The cellular distribution and oxidation state of platinum(II) and platinum(IV) antitumour complexes in cancer cells

The cellular distribution of platinum in A2780 ovarian cancer cells treated with cisplatin and platinum(IV) complexes with a range of reduction potentials has been examined using elemental analysis (synchrotron radiation-induced X-ray emission). The cellular distribution of platinum(IV) drugs after 24 h is similar to that of cisplatin, consistent with the majority of administered platinum(IV) drugs being reduced. Micro-X-ray absorption near-edge spectra of cells treated with cisplatin and platinum(IV) complexes confirmed the reduction of platinum(IV) to platinum(II). In cells treated, the most difficult to reduce complex, cis,trans,cis-[PtCl₂(OH)₂(NH₃)₂], platinum(IV) was detected in the cells along with platinum(II). The observations are in accordance with the relative ease of reduction of the platinum(IV) complexes used and support the requirement of reduction for activation of platinum(IV) complexes.Abbreviations en ethane-1,2-diamine - GM growth medium - PBS phosphate buffered saline - RPMI Roswell Park Memorial Institute - SRIXE synchrotron radiation-induced X-ray emission - XAFS X-ray absorption fine structure - XANES X-ray absorption near-edge spectroscopy     

MonodentateN coordination of 1aza4oxo1,3butadienes [R1NC(R2)C(R3)O] to platinum(II). X-ray structure of trans-[PtCl2(PEt3){σ-N-(t-BuNCHC(Me)O)}]

Reaction of dimeric trans-[PtCl₂(PR₃)]₂ with 1-aza-4-oxo-1,3-butadienes [R¹NC(R²)C(R³)O, R³ = Me, Ph, OMe, NEt₂] in a 1:2 molar ratio results in almost quantitative formation of mononuclear complexes trans·[PtCl₂(PR₃){σ-N-(R¹NC(R²)C(R³)O)}]. The ligands are bonded in the monodentate σ-N bonding mode to the platinum(II) centre. This has been established by an X-ray structure determination of trans-[PtCl₂(PEt₃){σ-N-(t-BuNCHC(Me)O)}]. Crystals of the latter compound are orthorhombic with space group Pc2₁n; cell constants are a = 14.712(3), b = 15.053(2), c = 9.025(5) Å, Z= 4 and R_w = 0.056 for 3281 reflections. The 1aza4oxol,3butadiene (α-iminoketone for R³ is alkyl or aryl) has the E-configuration about the imine bond (CN 1.34(4) Å), with a C(5)C(6) distance of 1.44(5) Å and a NC(5)/ C(6)O torsion angle of 89(4)°. As a result of this ligand conformation, the acetyl hydrogen atoms are positioned (on average) into the neighbourhood of the Pt-atom above the Pt-coordination plane. Infrared and NMR (¹H, ¹³C, ³¹p) data show that these structural features are also predominant in solution.     

Cytotoxic trans-oriented iminoether platinum complexes - Kinetics of binding to DNA oligonucleotides determined by N NMR spectroscopy

The kinetics of reactions between cytotoxic trans-oriented iminoether platinum complexes and DNA oligonucleotides have been studied by 1D and 2D [¹H, ¹⁵N] HMQC NMR spectroscopy. The results for the two isomers of the mono-iminoether compound trans-[PtCl₂(NH₃){E/Z-HNC(OMe)Me}] (trans-E and trans-Z) are compared with those of the bis-iminoether derivative trans-[PtCl₂{E-HNC(OMe)Me}₂] (trans-EE). Earlier we have shown that quite unexpectedly, trans-EE is practically inert towards a central GG residue in a 12-mer double-helical duplex. We now show that the less bulky trans-E and trans-Z compounds do bind to the interior of the duplex [5′-d(G₁G₂T₃A₄C₅C₆G₇G₈ T₉A₁₀C₁₁C₁₂)]₂ which contains terminal and central “hot” GG site. The platination by trans-E and trans-Z is as expected most pronounced for the solvent exposed, terminal GG-step but significantly, competitive binding is also observed for the central GG-step. The rate of platination of the terminal G-sites is almost an order of magnitude larger for the oligomer than for the monomer GMP which was studied for comparison. The role of trans-platinum carrier ligands in influencing the type and rate of formation of adducts with DNA and other relevant biomolecules is discussed.     

