Kinetic analysis of the cis-diamminedichloroplatinum(II)--cysteine reaction: implications to the extent of platinum--DNA binding

STEP: profiling cellular-specific targets and pathways of bioactive small molecules in tissues via integrating single-cell transcriptomics and chemoproteomics

Identifying the cellular targets of bioactive small molecules within tissues has been a major concern in drug discovery and chemical biology research. Compared to cell line models, tissues consist of multiple cell types and complicated microenvironments. Therefore, elucidating the distribution and heterogeneity of targets across various cells in tissues would enhance the mechanistic understanding of drug or toxin action in real-life scenarios. Here, we present a novel multi-omics integration pipeline called Single-cell TargEt Profiling (STEP) that enables the global profiling of protein targets in mammalian tissues with single-cell resolution. This pipeline integrates single-cell transcriptome datasets with tissue-level protein target profiling using chemoproteomics. Taking well-established classic drugs such as aspirin, aristolochic acid, and cisplatin as examples, we confirmed the specificity and precision of cellular drug-target profiles and their associated molecular pathways in tissues using the STEP analysis. Our findings provide more informative insights into the action modes of bioactive molecules compared to in vitro models. Collectively, STEP represents a novel strategy for profiling cellular-specific targets and functional processes with unprecedented resolution.

Discovery of cisplatin-binding proteins by competitive cysteinome profiling

Cisplatin is a widely used cancer metallodrug that induces cytotoxicity by targeting DNA and chelating cysteines in proteins. Here we applied a competitive activity-based protein profiling strategy to identify cisplatin-binding cysteines in cancer proteomes. A novel cisplatin target, MetAP1, was identified and functionally validated to contribute to cisplatin's cytotoxicity.

Elusive intermediates in cisplatin reaction with target amino acids: Platinum(II)-cysteine complexes assayed by IR ion spectroscopy and DFT calculations

The reactivity of a widely used metal based antineoplastic drug, cisplatin, cis-PtCl₂(NH₃)₂, with L-cysteine (Cys) has been investigated using a combination of electrospray ionization mass spectrometry (ESI-MS), IRMPD gas phase ion spectroscopy and DFT calculations. The cysteine lateral chain represents one of the main platination sites in proteins, which is believed to be related to the resistance mechanisms to cisplatin. The vibrational features of the mass-selected substitution product cis-[PtCl(NH₃)₂(Cys)]⁺ and the intercepted cis-[PtCl(NH₃)₂(H₂O)(Cys)]⁺ intermediate complex were compared to calculated IR spectra, enabling the assessment of the sampled ions structures. In cis-[PtCl(NH₃)₂(Cys)]⁺, cysteine was found to bind platinum through the sulfur atom as a thiolate zwitterion, highlighting the enhanced acidity of the cysteine thiol group upon metal coordination. The cis-[PtCl(NH₃)₂(H₂O)(Cys)]⁺ structure complies with the non-covalent encounter complex, formed by cis-[PtCl(NH₃)₂(H₂O)]⁺ and neutral cysteine. This species is able to undergo the substitution process to produce cis-[PtCl(NH₃)₂(Cys)]⁺ when activated as a mass-isolated ion suggesting its participation in the reaction mechanism of cisplatin with cysteine in solution. Finally, the DFT-calculated energy profile for the substitution reaction was correlated with the peculiar gas-phase reactivity of this non-covalent complex, resulting to be 10-fold less reactive toward substitution than the corresponding methionine complex.

Fate of cisplatin and its main hydrolysed forms in the presence of thiolates: a comprehensive computational and experimental study

Thiolations and bidentations drive the chemical fate of cisplatin compounds in intracellular medium.

Labile Pd-sulphur and Pt-sulphur bonds in organometallic palladium and platinum complexes [(COD)M(alkyl)(S-ligand)]n+-A speciation study

