Abstract:

Objective To discuss the effects of 5-aza-2'-deoxycytidine（5-Aza-CdR） on autophagy and apoptosis of the TPC-1 cells in subcutaneous xenograft tumor tissue of the nude mice， and to clarify its mechanism. Methods Sixteen female BALB/c nude mice were inoculated with human papillary thyroid carcinoma （PTC） TPC-1 cells in the right axilla to establish the xenograft tumor model. After tumor formation， the mice were randomly divided into control group and experiment group（n=8）. The nude mice in control group were given an intraperitoneal injection of saline， while the nude mice in experiment group were given the intraperitoneal injection of 5-Aza-CdR， administered once every other day for four weeks. The growth status of xenograft tumor of the mice in both groups was observed， and the mice were sacrificed after the final administration and the tumor weights of the nude mice in two groups were detected. HE staining was used to observe the pathomorphology of xenograft tumor tissue of the nude mice in both groups；immunohistochemistry was used to detect the expression levels of microtubule-associated protein light chain 3 （LC3）， B-cell lymphoma 2（Bcl-2）， and Bcl-2-associated X protein（Bax） in xenograft tumor tissue of the nude mice in two groups；real-time fluorescence quantitative PCR（RT-qPCR） and Western blotting methods were used to detect the expression levels of LC3， Beclin-1， Bcl-2， Bax， mitogen-activated protein kinase kinase（MEK）， extracellular signal-regulated kinase 1（ERK1）， extracellular signal-regulated kinase 2（ERK2）， phosphorylated EPK1（p-ERK1）， and phosphorylated EPK2（p-ERK2） mRNA and proteins in xenograft tumor tissue of the nude mice in two groups. Results Compared with control group， the tumor volume and weight of the nude mice in experiment group were significantly decreased（P<0.01）. The number of cancer cells of the nude mice in control group was high， and the cells were densely arranged， with irregular shapes， clear nuclear staining， large overlapping nuclei， and lobulation， showing significant pathological mitotic figures consistent with PTC pathological characteristics. The number of cancer cells of the nude mice in experiment group showed a significant decresing trend， and the cells were sparse arrangement， nuclear shrinkage， and less distinct nuclei， with a significant increase in connective tissue. Compared with control group， the expression levels of LC3B and Beclin-1 mRNA and proteins in xenograft tumor tissue of the nude mice in experiment group were significantly increased（P<0.05） and the ratio of and Bax/Bcl-2 was increased（P<0.05 or P<0.01）， while the expression levels of MEK， ERK1/2， and p-ERK1/2 mRNA and proteins were significantly decreased（P<0.05 or P<0.01）. Conclusion 5-Aza-CdR can inhibit the growth of TPC-1 cells in subcutaneous xenograft tumor tissue of the nude mice， induce the autophagy， and promote the apoptosis of the tumor cells. The mechanism may be related to the inhibition of the mitogen-activated protein kinase（MAPK）/MEK/extracellular signal-regulated kinase（ERK） signaling pathways.

Key words: Papillary thyroid carcinoma, Cell autophagy, Apoptosis, Transplantation tumor, 5-aza-2'-deoxycytidine