Oncolytic viral gene therapy for prostate cancer using two attenuated,replication-competent,genetically engineered herpes simplex viruses

BACKGROUND: Attenuated, replication-competent herpes simplex virus mutants offer an exciting new modality in cancer therapy through their ability to selectively replicate within and kill malignant cells with minimal harm to normal tissues. METHODS: This study investigates the efficacy of two such viruses, G207 and NV1020, in human prostatic carcinoma. In vitro studies were performed on four human prostatic carcinoma cell lines, and in vivo single/multiple dose studies were undertaken on mice by using two human cell types. Tumor volume, histopathology at necropsy, and serum prostate specific antigen (PSA) were used as measures of antiproliferative effect in the in vivo experiments. RESULTS: Both viruses were effective in producing cytolytic effects in vitro at various multiplicities of infection in all cell lines tested. Both viruses demonstrated antitumor effects in vivo with a statistically significant decrease in serum PSA and inhibition of growth of both PC-3 and C4-2 subcutaneous xenografts. Tumor-free animals at necropsy were observed in the treated groups but not in control animals. CONCLUSION: These results display impressive activity against human prostate cancer and offer promise for the use of this modality in the future.     

Replication-competent herpes virus NV1020 as direct treatment of pleural cancer in a rat model

OBJECTIVE: Innovative treatments are needed for metastatic disease involving the pleura. NV1020 is a novel, multimutated, replication-restricted herpes simplex virus under investigation for its ability to selectively kill tumors by means of direct cell lysis. This study examines NV1020 in a rat model of pleura-based lung cancer. METHODS: Cytotoxicity and viral proliferation were evaluated in vitro by exposure of the human non-small cell lung cancer cell line A549 to virus. NV1020 was also tested in an in vivo pleura-based cancer model established by injecting 1 x 10(7) A549 cells into the thoracic cavity of nude rats. Intrapleural treatments (1 x 10(7) viral particles) were given 3 hours or 3 days after tumor injection to model treatment of microscopic or macroscopic disease (n = 8-9/group). Tumor burden was assessed at 5 weeks. NV1020 infection and dissemination within the thoracic cavity was determined by means of immunohistochemistry. RESULTS: In vitro, at multiplicities of infection (viral particles per tumor cell) of 0.01, 0.1, and 1.0, cell killing of A549 by NV1020 was 66%, 90%, and 97%, respectively, at 7 days after infection. Viral burst occurred by day 2. Intrapleural treatment was effective for both the microscopic (P <.001) and macroscopic (P <.05) in vivo tumor models. Virus was detectable by means of immunohistochemistry in tumors but not in adjacent normal intrathoracic tissues. CONCLUSIONS: NV1020 is not only highly cytotoxic to the human lung cancer line A549 in vitro but can be delivered in a clinically relevant fashion to safely and effectively treat pleura-based tumor in vivo in a rat model.     

5-Fluorouracil and gemcitabine potentiate the efficacy of oncolytic herpes viral gene therapy in the treatment of pancreatic cancer