Reaction of various sulphur ligands L (SEt^-, SPh^-, SC₆F₄H-4^-, SEt₂, StBu₂, SnBu₂, DMSO, DPSO) with the precursors [(COD)M(R)Cl] (COD=1,5-cyclooctadiene, M=Pd or Pt; R=methyl (Me) or benzyl (Bn); DMSO=dimethyl sulfoxide; DPSO=diphenyl sulfoxide) allowed isolation and characterisation of mononuclear neutral (n=0) or cationic (n=1) complexes [(COD)Pt(R)(L)]ⁿ⁺. Reaction of l-cysteine (HCys) with [(COD)Pt(Me)Cl] under similar conditions gave the binuclear cationic complex in [{(COD)Pt(Me)}₂(μ-Cys)]Cl. Detailed NMR spectroscopy and single crystal X-ray diffraction in the case of [(COD)Pt(Me)(SEt₂)][SbF₆] and [(COD)Pt(Me)(DMSO)][SbF₆] reveal markedly labilised Pt-S bonds as a consequence of the highly covalent Pt-C bonds of the R coligands in these organometallic species. Cationic charge (n=1) seems to lower the Pt-S bond strength further. Consequently, most of these complexes are not stable long-term in aqueous DMF (N,N-dimethylformamide) solutions. This made the evaluation of their antiproliferative properties towards HT-29 colon carcinoma and MCF-7 breast adenocarcinoma cell lines impossible. Only the two complexes [(COD)Pt(R)(SC₆F₄H-4)] with R=Me or SC₆F₄H-4 coligands could be tested with the R=Me complex showing promising activity (in the range of cisplatin), while the R=SC₆F₄H-4 derivative is largely inactive, as were the phosphane complexes [(dppe)Pt(SC₆F₄H-4)₂] (dppe=1,2-bis(diphenylphosphino)ethane), cis-[(PPh₃)₂Pt(SC₆F₄H-4)₂] and cis-[(PPh₃)₂PtCl₂] which were tested for comparison. In turn, our findings might pave the way to new Pt anti-cancer drugs with largely reduced unwanted depletion of incorporated drugs and reduced side-effects from binding to S-containing biomolecules.

The trans influence in the modulation of platinum anticancer agent biology: the effect of nitrite leaving group on aquation, reactions with S-nucleophiles and DNA binding of dinuclear and trinuclear compounds

To examine the effect of leaving group and trans influence on the general reactivity of polynuclear platinum antitumor agents we investigated substitution of the chloride leaving groups with nitrite ion, which forms strong bonds to Pt. It was of interest to explore whether nitrite could be used to modulate biological properties of these agents, in particular the deactivating reactions that occur on reaction with S-nucleophiles, involving loss of the linking diamine under the trans influence of sulfur. Reported herein is a study of the synthesis, aquation, DNA binding and reactions with glutathione (GSH), methionine (Met) and acetylmethione (AcMet) of nitrito derivatives of di- and trinuclear platinum antitumor compounds: [{trans-PtNO(2)(NH(3))(2)}(2)(mu-NH(2)(CH(2))(6)NH(2))](NO(3))(2) (1-NO(2)) and [{trans-PtNO(2)(NH(3))(2)}(2)(mu-trans-Pt(NH(3))(2){NH(2)(CH(2))(6)NH(2)}(2))](NO(3))(4) (1'-NO(2)). {(1)H,(15)N}-HSQC NMR studies revealed that 1-NO(2) is inert to aquation reactions, even after prolonged incubation at physiological pH. Monitoring of the interaction of 1-NO(2) with the duplex 5'-d(ATATGTACATAT)(2) (I) showed only unreacted complex, consistent with activation by aquation being a requirement for covalent DNA binding. The reaction of 1-NO(2) with GSH was studied by (1)H, (195)Pt, (15)N and {(1)H,(15)N}-HSQC NMR spectroscopy. For the parent dichlorido compounds (1 and 1') substitution of chloride by GS(-) leads to drug degradation involving liberation of the diamine linker. While the same final products trans-[Pt(SG)(2)(NH(3))(2)] (5) and trans-[{Pt(SG)(NH(3))(2)}(2)-mu-SG] (6) are formed, different mechanisms are involved, consistent with the trans influence NO(2)(-) > Cl(-); the half-life is slightly longer for 1-NO(2) (1.8 h) compared with 1 (1.3 h). Identification of the intermediate trans-[Pt(NH(3))(2)(NO(2))(SG)] (4) shows that the nitrito group remains coordinated while the linker amine is substituted by coordination of GS(-), and then trans labilization of the nitrito group occurs leading to 5 and 6. Reaction of the trinuclear 1'-NO(2) with GSH follows essentially the same reaction pathway. Reaction of 1-NO(2) with Met and AcMet is much slower and only 20 % liberated amine was observed after reaction with Met for 24 h at 37 degrees C. The final product from reaction with AcMet is trans-[Pt(NH(3))(2)(NO(2))(AcMet)], as in this case coordination of the S-nucleophile does not lead to trans labilization of the nitrito group.

Cell proliferation and cell cycle alterations in oesophageal p53-mutated cancer cells treated with cisplatin in combination with photodynamic therapy

OBJECTIVES

The major goal of anti-cancer therapies is selective destruction of tumour cells with minimum side effects on normal cells. Towards this aim, combination of different therapeutic modalities has been evaluated for improving control of neoplastic diseases and quality of life for the patient. Photodynamic therapy (PDT) is a procedure for treatment of various types of cancer, but its combination with other established treatments has not been evaluated in detail. We have used KYSE-510 cells from a human oesophageal carcinoma as an in vitro model to investigate whether cisplatin (CDDP) could be combined with PDT to increase cell death with respect to single treatments.

