Synthesis and antitumor activity of ammine/amine platinum(II) and (IV) complexes

195 Pt NMR parameters as strong descriptors in one-parameter QSAR models for platinum-based antitumor compounds

Highly predictive one-parameter quantitative structure-activity relationship models have been developed for platinum-based anticancer drugs using the ¹⁹⁵ Pt NMR parameters as strong descriptors. The developed quantitative structure-activity relationship models were applied in diverse homogeneous sets of antiproliferative Pt(II) and Pt(IV) compounds. These observations form the basis for making predictions of cytotoxicity for a broad range of platinum-based antitumor compounds just from inspection of calculated or experimentally determined ¹⁹⁵ Pt NMR parameters. Copyright © 2016 John Wiley & Sons, Ltd.

Prediction of 195 Pt NMR of photoactivable diazido- and azine-Pt(IV) anticancer agents by DFT computational protocols

¹⁹⁵ Pt NMR chemical shifts for a series of large-sized photoactivable anticancer diazido-Pt(IV), homopiperizine-Pt(IV) and multifunctional azine-Pt(IV) complexes hardly to be probed experimentally and by sophisticated four-component and two-component relativistic calculations are predicted with high accuracy by density functional theory computational protocols. The calculated ¹⁹⁵ Pt NMR chemical shifts constitute a crucial descriptor for making highly predictive one-parameter quantitative structure activity relationships models that help in designing photoactivable Pt(IV)-based antitumor agents with high cytotoxicity and selectivity. Copyright © 2016 John Wiley & Sons, Ltd.

Improvements in the Synthesis and Understanding of the Iodo-bridged Intermediate en Route to the Pt(IV) Prodrug Satraplatin

Mixed amine/ammine motifs are important features in newer generation platinum anticancer agents, including the Pt(IV) prodrug satraplatin. One synthetic route that can be used to access platinum molecules with such structures exploits the trans effect during NH3-mediated cleavage of iodo-bridged platinum(II) dimers of the form [Pt(Am)I(μ-I)]2, where Am is an amine. A clear picture of the nature of these dimers that is consistent with the reactivity they exhibit has remained elusive. Moreover, technical aspects of this chemistry have impeded its more widespread use. We present here an improved strategy that permits isolation and use of [Pt(Am)I(μ-I)]2, where Am is cyclohexylamine, within minutes as opposed to weeks, as previously reported. A detailed spectroscopic, crystallographic, and chromatographic investigation of this intermediate in the synthesis of satraplatin is also presented with a discussion of the ability of both cis and trans isomers of the dimer to produce exclusively cis-[Pt(NH2C6H11)(NH3)I2] upon treatment with NH3.

Accurate prediction of 195Pt NMR chemical shifts for a series of Pt(ii) and Pt(iv) antitumor agents by a non-relativistic DFT computational protocol

Exhaustive benchmark DFT calculations reveal that the non-relativistic GIAO-PBE0/SARC-ZORA(Pt)∪6-31+G(d)(E) computational protocol predicts accurate ¹⁹⁵Pt NMR chemical shifts for a wide range of square planar Pt(ii) and octahedral Pt(iv) anticancer agents.

Conformational Isomerism of trans-[Pt(NH2C6H11)2I2] and the Classical Wernerian Chemistry of [Pt(NH2C6H11)4]X2 (X = Cl, Br, I)

X-ray crystallographic analysis of the compound trans-[Pt(NH₂C₆H₁₁)₂I₂] revealed the presence of two distinct conformers within one crystal lattice. This compound was studied by variable temperature NMR spectroscopy to investigate the dynamic interconversion between these isomers. The results of this investigation were interpreted using physical (CPK) and computational (molecular mechanics and density functional theory) models. The conversion of the salts [Pt(NH₂C₆H₁₁)₄]X₂ into trans-[Pt(NH₂C₆H₁₁)₂X₂] (X = Cl, Br, I) was also studied and is discussed here with an emphasis on parallels to the work of Alfred Werner.

