Metabolic studies of an orally active platinum anticancer drug by liquid chromatography-electrospray ionization mass spectrometry

Emerging platinum(IV) prodrug nanotherapeutics: A new epoch for platinum-based cancer therapy

Owing to the unique DNA damaging cytotoxicity, platinum (Pt)-based chemotherapy has long been the first-line choice for clinical oncology. Unfortunately, Pt drugs are restricted by the severe dose-dependent toxicity and drug resistance. Correspondingly, Pt(IV) prodrugs are developed with the aim to improve the antitumor performance of Pt drugs. However, as "free" molecules, Pt(IV) prodrugs are still subject to unsatisfactory in vivo destiny and antitumor efficacy. Recently, Pt(IV) prodrug nanotherapeutics, inheriting both the merits of Pt(IV) prodrugs and nanotherapeutics, have emerged and demonstrated the promise to address the underexploited dilemma of Pt-based cancer therapy. Herein, we summarize the latest fronts of emerging Pt(IV) prodrug nanotherapeutics. First, the basic outlines of Pt(IV) prodrug nanotherapeutics are overviewed. Afterwards, how versatile Pt(IV) prodrug nanotherapeutics overcome the multiple biological barriers of antitumor drug delivery is introduced in detail. Moreover, advanced combination therapies based on multimodal Pt(IV) prodrug nanotherapeutics are discussed with special emphasis on the synergistic mechanisms. Finally, prospects and challenges of Pt(IV) prodrug nanotherapeutics for future clinical translation are spotlighted.

Oxidation of the Platinum(II) Anticancer Agent [Pt{(p-BrC6F4)NCH2CH2NEt2}Cl(py)] to Platinum(IV) Complexes by Hydrogen Peroxide

PtIV coordination complexes are of interest as prodrugs of PtII anticancer agents, as they can avoid deactivation pathways owing to their inert nature. Here, we report the oxidation of the antitumor agent [PtII(p-BrC6F4)NCH2CH2NEt2}Cl(py)], 1 (py = pyridine) to dihydroxidoplatinum(IV) solvate complexes [PtIV{(p-BrC6F4)NCH2CH2NEt2}Cl(OH)2(py)].H2O, 2·H2O with hydrogen peroxide (H2O2) at room temperature. To optimize the yield, 1 was oxidized in the presence of added lithium chloride with H2O2 in a 1:2 ratio of Pt: H2O2, in CH2Cl2 producing complex 2·H2O in higher yields in both gold and red forms. Despite the color difference, red and yellow 2·H2O have the same structure as determined by single-crystal and X-ray powder diffraction, namely, an octahedral ligand array with a chelating organoamide, pyridine and chloride ligands in the equatorial plane, and axial hydroxido ligands. When tetrabutylammonium chloride was used as a chloride source, in CH2Cl2, another solvate, [PtIV{(p-BrC6F4)NCH2CH2NEt2}Cl(OH)2(py)].0.5CH2Cl2,3·0.5CH2Cl2, was obtained. These PtIV compounds show reductive dehydration into PtII [Pt{(p-BrC6F4)NCH=CHNEt2}Cl(py)], 1H over time in the solid state, as determined by X-ray powder diffraction, and in solution, as determined by 1H and 19F NMR spectroscopy and mass spectrometry. 1H contains an oxidized coordinating ligand and was previously obtained by oxidation of 1 under more vigorous conditions. Experimental data suggest that oxidation of the ligand is favored in the presence of excess H2O2 and elevated temperatures. In contrast, a smaller amount (1Pt:2H2O2) of H2O2 at room temperature favors the oxidation of the metal and yields platinum(IV) complexes.

Pt(IV) antitumor prodrugs: dogmas, paradigms, and realities

Platinum(II)-based drugs are widely used for the treatment of solid tumors, especially in combination protocols. Severe side effects and occurrence of resistance are the major limitations to their clinical use. To overcome these drawbacks, a plethora of Pt(IV) derivatives, acting as anticancer prodrugs, have been designed, synthesized and preclinically (often only in vitro) tested. Here, we summarize the recent progress in the development and understanding of the chemical properties and biochemical features of these Pt(IV) prodrugs, especially those containing bioactive molecules as axial ligands, acting as multi-functional agents. Even though no such prodrugs have been yet approved for clinical use, many show encouraging pharmacological profiles. Thus, a better understanding of their features is a promising approach towards improving the available Pt-based anticancer agents.