Oncolytic herpes viruses are attenuated, replication-competent viruses that selectively infect, replicate within, and lyse cancer cells and are highly efficacious in the treatment of a wide variety of experimental cancers. The current study seeks to define the pharmacologic interactions between chemotherapeutic drugs and the oncolytic herpes viral strain NV1066 in the treatment of pancreatic cancer cell lines. The human pancreatic cancer cell lines Hs 700T, PANC-1, and MIA P_aC_a-2 were treated in vitro with NV1066 at multiplicities of infection (MOI; ratio of the number of viral particles per tumor cell) ranging from 0.01 to 1.0 with or without 5-fluorouracil (5-FU) or gemcitabine. Synergistic efficacy was determined by the isobologram and combination-index methods of Chou and Talalay. Viral replication was measured using a standard plaque assay. Six days after combination therapy, 76% of Hs 700T cells were killed compared with 43% with NV1066 infection alone (MOI = 0.1) or 0% with 5-FU alone (2 βmol/L) (P < .01). Isobologram and combination-index analyses confirmed a strongly synergistic pharmacologic interaction between the agents at all viral and drug combinations tested (LD5 to LD95) in the three cell lines. Dose reductions up to 6- and 78-fold may be achieved with combination therapy for NV1066 and 5-FU, respectively, without compromising cell kill. 5-FU increased viral replication up to 19-fold compared with cells treated with virus alone. Similar results were observed by combining gemcitabine and NV1066. We have demonstrated that 5-FU and gemcitabine potentiate oncolytic herpes viral replication and cytotoxicity across a range of clinically achievable doses in the treatment of human pancreatic cancer cell lines. The potential clinical implications of this synergistic interaction include improvements in efficacy, treatment-associated toxicity, tolerability of therapeutic regimens, and quality of life. These data provide the cellular basis for the clinical investigation of combined oncolytic herpes virus therapy and chemotherapy in the treatment of pancreatic cancer. Presented at the Forty-Sixth Annual Meeting of The Society for Surgery of the Alimentary Tract, Chicago, Illinois, May 141-18, 2005 (oral presentation). Supported in part by training grant T 32 CA09501 (D.P.E. and K.J.H.), AACR-AstraZeneca Cancer Research and Prevention fellowship (P.S.A), grants RO1 CA 76416 and RO1 CA/DK80982 (Y.F.) from the National Institutes of Health, grant BC024118 from the U.S. Army (Y.F.), grant IMG0402501 from the Susan G. Komen Foundation (Y.F.), and grant 032047 from Flight Attendant Medical Research Institute (Y.F.).     

Interleukin 12 secretion enhances antitumor efficacy of oncolytic herpes simplex viral therapy for colorectal cancer

OBJECTIVE: To assess the strategy of combining oncolytic herpes simplex virus (HSV) therapy with immunomodulatory therapy as treatment for experimental colon cancer. The oncolytic HSV recombinant NV1023 and the interleukin 12 (IL-12)-secreting oncolytic NV1042 virus were evaluated in vitro and in vivo with respect to antitumor efficacy. SUMMARY BACKGROUND DATA: Genetically engineered, replication-conditional, attenuated HSVs have shown oncolytic activity against a wide variety of solid malignancies. Other strategies for treating cancer have involved immunomodulation and cytokine gene transfer using viral vectors. This study has combined both of these strategies by inserting the murine IL-12 gene into a replication-competent HSV. This approach allows oncolytic therapy to replicate selectively within and lyse tumor cells while providing the host immune system with the cytokine stimulus necessary to recruit and activate inflammatory cells needed to enhance the antitumor effect. METHODS: NV1023 is a multimutant HSV based on the wild-type HSV-1 F strain. NV1042 was created by insertion of the mIL-12 gene into NV1023. Cytotoxicity and viral proliferation of both NV1023 and NV1042 within murine CT26 colorectal cancer cells were first shown. Cells infected with NV1042 were then shown to produce significant levels of IL-12. Using an experimental flank model of colon cancer, mice were treated with both high and low doses of NV1023 or NV1042 and were followed up for both cure and reduction in tumor burden. RESULTS: Both viruses could replicate within and kill CT26 cells in vitro, with 100% cytotoxicity achieved after infection by either virus. Only NV1042 could produce mIL-12. Therapy using high viral doses to treat animals in vivo showed equal efficacy between NV1023 and NV1042, with five of seven cures for each virus. When viral doses were lowered, only the cytokine-producing NV1042 virus could reduce tumor burden and cure animals of their disease. CONCLUSIONS: Both NV1023 and NV1042 have the oncolytic potential to kill colon cancer cells at higher doses. Cytokine production by NV1042 may allow lower doses of viral therapy to be used without losing antitumor efficacy. The combination of oncolytic viral therapy and immunomodulatory strategies should be further investigated as treatment for colon cancer.     

