Nelfinavir for the Treatment of Gammaherpesvirus-Related Tumors

Epstein-Barr virus (EBV) and Kaposi sarcoma-associated herpesvirus (KSHV) are gammaherpesviruses that are associated with a variety of human cancers, including a subset of lymphomas, carcinomas, and sarcomas. In tumors the virus typically exists in a latent state. In latently infected cells, the vast majority of viral genes are not expressed and there is little to no production of infectious virions. The virus replicates in tandem with cell division using cellular machinery. This highly restricted pattern of gene expression allows the virus to evade immune recognition and clearance.

Currently, the treatment approach to virally-associated malignancies is no different than the treatment approach to the same tumors where there is no viral association. Yet, the presence of virus within these tumors offers an opportunity to develop virus-specific, targeted therapies in these diseases. Such therapies might not only be more effective but also less toxic. EBV- and KSHV-associated cancers are more common in patients with HIV, congenital immunodeficiencies, or other immunosuppression, such as transplant recipients. These patients in particular would benefit from more targeted treatment approaches to their malignancies, potentially sparing the toxicities of cytotoxic chemotherapy in an already immunocompromised patient population.

Activation of lytic gene expression in virally-infected tumors may enhance tumor-specific cell killing through multiple mechanisms. Importantly, the cytotoxic effects of antiviral nucleoside analogues, such as acyclovir and its cogeners, depend on the activity of viral kinases which are only expressed during lytic replication. Because EBV(+) or KSHV(+) tumors are characterized by latent viral infection, these antiviral drugs as a single agent are not active in these tumors. However, if lytic gene expression could be activated in virally-associated tumors, this could render EBV(+) and KSHV(+) tumor cells susceptible to killing by antiviral nucleoside analogues.

Nelfinavir (NFV), an FDA-approved protease inhibitor for the treatment of HIV, has been shown to be a potent activator of lytic gene expression of EBV(+) and KSHV(+) cancer cell lines. Furthermore, NFV is able to activate lytic gene expression of EBV and KSHV at drug levels that are achievable in humans. There is also growing evidence that NFV has antitumor activity.

The goals of this study is to determine if NFV activates lytic gene expression in the tumors and causes tumor regression in patients with EBV(+) or KSHV(+) cancers.