Kaposi's sarcoma is the most common malignancy in patients with AIDS and its occurrence is associated with infection by Kaposi's sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8. KSHV is potentially oncogenic because it cause transformation of human primary endothelial cells, and some KSHV genes induce tumorigenic transformation in transfected cells or tumor development in transgenic mice. Specific anti-KSHV drugs are still needed for treatment of KSHV-associated malignancies. Here, we propose to develop antisense phosphorodiamidate morpholino oligonucleotides (PMO) targeting six KSHV genes: ORFs K2 (vlL-6), K9 (v1RF), 50 (RTA), 72 (v-Cyclin), 73 (LANA) and 74 (vGCR). These genes encode products that cause transformation in transfected cells or play important roles in KSHV replication and infection. PMOs are analogs of DNA oligomers with modified sugar and phosphate moieties in the nucleotides. PMOs are third-generation antisense oligomers that exhibit high binding specificity, complete resistance to degradation in the lost, low toxicity and easy deliverability, suggesting future clinical application as a therapeutic drug. In our preliminary studies, we have demonstrated that a PMO against ORF50/RTA inhibited RTA expression in a dose-dependent manner. In this project, we will extend our studies on this PMO in blocking KSHV lytic replication and explore antisense PMOs against five other KSHV genes on inhibition of target gene expression in KSHV-infected BCBL-1 cells. These anti-KSHV PMOs will be evaluated in KSHV-infected endothelial cells to determine if they can block KSHV-induced transformation. It is our expectation that completion of these studies will provide us PMOs that can inhibit KSHV lytic replication and block target gene expression in KSHV-infected cells. Some of these PMOs are expected to suppress KSHV-induced transformation of endothelial cells. The effective PMOs will become candidates for clinical trials as specific antiviral compounds for treatment of KSHV-associated malignancies and good tools to study KSHV biology. These studies will also establish systems for examining other potential anti-KSHV targets. [unreadable] [unreadable] [unreadable]