The replication-competent oncolytic herpes simplex mutant virus NV1066 is effective in the treatment of esophageal cancer

BACKGROUND: The oncolytic herpes simplex-1 virus, NV1066, is a replication-competent virus that has been engineered to infect and lyse tumor cells selectively and to carry a transgene for enhanced green fluorescent protein (EGFP). The purpose of this study was to determine viral cytotoxicity in an esophageal cancer cell line and to determine whether EGFP expression could be used as a marker of viral infection. METHODS: BE3 esophageal adenocarcinoma cells were infected with NV1066 in vitro to determine cell kill and viral replication. EGFP expression was assessed by flow cytometry. The in vivo anti-tumor activity of NV1066 was tested in subcutaneous and intraperitoneal xenograft models. EGFP expression was localized in vivo by fluorescent microscopy and fluorescent laparoscopy. RESULTS: NV1066 effectively replicated within and killed BE3 cells in vitro and in vivo. EGFP expression identified infected tumor cells. After NV1066 treatment in vivo, EGFP expression localized to the tumor. In an intraperitoneal tumor model, EGFP could be visualized endoscopically using a laparoscope with a fluorescent filter. CONCLUSIONS: NV1066 has oncolytic activity against the BE3 cell line and may be a useful therapy against esophageal cancer. EGFP expression localizes the virus and may help to identify tumor deposits in vivo. Oncolytic activity with NV1066 against gastrointestinal cancers may potentially be tracked by endoscopy.     

G207, modified herpes simplex virus type 1, kills human pancreatic cancer cells in vitro

Pancreatic cancer is often fetal, and farther effective therapeutic options are needed. This study was designed to assess whether the replication-restricted herpes simplex virus, G207, was effective in killing human pancreatic cancer cells in vitro. G207, a multimutated strain of herpes simplex virus type 1 carrying lacZ reporter gene, is capable of efficient cytolytic growth in many dividing cells, including certain tumor cells, but not in nondividing cells. Three human pancreatic cell lines, AsPC-1, MIA PaCa-2, and BxPC-3, were infected with G207 at different multiplicities of infection. After 24 hours, expression of the lacZ reporter gene was tested using a histochemical X-gal assay. In addition, cell lines were infected with G207 for 24 to 48 hours; then the virus obtained from cell pellets and media supernatant was used to infect Vero cells to obtain G207 titers by plaque assay. To assess whether increasing viral immediate early gene expression would improve cytolysis and virus production, similar experiments were performed with the addition of 0.5 mmol/L of hexamethylene bisacetamide (HMBA) 1 hour after viral infection. Finally, MTS cell viability assays were performed to measure viable cells at 24 to 96 hours post infection. The X-gal assay data revealed a viral dose-dependent β-galactosidase expression, indicating G207 infectivity and expression of the lacZ reporter gene. Plaque assays demonstrated a viral dose-dependent increase in plaque formation, indicating viral production from all three cell lines. In addition, HMBA data indicated a modest increase in viral production. The MTS assay data indicated a dose-dependent cytotoxicity for G207 in the cell lines tested. G207 infects, replicates in, and is cytotoxic to the above-listed human pancreatic cell lines in vitro and warrants therapeutic evaluation in models of pancreatic cancer. Supported by the Wilmot Cancer Research Fellowship Program funded by the James P. Wilmot Foundation. Presented at the Thirty-Ninth Annual Meeting of The Society for Surgery of the Alimentary Tract, New Orleans, La., May 17–20,1998.     

Utilizing tumor hypoxia to enhance oncolytic viral therapy in colorectal metastases