A new class of antitumor trans-amine-amidine-Pt(II) cationic complexes: influence of chemical structure and solvent on in vitro and in vivo tumor cell proliferation

The reactions of cyclopropylamine, cyclopentylamine, and cyclohexylamine with trans-[PtCl2(NCMe)2] afforded the bis-cationic complexes trans-[Pt(amine)2(Z-amidine)2]2+[Cl-]2, 1-3. The solution behavior and biological activity have been studied in different solvents (DMSO, water, polyethylene glycol (PEG 400), and polyethylene glycol dimethyl ether (PEG-DME 500)). The biological activity was strongly influenced by the cycloaliphatic amine ring size, with trans-[Pt(NH2CH(CH2)4CH2)2{N(H) horizontal lineC(CH3)N(H)CH(CH2)4CH2}2]2+[Cl-]2 (3) being the most active compound. Complex 3 overcame both cisplatin and MDR resistance, inducing cancer cell death through p53-mediated apoptosis. Alkaline single-cell gel electrophoresis experiments indicated direct DNA damage, reasonably attributable to DNA adducts of trans-[PtCl(amine)(Z-amidine)2][Cl] species, which can evolve to produce disruptive and nonrepairable lesions on DNA, thus leading to the drug-induced programmed cancer cell death. Preliminary in vivo antitumor studies on C57BL mice bearing Lewis lung carcinoma highlighted that complex 3 promoted a significant and dose-dependent tumor growth inhibition without adverse side effects.

Synthesis, cytotoxicity and DNA binding levels of tri-functional mononuclear platinum(II) complexes

Seven new tri-functional mononuclear platinum(II) complexes (a-g) have been synthesized and characterized by elemental analysis, conductivity, thermal analysis, IR, UV and (1)H NMR spectral techniques. The cytotoxicity of these complexes was tested by MTT and SRB assays. The cell cycle analysis and the levels of total platinum bound to DNA were measured by flow cytometry and ICP-MS. The results indicate that the complexes (a-g) have selectivity against tested carcinoma cell lines; they have weaker cytotoxicity against HCT-8 and MCF-7. Complexes a, b, d and g also exert weaker cytotoxicity against BGC-823 and complexes a, b, e and f have better cytotoxicity against EJ, but their cytotoxicity is weaker than that of cisplatin. Complexes c, e and f, confer substantially greater cytotoxicity against HL-60 with an IC(50) value of 7.68+/-0.23, 3.87+/-0.19 and 2.41+/-0.18 microM, respectively, moreover, cytotoxicity of complex f is equal to that of cisplatin. Complexes c, e and f cause significant G(2)/M arrest and a concomitant decrease of cell population in G(1) and S phases. The total DNA-platination levels of them are higher than that of cisplatin under the same experimental conditions. It suggests that there is no correlation between total DNA-platination levels in HL-60 cells and cytotoxicity of complexes. When leaving groups are aromatic carboxylates, the complexes have better cytotoxicity, moreover, the substituent in benzene ring also influences cytotoxicity. In addition, when leaving groups are dicarboxylates, dicarboxylates coordinating with platinum through oxygen atoms form different chelate cycle and cycle size also affects their cytotoxicity.

Synthesis, cytotoxicity and DNA-binding levels of ammine/propylamine platinum(II) complexes with carboxylates

Seven new mixed ammine/propylamine platinum(II) complexes with carboxylates (a-g) have been synthesized and characterized by elemental analysis, conductivity, IR, UV, and (1)H NMR spectra techniques. The cytotoxicity of these complexes was tested by MTT assay. The levels of total platinum bound to DNA were measured by ICP-MS. The results indicate that the complexes (a-g) have better cytotoxicity against EJ and HL-60 than other carcinoma cell lines. The cytotoxicity increases in the sequence: g<f<e<d<b<c<a against tested carcinoma cell lines. The cytotoxicity of complexes (a-c) is equal to that of cisplatin against HL-60. The cytotoxicity of complex a is also equal to that of cisplatin against EJ. However, the complexes (a-g) are significantly less potent than cisplatin against BGC-823, HCT-8 and MCF-7. The total DNA-platination levels increase in the sequence: cisplatin<g<e<f<d<b<c<a under the same experimental conditions. It suggests that there is no correlation between total DNA-platination levels in HL-60 cells and cytotoxicity of ammine/propylamine platinum complexes. When leaving groups are aromatic carboxylates, the complexes have better cytotoxicity, and moreover, the substituent in benzene ring also influences cytotoxicity.

