Platinum(IV) complexes of trans-1,2-diamino-4-cyclohexene: Prodrugs affording an oxaliplatin analogue that overcomes cancer resistance

Six platinum(IV) compounds derived from an oxaliplatin analogue containing the unsaturated cyclic diamine trans-1,2-diamino-4-cyclohexene (DACHEX), in place of the 1,2-diaminocyclohexane, and a range of axial ligands, were synthesized and characterized. The derivatives with at least one axial chlorido ligand demonstrated solvent-assisted photoreduction. The electrochemical redox behavior was investigated by cyclic voltammetry; all compounds showed reduction potentials suitable for activation in vivo. X-ray photoelectron spectroscopy (XPS) data indicated an X-ray-induced surface reduction of the Pt(IV) substrates, which correlates with the reduction potentials measured by cyclic voltammetry. The cytotoxic activity was assessed in vitro on a panel of human cancer cell lines, also including oxaliplatin-resistant cancer cells, and compared with that of the reference compounds cisplatin and oxaliplatin; all IC50 values were remarkably lower than those elicited by cisplatin and somewhat lower than those of oxaliplatin. Compared to the other Pt(IV) compounds of the series, the bis-benzoate derivative was by far (5–8 times) the most cytotoxic showing that low reduction potential and high lipophilicity are essential for good cytotoxicity. Interestingly, all the complexes proved to be more active than cisplatin and oxaliplatin even in three-dimensional spheroids of A431 human cervical cancer cells

New oxaliplatin-pyrophosphato analogs with improved in vitro cytotoxicity

Two new Pt(II)-pyrophosphato complexes containing the carrier ligands cis-1,3- diaminocyclohexane (cis-1,3-DACH) and trans-1,2-diamine-4-cyclohexene (1,2-DACHEX), variants of the 1R,2R-diaminocyclohexane ligand present in the clinically used Pt-drug oxaliplatin, have been synthesized with the aim of developing new potential antitumor drugs with high bone tropism. The complexes are more stable at physiological pH than in acid conditions, with Na2[Pt(pyrophosphato)(cis-1,3-DACH)] (1) slightly more stable than Pt(dihydrogenpyrophosphato)(1,2-DACHEX)] (2). The greater reactivity at acidic pH ensures a greater efficacy at the tumor site. Preliminary NMR studies indicate that 1 and 2 react slowly with 5’-GMP (used as a model of nucleic acids), releasing the pyrophosphate ligand and affording the bis 5’-GMP adduct. In vitro cytotoxicity assays performed against a panel of four human cancer cell lines have shown that both compounds are more active than oxaliplatin. Flow cytometry studies on HCT116 cells showed that the pyrophosphato compounds with the non-classical 1,3- and 1,4- diaminocyclohexane ligands (1 and 4) are the most capable to induce cells’ death by apoptosis and necrosis

One-Pot Synthesis of New Organometallic Compounds with Platinum-Carbon Bond

Organometallic compounds of platinum containing ortho metalated para-nitro-benzamidate or 1-naphthalene-methylamine have been prepared by one-pot synthesis. The para-nitro-benzamidate [Pt{K2C,N-pNO2-C6H4C(O)NH}(R,R-DACH)] (compound 2) was obtained starting from [PtCl2(R,R-DACH)] and para-nitro-benzonitrile, which, in the reaction conditions, hydrolyzes to the corresponding amide and forms the dinuclear intermediate [Pt2{µ-N,O-pNO2-C6H4C(O)NH}2(R,R-DACH)2]SO4 (compound 1·SO4) with HH or HT arrangement of the two bridging amidato ligands. Compound 1·SO4, kept at 90 °C for few hours, transforms into 2. The ortho-metalated PtII derivative with 1-naphthalene-methylamine [PtCl{K2C,N-C10H6CH2NH2}(DMSO)] (3) was obtained by direct reaction of [PtCl2(DMSO)2] with the amine. Unlike compound 2 that has no labile ligands, compound 3 has Cl and DMSO ligands that can be released, allowing the formation of cross-links with DNA. Oxidation of 3 to the PtIV counterpart was performed with PhICl2 (compound 4). Unexpectedly, although six-coordinate complexes of PtIV are considered to be inert, 4 underwent spontaneous isomerization from the mer to the fac isomer. All compounds have been fully characterized by multinuclear NMR spectroscopy, which has enabled complete assignment of all proton resonances. In the case of compound 2, a single-crystal X-ray investigation was also performed, showing, with the only exception of the puckered cyclohexane ring, a complete planarity of the complex frame, which could favor an intercalative interaction with DNA

Effect of chirality on the anticancer activity of Pt(ii) and Pt(iv) complexes containing 1R,2Rand 1S,2Senantiomers of thetrans-1,2-diamino-4-cyclohexene ligand (DACHEX), an analogue of diaminocyclohexane used in oxaliplatin

Six enantiomerically pure, oxaliplatin-like, platinum compounds (two platinum(ii) and four platinum(iv)), all containing unsaturated cyclic diaminetrans-1,2-diamino-4-cyclohexene (DACHEX) as a substitute for thetrans-1,2-diaminocyclohexane used in oxaliplatin, were investigated. The complexes were characterized by elemental analyses, ESI-MS, and1H-NMR spectroscopy. For the four Pt(iv) complexes the electrochemical redox behaviour, investigated by cyclic voltammetry, showed that all complexes possess reduction potentials suitable for activationin vivo. The antiproliferative activity was assessedin vitroon human cancer cell lines, also selected for resistance to platinum-based drugs or belonging to the MultiDrug-Resistant (MDR) phenotype. All complexes exhibited antiproliferative activity superior to that of cisplatin and almost equivalent to or better than that of oxaliplatin; moreover, most complexes were also capable of overcoming both the cisplatin- and the oxaliplatin-resistance. By comparing the effectiveness of the enantiomerically pure compounds with the racemic one, theR,Renantiomer emerged as the most effective in the case of Pt(ii) complexes whereas theS,Senantiomer was the most effective in the case of the Pt(iv) derivatives. From the results obtained also against 3D spheroid tumor models,cis,trans,cis-[Pt(OXA)(OBz)2(1S,2S-DACHEX)] (OBz = benzoate) emerged as the most promising candidate for further preclinical investigation