Synthesis and Cytotoxicity Evaluation of Novel Coumarin-Palladium(II) Complexes against Human Cancer Cell Lines

Abstract

Two newly synthesized coumarin-palladium(II) complexes (C1 and C2) were characterized using elemental analysis, spectroscopy (IR and ¹H-¹³C NMR), and DFT methods at the B3LYP-D3BJ/6-311+G(d,p) level of theory. The in vitro and in silico cytotoxicity of coumarin ligands and their corresponding Pd(II) complexes was examined. For in vitro testing, five cell lines were selected, namely human cervical adenocarcinoma (HeLa), the melanoma cell line (FemX), epithelial lung carcinoma (A549), the somatic umbilical vein endothelial cell line (EA.hi926), and pancreatic ductal adenocarcinoma (Panc-1). In order to examine the in silico inhibitory potential and estimate inhibitory constants and binding energies, molecular docking studies were performed. The inhibitory activity of C1 and C2 was investigated towards epidermal growth factor receptor (EGFR), receptor tyrosine kinase (RTK), and B-cell lymphoma 2 (BCL-2). According to the results obtained from the molecular docking simulations, the inhibitory activity of the investigated complexes towards all the investigated proteins is equivalent or superior in comparison with current therapeutical options. Moreover, because of the low binding energies and the high correlation rate with experimentally obtained results, it was shown that, out of the three, the inhibition of RTK is the most probable mechanism of the cytotoxic activity of the investigated compounds.

Keywords: DFT optimization; artificial intelligence; cytotoxicity; in silico; molecular docking; palladium(II) complexes.

Scheme 1

The general procedure for the synthesis of the ligands L1 and L2, and consequently the complexes C1 and C2.

Figure 1

The main differences in the chemical shifts of the (A) ¹H and (B) ¹³C atom signal after complexation between the ligand L1 (lower spectrum) and its Pd(II) complex C1 (upper spectrum). Coordination coefficients (∆δ_coord.) are indicated to the lines in each case. The intensity in the downfield region of the 1H spectra (A) is multiplied by four.

Figure 1

The main differences in the chemical shifts of the (A) ¹H and (B) ¹³C atom signal after complexation between the ligand L1 (lower spectrum) and its Pd(II) complex C1 (upper spectrum). Coordination coefficients (∆δ_coord.) are indicated to the lines in each case. The intensity in the downfield region of the 1H spectra (A) is multiplied by four.

Figure 2

Optimized geometries of cis and trans isomers of C1 and C2.

Figure 3

Experimental and theoretical IR spectra for C1 and C2.

Figure 4

Cell cycle changes in phase distribution of HeLa cells induced by compound after 24 h of treatment.

Figure 5

Cell cycle changes in phase distribution of HeLa cells induced by investigated compounds 24 h after treatment.

Figure 6

Representative fluorescence photomicrographs of acridine orange-ethidium bromide-stained HeLa cells 24 h after treatment with compounds C1 and C2 (detached cells from culture supernatant). Arrows are showing cells with typical signs of apoptosis (rounding, membrane blebbing, and condensed or fragmented nuclei).

Figure 7

Scratch assay result chart showing percentages of gap reduction after 24 h treatments with IC₂₀ concentrations of compounds C1 and C2 (**** p < 0.0001).

Figure 8

Representative photomicrographs of scratch assay before and after 24 h treatments of EA.hy926 cells with IC₂₀ concentrations of compounds C1 and C2.

Figure 9

Representative photomicrographs of tube formation assay after 24 h treatments of EA.hy926 cells with IC₂₀ concentrations of compounds C1 and C2.

Figure 10

Molecular docking simulations: Interactions of L1, L2, C1, C2, and Bosutinib inside the active site of RTK, with H-bond receptor surface map.