Antitumor Platinum Research Articles

Recognition of DNA modified by trans‐[PtCl2NH3(4‐hydroxymethylpyridine)] by tumor suppressor protein p53 and character of DNA adducts of this cytotoxic complex

trans-[PtCl(2)NH(3)(4-Hydroxymethylpyridine)] (trans-PtHMP) is an analogue of clinically ineffective transplatin, which is cytotoxic in the human leukemia cancer cell line. As DNA is a major pharmacological target of antitumor platinum compounds, modifications of DNA by trans-PtHMP and recognition of these modifications by active tumor suppressor protein p53 were studied in cell-free media using the methods of molecular biology and biophysics. Our results demonstrate that the replacement of the NH(3) group in transplatin by the 4-hydroxymethylpyridine ligand affects the character of DNA adducts of parent transplatin. The binding of trans-PtHMP is slower, although equally sequence-specific. This platinum complex also forms on double-stranded DNA stable intrastrand and interstrand cross-links, which distort DNA conformation in a unique way. The most pronounced conformational alterations are associated with a local DNA unwinding, which was considerably higher than those produced by other bifunctional platinum compounds. DNA adducts of trans-PtHMP also reduce the affinity of the p53 protein to its consensus DNA sequence. Thus, downstream effects modulated by recognition and binding of p53 protein to DNA distorted by trans-PtHMP and transplatin are not likely to be the same. It has been suggested that these different effects may contribute to different antitumor effects of these two transplatinum compounds.

Effects of geometric isomerism in dinuclear antitumor platinum complexes on their interactions with N-acetyl-L-methionine

Effects of geometric isomerism in dinuclear antitumor platinum complexes on their interactions with N-acetyl-L-methionine

Effects of geometric isomerism in dinuclear platinum antitumor complexes on aquation reactions in the presence of perchlorate, acetate and phosphate

The aquation and subsequent reactions of the dinuclear Pt antitumor complexes [{trans-PtCl(NH(3))(2)}(2)(mu-NH(2)(CH(2))(6)NH(2))](2+) (1,1/t,t) and [{cis-PtCl(NH(3))(2)}(2)(mu-NH(2)(CH(2))(6)NH(2))](2+) (1,1/c,c) in 15 mM perchlorate, acetate or phosphate solutions were followed at 298 K by [(1)H,(15)N] HSQC 2D NMR spectroscopy. Rate and equilibrium constants for the initial reversible aquation and the subsequent reversible reaction with phosphate or acetate are reported. The rate constant for the first aquation step is two-fold lower for 1,1/c,c than 1,1/t,t but the anation rate constants are similar so that the equilibrium lies further towards the chloro form for the 1,1/c,c compound. A pK (a) value of 6.01+/-0.03 was determined for the diaquated species [{cis-Pt(NH(3))(2)(H(2)O)}(2)(mu-NH(2)(CH(2))(6)NH(2))](4+) (1,1/c,c-3) which is 0.4 units higher than that of the 1,1/t,t compound. The rate constants for the binding of acetate and phosphate to 1,1/t,t are similar, but the rate constant for the reverse reaction is close to ten-fold higher in the case of phosphate so that equilibrium conditions are attained more rapidly (12 h compared with 64 h). On the other hand, for 1,1/c,c the rate constants for the forward and reverse reactions with acetate and phosphate are quite similar so that equilibrium conditions are reached very slowly (80-100 h) and a greater proportion of phosphate-bound species are present. The reduced lability of the bound phosphate for 1,1/c,c is attributed to the formation of a macrochelate phosphate-bridged species which was characterized by (31)P NMR and ESI-MS. The speciation profiles of 1,1/t,t and 1,1/c,c under physiological conditions are explored.