OBJECTIVE: To determine the effects of hypoxia-induced ribonucleotide reductase (RR) production on herpes oncolytic viral therapy. SUMMARY BACKGROUND DATA: Hypoxia is a common tumor condition correlated with therapeutic resistance and metastases. Attenuated viruses offer a unique cancer treatment by specifically infecting and lysing tumor cells. G207 is an oncolytic herpes virus deficient in RR, a rate-limiting enzyme for viral replication. METHODS: A multimerized hypoxia-responsive enhancer was constructed (10xHRE) and functionally tested by luciferase assay. 10xHRE was cloned upstream of UL39, the gene encoding the large subunit of RR (10xHRE-UL39). CT26 murine colorectal cancer cells were transfected with 10xHRE-UL39, incubated in hypoxia (1% O2) or normoxia (21% O2), and infected with G207 for cytotoxicity assays. CT26 liver metastases, with or without 10xHRE-UL39, were created in syngeneic Balb/C mice (n = 40). Livers were treated with G207 or saline. Tumors were assessed and stained immunohistochemically for G207. RESULTS: 10xHRE increased luciferase expression 33-fold in hypoxia versus controls (P < 0.001). In normoxia, 10xHRE-UL39 transfection did not improve G207 cytotoxicity. In hypoxia, G207 cytotoxicity increased 87% with 10xHRE-UL39 transfection versus nontransfected cells (P < 0.001). CT26 were resistant to G207 alone. Combining 10xHRE-UL39 with G207 resulted in a 66% decrease in tumor weights (P < 0.0001) and a 65% reduction in tumor nodules (P < 0.0001) versus G207 monotherapy. 10xHRE-UL39-transfected tumors demonstrated greater viral staining. CONCLUSIONS: Hypoxia-driven RR production significantly enhances viral cytotoxicity in vitro and reduces tumor burden in vivo. G207 combined with RR under hypoxic control is a promising treatment for colorectal cancer, which would otherwise be resistant to oncolytic herpes virus alone.     

Oncolytic herpes viral therapy is effective in the treatment of hepatocellular carcinoma cell lines

The rising incidence of hepatocellular carcinoma (HCC) in western countries, along with the poor prognosis offered by present-day treatment modalities, makes novel therapies for this disease necessary. Oncolytic herpes simplex viruses (HSV) are replication-competent viruses that are highly effective in the treatment of a wide variety of experimental models of human malignancies. This study seeks to investigate the effectiveness of oncolytic herpes viruses in the treatment of primary HCC cell lines. Sixteen commercially available human HCC cell lines were studied. G207 is an attenuated, replication-competent, oncolytic HSV engineered to selectively replicate within cancer cells. Cell lines were tested for viral sensitivity to G207 and their ability to support viral replication using standard cytotoxicity and viral replication assays. Eleven of 16 cell lines were moderately to highly sensitive to G207 viral oncolysis. HCC cell lines additionally demonstrated the ability to support viral replication in vitro with as high as 800-fold amplification of the administered viral dose observed. G207 is cytotoxic to, and efficiently replicates within, HCC cell lines in vitro. From these data, we suggest that oncolytic HSV therapy may have a role in the treatment of HCC, and in vivo studies are warranted. Presented in part at the 2005 American Hepato-Pancreato-Biliary Association Congress, Hollywood, Florida, April 14–17, 2005. Supported by grants R01CA75461 and R01CA72632 from the National Institutes of Health, and by grant MBC-99366 from the American Cancer Society (Yuman Fong).     

Treatment of human renal cell carcinoma by a conditionally replicating herpes vector G207

PURPOSE: Surgical removal remains the only potentially curative therapy for renal cell carcinoma. In this study we evaluated the inhibitory effect of the replication competent engineered herpes simplex virus type 1, G207, for renal cell carcinoma in vitro and in vivo. MATERIALS AND METHODS: The nature of G207 enables it to replicate within cancer cells, thus, causing cytolysis, but replication is restricted within normal cells. The susceptibility of the human renal cancer cell lines ACHN and A498 to G207 at a multiplicity of infection of 0.1 was examined. In addition, the growth characteristics of G207 was assessed. In vivo athymic mice bearing subcutaneous tumors were inoculated with 1 x 10(7) plaque forming units of G207 intra-neoplastically. For pathological analysis subcutaneous tumors were stained with X-gal. RESULTS: Two cell lines were efficiently destroyed by G207 within 1 week. The viral yields of G207 increased in a time dependent manner. In vivo the intra-neoplastic inoculation of G207 caused significantly decreased tumor growth in athymic mice harboring subcutaneous human renal cancer cells. On day 14 the mean growth ratio of ACHN and A498 lesions was significantly inhibited in G207 treated compared to control tumors (p <0.005 and <0.0001, respectively). CONCLUSIONS: These results suggest that G207 should be considered another potential therapeutic agent for renal cell carcinoma.     

