Microfilament actin remodeling as a potential target for cancer drug development

Actin was first identified in non-muscle cells only about three decades ago, and at about the same time, it was found that actin filaments were disrupted in the malignant transformed cells. The actin network is a rather complex, yet important structural and functional system of all eukaryotic cells. Actin filaments provide the basic infrastructure for maintaining cell morphology and functions such as adhesion, motility, exocytosis, endocytosis, and cell division. Growing evidence from this laboratory and others shows that alterations of actin polymerization, or actin remodeling, plays a pivotal role in regulating the morphologic and phenotypic events of a malignant cell. Actin remodeling is the result of activation of oncogenic actin signaling pathways (e.g., Ras and Src), or inactivation of several important actin-binding proteins that have tumor suppressor functions (e.g., gelsolin). Distinctive protein expression patterns of some of these genes in cancer and progressive carcinogenic processes have been observed. It has become evident that actin dynamics are regulated by a complex interplay of the small GTPase proteins of Ras superfamily Rac, Rho, and Cdc42, and efforts to develop specific inhibitors for these small G proteins as anticancer drug are underway. In this review we will discuss how actin remodeling is altered in the malignant transformation process, the functional significance of actin alteration in association with malignant phenotypes, and the approaches of targeting actin remodeling for chemopreventive and chemotherapeutic drug development. Approaches including using nature products directly modulating actin polymerization, using inhibitors of actin pathway small G proteins, and using gene-augmentation for actin binding proteins will be discussed. In addition, the concept of using F/G-actin ratio as a surrogate marker for actin-pathway based therapy will also be introduced.