MATERIALS AND METHODS

p53-mutated KYSE-510 cells were treated with CDDP alone or in combination with PDT. Analyses of cell viability, cell cycle progression and apoptosis induction were carried out at specific times after treatments.

RESULTS

Decrease in cell viability, cell cycle arrest at the G(2)/M- and S-phases boundary, and apoptosis induction were observed after single and combined treatments.

CONCLUSIONS

Our results show that low CDDP doses (0.25-1 microm) induce cell mortality and cell cycle perturbation, which were more evident when given in combination with PDT, but in contrast to work of other authors no synergistic activity was found. Apoptosis occurred via intrinsic pathways in treated cells, although it did not represent the predominant mode of cell death.

A novel, species-specific class of uncompetitive inhibitors of gamma-glutamyl transpeptidase

Expression of gamma-glutamyl transpeptidase (GGT) in tumors contributes to resistance to radiation and chemotherapy. GGT is inhibited by glutamine analogues that compete with the substrate for the gamma-glutamyl binding site. However, the glutamine analogues that have been evaluated in clinical trials are too toxic for use in humans. We have used high throughput screening to evaluate small molecules for their ability to inhibit GGT and have identified a novel class of inhibitors that are not glutamine analogues. These compounds are uncompetitive inhibitors, binding the gamma-glutamyl enzyme complex. OU749, the lead compound, has an intrinsic K(i) of 17.6 microm. It is a competitive inhibitor of the acceptor glycyl-glycine, which indicates that OU749 occupies the acceptor site while binding to the gamma-glutamyl substrate complex. OU749 is more than 150-fold less toxic than the GGT inhibitor acivicin toward dividing cells. Inhibition of GGT by OU749 is species-specific, inhibiting GGT isolated from human kidney with 7-10-fold greater potency than GGT isolated from rat or mouse kidney. OU749 does not inhibit GGT from pig cells. Human GGT expressed in mouse fibroblasts is inhibited by OU749 similarly to GGT from human cells, which indicates that the species specificity is determined by differences in the primary structure of the protein rather than species-specific, post-translational modifications. These studies have identified a novel class of inhibitors of GGT, providing the basis for further development of a new group of therapeutics that inhibit GGT by a mechanism distinct from the toxic glutamine analogues.

Non-DNA-binding platinum anticancer agents: Cytotoxic activities of platinum-phosphato complexes towards human ovarian cancer cells

DNA is believed to be the molecular target for the cytotoxic activities of platinum (Pt) anticancer drugs. We report here a class of platinum(II)- and platinum(IV)-pyrophosphato complexes that exhibit cytotoxicity comparable with and, in some cases, better than cisplatin in ovarian cell lines (A2780, A2780/C30, and CHO), yet they do not show any evidence of covalent binding to DNA. Moreover, some of these compounds are quite effective in cisplatin- and carboplatin-resistant cell line A2780/C30. The lack of DNA binding was demonstrated by the absence of a detectable Pt signal by atomic absorption spectroscopy using isolated DNA from human ovarian cells treated with a platinum(II)-pyrophosphato complex, (trans-1,2-cyclohexanediamine)(dihydrogen pyrophosphato) platinum(II), (pyrodach-2) and from NMR experiments using a variety of nucleotides including single- and double-stranded DNA. Furthermore, pyrodach-2 exhibited reduced cellular accumulations compared with cisplatin in cisplatin- and carboplatin-resistant human ovarian cells, yet the IC(50) value for the pyrophosphato complex was much less than that of cisplatin. Moreover, unlike cisplatin, pyrodach-2 treated cells overexpressed fas and fas-related transcription factors and some proapoptotic genes such as Bak and Bax. Data presented in this report collectively indicate that pyrodach-2 follows different cytotoxic mechanisms than does cisplatin. Unlike cisplatin, pyrodach-2 does not undergo aquation during 1 week and is quite soluble and stable in aqueous solutions. Results presented in this article represent a clear paradigm shift not only in expanding the molecular targets for Pt anticancer drugs but also in strategic development for more effective anticancer drugs.

