Comparison between the antiproliferative effect and intracellular glutathione depletion induced by Casiopeína IIgly and cisplatin in murine melanoma B16 cells

Background: Casiopeína IIgly (Cas IIgly) [Cu(4,7-dimethyl-1,10-phenanthroline)(glycinate)]NO(3) induce oxidative damage in different human tumour cell strains, as the known anticancer agent cisplatin (CDDP) does.

Purpose: To compare glutathione (GSH) depletion induced by Cas IIgly and CDDP in murine melanoma B16 cells and its relationship with their antiproliferative effect.

Materials and methods: Cell growth was determined according to the sulforhodamine B assay. Intracellular GSH levels were measured by the reduction of Ellman's reagent (DTNB).

Results: Cas IIgly IC50 in B16 cells was 54.5 μM (24.21 μg/mL), which depleted GSH from 1092 to 585 ng per million cells in a 30 min incubation period. In the other hand, CDDP was less toxic at the same conditions with an IC50 equal to 197.76 μM (59.33 μg/mL), and depleted GSH to 50% of the normal only after a longer exposure period (4h). The addition of 1.8mM ascorbic acid (Asc) or 1mM buthionine sulfoximine (BSO) enhanced Cas IIgly toxicity, whereas it was prevented by 100 U/mL catalase. BSO sensitised B16 cells to CDDP, but neither Asc or catalase modified CDDP effects.

Conclusions: The antiproliferative effect of both drugs correlated to intracellular GSH levels. Unlike CDDP, GSH depletion induced by Cas IIgly occurs earlier, it is enhanced by ascorbic acid and preventable by catalase. Redox cycles, feasible only with Cas IIgly, may be an important difference in their mode of action.