634. Engineered Herpes Simplex Virus Expressing IL-12 for the Treatment of Experimental Brain Tumors
Authors: Shinya Miyamoto, Yasushi Ino, Hiroshi Fukuhara, Tomoki Todo
Journal: Molecular Therapy (2006)

Oncolytic herpes simplex virus type 1 (HSV-1) vectors are promising therapeutic agents for cancer. Their efficacy depends on the extent of both intratumoral viral replication and induction of a host antitumor immune response. Genetically engineered HSV-1 expressing various cytokines can improve survival when used in the treatment of experimental subcutaneous and brain tumors. Previous studies have shown that interleukin 12 (IL-12) is especially potent in inducing antitumor immunity when used in association withoncolytic HSV-1 vectors. IL-12 strongly induces interferon g secretion from T cells and helper T cell subset type 1 responses, and also plays an important role in cytotoxic T lymphocyte activities.A new oncolytic HSV-1 termed T-01 was created from a third- generation HSV-1, G47Δ. T-01 has triple deletions in the γ34.5, ICP6 and α47 genes, which confers high replication capability and cytotoxic activity selective to cancer cells without compromising the safety. We also developed a vector termed T-mfIL12 by inserting the fusion-type murine IL-12 gene into the deleted ICP6 region of T-01.When infected with T-mfIL12 in vitro, both Vero and Neuro2a (murine neuroblastoma) cells produced physiologically active levels of IL-12. T-mfIL-12 also showed strong cytopathic activity against Neuro2a cells comparable to T-01. When A/J mice bearing syngeneic Neuro2a subcutaneous tumors in bilateral flanks were treated by intratumoral inoculations (1 × 106 pfu) into the left tumor only, T-mfIL12 showed a significantly better antitumor activity than T-01 not only in the inoculated left tumors but also in the non-inoculated remote tumors. However, when A/J mice bearing intracerebral Neuro2a tumors were treated by a single stereotactic inoculation (2 × 105 or 1 × 106 pfu), both T-01- and T-mfIL12-treated animals showed a significantly longer survival than mock-treated animals, although no difference was observed between T-01- and T-mfIL12- treated groups irrespective of dosage. In vivo replicative capability of T-mfIL12 did not differ from that of T-01 in subcutaneous Neuro2a tumors.We conclude that an expression of IL-12 by an oncolytic HSV-1 vector enhances the antitumor activity for subcutaneous tumors, while its effect in the brain needs further exploration. The use of safe and yet potent third-generation vectors, such as G47Δ and T-01, as the backbone for expressing functional transgenes warrants future clinical application of newly created "armed" oncolytic HSV-1 vectors. Oncolytic herpes simplex virus type 1 (HSV-1) vectors are promising therapeutic agents for cancer. Their efficacy depends on the extent of both intratumoral viral replication and induction of a host antitumor immune response. Genetically engineered HSV-1 expressing various cytokines can improve survival when used in the treatment of experimental subcutaneous and brain tumors. Previous studies have shown that interleukin 12 (IL-12) is especially potent in inducing antitumor immunity when used in association withoncolytic HSV-1 vectors. IL-12 strongly induces interferon g secretion from T cells and helper T cell subset type 1 responses, and also plays an important role in cytotoxic T lymphocyte activities. A new oncolytic HSV-1 termed T-01 was created from a third- generation HSV-1, G47Δ. T-01 has triple deletions in the γ34.5, ICP6 and α47 genes, which confers high replication capability and cytotoxic activity selective to cancer cells without compromising the safety. We also developed a vector termed T-mfIL12 by inserting the fusion-type murine IL-12 gene into the deleted ICP6 region of T-01. When infected with T-mfIL12 in vitro, both Vero and Neuro2a (murine neuroblastoma) cells produced physiologically active levels of IL-12. T-mfIL-12 also showed strong cytopathic activity against Neuro2a cells comparable to T-01. When A/J mice bearing syngeneic Neuro2a subcutaneous tumors in bilateral flanks were treated by intratumoral inoculations (1 × 106 pfu) into the left tumor only, T-mfIL12 showed a significantly better antitumor activity than T-01 not only in the inoculated left tumors but also in the non-inoculated remote tumors. However, when A/J mice bearing intracerebral Neuro2a tumors were treated by a single stereotactic inoculation (2 × 105 or 1 × 106 pfu), both T-01- and T-mfIL12-treated animals showed a significantly longer survival than mock-treated animals, although no difference was observed between T-01- and T-mfIL12- treated groups irrespective of dosage. In vivo replicative capability of T-mfIL12 did not differ from that of T-01 in subcutaneous Neuro2a tumors. We conclude that an expression of IL-12 by an oncolytic HSV-1 vector enhances the antitumor activity for subcutaneous tumors, while its effect in the brain needs further exploration. The use of safe and yet potent third-generation vectors, such as G47Δ and T-01, as the backbone for expressing functional transgenes warrants future clinical application of newly created "armed" oncolytic HSV-1 vectors.