Steric control of DNA interstrand cross-link sites of <Emphasis Type="Italic">trans</Emphasis> platinum complexes: specificity can be dictated by planar nonleaving groups

trans -dichloroplatinum(II) complexes exhibit antitumor activity violate the classical structure-activity relationships of platinum(II) complexes. These novel “nonclassical”trans platinum complexes also comprise those containing planar aromatic amines. Initial studies have shown that these compounds form a considerable amount of DNA interstrand cross-links (up to ∼30%) with a rate markedly higher than clinically ineffective transplatin. The present work has shown, using Maxam-Gilbert footprinting, that trans-[PtCl₂(NH₃)(quinoline)] and trans-[PtCl₂(NH₃)(thiazole)], representatives of the group of new antitumor trans-dichloroplatinum complexes containing planar amines, preferentially form DNA interstrand cross-links between guanine residues at the 5′-GC-3′ sites. Thus, DNA interstrand cross-linking by trans-[PtCl₂(NH₃)(quinoline)] and trans-[PtCl₂(NH₃)(thiazole)] is formally equivalent to that by antitumor cisplatin, but different from clinically ineffective transplatin which preferentially forms these adducts between complementary guanine and cytosine residues. This result shows for the first time that simple chemical modification of the structure of an inactive compound alters its DNA binding site into a DNA adduct of an active drug. Received: 6 January 2000 / Accepted: 8 March 2000     

Synthesis and structures of platinum(II) complexes with 5-ferrocenylpyrimidine

Reaction of platinum(II) salts with 5-ferrocenylpyrimidine (FcPM) afforded cis-[Pt(NH₃)₂(FcPM)₂](PF₆)₂ (1), trans-[Pt(NH₃)₂(FcPM)₂](PF₆)₂ (2), cis-[PtCl₂(FcPM)₂] (3), and cis-[PtCl₂(DMSO)(FcPM)] (4): their spectroscopic and electrochemical properties were investigated. Complexes 1 and 2 were structurally characterized by X-ray crystallography.     

Benzylamidine complexes of platinum(II) derived by nucleophilic addition of primary and secondary amines. X-ray crystal structure of trans-[PtCl2{Z-N(H)C(NHMe)CH2Ph}2]

The reaction of cis- and trans-[PtCl₂(NCCH₂Ph)₂] with a 5-fold excess of MeNH₂ and Me₂NH in CH₂Cl₂ at −10 °C affords in high yield the bis-amidine derivatives cis- and trans-[PtCl₂{Z-N(H)C(NHMe)CH₂Ph}₂] (1a, 2a) and cis- and trans-[PtCl₂{E-N(H)C(NMe₂)CH₂Ph}₂] (3a, 4a), respectively. The complexes were characterized by means of elemental analysis, multinuclear NMR and FT-IR techniques. The X-ray diffraction analysis was carried out for trans-[PtCl₂{Z-N(H)C(NHMe)CH₂Ph}₂] (2a).Moreover, the in vitro cytotoxicity for the new derivatives was evaluated in a wide panel of human tumor cell lines.     

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, characterization, and cytotoxicities of platinum(II) complexes bearing pyridinecarboxaldimines containing bulky aromatic groups

Condensation of 2-pyridinecarboxaldehyde with several primary amines containing bulky aryl groups gave the corresponding pyridinecarboxaldimines (N-N′). Addition of these ligands to [PtCl₂(coe)]₂ (coe = cis-cyclooctene) gave complexes of the type cis-PtCl₂(N-N′) in moderate yields. The platinum complexes have been examined for their potential cytotoxicities against OV2008 (human ovarian carcinoma) and the analogous cisplatin-resistant cell line C13.     

