Intracellular localization of titanium within xenografted sensitive human tumors after treatment with the antitumor agent titanocene dichloride

Scope of organometallic compounds based on transition metal-arene systems as anticancer agents: starting from the classical paradigm to targeting multiple strategies

The advent of the clinically approved drug cisplatin started a new era in the design of metallodrugs for cancer chemotherapy. However, to date, there has not been much success in this field due to the persistence of some side effects and multi-drug resistance of cancer cells. In recent years, there has been increasing interest in the design of metal chemotherapeutics using organometallic complexes due to their good stability and unique properties in comparison to normal coordination complexes. Their intermediate properties between that of traditional inorganic and organic materials provide researchers with a new platform for the development of more promising cancer therapeutics. Classical metal-based drugs exert their therapeutic potential by targeting only DNA, but in the case of organometallic complexes, their molecular target is quite distinct to avoid drug resistance by cancer cells. Some organometallic drugs act by targeting a protein or inhibition of enzymes such as thioredoxin reductase (TrRx), while some target mitochondria and endoplasmic reticulum. In this review, we mainly discuss organometallic complexes of Ru, Ti, Au, Fe and Os and their mechanisms of action and how new approaches improve their therapeutic potential towards various cancer phenotypes. Herein, we discuss the role of structure-reactivity relationships in enhancing the anticancer potential of drugs for the benefit of humans both in vitro and in vivo. Besides, we also include in vivo tumor models that mimic human physiology to accelerate the development of more efficient clinical organometallic chemotherapeutics.

Differential cytotoxicity induced by the Titanium(IV)Salan complex Tc52 in G2-phase independent of DNA damage

BACKGROUND

Chemotherapy is one of the major treatment modalities for cancer. Metal-based compounds such as derivatives of cisplatin are in the front line of therapy against a subset of cancers, but their use is restricted by severe side-effects and the induction of resistance in treated tumors. Subsequent research focused on development of cytotoxic metal-complexes without cross-resistance to cisplatin and reduced side-effects. This led to the discovery of first-generation titanium(IV)salan complexes, which reached clinical trials but lacked efficacy. New-generation titanium (IV)salan-complexes show promising anti-tumor activity in mice, but their molecular mechanism of cytotoxicity is completely unknown.

METHODS

Four different human cell lines were analyzed in their responses to a toxic (Tc52) and a structurally highly related but non-toxic (Tc53) titanium(IV)salan complex. Viability assays were used to reveal a suitable treatment range, flow-cytometry analysis was performed to monitor the impact of dosage and treatment time on cell-cycle distribution and cell death. Potential DNA strand break induction and crosslinking was investigated by immunostaining of damage markers as well as automated fluorometric analysis of DNA unwinding. Changes in nuclear morphology were analyzed by DAPI staining. Acidic beta-galactosidase activity together with morphological changes was monitored to detect cellular senescence. Western blotting was used to analyze induction of pro-apoptotic markers such as activated caspase7 and cleavage of PARP1, and general stress kinase p38.

RESULTS

Here we show that the titanium(IV)salan Tc52 is effective in inducing cell death in the lower micromolar range. Surprisingly, Tc52 does not target DNA contrary to expectations deduced from the reported activity of other titanium complexes. Instead, Tc52 application interferes with progression from G2-phase into mitosis and induces apoptotic cell death in tested tumor cells. Contrarily, human fibroblasts undergo senescence in a time and dose-dependent manner. As deduced from fluorescence studies, the potential cellular target seems to be the cytoskeleton.

CONCLUSIONS

In summary, we could demonstrate in four different human cell lines that tumor cells were specifically killed without induction of major cytotoxicity in non-tumorigenic cells. Absence of DNA damaging activity and the cell-cycle block in G2 instead of mitosis makes Tc52 an attractive compound for further investigations in cancer treatment.

Metal complex interactions with DNA

Increasing numbers of DNA structures are being revealed using a diverse range of transition metal complexes and biophysical spectroscopic techniques. Here we present a review of metal complex-DNA interactions in which several binding modes and DNA structural forms are explored.

