Synthesis, structural investigations on organotin(IV) chlorin-e6 complexes, their effect on sea urchin embryonic development and induced apoptosis

Abstract

Four new organotin(IV) chlorin derivatives, [chlorin = chlorin-e6 = 21H,23H-porphine-2-propanoic acid, 18-carboxy-20-(carboxymethyl)- 8-ethenyl-13-ethyl-2,3-di-hydro-3,7,12,17-tetramethyl-(2S-trans)–], with formula (R2Sn)3(chlorin)2 Æ 2H2O (R = Me, n-Bu) and (R3Sn)3chlorin Æ 2H2O (R = Me, Ph) have been synthesized. The solid state and solution phase structures have been investigated by FT-IR, 119Sn Mo¨ssbauer, 1H and 13C NMR spectroscopy. In the solid state, (R2Sn)3(chlorin)2 Æ 2H2O complexes contain six coordinated Sn(IV), in a skew trapezoidal environment by forming trans-R2SnO4 polymeric units. As far as (R3Sn)3chlorin Æ 2H2O complexes are concerned, Sn(IV) is five coordinated in a polymeric (oligomeric) trigonal bipyramidal environment and eq-R3SnO2 units, in the solid state. In saturated solutions, a polymeric structure comparable to the solid phase, with carboxylate groups of the ligand behaving in monoanionic bidentate fashion bridging Sn(IV) atoms, was detected for the (Me3Sn)3chlorin Æ 2H2O complex, while in more diluted ones a tetrahedral configuration for the trimethyltin(IV) moieties was observed. Cytotoxic activity of the novel organotin(IV) chlorin was investigated in order to assay the effect on sea urchin embryonic development. The results obtained demonstrated that (n-Bu2Sn)3(chlorin)2 Æ 2H2O and (Ph3Sn)3chlorin Æ 2H2O exerted the antimitotic effect on the early stages of sea urchin development. In addition, the cytotoxic effect exerted by (n-Bu2Sn)3(chlorin)2 Æ 2H2O appeared with necrosis of the blastomeres, which were clearly destroyed. After treatment with (Ph3Sn)3chlorin Æ 2H2O, a programmed cell death was triggered, as shown by light microscope observations through morphological assays. The apoptotic events in 2-cell stage embryos revealed: (i) DNA fragmentation, with the TUNEL reaction (terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling); (ii) phosphatidylserine translocation in the membrane, with Annexin-V assay and (iii) cytoplasm blebbing, with the TUNEL reaction. The results demonstrated that the novel compound (Ph3Sn)3chlorin Æ 2H2O was the most toxic derivative, by exerting antimitotic effect very early and by triggering apoptosis in the 2-cell stage of sea urchin embryonic development.