Characterization of KSHV-Associated Disease Specific Gene Therapy

Kaposi's sarcoma-associated herpesvirus (KSHV) was discovered in 1994 and is one of the eight human herpesviruses. KSHV is the causative agent of Kaposi's sarcoma, two human lymphoproliferative diseases, primary effusion lymphoma, AIDS-related multicentric Castleman's disease, and a more recently described interleukin-6 related disease called KSHV-inflammatory cytokine syndrome. KSHV Latency-associated nuclear antigen (LANA) is consistently identified in those KSHV-infected tumor cells in patients and also plays a role in KSHV-mediated tumorigenesis through its manipulation of cell cycle machinery and deregulation of tumor suppressor pathways. Accordingly, many researchers have focused on the LANA protein as a therapeutic target for inhibiting tumorigenesis and KSHV replication. However, despite the continuous efforts to establish specific therapeutics to control KSHV-associated malignancies, we have not succeeded; we need to explore new directions. Capitalizing on the interaction between KSHV terminal repeat (TR) and LANA, as well as the enhancer properties of TR, we devised a gene therapy vector using the adeno-associated virus (AAV) system for KSHV- associated malignancies. This vector selectively expresses therapeutic genes in LANA-expressing KSHV- associated tumor cells. We selected the thymidine kinase (TK)/ ganciclovir (GCV) as an indirect gene therapy. This antiviral drug has been shown to control KSHV-associated tumor progression. The HSV-TK initiates the conversion of the GCV to the toxic metabolite GCV-triphosphate, which inhibits DNA synthesis and induces cell apoptosis. Introducing our AAV vector should facilitate cancer cell killing by adding exogenous TK to the endogenous KSHV TK with GCV treatment. To further enhance the therapeutic gene expression from our AAV vector in KSHV-infected cells, we will implement the combination therapy using FDA-approved drugs such as the histone deacetylase inhibitor Suberoylanilide Hydroxamic Acid or BET inhibitor. These drugs are known to trigger KSHV reactivation, potentially amplifying the therapeutic gene's effect and further promoting the killing of cancer cells. In this application, we aim to complete proof-of-concept studies, evaluating the biological activity and efficacy in killing cancer cells through in vitro assays and xenograft mouse models.