On the discovery, biological effects, and use of Cisplatin and metallocenes in anticancer chemotherapy

The purpose of this paper is to summarize mode of action of cisplatin on the tumor cells, a brief outlook on the metallocene compounds as antitumor drugs as well as the future tendencies for the use of the latter in anticancer chemotherapy. Molecular mechanisms of cisplatin interaction with DNA, DNA repair mechanisms, and cellular proteins are discussed. Molecular background of the sensitivity and resistance to cisplatin, as well as its influence on the efficacy of the antitumor immune response was evaluated. Furthermore, herein are summarized some metallocenes (titanocene, vanadocene, molybdocene, ferrocene, and zirconocene) with high antitumor activity.

Titanocene-phosphine derivatives as precursors to cytotoxic heterometallic TiAu2 and TiM (M = Pd, Pt) compounds. Studies of their interactions with DNA

A series of tri- and bimetallic titanium-gold, titanium-palladium, and titanium-platinum derivatives of the general formulas [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)(AuCl)}(2)]·2THF [n = 0 (1); n = 2 (2); n = 3 (3)] and [TiCl(2){η(5)-C(5)H(4)κ-(CH(2))(n)PPh(2)}(2)(MCl(2))]·2THF [M = Pd, n = 0 (4); n = 2 (5); n = 3 (6) ; M = Pt, n = 0 (7); n = 2 (8); n = 3 (9)] have been synthesized and characterized by different spectroscopic techniques and mass spectrometry. The molecular structures of compounds 1-9 have been investigated by means of density functional theory calculations. The calculated IR spectra of the optimized structures fit well with the experimental IR data obtained for 1-9. The stability of the heterometallic compounds in deuterated solvents [CDCl(3), dimethyl sulfoxide (DMSO)-d(6), and mixtures 50:50 DMSO-d(6)/D(2)O and 1:99 DMSO-d(6)/D(2)O at acidic and neutral pH] has been evaluated by (31)P and (1)H NMR spectroscopy showing a higher stability for these compounds than for Cp(2)TiCl(2) or precursors [Ti{η(5)-C(5)H(4)(CH(2))(n)PPh(2)}(2)]. The new compounds display a lower acidity (1-2 units) than Cp(2)TiCl(2). The decomposition products have been identified over time. Complexes 1-9 have been tested as potential anticancer agents, and their cytotoxicity properties were evaluated in vitro against HeLa human cervical carcinoma and DU-145 human prostate cancer cells. TiAu(2) and TiPd compounds were highly cytotoxic for these two cell lines. The interactions of the compounds with calf thymus DNA have been evaluated by thermal denaturation (1-9) and by circular dichroism (1, 3, 4, and 7) spectroscopic methods. All of these complexes show a stronger interaction with DNA than that displayed by Cp(2)TiCl(2) at neutral pH. The data are consistent with electrostatic interactions with DNA for TiAu(2) compounds and for a covalent binding mode for TiM (M = Pd, Pt) complexes.

Improvement of cytotoxicity of titanocene-functionalized mesoporous materials by the increase of the titanium content

