A Mutant Type 2 Herpes Simplex Virus Deleted for the Protein Kinase Domain of the ICP10 Gene Is a Potent Oncolytic Virus

Abstract

Replication-selective oncolytic herpes simplex virus (HSV) has shown considerable promise as an antitumor agent. Although the current oncolytic HSVs were exclusively constructed from HSV-1, HSV-2 has several unique features that could be exploited to convert the virus to an oncolytic agent. The N-terminus of the HSV-2 ICP10 gene product contains a well-defined serine/threonine protein kinase (PK) domain, which can activate the Ras/MEK/MAPK mitogenic pathway and thus facilitate efficient HSV-2 replication. Because the Ras signaling pathway is a key regulator of normal cell growth and malignant transformation, it is aberrantly activated in many human tumors. Here we report that a mutant HSV-2 (FusOn-H2), constructed by replacing the PK domain of ICP10 with the gene encoding the green fluorescent protein, can selectively replicate in and thus lyse tumor cells. Moreover, infection of FusOn-H2 led to syncytia formation in tumor cells, providing an additional tumor-destroying mechanism. A single moderate-dose injection of FusOn-H2 into established breast cancer xenografts completely eradicated the tumors in more than 80% of the animals, leading to their long-term survival. We conclude that this HSV-2 mutant is a safe and potent oncolytic agent useful for the treatment of malignant solid tumors such as breast cancer.

An HSV-2-based oncolytic virus deleted in the PK domain of the ICP10 gene is a potent inducer of apoptotic death in tumor cells

“…Although we previously described the ability of FusOn-H2 to induce syncytia formation by tumor cells, 12 this cell membrane fusion was not obvious except with FusOn-H2-infected SKOV3 cells, possibly because the relatively high virus dose used in this experiment led to a cell infection rate of nearly 100%. The fact that FusOn-H2 could induce apoptosis when syncytia formation was not obvious indicates that the fusogenic phenotype of this virus did not directly contribute to its ability to induce An oncolytic HSV-2 induces apoptosis in tumor cells X Fu et al apoptosis.…”

“…As FusOn-H2 carries the gene that encodes green fluorescent protein (GFP) inserted in its genome, 12 its presence in cells can be conveniently determined by detecting the expression of this marker gene. We therefore infected EC9706 cells with FusOn-H2 and then stained them with Hoechst dye An oncolytic HSV-2 induces apoptosis in tumor cells X Fu et al ( Figure 3).…”

“…10,11 We recently constructed a unique oncolytic virus, based on the HSV-2 backbone, that we designated as FusOn-H2. 12 To generate FusOn-H2, we deleted the serine/threonine protein kinase (PK) domain of the ICP10 gene, the homolog of the ICP6 gene in HSV-1. This domain can activate the Ras/MEK/MAPK mitogenic pathway by binding to and phosphorylating the GTPase-activating protein Ras-GAP and is therefore required for efficient HSV-2 replication.…”

“…This domain can activate the Ras/MEK/MAPK mitogenic pathway by binding to and phosphorylating the GTPase-activating protein Ras-GAP and is therefore required for efficient HSV-2 replication. 13,14 Deletion of the PK domain from the viral genome impairs virus growth in normal cells and in non-transformed cells with inactive Ras signaling, 12,15 but does not substantially affect virus replication in tumor cells, 12 where Ras signaling is frequently activated by mutations in the Ras gene itself or by alterations in upstream or downstream signaling components. 16 Preliminary studies indicate that FusOn-H2 kills tumor cells by at least two mechanisms: direct cytolysis and syncytia formation.…”

“…16 Preliminary studies indicate that FusOn-H2 kills tumor cells by at least two mechanisms: direct cytolysis and syncytia formation. 12,17 The induction of apoptosis in tumor cells is an attractive antitumor strategy that, in principle, could be implemented with oncolytic HSVs. 18 However, since premature apoptosis represents an important mechanism of host cell defense against viral infections, 19 HSV and several other viruses have developed mechanisms to prevent the early apoptotic death of infected cells.…”