Effects of geometric isomerism in dinuclear antitumor platinum complexes on their interactions with N-acetyl-L-methionine

In this study, the reactions of N-acetyl-L-methionine (AcMet) with [{trans-PtCl(NH(3))(2)}(2)-mu-H(2)N(CH(2))(6)NH(2)](NO(3))(2) (BBR3005: 1,1/t,t 1) and its cis analog [{cis-PtCl(NH(3))(2)}(2)-mu-{H(2)N(CH(2))(6)NH(2)}]Cl(2) (1,1/c,c 2) were analyzed to determine the rate and reaction profile of chloride substitution by methionine sulfur. The reactions were studied in PBS buffer at 37 degrees C by a combination of multinuclear ((195)Pt, {(1)H-(15)N} HSQC) magnetic resonance (NMR) spectroscopy and electrospray ionization time of flight mass spectrometry (ESITOFMS). The diamine linker of the 1,1/t,t trans complex was released as a result of the trans influence of the coordinated sulfur atom, producing trans-[PtCl(AcMet)(NH(3))(2)](+) (III) and trans-[Pt(AcMet)(2)(NH(3))(2)](2+) (IV). In contrast the cis geometry of the dinuclear compound maintained the diamine bridge intact and a number of novel dinuclear platinum compounds obtained by stepwise substitution of sulfur on both platinum centers were identified. These include (charges omitted for clarity): [{cis-PtCl(NH(3))(2)}-mu-NH(2)(CH(2))(6)NH(2)-{cis-Pt(AcMet)(NH(3))(2)}] (V); [{cis-Pt(AcMet)(NH(3))(2)}(2)-mu-NH(2)(CH(2))(6)NH(2)] (VI); [{cis-PtCl(NH(3))(2)}-mu-NH(2)(CH(2))(6)NH(2)-{PtCl(AcMet)NH(3)] (VII); [{PtCl(AcMet)(NH(3))}(2)-mu-NH(2)(CH(2))(6)NH(2)] (VIII); [{trans-Pt(AcMet)(2)(NH(3))}-mu-NH(2)(CH(2))(6)NH(2)-{PtCl(AcMet)(NH(3))] (IX) and the fully substituted [{trans-Pt(AcMet)(2)(NH(3))}(2)-mu-{NH(2)(CH(2))(6)NH(2)] (X). For both compounds the reactions with methionine were slower than those with glutathione (Inorg Chem 2003, 42:5498-5506). Further, the 1,1/c,c geometry resulted in slower reaction than the trans isomer, because of steric hindrance of the bridge, as observed previously in reactions with DNA and model nucleotides.

Preclinical anti-tumor activity of a new oral platinum(IV) drug LA-12

A novel anti-tumor platinum(IV) complex, coded as LA-12, with a bulky adamantylamine ligand displaying oral activity was prepared and its oral activity was evaluated. The murine ADJ/PC6 plasmacytoma and human A2780 ovarian carcinoma tumor model were used to evaluate the in vivo anti-tumor activity of a single dose and also of repeated doses with comparison to the activity of cisplatin and of the platinum(IV) complex satraplatin. The acute toxicity of LA-12 in mice is relatively low (maximum tolerated dose 1000 mg/kg), and the effective dose is comparable to that of cisplatin and higher than that of satraplatin. The therapeutic index derived from this is very high (250). In the human tumor model, two repeated dose schedule regimens were evaluated. LA-12 exerted a significantly higher anti-tumor activity than other substances, i.e. cisplatin and satraplatin, in repeated doses on the murine ADJ/PC6 plasmacytoma tumor model. The dailyx5 repeated dose regimen was selected for further evaluation.

Synthesis, characterization, and tumor selectivity of a polyphosphazene–platinum(II) conjugate

A new amphiphilic poly(organophosphazene) was synthesized by stepwise nucleophilic substitutions with a hydrophilic methoxy poly(ethylene glycol) with an average molecular weight of 350 (MPEG350) and a hydrophobic glycyl- l-glutamate as side groups, and then an antitumor (dach)platinum(II) (dach: trans-(±)-1,2-diaminocyclohexane) moiety was conjugated to the polymer using the dipeptide as a spacer. This polymeric platinum conjugate was found to be accumulated in the tumor tissue to a remarkably greater extent than in the normal tissue (tumor/tissue ratio >4), probably due to the excellent EPR effect and the long circulating properties of the polymer conjugate ( t 1/2β = 6.2 h and AUC = 4020 nmol h/ml) compared with carboplatin ( t 1/2β = 0.42 h and AUC = 120 nmol h/ml). The polymer conjugate also exhibited high in vitro cytotoxicity comparable to cisplatin against several human tumor cells tested.

