Synthesis and Evaluation of the Cytotoxic Activity of Water-Soluble Cationic Organometallic Complexes of the Type [Pt(η1-C2H4OMe)(L)(Phen)]+ (L = NH3, DMSO; Phen = 1,10-Phenanthroline)

Starting from the [PtCl(η1-C2H4OMe)(phen)] (phen = 1,10-phenanthroline, 1) platinum(II) precursor, we synthesized and characterized by multinuclear NMR new [Pt(η1-C2H4OMe)(L)(phen)]+ (L = NH3, 2; DMSO, 3) complexes. These organometallic species, potentially able to interact with cell membrane organic cation transporters (OCT), violating some of the classical rules for antitumor activity of cisplatin analogues, were evaluated for their cytotoxicity. Interestingly, despite both complexes 2 and 3 resulting in greater cell uptake than cisplatin in selected tumor cell lines, only 3 showed comparable or higher antitumor activity. General low cytotoxicity of complex 2 in the tested cell lines (SH-SY5Y, SK-OV-3, Hep-G2, Caco-2, HeLa, MCF-7, MG-63, ZL-65) appeared to depend on its stability towards solvolysis in neutral water, as assessed by NMR monitoring. Differently, the [Pt(η1-C2H4OMe)(DMSO)(phen)]+ (3) complex was easily hydrolyzed in neutral water, resulting in a comparable or higher cytotoxicity in cancer cells with respect to cisplatin. Further, both IC50 values and the uptake profiles of the active complex appeared quite different in the used cell lines, suggesting the occurrence of diversified biological effects. Nevertheless, further studies on the metabolism of complex 3 should be performed before planning its possible use in tissue- and tumor-specific drug design.

Insertion of terminal alkyne into Pt-N bond of the square planar [PtI2(Me2phen)] complex

The reactivity of [PtX₂(Me₂phen)] complexes (X = Cl, Br, I; Me₂phen = 2,9-dimethyl-1,10-phenanthroline) with terminal alkynes has been investigated. Although the dichlorido species [PtCl₂(Me₂phen)] exhibits negligible reactivity, the bromido and iodido derivatives lead in short time to the formation of five-coordinate Pt(ii) complexes of the type [PtX₂(Me₂phen)(η²-CH[triple bond, length as m-dash]CR)] (X = Br, I; R = Ph, n-Bu), in equilibrium with the starting reagents. Similar to analogous complexes with simple acetylene, the five coordinate species can also undergo dissociation of an halido ligand and formation of the transient square-planar cationic species [PtX(Me₂phen)(η²-CH[triple bond, length as m-dash]CR)]⁺. This latter can further evolve to give an unusual, sparingly soluble square planar product where the former terminal alkyne is converted into a :C[double bond, length as m-dash]C(H)(R) moiety with the α-carbon bridging the Pt(ii) core with one of the two N-donors of coordinated Me₂phen. The final product [PtX₂{κ²-N,C-(Z)-N[combining low line]1-N10-C[combining low line][double bond, length as m-dash]C(H)(R)}] (N1-N10 = 2,9-dimethyl-1,10-phenanthroline; X = Br, I) contains a Pt-N-C-C-N-C six-membered chelate ring in a square planar Pt(ii) coordination environment.

73Ge, 119Sn and 207Pb: general cooperative effects of single atom ligands on the NMR signals observed in tetrahedral [MXnY4-n] (M = Ge, Sn, Pb; 1 ≤ n ≤ 4; X, Y = Cl, Br, I) coordination compounds of heavier XIV group elements

An inverse linear relationship between ⁷³Ge, ¹¹⁹Sn and ²⁰⁷Pb NMR chemical shifts and the overall sum of ionic radii of coordinated halido ligands has been discovered in tetrahedral [MX_nY_4-n] (M = Ge, Sn, Pb; 1 ≤ n ≤ 4; X, Y = Cl, Br, I) coordination compounds. This finding is consistent with a previously reported correlation found in octahedral, pentacoordinate and square planar platinum complexes. The effect of the coordinated halido ligands acting on the metal as shielding conducting rings is therefore confirmed also by ⁷³Ge, ¹¹⁹Sn and ²⁰⁷Pb NMR spectroscopy.

