Mauro Coluccia

Current status of trans-platinum compounds in cancer therapy

Abstract Most of the structure/activity rules emerged from the initial studies by Rosenberg and Cleare and Hoeschele have now been questioned. Specifically: (i) trans compounds are inactive, (ii) charged compounds are inactive, (iii) complexes having only one leaving group are inactive, (iv) only complexes with two amine ligands, each carrying at least one H atom, are active. Exceptions to the first of these rules will be the subject of this article. These ‘exceptions’ which frequently show activity against cisplatin resistant tumour cells, fall in four classes: (1) trans-[PtCl2(L)(L′)] with L and/or L′=pyridine-like ligands; (2) platinum(IV) complexes of formula trans-[PtCl2X2(L)(L′)] with X=hydroxide or carboxylate, L=ammine, and L′=amine; (3) trans-[PtCl2(L)(L′)] with L=alkyl-substituted amine and L′=isopropylamine; and (4) trans-[PtCl2(L)(L′)] with L and/or L′=iminoether. Greater inertness in biological medium appears to be a common feature of these compounds. Increased binding affinity for alternating purine–pyrimidine sites and enhanced interstrand cross-linking ability was found for the first and third class of compounds. Inter-strand cross-links and single-strand breaks were both proposed as cytotoxic lesions for the platinum(IV) species which presumably require reduction to platinum(II) prior to their interaction with DNA. Finally, stable monofunctional adducts with duplex DNA, causing unique local distortions in DNA which are able to inhibit in vitro DNA and RNA synthesis, were found for platinum–iminoether complexes. The recent development of new highly active platinum based drugs that do not fit the classical structure-activity rules indicates the need for a reappraisal of these rules. It is unlikely that any new widely applicable relationship will emerge. All of which goes to show that serendipity still contributes much to the study of Pt drugs, which is only appropriate given how they began.

Trans-platinum complexes in cancer therapy.

The research of new platinum drugs active towards cisplatin refractory/resistant tumors has been mostly focussed on compounds with cis geometry because transplatin, the trans-isomer of cisplatin, is inactive. It is widely accepted that transplatin inactivity stems from two major factors: i) the kinetic instability promoting its deactivation and ii) the formation of DNA adducts characterized by a regioselectivity and a stereochemistry different from those of cisplatin. However, several exceptions to the general rule that the presence of two leaving groups in cis positions is necessary for antitumor activity of platinum complexes, have been reported. Substitution of transplatin ammine ligands by aromatic N-donor heterocycles, branched aliphatic amines, or imino ligands has lead to compounds with relevant in vitro tumor cell growth inhibitory potency, often active towards cisplatin refractory/resistant tumor cells, and in some cases endowed with significant activity also in vivo. From a mechanistic point of view, substitution of bulky ligands for ammines can retard substitution of the two chloride ligands, thus reducing the kinetic instability of the trans-platinum compounds. On the other hand, the formation of DNA adducts qualitatively and quantitatively different from those of cisplatin strongly supports the hypothesis that antitumor-active trans-platinum complexes can have a different spectrum of activity. It is hoped that the increasing knowledge of the biochemical and cellular processes underlying the antitumor-activity of trans-platinum complexes will foster their clinical development.

Inhibition of endothelial cell functions and of angiogenesis by the metastasis inhibitor NAMI-A

NAMI-A is a ruthenium-based compound with selective anti-metastasis activity in experimental models of solid tumours. We studied whether this activity was dependent on anti-angiogenic ability of NAMI-A. We thus investigated its in vitro effects on endothelial cell functions necessary for angiogenesis to develop, as well as its in vivo effects in the chick embryo chorioallantoic membrane model. Endothelial cell proliferation, chemotaxis, and secretion of the matrix-degrading enzyme metalloproteinase-2 were inhibited by NAMI-A in a dose-dependent manner, and without morphologic signs of cell apoptosis or necrosis. Lastly, NAMI-A displayed a dose-dependent in vivo anti-angiogenic activity in the chorioallantoic membrane model. These data suggest that the anti-angiogenic activity of NAMI-A can contribute to its anti-metastatic efficacy in mice bearing malignant solid tumours.