Preferential energy- and potential-dependent accumulation of cisplatin-gutathione complexes in human cancer cell lines (GLC4 and K562): A likely role of mitochondria

cis-Diamminedichloroplatinum(II) (CDDP) is an important chemotherapeutic agent used in the treatment of a wide variety of solid tumors. We have recently shown that aquated forms of cisplatin (aqua-Pt) rapidly accumulate in K562 and GLC4 cultured cells, in comparison to CDDP. Thus, when cells are incubated with aquated forms of cisplatin a gradient of concentration is observed after a short time, approximately 40 min, with an intracellular concentration of aqua-Pt of 20-30 times higher than that of extracellular aqua-Pt. The same gradient of concentration is observed when cells are incubated with CDDP but it takes a longer time, i.e., about 24 h. Therefore, the question arises as to the identity of the intracellular sites of accumulation of aqua-Pt. Using several agents to modulate membrane potential, acidic compartment pH and/or ATP level, we obtained evidence that aqua-Pt may accumulate rapidly inside mitochondria as this accumulation is energy- and membrane-potential-dependent. However, aqua-Pt complexes are not characterized by a delocalized charge and a lipophilic character that would permit their movement through the inner membrane. Therefore, it is suggested that intracellular aqua-Pt reacts rapidly with glutathione with the resultant complex being transported inside the mitochondria via one of the known glutathione transporters, i.e., dicarboxylate and/or 2-oxoglutarate transporters present in the inner membrane.

Oxaliplatin degradation in the presence of important biological sulphur-containing compounds and plasma ultrafiltrate

Oxaliplatin undergoes extensive non-enzymatic chemical transformation in the body. Complexes with sulphur-containing compounds have previously been found in plasma from patients treated with oxaliplatin. We have studied the kinetics for the reactions between oxaliplatin and cysteine, methionine, and glutathione, by determination of the degradation of oxaliplatin using liquid chromatography with UV-detection. We also studied the degradation of oxaliplatin in plasma ultrafiltrate (PUF). For the degradation of oxaliplatin in the presence of glutathione, methionine, and cysteine, the second-order rate constants were 4.7M(-1)min(-1) (95% confidence interval [C.I.], 4.4-5.0M(-1)min(-1)), 5.5M(-1)min(-1) (95% C.I., 5.2-5.7M(-1)min(-1)), and 15M(-1)min(-1) (95% C.I., 14-17M(-1)min(-1)), respectively. The reaction rate was much faster than previously reported kinetics for cisplatin. The degradation rate of oxaliplatin in PUF was biphasic. The rate constant for the first phase varied from 9.5x10(-3) to 0.13min(-1) and for the second phase from (1.7 to 1.8)x10(-3)min(-1) in PUF from five healthy volunteers. The first hours of the degradation of oxaliplatin in PUF are accounted for by the degradation of oxaliplatin in a cocktail of sodium chloride and sulphur-containing compounds at physiological plasma concentrations. In conclusion, the rate of the reaction of oxaliplatin with three sulphur-containing compounds was faster for oxaliplatin than what is previously known for cisplatin. This may be important with respect to differences in the cellular effects of cisplatin and oxaliplatin treatment.

A comparative kinetic study of modified Pt(dppf)Cl2 complexes and their interactions with l-cys and l-met

With the success of cisplatin (cis-diamminedichloroplatinum(II)), strong interest has developed in the application of inorganic metal complexes to the treatment of cancer. Research has focused on platinum(II) complexes with a variety of spectator ligands that provide novel physicochemical properties. In this paper we report a kinetic study of 1',1'-bis(diphenylphosphino)ferrocenedichloroplatinum(II) and two related compounds with either an acetate or amide ester substituent attached to the cyclopentadienyl ring. For all compounds the reactivity towards L-cysteine and L-methionine in aqueous solution has been investigated (25 degrees C, I= 0.010 M and pseudo-first-order conditions). For the reactions with l-cysteine and l-methionine the reactions proceeded via a steady-state aquated intermediate to form mono (0.92(2)-3.25(4)) x 10(-3) s(-1)) and bis adducts (0.97(2)-3.67(4)) x 10(-4) s(-1)). For reactions with l-cysteine, direct reactions with the starting complex also contributed (mono adduct: 0.36(2)-1.41(4) M(-1) s(-1), bis adduct: 0.080(1)-0.96(1) M(-1) s(-1)). The attached substituents were found to have a significant effect upon the reaction kinetics, with the substituted complexes found to have increased reactivity. It is proposed that the increased reactivity stems from hydrogen bonding between the substituent and the entering ligand and subsequent outer-sphere complex stabilisation. Evidence in support of this theory was obtained form measurements in dichloromethane with 1-propanethiol as the entering ligand. The reactivity of the dppf containing complexes was also compared to that of cisplatin (mono adduct: (0.170(1)-0.175(1)) x 10(-3) s(-1), bis adduct: (0.183(1)-0.397(1)) x 10(-4) s(-1)) and found to be significantly enhanced.