The reaction of [Ti(eta(5)-C(5)H(5))(2)Cl(2)] (1), with 3-mercaptopropyltrimethoxysilane or 3-mercaptopropyltriethoxysilane in the presence of triethylamine leads to the formation of the thiolate complexes [Ti(eta(5)-C(5)H(5))(2){SCH(2)CH(2)CH(2)Si(OMe)(3)}(2)] (2) and [Ti(eta(5)-C(5)H(5))(2){SCH(2)CH(2)CH(2)Si(OEt)(3)}(2)] (3), respectively. Complexes 2 and 3 have been characterized by traditional methods, in addition, structural studies based on DFT calculations are reported. 1-3 have been grafted onto dehydroxylated MCM-41 to give the novel materials MCM-41/[Ti(eta(5)-C(5)H(5))(2)Cl(2)] (S1), MCM-41/[Ti(eta(5)-C(5)H(5))(2){SCH(2)CH(2)CH(2)Si(OMe)(3)}(2)] (S2) and MCM-41/[Ti(eta(5)-C(5)H(5))(2){SCH(2)CH(2)CH(2)Si(OEt)(3)}(2)] (S3) which have been characterized by powder X-ray diffraction, X-ray fluorescence, nitrogen gas sorption, multinuclear MAS NMR spectroscopy, thermogravimetry, UV spectroscopy, SEM and TEM. Materials S2 and S3 present much higher values of Ti wt% (ca. 3%) than S1 (ca. 1%), indicating the higher functionalization rate induced by the substitution of the chloro ligands by the thiolato ligands in the starting titanocene derivatives. The cytotoxicity of the non-functionalized MCM-41 and S1-S3 toward human cancer cell lines such as adenocarcinoma HeLa, human myelogenous leukemia K562 and human malignant melanoma Fem-x has been studied. In addition the cytotoxicity of these materials on normal immunocompetent cells such as stimulated (PBMC+PHA) and non-stimulated (PBMC-PHA) peripheral blood mononuclear cells have been also studied. M(50) values (quantity of material needed to inhibit normal cell survival by 50%) of the studied surfaces show that non-functionalized MCM-41 was not active against any of the studied cells, while the functionalized surfaces S1-S3 were active against all the tested human cancer cells. The cytotoxic activity of surfaces S2 and S3 were very similar, however, S1 showed lower cytotoxic activity. This phenomenon indicates that the cytotoxicity of the titanocene-functionalized materials strongly depends on the titanium content.

Calorimetric, spectroscopic, and model studies provide insight into the transport of Ti(IV) by human serum transferrin

Evidence suggests that transferrin can bind Ti(IV) in an unhydrolyzed form (without bound hydroxide or oxide) or in a hydrolyzed form. Ti(IV) coordination by N,N'-di(o-hydroxybenzyl)ethylenediamine-N,N'-diacetic acid (HBED) at different pH values models the two forms of Ti(IV)-loaded transferrin spectrally and structurally. 13C NMR and stopped-flow kinetic experiments reveal that when the metal is delivered to the protein using an unhydrolyzed source, Ti(IV) can coordinate in the typical distorted octahedral environment with a bound synergistic anion. The crystal structure of TiHBED obtained at low pH models this type of coordination. The solution structure of the complex compares favorably with the solid state from pH 3.0 to 4.0, and the complex can be reduced with E1/2 = -641 mV vs NHE. Kinetic and thermodynamic competition studies at pH 3.0 reveal that Ti(citrate)3 reacts with HBED via a dissociative mechanism and that the stability of TiHBED (log beta = 34.024) is weaker than that of the Fe(III) complex. pH stability studies show that Ti(IV) hydrolyzes ligand waters at higher pH but still remains bound to HBED until pH 9.5. Similarly, at a pH greater than 8.0 the synergistic anion that binds Ti(IV) in transferrin is readily displaced by irreversible metal hydrolysis although the metal remains bound to the protein until pH 9.5. Thermal denaturation studies conducted optically and by differential scanning calorimetry reveal that Ti(IV)-bound transferrin experiences only minimal enhanced thermal stability unlike when Fe(III) is bound. The C- and N-lobe transition Tm values shift to a few degrees higher. The stability, competition, and redox studies performed provide insight into the possible mechanism of Ti2-Tf transport in cells.

DNA-metallodrugs interactions signaled by electrochemical biosensors: an overview

The interaction of drugs with DNA is an important aspect in pharmacology. In recent years, many important technological advances have been made to develop new techniques to monitor biorecognition and biointeraction on solid devices. The interaction between DNA and drugs can cause chemical and conformational modifications and, thus, variation of the electrochemical properties of nucleobases. The propensity of a given compound to interact with DNA is measured as a function of the decrease of guanine oxidation signal on a DNA electrochemical biosensor. Covalent binding at N7 of guanine, electrostatic interactions, and intercalation are the events that this kind of biosensor can detect. In this context, the interaction between a panel of antitumoral Pt-, Ru-, and Ti-based metallodrugs with DNA immobilized on screen-printed electrodes has been studied. The DNA biosensors are used for semiquantitative evaluation of the analogous interaction occurring in the biological environment.

