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Morbidity associated with hepatic and urogenital schistosomiasis stems primarily from the host immune response directed against schistosome eggs. When eggs become entrapped in host tissues, the development of fibrotic plaques drives downstream pathology. These events occur due to the antigenic nature of egg excretory/secretory products (ESPs). Both Schistosoma mansoni and S. japonicum ESPs have been shown to interact with several cell populations in the host liver including hepatocytes, macrophages, and hepatic stellate cells, with both immunomodulatory and pathological consequences. Several protein components of the ESPs of S. mansoni and S. japonicum eggs have been characterised; however, studies into the collective contents of schistosome egg ESPs are lacking. Utilising shotgun mass spectrometry and an array of in silico analyses, we identified 266, 90 and 50 proteins within the S. mansoni, S. japonicum and S. haematobium egg secretomes respectively. We identified numerous proteins with already established immunomodulatory activities, vaccine candidates and vesicle markers. Relatively few common orthologues within the ESPs were identified by BLAST, indicating that the three egg secretomes differ in content significantly. Having a clearer understanding of these components may lead to the identification of new proteins with uncharacterised immunomodulatory potential or pathological relevance. This will enhance our understanding of host-parasite interactions, particularly those occurring during chronic schistosomiasis, and pave the way towards novel therapeutics and vaccines.

IntroductionRecurrent urinary tract infections have been linked to increased risk of bladder cancer, suggesting a potential role of the urinary microbiome in bladder cancer pathogenesis.ObjectiveCompare the urinary microbiomes in mice with and without bladder.MethodsLongitudinal study of mice exposed to a dilute bladder-specific carcinogen (0.05% n-butyl-n-(4-hydroxybutyl) nitrosamine, BBN mice, n=10), and control mice (n=10). Urine was sampled monthly from individual mice for 4 months. Microbial DNA was extracted from the urine, and the V4 region of the 16S rRNA gene sequenced. Animals were sacrificed and their bladders harvested for histopathology. Bladder sections were graded by a blinded pathologist. The composition and diversity of the urinary microbiome were compared between the BBN and control mice. Metabolic pathway analysis was completed using PICRUST.ResultsBladder histology in the BBN group showed normal tissue with inflammation (BBN-normal, n=5), precancerous pathologies, (BBN-precancerous, n=3), and invasive cancer (BBN-cancer, n=2). Alpha diversity did not differ between the mice exposed to BBN and the control mice at any timepoint. There were no differences in the urinary microbiomes between the BBN and control mice at baseline. At month 4, mice exposed to BBN had higher proportion of both Gardnerella and Bifidobacterium compared to control mice. There were no differences in proportions of specific bacteria between either the BBN-precancer or BBN-cancer and controls at month 4. However, the BBN-normal mice had higher proportions of Gardnerella, Haemophilus, Bifidobacterium, and Ureaplasma Actinobaculum, and lower proportions of Actinomyces, compared to control mice at month 4. Functional pathway analysis demonstrated increases in genes related to purine metabolism, phosphotransferase systems, peptidases, protein folding, and bacterial toxins in the BBN-mice compared to control mice at month 4.ConclusionMice exposed to 4 months of BBN, a bladder-specific carcinogen, have distinct urine microbial profiles compared to control mice.

Herpes simplex virus type 1 (HSV-1) mutants lacking the γ(1)34.5 neurovirulence loci are promising agents for treating malignant glioma. Arming oncolytic HSV-1 to express immunostimulatory genes may potentiate therapeutic efficacy. We have previously demonstrated improved preclinical efficacy, biodistribution, and safety of M002, a γ(1)34.5-deleted HSV-1 engineered to express murine IL-12. Herein, we describe the safety and biodistribution of M032, a γ(1)34.5-deleted HSV-1 virus that expresses human IL-12 after intracerebral administration to nonhuman primates, Aotus nancymae. Cohorts were administered vehicle, 10(6), or 10(8) pfu of M032 on day 1 and subjected to detailed clinical observations performed serially over a 92-day trial. Animals were sacrificed on days 3, 31, and 91 for detailed histopathologic assessments of all organs and to isolate and quantify virus in all organs. With the possible exception of one animal euthanized on day 16, neither adverse clinical signs nor sex- or dose-related differences were attributed to M032. Elevated white blood cell and neutrophil counts were observed in virus-injected groups on day 3, but no other significant changes were noted in clinical chemistry or coagulation parameters. Minimal to mild inflammation and fibrosis detected, primarily in meningeal tissues, in M032-injected animals on days 3 and 31 had mostly resolved by day 91. The highest viral DNA levels were detected at the injection site and motor cortex on day 3 but decreased in central nervous system tissues over time. These data demonstrate the requisite safety of intracerebral M032 administration for consideration as a therapeutic for treating malignant brain tumors.

