CARD Proteins as Therapeutic Targets in Cancer

Proteins containing a caspase-associated recruitment domain (CARD) have been established as key regulators of cell death and, more recently, cytokine production. During the last several years, the number of proteins identified within this family has grown immensely and many aspects of their function point to their potential utility as novel drug targets in the treatment of cancer. Several CARD family proteins are critical components of the conserved cell death machinery which, when dysregulated, promotes oncogenesis and contributes prominently to tumor resistance to chemotherapy. The pro-apoptotic protein Apaf1, which is inactivated in some cancers, is a CARD protein that is indispensable for mitochondria-induced apoptosis. Other antiapoptotic CARD proteins, such as TUCAN / CARDINAL / CARD8, have been shown to protect tumors from cell death stimuli and to be over-expressed in certain forms of cancer. Therapeutics that activate or inhibit CARD proteins may therefore be potentially utilized as novel chemo-sensitizing agents when used in conjunction with conventional chemotherapy. Other CARD proteins influence cellular processes through the regulation of NF-kB or caspase-1, which governs the levels of interleukin-1β (IL-1β). In addition to its pro-inflammatory properties, this cytokine also contributes to neoplastic progression by promoting angiogenesis, proliferation, and the metastasis of many tumors. Many of the IL- 1β-regulating CARD proteins also contain a nucleotide binding / oligomerization domain known as a NACHT and may therefore be amenable to targeting by small molecule compounds. This review examines the role of CARD proteins in cytoprotection and cytokine processing in the context of neoplasia and presents strategies for using this information in devising potential novel anticancer agents.