Mechanistic Investigation into DNA Modification by a RuII ,RhIII Bimetallic Complex.

Despite significant progress in the treatment of cancer, there remains an urgent need for more effective therapies that also have less impact on patient wellbeing. Photodynamic therapy employs targeted light activation of a photosensitizer in selected tissues, thereby reducing off-target toxicity. Our group previously reported a RuII ,RhIII bimetallic architecture that displays multifunctional covalent photomodification of DNA in the therapeutic window in an oxygen-independent manner, features that are essential for treating deep and hypoxic tumors. Herein, we explore the mechanism by which a new analogue, [(phen)2 Ru(dpp)Rh(phen)Cl2 ]3+ , or RuII -RhIII , interacts with DNA. We established that RuII -RhIII exhibits "light switch" behavior in the presence of DNA, undergoing strong electrostatic interactions that might involve groove binding. Furthermore, these noncovalent interactions play a major role in the covalent photobinding and photocleavage of DNA, which occur according to an oxygen-independent mechanism. Polymerase chain reaction (PCR) revealed that covalent modification of DNA by RuII -RhIII , especially photobinding, is critical to inhibiting amplification, thus suggesting that the complex could exert its toxic activity by interfering with DNA replication in cells. This new structural motif, with phenanthroline at all three terminal ligand positions, has a number of properties that are promising for the continued refinement of photodynamic-therapy strategies.

Speciation of precious metal anti-cancer complexes by NMR spectroscopy.

Understanding the mechanism of action of anti-cancer agents is of paramount importance for drug development. NMR spectroscopy can provide insights into the kinetics and thermodynamics of the binding of metallodrugs to biomolecules. NMR is most sensitive for highly abundant I=1/2 nuclei with large magnetic moments. Polarization transfer can enhance NMR signals of insensitive nuclei at physiologically-relevant concentrations. This paper reviews NMR methods for speciation of precious metal anti-cancer complexes, including platinum-group and gold-based anti-cancer agents. Examples of NMR studies involving interactions with DNA and proteins in particular are highlighted.

Free Rhodium (II) citrate and rhodium (II) citrate magnetic carriers as potential strategies for breast cancer therapy.

BACKGROUND: Rhodium (II) citrate (Rh(2)(H(2)cit)(4)) has significant antitumor, cytotoxic, and cytostatic activity on Ehrlich ascite tumor. Although toxic to normal cells, its lower toxicity when compared to carboxylate analogues of rhodium (II) indicates (Rh(2)(H(2)cit)(4)) as a promising agent for chemotherapy. Nevertheless, few studies have been performed to explore this potential. Superparamagnetic particles of iron oxide (SPIOs) represent an attractive platform as carriers in drug delivery systems (DDS) because they can present greater specificity to tumor cells than normal cells. Thus, the association between Rh(2)(H(2)cit)(4) and SPIOs can represent a strategy to enhance the former's therapeutic action. In this work, we report the cytotoxicity of free rhodium (II) citrate (Rh(2)(H(2)cit)(4)) and rhodium (II) citrate-loaded maghemite nanoparticles or magnetoliposomes, used as drug delivery systems, on both normal and carcinoma breast cell cultures. RESULTS: Treatment with free Rh(2)(H(2)cit)(4) induced cytotoxicity that was dependent on dose, time, and cell line. The IC(50) values showed that this effect was more intense on breast normal cells (MCF-10A) than on breast carcinoma cells (MCF-7 and 4T1). However, the treatment with 50 µM Rh(2)(H(2)cit)(4)-loaded maghemite nanoparticles (Mag(h)-Rh(2)(H(2)cit)(4)) and Rh(2)(H(2)cit)(4)-loaded magnetoliposomes (Lip-Magh-Rh(2)(H(2)cit)(4)) induced a higher cytotoxicity on MCF-7 and 4T1 than on MCF-10A (p < 0.05). These treatments enhanced cytotoxicity up to 4.6 times. These cytotoxic effects, induced by free Rh(2)(H(2)cit)(4), were evidenced by morphological alterations such as nuclear fragmentation, membrane blebbing and phosphatidylserine exposure, reduction of actin filaments, mitochondrial condensation and an increase in number of vacuoles, suggesting that Rh(2)(H(2)cit)(4) induces cell death by apoptosis. CONCLUSIONS: The treatment with rhodium (II) citrate-loaded maghemite nanoparticles and magnetoliposomes induced more specific cytotoxicity on breast carcinoma cells than on breast normal cells, which is the opposite of the results observed with free Rh(2)(H(2)cit)(4) treatment. Thus, magnetic nanoparticles represent an attractive platform as carriers in Rh(2)(H(2)cit)(4) delivery systems, since they can act preferentially in tumor cells. Therefore, these nanopaticulate systems may be explored as a potential tool for chemotherapy drug development.