Metastatic involvement of the skeleton is a frequent consequence of advanced prostate cancer. These skeletal metastases cause a number of debilitating complications and are refractory to current treatments. New therapeutic options are being explored, including conditionally replicating adenoviruses (CRAds). CRAds are engineered to selectively replicate in and destroy tumor cells and can be 'armed' with exogenous transgenes for enhanced potency. We hypothesized that a CRAd armed with osteoprotegerin (OPG), an inhibitor of osteoclastogenesis, would inhibit the progression of prostate cancer bone metastases by directly lysing tumor cells and by reducing osteoclast activity. Although prostate cancer bone metastases are predominantly osteoblastic in nature, increased osteoclast activity is critical for the growth of these lesions. Ad5-Δ24-sOPG-Fc-RGD is a CRAd that carries a fusion of the ligand-binding domains of OPG and the Fc region of human IgG1 in place of the viral E3B genes. To circumvent low tumor cell expression of the native adenoviral receptor, an arginine-glycine-aspartic acid (RGD) peptide insertion within the viral fiber knob allows infection of cells expressing α(v) integrins. A 24-base pair deletion (Δ24) within viral E1A limits replication to cells with aberrant retinoblastoma cell cycle regulator/tumor suppressor expression. We have confirmed that Ad5-Δ24-sOPG-Fc-RGD replicates within and destroys prostate cancer cells and, in both murine and human coculture models, that infection of prostate cancer cells inhibits osteoclastogenesis in vitro. In a murine model, progression of advanced prostate cancer bone metastases was inhibited by treatment with Ad5-Δ24-sOPG-Fc-RGD but not by an unarmed control CRAd.

Purpose: Current treatments for ovarian cancer have limited therapeutic outcomes due to advanced stage of the disease at diagnosis. Among new therapies, conditionally replicating adenoviruses (CRAds), designed to selectively lyse cancer cells, hold promise. In clinical trials, CRAds exhibited limited efficacy thus far. Second-generation CRAds are being developed to express a therapeutic protein to enhance antitumor efficacy. One attractive target in the tumor microenvironment is the matrix metalloproteinases (MMPs) that degrade the extracellular matrix, and are upregulated in ovarian cancer. Tissue inhibitor of metalloproteinase 2 (TIMP2) is an endogenous inhibitor of MMPs. The present study developed and evaluated a novel CRAd (Ad5/3-CXCR4-TIMP2) for ovarian cancer therapy. Experimental Design: A targeted CRAd, Ad5/3-CXCR4-TIMP2 was developed using the CXCR4 promoter for enhanced replication, and expressing the TIMP2 transgene. The efficacy of this armed CRAd was determined in both established human ovarian cancer cell lines and in primary ovarian tumor samples. Results: Ad5/3-CXCR4-TIMP2 mediated expression of functional TIMP2, as demonstrated by the inhibition of MMP activity. In addition, arming with TIMP2 did not inhibit viral replication or oncolytic potency, as the TIMP2-armed viruses showed enhanced killing of cancer cells when compared to the unarmed viruses. We also examined viral replication in primary ovarian cancer tissues obtained from patients with stage III and IV ovarian cancer. In four of the five tumor samples, Ad5/3-CXCR4-TIMP2 revealed a 21- to 89-fold increase in replication when compared to the Ad5/3 virus. Conclusion: Results support the translational potential of Ad5/3-CXCR4-TIMP2 for treatment of patients with advanced ovarian cancer. Clin Cancer Res; 17(3); 538–49. ©2010 AACR.

