Adenovirus expressing RIZ1 in tumor suppressor gene therapy of microsatellite-unstable colorectal cancers.

Viral vector-mediated delivery of tumor suppressor genes represents a promising strategy of cancer therapy. Several best-studied tumor suppressor genes, such as p53 and retinoblastoma (Rb), have been evaluated for gene therapy of tumors that carry mutations in these genes. However, these genes may not be applicable to microsatellite instability positive [MSI(+)] tumors because they are rarely mutated in these tumors. The Rb-interacting zinc finger gene RIZ1 is commonly mutated in MSI(+) colorectal, gastric, and endometrial cancers and has demonstrated a capacity to induce cell cycle arrest and apoptosis. Here, we found that RIZ1 expression through adenovirus vectors suppressed growth of MSI(+) HCT116 colorectal xenograft tumors that carry RIZ1 mutations. Malignant cells in the established tumors were efficiently transduced by RIZ1 adenoviruses and underwent apoptosis in response to RIZ1 expression. In comparison, a recombinant p53 adenovirus did not induce apoptosis and tumor suppression. These results suggest that RIZ1 may be useful in gene therapy of MSI(+) colorectal cancers.