Ionizing radiation potentiates the antitumor efficacy of oncolytic herpes simplex virus G207 by upregulating ribonucleotide reductase

BACKGROUND: Replication-competent herpes simplex virus-1 (HSV-1) mutants have an oncolytic effect on human and animal cancers. The aim of this study was to determine whether G207, an HSV-1 mutant, can be combined with ionizing radiation (IR) to increase antitumor activity while decreasing treatment-associated toxicity. METHODS: This study was performed by using G207, a replication-competent HSV-1 mutant deficient in viral ribonucleotide reductase (RR) and the gamma(1)34.5 neurovirulence protein. The antitumor activity of G207 or IR was tested against HCT-8 human colorectal cancer cells in vitro and in an in vivo mouse subcutaneous tumor model. RESULTS: We demonstrated that G207 has significant oncolytic effect on HCT-8 cells in vitro in a cytotoxicity assay and in vivo in a mouse flank tumor model and that these effects are improved with low-dose IR. We further illustrated that the increased tumoricidal effect is dependent on the up-regulation of cellular RR by IR measured by a functional bioassay for RR activity. Chemical inhibition of RR by hydroxyurea abrogates the enhanced effect. In contrast to G207, R3616, the parent virus of G207 that expresses functional RR, does not exhibit enhanced oncolysis when combined with IR. CONCLUSIONS: These data encourage clinical investigation of combination radiation therapy and HSV oncolytic therapy.     

Carcinoembryonic antigen directed herpes viral oncolysis improves selectivity and activity in colorectal cancer

BACKGROUND: G207 is an oncolytic herpes virus whose replicative cycle requires cellular ribonucleotide reductase (RR) for viral DNA synthesis. We attempt to enhance viral cytotoxicity in carcinoembryonic antigen (CEA)-producing colorectal cancer (CRC) cells through CEA-driven RR production. METHODS: CEA enzyme-linked immunosorbent assay was performed on LS174T and HCT-8 human CRC cells. The CEA enhancer-promoter (CEA E-P) was functionally assessed by luciferase assay. CEA E-P was cloned upstream of UL39, the gene encoding the large subunit of RR. Cells were transfected with CEA E-P/UL39 and infected with G207 for cytotoxicity assays. LS174T, with or without CEA E-P/UL39, were implanted into athymic mouse flanks (n = 28) and treated with G207. RESULTS: CEA levels were 7-fold higher in LS174T versus HCT-8 ( P <.00001). CEA E-P increased luciferase expression 7.5-fold in LS174T ( P <.01), with no increase in HCT-8. G207 cytotoxicity of'CEA E-P/UL39-transfected LS174T cells increased 69% by day 10 versus nontransfected cells ( P <.001), with no significant increase in HCT-8. Combining CEA E-P/UL39 with G207 in LS174T flank tumors resulted in a 65% decrease in tumor volume versus G207, phosphate-buffered saline, or'CEA E-P/UL39 alone ( P <.0001). CONCLUSIONS: CEA-driven RR production by CEA-secreting CRC cells significantly improves oncolytic viral cytotoxicity and specificity in vitro, and reduces tumor burden in vivo.     

Utilizing alpha-fetoprotein expression to enhance oncolytic viral therapy in hepatocellular carcinoma