Most patients with advanced breast cancer develop osteolytic bone metastases, which have numerous complications. Because current therapies are not curative, new treatments are needed. Conditionally replicating adenoviruses (CRAds) are anticancer agents designed to infect and lyse tumor cells. However, in spite of their promise as selective cancer therapeutics, replicating adenoviruses have shown limited efficacy in the clinical setting. We hypothesized that a CRAd armed with osteoprotegerin (OPG) would eradicate bone metastases of breast cancer both directly, by oncolysis, and indirectly, by inhibiting osteoclastic bone resorption, and thus reducing the tumor burden. We constructed an armed CRAd (Ad5-Δ24-sOPG-Fc-RGD) by replacing viral E3B genes with a fusion of the ligand-binding domains of OPG and the Fc portion of human IgG1. Conditional replication was conferred by a 24-base pair deletion within E1A (Δ24), which prevents the binding of E1A to the retinoblastoma tumor suppressor/cell cycle regulator protein and limits replication in normal cells. Enhanced infection of cells expressing low levels of the primary Ad5 receptor was conferred by incorporating an arginine-glycine-aspartic acid (RGD) peptide sequence into the fiber knob to mediate binding to α(v) integrins. After characterization of the armed CRAd, we demonstrated that infection of breast cancer cells by Ad5-Δ24-sOPG-Fc-RGD both killed the infected cells by oncolysis and inhibited the formation of osteoclasts in an in vitro co-culture model. In a murine model of osteolytic bone metastases of breast cancer, the CRAd armed with shortened OPG (sOPG)-Fc reduced tumor burden in the bone and inhibited osteoclast formation more effectively than an unarmed CRAd.

Herpes simplex virus 1 (HSV-1) mutants that lack the γ 1 34.5 gene are unable to replicate in the central nervous system but maintain replication competence in dividing cell populations, such as those found in brain tumors. We have previously demonstrated that a γ 1 34.5-deleted HSV-1 expressing murine interleukin-12 (IL-12; M002) prolonged survival of immunocompetent mice in intracranial models of brain tumors. We hypothesized that M002 would be suitable for use in clinical trials for patients with malignant glioma. To test this hypothesis, we (i) compared the efficacy of M002 to three other HSV-1 mutants, R3659, R8306, and G207, in murine models of brain tumors, (ii) examined the safety and biodistribution of M002 in the HSV-1-sensitive primate Aotus nancymae following intracerebral inoculation, and (iii) determined whether murine IL-12 produced by M002 was capable of activating primate lymphocytes. Results are summarized as follows: (i) M002 demonstrated superior antitumor activity in two different murine brain tumor models compared to three other genetically engineered HSV-1 mutants; (ii) no significant clinical or magnetic resonance imaging evidence of toxicity was observed following direct inoculation of M002 into the right frontal lobes of A. nancymae ; (iii) there was no histopathologic evidence of disease in A. nancymae 1 month or 5.5 years following direct inoculation; and (iv) murine IL-12 produced by M002 activates A. nancymae lymphocytes in vitro . We conclude that the safety and preclinical efficacy of M002 warrants the advancement of a Δγ 1 34.5 virus expressing IL-12 to phase I clinical trials for patients with recurrent malignant glioma.

The metastasis of breast cancer to the brain and central nervous system (CNS) is a problem of increasing importance. As improving treatments continue to extend patient survival, the incidence of CNS metastases from breast cancer is on the rise. New treatments are needed, as current treatments are limited by deleterious side effects and are generally palliative. We have previously described an oncolytic herpes simplex virus (HSV), designated M002, which lacks both copies of theγ134.5 neurovirulence gene and carries a murine interleukin 12 (IL-12) expression cassette, and have validated its antitumor efficacy in a variety of preclinical models of primary brain tumors. However, M002 has not been yet evaluated for use against metastatic brain tumors. Here, we demonstrate the following: both human breast cancer and murine mammary carcinoma cells support viral replication and IL-12 expression from M002; M002 replicates in and destroys breast cancer cells from a variety of histological subtypes, including “triple-negative” and HER2 overexpressing; M002 improves survival in an immunocompetent model more effectively than does a non-cytokine control virus. Thus, we conclude from this proof-of-principle study that aγ134.5-deleted IL-12 expressing oncolytic HSV may be a potential new therapy for breast cancer brain metastases.