Water-Soluble Ruthenium(III)-Dimethyl Sulfoxide Complexes:Chemical Behaviour and Pharmaceutical Properties

In this paper we report a review of the results obtained in the last few years by our group in the development of ruthenium(III) complexes characterized by the presence of sulfoxide ligands and endowed with antitumor properties. In particular, we will focus on ruthenates of general formula Na[trans-RuCl4(R1R2SO)(L)], where R1R2SO = dimethylsulfoxide (DMSO) or tetramethylenesulfoxide (TMSO) and L = nitrogen donor ligand. The chemical behavior of these complexes has been studied by means of spectroscopic techniques both in slightly acidic distilled water and in phosphate buffered solution at physiological pH. The influence of biological reductants on the chemical behavior is also described. The antitumor properties have been investigated on a number of experimental tumors. Out of the effects observed, notheworthy appears the capability of the tested ruthenates to control the metastatic dissemination of solid metastasizing tumors. The analysis of the antimetastatic action, made in particular on the MCa mammary carcinoma of CBA mouse, has demonstrated a therapeutic value for these complexes which are able to significantly prolong the survival time of the treated animals. The antimetastatic effect is not attributable to a specific cytotoxicity for metastatic tumor cells although in vitro experiments on pBR322 double stranded DNA has shown that the test ruthenates bind to the macromolecule, causing breaks corresponding to almost all bases, except than thymine, and are able to cause interstrand bonds, depending on the nature of the complex being tested, some of which results active as cisplatin itself.

Synthesis, crystal structure, spectral properties and cytotoxic activity of platinum(II) complexes of 2-acetyl pyridine and pyridine-2-carbaldehyde N(4)-ethyl-thiosemicarbazones

The reactions of Na2PtCl4 with pyridine-2-carbaldehyde and 2-acetyl pyridine N(4)-ethyl-thiosemicarbazones, HFo4Et and HAc4Et respectively, afforded the complexes [Pt(Fo4Et)Cl], [Pt(HFo4Et)2]Cl2, [Pt(Fo4Et)2] and [Pt(Ac4Et)Cl], [Pt(HAc4Et)2]Cl2 x 2H2O, [Pt(Ac4Et)2]. The new complexes have been characterized by elemental analyses and spectroscopic studies. The crystal structure of the complex [Pt(Ac4Et)Cl] has been solved. The anion of Ac4E coordinates in a planar conformation to the central platinum(II) through the pyridyl N, azomethine N and thiolato S atoms. Intermolecular hydrogen, non-hydrogen bonds, pi-pi and weak Pt-pi contacts lead to aggregation and a supramolecular assembly. The cytotoxic activity for the platinum(II) complexes in comparison to that of cisplatin and thiosemicarbazones was evaluated in a pair of cisplatin-sensitive and -resistant ovarian cancer cell lines A2780 and A2780/Cp8. The platinum(II) complexes showed a cytotoxic potency in a very low micromolar range and were found able to overcome the cisplatin resistance of A2780/Cp8 cells.

Platinum(II) complexes containing iminoethers: a trans platinum antitumour agent

The biological activity of cis and trans complexes of formula [PtCl2(HN = C(OMe)Me)2] has been investigated. The iminoether ligands can have either E or Z configuration about the C = N double bond, therefore EE, EZ and ZZ isomers are obtainable. Substitution of iminoether with EE configuration for amine leads to unexpectedly high antitumor activity for the complex with trans geometry which turns out to be more active than the cis congener in the P388 leukaemia system. The same trans-EE complex shows an activity comparable to that of cisplatin in reducing the primary tumour mass and lung metastases in mice bearing Lewis lung carcinoma, thus representing a trans platinum complex active on both limphoproliferative and solid metastasizing murine tumours. Also the cytotoxicity, the inhibition of DNA synthesis and the mutagenic activity, which are greater for the cis- with respect to the trans-isomer in the amine complexes, are instead greater for the trans- than for the cis- isomer in the case of iminoether compounds. Binding to calf thymus DNA is slower for iminoether complexes than it is for amine complexes, however after 24 h reaction time the level of binding is similar for both types of complexes. Trans-EE, like trans-DDP, does not give the DNA conformational alterations (terbium fluorescence) typical of antitumour-active cis- platinum compounds, but, under strictly analogous experimental conditions, shows a greatly reduced DNA interstrand cross-linking ability (heat denaturation/renaturation assay) with respect to either trans-DDP or cis-EE and cis-DDP. The data in hand point to a new trans platinum antitumour complex with a mechanism of action different from that of cis-DDP and classical analogues.