Cytotoxicity, mutagenicity, cellular uptake, DNA and glutathione interactions of lipophilic trans-platinum complexes tethered to 1-adamantylamine

Cytotoxicity and mutagenicity of trans,trans,trans-[PtCl₂(CH₃COO)₂(NH₃)(1-adamantylamine)] [trans-adamplatin(IV)] and its reduced analog trans-[PtCl₂(NH₃)(1-adamantylamine)] [trans-adamplatin(II)] were examined. In addition, the several factors underlying biological effects of these trans-platinum compounds using various biochemical methods were investigated. A notable feature of the growth inhibition studies was the remarkable circumvention of both acquired and intrinsic cisplatin resistance by the two lipophilic trans-compounds. Interestingly, trans-adamplatin(IV) was considerably less mutagenic than cisplatin. Consistent with the lipophilic character of trans-adamplatin complexes, their total accumulation in A2780 cells was considerably greater than that of cisplatin. The results also demonstrate that trans-adamplatin(II) exhibits DNA binding mode markedly different from that of ineffective transplatin. In addition, the reduced deactivation of trans-adamplatin(II) by glutathione seems to be an important determinant of the cytotoxic effects of the complexes tested in the present work. The factors associated with cytotoxic and mutagenic effects of trans-adamplatin complexes in tumor cell lines examined in the present work are likely to play a significant role in the overall antitumor activity of these complexes.     

Specificity of the interaction of DNA-platinum, amount of platinum, and pH measurement]

Interaction between the sodium salt of a DNA extracted from salmon sperm (41% GC) with [Pt(NH₃)₄]Cl₂, [Pt(NH₂? (CH₂)₂? NH? (CH₂)₂? NH₂Cl]Cl, cis-Pt(NH₂? (CH₂)₂? NH₂)Cl₂, cis-Pt(NH₃)₂Cl₂, trans-Pt(NH₃)₂Cl₂, K[Pt(C₂H₄)Cl₃], and K₂[PtCl₄) indicates at least three types of complexation. A correlation is found between the change of pH and the number of platinum atoms fixed per (AT + GC) unit. The first binding site is located on the G-C pairs (guanine–cytosine), most likely the N-7(G) site, as it was shown in a previous study of the guanosine-platinum salts. The fixation of the second platinum atom by the pair (AT + GC) takes place with liberation of protons. In the case of the complexes cis-Pt(NH₂? (CH₂)₂? NH₂)Cl₂, cis-Pt(NH₃)₂Cl₂, and trans-Pt(NH₃)₂Cl₂ the second interaction seems to involve simultaneously the N-7(A) and the N-1(G) and N-3(C) sites. This latter intercrosslink between guanine and cytosine obviously liberates protons and the decrease of pH is related in this case to the trans effect of the platinum compounds. The first two platinum atoms in the reaction of K₂PtCl₄] or the Zeise salt, K[Pt(C₂H₄)Cl₃] with DNA are fixed on the G-C pairs. A maximum of six platinum atoms per (AT + GC) unit were fixed in this case. Preliminary experiments with a DNA extracted from bacteria Micrococcus lysodeikticus (72% GC) give similar results.     

Structural characterization and DNA interactions of new cytotoxic transplatin analogues containing one planar and one nonplanar heterocyclic amine ligand

trans-Diaminedicholoroplatinum(II) complexes with one planar and one non-planar heterocyclic amine ligand were designed as new potential antitumor drugs. The X-ray crystallographic structures of trans-[PtCl₂(4-picoline)(piperidine)] and trans-[PtCl₂(4-picoline)(piperazine)]·HCl revealed that the piperidine and piperazine ligands bind to the platinum through the equatorial position and that the ligands adopt the chair conformation. The nonplatinated amine of the piperazine can form hydrogen bonds with atoms that are approximately 7.5 Å away from the Pt binding site. DNA is considered a major pharmacological target of platinum compounds. Hence, to expand the database correlating structural features of platinum compounds and DNA distortions induced by these compounds, which may facilitate identification of more effective anticancer platinum drugs, we describe the DNA binding mode in a cell-free medium of trans-[PtCl₂(4-picoline)(piperidine)] and trans-[PtCl₂(4-picoline)(piperazine)]·HCl. Interestingly, the overall impact of the replacement of the second ammine group in transplatin by the heterocyclic ligands appears to change the character of the global conformational changes induced in DNA towards that induced by cisplatin. The clinical ineffectiveness of the parent transplatin has been proposed to be also associated with its reduced capability to form bifunctional adducts in double-helical DNA. The results of the present work support the view that replacement of both ammine groups of transplatin by heterocyclic ligands enhances cytotoxicity probably due to the marked enhancement of the stability of intrastrand cross-links in double-helical DNA.     