Kinetic study on the reaction of cisplatin with metallothionein

The binding of cisplatin to metallothionein (MT) was investigated at 37 degrees C in 10 mM Tris-NO3 (pH approximately 7.4) and 4.62 mM NaCl. The conditions were chosen to mimic passage of clinical concentrations of cisplatin through the cytosol. The reactions were monitored by high-performance liquid chromatography (HPLC), atomic absorption spectroscopy, and ultraviolet (UV) absorption spectroscopy. The UV data showed that several reactions occur, the first of which does not affect the absorbance (no Pt-sulfur bond formation). They also suggested that if [cisplatin] is large compared with [MT], the rate of subsequent reaction is between first and second order in [cisplatin] and between zeroth and first order in [MT]. HPLC eluates with 24 < retention time (tR) < 27 min contained undialyzable Pt, which increased with reaction time and corresponded to Pt-thionein product. Eluates with 3 < tR < 7 min corresponded to unbound cisplatin and allowed determination of second-order rate constants (k), using the second-order rate equation. The k value for cisplatin reacting with apo-MT was approximately 0.14 M-1 s-1, Cd/Zn-MT approximately 0.75 M-1 s-1, Cd7-MT approximately 0.53 M-1 s-1, and Zn7-MT approximately 0.65 M-1 s-1. Thus, cisplatin displaced Cd and Zn equally well. Leukocyte MT concentration was approximately 1.0 mM, so that the kinetics of cisplatin binding to cellular MT is pseudo-first order (pseudo-first-order rate constant, approximately 0.63 x 10-3 s-1; half-life, approximately 18 min). With [cisplatin] = 10 microM, the rate of cisplatin reaction with MT is approximately 6.3 micromol s-1 cm-3. We conclude that cellular MT can trap significant amounts of cisplatin and may efficiently contribute to cisplatin resistance.

High pressure liquid chromatography and mass spectrometry characterization of the nephrotoxic biotransformation products of Cisplatin

Previous studies have shown that cisplatin requires metabolic activation to become nephrotoxic. The activation is proposed to be via the metabolism of a glutathione-platinum conjugate to a cysteinyl-glycine-platinum conjugate, which is further processed to a cysteine conjugate. Preincubating cisplatin with glutathione (GSH), cysteinyl-glycine, or N-acetylcysteine (NAC) results in a transient increase in the toxicity of cisplatin toward renal proximal tubular cells. In this study, the preincubation solutions were analyzed by high pressure liquid chromatography (HPLC), atomic absorption spectrometry, and mass spectrometry (MS) to characterize the formation and structure of the platinum conjugates. HPLC analysis of the cisplatin-GSH, cisplatin-cysteinyl-glycine, and cisplatin-NAC preincubation solutions revealed two new platinum-containing peaks in each of the solutions. MS-MS analysis of the peaks revealed a diplatinum- and a monoplatinum conjugate in each of the solutions. Analysis of the composition and toxicity of the solutions with time showed that the transient increase in toxicity correlated with the formation of the monoplatinum conjugate whereas prolonged preincubation decreased toxicity and correlated with the formation of the diplatinum conjugate. The monoplatinum-monoglutathione conjugate is a substrate for gamma-glutamyl transpeptidase, an enzyme that is essential for the nephrotoxicity of cisplatin. The monoplatinum-mono-NAC conjugate can be deacetylated to a cysteine conjugate, which is a substrate for pyroxidol phosphate (PLP)-dependent cysteine S-conjugate beta-lyase. This PLP-dependent enzyme is proposed to catalyze the final step in the metabolic activation of cisplatin. Identification of the structure and toxicity of these conjugates further elucidates the metabolism of cisplatin to a nephrotoxin.

