An Experimental Study Of Low-dose High Intensity Focused Ultrasound On Apoptosis And Gene Expression In Pancreatic Cancer Xenograft Model

Objective:To assess the efficacy and safety of low-dose high intensity focused ultrasound(HIFU) on pancreatic cancer of xenograft model; To investigate the effects and mechanism of low-dose HIFU on apoptosis、gene expression in pancreatic cancer. To provide theoretical bases of low-dose HIFU for pancreatic cancer treatment.Methods:1.30nude mice were randomly devided into contol group, low-dose group and high-dose group. Human pancreatic (YY-1) subcutaneous models in nude mice were set as a research platform. After HIFU ablations, therapeutic effects were analysised by the volume of tumors at different time points、tumor growth velocity and side effects as well. The expressions of Bax and Bcl-2were tested by Western blot, tumor cell apoptosis was also analysised by TUNEL.2. The expression of the genes was analyzed by Agilent human gene expression chip. Selected differentially expressed genes were validated by real-time quantitative PCR.Results:1. After HIFU ablation, the volume of tumors in low-dose group and high-dose group was both smaller than that in control group (P<0.05). At the3st、7st and14st day, the tumor growth velocity of low-dose group and high-dose group was both lower than that of controll group (P<0.001). The volume of tumors and tumor growth velocity of low-dose group showed no statistically significant difference (P>0.05). The incidence of side effects in high-dose group was higher than that in low-dose group (P<0.05), mainly including skin burns (60%) and tissue impairments(20%).2. Compared with control group at the7st and14st day, the expression of Bax in both low-dose and high-dose group was higher with statistically significant difference (P<0.05), the expression of Bcl-2in both low-dose and high-dose group was lower with statistically significant difference. Higher Bax and lower Bcl-2expression were observed in high-dose group compared with that of low-dose group. At the7st and14st day, the rates of tumor cell apoptosis in low-dose group and high-dose group were both higher than that of control group (P<0.001). There was no statistically significant difference between low-dose group and high-dose group (P>0.05)3. Gene expression profiles revealed a total of4767differentially expressed genes by50change folds, among which,3958were up-regulated, and the other809were down-regulated. Gene Ontology(GO) and pathway analysis showed up-regulated FAS、Bid、ILl-R、Apaf-1、Caspase-8、Caspase-9, indicating that HIFU could induce apoptosis by both intrinsic and extrinsic pathways. Differentially expressed genes in p53pathway、MAPK pathway、PI3K-Akt pathway implied indirect influence of HIFU in regulating apoptosis.4. Seleted genes of Caspase-8、Caspase-9、Fas、Bcl-xL were validated by RT-qPCR analysis. The resulting comparison demonstrated high concordance between these data sets.Conclusion:1. With less incidence of side effects, low-dose HIFU is safe and feasible in treating human pancreatic cancer in BALB/c nude mice models.2. The expression of Bax was increased while the expression of Bcl-2was decreased after HIFU ablation, both having a relationship with irradiation dose and time.3. Low-dose and high-dose HIFU both promote the rate of apoptosis. The rate of tumor cell apoptosis in low-dose group showed no statistically significant difference compared with that in high-dose group4. HIFU could induce apoptosis in both intrinsic and extrinsic pathways through direct and indirrect ways.