OBJECTIVE: To determine whether alpha-fetoprotein (AFP)-regulated ribonucleotide reductase (RR) production would promote more vigorous and specific viral killing in AFP-expressing hepatocellular carcinoma (HCC). BACKGROUND: AFP is expressed in over 70% of primary HCC but not in normal adult liver. AFP production by HCC can be exploited to target viral killing of tumor cells. G207 is an oncolytic herpes virus lacking UL39, the gene encoding RR. RR is an enzyme required for viral DNA synthesis and cytotoxicity. METHODS: Enzyme-linked immunosorbent assay (ELISA) was performed for AFP levels on Hep3B and PLC5 human HCC cells. An AFP-albumin enhancer-promoter complex (AFP-alb) was constructed in a luciferase vector to assess function. AFP-alb was cloned upstream of UL39 (AFP-alb/UL39) and transfected into HCC cells for G207 cytotoxicity assays. Viral plaque forming assays evaluated G207 replication. Hep3B flank tumors, with and without AFP-alb/UL39 transfection, were established in athymic mice (n = 28) and treated with G207. RESULTS: Hep3B had 5-fold higher AFP levels than PLC5 (P < 0.00001). AFP-alb increased luciferase expression 72-fold in Hep3B (P < 0.001) and 3-fold in PLC5 (P < 0.001). AFP-alb/UL39 transfection increased G207 cytotoxicity 93% in Hep3B (P < 0.0005), with no significant increase in PLC5. Peak viral titers were 46-fold higher in Hep3B transfected with AFP-alb/UL39 versus mock-transfected cells (P < 0.01), with no significant change in PLC5. Flanks tumors transfected with AFP-alb/UL39 and treated with G207 demonstrated a 76% volume reduction versus mock-transfected tumors infected with G207 (P < 0.0001). CONCLUSIONS: AFP-driven RR production by hepatoma cells significantly enhances herpes viral cytotoxicity and specificity in vitro and reduces tumor burden in vivo.     

Myxoma Virus Is Oncolytic for Human Pancreatic Adenocarcinoma Cells

Background  Viral oncolytic therapy, which seeks to exploit the use of live viruses to treat cancer, has shown promise in the treatment of cancers resistant to conventional anticancer therapies. Among the most difficult to treat cancers is advanced pancreatic adenocarcinoma. Our study investigates the ability of a novel oncolytic agent, myxoma virus, to infect, productively replicate in, and kill human pancreatic cancer cells in vitro. Methods  The myxoma virus vMyxgfp was tested against a panel of human pancreatic adenocarcinoma cell lines. Infectivity, viral proliferation, and tumor cell kill were assessed. Results  Infection of tumor cells was assessed by expression of the marker gene enhanced green fluorescent protein (e-GFP). vMyxgfp had the ability to infect all pancreatic cancer cell lines tested. Killing of tumor cells varied among the 6 cell lines tested, ranging from >90% cell kill at 7 days for the most sensitive Panc-1 cells, to 39% in the most resistant cell line Capan-2. Sensitivity correlated to replication of virus, and was found to maximally exhibit a four-log increase in foci-forming units for the most sensitive Panc-1 cells within 72 h. Conclusion  Our study demonstrates for the first time the ability of the myxoma virus to productively infect, replicate in, and lyse human pancreatic adenocarcinoma cells in vitro. These data encourage further investigation of this virus, which is pathogenic only in rabbits, for treatment of this nearly uniformly fatal cancer.     

Use of an oncolytic virus secreting GM-CSF as combined oncolytic and immunotherapy for treatment of colorectal and hepatic adenocarcinomas

BACKGROUND: Oncolytic cancer therapy using herpes simplex viruses (HSV) that have direct tumoricidal effects and cancer immunotherapy using the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF) have each been effective in preclinical testing. NV1034 is a multimutated oncolytic HSV carrying the gene for murine GM-CSF that attempts to combine these 2 anticancer strategies. The purpose of this study was to compare NV1034 to NV1023, the parent HSV mutants lacking GM-CSF, to determine if such combined oncolytic and immunotherapy using a single vector has advantages over oncolytic therapy alone. METHODS: Expression GM-CSF in vitro did not alter the infectivity, cytotoxicity, or replication of NV1034 compared to the noncytokine-secreting control. Tumors infected with NV1034 produced GM-CSF in picogram quantities. In vivo efficacy of the viruses against murine colorectal carcinoma CT26 and murine hepatoma Hepa l-6 was then tested in subcutaneous tumors in syngeneic Balb/c and C57 L/J mice, respectively. In these immune-competent models, NV1034 and NV1023 each demonstrated potent antitumor activity. RESULTS: Treatment with NV1034 had significantly better antitumor effect compared to treatment with NV1023. Furthermore, there was no difference in the antitumor efficacy of these viruses in mice depleted of CD4+ and CD8+ T lymphocytes. CONCLUSIONS: Viral vectors combining oncolytic and immunotherapy are promising agents in treatment of colorectal carcinoma and hepatoma.     