Metabolism of Cisplatin to a nephrotoxin in proximal tubule cells

Cisplatin, a commonly used chemotherapeutic agent, is nephrotoxic. The mechanism by which cisplatin selectively kills the proximal tubule cells was heretofore unknown. Recent studies in mice and rats have shown that the nephrotoxicity of cisplatin can be blocked by acivicin or (aminooxy)acetic acid, the same enzyme inhibitors that block the metabolic activation of a series of nephrotoxic halogenated alkenes. In this study, it was hypothesized that cisplatin is activated in the kidney to a toxic metabolite through the same pathway that has been shown to activate the halogenated alkenes. This activation begins with the formation of a glutathione-conjugate that is metabolized to a cysteinyl-glycine-conjugate, to a cysteine-conjugate, and finally to a reactive thiol. In this study, a protocol was developed in which confluent monolayers of LLC-PK(1) cells were exposed to clinically relevant concentrations of cisplatin or cisplatin-conjugate for 3 h. Cell viability was assayed at 72 h. The role of gamma-glutamyl transpeptidase (GGT) and cysteine-S-conjugate beta-lyase in the metabolism of each of the cisplatin-conjugates was investigated. Pre-incubation of cisplatin with glutathione, cysteinyl-glycine, or N-acetyl-cysteine to allow for the spontaneous formation of cisplatin-conjugates increased the toxicity of cisplatin toward LLC-PK(1) cells. Inhibition of GGT activity showed that GGT was necessary only for the toxicity of the cisplatin-glutathione-conjugate. Inhibition of cysteine-S-conjugate beta-lyase reduced the toxicity of each of the cisplatin-conjugates. These data demonstrate that metabolism of cisplatin in proximal tubule cells is required for its nephrotoxicity. The elucidation of this pathway provides new targets for the inhibition of cisplatin nephrotoxicity.

Kinetic study of the reaction of cisplatin with thiols

The reactions of cisplatin [cis-diamminedichloroplatinum(II), CDDP] with glutathione (GSH) and drug thiols were investigated at 37 degrees C in 100 mM Tris-NO(3), pH approximately 7.4, using a clinically relevant concentration of CDDP (33 micro M), a large excess of GSH (16.5 mM), and [NaCl] of 4.62 mM. The conditions were designed to mimic passage of CDDP through the cytosol. The reactions were studied by UV-absorption spectroscopy, high-pressure liquid chromatography (HPLC), and atomic absorption spectroscopy. The initial rates, detected by UV absorbance, confirmed that the reactions are first order in [CDDP]. The HPLC peak corresponding to CDDP was analyzed for platinum content by atomic absorption spectroscopy, which decreased exponentially with time, confirming that the reactions are first order in [CDDP] and allowing determination of the pseudo first order rate constants (k(1)). For reaction of the dichloro form of CDDP with GSH, the k(1) value was approximately 2.2 x 10(-4) s(-1) (t(1/2) of approximately 53 min), giving the second order rate constant value (k(2)) of approximately 1.3 x 10(-2) M(-)1 s(-1). Reaction of a mixture of the aquated forms of CDDP with GSH gave a lower k(1) value ( approximately 0.9 x 10(-4) s(-1)). Reaction of CDDP with sodium 2-mercaptoethanesulfonate (mesna) gave a k(1) value of approximately 1.8 x 10(-4) s(-1) (t(1/2) of approximately 65 min and k(2) of approximately 1.1 x 10(-2) M(-1) s(-1)). Reaction of CDDP with S-2-(3-aminopropylamino)ethanethiol (WR-1065) gave a k(1) value of approximately 12.0 x 10(-4) s(-1) (t(1/2) of approximately 10 min and k(2) of approximately 7.3 x 10(-2) M(-)1 s(-1)). The relatively slow reaction rate of CDDP with GSH is consistent with the efficient DNA platination by CDDP in the presence of millimolar concentration of GSH in the cytosol.

Kinetics of cisplatin binding to cellular DNA and modulations by thiol-blocking agents and thiol drugs

DNA platination by cisplatin (CDDP) was investigated in peripheral blood mononuclear cells and ovarian cancer cells using atomic absorption spectroscopy. Plots showing the amount of platinum (Pt) bound to DNA versus the molar concentration of cisplatin in the incubation medium ([CDDP]) were nonlinear. For [CDDP] < about 5 microM, the amount of Pt bound to DNA increased slowly with added drug. However, for larger [CDDP], the slope of the plot increased significantly. To study the role of thiols in affecting cisplatin binding to DNA, cells were treated with N-ethylmaleimide, which modifies thiol groups, rendering them incapable of binding cisplatin. Analysis using high-pressure liquid chromatography showed that approximately 99% of cellular glutathione was modified by N-ethylmaleimide. A plot of the amount of Pt bound to DNA versus [CDDP] for thiol-blocked cells is linear, with a slope similar to that of unblocked cells at high [CDDP]. Neither S-2-(3 aminopropylamino)ethanethiol (WR-1065) nor mesna, when added at clinically achievable concentrations (i.e., < approximately 300 microM), affected DNA platination. However, DNA platination was totally abolished by millimolar concentrations of the drug thiols (approximately 1.25 mM WR-1065 or approximately 5 mM mesna). Thus, the data show that endogenous thiols intercept cellular cisplatin, but this mechanism is less important at high [CDDP]. Moreover, therapeutic concentrations of drug thiols do not significantly affect DNA platination. A simple model that reproduces the experimental results of the amount of cisplatin binding to DNA as a function of [CDDP], time, and thiol content is proposed. The model takes into account passage of cisplatin and thiols through the cell membrane, binding of cisplatin to cellular thiols, and platination of DNA.

