotoxin in the tumor and enhanced mesothelioma growth inhibition. We demonstrate that the vascular changes induced by RAPTA-T are related, in part, to the inhibition of poly-(ADP-ribose) polymerase 1 (PARP-1) which is associated to tumor vascular stabilization. These findings suggest novel therapeutic implications for RAPTA-T to create conditions for superior drug uptake and efficacy of approved cytotoxic anti-cancer drugs in malignant pleural mesothelioma and potentially other chemoresistant tumors.

Palladium(II)-Stabilized Pyridine-2-Diazotates: Synthesis, Structural Characterization, and Cytotoxicity Studies.

Well-defined diazotates are scarce. Here we report the synthesis of unprecedented homoleptic palladium(II) diazotate complexes. The palladium(II)-mediated nitrosylation of 2-aminopyridines with NaNO2 results in the formation of metal-stabilized diazotates, which were found to be cytotoxic to human ovarian cancer cells.

Synthesis, characterization and cytotoxicity of arene-ruthenium(ii) complexes with acylpyrazolones functionalized with aromatic groups in the acyl moiety.

A series of neutral ruthenium(ii)-arene complexes, [(arene)Ru(QR)Cl] (arene = p-cymene or hexamethylbenzene), containing 4-acyl-5-pyrazolonate (QR) ligands with aromatic substituents in the acyl moiety (a phenyl in QPh and a 1-naphthyl in Qnaph) and related ionic complexes [(arene)Ru(QR)(PTA)][PF6] (PTA = 1,3,5-triaza-7-phosphaadamantane) have been synthesized and characterized by IR, 1H, 13C and 31P NMR spectroscopy, elemental analysis and ESI mass spectrometry. The structures of five of these compounds were also determined by X-ray crystallography. DFT studies have been performed on all complexes and, in the case of two cationic [(arene)Ru(Qnaph)(PTA)][PF6], the existence of two conformers with a different relative orientation of the naphthyl group in the Qnaph ligand has been assessed, showing that they possess similar energies, in agreement with the experimentally observed NMR spectra in solution. The cytotoxicity of the 4-acyl-5-pyrazolonate proligands (HQR) and complexes was evaluated in vitro against human ovarian carcinoma cells (A2780 and A2780cisR) and non-tumorous human embryonic kidney (HEK293) cells. In general, each complex is about equally cytotoxic to all three cell lines and the PTA derivatives with the naphthyl-modified QR ligands are the most active of the series.

Drug Repurposing Approach Identifies a Synergistic Drug Combination of an Antifungal Agent and an Experimental Organometallic Drug for Melanoma Treatment.

By screening a drug library comprising FDA approved compounds, we discovered a potent interaction between the antifungal agent haloprogin and the experimental organometallic drug RAPTA-T, to synergistically induce cancer cell killing. The combination of these two small molecules, even at low doses, elicited an improved therapeutic response on tumor growth over either agent alone or the current treatment used in the clinic in the highly aggressive syngeneic B16F10 melanoma tumor model, where classical cytotoxic chemotherapeutic agents show little efficacy. The combination with the repurposed chemodrug haloprogin provides the basis for a new powerful treatment option for cutaneous melanoma. Importantly, because synergistic induction of tumor cell death is achieved with low individual drug doses, and cellular targets for RAPTA-T are different from those of classical chemotherapeutic drugs, a therapeutic strategy based on this approach could avoid toxicities and potentially resistance mechanisms, and could even inhibit metastatic progression.

Nucleosome acidic patch-targeting binuclear ruthenium compounds induce aberrant chromatin condensation.

The 'acidic patch' is a highly electronegative cleft on the histone H2A-H2B dimer in the nucleosome. It is a fundamental motif for protein binding and chromatin dynamics, but the cellular impact of targeting this potentially therapeutic site with exogenous molecules remains unclear. Here, we characterize a family of binuclear ruthenium compounds that selectively target the nucleosome acidic patch, generating intra-nucleosomal H2A-H2B cross-links as well as inter-nucleosomal cross-links. In contrast to cisplatin or the progenitor RAPTA-C anticancer drugs, the binuclear agents neither arrest specific cell cycle phases nor elicit DNA damage response, but rather induce an irreversible, anomalous state of condensed chromatin that ultimately results in apoptosis. In vitro, the compounds induce misfolding of chromatin fibre and block the binding of the regulator of chromatin condensation 1 (RCC1) acidic patch-binding protein. This family of chromatin-modifying molecules has potential for applications in drug development and as tools for chromatin research.

