Newtrans-Platinum Drugs with Phosphines and Amines as Carrier Ligands Induce Apoptosis in Tumor Cells Resistant to Cisplatin

Co-targeting CDK 4/6 and C-MYC/STAT3/CCND1 axis and inhibition of tumorigenesis and epithelial-mesenchymal-transition in triple negative breast cancer by Pt(II) complexes bearing NH3 as trans-co-ligand

In search of potential anticancer agents, we synthesized SNO-donor salicylaldimine main ligand-based Pt(II) complexes bearing NH3 as co-ligand at trans-position (C1-C6). These complexes showed similarity in structure with transplatin as the two N donor atoms of the main ligand and NH3 co-ligand were coordinated to Pt in trans position to each other. Each complex with different substituents on the main ligand was characterized thoroughly by detailed spectroscopic and spectrophotometric methods. Four of these complexes were studied in solid state by single crystal X-ray analysis. The stability of reference complex C1 was measured in solution state in DMSO‑d6 or its mixture with D2O using 1H NMR methods. These complexes were further investigated for their anticancer activity in triple-negative-breast (TNBC) cells including MDA-MB-231, MDA-MB-468 and MDA-MB-436 cells. All these complexes showed satisfactory cytotoxic effect as revealed by the MTT results. Importantly, the highly active complex C4 anticancer effect was compared to the standard chemotherapeutic agents including cisplatin, oxaliplatin and 5-fluorouracil (5-FU). Functionally, C4 suppressed invasion, spheroids formation ability and clonogenic potential of cancer cells. C4 showed synergistic anticancer effect when used in combination with palbociclib, JQ1 and paclitaxel in TNBC cells. Mechanistically, C4 inhibited cyclin-dependent kinase (CDK)4/6 pathway and targeted the expressions of MYC/STAT3/CCND1/CNNE1 axis. Furthermore, C4 suppressed the EMT signaling pathway that suggested a role of C4 in the inhibition of TNBC metastasis. Our findings may pave further in detailed mechanistic study on these complexes as potential chemotherapeutic agents in different types of human cancers.

Trans-[Pt(amine)Cl2(PPh3)] Complexes Target Mitochondria and Endoplasmic Reticulum in Gastric Cancer Cells

Gastric cancer prognosis is still notably poor despite efforts made to improve diagnosis and treatment of the disease. Chemotherapy based on platinum agents is generally used, regardless of the fact that drug toxicity leads to limited clinical efficacy. In order to overcome these problems, our group has been working on the synthesis and study of trans platinum (II) complexes. Here, we explore the potential use of two phosphine-based agents with the general formula trans-[Pt(amine)Cl2(PPh3)], called P1 and P2 (with dimethylamine or isopropylamine, respectively). A cytotoxicity analysis showed that P1 and especially P2 decrease cell viability. Specifically, P2 exhibits higher activity than cisplatin in gastric cancer cells while its toxicity in healthy cells is slightly lower. Both complexes generate Reactive Oxygen Species, produce DNA damage and mitochondrial membrane depolarization, and finally lead to induced apoptosis. Thus, an intrinsic apoptotic pathway emerges as the main type of cell death through the activation of BAX/BAK and BIM and the degradation of MCL1. Additionally, we demonstrate here that P2 produces endoplasmic reticulum stress and activates the Unfolded Protein Response, which also relates to the impairment observed in autophagy markers such as p62 and LC3. Although further studies in other biological models are needed, these results report the biomolecular mechanism of action of these Pt(II)-phosphine prototypes, thus highlighting their potential as novel and effective therapies.

Dithiobiureas Palladium(II) complexes' studies: From their synthesis to their biological action

Dithiobiureas coordination chemistry towards palladium (II) ions and their possible application is presented and discussed. 1,6-(4-Methoxyphenyl)-2,5-dithiobiurea and 1,6-(4-chlorophenyl)-2,5-dithiobiurea afford two Pd(II) complexes with the general formula [Pd2(H2L)Cl2(PPh3)2]. The metal ion forms one chelate ring with the dithiobiurea, and binds to a triphenylphosphine and an additional leaving group cisplatin like. One of the complexes (1) is endowed not only with stability in DMSO and aqua solutions containing a biological buffer but also with cytotoxicity versus gastric cancer cell lines. Complex 1 does not interact covalently to DNA models, neither activates p53 or Checkpoint Kinase 1 key proteins for DNA damage response. Thus, we propose that complex 1 exerts its action by activating Mitogen-Activated Protein Kinases [p38, Extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs)] as cell death inductors.