A Surprisingly Stable Macrochelate Formed from the Reaction of Cis Dinuclear Platinum Antitumor Compounds with Reduced Glutathione

The structurally unique macrochelate [{Pt(en)}2-mu-{H2N(CH2)6 NH2}-mu-(SG)] (I) is the principal product of the reaction of the dinuclear compound [{PtCl(en)}2-mu-{H2N(CH2)6 NH2}]Cl2 (1) with reduced glutathione (GSH) in a stoichiometric 1:1 ratio in phosphate buffered saline (PBS) (pH 7.35). The macrochelate is formed through simultaneous bridging of the hexanediamine linker and glutathione thiolate. This represents a novel structure for glutathione adducts of platinum. At higher (1:4) ratios of Pt complex to GSH, an interesting interchange between bridged Pt-(SG)-Pt and terminal Pt-SG species is observed with the diamine linker still remaining intact in all cases. The integrity of I is further evident when reaction ratios are increased to 1:4 (Pt complex/GSH), and additional minor products are identified as [{Pt(en)SG}2-mu-{NH2(CH2)6 NH2}] (II), which transforms to [{Pt{NH2(CH2)2 NH2}(SG)}2-mu-{H2N(CH2)6 NH2}-mu-(SG)] (III), where the chelate ring is broken to produce a dangling monodentate ethylenediamine. The chemical shifts of the Pt-NH2 linker in all compounds are explained by consideration of the enhanced rigidity of the macrochelate (I) leading to shielding in comparison to the "open" monodentate structures (II, III). The remarkable stability of I is discussed in terms of possible biological implications.

Experimental study of renal disorder caused by oxaliplatin in rat renal cortical slices

Oxaliplatin is a newly developed antitumor platinum complex that is known to have low nephrotoxicity. The inhibitory effects of oxaliplatin on several tubular functions were compared with those of cisplatin and carboplatin, using a renal cortical slice system. Rat renal cortical slices were incubated with 0.25 mM to 2.0 mM of oxaliplatin, cisplatin, on carboplatin at 37 degrees C for 120 min. Para-amino hippuric acid (PAH) accumulation, gluconeogenesis, and ATP content in the rat renal slices were determined. PAH accumulation was not inhibited by carboplatin, but it was significantly inhibited by oxaliplatin and cisplatin. Inhibition of PAH accumulation by cisplatin was greater than that by oxaliplatin. Gluconeogenesis was not decreased by carboplatin, but it was suppressed by oxaliplatin and cisplatin in a dose-dependent manner. The decrease in gluconeogenesis induced by oxaliplatin was significantly greater than that induced by cisplatin. ATP content in the renal slices was decreased by oxaliplatin, cisplatin, and carboplatin to almost the same extent. As an in vivo experiment, 21.6 mmole/kg of oxaliplatin, cisplatin, or carboplatin was injected into rats; then blood urea nitrogen (BUN) and serum creatinine were determined on day 4. Significantly elevated levels of BUN and serum creatinine were observed only in the rats injected with cisplatin. Oxaliplatin did not cause nephrotoxicity in the in vivo study; however, the nephrotoxic pattern of oxaliplatin observed in the renal cortical-slice system resembled that of cisplatin. The reason why oxaliplatin is less nephrotoxic than cisplatin in vivo could not be fully elucidated in the present experiment using the renal cortical-slice system.

Immunohistochemical localizations of secretin, cholecystokinin, and somatostatin in the rat small intestine after acute cisplatin treatment

Cisplatin (CDDP) is an antitumor platinum complex that causes the well-studied side effect of renal tubular failure. In the present study, the acute effects of CDDP treatment on the localization of gut hormones in the rat small intestine were examined by immunohistochemistry. Male Sprague–Dawley rats were used for these experiments. Rats were injected intravenously with CDDP (3 mg/kg) in saline or were left untreated (control). After the rats were euthanized at 1, 3, 5, or 10 days after CDDP treatment, the small intestines (duodenum, jejunum, and ileum) were quickly removed, fixed, embedded in paraffin, and cut. No mucosal toxicity was detected by histopathological observation in any of the intestines of CDDP-treated rats. The immunohistochemical detection was performed using anti-secretin, anti-cholecystokinin (CCK), and anti-somatostatin with the avidin–biotin-immuno-peroxidase procedure. The total number of immunoreactive cells per complete cross-section was counted. In the duodenum, the numbers of secretin-immunoreactive cells and somatostatin-immunoreactive cells were dramatically increased 5 days after CDDP treatment. In the jejunum, the number of CCK-immunoreactive cells was increased 1 day after CDDP treatment and those of secretin-immunoreactive cells and CCK-immunoreactive cells were increased 5 days after CDDP treatment. In the ileum, the number of CCK-immunoreactive cells was increased 1 day after CDDP treatment. The change in the secretin-immunoreactive cell count may be caused by metabolic inhibition of gastrin following CDDP-induced nephrotoxicity. The change in the CCK-immunoreactive cell count may promote the excretion of bile. Therefore, somatostatin may regulate secretin and CCK secretion. We conclude that the distribution of these hormone-immunoreactive cells in the rat small intestine might be controlled by CDDP-induced nephrotoxicity without gut mucosal toxicity.