Cytotoxic Half-Sandwich Rh(III) and Ir(III) ß-Diketonates.

A series of half-sandwich pentamethylcyclopentadienyl rhodium(III) and iridium(III) complexes [Cp*M(DBM/HDB/AVB)Cl] and [Cp*M(DBM/HDB/AVB)(PTA)][SO3CF3], where Cp* = pentamethylcyclopentadienyl, the proligands DBMH = dibenzoylmethane, HDBH = o-hydroxydibenzoylmethane, AVBH = avobenzone, and PTA = 1,3,5-triaza-7-phosphaadamantane, is reported. All the complexes were characterized by IR, 1H and 13C NMR spectroscopy, electrospray ionization mass spectrometry, elemental analysis, and DFT calculations. Five of the complexes have also been characterized in the solid-state by X-ray crystallography. The cytotoxicity of the complexes has been evaluated against human ovarian A2780 and A2780cisR cell lines and, with the only exception of complexes 1 and 2 that display a negligible cytotoxicity, exhibit moderate cytotoxicity toward both cancer cell lines. However, the complexes do not show cancer cell selectivity with respect to human embryonic kidney HEK293 cells.

Perfluorinated HDAC inhibitors as selective anticancer agents.

A series of potent histone deacetylase inhibitors is presented that incorporate alkyl or perfluorinated alkyl chains. Several new compounds show greater in vitro antiproliferative activity than the clinically approved inhibitor, SAHA. Furthermore, the new compounds show up to 5-fold greater activity against cancer cells than healthy cells. This selectivity is in contrast to SAHA, which is more active against the healthy cell line than the cancer cell line tested. Finally, we report an increase in activity for SAHA under mild hyperthermia, indicating that it could be an interesting candidate to use in combination with thermal therapy.

Differences in cisplatin distribution in sensitive and resistant ovarian cancer cells: a TEM/NanoSIMS study.

Cisplatin is a widely used anti-cancer drug, but its effect is often limited by acquired resistance to the compound during treatment. Here, we use a combination of transmission electron microscopy (TEM) and nanoscale-secondary ion mass spectrometry (NanoSIMS) to reveal differences between cisplatin uptake in human ovarian cancers cells, which are known to be susceptible to acquired resistance to cisplatin. Both cisplatin sensitive and resistant cell lines were studied, revealing markedly less cisplatin in the resistant cell line. In cisplatin sensitive cells, Pt was seen to distribute diffusely in the cells with hotspots in the nucleolus, mitochondria, and autophagosomes. Inductively coupled plasma mass spectrometry (ICP-MS) was used to validate the NanoSIMS results.

New Class of Half-Sandwich Ruthenium(II) Arene Complexes Bearing the Water-Soluble CAP Ligand as an in Vitro Anticancer Agent.

Ruthenium(II) arene complexes of 1,4,7-triaza-9-phosphatricyclo[5.3.2.1]tridecane (CAP) were obtained. Cytotoxicity studies against cancer cell lines reveal higher activity than the corresponding PTA analogues and, in comparison to the effects on noncancerous cells, the complexes are endowed with a reasonable degree of cancer cell selectivity.

Allosteric cross-talk in chromatin can mediate drug-drug synergy.

Exploitation of drug-drug synergism and allostery could yield superior therapies by capitalizing on the immensely diverse, but highly specific, potential associated with the biological macromolecular landscape. Here we describe a drug-drug synergy mediated by allosteric cross-talk in chromatin, whereby the binding of one drug alters the activity of the second. We found two unrelated drugs, RAPTA-T and auranofin, that yield a synergistic activity in killing cancer cells, which coincides with a substantially greater number of chromatin adducts formed by one of the compounds when adducts from the other agent are also present. We show that this occurs through an allosteric mechanism within the nucleosome, whereby defined histone adducts of one drug promote reaction of the other drug at a distant, specific histone site. This opens up possibilities for epigenetic targeting and suggests that allosteric modulation in nucleosomes may have biological relevance and potential for therapeutic interventions.

Synthesis, Structure, and Anticancer Activity of Arene-Ruthenium(II) Complexes with Acylpyrazolones Bearing Aliphatic Groups in the Acyl Moiety.

