**3.5 Survivin**

Survivin is a recently discovered tumor-specific inhibitor of the apoptosis protein family. There is no or micro expression in well differentiated tissues, and high expression in embryonic and most human malignant tumor tissues. It inhibits apoptosis of tumor cells, thus promoting cell growth and regulating cell division. In addition, it is closely associated with infiltration and metastasis of tumor cells. Survivin is found expressing in common malignant tumors such as breast cancer, gastric cancer, kidney cancer, melanoma, intestinal cancer, neuroblastoma cancer and ovarian cancer. In their retrospective analysis of tumor treatment, Kanwar (Kanwar *et al,* 2010)demonstrated that survivin-targeted molecular therapy could inhibit the growth of tumor cells. Recently, Chen (Chen&Deng,2008) injected gastric cancer MGC-803 cells treated with plasmids expressing survivin-siRNA and controltreated plasmids, and those without intervention into nude mice subcutaneously. Four weeks later, the mean tumor volume in the intervention group, control group and nonintervention group was 831mm3, 2617mm3 and 2536mm3 respectively, indicating that the apoptosis rate in siRNA intervention group was significantly higher than that in the control and non-intervention groups (27.63% vs 2.15% vs 2.31%). In their experiment study with survivin-target RNAi for the treatment of urinary bladder cancer, Seth (Seth *et al,* 2011) reported the similar result and further confirmed that survivin-target RNAi could inhibit tumor cell growth effectively.

### **3.6 ERK-MAPK**

ERK-MAPK is activated in many malignant tumors, and plays a primarily important role in cell growth, differentiation and survival. siRNA specific to extracelluar signal regulating kinase 1/2 (ERK1/2) could inhibit the proliferation of ovarian cancer cells and

**3.9 MYC** 

control group.

**3.11 CD147** 

tumor treatment.

**3.10 Epithelial cellular adhesion molecule** 

RNA Interference for Tumor Therapy 69

Myc gene is a group of cancer genes discovered earlier, including C-myc, N-myc and L-myc, belonging to nucleoprotein-coding cancer gene. All the three genes encode a nuclear DNAbinding protein related to cell cycle regulation. The Myc gene family and its products can promote cell proliferation, immortalization, dedifferentiation and transformation, and play an important role in the formation of various tumors. Super-expression of Myc gene has been detected in gastric cancer, breast cancer, colon cancer, cervical cancer, Hodgkin's disease and head tumors. Zhang (Zhang *et al,* 2009)injected Myc-target siRNA between transplanted colon cancer tissues in nude mice, and found that the expression level of Myc decreased by 40%; large patches of necrosed cells were seen in tumor tissues; the proliferation of tumor cells was inhibited; and the mean tumor size was about 50% of the

Epithelial cellular adhesion molecule (EpCAM) is a recognized tumor-related protein encoded by TACSTDl gene. EpCAM is more than an adhesion molecule, and also has many other functions including participation in regulating cell migration, metastasis, differentiation, signal transduction, cell cycle and metabolism. Studies have demonstrated that EpCAM presents high expression in most solid tumors. In addition, the level of EpCAM expression is positively correlated with lymphatic metastasis. Du (Du *et al,* 2009) transfected lipofectamine 2000 with EpCAM-target siRNA to treat two gastric cell lines (AGS and SGC7901) in transplanted tumor-bearing nude mice, and found that the size of both tumors was about 50% smaller than that of the control group. They also found that the level of CCND1 expression in tumor tissues was decreased, and cell division was blocked at G1.