A new route to N(1)-5R-tetrazole complexes via azidation to nitriles coordinated to Pt(II) and Pt(IV)

New tetrazolate complexes trans-[PtCl₂(RCN₄)₂]²⁻, trans-[PtCl₄(RCN₄)₂]²⁻ with Ph₃PCH₂Ph⁺ and (CH₃)₂NH₂⁺ counterions have been obtained by azidation of nitriles coordinated to Pt(II) and Pt(IV) {trans-[PtCl₂(RCN)₂] and trans-[PtCl₄(RCN)₂] (R = Et, Ph)} and characterized. The composition and the molecular structure of the complexes obtained were established by the СHN elemental analyses, ¹Н and ¹³С NMR spectroscopy, IR spectroscopy, mass spectrometry, and X-ray diffraction. The coordination of nitriles to Pt(II) and Pt(IV) is shown significantly activate the azidation: the reaction proceeds with a higher rate and at relatively low temperature compared with the classical 1,3-dipolar addition of azides to nitriles.     

Kinetics and mechanism for reduction of halo- and haloam(m)ine platinum(IV) complexes by l-ascorbate

Reduction of the model platinum(IV) complexes cis-[PtCl₄(NH₃)₂] (1), trans-[PtCl₄(NH₃)₂] (2), trans-[PtCl₂(en)₂]²⁺ (3), trans-[PtBr₂(NH₃)₄]²⁺ (4), [PtCl₆]²⁻ (5), and [PtBr₆]²⁻ (6) with l-ascorbic acid (H₂Asc) in 1.0 M aqueous medium at 25 °C in the region 1.75≤pH≤7.20 has been investigated using stopped-flow spectrophotometry. The redox reactions follow the rate law: −d[Pt(IV]/dt=k[H₂Asc]_tot[Pt(IV)] where k is a pH-dependent second-order rate constant and [H₂Asc]_tot, the total concentration of ascorbic acid. The pH-dependence of k is attributed to parallel reduction of Pt(IV) by the protolytic species HAsc⁻ and Asc²⁻. Analysis of the kinetics data reveals that the ascorbate anion Asc²⁻ is up to seven orders of magnitude more reactive than HAsc⁻ while H₂Asc is unreactive. Electron transfer from HAsc⁻/Asc²⁻ to the Pt(IV) compounds is suggested to take place by a mechanism involving a reductive attack on any one of the mutually trans-halide ligands by Asc²⁻ and/or HAsc⁻ forming a halide-bridged activated complex. The rapid reduction of these complexes supports the assumption that ascorbate Asc²⁻ might be an important reductant at physiological conditions for anticancer active Pt(IV) pro-drugs capable of undergoing reductive trans elimination. The parameters ΔH^≠ and ΔS^≠ for reduction of Pt(IV) with Asc²⁻ have been determined from the study of the temperature dependence of k.     

Kinetics and mechanism for reduction of anticancer-active tetrachloroam(m)ine platinum(IV) compounds by glutathione

trans -[PtCl₄(NH₃)(thiazole)] (1), trans-[PtCl₄(cha)(NH₃)] (2), cis-[PtCl₄(cha)(NH₃)] (3) (cha =cyclohexylamine), and cis-[PtCl₄(NH₃)₂] (4) has been investigatedat 25 °C in a 1.0 M aqueous medium at pH 2.0–5.0 (1) and 4.5–6.8 (2–4) using stopped-flow spectrophotometry. The redox reactions follow the second-order rate law , where k is a pH-dependent rate constant and [GSH]_tot the total concentration of glutathione. The reduction takes place via parallel reactions between the platinum(IV) complexes and the various protolytic species of glutathione. The pH dependence of the redox kinetics is ascribed to displacement of these protolytic equilibria. The thiolate species GS⁻ is the major reductant under the reaction conditions used. The second-order rate constants for reduction of compounds 1–4 by GS⁻ are (1.43±0.01)×10⁷, (3.86±0.03)×10⁶, (1.83±0.01)×10⁶, and (1.18±0.01)×10⁶M⁻¹s⁻¹, respectively. Rate constants for reduction of 1 by the protonated species GSH are more than five orders of magnitude smaller. The mechanism for the reductive elimination reactions of the Pt(IV) compounds is proposed to involve an attack by glutathione on one of the mutually trans coordinated chloride ligands, leading to two-electron transfer via a chloride-bridged activated complex. The kinetics results together with literature data indicate that platinum(IV) complexes with a trans Cl-Pt-Cl axis are reduced rapidly by glutathione as well as by ascorbate. In agreement with this observation, cytotoxicity profiles for such complexes are very similar to those for the corresponding platinum(II) product complexes. The rapid reduction within 1 s of the platinum(IV) compounds with a trans Cl-Pt-Cl axis to their platinum(II) analogs does not seem to support the strategy of using kinetic inertness as a parameter to increase anticancer activity, at least for this class of compounds. Received: 8 December 1999 / Accepted: 15 February 2000     