A series of neutral ruthenium(II) arene complexes [(arene)Ru(QR)Cl] (arene = p-cymene (cym) or hexamethylbenzene (hmb)) containing 4-acyl-5-pyrazolonate QR ligands with different electronic and steric substituents (R = 4-cyclohexyl, 4-stearoyl, or 4-adamantyl) and related ionic complexes [(arene)Ru(QR)(PTA)][PF6] (PTA = 1,3,5-triaza-7-phosphaadamantane) were synthesized and characterized by spectroscopy (IR, UV-vis, ESI-MS, and 1H and 13C NMR), elemental analysis, X-ray crystallography, and density functional theory studies. The cytotoxicity of the proligands and metal complexes was evaluated in vitro against human ovarian carcinoma cells (A2780 and A2780cisR), as well as against nontumorous human embryonic kidney (HEK293) cells. In general the cationic PTA-containing complexes are more cytotoxic than their neutral precursors with a chloride ligand in place of the PTA. Moreover, the complexes do not show cross-resistance and are essentially equally cytotoxic to both the A2780 and A2780cisR cell lines, although they only show limited selectivity toward the cancer cell lines.

Regulating the anticancer properties of organometallic dendrimers using pyridylferrocene entities: synthesis, cytotoxicity and DNA binding studies.

A new series of eight first- and second-generation heterometallic ferrocenyl-derived metal-arene metallodendrimers, containing ruthenium(ii)-p-cymene, ruthenium(ii)-hexamethylbenzene, rhodium(iii)-cyclopentadienyl or iridium(iii)-cyclopentadienyl moieties have been prepared. The metallodendrimers were synthesized by first reacting DAB-(NH2)n (where n = 4 or 8, DAB = diaminobutane) with salicylaldehyde, and then the Schiff-base dendritic ligands were reacted in a one-pot reaction with the appropriate [(η(6)-p-iPrC6H4Me)RuCl2]2, [(η(6)-C6Me6)RuCl2]2, [(η(5)-C5Me5)IrCl2]2 or [(η(5)-C5Me5)RhCl2]2 dimers, in the presence of 4-pyridylferrocene. Heterometallic binuclear analogues were prepared as models of the larger metallodendrimers. All complexes have been characterized using analytical and spectroscopic methods. The cytotoxicity of the heterometallic metallodendrimers and their binuclear analogues were evaluated against A2780 cisplatin-sensitive and A2780cisR cisplatin-resistant human ovarian cancer cell lines and against a non-tumorigenic HEK-293 human embryonic kidney cell line. The second generation Ru(ii)-η(6)-C6Me6 metallodendrimer is the most cytotoxic and selective compound. DNA binding experiments reveal that a possible mode-of-action of these compounds involves non-covalent interactions with DNA.

Fighting Cancer with Transition Metal Complexes: From Naked DNA to Protein and Chromatin Targeting Strategies.

Many transition metal complexes have unique physicochemical properties that can be efficiently exploited in medicinal chemistry for cancer treatment. Traditionally, double-stranded DNA has been assumed to be the main binding target; however, recent studies have shown that nucleosomal DNA as well as proteins can act as dominant molecular binding partners. This has raised new questions about the molecular determinants that govern DNA versus protein binding selectivity, and has offered new ways to rationalize their biological activity and possible side effects. To address these questions, molecular simulations at an atomistic level of detail have been used to complement, support, and rationalize experimental data. Herein we review some relevant studies-focused on platinum and ruthenium compounds-to illustrate the power of state-of-the-art molecular simulation techniques and to demonstrate how the interplay between molecular simulations and experiments can make important contributions to elucidating the target preferences of some promising transition metal anticancer agents. This contribution aims at providing relevant information that may help in the rational design of novel drug-discovery strategies.

Organometallic rhodium(III) and iridium(III) cyclopentadienyl complexes with curcumin and bisdemethoxycurcumin co-ligands.

A series of half-sandwich cyclopentadienyl rhodium(III) and iridium(III) complexes of the type [Cp*M(curc/bdcurc)Cl] and [Cp*M(curc/bdcurc)(PTA)][SO3CF3], in which Cp* = pentamethylcyclopentadienyl, curcH = curcumin and bdcurcH = bisdemethoxycurcumin as O^O-chelating ligands, and PTA = 1,3,5-triaza-7-phosphaadamantane, is described. The X-ray crystal structures of three of the complexes, i.e. [Cp*Rh(curc)(PTA)][SO3CF3] (5), [Cp*Rh(bdcurc)(PTA)][SO3CF3] (6) and [Cp*Ir(bdcurc)(PTA)][SO3CF3] (8), confirm the expected "piano-stool" geometry. With the exception of 5, the complexes are stable under pseudo-physiological conditions and are moderately cytotoxic to human ovarian carcinoma (A2780 and A2780cisR) cells and also to non-tumorigenic human embryonic kidney (HEK293) cells, but lack the cancer cell selectivity observed for related arene ruthenium(II) complexes.

