Utilizing Ras Signaling Pathway to Direct Selective Replication of Herpes Simplex Virus-1

Abstract

Re-engineering the tropism of viruses is an attractive translational strategy for targeting cancer cells. The Ras signal transduction pathway is a central hub for a variety of pro-oncogenic events with a fundamental role in normal and neoplastic physiology. In this work we were interested in linking Ras activation to HSV-1 replication in a direct manner in order to generate a novel oncolytic herpes virus which can target cancer cells. To establish such link, we developed a mutant HSV-1 in which the expression of ICP4 (infected cell protein-4, a viral protein necessary for replication) is controlled by activation of ELK, a transcription factor down-stream of the Ras pathway and mainly activated by ERK (extracellular signal-regulated kinase, an important Ras effector pathway). This mutant HSV-1 was named as Signal-Smart 1 (SS1). A series of prostate cells were infected with the SS1 virus. Cells with elevated levels of ELK activation were preferentially infected by the SS1 virus, as demonstrated by increased levels of viral progeny, herpetic glycoprotein C and overall SS1 viral protein production. Upon exposure to SS1, the proliferation, invasiveness and colony formation capabilities of prostate cancer cells with increased ELK activation were significantly decreased (p<0.05), while the rate of apoptosis/necrosis in these cells was increased. Additionally, high Ras signaling cells infected with SS1 showed a prominent arrest in the G1 phase of the cell cycle as compared to cells exposed to parental HSV-1. The results of this study reveal the potential for re-modeling the host-herpes interaction to specifically interfere with the life of cancer cells with increased Ras signaling. SS1 also serves as a “prototype” for development of a family of signal-smart viruses which can target cancer cells on the basis of their signaling portfolio.

Ral signaling pathway in health and cancer

“…Oncolytic virus therapy is based on the ability of viruses to effectively infect and kill tumor cells without harming the normal tissues. While some viruses seem to have a natural preference for tumor cells, most viruses require the modification in their tropism to specifically enter and/or replicate in cancer cells . Permissiveness of cells to reovirus (a RNA oncolytic virus currently in advanced clinical trials ) has been shown to be dependent on RalA signaling .…”

Regional Liver Therapy Using Oncolytic Virus to Target Hepatic Colorectal Metastases

“…Intended functions range from activating chemotherapy prodrugs (38–43), to augmenting host immune response to tumor cells (44–49), to inducing anti-angiogenesis proteins (50–54). Still other vectors have been constructed with tumor-specific promoters, designed to respond either to certain elements of a microenvironment, like hypoxia (typical of tumor cells), or to an antigen or protein expressed predominantly by cancer cells (16;55–58). The progress of these armed vectors marks a promising future for targeted oncolytic virotherapies.…”

Pancreatic cancer from bench to bedside: molecular pathways and treatment options

“…In recently published literature, gene silencing by RNA interference technology to achieve tumor selectivity has also been utilized (145). Furthermore; another strategy used is to involve the insertion of a tumorspecific promoter (148,149), by doing this the expression of a gene necessary for viral replication in order to restrict its replication in tumor cells is overexpressed (145). TOVs can also be engineered to express cell surface receptors unique to tumor cells (150,151), which allow specific tropism (145).…”