Antileukemic properties of organoplatinum complexes

Crystal structure of di-chlorido-(1,2-phenyl-enedi-amine-κ2N,N')platinum(II)

In the crystal structure of the title compound, almost planar [PtCl₂{(C₆H₄)(NH₂)₂}] mol­ecules are stacked into columns along the c axis, suggesting Pt⋯Pt inter­actions.

The Pt^II atom in the title compound, [PtCl₂{(C₆H₄)(NH₂)₂}], lies on a twofold rotation axis and has a slightly distorted square-planar coordination environment defined by two N atoms of an 1,2-phenyl­enedi­amine ligand and two Cl⁻ ions. In the crystal, the planar complex mol­ecules are stacked parallel to the c axis, resulting in a columnar structure. In a column, an infinite almost straight Pt⋯Pt chain is formed, suggesting weak metal–metal inter­actions [Pt⋯Pt = 3.3475 (8) Å]. The crystal packing is stabilized by a three-dimensional N—H⋯Cl hydrogen-bonding network between the amino groups and the Cl ligands of adjacent mol­ecules.

Novel Palladium(II) and Platinum(II) Complexes with a Fluoropiperazinyl Based Ligand Exhibiting High Cytotoxicity and Anticancer ActivityIn Vitro

cis-Dichloro-palladium(II) andcis-dichloro-platinum(II) complexes (2,4) of the general formula [M(N-N)Cl2] (M=Pd(II) and Pt(II), N-N= 1,2-diamino-4-fluoro-5-(4-methyl-1-piperazinyl) benzene, (DFMPB)) and the dicationic palladium(II) complex [Pd(N-N)(CH3CN)2](BF4)2(3) have been prepared and characterized by elemental analysis,1H-NMR-, mass spectroscopy, and IR spectroscopy. The cytotoxic effect of these complexes against MDA-231 and MCF-7 human breast cancer cell lines and K562 human leukemia cell line has been studied. The influence was dose dependent and varies with cell type. The palladium(II) complex (2) showed superior cytotoxic effect compared with the corresponding platinum(II) complex and the standard, cisplatin, when tested against all the above cell lines.

Unusual reactivity of cisplatin analogs that bear o-phenylenediamine ligands: insights for the design of more effective cytotoxic agents

The stabilities of dichloro(o-phenylenediamine)platinum(II) (1) and several 4,5-disubstituted analogs [i.e., with: Cl (2), Br (3), Me (4), or MeO (5)] were investigated under various aqueous conditions. The Pt complexes 1-5- decomposed by reactions which were independent of the amount of chloride in the medium. The poor aqueous stabilities of 1-5 were attributed to two factors: 1) The compounds underwent facile oxidation reactions in aqueous solution at pH 7.4 and 37 degrees C, resulting in the formation of intensely colored Pt-species as well as H2O2. Compounds 2 and 3 oxidized considerably faster than 1, 4, and 5. Based on the redox behavior and UV-Vis spectra of the decomposition products, it is proposed that they are o-benzoquinonediimine Pt complexes. 2) Compound 4 underwent an unusually rapid substitution reaction with L-methionine, a component of the culture medium, whereby both of the chloro ligands of platinum were replaced by an N,S-chelated methionine. At an L-methionine concentration of 0.5 mM, the reaction ran to completion within 1 min. Thus, the weak growth inhibitory activities of 1-5 on human cancer cells in vitro was likely a result of their poor chemical stability in the culture medium. Based on a knowledge of the decomposition pathways, analogs were designed to be resistant to these types of reactions. Dichloro(o-aminomethylaniline)platinum(II) (6) and [bis-1,2(aminomethyl)benzene]-di-chloroplatinum(II) (7) were synthesized and their aqueous stabilities investigated. Both 6 and 7 were considerably more stable than 1-5 under aqueous conditions, as well as being more effective in inhibiting the growth of human cancer cells in vitro.