The reduction of cis-platinum(iv) complexes by ascorbate and in whole human blood models using 1H NMR and XANES spectroscopy

The efficacy of platinum(iv) prodrugs depends on their relative resistance to reduction in the extra- and intra-cellular environments. In the study reported here we investigated the influence of the nature of the axial and equatorial ligands on the pathway of reduction of the platinum(iv) complexes by the endogenous reductant, ascorbate, and their relative resistance to reduction in human blood serum and in a whole human blood model. The pathway of reduction of platinum(iv) complexes in the presence of excess ascorbate was found to be dependent on the nature of their axial and equatorial ligands in that complexes with chloride in the equatorial sites lost either both axial ligands or combinations of axial and equatorial ligands while those with oxalate occupying the equatorial sites lost both axial ligands only. Using XANES spectroscopy, complexes with axial hydroxide ligands were found to be highly resistant to reduction in blood serum and were only slowly and incompletely reduced in whole blood. The dihydroxide complex with an oxalate ligand occupying the equatorial leaving group sites was more resistant to reduction, both in serum and in whole blood, than the complex with chloride ligands in these sites. cis, trans-[PtCl2(OAc)2(en)] and trans-[Pt(OAc)2(ox)(en)] were observed to be reduced rapidly and almost completely in whole blood but the latter was substantially resistant to reduction in human blood serum, and consequently demonstrates many of the features of an optimal platinum(iv) anticancer agent.

Exploring the Hydrolytic Behavior of the Platinum(IV) Complexes with Axial Acetato Ligands

Platinum(IV) complexes are generally thought to be kinetically inert, and are expected to be stable enough to resist premature aquation before entering the cancer cells. Nevertheless, in this work, complex 2 with axial acetato ligands can hydrolyze relatively quickly under biologically relevant conditions with a half-life of 91.7 min, resulting in the loss of the equatorial chlorido ligand. Further study indicated that the fast hydrolysis of complex 2 may be attributed to the strong σ-donor ability of N-isopropyl-1R,2R-diaminocyclohexane, and an increasing σ-donor ability of the amine group can promote the hydrolysis rate of the corresponding platinum(IV) complex. The experiment results were proven by the corresponding DFT calculation. Our study can help to re-evaluate the aqueous properties of the platinum(IV) complexes with axial acetate, which may be less inert to hydrolysis than expected under biologically relevant conditions.

A new entry to asymmetric platinum(IV) complexes via oxidative chlorination

Pt(IV) complexes are usually prepared by oxidation of the corresponding Pt(II) counterparts, typically using hydrogen peroxide or chlorine. A different way to synthesize asymmetrical Pt(IV) compounds is the oxidative chlorination of Pt(II) counterparts with N-chlorosuccinimide. The reaction between cisplatin cis-[PtCl2(NH3)2], carboplatin, cis-[PtCl2(dach)] and cis-[Pt(cbdc)(dach)] (cbdc = cyclobutane-1,1'-dicarboxylato; dach = cyclohexane-1R,2R-diamine) with N-chlorosuccinimide in ethane-1,2-diol was optimized to produce the asymmetric Pt(IV) octahedral complexes [PtA2Cl(glyc)X2] (A2 = 2 NH3 or dach; glyc = 2-hydroxyethanolato; X2 = 2 Cl or cbdc) in high yield and purity. The X-ray crystal structure of the [Pt(cbdc)Cl(dach)(glyc)] complex is also reported. Moreover, the oxidation method proved to be versatile enough to produce other mixed Pt(IV) derivatives varying the reaction medium. The two trichlorido complexes easily undergo a pH-dependent hydrolysis reaction, whereas the dicarboxylato compounds are stable enough to allow further coupling reactions for drug targeting and delivery via the glyc reactive pendant. Therefore, the coupling reaction between the [Pt(cbdc)Cl(dach)(glyc)] and a model carboxylic acid, a model amine, and selectively protected amino acids is reported.

Platinum(IV) prodrugs with haloacetato ligands in the axial positions can undergo hydrolysis under biologically relevant conditions

Losing ligands rapidly: Pt(IV) complexes with haloacetato ligands can hydrolyze rapidly under biological conditions (pH 7 and 37 °C, see scheme) and the rate increases with increasing pH value. Possible mechanisms for this hydrolysis are examined using H2(18)O and ESI-MS analysis.