Metal-based antitumor compounds: beyond cisplatin.

Despite improvements in the 5-year survival rate to over 80% in cancers, such as Hodgkin lymphoma and testicular cancer, more aggressive tumors including pancreatic and brain cancer still have extremely low survival rates. The establishment of chemoresistance, responsible for the reduction in treatment efficiency and cancer relapse, is one possible explanation for this setback. Metal-based compounds, a class of anticancer drugs, are largely used in the treatment of cancer. Herein, we will review the use of metal-based small molecules in chemotherapy, focusing on recent studies, and we will discuss how new nonplatinum-based agents are prompting scientists to increase drug specificity to overcome chemoresistance in cancer cells.

Absorbed dose distributions from ophthalmic 106 Ru/106 Rh plaques measured in water with radiochromic film.

PURPOSE: Brachytherapy with 106 Ru/106 Rh plaques offers good outcomes for small-to-medium choroidal melanomas and retinoblastomas. The dose measurement of the plaques is challenging, due to the small range of the emitted beta particles and steep dose gradients involved. The scarce publications on film dosimetry of 106 Ru/106 Rh plaques used solid phantoms. This work aims to develop a practical method for measuring the absorbed dose distribution in water produced by 106 Ru/106 Rh plaques using EBT3 radiochromic film. METHODS: Experimental setups were developed to determine the dose distribution at a plane perpendicular to the symmetry axis of the plaque and at a plane containing the symmetry axis. One CCA and two CCX plaques were studied. The dose maps were obtained with the FilmQA Pro 2015 software, using the triple-channel dosimetry method. The measured dose distributions were compared to published Monte Carlo simulation and experimental data. RESULTS: A good agreement was found between measurements and simulations, improving upon published data. Measured reference dose rates agreed within the experimental uncertainty with data obtained by the manufacturer using a scintillation detector, with typical differences below 5%. The attained experimental uncertainty was 4.1% (k = 1) for the perpendicular setup, and 7.9% (k = 1) for the parallel setup. These values are similar or smaller than those obtained by the manufacturer and other authors, without the need of solid phantoms that are not available to most users. CONCLUSIONS: The proposed method may be useful to the users to perform quality assurance preclinical tests of 106 Ru/106 Rh plaques.

Preparation of Rhodium(III) complexes with 2(1H)-quinolinone derivatives and evaluation of their in vitro and in vivo antitumor activity.

A series of 2(1H)-quinolinone derivatives and their rhodium (III) complexes were designed and synthesized. All the rhodium (III) complexes exhibited higher in vitro cytotoxicity for Hep G2, HeLa 229, MGC80-3, and NCI-H460 human tumor cell lines than their ligands and cisplatin, and among them complex 9 was found to be selectively cytotoxic to tumor cells. Further investigation revealed that complex 9 caused cell cycle arrest at the G2/M phase and induced apoptosis, and inhibited the proliferation of Hep G2 cells by impeding the phosphorylation of epidermal growth factor receptor (EGFR) and its downstream enzymes. Complex 9 also up-regulated the proapoptotic proteins Bak, Bax, and Bim, which altogether activated caspase-3/9 to initiate cell apoptosis. Notably, complex 9 effectively inhibited tumor growth in the NCI-H460 xenograft mouse model with less adverse effect than cisplatin.

The interaction of rhodium(II) carboxylates with enzymes.

