**5.** *LAPTM4B* **gene and the encoded LAPTM4B-35 protein as a novel therapeutic targets**

#### **5.1 Adjusting the expression equilibrium between LAPTM4B-35 and LAPTM4B-24 can be a novel strategy for biotherapy of hepatocellular carcinoma**

As described in section 3, the expression equilibrium of LAPTM4B-35 and LAPTM4B-24 plays a pivotal role in maintaining the physiological status of cells. LAPTM4B-35 promotes resistance to apoptosis, deregulation of proliferation, enhancement of migration and invasion, and multi-drug resistance. On the other hand, up-regulation of LAPTM4B-24 increases sensitivity to induction of apoptosis and autophagocytosis. As we have demonstrated in our laboratory knockdown of the high expression of the endogenous cancer-promoting protein LAPTM4B-35 via RNAi, or elevating the relatively low expression of the cancer-inhibiting protein LAPTM4B-24 by transgenic therapy can significantly inhibit cancer growth and metastasis and thus may be applicable in cancer biotherapy. Therefore, we suggest knockdown of LAPTM4B-35 expression via RNAi or microRNA, and/or upregulation of LAPTM4B-24 expression may provide effective strategies for treatment of HCC and possibly other cancers.

### **5.2 LAPTM4B-35 is a novel therapeutic target for neoadjuvant chemotherapy**

Neoadjuvant chemotherapy generally targets one or more molecules in signaling pathways. As discussed in section 3, over-expression of LAPTM4B-35 promotes hepatocarcinogenesis, faster growth of human HCC xenografts and metastasis in mice, and leads to anti-apoptosis, deregulation of proliferation, and enhancement of migration and invasion and multi-drug resistance. In addition, over-expression of LAPTM4B-35 leads to accumulation of a number of cell cycle promoting proteins and survival proteins, and results in down-regulation of a number of cell cycle inhibiting proteins and proapoptotic proteins by activating a signaling network including at least 4 different signaling pathways. Based on our studies in vitro and in vivo, it is clear that LAPTM4B-35 has significant potential as an important novel target for cancer treatment. Recently, we have screened out a few small molecules from various libraries containing nearly 2000 chemically synthetic compounds. These small molecules are able to kill a variety of cancer cells that over-express the *LAPTM4B* gene and LAPTM4B-35 protein in vitro, but do not harm the normal fetal liver cells which do not over-express this gene. One of these small molecules has been demonstrated to inhibit growth and metastasis of human HCC xenografts in nude mice, and results in cellular and molecular alterations opposite to those that result from over-expression of LAPTM4B-35 in HCC cells. Some of these active small molecules have been demonstrated to be inhibitors of tyrosine kinase (unpublished data).

In summary, this gene and the proteins it encodes harbor great potential for application in cancer biotherapy and chemotherapy.