Clinical and pharmacokinetic evaluation of satraplatin

INTRODUCTION

The toxicities of cisplatin, that is, nephrotoxicity, neurotoxicity and emesis, provided the impetus for the development of more tolerable platinum analogs. Satraplatin is an investigational third-generation orally available lipophilic platinum, which has demonstrated safety and antitumor activity in multiple settings.

AREAS COVERED

The clinical activity of satraplatin in metastatic castrate-resistant prostate cancer (mCRPC), breast, lung and other advanced solid tumors is discussed with a focus on its pharmacokinetic properties. The article was formulated using publications found through PubMed search in addition to presentations given at major conferences.

EXPERT OPINION

Satraplatin was associated with dose-limiting myelosuppression, but no significant ototoxicity, neurotoxicity or nephrotoxicity. Despite the activity of satraplatin in mCRPC, survival was not extended in an unselected population included in a Phase III trial. While further development of satraplatin in large Phase III trials is not planned at this time, efforts are ongoing to develop tailored therapy in mCRPC based on excision repair cross-complementing group 1 expression or BRCAness. Moreover, based on potentially better central nervous system penetration due to lipophilicity, evaluation in patients with brain tumors is ongoing. Given the favorable toxicity profile and convenient oral administration, satraplatin may warrant development in settings that preclude cisplatin, for example, underlying renal dysfunction, elderly age and poor performance status.

Current status and future prospects for satraplatin, an oral platinum analogue

Platinum drugs are major chemotherapeutic agents that are used alone or in combination with other systemic agents and/or radiation therapy in the management of many human malignancies. All three platinum drugs approved by the Food and Drug Administration, cisplatin, carboplatin, and oxaliplatin, are administrated intravenously. Satraplatin is the first orally administered platinum drug under active clinical investigation. Satraplatin and its major metabolite, JM118, have shown antineoplastic activity in in vitro, in vivo, and in clinical settings. Use of satraplatin as an alternative platinum cytotoxic agent is particularly attractive because of the convenience of administration, milder toxicity profile, lack of cross-resistance with cisplatin, theoretical advantage as a radiosensitizer, and activity in cancers historically nonresponsive to platinum drugs. The most mature clinical data for satraplatin come from the recently completed phase III trial that investigated the efficacy of satraplatin and prednisone on hormone-refractory prostate cancer patients who had failed a course of other chemotherapy agents. Preliminary reports show that the combination is statistically superior to placebo and prednisone in multiple end points, including progression-free survival, prostate-specific antigen response, objective tumor response, pain response, and duration of pain response. The difference in overall survival, however, did not reach statistical significance.

Hydrolysis process of the second generation platinum-based anticancer drug cis-amminedichlorocyclohexylamineplatinum(II)

The hydrolysis process of the anticancer drug cis-amminedichlorocyclohexylamineplatinum(II) (JM118 or cis-[PtCl2(NH3)cyclohexylamine]) and the influence of solvent models therein have been studied using hybrid density functional theory (B3LYP). The aquation reactions leading to the activated drug forms a key step for the reaction with the target DNA. In this study, the stepwise hydrolysis, cis-[PtCl2(NH3)cyclohexylamine] + 2 H2O --> cis-[Pt(NH3)cyclohexylamine(OH2)2]2+ + 2 Cl- was explored, using three different models. Implicit solvent effects were incorporated through polarized continuum models. The stationary points on the potential energy surfaces for the first and second hydrolysis steps, proceeding via a general S(N)2 pathway, were fully optimized and characterized. It was found that the explicit solvent effects originating from the inclusion of extra water molecules into the system are significantly stronger than those arising from the bulk aqueous medium, especially for the second aquation step, emphasizing the use of appropriate models for these types of problems. In comparison with previous work on the parent compound cisplatin, a slower rate of hydrolysis is determined for the first (rate determining) reaction. The results furthermore imply that the doubly aquated form of JM118 will be the main DNA binding form of the drug. The results provide detailed energy profiles for the mechanism of hydrolysis of JM118, which may assist in understanding the reaction mechanism of the drug with the DNA target and in the design of novel Pt-containing anticancer drugs.