Antitumour bis(cyclopentadienyl) metal complexes: titanocene and molybdocene dichloride and derivatives

This Perspective will focus on recent developments in the field of antitumour metallocenes structurally related to titanocene dichloride. Despite extensive testing of titanocene dichloride which culminated in phase I and II clinical trials, further trials have been abandoned. While DNA has been implicated as the major target related to anticancer activity, identification of the active species and mechanism of action has been poorly understood and hence the design of second generation titanocene derivatives has not been possible. Recent mechanistic studies have provided a plausible mechanism for delivery of Ti to cancer cells via transferrin mediated endocytosis. This mechanism requires the presence of labile Cp-Ti bonds that hydrolyse on a time scale to deliver Ti to transferrin. A large range of titanocene derivatives in which the cyclopentadienyl rings have been substituted by both electron withdrawing and donating groups, including aromatic, alkyl and cyclic amines, have been prepared and tested for activity in the last 5 years. These results have shown that subtle structural effects can have a significant effect on biological activity and that biological activity is highly cell line dependent. However, the biological chemistry and cellular studies required to determine the mechanism of action of these new titanocenes have not been reported. In contrast, the bioorganometallic chemistry and cellular studies of molybdocene dichloride have implicated interaction with cellular thiols as the key reaction related to biological activity. Tailoring of the pseudohalide ligands by tuning the strength of the Mo-S bonds provides the opportunity to enhance cell uptake. Further research is required to establish the origin of antitumour activity.

Mechanism of Action of Anticancer Titanocene Derivatives: An Insight from Quantum Chemical Calculations

Titanocene derivatives exhibit high potential in the treatment of cisplatin-resistant tumor types. Density functional theory calculations were performed on the hydrated form of five drug candidates differing in the pendant arms attached to the aromatic rings. A qualitative correlation has been found between the experimentally measured anticancer activity of alkylammonium-functionalized titanocene derivatives and the computed free energy change of the proton-induced dissociation reaction of these compounds. The results indicate that differences in the cytotoxic activities could be related to the solvation properties of the protolysis products, whereas no correlation was found with gas-phase properties of these molecules. Contrary to the free energy change of the protolysis reaction, other molecular properties, such as the geometrical parameters or the binding energies of the cyclopentadienyl rings in solution, do not correlate with the in vitro cytotoxic activity of these drug candidates.

Coordination chemistry of the antitumor metallocene molybdocene dichloride with biological ligands

The relative affinity of molybdocene dichloride (Cp(2)MoCl(2)) for the thiol, amino, carboxylate, phosphate(O) and heterocyclic(N) donor ligands present in amino acids and nucleotides, has been studied in aqueous solutions at pH 2-7, using (1)H, (13)C and (31)P NMR spectroscopy. Molybdocene dichloride forms the highly water soluble, air-stable complexes Cp(2)Mo(Cys)(2) and Cp(2)Mo(GS)(2) with cysteine and glutathione respectively, via coordination of the deprotonated thiol groups. While coordination to the imidazole nitrogen in histidine was observed, no evidence for coordination of the amino or carboxylate groups in the amino acids cysteine, histidine, alanine or lysine to Cp(2)MoCl(2) was detected. Competition experiments with dAMP, ribose monophosphate and histidine showed preferential coordination to the cysteine thiol over the phosphate(O) and heterocyclic(N) groups. Cp(2)Mo(Cys)(2) is stable in the presence of excess dAMP or ribose monophosphate and Cys displaces coordinated histidine, dAMP or ribose monophosphate to give Cp(2)Mo(Cys)(2). These results provide further evidence against interaction with DNA as the key interaction that is related to the antitumor activity of molybdocene dichloride. The implications of these results for the biological activity of the antitumor metallocene and the likely species formed in vivo are discussed.