Platinum anticancer agents and antidepressants: desipramine enhances platinum-based cytotoxicity in human colon cancer cells

A unique synergistic effect on platinum drug cytotoxicity is noted in the presence of the tricyclic antidepressant desipramine. Desipramine is used for treating neuropathic pain, particularly in prostate cancer patients. The clinically used drugs cisplatin (cis-[PtCl₂(NH₃)₂]), oxaliplatin [1,2-diaminocyclohexaneoxalatoplatinum(II)], and the cationic trinuclear agent BBR3464 [{trans-PtCl(NH₃)₂}₂-μ-(trans-Pt(NH₃)₂(H₂N(CH₂)₆NH₂)₂)]⁴⁺, which has undergone evaluation in phase II clinical trials for activity in lung and ovarian cancers, were evaluated. Surprisingly, desipramine greatly augments the cytotoxicity of all the platinum-based chemotherapeutics in HCT116 colorectal carcinoma cell lines. Desipramine enhanced cellular accumulation of cisplatin, but had no effect on the accumulation of oxaliplatin or BBR3464, suggesting that enhanced accumulation could not be a consistent means by which desipramine altered the platinum-drug-mediated cytotoxicity. The desipramine/cisplatin combination resulted in increased levels of p53 as well as mitochondrial damage, caspase activation, and poly(ADP ribose) polymerase cleavage, suggesting that desipramine may synergize with cisplatin more than with other platinum chemotherapeutics partly by activating distinct apoptotic pathways. The study argues that desipramine may be a means of enhancing chemoresponsiveness of platinum drugs and the results warrant further investigation. The results emphasize the importance of understanding the differential pharmacological action of adjuvants employed in combinations with cancer chemotherapeutics.     

NMR studies of the interaction of cis-diamminedichloro-platinum(II) and corresponding hydrolysis products with adenosine phosphates

Complexes formed in aqueous solution between cisplatin or hydrolysis species and 5′ adenosine monophosphate (AMP) or 5′ adenosine triphosphate (ATP), the latter with and without chloride ions, have been determined using ¹⁹⁵Pt, ³¹P, ¹³C and ¹H NMR. The present results lead to the conclusion that the only monodentate complexes with AMP are cis-Pt(NH₃)₂(AMP-N7)Cl at acid pH and cis-Pt(NH₃)₂(AMP-N7)OH at neutral and basic pH. Other bidentate complexes were identified as cis-Pt(NH₃)₂(AMP-N7)₂ and cis-Pt(NH₃)₂(AMP-N7)(AMP-PO). Also discussed herein are the binding of platinum to the phosphate group Pγ with ATP and at acid pH, and the formation of the [cis-Pt(NH₃)₂(ATP-N7)H₂O]⁺ complex. In neutral and basic pH ranges, the phosphate moiety of ATP is the most reactive site. In the presence of an excess of chloride ions, the complexation rates between the ATP and the cisplatin are decreased. Furthermore, in the experimental conditions used neither the ATP nor the AMP have shown binding to N1.     