Synthesis, characterization, DNA binding and cytotoxic studies of platinum(II) and palladium(II) complexes of the 2,2'-bipyridine and an anion of 1,1-cyclobutanedicarboxylic acid

Two neutral complexes of formula [M(bpy)(cbdca)] [where M is palladium(II) (Pd(II)) or platinum(II) (Pt(II)), bpy is 2,2'-bipyridine and cbdca is anion of 1,1-cyclobutanedicarboxylic acid] have been synthesized. These water soluble complexes have been characterized by chemical analysis and conductivity measurements as well as 1H-NMR, ultraviolet-visible and infrared spectroscopy. In these complexes the ligand cbdca coordinates to Pt(II) or Pd(II) as bidentate with two oxygen atoms. They are nonelectrolyte in conductivity water. These complexes inhibit the growth of P388 lymphocytic leukemia cells and their targets are DNA. They invariably show ID50 values less than cisplatin. [Pt(bpy)(cbdca)] and [Pd(bpy)(cbdca)] have been interacted with calf thymus DNA and bind to DNA through coordinate covalent bond. In addition, the influence of binding of these complexes on the intensity of EtBr-DNA have been studied. They bind to DNA via a nonintercalating mode.

Comparison of the reactivity of oxaliplatin, pt(diaminocyclohexane)Cl2 and pt(diaminocyclohexane1)(OH2)2(2+) with guanosine and L-methionine

The initial rates of reactivity of oxaliplatin, its metabolites Pt(dach)Cl2 and Pt(dach)(OH2)2(2+) with guanosine and L-met in water, NaCl and phosphate were compared. Versus guanosine, the most reactive molecule was Pt(dach)(OH2)2(2+), about 40 fold that of oxaliplatin, the least reactive was Pt(dach)Cl2, Versus L-met, Pt(dach)(OH2)2(2+), was also the most reactive species but only about 2 fold more reactive than Pt(dach)Cl2 and oxaliplatin. Pt(dach)(OH2)2(2+) was approximately 3 fold less reactive versus methionine than guanosine whereas oxaliplatin and Pt(dach)Cl2 were about seven fold more reactive versus methionine than guanosine. Thus, the three platinum compounds oxaliplatin, Pt(dach)Cl2 and Pt(dach)(OH2)2(2+) react with L-met but only the Pt(dach)(OH2)2(2+) has a high reactivity with guanosine. Oxaliplatin, which is stable in water, has to be transformed in the presence of chloride in chloro-derivatives which are aquated to become active particularly versus guanosine. These data demonstrate that oxaliplatin has similarities with cisplatin in terms of chloride versus water coordination and in terms of dependence on chloride concentration for transformations.

Reactions of cisplatin hydrolytes with methionine, cysteine, and plasma ultrafiltrate studied by a combination of HPLC and NMR techniques

The reactions of cis-[PtCl(NH3)2(H2O)]+ with L-methionine have been studied by 1D 195Pt and 15N NMR, and by 2D[1H, 15N] NMR. When the platinum complex is in excess, the initial product, cis-[PtCl(NH3)2(Hmet-S)]+ undergoes slow ring closure to [Pt(NH3)2(Hmet-N,S)]2+. Slow ammine loss then occurs to give the isomer of [PtCl(NH3)(Hmet-N,S)]+ with chloride trans to sulfur. When methionine is in excess, a reaction sequence is proposed in which trans-[PtCl(NH3)(Hmet-S)2]+ isomerises to the cis-isomer, with subsequent ring closure reactions leading to cis-[Pt(Hmet-N,S)2]2+. Near pH 7, methionine is unreactive toward cis-[PtCl(OH)(NH3)2]. By contrast, L-cysteine reacts readily with cis-[PtCl(OH)(NH3)2] at pH 7, but there were many reaction products, including bridged species. Cis-[PtCl(OH)(NH3)2] reacts with reduced thiols in ultrafiltered plasma but these are oxidized if the plasma is not fresh or appropriately stored. With very low concentrations of the platinum complexes (35.5 microM), HPLC experiments (UV detection at 305 nm) indicate that the thiolate (probably cysteine) reactions become simpler as bridging becomes less important.

Inhibition of Escherichia coli DNA polymerase-I by the anti-cancer drug cis-diaminedichloroplatinum(II): what roles do polymerases play in cis-platin-induced cytotoxicity?

