3.5 TA inhibits the STAT3 pathway in vivo
We previously showed that TA inhibited the proliferation and growth of PANC-1 cells by down-regulating the expression levels of p-STAT3 (Tyr705) and STAT3-regulated proteins. To examine whether TA also suppressed the biological functions of STAT3 in vivo , we first evaluated the expression levels of total STAT3, p-STAT3 (Tyr705), and STAT3-regulated proteins in the tumor tissues. As shown in Figure 5a, TA evidently down-regulated the expression of p-STAT3 (Tyr705) and STAT3 downstream target proteins such as c-Myc, Survivin, and ICAM-1 in the high-dose group (40 mg/kg/d), while had no remarkable effect on the protein expression of total STAT3, Cyclin D1, and Bcl-2. Furthermore, immunohistological analysis of tumor tissue sections also indicated that the expression of p-STAT3 (Tyr705), c-Myc, Survivin, MMP-9, and ICAM-1 was markedly reduced in the TA-treated groups compared with the negative control group (Figure 5b).
To further validate whether TA inhibited STAT3 signaling pathwayin vivo , the protein expression of p-STAT3 (Tyr705) was determined by the tissue immunofluorescence staining. TA significantly decreased the expression of p-STAT3 (Tyr705) protein in the tumor tissues (Figure S8a). In addition, the mRNA expression levels of STAT3 target genes were measured by the qRT-PCR to examine whether TA had an impact on the expression of STAT3 downstream genes in the tumor tissues. TA dramatically decreased endogenous BCL2 , MYC ,VEGF , CASP3 , MMP9 , ICAM1 , and IL6mRNA expression, and upregulated CCND1 mRNA expression but had no impact on MMP2 mRNA expression in the high-dose group (40 mg/kg/d) (Figure S8b). In summary, our data demonstrated that TA substantially suppressed tumor growth via inhibiting STAT3 signaling pathway in vivo .