Synthesis and structure-activity relationship of novel antitumoral platinum xanthate complexes.

To establish structure-activity relationships, derivatives of a recently described sulfur-containing antitumoral platinum complex, bis(O-ethyldithiocarbonato)platinum(II), named thioplatin, were analyzed. Twenty different bis(O-alkyldithiocarbonato)platinum(II) complexes were synthesized and tested for cytotoxic activity in a panel of six human tumor lines. Derivatives with up to 7-fold increased activity compared to thioplatin and up to 25-fold more activity than cisplatin were identified. Bis(O-alkyldithiocarbonato)platinum(II) complexes with short n-alkyl chains such as methyl, ethyl, propyl, and butyl were found to be superior to compounds with long n-alkyl chains such as hexyl, octyl, and decyl. Complexes derived from secondary xanthates displayed significantly higher activity than those derived from primary xanthates with the same number of C atoms. Like thioplatin, all tested platinum complexes were more active at pH 6.8 than at pH 7.4. A pH of 6.8 and lower has been frequently found in solid tumors because of the tendency of tumor cells to undergo anaerobic fermentation. Drugs with such pH-dependent antitumoral activity have an improved therapeutic index compared to drugs that are active irrespective of pH.

DNA interactions of new antitumor platinum complexes with trans geometry activated by a 2-metylbutylamine or sec-butylamine ligand

The global modification of mammalian and plasmid DNAs by novel platinum compounds, trans-[PtCl 2(NH 3)(Am)], where Am=2-methylbutylamine or sec-butylamine was investigated in cell-free media using various biochemical and biophysical methods. These modifications were analyzed in the context of the activity of these new compounds in several tumor cell lines including those resistant to antitumor cis-diamminedichloroplatinum(II) (cisplatin). The results showed that the replacement of one amine group by 2-methylbutylamine or sec-butylamine ligand in clinically ineffective trans-diamminedichloroplatinum(II) (transplatin) resulted in a radical enhancement of its activity in tumor cell lines so that they are more cytotoxic than cisplatin and exhibited significant antitumor activity including activity in cisplatin-resistant tumor cells. Importantly, this replacement also markedly altered DNA binding mode of transplatin and reduced the efficiency of repair systems to remove the adducts of the new analogues from DNA. The results support the view that one strategy to activate trans geometry in bifunctional platinum(II) compounds including circumvention of resistance to cisplatin may consist in a chemical modification of the ineffective transplatin which results in an increased efficiency to form DNA interstrand cross-links.

DNA-protein cross-linking by trans-[PtCl(2)(E-iminoether)(2)]. A concept for activation of the trans geometry in platinum antitumor complexes.