Synthesis and antitumor activities of platinum complexes of unsymmetrical alicyclic diamines as carrier ligands

The synthesis and biological activities of the platinum complexes of 2-aminomethylaziridine, 2-aminomethylazetidine, 2-aminomethylpyrrolidine, 2-aminomethylpiperidine as carrier ligands are described. The platinum complexes of 2-aminomethylazetidine and 2-aminomethylpyrrolidine are significantly effective against murine tumors. In particular, 2-aminomethylazetidine (1,1-cyclobutanedicarboxylato)platinum II (13) and 2-aminomethylpyrrolidine(1,1-cyclobutanedicarboxylato)platin um II (16) exhibited potent antitumor activity and were soluble in water, and their antitumor activities against Colon 26 carcinoma (sc-ip system) were superior to CBDCA and comparable to CDDP.

Structural characterization of cisplatin analogues by fast atom bombardment (FAB) and laser microprobe mass spectrometry (LAMMA)

The present study is concerned with the investigation of the potentials and limitations of fast atom bombardment (FAB) and laser microprobe mass spectrometry (LAMMA) for the structural characterization of a series of cisplatin analogues. The limiting factors for obtaining good quality FAB spectra are the solubility and the stability of the organometallic platinum complexes in the FAB matrix. In the case of a suitable matrix being found, molecular weight information is derived from the (M + H)+ and/or (M - H)- ions. Drawbacks of the application of FAB are (i) the low signal intensities of the molecular ion-like species as compared to the matrix signals and (ii) the scarcity of fragmentation necessary for structure determination. Combination of FAB with tandem mass spectrometry was used to overcome these problems. LAMMA provides a valuable alternative for the direct mass spectral analysis of cisplatin analogues. For some compounds, LAMMA results in useful mass spectra, whereas FAB fails. The abundant fragmentation yields structural information which is complementary for positive and negative ions. The laser power density applied to the sample is of critical importance for the quality of the spectra.

Displacement of the bidentate malonate ligand from (d,l-trans-1,2-diaminocyclohexane)malonatoplatinum(II) by physiologically important compounds in vitro

Previous studies of platinum(II) compounds with bidentate leaving ligands have emphasized the contrast between the stability of the bidentate leaving ligand in vitro (T1/2 greater than 11 days in water) and the apparent reactivity of these bidentate platinum compounds in vivo. However, none of these studies actually measured the stability of these compounds in tissue culture medium (or in any other reaction mixture resembling in vivo conditions). The experiments described in this paper were designed to measure the stability and fate of (d,l-trans-1,2-diaminocyclohexane)malonatoplatinum(II) [Pt(mal)(trans-dach)] in RPMI-1640 tissue culture medium. The T1/2 for displacement of the malonate ligand in this medium was 9.5 hr at 37 degrees. Of the inorganic anions present in the medium, chloride accounted for the greatest displacement of the malonate ligand. However, at the concentrations with which it is found in tissue culture medium and in blood, bicarbonate was nearly as effective as chloride at displacing the malonate ligand. This observation is of particular significance because the bicarbonatoplatinum complex is unstable and the bicarbonate displacement reaction appears to represent a major non-enzymatic pathway for the formation of the biologically active aquated platinum complexes. At the concentrations with which they occur inside the cell, phosphates may play a similar role. Of the amino acids present in the medium, glutathione and the sulfur-containing amino acids were 50- to 400-fold more effective at displacing the malonate ligand than the other amino acids in RPMI-1640 medium. In the case of methionine, the reaction with Pt(mal)(trans-dach) was shown to be a direct displacement (SN2) reaction at physiological methionine concentrations. When Pt(mal)(trans-dach) was incubated at 37 degrees for 24 hr in RPMI-1640 medium, the major transformation products formed were (d,l-trans-1,2-diaminocyclohexane)methionineplatinum(II) (38%), other amino acid-platinum complexes (19%), and (d,l,-trans-1,2-diaminocyclohexane)dichloroplatinum(II) (14%). Eleven percent of the Pt(mal)(trans-dach) remained intact. Mass spectrometry and 1H-NMR indicated that the (d,l-trans-1,2-diaminocyclohexane)methionineplatinum(II) complexes that formed in RPMI-1640 medium consisted of approximately 60% of the bidentate mono-methionine complex coordinated to platinum at the sulfur and alpha-amino positions and 40% of the bis-methionine complex, presumably coordinated at the sulfurs.(ABSTRACT TRUNCATED AT 400 WORDS)

