**3.17 Erythropoietin**

Erythropoietin (EPO) was initially found to play a main regulatory role in the proliferation and differentiation of erythroid cells. Studies have shown that t EPO and erythropoietin receptor (EPOR) are expressed in many different nonhematopoietic organs and tissues, playing a role in promoting angiogenesis and protecting tissues. Many recent studies have discovered extensive expressions of EPO and EPOR in many malignant tumors, the autocrine/paracrine pathways of which are associated with tumor microangiogenesis, stimulation of tumor cell proliferation and sensitivity to chemotherapy. In addition, Paragh(Paragh *et al,* 2009) found that EPOR had a function independent of EPO in tumors. It was found that EPOR was highly expressed in ovarian cancer A2780 cell line, but no expression of EPO was observed in normal or hypoxic conditions. Use of exogenous EPO to intervene 2780 cells did not alter their biological effect. Paragh(Paragh *et al,* 2009) transplanted ovarian cancer cells treated with EPORtarget shRNA and those with a negative control vector in mice subcutaneously for 7 weeks, and found that the mean tumor size of the negative control group was 10-fold larger than that of the intervention group. This difference in tumor size is mainly due to decreased cell proliferation in the intervention group. However, the apoptotic rate was

RNA Interference for Tumor Therapy 73

2. bcr-abl: chronic myeloid leukemia (CML) is associated with chromosomal translocation. Protein tyrosine kinase encoded by fusion gene bcr-abl formed durin translocation plays a very important role in the development of CML. Many studies on bcr-abl interference showed that the interference was effective on fusion gene, as shown by down-regulated expression of bcr-abl protein expression, inhibition on cell growth and apoptosis, increased sensitivity to the anti-cancer agent imatinib mesylate, while it had no effect on the wild-type gene in normal tissues. Koldehoff *et al* (Koldehoff *et al,* 2007) first reported the successful use of bcr-abl siRNA in the human body. It enhanced the sensitivity to the anti-cancer agent imatinib mesylate, inhibited the expression of bcrabl, and promoted cell apoptosis. However, siRNA directing at bcr-abl homologous chromosomes could not enhance the sensitivity to imatinib mesylate and had no effect at all(Lima *et al,* 2004). The reason may be due to different degrees of down-regulation

3. p53: 50% tumors have mutated-type p53, which attenuates the function of the wildtype. Inhibiting the expression of the mutated-type p53 can help recover the function of the wild-type. A large-scale study on loss of gene function by using RNA Databank(Berns *et al,* 2004) revealed one known and five new p53-dependent hyperplasia suppressor genes (HSG). Inhibition on the expression of these genes can counteract the anti-proliferation function of p53and p19ARF, and thus remove G1 arrest

Local and systemic drug administrations are the main routes of drug delivery in current clinical trials *in vivo*. Local drug administration depends on the type of target tissue, including intravitreal injection for ophthalomological diseases; intranasal administration for respiratory diseases caused by respiratory syncytial virus; intracranial injection for central nervous system diseases; intratumor injection for carcinogenic genes; and intramuscular injection for muscle tissue diseases such as rheumatoid arthritis. Drugs delivered by local administration can directly act on the target organ, thus reducing the probability of degradation of siRNA by nuclease and the dosage of siRNA. Systemic drug administration mainly depends on intraperitoneal and intravenous injection. Systemic drug administration often needs more siRNA to enable the target organ or tissue to obtain an efficacious drug

A lot of studies have demonstrated that RNAi has substantial potential for tumor treatment. Several RNAi agents have entered clinical trials in the world (Table 1). In May 2008, RNAi agent CALAA-01 for the treatment of solid tumors, developed by Calando Pharmaceuticals, was approved by the Food and Drug Administration (FDA) of the United States for Phase I clinical trial. CALAA-01 is a complex of siRNA and cyclodextrin-transferrin-adamant-PEG nanoparticles, in which human transferrin can specifically interact with transferrin receptor

same result in animal models.

of bcr-Abl protein expression by the siRNA.

arising from DNA injury.

**4. Clinical trials** 

concentration.

and mutated-type Ras. Previous methods of gene therapy were unable to inhibit the expression of mutated-type Ras effectively. Researchers have succeeded in using retrovirus-mediated RNA intervention technique to inhibit the expression of mutant KrasV12 without affecting the other Ras subtypes (Brummelkamp *et al,* 2002). It not only inhibited neoplastic growth and transformation in experiments in vitro but obtained the

similar between the two groups, indicating that EPOR plays a role in regulating cell proliferation, and this effect is independent of EPO.