Broadening the clinical use of platinum drug-based chemotherapy with new analogues. Satraplatin and picoplatin

The three platinum-containing drugs that have been thus far approved by the FDA - cisplatin, carboplatin and oxaliplatin - have had a significant effect in the treatment of patients with some malignancies such as testicular, ovarian and colorectal cancer. However, much more remains to be achieved to widen the therapeutic use of this important class of drug, either via further analogue development or by judicious use of combining the existing drugs with new molecularly targeted agents. Two analogues arising from an academic (Institute of Cancer Research)/pharmaceutical (Johnson Matthey/AnorMed) collaboration - satraplatin (JM-216) and picoplatin (JM-/AMD-473) - have recently shown promising clinical activity; satraplatin (an orally available drug) in hormone-refractory prostate cancer and picoplatin in small-cell lung cancer. There have also been advances in delivery vehicles for platinum drugs (e.g., the diaminocyclohexane [DACH]-based AP-5346 and aroplatin/liposomal cis-bis-neodecanoato-trans-(R,R)-1,2-diaminocyclohexane platinum (II) [L-NDDP] are in early clinical development). Platinum-based drugs have also been successfully combined with molecularly targeted drugs (e.g., the recent approval of the vascular endothelial growth factor monoclonal antibody bevacizumab with carboplatin and paclitaxel in patients with NSCLC).

The Gas-Phase Chemistry ofcis-Diammineplatinum(II) Complexes: A Joint Experimental and Theoretical Study

Prior to reactions with DNA, the anticancer drug cisplatin [Pt(II)(NH(3))(2)Cl(2)] forms a series of solvolysis intermediates by successive replacement of the chloro ligands by water or hydroxyl groups. The bonding of water to Pt(II) is weak, and it is easily substituted by donor ligands present in the solution, for example, amines or alcohols. We studied such compounds using high-resolution electrospray mass spectrometry with a linear ion trap and DFT computations. This combination allows for the first time a detailed description of the reactions initiated by the central atom of the complexes. Positively charged cisplatin adducts with primary and secondary alcohols ([Pt(II)(NH(3))(2)(ROH)Cl](+)) show unexpected reactions when fragmented in a linear ion trap. Either water loss is accompanied by formation of the corresponding carbene complex, or loss of the corresponding aldehyde/ketone leads to the formation of the complex [Pt(NH(3))(2)(H(2))Cl](+). Complete loss of the alcohol ligand is not observed for kinetic reasons. A detailed investigation by DFT and molecular dynamics for the cisplatin/methanol complex [Pt(II)(NH(3))(2)(CH(3)OH)Cl](+) allowed identification of the reaction mechanisms leading to the observed fragmentation patterns. The initial step for both fragmentation pathways is activation of the alpha-CH bond and subsequent H transfer within the complex. Direct activation of the OH or CO bond is less favorable. Ligands bound to the Pt(II) center such as the chloro ligand can directly catalyze the reaction by intermediate binding of H atoms. Upon collision activation, adducts without an alpha-H atom such as [Pt(NH(3))(2){(CH(3))(3)COH}Cl](+) show loss of water or the corresponding alkene.

A combination of access to preassociation sites and local accumulation tendency in the direct vicinity of G-N7 controls the rate of platination of single-stranded DNA

Adduct formation between cationic reagents and targets on DNA are facilitated by the ability of DNA to attract cations to its surface. The electrostatic interactions likely provide the basis for the documented preference exhibited by cisplatin and related compounds for nuclear DNA over other cellular constituents. As an extension of a previous communication, we here present an investigation illustrating how the rate of adduct formation with the naturally occurring base guanine (G-N7) can be modulated by i) bulk solvent conditions, ii) local nature and size of the surrounding DNA and, iii) increasing DNA concentration. A series of single-stranded DNA oligomers of the type d(TnGTm); n= 0, 2, 4, 6, 8, 10, 12, 14, 16 and m= 16 -n or n=m= 4, 6, 8, 12, 16, 24 were allowed to react with the active metabolite of a potential orally active platinumIV drug, cis-[PtCl(NH3))(c-C6H11NH2)(OH2)]+ in the presence of three different bulk cations; Na+, Mg2+, and Mn2+. For all positions along the oligomers, a change from monovalent bulk cations to divalent ones results in a decrease in reactivity, with Mn2+ as the more potent inhibitor as exemplified by the rate constants determined for interaction with d(T8GT8): 10(3) x k obs/s(-1)= 6.5 +/- 0.1 (Na+), 1.8 +/- 0.1 (Mg2+), 1.0 +/- 0.1 (Mn2+) at pH 4.2 and 25 degrees C. Further, the adduct formation rate was found to vary with the exact location of the binding site in the presence of both Na+ and Mg2+, giving rise to reactivity maxima at the middle position. Increasing the size of the DNA-fragments was found to increase the reactivity only up to a total length of ca. 20 bases. The influence from addition of further bases to the reacting DNA was found to be salt dependent. At [Na+]= 0.5 mM a retardation in reactivity was observed whereas [Na+] < or = 4.5 mM give rise to length independent kinetics. Finally, for the first time we have here been able to evaluate the influence from an increasing concentration of non-reactive DNA bases on the adduct formation process. The latter data were successfully fitted to an inhibition model suggesting that non-productive association of the platinum complex with sites distant from G-N7 competes with productive ones in the vicinity of the G-N7 target. Taken together, the kinetics support a reaction mechanism in which access to suitable association sites in the direct vicinity of the target site controls the rate of platination.