Fluorination and hydrolytic stability of water-soluble platinum complexes with a borane-bridged diphosphoramidite ligand

The high fluorophilicity of borane-containing ligands offers promise for accessing new metallodrug candidates capable of bifunctional [¹⁸F]-positron emission tomography (PET) imaging, but this requires water soluble and hydrolytically stable ligands that can be fluorinated under mild conditions. Toward this goal, here we report the synthesis and characterization of water-soluble Pt(II) complexes containing a triaminoborane-bridged diphosphoramidite ligand called ^MeOTBDPhos that can be fluorinated using simple fluoride salts. NMR and XRD studies show that (^MeOTBDPhos)PtCl₂ (1) dissolves in water with cooperative H-OH addition across the bridgehead N-B bond to form 1-H2O. The B-OH bond in 1-H2O undergoes rapid displacement with fluoride (<10 min) when treated with CsF in MeCN to form 1-HF. 1-HF can also be prepared in <10 min by addition of KF to 1 in the presence Kryptofix® 222 and (HNEt₃)Cl in MeCN. In addition to using fluoride salts, we show how mononuclear 1 can be fluorinated with HBF₄·Et₂O to form dinuclear [(^MeOTBDPhos-HF)Pt(μ-Cl)]₂(BF₄)₂ (4-HF). Comparative studies show that the B-F bond in 1-HF undergoes hydrolysis as soon as it is dissolved in water or saline, but the B-F bond persists for hours when the pH of the solution is lowered to pH ≤ 2. In contrast to 1-HF, the B-F bond in dinuclear 4-HF persists for days when dissolved in water, which may be attributed to slow, sacrificial release of fluoride from the BF₄^- anion. The results show how cooperative N-B reactivity on the ligand can be leveraged to rapidly fluorinate water-soluble ^MeOTBDPhos complexes under mild conditions and afford suggestions for how to enhance hydrolytic B-F stability, as required for use in biomedical applications.

trans-Dichloro(triphenylarsino)(N,N-dialkylamino)platinum(II) Complexes: In Search of New Scaffolds to Circumvent Cisplatin Resistance

The high incidence of the resistance phenomenon represents one of the most important limitations to the clinical usefulness of cisplatin as an anticancer drug. Notwithstanding the considerable efforts to solve this problem, the circumvention of cisplatin resistance remains a challenge in the treatment of cancer. In this work, the synthesis and characterization of two trans-dichloro(triphenylarsino)(N,N-dialkylamino)platinum(II) complexes (1 and 2) were described. The trypan blue exclusion assay demonstrated an interesting antiproliferative effect for complex 1 in ovarian carcinoma-resistant cells, A2780cis. Quantitative analysis performed by ICP-AES demonstrated a scarce ability to platinate DNA, and a significant intracellular accumulation. The investigation of the mechanism of action highlighted the ability of 1 to inhibit the relaxation of supercoiled plasmid DNA mediated by topoisomerase II and to stabilize the cleavable complex. Cytofluorimetric analyses indicated the activation of the apoptotic pathway and the mitochondrial membrane depolarization. Therefore, topoisomerase II and mitochondria could represent possible intracellular targets. The biological properties of 1 and 2 were compared to those of the related trans-dichloro(triphenylphosphino)(N,N-dialkylamino)platinum(II) complexes in order to draw structure–activity relationships useful to face the resistance phenotype.

Silver(I) complexes of 3-methoxy-4-hydroxybenzaldehyde thiosemicarbazones and triphenylphosphine: structural, cytotoxicity, and apoptotic studies

Novel silver(i) complexes of the type [AgCl(PPh3)2(L)] {PPh3 = triphenylphosphine; L = VTSC = 3-methoxy-4-hydroxybenzaldehyde thiosemicarbazone (1); VMTSC = 3-methoxy-4-[2-(morpholine-1-yl)ethoxy]benzaldehyde thiosemicarbazone (2); VPTSC = 3-methoxy-4-[2-(piperidine-1-yl)ethoxy]benzaldehyde thiosemicarbazone (3)} were synthesized and fully characterized by spectroscopic techniques. The molecular structures of complexes 2 and 3 were determined by single crystal X-ray diffraction. Compounds 1-3 exhibited appreciable cytotoxic activity against human tumor cells (lung A549, breast MDA-MB-231 and MCF-7) with IC50 values in 48 h of incubation ranging from 5.6 to 18 μM. Cellular uptake studies showed that complexes 1-3 were efficiently internalized after 3 hours of treatment in MDA-MB-231 cells. The effects of complex 1 on the cell morphology, cell cycle, induction of apoptosis, mitochondrial membrane potential (Δψm), and reactive oxygen species (ROS) production have been evaluated in triple negative breast cancer (TNBC) cells MDA-MB-231. Our results showed that complex 1 induced typical morphological alterations of cell death, an increase in cells at the sub-G1 phase, apoptosis, and mitochondrial membrane depolarization. Furthermore, DNA binding studies evidenced that 1 can bind to ct-DNA and does so without modifying the B-structure of the DNA, but that the binding is weak compared to that of Hoechst 33258.