In vitroAntitumor Activity of 2-Acetyl Pyridine 4N-Ethyl Thiosemicarbazone and Its Platinum(II) and Palladium(II) Complexes

The reaction of platinum(II) [Pt(II)] or palladium(II) [Pd(II)] with 2-acetyl pyridine 4N-ethyl thiosemicarbazone, HAc4Et (1) results in the complexes [Pt(Ac4Et)2] (2) and [Pd(Ac4Et)2] (3). In a panel of human tumor cell lines of different origins (breast, colon, and ovary cancers), and containing also cisplatin-refractory/resistant cell lines, the in vitro growth inhibitory effect of 1–3 was compared to that of cisplatin by using the sulforodamine B assay. After a 96-hour continuous treatment, both the thiosemicarbazone HAc4Et and the metal compounds [Pt(Ac4Et)2] and [Pd(Ac4Et)2] exhibit very remarkable growth inhibitory activities with mean IC50 values of 0.9 nM (0.22–2.47 nM), 0.7 nM (0.15–2 nM) and 0.5 nM (0.17–1.02 nM), respectively. In contrast, cisplatin shows a markedly lower growth inhibitory potency, the mean IC50 in the panel being 2.8 µM (0.2–8 µM). In addition to their major cell growth inhibitory potency, complexes 1–3 are characterized by a growth inhibitory profile different from that of cisplatin, being active towards cisplatin-refractory tumor cell lines. These findings, along with the ability of completely overcoming acquired cisplatin resistance from either multifocal or reduced uptake origin, confirm the antitumor potential of HAc4Et and support the hypothesis that both [Pt(Ac4Et)2] and [Pd(Ac4Et)2] complexes can be characterized by cellular pharmacological properties distinctly different from those of cisplatin.

Zoledronic acid affects over-angiogenic phenotype of endothelial cells in patients with multiple myeloma

Therapeutic doses of zoledronic acid markedly inhibit in vitro proliferation, chemotaxis, and capillarogenesis of bone marrow endothelial cells of patients with multiple myeloma. Zoledronic acid also induces a sizeable reduction of angiogenesis in the in vivo chorioallantoic membrane assay. These effects are partly sustained by gene and protein inhibition of vascular endothelial growth factor and vascular endothelial growth factor receptor 2 in an autocrine loop. Mevastatin, a specific inhibitor of the mevalonate pathway, reverts the zoledronic acid antiangiogenic effect, indicating that the drug halts this pathway. Our results provide evidence of a direct antiangiogenic activity of zoledronic acid on multiple myeloma patient-derived endothelial cells due to at least four different mechanisms identified either in vitro or in vivo. Tentatively, we suggest that the zoledronic acid antitumoral activity in multiple myeloma is also sustained by antiangiogenesis, which would partly account for its therapeutic efficacy in multiple myeloma. [Mol Cancer Ther 2007;6(12):3256–62]

In vitro and in vivo antitumour activity and cellular pharmacological properties of new platinum–iminoether complexes with different configuration at the iminoether ligands

In order to widen our knowledge on antitumour trans-[PtCl2(iminoether)2] complexes, we have synthesised two new derivatives, trans-[PtCl2¿E-HN = C(OEt)Me¿2] (1) and trans-[PtCl2¿Z-HN = C(OEt)Me¿2] (2), which differ in the configuration of the iminoether ligands. Isomer 1 showed an in vitro cytotoxicity similar to that of cisplatin in a panel of human tumour cell lines (mean IC50 = 8 and 7.7 microM, respectively), whereas isomer 2 showed a lower activity (IC50 = 14.3 microM). Both 1 and 2 isomers overcame cisplatin resistance of ovarian cancer cell line A2780/Cp8. In agreement with the n-octanol/saline partition ratios, intracellular platinum content (and DNA platination) after a 2-h exposure to equimolar drug concentrations was in the order 1 > 2 >> cisplatin, thus indicating that substitution of imminoethers for ammines determines a major lipophilicity and cellular uptake of the platinum drug. Both 1 and 2 showed a major toxic effect towards an excision repair-defective Drosophila strain, thus indicating cellular DNA as cytotoxic target. Finally, both 1 and 2 were active in vivo against the murine P388 system, but, contrary to the in vitro activity, isomer 2 was slightly more active than 1. On the whole, the results confirm the antitumour activity of trans-[PtCl2(iminoether)2] complexes, and indicate that the configuration of the iminoether ligands may affect the pharmacological properties of this class of complexes.

Rhodium(III) analogues of antitumour-active ruthenium(III) compounds: the crystal structure of [ImH][trans-RhCl4(Im)2] (Im= imidazole)

A series of neutral and anionic Rh(III)-chloride compounds bearing ammonia or imidazole (Im) ligands, and isostructural to Ru(III) complexes endowed with antineoplastic activity, were synthesized and characterized spectroscopically. The X-ray crystal structure of [ImH][ trans -RhCl 4 (Im) 2 ] was determined. Crystal data: monoclinic, space group C 2/ c , Z =4, a =13.133(3), b =7.977(1), c =16.683(4) A, β =113.84(2)°. The solution behaviour and some biological parameters of the new rhodium compounds, including cytotoxicity, in vitro interactions with DNA and in vivo antitumour activity against a tumour model, were investigated and compared with those of the corresponding ruthenium analogues.