Regulation of herpes simplex virus γ134.5 expression and oncolysis of diffuse liver metastases by Myb34.5

Abstract

Myb34.5 is a herpes simplex virus 1 (HSV-1) mutant deleted in the gene for ribonucleotide reductase (ICP6). It also carries a version of γ 1 34.5 (a viral gene product that promotes the dephosphorylation of eIF-2α) that is under control of the E2F-responsive cellular B-myb promoter, rather than of its endogenous promoter. Myb34.5 replication in tumor cells results in their destruction (oncolysis). γ 1 34.5 expression by HSV-1 subverts an important cell defense mechanism against viral replication by preventing shutoff of protein synthesis after viral infection. Infection of colon carcinoma cells with Myb34.5 results in greater eIF-2α dephosphorylation and viral replication compared with infection with HSV-1 mutants completely defective in γ 1 34.5 expression. In contrast, infection of normal hepatocytes with Myb34.5 results in low levels of eIF-2α dephosphorylation and viral replication that are similar to those observed with HSV-1 mutants completely defective in γ 1 34.5 and ICP6. When administered intravascularly into mice with diffuse liver metastases, Myb34.5 has greater antineoplastic activity than HSV-1 mutants with completely defective γ 1 34.5 expression and more restricted biodistribution compared with HSV-1 mutants with wild-type γ 1 34.5 expression. Myb34.5 displays reduced virulence and toxicity compared to HSV-1 mutants with wild-type γ 1 34.5 expression. Portal venous administration of Myb34.5 significantly reduces liver tumor burden in and prolongs the life of mice with diffuse liver metastases. Preexisting Ab's to HSV-1 do not reduce the antitumor efficacy of Myb34.5 in vivo. reductase), is effectively complemented by liver metastases but not by normal liver, which results in hrR3 replication preferentially in liver metastases rather than in normal liver. However, hrR3 can replicate at low levels in non-neoplastic cells and demonstrates virulence in vivo at high titer. Accordingly, we have concentrated our efforts on development and characterization of an HSV-1 mutant that is as effective in its oncolytic potential, but less toxic and virulent in vivo.Myb34.5 is a second-generation replication-conditional HSV-1 mutant in which ICP6 expression is defective and expression of the HSV-1 γ 1 34.5 gene is regulated by the cellular B-myb promoter (14). Following HSV-1 infection, γ 1 34.5 normally interacts with the cellular protein phosphatase-1α, which leads to eIF-2α dephosphorylation (Figure 1) (15)(16)(17)(18). This allows initiation of protein translation to proceed, which is necessary for robust viral replication. HSV-1 mutants with completely defective γ 1 34.5 expression display significantly attenuated replication in both normal and neoplastic cells. In contrast, regulation of γ 1 34.5 expression by the cellular B-myb promoter following infection by Myb34.5 theoretically permits γ 1 34.5 expression in cycling cells and in cells with deregulated E2F activation. Accordingly, Myb34.5 replication in quiescent cells should be more attenuated than that of ICP6-defective HSV-1 mutants with normal γ 1 3...

Efficacy and Safety of the Oncolytic Herpes Simplex Virus rRp450 Alone and Combined With Cyclophosphamide

“…28 Our toxicity data using wild-type HSV-1 suggest it a suitable model. Nakamura et al assessed the safety of the ICP6 mutant hrR3 and found one of four mice died when receiving 10 8 pfu, when administered intrasplenically, 29 though the significance in toxicity observed via this route is unclear. Certainly, the administration of IV or IC rRp450, even when combined with systemic CPA (50 mg/kg), produced no adverse signs and symptoms in our studies.…”

Augmented Therapeutic Efficacy of an Oncolytic Herpes Simplex Virus Type 1 Mutant Expressing ICP34.5 Under the Transcriptional Control ofmusashi1Promoter in the Treatment of Malignant Glioma

“…For example, Chung et al engineered Myb34.5, an HSV mutant with deletion in the gene for RR and that carries a version of ␥34.5 that is under the control of the E2F-responsive cellular B-myb promoter, rather than of its endogenous promoter (Chung et al, 1999). Compared with HSV mutants with defective ␥34.5 expression, Myb34.5 showed enhanced oncolytic efficacy against cycling cells in culture, and showed greater antineoplastic activity in mice with diffuse liver metastases from colon carcinoma (Chung et al, 1999;Nakamura et al, 2002). Kambara et al have described rQNestin34.5, an HSV mutant with deletion in the gene for RR and that carries a version of ␥34.5 that is under control of a synthetic Nestin promoter and its second intronic enhancer (Kambara et al, 2005).…”

HSV-1 Viral Oncolysis and Molecular Imaging with PET

“…Myb34.5 exhibits decreased virulence and toxicity in mice as compared to HSV-1 mutants with wild-type γ 1 34.5 expression. Myb34.5 infusion into the portal vein significantly lowers the hepatic tumor burden and improves survival of mice with diffuse hepatic metastases [17].…”

“…Tissue biopsies are subjected to molecular analysis such as immunohistochemical staining, polymerase chain reaction (PCR) amplification of viral DNA or RT-PCR of viral mRNA [17]. Tissue biopsy of numersous sites is invasive, cumbersome, not readily repeatable and is generally not feasible in human clinical trials.…”