Development of an oncolytic herpes simplex virus using a tumor-specific HIF-responsive promoter

Abstract

We exploited the differential activation of hypoxia-inducible factor (HIF)-dependent gene expression in tumors versus normal tissue for the design of a targeted oncolytic Herpes simplex virus type-1 (HSV-1). A gene that is essential for viral replication, ICP4, was placed under the regulation of a HIF-responsive promoter and then introduced into the thymidine kinase locus (UL23) of HSV d120 which contains partial deletions in the two endogenous ICP4 genes. Recombinant HIF-HSV were isolated and their derivation from d120 was verified by expression of a truncated, nonfunctional form of ICP4 protein. Disruption of the UL23 locus was confirmed by loss of thymidine kinase expression and resistance to acyclovir. Unexpectedly, HIF-HSV expressed ICP4 and induced tumor cell lysis at similar levels under normoxia and hypoxia. The lack of HIF-dependent ICP4 transgene expression by HIF-HSV was due to two factors that have not previously been reported- reversion of the ICP4 gene region to its wild-type configuration and increased HIF-transcriptional activity under normoxia when cells were infected with any strain of HSV-1. The findings that an oncolytic HSV-1 is genetically unstable and can activate a tumor-related promoter in a non-specific manner have important implications for any proposed use of this virus in cancer therapy.

The protein kinase Akt1 regulates the interferon response through phosphorylation of the transcriptional repressor EMSY

“…A variety of such viruses have been tried to date. Among them are variants of HSV-1 and VSV (34,35), both of which appear to be regulated by the Akt1/EMSY/ BRCA2 pathway. Our data show that virus infection and replication are enhanced in cells expressing the ISG transcriptional repressor EMSY and that activated Akt1, which relieves the EMSY-mediated repression, inhibits virus replication.…”

Advances in the mechanisms of action of cancer-targeting oncolytic viruses (Review)

“…The approach to achieving tumor-selective viral replication has been to alter the function of the control of genetic transcription, which is essential in viral replication, to a tissue-or tumor-specific promoter. These promoters include human telomerase reverse transcription (hTERT) (19), hypoxia-inducible factor-1 (20), prostate-specific antigen (21) and α-fetoprotein (22), among others. hTERT has been identified as a major protein that functions to maintain telomere length in tumors; however, it demonstrates little or no expression in normal cells, allowing cancer cells to subvert the Hayflick limit (23).…”

Gene and Viral Therapy for Glioblastoma

“…41 Most of the molecular strategies used to achieve this rely on 3 major mechanisms: (1) deletion of components of the viral genome necessary for viral replication that seem not to be expressed in normal cells but aberrantly expressed in cancer cells, 15 (2) the insertion of promoter sequences into the viral genome that drive the expression replication genes under the control of unique transcription factors found to be overexpressed in cancer, 42 and (3) engineering viral capsid proteins to selectively transduce targeted cancer cells via unique molecular targeting. This remarkable achievement in virology continues to be an exciting and rapidly growing field but one that is made possible by exploiting the aberrant molecular/genetic pathways in tumors, thus limiting viral replication and lytic destruction in cancer cells only.…”