Synthesis and Antiproliferative Activity of New Ruthenium Complexes with Ethacrynic-Acid-Modified Pyridine and Triphenylphosphine Ligands.

Pyridine- and phosphine-based ligands modified with ethacrynic acid (a broad acting glutathione transferase inhibitor) were prepared and coordinated to ruthenium(II)-arene complexes and to a ruthenium(III) NAMI-A type complex. All the compounds (ligands and complexes) were fully characterized by analytical and spectroscopic methods and, in one case, by single-crystal X-ray diffraction. The in vitro anticancer activity of the compounds was studied, with the compounds displaying moderate cytotoxicity toward the human ovarian cancer cell lines. All the complexes led to similar levels of residual GST activity in the different cell lines, irrespective of the stability of the Ru-ligand bond.

Synthesis of triazenes with nitrous oxide.

Triazenes are valuable compounds in organic chemistry and numerous applications have been reported. Furthermore, triazenes have been investigated extensively as potential antitumor drugs. Here, we describe a new method for the synthesis of triazenes. The procedure involves a reagent which is rarely used in synthetic organic chemistry: nitrous oxide (N2 O, "laughing gas"). Nitrous oxide mediates the coupling of lithium amides and organomagnesium compounds while serving as a nitrogen donor. Despite the very inert character of nitrous oxide, the reactions can be performed in solution under mild conditions. A key advantage of the new procedure is the ability to access triazenes with alkynyl and alkenyl substituents. These compounds are difficult to prepare by conventional methods because the required starting materials are unstable. Some of the new alkynyltriazenes were found to display high cytotoxicity in in vitro tests on ovarian and breast cancer cell lines.

Preclinical combination therapy of the investigational drug NAMI-A(+) with doxorubicin for mammary cancer.

AIM OF THE STUDY: The tumor metastases targeting ruthenium complex NAMI-A synergistically improves the activity of gemcitabine in combination therapies. High-throughput screening was used to identify other potential drug combinations from a library of FDA approved drugs. Doxorubicin was identified as a hit compound and was therefore evaluated in combination with NAMI-A in vitro and in a preclinical in vivo model. RESULTS: High-throughput screening identified eight structurally diverse compounds that synergize with NAMI-A including doxorubicin. The combination index on MCF-7 cells showed synergism as the concentration of NAMI-A increases independent of the doxorubicin concentration. In MCa mammary carcinoma of CBA mice, NAMI-A (35 mg/kg/day i.p. on days 7-12) followed by doxorubicin (10 mg/kg i.p. on day 16), significantly increased the effects of the individual drugs on metastases with 70 % animals resulting free of macroscopically detectable tumor nodules in the lungs at sacrifice. NAMI-A, unlike doxorubicin, cured 60 % of the treated mice but the combination therapy was toxic to the animals. CONCLUSIONS: The combined therapy of NAMI-A with doxorubicin synergizes on lung metastasis in a preclinical mouse model. The combination therapy at the maximum tolerated doses of the two drugs is toxic. Hence, this combination is not suitable for clinical studies using maximum tolerated doses.

Ruthenium(II) and osmium(II) 1,2,3-triazolylidene organometallics: a preliminary investigation into the biological activity of 'click' carbene complexes.

Taking advantage of the facile and versatile synthetic properties of 'click' 1,2,3-triazolylidene N-heterocyclic carbenes (tzNHC's), a range of new organometallic Ru(II) and Os(II) arene complexes containing functionalised tzNHC ligands, [M(η(6)-p-cymene)(tzNHC)Cl2] [M = Ru(II), Os(II)], have been synthesised and fully characterised, including the X-ray crystal structure of one of the Os(II) complexes. The tzNHC ligands remain coordinated to the metal centres under relevant physiological conditions, and following binding to the model protein, ubiquitin. The in vitro cytotoxicity of the compounds towards human ovarian cancer cells is dependent on the substituent on the tzNHC ligand but is generally <50 µM and in some cases <1 µM, whilst still retaining a high degree of selectivity towards cancer cells over healthy cells (1.85 µM in A2780 ovarian cancer cells versus 435 µM in human embryonic kidney cells in one case).