Electrospray ionization mass spectrometry coupled to liquid chromatography for detection of cisplatin and its hydrated complexes

Electrospray ionization mass spectrometry (ESI-MS) coupled to liquid chromatography (LC) has been applied to investigate cisplatin and its hydrated complexes. Three hydrolysis products were identified following incubation of cisplatin in aqueous solution: monohydrated species, dihydrated species and the hydroxo-bridged dimer, each of which exhibited characteristic mass spectrometric behavior. The technique was employed to investigate the time- and pH-dependent hydrolysis of cisplatin in aqueous solution. The results have demonstrated that LC/ESI-MS is a powerful technique for the analysis of Pt(II) complexes and for monitoring their hydrolysis reactions.

Biomedical and biological mass spectrometry

This review focuses on biological and biomedical mass spectrometry, and covers a selection of publications in this area included in the MEDLINE database for the period 1987-2001. Over the last 15 years, biological and biomedical mass spectrometry has progressed out of all recognition. The development of soft ionization methods, such as electrospray ionization and matrix-assisted laser desorption ionization, has mainly contributed to the remarkable progress, because they can easily produce gas-phase ions of large, polar, and thermally labile biomolecules, such as proteins, peptides, nucleic acids and others. The innovations of ionization methods have led to remarkable progress in mass spectrometric technology and in biochemistry, biotechnology and molecular biology research. In addition, mass spectrometry is one of the powerful and effective technologies for drug discovery and development. It is applicable to studies on structural determination, drug metabolism, including pharmacokinetics and toxicokinetics, and de novo drug discovery by applying post-genomic approarches. In the present review, the innovative soft ionization methods are first discussed along with their features. Also, the characteristics of the mass spectrometers which are active in the biological and biomedical research fields are also described. In addition, examples of the applications of biological and biomedical mass spectrometry are provided.

Validation of an AAS method for the determination of platinum in biological fluids from patients receiving the oral platinum derivative JM216

A flameless atomic absorption spectrometric (AAS) method has been developed and validated for the determination of platinum (Pt) in human plasma, plasma ultrafitrate and urines from cancer patients receiving the orally available platinum derivative, JM216. Sample pretreatment is minimal for urine, which is diluted with 10% HCl prior to AAS analysis. Pt analysis in plasma requires the application of the matrix modifier 5% Triton X-100 directly onto the integrated L'vov platform of the graphite furnace prior to the addition of plasma samples. For Pt in ultrafiltrates, enhanced sensitivity is achieved by pre-concentrating ultrafiltrate samples onto the platform prior to the ashing/atomisation step. The AAS program was set specifically for each considered matrix enabling to achieve limit of quantitations as low as 50, 10 and 5 ng Pt ml(-1) for urine, plasma and plasma ultrafiltrate, respectively. The calibration was linear (r(2)>0.993) over the working range 5-150 ng Pt ml(-1). The method has been validated according to the Recommendations on Bioanalytical Methods Validation. The stability of Pt in samples has been explored, as well as the specificity of the method. In the urine intra-assay precision of control samples at 60, 90 and 140 ng Pt ml(-1) is always lower than 3.0, 1.3 and 4.7%, respectively, with concentrations not deviating more than -5.5 to -1.0% from their nominal values, while inter-assay precision is within 5.7-7.7% and inter-assay deviation within the -1.9 to +4.3% range. Intra-assay precision of plasma control samples at 20, 70 and 140 ng Pt ml(-1) is always lower than 8% and concentrations never deviating more than 7.1% from their nominal values. Inter-assay precision of plasma control samples is always lower than 9% with inter-assay deviation from their nominal concentrations within the -3.9 to +1.8% range. In plasma ultrafiltrate, intra-assay CVs of control samples at 12, 25 and 45 ng Pt ml(-1) are always lower than 2.6, 1.7 and 6.8%, respectively, with concentrations not deviating more than -2.6 to -0.2% from their nominal values, while inter-assay CVs are within 5.1-9.5% and inter-assay deviation within the -1.6 to +5.3% range. The proposed method has, therefore, the required performance to measure Pt in biological samples and has been successfully applied to the determination of Pt in samples from cancer patients receiving JM216 in a phase I (daily administration for 14 days, dose escalation 10-50 mg m(-2)) and a phase II (fixed dose 120 mg m(-2) over 5 days) clinical study. In phase I study, both total and ultrafiltrable Pt accumulated upon repetitive dosings, showed long elimination half-lives (t(1/2)) and were measurable 2 weeks after the end of JM216 administration.