Synthesis, characterization, and in vitro evaluation of new coordination complexes of platinum(II) and rhenium(I) with a ligand targeting the translocator protein (TSPO)

The 18 kDa translocator protein (TSPO) is overexpressed in many types of cancers and is also abundant in activated microglial cells occurring in inflammatory neurodegenerative diseases. The TSPO-selective ligand 2-(8-(2-(bis-(pyridin-2-yl-methyl)amino)acetamido)-2-(4-chlorophenyl)H-imidazo[1,2-a]pyridin-3-yl)-N,N-dipropylacetamide (CB256), which fulfills the requirements of a bifunctional chelate approach, has been used to synthesize coordination complexes containing either Pt (1) or Re (3), or both metal ions (2). The new metal complexes showed a cellular uptake markedly greater than that of the precursor metallic compounds and were also able to induce apoptosis in C6 glioma cells. The good cytotoxicity of the free ligand CB256 towards C6, A2780, and A2780cisR tumor cell lines was attenuated after coordination of the dipicolylamine moiety to Pt while coordination of the imidazopyridine residue to Re reduces the affinity towards TSPO. The results of the present investigation are essential for the design of new imidazopyridine bifunctional chelate ligands targeted to TSPO.

Insertion of alkynes into Pt-X bonds of square planar [PtX2(N^N)] (X = Cl, Br, I) complexes

The reactivity with acetylene of [PtX2(Me2phen)] (X = Cl, Br, I) complexes has been investigated. Whereas the chlorido species [PtCl2(Me2phen)] exhibits negligible reactivity at short reaction times, the bromido and iodido species [PtBr2(Me2phen)] and [PtI2(Me2phen)] lead initially to formation of Pt(II) five-coordinate complexes, [PtX2(η(2)-CH≡CH)(Me2phen)], that evolve to four-coordinate alkenyl complexes of the type [PtX(η(1)-E-CH=CHX)(Me2phen)]. The alkenyl complexes, in the presence of excess acetylene, establish an equilibrium with the five-coordinate alkyne-alkenyl species [PtX(η(1)-E-CH=CHX)(η(2)-CH≡CH)(Me2phen)] (X = Br, I). The π-bonded acetylene can be exchanged with free olefins or C≡O, affording the new alkene-alkenyl or carbonyl-alkenyl complexes [PtX(η(1)-E-CH=CHX)(η(2)-olefin)(Me2phen)] and [PtX(η(1)-E-CH=CHX)(C≡O)(Me2phen)]. The five-coordinate geometry of the alkyne-alkenyl and alkene-alkenyl complexes was assessed from NMR data and is fully consistent with that of a previously determined X-ray structure of [PtBr(η(1)-E-CH[double bond, length as m-dash]CHBr)(η(2)-CH2=CH2)(Me2phen)].

Metalated nucleotide chemisorption on hydroxyapatite

The experiments here reported evidence on the importance of the residual charge of a nucleotide derivative, for the adsorption on nHAP (hydroxyapatite nanocrystals), in water solution. We found that the simple presence of phosphates on the nucleotide derivative does not guarantee adsorption on nHAP. On the other hand, we demonstrated that a cationic or neutral charge on a nucleotide derivative produces a strongly reduced chemical adsorption (chemisorption) whereas, in the presence of a net negative charge, relevant adsorption on nHAP is observed. The number of phosphates can only modulate the adsorption efficiency of a molecule provided that this latter bears an overall negative charge. The neutral zwitterionic nucleotide Pt(II) complexes, bearing negatively charged phosphates, are unable to give stable chemisorption. Previous considerations are important to model the binding ability of phosphate bearing nucleotide derivatives or molecules on hydroxyapatite. The findings reported in the present paper could be relevant in bone tissue targeting or nHAP mediated drug delivery.

General cooperative effects of single atom ligands on a metal: a195Pt NMR chemical shift as a function of coordinated halido ligands’ ionic radii overall sum

An inverse linear relationship between the experimentally observed¹⁹⁵Pt NMR signals and the overall sum of coordinated halido X ligands’ ionic radii was discovered in Pt(ii) and Pt(iv) complexes.

Transport of platinum bonded nucleotides into proteoliposomes, mediated by Drosophila melanogaster thiamine pyrophosphate carrier protein (DmTpc1)

The results of the present study suggest that DmTpc1 is actively implicated in the specific uptake of free cytoplasmic Pt bonded nucleotides, and therefore could be linked to the mechanism of action of some platinum-based antitumor drugs. Although DmTpc1 has a low affinity for model [Pt(dien)(N7-5'-dGTP)] and cis-[Pt(NH3)2(py)(N7-5'-dGTP)] compared to dATP it's well known that DNA platination level of few metal atoms per double-stranded molecule may account for the pharmacological activity of platinum based antitumor drugs. This is the first investigation where it has been demonstrated that a mitochondrial carrier is directly involved in the transport of metalated purines related with the cisplatin mechanism of action. Moreover it is shown as a lower hindrance of nucleotide bonded platinum complexes could strongly enhance mitochondrial uptake. Furthermore, a new application of ICP-AES addressed to measure the transport of metalated nucleobases, by using a recombinant protein reconstituted into liposomes, has been here, for the first time, developed and compared with a standard technique such as the liquid scintillation counting.