The effect of rhodium(II) acetate, propionate, and methoxyacetate on the activity of 17 enzymes was evaluated. The enzymes were preincubated with the rhodium(II) complexes in order to detect irreversible inhibition. All enzymes that have essential sulfhydryl groups in or near their active site were found to be irreversibly inhibited. Those enzymes without essential sulfhydryl groups were not affected. In each case, the rate of inactivation closely paralleled the observed toxicity and antitumor activity of rhodium(II) carboxylates; that is, rhodium(II) propionate greater than rhodium(II) acetate greater than rhodium(II) methoxyacetate. In addition, those enzymes that have been demonstrated to be most sensitive to established sulfhydryl inhibitors, such as glyceraldehyde-3-phosphate dehydrogenase, were also most sensitive to rhodium(II) carboxylate inactivation. Proton nuclear magnetic resonance measurements made during the titration of rhodium(II) acetate with cysteine showed that breakdown of the carboxylate cage occurred as a result of reaction with this sulfhydryl-containing amino acid.

Rhodium complexes as therapeutic agents.

The landscape of inorganic medicinal chemistry has been dominated by the investigation of platinum, and to a lesser extent ruthenium, complexes over the past few decades. Recently, complexes based on other metal centers such as rhodium have attracted attention due to their tunable chemical and biological properties as well as distinct mechanisms of action. This perspective highlights recent examples of rhodium complexes that show diverse biological activities against various targets, including enzymes and protein-protein interactions.

A simple calibration method for 106Ru-106Rh eye applicators.

Ru-Rh eye applicators are used for the radiotherapy of eye malignancies such as melanomas. We present a method of dosimetry of these beta particle emitting applicators. Method is based on a Plexiglas phantom (constructed for this purpose) containing spherical shells and very small, 1x1x1mm3 thermoluminescent dosimeters (TLD) as dosimeters. We determined 3-D depth doses and interpolated depth dose functions. Surface dose rate inhomogeneities and the consequences were considered and discussed. A possible influence of photon component of the emission on the results was analysed. The method has overall combined uncertainty + or -6% which is comparable, and slightly better, than other recent dosimetric methods.

Rhodium and its compounds as potential agents in cancer treatment.

The antitumor activity of the inorganic complex cis-diammine-dichloroplatinum(II) (cisplatin) led to the development of other types of non-organic cytostatic drugs. Numerous platinum other platinum and non-platinum metal compounds were shown to be effective against animal model tumors as well as tumors in man. However, the introduction of novel transition metal agents in clinical treatment is exceptionally slow. So far, Ru(II) and Ru(III) complexes have shown very promising properties while the Ru(III) compound, [ImH][trans-Cl4(Me2SO)(Im)Ru(III)] (Im=imidazole, NAMI-A), is the first ruthenium compound that successfully entered phase I clinical trials. Rhodium belongs to the same group as platinum and ruthenium. However, rhodium compounds, analogues to the corresponding platinum and ruthenium compounds that possess significant antitumor properties, were found to be less effective as anticancer agents mainly due to their toxic effects. Dimeric mu-Acetato dimers of Rh(II) as well as monomeric square planar Rh(I) and octahedral Rh(III) complexes have shown interesting antitumor properties.

Hydrophobicity of several rhodium(II) carboxylates correlated with their biologic activity.

Rhodium(II) carboxylates differ greatly in antitumor activity and toxicity depending on the properties of the carboxylate group (methoxyacetate, propionate, butyrate, etc.) involved. The solubility characteristics of rhodium(II) carboxylates correlate well with both the antitumor activity and toxicity that these compounds display. The amount of rhodium which is adsorbed by tumor cells in vitro also correlates with the partition coefficient of the rhodium(II) compounds studied. Survival and toxicity studies show rhodium(II) pentanoate to possess the highest therapeutic index against the Ehrlich ascites tumor strain and also show that lengthening the carboxylate R chain beyond the pentanoate reduces the drugs' therapeutic efficacy.

beta-Irradiation of choroidal melanoma with 106Ru/106Rh applicators. 16 Years' experience.

From 1964 to 1980, 205 patients with choroidal melanoma were treated with 106Ru/106Rh beta-ray applicators (8,000 to 10,000 rad at the summit of the tumor within 14 days). In 132 (64.4%) cases, this treatment was successful. Thirty-six (17.6%) had to be enucleated after irradiation and 37 died, 21 of them of metastases. Of the 132 successfully treated patients, 60 (45.5%) had flat scars and 34 (25.8%) retained a visual acuity of 0.5 to 1.5. Radiogenic late complications with damage to the retinal capillary system were the main causes of visual deterioration, especially in eyes with tumors close to the posterior pole. The survival rate of 85.1% after five years is substantially higher than that for patients who were primarily treated with enucleation.