Pentafluorophenyl Platinum(II) Complexes of PTA and its N-Allyl and N-Benzyl Derivatives: Synthesis, Characterization and Biological Activity

From the well-known 1,3,5-triaza-phosphaadamantane (PTA, 1a), the novel N-allyl and N-benzyl tetrafuoroborate salts 1-allyl-1-azonia-3,5-diaza-7-phosphaadamantane (APTA(BF₄), 1b) and 1-benzyl-1-azonia-3,5-diaza-7-phosphaadamantane (BzPTA(BF₄), 1c) were obtained. These phosphines were then allowed to react with (Pt(μ-Cl)(C₆F₅)(tht))₂ (tht = tetrahydrothiophene) affording the water soluble Pt(II) complexes trans-(PtCl(C₆F₅)(PTA)₂) (2a) and its bis-cationic congeners trans-(PtCl(C₆F₅)(APTA)₂)(BF₄)₂ (2b) and trans-(PtCl(C₆F₅)(BzPTA)₂)(BF₄)₂ (2c). The compounds were fully characterized by multinuclear NMR, ESI-MS, elemental analysis and (for 2a) also by single crystal X-ray diffraction, which proved the trans configuration of the phosphine ligands. Furthermore, in order to evaluate the cytotoxic activities of all complexes the normal human dermal fibroblast (NHDF) cell culture were used. The antineoplastic activity of the investigated compounds was checked against the human lung carcinoma (A549), epithelioid cervix carcinoma (HeLa) and breast adenocarcinoma (MCF-7) cell cultures. Interactions between the complexes and human serum albumin (HSA) using fluorescence spectroscopy and circular dichroism spectroscopy (CD) were also investigated.

Computational studies, design and synthesis of Pd(II)-based complexes: Allosteric inhibitors of the Human Topoisomerase-IIα

Herein, a robust docking protocol was developed by using a low-cost workflow to highlight the modulation at ATPase domain from Human Topoisomerase-IIα (TOP2A) towards four novel Pd(II)-complexes bearing N,S-donor ligands. In vitro TOP2A inhibition assay confirmed the ability of them to prevent the enzyme functions into concentration ranging at 6.25-25μM. These results exhibited more effectivity than anticancer agent etoposide (35μM) and merbarone (40-50μM). The compounds were screened via Resazurin assay against MCF-7, MDA-MB-231 (Human breast), DU-145 (Human prostate), A549 (Human lung) and Cal27 (Human tongue) tumor cell lines revealing great cytotoxic effects, primarily to MCF-7 (IC₅₀=1.81-4.46μM). As well, 1-4 exhibited their selectivity index (SI) higher than cisplatin against HEK-293 (human kidney) normal cells, at least 11.6-fold (SI_1-4=1.4-5.0; SI_cis=0.12). Further, Red Blood Cell hemolytic test suggested in vitro non-toxic character for compound 4, previously evaluated as the most effective TOP2A inhibitor.

Synthesis, characterization and biological investigation of platinum(ii) complexes with asparagusic acid derivatives as ligands

After more than 50 years of platinum-based anticancer research only three compounds are in clinical use worldwide. The use of the well-known lead compound of this class of anticancer agents, cisplatin, is limited by its side effects and varying resistance mechanisms. Therefore, we report on platinum(ii) compounds with asparagusic acid derivatives as ligands which show interesting anticancer results on cisplatin resistant cell lines.