Advances in platinum cancer chemotherapy. Advances in the design of cisplatin analogues

In the past 4 years substantial progress has been made in the development of platinum cancer chemotherapy. A number of drug candidates have undergone clinical trials and one 'second generation' platinum drug, carboplatin, has been approved for use in the treatment of ovarian and small cell lung cancer. This review covers the major developments since the last international conference on Platinum Chemotherapy in Vermont, and attempts to highlight the primary factors that appear to be influencing the synthesis and screening of potential third generation platinum drugs. A predominant feature in the evaluation of analogues has been the emphasis on chelating diamine complexes, in particular those of diaminocyclohexane, which show activity in L1210 tumours that are resistant to cisplatin, and the use of a wide range of carboxylate ligands as a means of circumventing solubility and toxicity problems inherent in the parent compounds. There has also been an increased effort in studies relating to complexes containing mixed amines and functionalised amines, building on the assumption, which remains valid to date, that two amines are a necessary requirement for anti-tumour activity. Efforts have also been made to address the use of complexes containing biologically active ligands, and the concept of targeting compounds to specific organs and formulating drugs to achieve more specific activity or controlled release of drugs with lower toxicities. These may provide a viable route to drugs that can be administered more easily, for example by an oral route, or show a different spectrum of activity. However, it may prove difficult to adequately characterise these more complex systems. The major problem encountered in evaluating cisplatin analogues, as with other prospective cancer drugs, is finding reproducible anti-tumour screens that are predictive of the behaviour of the drugs in the clinic. Progress is being made in the development of sensitive and resistant human tumour xenograft lines and this area should be monitored with interest, as it may provide a key to the development of a future platinum drug, hopefully with a wider range of activity than either cisplatin or carboplatin.

Toxicity, mutagenicity, intracellular drug concentration and DNA binding in Escherichia coli treated with cis-platinum(II) complexes

The genotoxic effects of six cis-platinum(II)chloramine complexes with different alkyl substituents on their amine ligands have been measured using Escherichia coli. The toxicity and mutagenicity of these compounds were compared, after exposure of bacteria, to drug concentrations which gave known quantities of platinum-DNA lesions. The results permit several observations concerning structure-activity relations of platinum(II) complexes. Firstly, methyl substitution on the amine ligands of cis-diamminedichloro-platinum(II) (DDP) is reported to reduce its antitumor activity. The methyl group did not exert an effect in bacteria where the toxicity and mutagenicity of cis-bis(methylamine)dichloroplatinum(II) and DDP were equivalent. In fact, at equal levels of DNA binding, complexes with substituted amines were generally more toxic toward bacteria than DDP. Secondly, replacement of the chloro groups of DDP by nitrato ligands increased its toxicity and mutagenicity at a given level of DNA binding. Hence, although DDP and its dinitrato derivative have identical ammine ligands, they may form different platinum-DNA lesions in bacteria. Finally, cis-bis(cyclohexylamine)-dichloroplatinum(II) was unique among the compounds studied since it did not cause bacterial filamentation or mutagenesis. These results suggest that, although this compound binds to the bacterial genome, it may not induce the SOS response.