Study of the synthesis, antiproliferative properties, and interaction with DNA and polynucleotides of cisplatin-like Pt(II) complexes containing carcinogenic polyaromatic amines

The chemical and biological features of two newly synthesized [PtCl₂(L)(2-aminonaphthalene)] complexes (L is NH₃ or 2-aminonaphthalene) were compared with those of two already reported enantiomeric complexes of formula [PtCl₂(DABN)] [DABN is (R)-1,1′-binaphthyl-2,2′-diamine or (S)-1,1′-binaphthyl-2,2′-diamine]. Solution behavior, lipophilicity, cytotoxicity with regard to one colorectal (HCT116) and two ovarian (A2780 and A2780Cp8) human carcinoma cell lines, and in vitro DNA- and G-quadruplex-binding properties were evaluated. In particular, the cytotoxicity of [PtCl₂(NH₃)(2-aminonaphthalene)] was better than that of cisplatin for all cell lines, and rather resembled that of oxaliplatin. The solution behavior of the whole series of complexes and the absence of an evident relationship between lipophilicity and cytotoxicity seem to suggest that all these experimental parameters are probably smoothed out during the 3-day cytotoxicity experiments and do not strongly affect the half-maximal inhibitory concentrations. The results of electrophoretic studies indicate that different kinds of interaction with DNA can be involved in the mode of action of these complexes, with intercalation in double-stranded DNA and stacking on G-quadruplex DNA being strongly implicated in particular for [PtCl₂(NH₃)(2-aminonaphthalene)].     

Antitumor complexes of platinum with carrier molecules. 2 [1]. Mixed complexes of amino acids and tert-butylamine

In the search for a fine modulation of cisplatin analogues we have synthesized complexes with two different inert ligands bound to platinum in the cis- position. This paper reports on compounds of formula cis-[PtCl₂(aaH)(tba)] (aaH, amino acid; tba, tert-butylamine). These complexes have been synthesized with the aim of obtaining liposoluble cisplatin analogues bound to natural carrier groups. The derivatives of glycine, D-alanine, L-threonine, and L-serine were found to be moderately active against murine P388 and L1210 leukemia models. The compound K[PtCl₃(tba)] was also found to be active against the same tumor models. Their activity and potency was, however, much lower than that of cisplatin.     

Reactivity of trans-[PtCl2(NCMe)2] with cycloaliphatic amines: An ESI and NMR study. X-ray structure of

The reactivity of the cyclic primary aliphatic amines cyclopropyl-, cyclopentyl- and cyclohexylamine with cis- and trans-[PtCl₂(NCMe)₂], under the same experimental conditions, is compared. Whereas cis-[PtCl₂(NCMe)₂] yields the neutral diamidine compounds, the reactions with trans-[PtCl₂(NCMe)₂] take place either with addition or substitution processes yielding the neutral diamidine complexes trans-[PtCl₂(Amidine)₂], the monocationic trans-[PtCl(Amine)(Amidine)₂]Cl and the dicationic trans-[Pt(Amine)₂(Amidine)₂]Cl₂ salts. An NMR and ESI study indicate that the main species formed is the monocationic trans-[PtCl(Amine)(Amidine)₂]Cl complex.The X-ray structure of is reported and its supramolecular arrangement is described.     

The trans labilization of cis-[PtCl2(13CH3NH2)2] by glutathione can be monitored at physiological pH by [1H,13C] HSQC NMR

In order to monitor the trans labilization of cisplatin at physiological pH we have prepared the complex cis-[PtCl₂(¹³CH₃NH₂)₂] and studied its interactions with excess glutathione in aqueous solution at neutral pH by two-dimensional [1H,13C] heteronuclear single-quantum correlation (HSQC) NMR spectroscopy. [1H,13C] HSQC spectroscopy is a good method for following the release of ¹³CH₃NH₂ but is not so good for characterizing the Pt species in solution. In the reaction of cisplatin with glutathione, Pt–S bonds are formed and Pt–NH₃ bonds are broken. The best technique for following the formation of Pt–S bonds of cisplatin is by UV spectroscopy. [1H,13C] HSQC spectroscopy is the best method for following the breaking of the Pt–N bonds. [1H,15N] HSQC spectroscopy is the best method for characterizing the different species in solution. However, the intensity of the peaks in the ¹⁵NH₃–Pt–S region, in [1H,15N] HSQC, reflects a balance between the formation of Pt–S bonds, which increases the signal intensity, and the trans labilization, which decreases the signal intensity. [1H,15N] HSQC spectroscopy and [1H,13C] HSQC spectroscopy are complementary techniques that should be used in conjunction in order to obtain the most accurate information on the interaction of platinum complexes with sulfur-containing ligands.