Structures and anticancer activity of chlorido platinum(II) saccharinate complexes with mono- and dialkylphenylphosphines

cis-[PtCl(sac)(PPh₂Me)₂] (1), cis-[PtCl(sac)(PPhMe₂)₂] (2), trans-[PtCl(sac)(PPh₂Et)₂] (3) and trans-[PtCl(sac)(PPhEt₂)₂] (4) complexes (sac = saccharinate) were synthesized and characterized by elemental analysis and spectroscopic methods. The structures of 2-4 were determined by X-ray single-crystal diffraction. The interaction of the complexes with DNA was studied various biochemical, biophysical and molecular docking methods. Only the cis-configured complexes (1 and 2) showed nuclease activity and their binding affinity towards DNA was considerably higher than those of their trans-congeners (3 and 4). The chlorido ligand in the cis-configured complexes underwent aquation, making them more reactive towards DNA. Furthermore, 1 and 2 exhibited anticancer potency on breast (MCF-7) and colon (HCT116) cancer cells similar to cisplatin, whereas 3 and 4 were biologicallly inactive. Mechanistic studies on MCF-7 cells showed that higher nuclear uptake, cell cycle arrest at the S phase, dramatically increased DNA double-strand breaks, apoptosis induction, elevated levels of reactive oxygen species (ROS) and high mitochondrial membrane depolarization greatly contribute to the anticancer potency of 1 and 2.

Four-component relativistic 31P NMR calculations for trans-platinum(ii) complexes: importance of the solvent and dynamics in spectral simulations

We report a combined experimental-theoretical study on the 31P NMR chemical shift for a number of trans-platinum(ii) complexes. Validity and reliability of the 31P NMR chemical shift calculations are examined by comparing with the experimental data. A successful computational protocol for the accurate prediction of the 31P NMR chemical shifts was established for trans-[PtCl2(dma)PPh3] (dma = dimethylamine) complexes. The reliability of the computed values is shown to be critically dependent on the level of relativistic effects (two-component vs. four component), choice of density functionals, dynamical averaging, and solvation effects. Snapshots obtained from ab initio molecular dynamics simulations were used to identify those solvent molecules which show the largest interactions with the platinum complex, through inspection by using the non-covalent interaction program. We observe satisfactory accuracy from the full four-component matrix Dirac-Kohn-Sham method (mDKS) based on the Dirac-Coulomb Hamiltonian, in conjunction with the KT2 density functional, and dynamical averaging with explicit solvent molecules.

Controlling with light the interaction between trans-tetrapyridyl ruthenium complexes and an oligonucleotide

Three new trans-ruthenium(ii) complexes coordinated to tetrapyridyl ligands, namely [Ru(bapbpy)(dmso)Cl]Cl ([2]Cl), [Ru(bapbpy)(Hmte)₂](PF₆)₂ ([3](PF₆)₂), and [Ru(biqbpy)(Hmte)₂](PF₆)₂ ([4](PF₆)₂), were prepared as analogues of [Ru(biqbpy)(dmso)Cl]Cl ([1]Cl), a recently described photoactivated chemotherapy agent. The new complexes were characterized, and their crystal structures showed the distorted coordination octahedron typical of this family of complexes. Their photoreactivity in solution was analyzed by spectrophotometry and mass spectrometry, which showed that the sulfur ligand was substituted upon blue light irradiation. The binding of the ruthenium complexes to a reference single-stranded oligonucleotide (s(^5'CTACGGTTTCAC^3')) was explored both in the dark and under light irradiation by gel electrophoresis and high-resolution mass spectrometry. While adduct formation in the dark was negligible for the four complexes, light irradiation led to the formation of adducts with one or two ruthenium centers per oligonucleotide. The absence of interactions in the dark and the presence of complex-oligonucleotide adducts demonstrate that visible light controls the interaction of these ruthenium complexes with nucleic acids.

Morin P, Westcott SA. Synthesis, characterization, and anticancer properties of iminophosphineplatinum(II) complexes containing boronate esters

Three new iminophosphines containing pinacol-derived boronate esters have been prepared and ligated to dichloridoplatinum(II) fragments. All compounds have been characterized fully, including an X-ray diffraction study carried out for the platinum complex 8, which is derived from 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)aniline. These three new platinum complexes, along with the non-boron containing control, have been examined for their initial cytotoxic properties against two glioma cell lines using the MTT method.

New trans dichloro (triphenylphosphine)platinum(II) complexes containing N-(butyl),N-(arylmethyl)amino ligands: Synthesis, cytotoxicity and mechanism of action

Some new platinum(II) complexes have been prepared, of general formula trans-[PtCl2(PPh3){NH(Bu)CH2Ar}], where the dimension of the Ar residue in the secondary amines has been varied from small phenyl to large pyrenyl group. The obtained complexes, tested in vitro towards a panel of human tumor cell lines showed an interesting antiproliferative effect on both cisplatin-sensitive and -resistant cells. For the most cytotoxic derivative 2a the investigation on the mechanism of action highlighted the ability to induce apoptosis on resistant cells and interestingly, to inhibit the catalytic activity of topoisomerase II.