Cisplatin: from DNA damage to cancer chemotherapy

Cisplatin [cis-DDP, cis-diamminedichloroplatinum(II)] is a potent anticancer drug that has been used successfully to treat tumors of the head, neck, lungs, and genitourinary tract. The biological activity of cisplatin was discovered serendipitously more than 30 years ago, and since that time research efforts have focused on elucidating its mechanism of action. The present review provides a historical perspective of our attempts to understand this complex phenomenon and the results of recent work that guides our current activities in this field. Continued efforts to understand the mechanism of genotoxicity of cisplatin are expected to lead to the discovery of new drugs and combinations for the improvement of cancer chemotherapy.

Synthesis and antitumor activity of cyclotriphosphazene-(diamine)platinum(II) conjugates

A new class of water-soluble cyclotriphosphazene-(diamine)platinum(II) conjugate drugs [NP(Am-Li2)(Am.PtA2)]3 (Am: dicarboxylic amino acid; A2: diamine) has been synthesized and characterized by means of elemental analysis, multinuclear (1H, 31P, 13C, 195Pt) NMR and IR spectroscopies. All the title compounds were subjected to both in vitro and in vivo assays against the murine leukemia L1210 cell line and selected human tumor cells. Most of the title compounds have shown higher in vivo antitumor activity than cisplatin and carboplatin, and, in particular, [NP(L-Glu-Li2)(L-Glu.Pt(-dach)]3 (Glu=glutamate, dach=trans(+/-)-1,2-diaminocyclohexane) showed extraordinary high activity (ILS>500%) equally against both parent and cisplatin-resistant leukemia L1210 cell lines. Furthermore, this candidate compound (KI 60606) exhibited a wider spectrum of in vitro activity by showing higher cytotoxicity against all the selected human tumor cells than cisplatin and, therefore, was subjected to preclinical studies which are now near completion.

The synthesis of 191Pt labelled JM216, an orally active platinum anti-tumour agent

The orally active platinum anti-tumour complex JM216[bis-acetatoamminedichlorocyclohexylamineplatinum(IV)] is at present in stage II clinical trials. A procedure for synthesising the complex labelled with 191Pt or 188Pt at the platinum centre has been developed. The purity (shown by HPLC) is 98% and the specific activity (0.3-0.4 Ci/kg) is enough for in vivo and in vitro studies.

Ammine/amine platinum (II) complexes effective in vivo against murine tumors sensitive or resistant to cisplatin and tetraplatin

Three homologous series, each differing from the other in the coordinated amine ligand class, namely alicyclic, heterocyclic or isoaliphatic, were highly effective against wild-type murine leukemia L1210/0 cells in vivo (T/C = 171%-426% at optimal doses). Of the 13 complexes comprising the three series, 3 were inactive in the cisplatin-resistant L1210/DDP model, but the other 10 maintained good efficacy (T/C = 131%-167%). Long-term survivors, frequently observed with these complexes in the L1210/0 model, were also seen in the L1210/DDP model but to a lesser extent. In the homologous alicyclic series, which contained six analogs, as the alicyclic ring size increased, potency against L1210/0 and L1210/DDP cells also increased up to cyclohexylamine, and then declined. Four ammine/alicyclic amine analogs were evaluated against L1210/DACH cells, which are cross-resistant to tetraplatin, and the clinically predictive M5076 reticulosarcoma. Although the congeners were ineffective or minimally effective in prolonging the survival time of L1210/DACH-bearing mice (T/C = 111%-134%), 20%-40% cure rate was consistently observed and suggested that the compounds possessed a low inherent ability to circumvent resistance in these tumor cells also. In the solid M5076 model, activity was greatest (tumor growth delays of about 25 days) for the alicyclic homologs containing the ammine/cyclobutylamine or ammine/cyclopentylamine carrier ligand combination. In summary, ammine/amine platinum (II) analogs have demonstrated promise at the preclinical level in their ability to circumvent acquired resistance, which is a major drawback of cisplatin use in treating cancer.