The structure-pharmacological activity relationships generally accepted for antitumor platinum compounds stressed the necessity for the cis-[PtX(2)(amine)(2)] structure while the trans-[PtX(2)(amine)(2)] structure was considered inactive. However, more recently, several trans-platinum complexes have been identified which are potently toxic, antitumor-active and demonstrate activity distinct from that of conventional cisplatin (cis-[PtCl(2)(NH(3))(2)]). We have shown in the previous report that the replacement of ammine ligands by iminoether in transplatin (trans-[PtCl(2)(NH(3))(2)]) results in a marked enhancement of its cytotoxicity so that it is more cytotoxic than its cis congener and exhibits significant antitumor activity, including activity in cisplatin-resistant tumor cells. In addition, we have also shown previously that this new trans compound (trans-[PtCl(2)(E-iminoether)(2)]) forms mainly monofunctional adducts at guanine residues on DNA, which is generally accepted to be the cellular target of platinum drugs. In order to shed light on the mechanism underlying the antitumor activity of trans-[PtCl(2)(E-iminoether)(2)] we examined oligodeoxyribonucleotide duplexes containing a single, site-specific, monofunctional adduct of this transplatin analog by the methods of molecular biophysics. The results indicate that major monofunctional adducts of trans-[PtCl(2)(E-iminoether)(2)] locally distort DNA, bend the DNA axis by 21 degrees toward the minor groove, are not recognized by HMGB1 proteins and are readily removed from DNA by nucleotide excision repair (NER). In addition, the monofunctional adducts of trans-[PtCl(2)(E-iminoether)(2)] readily cross-link proteins, which markedly enhances the efficiency of this adduct to terminate DNA polymerization by DNA polymerases in vitro and to inhibit removal of this adduct from DNA by NER. It is suggested that DNA-protein ternary cross-links produced by trans-[PtCl(2)(E-iminoether)(2)] could persist considerably longer than the non-cross-linked monofunctional adducts, which would potentiate toxicity of this antitumor platinum compound toward tumor cells sensitive to this drug. Thus, trans-[PtCl(2)(E-iminoether)(2)] represents a quite new class of platinum antitumor drugs in which activation of trans geometry is associated with an increased efficiency to form DNA-protein ternary cross-links thereby acting by a different mechanism from 'classical' cisplatin and its analogs.

Uptake of antitumor platinum(II)-complexes by cancer cells, assayed by inductively coupled plasma mass spectrometry (ICP-MS)

A systematic study on intracellular Pt uptake and Pt accumulation ratio in breast cancer MCF-7 cell line has been performed on a number of Pt(II)-complexes, namely cisplatin, carboplatin and oxaliplatin, clinically employed as antitumor drugs, trans- and cis-[Pt(Cl)2(pyridine)2] and cis-[Pt(Cl)2(pyridine)(5-SO3H-isoquinoline)] complexes, previously investigated also as potential telomerase inhibitors. In particular, long incubation times have been chosen in order to understand the fate of the complexes in the cells. For this purpose, sub-acute drug concentrations must be employed and, therefore, a very sensitive method of analysis like as inductively coupled plasma mass spectrometry (ICP-MS) superior to the widely employed atomic absorption spectroscopy (AAS) has been adopted. Any relationships among uptake/accumulation and several parameters such as drug structure, lipophilicity, drug concentration and incubation time have been sought and analyzed: the bulk of data point for a passive diffusion mechanism through the cell membrane.

Enhanced antitumor activitiy of trans(±)-1,2-Diaminocyclo- hexaneglutamatoplatinum(II) formulated with stealth liposome

The antitumor platinum(II) compound, [Pt(dach)(Glu)] (dach= trans(±)-1,2-diaminocyclohexane, Glu=glutamate) was formulated with a stealth liposome to improve its biological activity. Liposomes were composed of PC/PEG2000-PE/CH (PC=1,2-diacyl-glycero-3-phosphocholine; PEG2000-PE=poly(ethylene glycol)2000-1,2-diacyl-glycero-3-phosphoethanolamine; CH=cholesterol) involving different acyl moieties of phospholipids such as DO (dioleoyl), DM (dimyristoyl) or DS (distearoyl) group. Among the different acyl groups in the stealth liposomes, the DM formulation was optimal for the preparation of the liposomal [Pt(dach)(Glu)] at the mole ratio of DMPC/PEG2000-DMPE/CH=50/5/45 and at the weight ratio of drug/lipid=1/20, which is represented as l-[Pt(dach)(Glu)]. In vitro cytotoxicity was examined in sensitive A2780 and ME180 and their cisplatin-resistant A2780/PDD and ME180/PDD cancer cells. l-[Pt(dach)(Glu)] was 2∼3 times more cytotoxic than the free complex [Pt(dach)(Glu)] and cisplatin in sensitive cells, and 4∼8 times more cytotoxic in resistant cells. Thus, the resistance index of l-[Pt(dach)(Glu)] was 1.3∼2 while those of the free complex and cisplatin were 5∼6, which indicates that l-[Pt(dach)(Glu)] overcome the cisplatin resistance in both resistant cells. In vivo antitumor activity was assayed against the L1210/S leukemia. The optimal activities (% T/C) of the free complex and l-[Pt(dach)(Glu)] were >459/20 and >442/200 mg/kg, respectively. Considering the amount of the platinum complex in l-[Pt(dach)(Glu)], the liposomal [Pt(dach)(Glu)] displayed 2-fold higher drug potency than the free complex. The biodistribution experiment using LE52 tumor-bearing mouse showed excellent lung targeting property of l-[Pt(dach)(Glu)].