Synthesis, cytotoxicity, DNA interaction and cell cycle studies of trans-diiodophosphine Pt(ii) complexes

Diiodido phosphine Pt complexes were synthesized and their biological activity studied. The complex with isopropylamine was the best candidate.

Interaction of cisplatin and two potential antitumoral platinum(ii) complexes with a model lipid membrane: a combined NMR and MD study

Multinuclear NMR and MD calculations highlighted the different interactions of cisplatin and two potential antitumoral Pt(ii) complexes with a model membrane.

Design and biological evaluation of new platinum(II) complexes bearing ligands with DNA-targeting ability

A novel series of platinum(II) complexes bearing aliphatic amines and ligands with DNA-targeting properties was synthesized to achieve more potent and selective metallodrugs. We developed six new platinum-based drugs, which contain methylamine, 1a-c, and isopropylamine, 2a-c, both in the trans position to a selected targeting ligand: naphthalimide. The activity of the complexes has been evaluated in order to confirm the improvements from our proposed approach, and the complexes demonstrate better cytotoxic activity on cancer cell lines when compared with the ligands and, importantly, with cisplatin. Further studies were performed to assess their subcellular localization and binding mode to DNA.

Utilizing redox-mediated Bergman cyclization toward the development of dual-action metalloenediyne therapeutics

Reaction of 2 equiv of 1,2-bis((diphenylphosphino)ethynyl)benzene (dppeb, 1) with Pt(cod)Cl2 followed by treatment with N2H4 yields the reduced Pt(0) metalloenediyne, Pt(dppeb)2, 2. This complex is stable to both air oxidation and metal-mediated Bergman cyclization under ambient conditions due to the nearly idealized tetrahedral geometry. Reaction of 2 with 1 equiv of I2 in the presence of excess 1,4-cyclohexadiene (1,4-CHD) radical trap rapidly and near-quantitatively generates the cis-Bergman-cyclized, diiodo product 3 ((31)P: δ = 41 ppm, J(Pt-P) = 3346 Hz) with concomitant loss of 1 equiv of uncyclized phosphine chelate ((31)P: δ = -33 ppm). In contrast, addition of 2 equiv of I2 in the absence of additional radical trap instantaneously forms a metastable Pt(dppeb)2(2+) intermediate species, 4, that is characterized by δ = 51 ppm in the (31)P NMR (J(Pt-P) = 3171 Hz) and ν(C≡C) = 2169 cm(-1) in the Raman profile, indicating that it is an uncyclized, bis-ligated complex. Over 24 h, 4 undergoes ligand exchange to form a neutral, square planar complex that spontaneously Bergman cyclizes at ambient temperature to give the crystalline product Pt(dppnap-I2)I2 (dppnap-I2 = (1,4-diiodonaphthalene-2,3-diyl)bis(diphenylphosphine)), 5, in 52% isolated yield. Computational analysis of the oxidation reaction proposes two plausible flattened tetrahedral structures for intermediate 4: one where the phosphine core has migrated to a trans-spanning chelate geometry, and a second, higher energy structure (3.3 kcal/mol) with two cis-chelating phosphine ligands (41° dihedral angle) via a restricted alkyne-terminal starting point. While the energies are disparate, the common theme in both structures is the elongated Pt-P bond lengths (>2.4 Å), indicating that nucleophilic ligand substitution by I(-) is on the reaction trajectory to the cyclized product 5. The efficiency of the redox-mediated Bergman cyclization reaction of this stable Pt(0) metalloenediyne prodrug and resulting cisplatin-like byproduct represents an intriguing new strategy for potential dual-threat metalloenediyne therapeutics.

