Ionizing Radiation Activates Late Herpes Simplex Virus 1 Promoters via the p38 Pathway in Tumors Treated with Oncolytic Viruses

Abstract

Ionizing radiation potentiates the oncolytic activity of attenuated herpes simplex viruses in tumors exposed to irradiation at specific time intervals by inducing higher virus yields. Cell culture studies have shown that an attenuated virus lacking the viral ; 1 34.5 genes underproduces late proteins whose synthesis depends on sustained synthesis of viral DNA. Here we report that ionizing radiation enhances gene expression from late viral promoters in transduced cells in the absence of other viral gene products. Consistent with this result, we show that in tumors infected with the attenuated virus, ionizing radiation increases 13.6-fold above baseline the gene expression from a late viral promoter as early as 2 hours after virus infection, an interval too short to account for viral DNA synthesis. The radiation-dependent upregulation of late viral genes is mediated by the p38 pathway, inasmuch as the enhancement is abolished by p38 inhibitors or a p38 dominant-negative construct. The p38 pathway is not essential for wild-type virus gene expression. The results suggest that ionizing radiation up-regulates late promoters active in the course of viral DNA synthesis and provide a rationale for use of radiation to up-regulate cytotoxic genes introduced into tumor cells by viral vectors for cytoreductive therapy. (Cancer Res 2005; 65(20): 9479-84)

Increased oncolytic efficacy for high-grade gliomas by optimal integration of ionizing radiation into the replicative cycle of HSV-1

“…Moreover, IR enhances transcription of viral late promoters by phosphorylating and activating p38 mitogen-activated protein kinase. 22 These multiple mechanisms of IR-mediated enhancement of HSV-1 viral replication are supported by our data. IR delivered at various time points in the HSV-1 replicative cycle increased viral replication, suggesting the pleiotropic role of IR in enhancing viral replication.…”

“…R2636 is a neuro-attenuated HSV-1 deleted in both copies of g 1 34.5 and encodes the luciferase gene. 22 R2636 was injected into glioma xenografts in the hindlimb of athymic nude mice on day 0 at time 0 h. In irradiated glioma xenografts, 20 Gy was given either before (6 h) or after (0.5, 6, 12, or 24 h) viral injection. Glioma xenografts were serially imaged on days 1, 2, 3, 4, 5 and 7 days post infection to detect viral luciferase expression ( Figure 1a).…”

“…10 R2636 is also a HSV-1 mutant deleted for both copies of g 1 34.5, but encodes the luciferase gene under the control of the HSV-1 gC promoter as described previously. 22 Glioma xenograft bioluminescence imaging U-87MG xenografts were grown in the right hindlimb of athymic nude mice by subcutaneous injection of 1Â10 7 cells in 100 ml of PBS. For timing experiments, tumor xenografts were injected simultaneously with 2Â10 7 pfu R2636 in 10 ml of buffer at time defined as day 0, time 0 h from the same aliquot of stock of virus.…”

“…[11][12][13][14][15][16][17][18][19][20][21][22][23] Specifically, g 1 34.5 deleted HSV-1 combined with IR resulted in increased viral replication and glioma-xenograft regression in hindlimb and orthotopic preclinical murine glioma models. 11,17 Mechanistic studies have elucidated multiple pathways through which IR enhances viral replication.…”

“…It has been shown that IR can enhance transcription of late HSV-1 viral promoters by activating the p38 mitogen-activated protein kinase pathway. 22 The elucidation of mechanisms through which IR enhances viral replication predicts that sequencing of IR and oncolytic viruses may be clinically relevant.…”