Effects of a piperidine ligand on DNA modification by antitumor cisplatin analogues.

Replacement of the ammine group in antitumor cisplatin by a heterocyclic ligand (piperidine, piperazine, or 4-picoline) results in reduction of cytotoxicity in human ovarian cancer cells. DNA is generally believed to be a major pharmacological target of antitumor platinum complexes. Therefore, we examined conformation of oligodeoxyribonucleotide duplexes containing a cross-link of cis-[PtCl(2)(NH(3))(piperidine)], their recognition by high mobility group proteins, and nucleotide excision repair; that is, some of the processes that may mediate antitumor effects of platinum drugs. The replacement does not affect the DNA binding mode including conformational alterations and excision of the cross-links. The results suggest that in certain cancer cells the lower cytotoxicity of cis-[PtCl(2)(NH(3))(piperidine)] might be partially associated with reduced affinity of the high mobility group proteins to the major intrastrand cross-links of this analogue relative to the same adducts of cisplatin. Besides this and a number of other biochemical factors, the reduced intracellular accumulation with subsequent effects on the level of DNA platination in the cells may also contribute to the reduced cytotoxicity of cis-[PtCl(2)(NH(3))(piperidine)]. The results support the view that the concept based on the design of the complexes structurally derived from cisplatin that do not present an altered DNA binding mode may be less effective in the search for new platinum drugs that would overcome cisplatin resistance.

Toward the design of novel polynuclear platinum antitumor complexes: a polydentate ligand system based on dipyridylamine and 1,3,5-trimethylenebenzene.

A novel hexadentate ligand, N,N,N',N',N",N"-hexa(2-pyridyl)-1,3,5-tris(aminomethyl)benzene (L), was designed and synthesized. The X-ray structure analysis reveals that the three dipyridylamine (DPA) groups of L are almost perpendicular to the central trimethylenebenzene, and two of them are spacially close to each other while the third one is further apart. The trinuclear Pt(II) complexes [Pt(3)LCl(6)] (1) and [Pt(3)L(CBDCA)(3)] (2) (where CBDCA represents cyclobutane dicarboxylic acid) were prepared and fully characterized by IR, NMR, and ESMS spectroscopy. A mononuclear complex, [PtL(CBDCA)] (3), was also prepared and structurally characterized, which suggests that controlled formation of mono-, di-, and trinuclear complexes with L is possible. Spectroscopic data showed that complexes 2 and 3 are able to bind to calf thymus DNA and their CBDCA group can be readily replaced by thiourea.

Reaction of polynuclear platinum antitumor compounds with reduced glutathione studied by multinuclear (1H, 1H-15N gradient heteronuclear single-quantum coherence, and 195Pt) NMR spectroscopy.

A possible explanation for the low bioavailability of platinum antitumor compounds is their high reactivity with the sulfur-containing tripeptide glutathione (GSH; deprotonated GSH = SG). GSH is located in the intracellular matrix of the cell with a normal concentration of 5-10 mM. In vivo, only a small fraction of the administered drug will migrate into the cell, resulting in relatively high concentrations of GSH compared to that of the drug. The products of the reactions of [[trans-PtCl(NH(3))(2)](2)-mu-[trans-Pt(NH(3))(2)(NH(2)(CH(2))(6)NH(2))(2)]](NO(3))(4) (BBR3464; 1,0,1/t,t,t, n = 6), [[trans-PtCl(NH(3))(2)](2)-mu-(H(2)N(CH(2))(6)NH(2))](NO(3))(2) (BBR3005; 1,1/t,t, n = 6), [[trans-PtCl(NH(3))(2)](2)-mu-(H(2)N(CH(2))(3)NH(2)(CH(2))(4)NH(2))]Cl(3) (BBR3571; 1,1/t,t-spermidine, n = 3, 4), and trans-[PtCl(2)(NH(3))(2)] (t-DDP) with reduced GSH in phosphate-buffered saline (pH 7.35) have been characterized by (1)H, (195)Pt, and (1)H(-)(15)N gradient heteronuclear single-quantum coherence NMR spectroscopy and high-performance liquid chromatography (HPLC) coupled with electrospray ionization time-of-flight mass spectrometry to determine likely metabolites of the complexes with GSH. Chemical shifts (NMR) and retention times (HPLC) established via analysis of the t-DDP profile served as a fingerprint to compare results obtained for the products afforded by the degradation of the polynuclear compounds by GSH. Identical kinetic profiles and chemical shifts between the metabolites and the t-DDP/GSH products allowed identification of the final product for the 1:2 Pt:GSH reaction as a dinuclear species [[trans-Pt(SG)(NH(3))(2)](2)-mu-SG], in which glutathione bridges the two platinum centers via only the sulfur atom.

