Reversal of Chemoresistance in Human Lung Cancer Cell Line A549/Taxol by Synthetic Second Mitochondria-Derived Activator of Caspase Peptide.

ABSTRACT

BACKGROUND: Chemoresistance is a leading cause of treatment failure in advanced lung cancer, including that with the extensively prescribed taxol. Recently, a series of structurally unique second mitochondria-derived activators of caspase (Smac) that act as antagonists of inhibitor of apoptosis proteins (IAPs) have been discovered, exhibiting the ability of inducing enhanced apoptosis of various cancer cell types when combined with chemotherapy. In the present study, we synthesized the second mitochondria-derived activator of caspase peptide (Smac-N7 for short) and explored its capacity in combination with taxol in vitro. METHODS: The sensitivity assay and reversal ability of Smac-N7 were tested by MTT. Flow cytometry was used to analyze apoptosis of cells with Annexin V/PI double staining technique. Cell cloning ability was performed to reflect its biological behavior in each group. RESULTS: Concentrations with inhibitory rates < 10% were selected as the reversal value of Smac-N7 peptide using MTT. The reversal folds were 2.52, 3.26, 3.67, and 5.4 in taxol + Smac-N7 (0.0390625, 0.078125, 0.15625, 0.3125 µg/mL, respectively), and concentrations of Smac-N7 and reversal folds appeared in an obvious positive correlation (r(s) = 1, p = 0.000). Apoptosis analyzed at 48 hours by flow cytometry showed the apoptotic rates in taxol and 0.0390625, 0.078125, 0.15625, and 0.3125 µg/mL Smac-N7 + taxol groups were 15.4 ± 1.09%, 20.8% ± 2.18%, 28.4% ± 4.17%, 37.64% ± 6.41%, and 46.6% ± 7.76%, respectively. Concentrations of Smac-N7 appeared to have negative correlations with PE and SF (r(s) = -1, p < 0.05), which showed that the cells' cloning ability in 0.3125 µg/mL Smac-N7 + taxol group was worse than that of other groups. CONCLUSIONS: When combined with taxol, 0.3125 µg/mL Smac-N7 peptide may significantly increase taxol-induced apoptosis in chemoresistant A549/taxol lung cells at 48 hours, and is potentially useful as a reversal agent in lung cancer therapy.