Transferrin/transferrin receptor-mediated drug delivery

Since transferrin was discovered more than half a century ago, a considerable effort has been made towards understanding tranferrin-mediated iron uptake. However, it was not until recently with the identification and characterization of several new genes related to iron homeostasis, such as the hemochromatosis protein HFE and the iron transporter DMT1, that our knowledge has been advanced dramatically. A major pathway for cellular iron uptake is through internalization of the complex of iron-bound transferrin and the transferrin receptor, which is negatively modulated by HFE, a protein related to hereditary hemochromatosis. Iron is released from transferrin as the result of the acidic pH in endosome and then is transported to the cytosol by DMT1. The iron is then utilized as a cofactor by heme and ribonucleotide reductase or stored in ferritin. Apart from iron, many other metal ions of therapeutic and diagnostic interests can also bind to transferrin at the iron sites and their transferrin complexes can be recognized by many cells. Therefore, transferrin has been thought as a "delivery system" for many beneficial and harmful metal ions into the cells. Transferrin has also be widely applied as a targeting ligand in the active targeting of anticancer agents, proteins, and genes to primary proliferating malignant cells that overexpress transferrin receptors. This is achieved by conjugation of transferrin with drugs, proteins, hybride systems with marcomolecules and as liposomal-coated systems. Conjugates of anticancer drugs with transferrin can significantly improve the selectivity and toxicity and overcome drug resistance, thereby leading to a better treatment. The coupling of DNA to transferrin via a polycation such as polylysine or via cationic liposomes can target and transfer of the extrogenous DNA particularly into proliferating cells through receptor-mediated endocytosis. These kinds of non-viral vectors are potential alternatives to viral vectors for gene therapy, if the transfection efficiency can be improved. Moreover, transferrin receptors have shown potentials in delivery of therapeutic drugs or genes into the brain across blood-brain barrier.

Ti(IV) uptake and release by human serum transferrin and recognition of Ti(IV)-transferrin by cancer cells: understanding the mechanism of action of the anticancer drug titanocene dichloride

The organometallic anticancer agent titanocene dichloride, Cp(2)TiCl(2), is now in phase II clinical trials as an anticancer drug, but its mechanism of action is poorly understood. We show here that the interactions of Cp(2)TiCl(2) with human serum transferrin (hTF) and that of Ti(2)-hTF with adenosine triphosphate (ATP) have characteristics that could allow transferrin to act as a mediator for titanium delivery to tumor cells. Such reactions may therefore be important to the anticancer activity of this new class of drugs. Cp(2)TiCl(2) reacts rapidly with human apo-transferrin under physiological conditions (100 mM NaCl, 25 mM bicarbonate, and 4 mM phosphate, pH 7.4) with carbonate as a synergistic anion. The Cp ligands are released from the drug. Two-dimensional [(1)H, (13)C] NMR studies of epsilon-[(13)C]Met-hTF show that Ti(IV) loads the C-lobe first followed by the N-lobe and binds in the specific Fe(III) sites. The protein conformational changes induced by Ti(IV) appear to be similar to those induced by Fe(III). Carbonate can act as a synergistic anion in Ti(2)-hTF but does not appear to be essential. A specific Ti(IV)-hTF adduct is formed even in the absence of bicarbonate. When the pH of Ti(2)-hTF solutions is lowered, no Ti(IV) is released at the endosomal pH of ca. 5.0-5.5, but one Ti(IV) dissociates between pH 4.5-2.0. In contrast, in the presence of 1 mM ATP, all Ti(IV) is readily released from both lobes when the pH is lowered from 7.0 to 4.5. Moreover, Fe(III) displaces Ti(IV) rapidly from the C-lobe of Ti(2)-hTF (<5 min) but only slowly (days) from the N-lobe. Thus, the species Fe(C)Ti(N)-hTF might also provide a route for Ti(IV) entry into tumor cells via the transferrin receptor. Ti(2)-hTF effectively blocked cell uptake of radiolabeled (59)Fe-hTF into BeWo cells, a human placental choriocarcinoma cell line in culture. These results imply that titanium transferrin might be recognized by the transferrin receptor and be taken up into cancer cells.

