| Summary: | <p>Complexes of lanthanum(III) with bis-coumarins: 3,<mml:math alttext="$3'$"> <mml:msup> <mml:mn>3</mml:mn> <mml:mo>′</mml:mo> </mml:msup> </mml:math>-benzylidene-bis(4-hydroxy-2H-1-benzopyran-2-one) (<mml:math alttext="$chem{H_{2}}$"> <mml:msub> <mml:mtext>H</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math>L1) and bis(4-hydroxy-2-oxo-2H-chromen-3-yl)-(1H-pyrazol-3-yl)-methane (<mml:math alttext="$chem{H_{2}}$"> <mml:msub> <mml:mtext>H</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math>L2) were synthesized by reaction of lanthanum(III) salt and the ligands, in amounts equal to metal : ligand molar ratio of <mml:math alttext="$1 : 2$"> <mml:mn>1</mml:mn><mml:mo>:</mml:mo><mml:mn>2</mml:mn> </mml:math>. The complexes were prepared by adding an aqueous solution of lanthanum(III) salt to an aqueous solution of the ligand subsequently raising the pH of the mixture gradually to circa 5.0 by adding dilute solution of sodium hydroxide. The lanthanum(III) complexes with bis-coumarins were characterized by different physicochemical methods—elemental analysis, IR-, <mml:math alttext="$chem{{}^{1}H}$"> <mml:msup> <mml:mi></mml:mi> <mml:mn>1</mml:mn> </mml:msup> <mml:mtext>H</mml:mtext> </mml:math>-, and <mml:math alttext="$chem{{}^{13}C}$"> <mml:msup> <mml:mi></mml:mi> <mml:mrow> <mml:mn>13</mml:mn> </mml:mrow> </mml:msup> <mml:mtext>C</mml:mtext> </mml:math>-NMR-spectroscopies, and mass spectral data. The spectral data of lanthanum(III) complexes were interpreted on the basis of comparison with the spectra of the free ligands. This analysis showed that in the <mml:math alttext="$chem{La(III)}$"> <mml:mtext>La</mml:mtext><mml:mrow><mml:mo>(</mml:mo> <mml:mrow> <mml:mtext>III</mml:mtext> </mml:mrow> <mml:mo>)</mml:mo></mml:mrow> </mml:math> complexes, the ligands coordinated to the metal ion through both deprotonated hydroxyl groups. On the basis of the <mml:math alttext="$ u({C}={O})$"> <mml:mi>ν</mml:mi><mml:mrow><mml:mo>(</mml:mo> <mml:mrow> <mml:mtext>C</mml:mtext><mml:mo>=</mml:mo><mml:mtext>O</mml:mtext> </mml:mrow> <mml:mo>)</mml:mo></mml:mrow> </mml:math> red shift observed, participation of the carbonyl groups in the coordination with the metal ion was also suggested. In the present study, we performed a cytotoxic-effects screening of the lanthanum complexes with <mml:math alttext="$chem{H_{2}}$"> <mml:msub> <mml:mtext>H</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math>L1 and <mml:math alttext="$chem{H_{2}}$"> <mml:msub> <mml:mtext>H</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math>L2 in a panel of human tumor cell lines, using the standard MTT-dye reduction assay for cell viability. The panel consisted of the acute myeloid leukemia-derived HL-60 and the chronic myeloid leukemia-derived BV-173. Following a 24- hour treatment of BV-173 cells with lanthanum complex of <mml:math alttext="$chem{H_{2}}$"> <mml:msub> <mml:mtext>H</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math>L1 at 100 or 200 <mml:math alttext="$mu$"> <mml:mi>μ</mml:mi> </mml:math>M led to a DNA-laddering. The findings suggest that the observed cytotoxicity of the lanthanum complex of <mml:math alttext="$chem{H_{2}}$"> <mml:msub> <mml:mtext>H</mml:mtext> <mml:mn>2</mml:mn> </mml:msub> </mml:math>L1 on BV-173 is at least partly mediated through induction of programmed cell death.</p>
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