DNA Interaction Studies of a New Platinum(II) Complex Containing Different Aromatic Dinitrogen Ligands

A new mononuclear Pt(II) complex, [Pt(DMP)(DIP)]Cl(2).H(2)O, in which DMP is 4,4-dimethyl-2,2-bipyridine and DIP is 4,7-diphenyl-1,10-phenantroline, has been synthesized and characterized by physicochemical and spectroscopic methods. The binding interaction of this complex with calf thymus DNA (CT-DNA) was investigated using fluorimetry, spectrophotometry, circular dichroism, viscosimetry and cyclic voltametry (CV). UV-VIS spectrum showed 4 nm bathochromic shift of the absorption band at 280 nm along with significant hypochromicity for the absorption band of the complex. The intrnisic binding constant (K(b) = 2 × 10(4) M(-1)) is more in keeping with intercalators and suggests this binding mode. The viscosity measurements showed that the complex-DNA interaction can be hydrophobic and confirm intercalation. Moreover, the complex induced detectable changes in the CD spectrum of CT-DNA. The fluorescence studies revealed that the probable quenching mechanism of fluorescence of the complex by CT-DNA is static quenching. The thermodynamic parameters (ΔH > 0 and ΔS > 0) showed that main interaction with hydrogenic forces occurred that is intercalation mode. Also, CV results confirm this mode because, with increasing the CT-DNA concentration, shift to higher potential was observed.

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.

The role of p53 in the cellular toxicity by active trans-platinum complexes containing isopropylamine and hydroxymethylpyridine

Despite some initial research that reported a lack of activity of trans geometry, complexes with general formula trans-[PtCl2(L)(L')] exhibit an important cytotoxic activity in cisplatin-sensitive and resistant cell lines. Based on the proposed mechanism of action for the trans-platinum compounds, they might form DNA adducts initiating a DNA-damage response and ultimately ending in the activation of the p53 protein. In the present work, we have studied the biochemical properties of the trans-[PtCl2(isopropylamine)(L)] complexes (where L is 3- or 4-(hydroxymethyl)-pyridine) against several cell lines and the relationship between cytotoxicity and the protein p53. Both complexes showed different antitumoral properties depending on the presence or absence of protein p53 in isogenic colon carcinoma HCT116 cell lines. Cell cycle studies with the complexes in these cell lines were performed to investigate their antitumoral activity. Apoptosis was observed to be launched from G1 or G2/M accumulations. Confocal microscopy showed the different behaviour of isogenic tumoral cell lines treated with the trans-platinum complexes. Our data suggest that small differences in the carrier ligands could play an important role in the overall biological effects. The body of the research regarding structure-activity relationships such as the different position of groups in the carrier ligands will provide new rational basis for the design of new platinum antitumor drugs.

Influence of amine ligands on the aquation and cytotoxicity of trans-diamine platinum(II) anticancer complexes

Three (15)N-labelled trans-Pt(ii) amine complexes with isopropylamine ((15)N-ipa), methylamine ((15)N-ma) and dimethylamine ((15)N-dma) have been prepared and characterized. 2D [(1)H,(15)N] HSQC NMR spectroscopy was used to obtain the rate and equilibrium constants for the aquation of trans-[PtCl(2)((15)N-ipa)((15)N-ma)] ((15)N-1), trans-[PtCl(2)((15)N-dma)((15)N-ma)] ((15)N-2) and trans-[PtCl(2)((15)N-dma)((15)N-ipa)] ((15)N-) in 100 mM NaClO(4) solutions at 298 K. New (15)N shift ranges for H(2)N-Pt(II)-N and HN-Pt(II)-N groups are reported. Formation of the diaqua complex was not observed for and accounted for <2% of the species at equilibrium for 1 and 2 . The first aquation step is significantly faster for 2 (k(1) = 14 x 10(-5) s(-1)) than for the two complexes with the bulkier ipa ligand (k(1) = 5.5 x 10(-5) s(-1) (), 6.1 x 10(-5) s(-1) (3)), but 2 is the least aquated of the three complexes at equilibrium. The pK(a) values for the monoaqua adducts of 1-3 are similar (5.98, 5.85 and 5.91, respectively) and 0.4 pH units lower than the related cis complex cis-[PtCl(2)(dma)(2)], indicating a smaller proportion of more reactive aqua species will exist at physiological pH. The pK(a) values for the diaqua adduct of 2 (4.59 and 7.98) are 0.3-0.6 pH units higher than those of 1(4.31 and 7.30) and 3 (4.28 and 7.29), which have very similar values. The speciation profiles of 1-3 , calculated on the basis of the calculated equilibrium and dissociation constants, indicate that <1% hydrolyzed species will exist under physiological conditions in cancer cells. The cytotoxicity of 1-3 (non-(15)N-labelled) was assessed in three cancer lines (SF268, MCF-7 and NCI-H460). The new trans-Pt(ii) diamine complex 2 is more active than 1 and 3 in all cases and is more potent than cisplatin in the MCF-7 adenocarcinoma cell line.