Complexes of gallium(III) and other metal ions and their potential in the treatment of neoplasia

The metal complexes of a variety of ligands show diverse pharmacological properties. The potential of these compounds as antineoplastic agents is underlined by the success of the clinically used platinum complex cisplatin (cis-[(NH(3))(2)PtCl(2)]). In the current review, specific examples of gallium, copper, ruthenium and titanium complexes are discussed with special relevance to their use in the treatment of cancer. Some of these complexes have demonstrated marked activity in a number of animal models and for some compounds, clinical trials are anticipated or have already begun. Collectively, the results in the literature indicate that the study of metal complexes as antineoplastic agents deserves continued intensive investigation.

Stereoselective formation of seven-coordinate titanium(IV) monomer and dimer complexes of ethylenebis(o-hydroxyphenyl)glycine

Reactions between the antitumor agent titanocene dichloride (Cp2TiCl2) and the hexadentate ligand N,N'-ethylenebis-(o-hydroxyphenylglycine) (H4ehpg) have been investigated in aqueous solution and the solid state. The racemic ligands give crystals of the monomer [Ti(ehpg)(H2O)] x (11/3)H2O (1), while the meso ligand gives the oxo-bridged dimer [[Ti(Hehpg)(H2O)]2O] x 13H2O (2). Complex 1 crystallizes in the monoclinic space group C2/c with a = 24.149(4) A, b = 14.143(3) A, c = 19.487(3) A, beta = 105.371(13) degrees, V = 6417.7(19) A3, Z = 12, and R(F) = 0.0499 for 4,428 independent reflections having I > 2sigma(I), and contains seven-coordinate pentagonal-bipyramidal TiIV with two axial phenolate ligands (Ti-O, 1.869(2) A). The pentagonal plane contains the two N-atoms at 2.210(2) A, two carboxylate O-atoms at 2.061(2) A, and a water molecule (Ti-OH2, 2.091(3) A). Complex 2 crystallizes as an oxygen-bridged dimer in the triclinic space group P-1 with a = 12.521(6) A, b = 14.085(7) A, c = 16.635(8) A, alpha = 80.93(2) degrees beta = 69.23(2) degrees, gamma = 64.33(2) degrees , V = 2472(2) A3, Z = 4, and R(F) = 0.0580 for 5956 independent reflections having I > 2sigma(I). Each seven-coordinate, pentagonal-bipyramidal TiIV has a bridging oxide and a phenolate as axial ligands. The pentagonal plane donors are H2O, two carboxylate O-atoms, and two NH groups, which form H-bonds to O-atoms both in the same half-molecule (O...N, 2.93-3.13 A) and in the other half-molecule (O...N, 2.73-2.75 A); the second phenoxyl group of each Hehpg ligand is protonated and not coordinated to TiIV, but H-bonds to a nearby amine proton (O...N, 2.73-2.75 A) from the same ligand and to a nearby H2O (O...O, 2.68 A). In contrast to all previously reported crystalline metal-EHPG complexes containing racemic ligands, in which the N(S,S)C(R,R) or N(R,R)C(S,S) form is present, complex 1 unexpectedly contains the N(S,S)C(S,S) and N(R,R)C(R,R) forms. This is attributed to the presence of ring strain in seven-coordinate TiIV complexes. Moreover, the rac ligands selectively form crystals of monomeric 1, while the meso ligand selectively forms crystals of the dimer 2 (N(R,R)C(R,S) or N(S,S)C(S,R)). Complexes 1 and 2 exhibit phenolate-to-TiIV charge-transfer bands near 387 nm, and 2D NMR studies indicate that the structures of 1 and 2 in solution are similar to those in the solid state. Complex 1 is stable over the pH range 1.0-7.0, while 2 is stable only between pH 2.5 and pH 5.5. Cp2TiCl2 reacts with EHPG at pH* 7.0 to give complex 1 with a t 1/2 of ca. 50 min (298 K), but complex 2 was not formed at this pH* value. At pH* 3.7, the reaction is very slow: 1 forms with a half-life of ca. 2.5 d, and 2 after ca. 1 week at ambient temperature. The relevance of these data to the possible role of serum transferrin as a mediator for the delivery of TiIV to tumor cells is discussed.

