Validation data supporting the characterization of novel copper complexes as anticancer agents

Abstract

Three copper(II) complexes, Cu(Sal-Gly)(phen), Cu(Sal-Gly)pheamine, Cu(Sal-Gly)phepoxy were synthesized and characterized for their anticancer properties and mechanism of action (Acilan et al., in press) [1]. Here, we provide supporting data on colon cancer cell lines complementing our previous findings in cervix cells. This paper also contains a data table for the fold changes and p-values of all genes analyzed in this study via a custom RT-qPCR array. All compounds induced DNA damage (based on 8-oxo-guanidine, ɣH2AX staining in cells) and apoptosis (based on elevated DNA condensation/fragmentation, Annexin V staining, caspase 3/7 activity and mitochondrial membrane depolarization) in HCT-116 colon cancer cells. The increase in oxidative stress was also further confirmed in these cells. Further interpretation of the data presented here can be found in the article entitled "Synthesis, biological characterization and evaluation of molecular mechanisms of novel copper complexes as anticancer agents" (Acilan et al., in press) [1].

Fig. 1

UV–vis absorption spectra measured with increasing time (time interval between spectra=5 min) for solutions of the Cu-complexes in PBS. (A) Cu(Sal-Gly)(phen) 20 μM (0.6% DMSO) total time=55 min; (B) [Cu(Sal-Gly)(pheamine) 20 μM (0.6% DMSO) total time=55 min and (C) [Cu(Sal-Gly)(phepoxy) 60 μM (1% DMSO) total time=100 min. Arrows indicate changes with time.

Fig. 2

First derivative X-band EPR spectra measured for frozen solutions (77 K) of the complexes with time. (A) Cu(Sal-Gly)(phen) 4.0 mM in MeOH, and Cu(Sal-Gly)(pheamino) (B) and Cu(Sal-Gly)(phepoxy) 1.0 mM in DMSO.

Fig. 3

Circular dichroism spectra (1 cm optical path) of CT-DNA (60 μM) in the absence and presence of different % (v/v) of DMSO.

Fig. 4

UV–vis absorption data: (A) Relative absorption values measured with time for solutions containing Cu(Sal-Gly)(phen) (20 μM) with and without CT-DNA (1 mol equivalent); (B) UV–vis absorption spectra measured for a solution of Cu(Sal-Gly)(pheamine) (40 μM) and increasing amounts of CT-DNA (from 0 to 180 μM); inset – changes observed in the ε values (M⁻¹cm⁻¹) at 256 and 278 nm. (C) UV–vis absorption spectra measured for a solution of Cu(Sal-Gly)(phepoxy) (27 μM) and increasing amounts of CT-DNA (from 0 to 28 μM). The arrow indicates increasing DNA concentration.

Fig. 5

Cytotoxicity of the Cu compounds as determined by SRB analysis. Cytotoxicity in response to three different Cu-complexes was reevaluated using a different viability assay (SRB technique) upon increasing doses (0–12.5 µM) at different time points (24 h, 72 h) in a subset of cancer cells (A-549, HCT-116, HeLa). x-axis: concentration in µM, y-axis: cell viability normalized to untreated controls.

Fig. 6

Changes in nuclear morphology in response to Cu complexes. HCT-116 cells displayed typical features of apoptosis such as fragmentation and condensation. HCT-116 cells treated with 12.5 μM of Cu complexes are shown in the figure. Insets indicate enlarged views of selected cells exhibiting these features.

Fig. 7

Annexin V/PI staining supports apoptotic form of cell death in response to Cu compounds. HCT-116 cells were treated with the Cu complexes and were stained with Annexin V/dead cell marker and counted with a flow cytometer as described in materials and methods. (A) Representative plots for HCT-116 cells following 24 h drug exposure are shown in the figure. (B) The graphs represent averages from 2 independent experiments from 24 h of exposure (left graph) and 48 h of exposure (right graph), where 10.000 cells were scored. x-axis: % cells, y-axis: name of the drug, NC: negative control, mock treated cells.

Fig. 8

Analysis of caspase 3/7 activity using a flow cytometric assay. HCT-116 cells were treated with the Cu-complexes and were stained using Caspase 3/7 kit and counted with a flow cytometer as described in materials and methods. (A) Representative plots for HCT-116 cells following 48 h drug exposure are shown in the figure. (B) The graphs represent averages from 2 independent experiments from 24 h of exposure (left graph) and 48 h of exposure (right graph), where 10.000 cells were scored. x-axis: % cells, y-axis: name of the drug, NC: negative control, mock treated cells.

Fig. 9

Induction of MMP in response to Cu complexes. HCT-116 cells were treated with the Cu complexes and were stained using MitoPotential kit and counted with a flow cytometer as described in materials and methods. (A) Representative plots for HCT-116 cells following 48 h drug exposure are shown in the figure. (B) The graphs represent averages from 2 independent experiments from 24 h of exposure (left graph) and 48 h of exposure (right graph), where 10.000 cells were scored. x-axis: % cells, y-axis: name of the drug, NC: negative control, mock treated cells.

Fig. 10

Increase in ROS in response to Cu-complexes. (A) Cells were pretreated with DCFDA with the indicated doses of Cu-complexes for 6–72 h and ROS were measured as described in materials and methods. Averages from three replicates from HCT-116 cells are shown in the graphs. y-axis: fold increase in DCFDA staining of cells relative to untreated controls, x-axis: concentration of Cu-complexes (µM). Asterisks indicate significance compared to untreated controls (paired samples t-test, p<0.05). (^⁎:Cu(Sal-Gly)(pheamine), ^⁎⁎: Cu(Sal-Gly)(phepoxy), ^⁎⁎⁎: Cu(Sal-Gly)(phen)). (B) HCT-116 cells were treated with 12.5 µM of the Cu-complexes and lysed 24 h post incubation. The cellular GSSG/GSH (oxidized/reduced forms of glutathione) levels were measured, and an increase in oxidation was observed with all three Cu-complexes. Significance is indicated by asterisks (paired samples t-test, p<0.05).

Fig. 11

Oxidative DNA damage induced by the Cu-complexes. HCT-116 cells were treated with the 12.5 μM of Cu complexes for 24 h and were stained for DNA (blue) and 8-oxo-guanine (red), the most common lesion in response to oxidative stress. 8-oxo-G staining was increased upon treatment with all Cu complexes.

Fig. 12

Induction DNA double strand breaks as a result of treatment with the Cu-complexes. (A) HCT-116 cells were treated with IC₉₀ values of the Cu complexes for 12 h, and were stained with both anti-phospho-Histone H2AX (Ser139) and anti-Histone H2AX antibodies, and quantified using a flow cytometer. Non-expressing quadrant indicates cells that do not express H2AX antigen, inactivated quadrant indicates the cells expressing H2AX without phosphorylation and activated quadrant indicates the ɣH2AX phosphorylated cells. The quantification of results is shown in the graphs. (B) In order to visually determine ɣH2AX positivity, HCT-116 cells were treated with 12.5 and 25 µM of the Cu complexes, stained for ɣH2AX and observed under the fluorescence microscope. Images were taken using 100x magnification.

Scheme 1

Formulation of the complexes.