Inhibition of Indoleamine-2,3-dioxygenase (IDO) in Glioblastoma Cells by Oncolytic Herpes Simplex Virus.

Successful oncolytic virus treatment of malignant glioblastoma multiforme depends on widespread tumor-specific lytic virus replication and escape from mitigating innate immune responses to infection. Here we characterize a new HSV vector, JD0G, that is deleted for ICP0 and the joint sequences separating the unique long and short elements of the viral genome. We observed that JD0G replication was enhanced in certain glioblastoma cell lines compared to HEL cells, suggesting that a vector backbone deleted for ICP0 may be useful for treatment of glioblastoma. The innate immune response to virus infection can potentially impede oncolytic vector replication in human tumors. Indoleamine-2,3-dioxygenase (IDO) is expressed in response to interferon γ (IFNγ) and has been linked to both antiviral functions and to the immune escape of tumor cells. We observed that IFNγ treatment of human glioblastoma cells induced the expression of IDO and that this expression was quelled by infection with both wild-type and JD0G viruses. The role of IDO in inhibiting virus replication and the connection of this protein to the escape of tumor cells from immune surveillance suggest that IDO downregulation by HSV infection may enhance the oncolytic activity of vectors such as JD0G.

Impact of decaying dose rate in gamma knife radiosurgery: in vitro study on 9L rat gliosarcoma cells.

PURPOSE: Leksell Gamma Knife (LGK) installations replace their Co-60 sources every 5-10 years corresponding to one two Co-60 half-lives. Between source replacements the dose rate gradually declines. The purpose of this study was to assess whether the decreasing dose rates associated with radioactive decay of Co-60 may affect the radiobiological response of a given dose delivered to 9L rat gliosarcoma cells. METHOD AND MATERIALS: 9L rat gliosarcoma cells were irradiated using LGK U, LGK 4C, and LGK Perfexion providing three different dose rates of 0.770 Gy/ min (sources reloaded 12.0 years ago), 1.853 Gy/min (sources reloaded 5.0 years ago) and 2.937 Gy/min (sources reloaded 1.6 years ago), respectively. After irradiation of cell samples to 4.0 Gy, 8.0 Gy and 16.0 Gy using each of the LGK units, the irradiated cells were plated into petri dishes. Two weeks later cell colonies with greater than 50 cells were counted. The survival of cells was plotted as a function of dose over the range of delivered doses and fitted to a linear quadratic function of the form SD = e-αD-ßD2 , where α and ß are terms fit using the Levenberg-Marquardt algorithm. CONCLUSIONS: This study demonstrated no difference in tumor cell kill in the range of dose rates when using actual LGK unit with new sources or with sources decayed even for two half lives. This study focused on tumor cells. In future studies we will reassess the dose rate effect on cultured neurons to simulate response of normal healthy brain tissue to different dose rates.

Survival of transplanted neural progenitor cells enhanced by brain irradiation.

OBJECT: Authors of previous studies have reported that adult transplanted neural progenitor cells (NPCs) are suitable for brain cell replacement or gene delivery. In this study, the authors evaluated survival and integration of adult rat-derived NPCs after transplantation and explored the potential impact on transplant survival of various mechanical and biological factors of clinical importance. METHODS: Adult female Fischer 344 rats were used both as a source and recipient of transplanted NPCs. Both 9L and RG2 rat glioma cells were used to generate in vivo brain tumor models. On the 5th day after tumor implantation, NPCs expressing green fluorescent protein (GFP) were administered either intravenously (3.5 x 10(7) cells) or by stereotactic injection (1 x 10(4)-1 x 10(6) cells) into normal or tumor-bearing brain. The authors evaluated the effect of delivery method (sharp compared with blunt needles, normal compared with zero-volume needles, phosphate-buffered saline compared with medium as vehicle), delivery sites (intravenous compared with intratumoral compared with intraparenchymal), and pretreatment with an immunosuppressive agent (cyclosporin) or brain irradiation (20-40 Gy) on survival and integration of transplanted NPCs. RESULTS: Very few cells survived when less than 10(5) cells were transplanted. When 10(5) cells or more were transplanted, only previously administered brain irradiation significantly affected survival and integration of NPCs. Although GFP-containing NPCs could be readily detected 1 day after injection, few cells survived 4 days to 1 week unless preceded by whole-brain radiation (20 or 40 Gy in a single fraction), which increased the number of GFP-containing NPCs within the tissue more than fivefold. CONCLUSIONS: The authors' findings indicate that most NPCs, including those from a syngeneic autologous source, do not survive at the site of implantation, but that brain irradiation can facilitate subsequent survival in both normal and tumor-bearing brain. An understanding of the mechanisms of this effect could lead to improved survival and clinical utility of transplanted NPCs.

The characterization of tumor apoptosis after experimental radiosurgery.

We sought to evaluate whether radiosurgery induces apoptosis in an experimental glioma model and to elucidate the time course of this radiobiologic phenomenon. Fischer 344 rats harboring established intracranial 9L gliosarcomas underwent radiosurgery (n = 42) or no radiosurgery (n = 45). Animals were sacrificed at 3, 6, 12, 24, 48, 72 h, and 1 or 2 weeks after treatment and in situ tumor apoptosis was assessed by specific staining. Tumor apoptosis was noted to be statistically higher in radiosurgery-treated animals relative to controls at the 6-, 24-, and 48-hour time points following radiosurgery. Radiosurgery induces apoptosis in the rat intracranial 9L gliosarcoma in a time-dependent fashion. The time course of this radiobiologic phenomenon begins at approximately 6 h following radiosurgery, continues up to 48 h, and begins to decline by 72 h.

Gene transfer to glial tumors using herpes simplex virus.

Glial tumors occur as intraaxial masses in the brain and are uniformly fatal due to lack of effective therapy. Resection combined with radiation and chemotherapy fails to eradicate malignant cells infiltrating into normal brain, and recurrence at the original site is ultimately fatal. Gene transfer offers the potential to enhance tumor cell killing while sparing surrounding normal brain. Several approaches have been developed to deliver genes to tumor cells in order to kill these cells. The first strategy involves the use of viral vectors that are replication-competent, but depend on attributes unique to the tumor cell to support viral growth. Both replication-competent adenovirus and herpes simplex virus (HSV) vectors have been employed in pre-clinical studies and most recently in human clinical trials. For this purpose, HSV vectors have been engineered that replicate in dividing cells, such as tumor cells, but not in normal neurons. The use of conditional replication competent viruses could allow for their spread in tumor tissue while minimizing damage to normal brain, thus increasing the specificity and effectiveness. Such mutants include those lacking the viral thymidine kinase (tk) gene (4-7), ribonucleotide reductase gene (8,9), a protein kinase gene, or a gene (gamma34.5) required for growth specifically in neurons (11-13).