An update on satraplatin: the first orally available platinum anticancer drug

This update focuses on the clinical development of the first orally available platinum-containing anticancer drug, satraplatin (JM216, BMS 182751, BMY 45594). Satraplatin was selected for clinical study on the basis of possessing several promising preclinical features the first of which is it's potent in vitro growth inhibitory properties against several tumour types (mean IC(50) approximately 1 microM). Secondly, it possesses in vivo oral antitumour activity against a variety of murine and human sc. tumour models, broadly comparable to the level of activity obtainable with parenterally administered cisplatin or carboplatin. Lastly, it has a relatively mild toxicity profile with myelosuppression being dose-limiting. Satraplatin entered clinical trials in 1992 and is now undergoing Phase III evaluation. Non-linear pharmacokinetics, probably due to saturable absorption, was observed when the drug was administered as a bolus every 3 - 4 weeks. Subsequent Phase II trials have used a daily schedule for five consecutive days, at doses of around 120 mg/m(2)/day. The drug produced relatively mild side effects with controllable nausea and vomiting and, as predicted from the mouse studies, myelosuppression as the dose-limiting effect (neutropoenia and thrombocytopoenia). Combination trials are also ongoing with paclitaxel or radiation. The metabolism of satraplatin is complex, with at least six biotransformation products observed in the plasma of patients. The platinum(II) complex JM118 is the main metabolite, three other minor metabolites have been identified, there is no detectable parent drug. Tumour responses have been recorded, particularly in patients with small cell lung cancer and hormone refractory prostate cancer. These clinical studies with satraplatin indicate that oral platinum-based chemotherapy is feasible.

Kinetics and mechanism for reduction of the anticancer prodrug trans,trans,trans-[PtCl2(OH)2(c-C6H11NH2)(NH3)] (JM335) by thiols

The reduction of the platinum(IV) prodrug trans,trans,trans-[PtCl2(OH)2(c-C6H11NH2)(NH3)] (JM335) by L-cysteine, DL-penicillamine, DL-homocysteine, N-acetyl-L-cysteine, 2-mercaptopropanoic acid, 2-mercaptosuccinic acid, and glutathione has been investigated at 25 degrees C in a 1.0 M aqueous perchlorate medium with 6.8 < or = pH < or = 11.2 using stopped-flow spectrophotometry. The stoichiometry of Pt(IV):thiol is 1:2, and the redox reactions follow the second-order rate law -d[Pt(IV)]/dt = k[Pt(IV)][RSH]tot, where k denotes the pH-dependent second-order rate constant and [RSH]tot the total concentration of thiol. The pH dependence of k is ascribed to parallel reductions of JM335 by the various protolytic species of the thiols, the relative contributions of which change with pH. Electron transfer from thiol (RSH) or thiolate (RS-) to JM335 is suggested to take place as a reductive elimination process through an attack by sulfur at one of the mutually trans chloride ligands, yielding trans-[Pt(OH)2(c-C6H11NH2)(NH3)] and RSSR as the reaction products, as confirmed by 1H NMR. Second-order rate constants for the reduction of JM335 by the various protolytic species of the thiols span more than 3 orders of magnitude. Reduction with RS- is approximately 30-2000 times faster than with RSH. The linear correlation log(kRS) = (0.52 +/- 0.06)-pKRSH--(2.8 +/- 0.5) is observed, where kRS denotes the second-order rate constant for reduction of JM335 by a particular thiolate RS- and KRSH is the acid dissociation constant for the corresponding thiol RSH. The slope of the linear correlation indicates that the reactivity of the various thiolate species is governed by their proton basicity, and no significant steric effects are observed. The half-life for reduction of JM335 by 6 mM glutathione (40-fold excess) at physiologically relevant conditions of 37 degrees C and pH 7.30 is 23 s. This implies that JM335, in clinical use, is likely to undergo in vivo reduction by intracellular reducing agents such as glutathione prior to binding to DNA. Reduction results in the immediate formation of a highly reactive platinum(II) species, i.e., the bishydroxo complex in rapid protolytic equilibrium with its aqua form.