Molecular genotoxicity profiles of apoptosis-inducing vanadocene complexes

Metallocene complexes containing vanadium induce apoptosis in human cancer cells by an as yet unknown mechanism and may therefore be useful as a new class of cytotoxic anticancer drugs. Ultrastructural studies showing the formation of metallocene-DNA complexes prompted the hypothesis that their mechanism of action may resemble the DNA damage induced by cisplatin. Molecular genotoxicity testing provides insights into the mechanisms of action of new chemotherapeutic agents. Therefore, we determined the effects of three cytotoxic vanadocene complexes, vanadocene dichloride, vanadocene dithiocyanate, and vanadocene dioxycyanate, on genomic stability using the yeast DEL recombination assay and transcriptional activation of genotoxic stress-specific promoters in human HepG2 cells using the CAT-Tox(L) assay. Cisplatin caused an 11-fold increase of recombination frequency in yeast and induced transcriptional activation of the DNA damage-associated promoters such as the minimum promoter containing p53 response elements and the GADD45 promoter in addition to activating the promoters for c-fos, heat shock protein 70, metallothionine IIa, and the minimum promoter containing nuclear factor kappa(kappa)B response elements. In contrast to cisplatin, vanadocene complexes did not increase the DEL recombination frequency in yeast nor did they activate any of the DNA damage-associated promoters in HepG2 cells. Vanadocene complexes triggered activation of the c-fos promoter without affecting the minimum promoter containing p53 response elements or the GADD45 promoter. These results indicate that the apoptotic signal of vanadocene complexes is not triggered by primary DNA damage and it does not require p53 induction, thereby disproving the hypothesis that it mechanistically resembles the cytotoxic action of cisplatin.

Antitumor activity of titanocene amino acid complexes

Seven ionic titanocene alpha-amino acid (aa) complexes [(C5H5)2Ti(aa)2]2+[X]2- with aa = glycine, L-alanine, 2-methylalanine, D-L-phenylalanine, D,L-4-fluorophenylalanine and X = Cl or AsF6, were investigated for antitumor activity against fluid Ehrlich ascites tumor growing in CF1 mice. These complexes are the first stable model compounds of titanocene units with protein components, synthesized from a water-like, methanolic medium. All titanocene amino acid complexes induced antitumor activity which was manifested by maximum cure rates ranging from 30 to 70% and increases in life span from 78 to 276% in comparison with untreated control animals. The complexes containing chloride as anion X were more effective than the hexafluoroarsenate derivatives, which surprisingly showed a low substance toxicity. In all cases, the antitumor activity of the ionic titanocene amino acid complexes tested was less pronounced than that of the neutral parent compound [(C5H5)2TiCl2].

The use of parallel EEL spectral imaging and elemental mapping in the rapid assessment of anti-cancer drug localization

Both electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS) have great potential for use in several areas of cancer research. In biologically targeted radiotherapy, cytotoxic drug therapy and boron neutron capture therapy the effectiveness of many drugs is often critically dependent upon the intracellular localization of the agent employed. We describe the use of parallel EEL spectral imaging to assess the penetration and location of the iodine-containing drug meta-iodobenzyl guanidine, of potential value in targeted radiotherapy, and for the rapid detection of boron within borate-adsorbed polystyrene beads, of potential value in boron neutron capture therapy. We also describe elemental mapping of boron following low-temperature embedding. These results show how the techniques could be applied to many forms of cancer research by discussing the validity and limitations of the techniques experimentally. We also provide an outline of other areas in this field which could benefit from the future application of ESI and EELS.