Synthesis and antitumor activity of novel thermosensitive platinum(II)–cyclotriphosphazene conjugates

Thermosensitive cyclotriphosphazenes bearing alkoxy poly(ethylene glycol) and amino acid esters as side groups could be functionalized to chelate the antitumor (diamine)platinum(II) moiety through the dicarboxylate group of the amino acid substituent on the cyclic phosphazene ring. Surprisingly, like the precursor cyclotriphosphazenes, these (diamine)platinum(II)–cyclotriphosphazene conjugates were also found to exhibit variable lower critical solution temperatures (LCST) in the wide range of 12 to 92 °C. Furthermore, the present conjugates have shown outstanding in vitro and in vivo antitumor activities due to controlled release of the antitumor (diamine)platinum(II) moiety with hydrolytic degradation of the phosphazene ring. A few of these conjugates have shown LCSTs below body temperature, and it has been shown from a model animal experiment that the conjugates with a LCST below body temperature may be applied to local drug delivery by direct intratumoral injection.

Genotoxic Action of Cycloplatam, a New Platinum Antitumor Drug, on Mammalian Cells in vivo and in vitro

Cycloplatam (CP), a new antitumor platinum compound of the second generation, was first synthesized in Russia. This drug shows less toxicity in vivo than the widely used cisplatin and carboplatin and a higher antitumor activity than carboplatin. CP is not nephrotoxic with respect to the platinum-based antitumor agents. CP is actually studied in clinical phase II trials in Russia and Armenia. Promising results were obtained in patients with lung, ovary, and prostate cancers. The aim of this work was to study the micronuclei (MN) inducing effect of CP in vivo in murine bone marrow cells and in human lymphocytes in vitro. The mutagenic activity of CP in bone marrow of mice was significantly lower than that of cisplatin at equitoxic doses. In human lymphocytes CP induced a dose-dependent increase of MN, beginning at a very low dose (0.1 µM). Our results showed that CP is much less toxic and MN inducing in vivo in murine bone marrow than cisplatin. In vitro data evidenced that CP is more toxic and genotoxic to human cells than cisplatin. The evidence of a MN-induced activity of an antitumor drug suggests a potential risk for long-time survivors.

New clues for platinum antitumor chemistry: kinetically controlled metal binding to DNA.

From the metal ions and metal compounds that are known to bind to DNA, many anticancer Pt(II) and Ru(II)Ru(III) compounds are known to have ligand-exchange kinetics in the same order of magnitude as the division of tumor cells. The present article discusses this process in detail with special attention to cisplatin and related compounds and the cellular binding sites and processes of such compounds. Detailed platinated DNA structures are presented and discussed in light of the mechanistic studies of metal antitumor compounds. It is now known that platinum antitumor drugs eventually end up on the DNA. However, it remains a challenge to understand how (fast) they reach the DNA and how they are removed. The kinetics of ligand exchange around platinum appear to play a crucial role, and the possible role of other ligands as intermediates, especially those with S-donor sites, is of great interest. New types of Pt compounds with additional functionalities influencing DNA binding and kinetics are discussed in the context of steric and H-bonding properties. A comparison is made with more sterically crowded Ru complexes. The effects on activity and correlations with structural and kinetic properties are clues in understanding the biological activities of these classes of compounds.