Cytotoxic and antiproliferative effect of tepary bean lectins on C33-A, MCF-7, SKNSH, and SW480 cell lines

Abstract

For many years, several studies have been employing lectin from vegetables in order to prove its toxic effect on various cell lines. In this work, we analyzed the cytotoxic, antiproliferative, and post-incubatory effect of pure tepary bean lectins on four lines of malignant cells: C33-A; MCF-7; SKNSH, and SW480. The tests were carried out employing MTT and 3[H]-thymidine assays. The results showed that after 24 h of lectin exposure, the cells lines showed a dose-dependent cytotoxic effect, the effect being higher on MCF-7, while C33-A showed the highest resistance. Cell proliferation studies showed that the toxic effect induced by lectins is higher even when lectins are removed, and in fact, the inhibition of proliferation continues after 48 h. Due to the use of two techniques to analyze the cytotoxic and antiproliferative effect, differences were observed in the results, which can be explained by the fact that one technique is based on metabolic reactions, while the other is based on the 3[H]-thymidine incorporated in DNA by cells under division. These results allow concluding that lectins exert a cytotoxic effect after 24 h of exposure, exhibiting a dose-dependent effect. In some cases, the cytotoxic effect is higher even when the lectins are eliminated, however, in other cases, the cells showed a proliferative effect.

Figure 1

Affinity chromatography in immobilized fetuin of the aqueous extract from tepary beans after precipitation with ammonium sulfate. The lectin fraction was eluted with an acid solution (50 mM glycine-HCl, pH 2.5).

Figure 2

Cytotoxicity of tepary bean lectin (TBL) toward SKNSH, SW480, MCF-7, and C33-A cells after 24 h of exposure employing the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell assay. All values are expressed as mean ± SEM of three independent experiments.

Figure 3

Effect of tepary bean lectin on cell proliferation after 24 h of exposure, in SKNSH, SW480, MCF-7, and C33-A cells employing the ³[H]-thymidine assay. All values are expressed as mean ± SEM of three independent experiments.

Figure 4

Cytotoxicity of lectin after 24 h, during which lectins were removed from the cells employing the 3-(4,5-dimethylthazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell assay. The cells were previously incubated for 24 h with the lectin solution; then, the solutions were removed and the cells were incubated for 24 h only with cell culture solutions [Dulbecco’s modified Eagle’s medium (DMEM) and fetal bovine serum (FBS)]. All values are expressed as mean ± SEM of three independent experiments.

Figure 5

Cytotoxicity of lectin after 48 h, showing that the lectins were removed from the cells, employing the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell assay. The cells were previously incubated for 24 h with the lectin solution. Then, the solution was removed and the cells were incubated for only 48 h with the cell culture solution [Dulbecco’s modified Eagle’s medium (DMEM) and fetal bovine serum (FBS)]. All values are expressed as mean ± SEM of three independent experiments.

Figure 6

Effect of lectin on cell proliferation after 24 h during which lectins were removed from the cells, employing the ³[H]-thymidine assay. The cells were previously incubated for 24 h with lectin solution; then, the solution was removed and the cells were incubated for only 24 h with the cell culture solutions [Dulbecco’s modified Eagle’s medium (DMEM) and fetal bovine serum (FBS)]. All values are expressed as mean ± SEM of three independent experiments.

Figure 7

Effect of lectin on cell proliferation 48 h after the lectins were removed from the cells, employing the ³[H]-thymidine assay. Cells were previously incubated for 24 h with the lectin solutions; then, the solutions were removed and the cells were incubated for only 48 h with the culture cell solutions [Dulbecco’s modified Eagle’s medium (DMEM) and fetal bovine serum (FBS)]. All values are expressed as mean ± SEM of three independent experiments.