CD147 is a transmembrane glycoprotein extensively expressing in various tissues of the human body, belonging to the immunoglobulin super-family participating in various physilogical and pathological processes of the body. CD147 interacts with integrin, central avidin, monocarboxylate transporter 1 (MCT1), MCT3 and MCT4 proteins. It is also related to the expression of lactate transporters. These proteins may act as candidate ligands or receptors of CD147 molecule and mediate the biological function of epithelial cells via protein-protein interactions. High expression of CD147 is detected in multiple tumor tissues, especially in pancreatic cancer (Zhang *et al,* 2007), where it promotes invasion, metastasis and anchorage-independent growth of tumor cells, and induces tumor angiogenesis. Schneiderhan (Schneiderhan *et al,* 2009) used CD147-target RNAi to treat pancreatic cancer cells and found that MCT1 and MCT4 were inhibited in tumor cells, and the intracellular concentration of lactate was increased, thus inhibiting the growth of tumor cells. In vivo experiments using shRNA-target silencing of CD147 to treat transplanted pancreatic cancer tumors in nude mice showed that the tumor size of the experiment group was significantly smaller than that of the control group (39.7mm3 vs 89.7mm3), indicating that CD147 as a helper protein could also be used as the target for

induce their apoptosis and death, but it had no effect on normal ovarian cells (Zeng *et al,*  2005). Super-expression of epithelial growth factor receptor HER2/neu was detected in many breast cancers, but its expression in patients with good prognosis was low. Transfection of HER2/neu siRNA led to an antiproliferative and apoptosis-inducing effect in breast cancer cells with high expression of HER2, and this effect was not observed in cells without HER2 expression, suggesting that interference with HER2 could be used as an effective strategy for the treatment of breast cancer with high expression of HER2(Faltus *et al,* 2004).

#### **3.7 Osteopontin**

Osteopontin (OPN) is a secretory extracellular matrix protein and a cytokine as well. It can promote cell chemotaxis, adhesion and migration. More studies (Wai&Kou, 2008; Wise & King, 2008;Ramaiah&Rittling,2008) have demonstrated that OPN can interact with αVβ3 and CD44 to participate in cell inflammatory response, promote cell migration, adhesion and transduction of related signals, regulate the expression of genes related to tumor development and progression, promote degradation of extracellular matrix, suppress the immune function of the body against tumors, and accelerate tumor progression. Studies(Coppola *et al,* 2004; Cui *et al,* 2007;Tang *et al,* 2007)have found that the level of OPN expression is generally increased in lung, gastrointestinal, urogenital and gynecological tumors. Zhang (Zhang *et al,* 2010) used plasmid-mediated OPN-target siRNA to transfect lung cancer A549 cells and found that the invasion and proliferation abilities of A549 cell decreased. Gong (Gong *et al,* 2010) used PEI as the carrier of OPNsiRNA and injected it between tumor tissues in nude mice bearing transplanted gastric cancer tumors. It was found that the tumor size of the experiment group was only onethird of the control group, and survival of the mice was also prolonged (animals in the control group survived 40 days, and 50% of the animals in the experiment group remained surviving at 60 days).

#### **3.8 β-catenin**

β-catenin is a multi-functional adapter protein encoded by human CTNNB1 gene. Its function is expressed in two aspects: One is acting as an important component of the Wnt signaling pathway to mediate signal movement from the membrane to the cytoplasm and to the nucleus, regulating transcription of target genes (such as c-myc,cyclin D1, MMP-7 and cyclooxygenase-2). The other is participating in E-cadherin-mediated intercellular adhesion. β-catenin participates in cell growth, proliferation, invasion and metastasis in malignant tumor tissues. It was found that β-catenin expression was extraordinarily high in many tumors, especially in esophageal cancer. Wang (Wang *et al,* 2009,2010) used β-catenintargeted RNA to interfere with plasmid pGen-3-CTNNB1 and found that pGen-3-CTNNB1 could lower the expression level of β-catenin in esophageal cancer tissue, and reduce the invasion and metastasis abilities of cancer cells. The result of the experiment with nude mice bearing transplanted esophageal cancer showed that the mean volume of tumors in βcatenin RNAi plasmid group was 909.3mm3 versus 2684.4mm3 in the negative control group and 2722.6mm3 in the non-intervention group, indicating that β-catenin-target RNAi could inhibit the growth of esophageal cancer tumors.
