Mechanism of action of a triazolyl peptidyl penicillin in melanoma cells and synergistic antitumor effect of its combination with thapsigargin

Abstract

In a previous study, we demonstrated that TAP7f, a synthetic triazolylpeptidyl penicillin, induces an apoptotic response and behaves as an effective antitumor agent in murine melanoma cells. In this work, we comparatively examined its mechanism of action in murine B16-F0 and human A375 melanoma cells. We first studied the contribution of an endoplasmic reticulum (ER) stress response to the apoptotic effect induced by the derivative. To this end, the expression levels of different ER stress-related proteins were evaluated by Western blot assays in both melanoma cell lines. A significant increase in the amount of ATF4, GADD153/CHOP, calnexin and GRP78/BIP was observed after incubating B16-F0 cells for 3 h or 6 h with a 20 µM concentration of TAP7f. A similar effect was observed in A375 cells for some of these ER markers. It was also shown that TAP7f increased phosphorylation levels of p38, JNK and Akt in both melanoma cell lines. Based on the effectiveness of combined therapies for cancer treatment, we decided to investigate the in vitro antiproliferative effect of TAP7f with thapsigargin, a well-known ER stress activator. The simultaneous incubation of different concentrations of both compounds showed a higher inhibition of cell growth with respect to the effect of each individual agent both in B16-F0 and A375 melanoma cells. The quantitative analysis of dose-effect curves obtained by using the Compusyn software rendered combination indexes lower than 1 (0.48-0.62 for B16-F0 and 0,41-0.76 for A375), indicating synergism. In conclusion, we showed that induction of ER stress and activation of p38, JNK and PI3K-I/Akt pathways are involved in the antitumor effect induced by TAP7f in melanoma cells. The efficacy of the combination of TAP7f with thapsigargin suggested that this therapy could be considered an auspicious tool for melanoma treatment.