Correlation of total and interstrand DNA adducts in tumor and kidney with antitumor efficacies and differential nephrotoxicities of cis-ammine/cyclohexylamine-dichloroplatinum(II) and cisplatin

Mixed amine platinum complexes have been identified as a new class of antitumor agents with activity in some cisplatin-resistant tumor models. cis-Ammine/cyclohexylamine-dichloroplatinum(II) is one such analog that we have evaluated in vivo and found it to have antitumor activity that was comparable to that of cisplatin in a solid murine fibrosarcoma tumor model. In contrast to the nephrotoxicity observed with cisplatin, the analog was free from inducing this side-effect. Pharmacokinetics of the two compounds administered i.v. at equitoxic dose levels to tumor-bearing mice indicated similar decay kinetics of total platinum in plasma, kidney and the tumor. Furthermore, DNA-platinum adducts of the two agents were similar in the tumor. Total adduct levels in the kidney, on the other hand, were significantly greater (P < 0.5) by up to 4-fold for cisplatin compared with the mixed amine analog. Likewise, the levels of interstrand cross-links of the two platinum complexes were comparable in the tumor, but significantly greater (P < 0.05) in the kidney for cisplatin. The data indicate that the greater renal levels of total and interstrand DNA-platinum adducts formed by cisplatin correlate with renal damage associated with this agent, and suggest that adduct levels, and not total tissue platinum levels, provide a more useful correlation with pharmacodynamic observations.

Kinetics of tissue disposition of cis-ammine/cyclohexylamine-dichloroplatinum(II) and cisplatin in mice bearing FSaIIC tumors

The clinical potential of mixed amine platinum(IV) complexes has been identified, and interest in this new class of antitumor agents has been heightened by demonstration of their activity in cisplatin-resistant neoplasms. These tetravalent platinum agents are expected to undergo a reductive reaction to form the corresponding platinum(II) drug prior to eliciting biological activity. cis-Ammine/cyclohexylamine-dichloroplatinum(II) is one such product that we evaluated with cisplatin in vivo, and we found the two complexes given i.v. or i.p. to have comparable activities against a solid murine fibrosarcoma. Following i.v. administration of the two compounds at equitoxic dose levels (20 mg/kg) to tumor-bearing mice, platinum levels in the plasma were consistently higher for cisplatin. Tissue platinum levels, in contrast, were comparable between the agents or higher for the mixed amine analog at the earliest (3-h) time point. The temporal profiles determined for the concentrations over 48 h were tissue- and/or drug-specific and could be described by terminal-phase constants or half-lives of platinum in most tissues. In the plasma, kidney, lung, and jejunum, platinum levels arising from both compounds decayed with half-lives of 24-92 h. The terminal-phase constants of platinum determined in the heart for the two complexes were not significantly different from zero, indicative of levels remaining steady, whereas the constants were negative in the spleen, indicative of an increase in tissue drug concentration. In the tumor, liver, and testes, positive values for the decay-phase constants corresponding to half-lives of 47, 256, and 79 h, respectively, were seen with the mixed amine complex; this pattern contrasted with that found for cisplatin, for which the terminal-phase constant was either zero or negative. In vitro binding studies demonstrated the mixed amine complex to be more reactive. Thus, the presence of one ammine and one cyclohexylamine carrier ligand in the mixed amine complex, as opposed to the diammine ligands in cisplatin, leads to an increase in drug distribution and an alteration in the kinetics of tissue binding and removal of platinum.