Gene-specific repair of Pt/DNA lesions and induction of apoptosis by the oral platinum drug JM216 in three human ovarian carcinoma cell lines sensitive and resistant to cisplatin

JM216, an oral platinum drug entering into phase III clinical trial, exhibited comparable cytotoxicity to cisplatin in three human ovarian carcinoma cell lines: the sensitive (CH1), acquired resistant (CH1cisR) and intrinsically resistant (SKOV-3). Platinum accumulation and binding to DNA were similar in each of the three cell lines at equimolar doses, indicating that the resistant cell lines could tolerate higher intracellular platinum levels and platinum bound to DNA at IC50 concentrations of drug. Comparison with cisplatin demonstrated that intracellular platinum levels were marginally higher with JM216, but that platinum binding to DNA was similar for the two drugs in each of the cell lines. Each of the cell lines exhibited an ability to repair JM216 induced platinum/DNA lesions in the N-ras gene (gene-specific repair) at equitoxic concentrations of drug. However, this occurred to a greater extent in the two resistant cell lines such that by 24 h the CH1cisR and SKOV-3 had removed 72% and 67% respectively compared with approximately 32% for the CH1. Reduced gene-specific repair capacity in CH1 cells was also seen following incubation with 25 microM (or 5 microM - 2 x IC50) cisplatin, whereas the CH1cisR and SKOV-3 cell lines were repair proficient. JM216 induced apoptosis in the three cell lines following a 2h incubation with 2 x the IC50 of drug. Fluorescent microscopy of cells stained with propidium iodide showed that the detached cell population displayed typical apoptotic nuclei. Furthermore, field inversion gel electrophoresis demonstrated the presence of DNA fragments approximately 23-50 kb in size, indicative of apoptosis, in the detached cells. JM216 induced an S phase slow down in each of the three cell lines accompanied by a G2 block in the CH1 pair. Incubation with this concentration of JM216 also resulted in the induction of p53 in the CH1 and CH1cisR. These studies suggest that the relative sensitivity of the CH1 cell line to cisplatin and JM216 is at least partly attributable to a deficiency in gene-specific repair. The oral platinum drug, JM216, exerts its cytotoxic effects through the induction of apoptosis following a slow-down in S phase in both the sensitive and resistant lines.

Hyphenated liquid chromatographic techniques in forensic toxicology

The prerequisite of applicability of hyphenated methods in forensic analysis is the achievement of a stage of "final maturity". In the field of liquid chromatography, HPLC coupled with diode array detection (DAD) seems to fulfill this criterion, whilst the combination with atmospheric pressure ionization mass spectrometry (HPLC-API-MS) is still in a development stage. HPLC-DAD is broadly used as identification tool in forensic and in emergency toxicology. Two main approaches were observed; development of retention index scales for intra-laboratory exchange of data and establishing of databases only for intra-laboratory use. Using these approaches, several databases were established for toxicological relevant substances (illicit and therapeutic drugs and their metabolites, environmental poisons etc.) in biological fluids. Also, complete HPLC-DAD identification systems are commercially available. Further possibility of progress depends on the on-line combination ("triple hyphenation") with other detection methods, preferably API-MS. HPLC-API-MS, both in electrospray (ESI) and atmospheric pressure chemical ionization (APCI) options, underwent dramatic development in the last decade and is reaching its final shape. The method was broadly applied for various groups of toxicologically relevant substances, a lot of them unaccessible for other techniques, including GC-MS. Particularly important was application of HPLC-API-MS for detection and quantitation of active, polar metabolites of various drugs and for analysis of macromolecules. APCI seems to be more useful for analysis of less polar compounds, whereas ESI is particularly valuable for determination of polar, large molecules (e.g., toxic peptides, polar metabolites etc.) Up to now, HPLC-API-MS has been mainly applied for dedicated analyses, but the introduction of APCI or ESI in systematic toxicological screening may be expected in the near future.

