Electrospray ionization multi-stage mass spectrometric study of the interaction products of the cytotoxic complex [Cu(thp)₄][PF₆] with methionine-rich model peptides

Interaction products of cytotoxic Cu(I) complexes with different solvent mixtures: an electrospray ionization mass spectrometry and density functional theory study

RATIONALE

[Cu(P)₄ ][BF₄ ]-type complexes (P = tertiary phosphine) have shown significant antitumor activity. This biological property appears to be activated via formation of coordinative unsaturated [Cu(P)_n ]⁺ species (n < 4), that may interact with various molecules starting from the solvent(s) in which they are dissolved. Aim of our study was to investigate the interaction of these species with different solvent mixtures.

METHODS

The interaction has been investigated by electrospray ionization mass spectrometry, and the interaction products have been characterized by multiple collisional experiments, using an ion trap mass instrument. Density functional theory (DFT) calculation studies, using a meta-hybrid exchange correlation (xc) functional and an implicit solvent model, were employed to investigate the equilibrium distribution of species in solution.

RESULTS

Depending on the nature of the solvent mixture and coordinated phosphine, three [Cu(P)₄ ][BF₄ ]-type complexes undergo dissociation with formation of [Cu(P)₂ ]⁺ , [Cu(P)(solv)]⁺ and [Cu(solv)₂ ]⁺ species (solv = solvent). Preferred collisional-induced fragmentation pathways provide qualitative information on the selectivity of [Cu(P)_n ]⁺ for specific solvents and donor atoms. Formation free energies and equilibrium constants pertaining to [Cu^I (PTA)_n ]⁺ , [Cu^I/II (solv)_n ]^m+ (n ≤ 4; m = 1, 2) and [Cu^I (PTA)_2-k (sol)_k ]⁺ (k = 1, 2) provide a comprehensive picture of equilibria in solution.

CONCLUSIONS

Dimethyl sulfoxide (DMSO) and acetonitrile (MeCN) strongly affect [Cu(P)_n ]⁺ assemblies producing mixed-ligand [Cu(P)(DMSO)]⁺ and [Cu(P)(MeCN)]⁺ species. Excess of both DMSO and MeCN solvents are able to fully displace coordinated phosphines giving [Cu(solv)₂ ]⁺ -type adducts. The presence of phosphines in the native complex is mandatory to retain the reduced oxidation state of copper. Instead, the more labile [Cu^I (MeCN)₄ ]⁺ complex dissolved in DMSO and MeCN displays a combination of Cu(I) and Cu(II) adducts. Copyright © 2016 John Wiley & Sons, Ltd.

Novel metalloantimalarials: Transmission blocking effects of water soluble Cu(I), Ag(I) and Au(I) phosphane complexes on the murine malaria parasite Plasmodium berghei

The water soluble phosphane complexes [M(L)₄]PF₆ (M=Cu(I), Ag(I)) and [Au(L)₄]Cl (L=thp (tris(hydroxymethyl)phosphane) or PTA (1,3,5-triaza-7-phosphaadamantane)) showed notable in vitro activity against Plasmodium early sporogonic stages, the sexual forms of the malaria parasite that are responsible for infection of the mosquito vector. Effects varied according to both, the type of metal and phosphane ligands. [Ag(thp)₄]PF₆ was the best performing complex exhibiting a half inhibitory concentration (IC₅₀) value in the low micromolar range (0.3-15.6μM). The silver complex [Ag(thp)₄]PF₆ was characterized by X-ray crystallography revealing that the structure comprises the cationic complex [Ag(thp)₄]⁺, the PF₆^- anion, and a water molecule of crystallization. Our results revealed that Cu(I), Ag(I) and Au(I) phosphanes complexes elicited similar activity profiles showing potential for the development of antimalarial, transmission blocking compounds. Molecules targeting the sexual parasite stages in the human and/or mosquito host are urgently needed to complement current artemisinin based treatments and next generation antimalarials in a vision not only to cure the disease but to interrupt its transmission.