Activities of Escherichia coli DNA polymerase-I were examined in the presence of the anti-tumor drug cis-diaminedichloroplatinum(II) and its inactive geometric isomer trans-diaminedichloroplatinum(II). The trans-isomer did not inhibit the enzyme activity. The anti-tumor drug, on the other hand, retarded the enzyme in its ability to extend the primer strand of DNA. Two alternative mechanisms of inhibition, covalent binding of cis-diaminedichloroplatinum(II) to the polymerase and to the template DNA, were explored. Selective preincubations of the platinum drug with the polymerase and DNA reveal that the inhibition is primarily due to covalent binding to the enzyme. The rates of inhibition were found to be first order in enzyme and zeroth order in platinum in the concentration range 0.05-3.0 mM. A mechanism that deals with the formation of an initial platinum-polymerase-I complex with a binding constant > 10(5) M(-1) followed by a further reaction to form an inhibitory complex is consistent with the kinetic data. The rate limiting first order rate constant for the formation of the inhibitory complex is comparable to that observed for the thiol coordination of peptides containing cysteine residues. Analyses of known structures and functions of catalytic domains of various polymerases point to the direction that the inhibition is perhaps due to the distortion of the DNA binding domain of the enzyme due to platinum coordination.

NMR structures of a nonapeptide from DNA binding domain of human polymerase-alpha determined by iterative complete-relaxation-matrix approach

Nuclear magnetic resonance structures of a nonapeptide, ERFKCPCPT, selected from the DNA binding domain of human polymerase-alpha, were determined by complete relaxation matrix analysis of transverse NOE data. The structures exhibit a type III turn with residues KCPC, and the remaining residues exhibit non-ordered structures. The turn was confirmed by alpha, N (i,i+3) connectivity, a low temperature coefficient of NH chemical shift (-3.1 x 10(-3)) of the fourth residue, 3J(NHalpha) coupling constants, and characteristic CD peaks at 228 and 200 nm. Furthermore, phi and psi dihedral angles for the i + 1, and i + 2 residues of the turn are found to be -80 and -41 and -60 and -40 degrees. The first proline residue is trans- while the second exists in both cis- and trans- configurations, with trans- being more than 80% populated. The trans-configuration was established from C5alpha-P6alpha correlation and phi and psi angles of the proline. The five-membered proline ring is in DOWN puckered (C-beta-exo/C-gamma-endo) conformation. The structure of the peptide reveals that the two cysteine thiols are approximately 5 A(o) apart and appropriately positioned to covalently bind cis-diamminedichloroplatinum(II), a widely used anti-cancer drug.

Mechanisms of reaction of L-methionine with carboplatin and oxaliplatin in different media: a comparison with cisplatin

The activity of platinum compounds is dependent on nucleophile substitution reactions. In this paper, we study the reactivity of L-met with carboplatin, oxaliplatin and cisplatin by following with HPLC-UV the concentration of L-met and by characterizing the resulting adducts with LC-MS. In the absence of NaCl, in water, the initial rate at which L-met concentration decreases with cisplatin, oxaliplatin and carboplatin is 0.25 +/- 0.007, 0.057 +/- 0.01 and 0.17 +/- 0.02 mM h(-1), respectively. In phosphate buffer this rate is 0.056 +/- 0.009 for cisplatin, 0.019 +/- 0.001 and 0.13 +/- 0.02 for carboplatin and oxaliplatin, respectively. Reactions of L-met with cisplatin occurred via its conversion into monoaqua species in water and into phosphato-derivatives (AP) in phosphate buffer but finally the same methionine-platinum adducts M2 [(NH3)2(met)]Pt, M4 and M5 [(met)2]Pt were characterized. Reaction of carboplatin with L-met occurred via the formation of M0 [(NH3)2(met)(CBDCA)]Pt whose structure is consistent with the direct interaction of L-met with carboplatin. However, the same final products as those found with cisplatin were characterized. The reaction of oxaliplatin with L-met proceeded through a mechanism similar to that of carboplatin to give M7 [(met)(DACH)]Pt. In the presence of NaCl, cisplatin directly reacted with L-met to yield at least five methionine-platinum adducts. The reaction of carboplatin gave the same adducts suggesting its transformation into cisplatin. The reaction of oxaliplatin with L-met occurred via the formation of aquated species A [(OH)(Cl)(DACH)]Pt which readily underwent reaction with L-met to form M6 [(met)(Cl)(DACH)]Pt and M7. This study shows that the reactivity of cisplatin, carboplatin and oxaliplatin is dependent on the media in which they occur. The discrepancy between their reactions with L-met could partly explain their therapeutic differences.