The design and the dosimetry of bi-nuclide radioactive ophthalmic applicators.

A novel type of applicator for the treatment of intra-ocular tumors has been developed, based on the two radionuclides 106Ru/106Rh and 125I. The dose distribution of this ophthalmic plaque combines advantageous features of both radionuclides and can be optimally adapted to a tumor thickness in the range 6.5-9 mm, a size which is beyond the dosimetric limitations of the 106Ru/106Rh plaque therapy. Compared with 125I plaques a bi-nuclide plaque allows to maintain the tumor dosage while the dose in the irradiated volume outside of the target volume is significantly reduced. Consequently, radiosensitive structures within the eye can be spared more effectively. Dedicated methods have been developed for the dosimetry of this plaque. These methods are based on our own extensive dosimetric investigations with plastic scintillators. The precondition was the availability, developed in recent years, of a more accurate determination of the absolute dose rate to water of beta- and low energy emitters.

Dosimetry of beta-ray ophthalmic applicators: comparison of different measurement methods.

An international intercomparison of the dosimetry of three beta particle emitting ophthalmic applicators was performed, which involved measurements with radiochromic film, thermoluminescence dosimeters (TLDs), alanine pellets, plastic scintillators, extrapolation ionization chambers, a small fixed-volume ionization chambers, a diode detector and a diamond detector. The sources studied were planar applicators of 90Sr-90Y and 106Ru-106Rh, and a concave applicator of 106Ru-106Rh. Comparisons were made of absolute dosimetry determined at 1 mm from the source surface in water or water-equivalent plastic, and relative dosimetry along and perpendicular to the source axes. The results of the intercomparison indicate that the various methods yield consistent absolute dosimetry results at the level of 10%-14% (one standard deviation) depending on the source. For relative dosimetry along the source axis at depths of 5 mm or less, the agreement was 3%-9% (one standard deviation) depending on the source and the depth. Crucial to the proper interpretation of the measurement results is an accurate knowledge of the detector geometry, i.e., sensitive volume and amount of insensitive covering material. From the results of these measurements, functions which describe the relative dose rate along and perpendicular to the source axes are suggested.

Calculation of beta-ray dose distributions from ophthalmic applicators and comparison with measurements in a model eye.

Dose distributions throughout the eye, from three types of beta-ray ophthalmic applicators, were calculated using the EGS4, ACCEPT 3.0, and other Monte Carlo codes. The applicators were those for which doses were measured in a recent international intercomparison [Med. Phys. 28, 1373 (2001)], planar applicators of 106Ru-106Rh and 90Sr-90Y and a concave 106Ru-106Rh applicator. The main purpose was to compare the results of the various codes with average experimental values. For the planar applicators, calculated and measured doses on the source axis agreed within the experimental errors (<10%) to a depth of 7 mm for 106Ru-106Rh and 5 mm for 90Sr-90Y. At greater distances the measured values are larger than those calculated. For the concave 106Ru-106Rh applicator, there was poor agreement among available calculations and only those calculated by ACCEPT 3.0 agreed with measured values. In the past, attempts have been made to derive such dose distributions simply, by integrating the appropriate point-source dose function over the source. Here, we investigated the accuracy of this procedure for encapsulated sources, by comparing such results with values calculated by Monte Carlo. An attempt was made to allow for the effects of the silver source window but no corrections were made for scattering from the source backing. In these circumstances, at 6 mm depth, the difference in the results of the two calculations was 14%-18% for a planar 106Ru-l06Rh applicator and up to 30% for the concave applicator. It becomes worse at greater depths. These errors are probably caused mainly by differences between the spectrum of beta particles transmitted by the silver window and those transmitted by a thickness of water having the same attenuation properties.

Model of metastatic growth valuable for radionuclide therapy.