Application of conditionally replicating herpes vector for gene therapy treatment of urologic neoplasms

Herpes vector has been widely used for experimental gene therapy. We herein review the strategies of such therapy for the treatment of urologic neoplasms. Most experimental studies of genetically altered viruses have employed replication-incompetent vectors. However, such viruses are unable to infect additional cells subsequent to the initial infection event. Therefore, this strategy has relied heavily on the bystander effect because a large number of noninfected tumor cells remain. Conditionally replicating herpes vector G207 has been developed in order to overcome potential problems of safety and tumor specificity for human use. It has been used to treat malignant brain tumors because of its neural tropism. In the last few years, applications of G207 for non-neural tumors have been reported. Because G207 may be useful for the treatment of urologic malignant tumors, we evaluated the antitumor effect against several types of tumor cells both in vitro and in vivo. Our data suggest that G207 may be applicable for the treatment of urologic malignant tumors.     

Viral Oncolysis for Malignant Liver Tumors

Viral oncolysis represents a unique strategy to exploit the natural process of viral replication to kill tumor cells. Although this concept dates back nearly a century, recent advances in the fields of molecular biology and virology have enabled investigators to genetically engineer viruses with greater potency and tumor specificity. In this article we review the general mechanisms by which oncolytic viruses achieve their antineoplastic efficacy and specificity. We focus on the development of several classes of oncolytic viruses for the treatment of malignant liver tumors, including adenoviruses, vaccinia viruses, and herpes simplex viruses, and discuss the results of clinical trials for these viruses. We also describe results from our laboratory research program, which is focused on developing effective, liver tumor–specific Herpes simplex virus 1 mutants.     

Employing Tumor Hypoxia for Oncolytic Therapy in Breast Cancer

Hypoxia is a common tumor condition associated with metastases, therapeutic resistance, and poor patient survival. Forty percent of breast cancers are hypoxic, with a median oxygen concentration of 3.9%, and a third of tumors have regions less than 0.3%. Normal breast tissue is reported to have oxygen concentrations greater than 9%. This tumor hypoxia in breast cancer confers resistance to conventional radiation therapy and chemotherapy, as well as making estrogen-receptor-positive tumors less sensitive to hormonal therapy. Novel treatment modalities are needed to target hypoxic tumor cells. Lower tumor oxygen levels compared with surrounding normal tissues may be utilized to target and enhance herpes oncolytic viral therapy in breast cancer. Attenuated oncolytic herpes simplex viruses offer a unique cancer treatment by specifically infecting, replicating within, and lysing tumor cells. They carry genetically engineered mutations to reduce their virulence and attenuate their ability to infect normal tissues. Studies have shown the safety and efficacy of oncolytic herpes simplex viruses in treating breast cancer both in humans and in preclinical models. The placement of essential viral genes under the control of a hypoxia-responsive enhancer, which is upregulated selectively in hypoxic tissue, represents a promising strategy to target oncolytic viruses precisely to hypoxic cancer cells. In this review we describe strategies to harness hypoxia as a trigger for oncolytic viral gene expression in breast cancer, thereby increasing the specificity of viral infection, replication, and cytotoxicity to hypoxic areas of tumor. Such a targeted approach will increase efficacy in the therapy of hypoxic tumors while achieving a reduction in total dose of viral therapy.Supported in part by AACR-Astra Zeneca Cancer Research and Prevention Foundation Fellowship (P.S.A), grants RO1 CA 75416 and RO1 CA/DK80982 (Y.F.) from the National Institutes of Health, grant MBC-99366 (Y.F.) from the American Cancer Society, grant BC024118 from the US Army (Y.F.), grant IMG0402501 from the Susan G. Komen Breast Cancer Foundation (Y.F. and P.S.A.) and grant 032047 from Flight Attendant Medical Research Institute (Y.F. and P.S.A.)