Abstract: Objective To investigate the in vitro effect of sirolimus on the apoptosis of a cutaneous squamous cell carcinoma cell line, Colo-16 cells. Methods Cultured Colo-16 cells were treated with different concentrations （50, 100, 150, 200 nmol/L） of sirolimus for various durations （12, 24, 48, 72 hours）. Subsequently, cell proliferation was detected by MTT assay, and cell apoptosis by Annexin V-FITC and PI double staining. Morphological changes of the cells were observed with Hoechst 33258 fluorescent staining. Total RNA was extracted from Colo-16 cells treated with sirolimus for 48 hours, and subjected to reverse transcription （RT）-PCR for the detection of mRNA expression of B cell lymphoma/leukmia-2 （Bcl-2） and Bcl-2-associated X Protein （Bax）. Results Sirolimus inhibited the proliferation of Colo-16 cells in a time- and dose-dependent fashion. The early apoptosis rate was 7.26% ± 0.26%, 8.34% ± 0.19%, 9.86% ± 0.14%, 11.92% ± 0.15% in Colo-16 cells treated with sirolimus of 50, 100, 150, and 200 nmol/L, respectively, significantly higher than that in untreated cells （1.53% ± 0.09%, P < 0.05）; a positive correlation was observed between the apoptosis rate and concentrations of sirolimus （r = 0.955, P = 0.000）. Typical morphological changes of apoptosis, such as chromatin condensation and margination as well as nuclear fragmentation were observed by fluorescence staining. After treatment with sirolimus for 48 hours, a significant decrease was observed in the mRNA expression of Bcl-2, while an increase in that of Bax was noticed. Conclusion Sirolimus could induce Colo-16 cells apoptosis in vitro, which may be associated with the modulation of expression of apoptosis-regulating genes, such as Bcl-2 and Bax.

Key words: Rapamycin, cutaneous cell carcinoma, Colo-16cell, apoptosis