The aim was to make a Monte Carlo simulation approach to estimate the distribution of tumor sizes and to study the curative potential of three candidate radionuclides for radionuclide therapy: the high-energy electron emitter 90Y, the medium-energy electron emitter 177Lu and the low-energy electron emitter 103mRh. A patient with hepatocellular carcinoma with recently published serial CT data on tumor growth in the liver was used. From these data the growth of the primary tumor, and the metastatis formation rate, were estimated. Assuming the same tumor growth of the primary and all metastases and the same metastatis formation rate from both primary and metastases the metastatic size distribution was simulated for various time points. Tumor cure of the metastatic size distribution was simulated for uniform activity distribution of three radionuclides; the high-energy electron emitter 90Y, the mean-energy electron emitter 177Lu and the low-energy electron emitter 103mRh. The simulation of a tumor cure was performed for various time points and tumor-to-normal tissue activity concentrations, TNC. It was demonstrated that it is important to start therapy as early as possible after diagnosis. It was of crucial importance to use an optimal radionuclide for therapy. These simulations demonstrated that 90Y was not suitable for systemic radionuclide therapy, due to the low absorbed fraction of the emitted electrons in small tumors (< 1 mg). If TNC was low 103mRh was slightly better than 177Lu. For high TNC values low-energy electron emitters, e.g., 103mRh was the best choice for tumor cure. However, the short half-life of 103mRh (56 min) might not be optimal for therapy. Therefore, other low-energy electron emitters, or alpha emitters, should be considered for systemic targeted therapy.

Metal complexes of bleomycin: evaluation of [Rh-105]-bleomycin for use in targeted radiotherapy.

Bleomycin has been used as a carrier for several radioisotopes; however, its potential for clinical use has been limited either by the in vivo stability of the complexes or the half-life of the isotope used. The chemical, biological, and radiological properties of 105Rhodium appear to make it an ideal choice for targeted radiotherapy. The synthesis and purification of a hereto unreported 105Rhodium-bleomycin (105Rh-BLM) complex is described. The stability of this complex in plasma is sufficient to allow targeted delivery of the radioisotope. 57Cobalt-bleomycin was studied under identical conditions for comparative purposes. The suitability of 105Rh-BLM for targeted therapy, which appears to be limited by the renal clearance of this agent, is discussed.

Treatment of bilateral choroidal malignant melanoma.

A history is presented of a 40-year-old male patient suffering from bilateral choroidal melanoma. Both eyes were treated with 106Ru/106Rh beta-irradiation. 2 years later one eye was enucleated because of radiogenic central vein thrombosis with secondary glaucoma. Histologically the tumor cells showed radiogenic damages and there were no signs of a new tumor growth. The other eye, however, is still functioning 6 years later with a visual acuity of 1.0.

Antitumor effect of some rhodium(I) derivatives on MCa mammary carcinoma.

The antitumor action of two square planar Rhodium complexes was tested on MCa mammary carcinoma and was seen to depend upon the compound used. The complex cyclooctadiene(2-pyridinalmethylimine)-Rh(I)chloride [Rh(COD)PMI]+ Cl- confirmed the antineoplastic action already shown in the Lewis lung carcinoma model. The examination of the activity of [Rh(COD)PMI]+ Cl- on the lung metastatic tumor indicates that its antineoplastic properties do not seem simply related to a cytotoxic action. It appears more likely that modifications occurring at the primary tumor level, probably different from lethal effects directed to tumor cells, are responsible for the reduction of spontaneous lung metastasis formation observed in the treated animals. The trophic effects observed on the spleen of the treated animals seem to suggest that these compounds are endowed with properties typical of biological response modifiers.

Antitumor effects of rhodium(I), iridium(I) and ruthenium(II) complexes in comparison with cis-dichlorodiammino platinum(II) in mice bearing Lewis lung carcinoma.

The effects of square planar rhodium, [RhacacCOD]o and iridium, [IracacCOD]o complexes and of octahedral ruthenium, [cis-RuCl2 (DMSO)4]o complex have been examined in comparison with cis-dichlorodiammino platinum(II) (cis-PDD). The toxicity in BDF1 mice varies widely and decreasing LD50-values, ranging from 0.94 mg/kg to 1000 mg/kg, have been obtained for cis-PDD, [RhacacCOD]o, [IracacCOD]o and [cis-RuCl2(DMSO)4]o, respectively. All the tested complexes similarly inhibit the growth of subcutaneous Lewis lung carcinoma and the development of spontaneous as well as of artificial metastases, with the exception of [IracacCOD]o which is inactive on metastases. The antitumor activity of [RhacacCOD]o and [cis-RuCl2(DMSO)4]o appears interesting, since it is of the same magnitude as that of cis-PDD, considering also that they were found to be only marginally nephrotoxic.