Structure-antitumor activity relationship for new analogs of thecis-dichloro(l,2-diamino cyclohexane) platinum(II) complex

In 1977, Gale and associates reported the synthesis and antitumor activity of a series of Pt(II) complexes containing 1,2-diaminocyclohexane as the ligand. Certain of these complexes showed superior activity and greater water solubility compared to cis-Pt(NH3)2Cl2 complexes ("Neoplatin"). In this paper we report the synthesis and antitumor activity of some 40 new water soluble platinum(II) and platinum(IV) complexes. The following classes of the cis-Pt(L)Cl2 complexes were obtained, where L = 1,2-diaminocyclohexane: (a) cis-Pt(L)(X), where X is a derivative of homophthalic acid or a derivative of 1,3-benzendicarboxylic acid, (b) cis-Pt(L)(X)(OH)2 and cis-Pt(L)(X)(Cl)2 complexes, where L and X are the above-mentioned ligands, (c) cis-Pt(L)(X)2 complexes where X is the monoanion of an organic xanthate or dithiocarbamate and L = 1,2-diaminocyclohexane, (d) their corresponding Pt(IV) analogues, Pt(L)(X)2(OH)2 and Pt(L)(X)2(Cl)2. All complexes were assayed against P388 tumors and/or KB cell-bearing mice. The observed antitumor activities were correlated with the structures and spectra of the complexes as well as with the results of EHMO calculations performed on the leaving ligand molecules. A number of the most active complexes were also tested for activity against ADJ/PC6 Yoshida and S-180 tumors in vivo.

Mutagenic potential of cis-dichlorodiammine platinum II in rodents

The ability of cis-dichlorodiammine platinum II to cause chromosomal aberrations in rats and dominant lethality in mice was studied. Five daily intraperitoneal doses ranging from 0.25 to 2.00 mg/kg/day failed to result in the observance of dominant lethal mutations in mice. Intraperitoneal doses of 0.13 and 0.52 mg/kg/day for 5 days in rats did, however, cause chromosomal aberrations in bone marrow cells collected and harvested 24 h after the last dose. The incidence of total aberrations observed at the 0.52 mg/kg/day dose level was 5.5-fold greater than that seen for the vehicle control group. Thus, cis-dichlorodiammine platinum II appears to be clastogenic in rats.

Platinum nephrotoxicity

Platinum coordination complexes have recently been introduced in cancer chemotherapy with considerable success. However, significant nephrotoxicity has emerged as a factor that limits the therapeutic usefulness of these compounds. In this article we review the available knowledge on platinum nephrotoxicity and its prevention that has been derived from both toxicologic studies in animals and clinical trials in human subjects.

Synergistic action of high-dose hydroxyurea when used with cyclophosphamide and certain new organoplatinum complexes in treatment of advanced L1210 leukemia

Seven new organoplatinum (Pt) compounds, cyclophosphamide (CY), and hydroxyurea (HU) were used singly and in combination in treatment of advanced L1210 leukemia in C57BL/6 X DBA/2 mice. In each experiment the Pt + CY combination was supra-additive, as has been shown with other Pt compounds when used with CY. HU at the dose used (1000 mg/kg) was only minimally effective when used alone. However, six of the seven Pt + CY + HU combination regiments enhanced markedly the increased life span of treated mice when compared with the corresponding dual Pt + CY combination. The triple drug regimen yielded cure rates (760-day survival) up to 70% in individual experiments. Collectively, the cure rate was 11% with the various Pt + CY combinations, and was increased to 53% upon inclusion of HU in the regimen. It is suggested that HU may inhibit a process whereby potentially lethal DNA damage produced by Pt + CY would otherwise be repaired. A reduced efficacy of HU when used at a single, high-dose level was also noted, and a possible mechanism and potential significance of this observation are discussed.

Effects of certain antitumor platinum compounds on kidney esterases

In a study of the biochemical mechanism of renal toxicity of certain antitumor platinum compounds, particularly cis-dichlorodiammineplatinum(II) (NSC-119875), qualitative and quantitative studies of the soluble nonspecific kidney esterases were carried out using (C57BL/L X DBA/2) mice. There was a major suppression of the testosterone-dependent esterases of treated male mice; these levels dropped to levels below those found in untreated females within 72 h after certain of the drugs were administered. This effect appeared to be in inverse relationship to the numerical value of the LD50 values of the compounds investigated.