Modifying the properties of platinum (IV) complexes in order to increase biological effectiveness

The preparation of a series of novel Pt(IV) complexes containing the anionic polyfluoroaryl ligands, 2,3,5,6-tetrafluorophenyl (p-HC6F4), 2,3,5,6-tetrafluoro-4-methoxyphenyl (p-MeOC6F4) and pentafluorophenyl (C6F5) are described. The crystal structure of a representative complex, [Pt(p-MeOC6F4)2(O2CEt)2(en)] (en = ethane-1,2-diamine) was determined and confirms the trans arrangement of the carboxylato ligands. Reduction potentials of the series of complexes reveal that replacement of equatorial chloro ligands by polyfluoroaryl ligands makes reduction substantially more difficult. They also confirm previously reported trends in that complexes having axial carboxylato ligands are more readily reduced than those having axial hydroxo ligands. Reduction potentials and in vitro activities showed no obvious correlations. Moderate to high activity was observed for many complexes in the series, including some of those that were very difficult to reduce.

Quantitative determination of a nonpeptide antithrombotic in dog plasma by microbore high-performance liquid chromatography-tandem mass spectrometry utilizing pneumatically assisted electrospray ionization

A method has been developed and is described for the quantitative determination of a nonpeptide antithrombotic in dog plasma. The assay employs reversed phase microbore high-performance liquid chromatography in conjunction with tandem mass spectrometry utilizing pneumatically assisted electrospray ionization. The analyte and internal standard are isolated from the plasma matrix by solid-phase extraction. The mass spectrometer is operated in the positive ion multiple reaction monitoring mode and is set to detect the presence of a precursor-product ion pair for both the analyte and internal standard to generate product ion chromatograms for both species. The analyte is quantified by using weighted least-squares regression of the peak height ratio of drug:internal standard. The method provides linear response for plasma concentrations ranging from 5 ng/mL (25 pg on-column) to 2500 ng/mL. Statistical evaluation and examples of authentic sample assays are also presented.

Intracellular metabolism of the orally active platinum drug JM216: influence of glutathione levels

JM216 (bis-acetato ammine dichloro cyclohexylamine Pt IV) is an oral platinum complex presently undergoing phase II clinical trials. Previous studies have identified some of its biotransformation products in clinical materials. This study evaluated the nature of JM216 biotransformation products intracellularly in two different human ovarian carcinoma cell lines, one relatively sensitive to platinum agents (CH1: JM216 4 h IC50 of 5.8 microM) and the other relatively resistant (SKOV3: JM216 4 h IC50 of 60.7 microM). Metabolic profiles were also evaluated at different growth status and in cells pretreated with buthionine sulphoximine (BSO), an agent known to decrease intracellular glutathione levels. Results showed that JM216 enters the cells and that the nature and percentage of biotransformation products was dependent upon glutathione levels. Furthermore, results support the view that the previously reported peak A biotransformation product contains a glutathione adduct. In exponentially growing SKOV3 cells which contain higher glutathione levels than CH1, (82.5 vs 37.8 nmol mg-1 protein), peak A represented 89% of total platinum 4 h after JM216 exposure compared with only 24% in CH1. Moreover, 60-70% depletion of glutathione achieved by 24 h pretreatment of cells with BSO resulted in a significant decrease in peak A in both cell lines and increased the cytotoxicity of JM216 in both CH1 and SKOV3 by approximately 2-fold. Following a 4 h exposure of exponentially growing SKOV3 cells to JM216, only peak A (89%) and JM216 (11%) could be detected whereas in CH1 cells, peak A (24%), JM216 (73%) and JM118 [cis-ammine dichloro (cyclohexylamine) platinum II] (3%) were detected. However, in CH1 cells at confluence, where glutathione is lower (8 nmol mg-1 protein) four metabolites (plus JM216 itself) were detected following exposure to 50 microM JM216; peak A, JM118, JM383 (bis-acetato ammine (cyclohexylamine) dihydroxy platinum IV) and an unidentified metabolite (D), also observed in patient's plasma ultrafiltrate. In confluent SKOV3 cells exposed to 50 microM JM216, peak A, JM216 and JM118 were detected. A further unidentified metabolite observed in patients receiving JM216 (metabolite F) was not formed inside these tumour cells. Overall, these data suggest that glutathione conjugation represents a major deactivation pathway for JM216.