Inherently unstable mRNAs contain AU-rich elements (AREs) in the 3' untranslated regions. Expression of ARE-containing type I interferon transcripts is robustly induced upon viral infection and rapidly shut off thereafter. Their transient accumulation is partly mediated through posttranscriptional regulation. Here we show that mouse embryonic fibroblasts derived from knockout mice deficient in KH-type splicing regulatory protein (KSRP), an RNA-binding protein required for ARE-mediated mRNA decay, produce higher levels of Ifna and Ifnb mRNAs in response to viral infection as a result of decreased mRNA decay. Functional analysis showed that KSRP is required for the decay of Ifna4 and Ifnb mRNAs by interaction with AREs. The increased IFN expression renders Ksrp(-)(/)(-) cells refractory to herpes simplex virus type 1 and vesicular stomatitis virus infection. These findings support a role of a posttranscriptional mechanism in the control of type I IFN expression and highlight the function of KSRP in innate immunity by negatively regulating IFN production.

Osteoclasts are large, multinucleated cells responsible for the resorption of mineralized bone matrix. These cells are critical players in the bone turnover involved in bone homeostasis. Osteoclast activity is connected to the establishment and expansion of skeletal metastases from a number of primary neoplasms. Thus, the formation and activation of osteoclasts is an area of research with many potential avenues for clinical translation. Past studies of osteoclast biology have utilized primary murine cells cultured in vitro. Recently, techniques have been described that involve the generation of osteoclasts from human precursor cells. However, these protocols are often time-consuming and insufficient for generating large numbers of osteoclasts. We therefore developed a simplified protocol by which human osteoclasts may be easily and reliably generated in large numbers in vitro. In this study, osteoclasts were differentiated from bone marrow cells that had been aliquotted and frozen. Cells were generated by culture with recombinant macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). Both human and murine RANKL were shown to efficiently generate osteoclasts, although higher concentrations of murine RANKL were required. Formation of osteoclasts was demonstrated qualitatively by tartrate-resistant acid phosphatase (TRAP) staining. These cells were fully functional, as confirmed by their ability to form resorption pits on cortical bone slices. Functional human osteoclasts can be difficult to generate in vitro by current protocols. We have demonstrated a simplified system for the generation of human osteoclasts in vitro that allows for large numbers of osteoclasts to be obtained from a single donor.

Ovarian cancer remains difficult to treat mainly due to presentation of the disease at an advanced stage. Conditionally-replicating adenoviruses (CRAds) are promising anti-cancer agents that selectively kill the tumor cells. The present study evaluated the efficacy of a novel CRAd (Ad5/3-CXCR4-TIMP2) containing the CXCR4 promoter for selective viral replication in cancer cells together with TIMP2 as a therapeutic transgene, targeting the matrix metalloproteases (MMPs) in a murine orthotopic model of disseminated ovarian cancer. An orthotopic model of ovarian cancer was established in athymic nude mice by intraperitonal injection of the human ovarian cancer cell line, SKOV3-Luc, expressing luciferase. Upon confirmation of peritoneal dissemination of the cells by non-invasive imaging, mice were randomly divided into four treatment groups: PBS, Ad-ΔE1-TIMP2, Ad5/3-CXCR4, and Ad5/3-CXCR4-TIMP2. All mice were imaged weekly to monitor tumor growth and were sacrificed upon reaching any of the predefined endpoints, including high tumor burden and significant weight loss along with clinical evidence of pain and distress. Survival analysis was performed using the Log-rank test. The median survival for the PBS cohort was 33 days; for Ad-ΔE1-TIMP2, 39 days; for Ad5/3-CXCR4, 52.5 days; and for Ad5/3-CXCR4-TIMP2, 63 days. The TIMP2-armed CRAd delayed tumor growth and significantly increased survival when compared to the unarmed CRAd. This therapeutic effect was confirmed to be mediated through inhibition of MMP9. Results of the in vivo study support the translational potential of Ad5/3-CXCR4-TIMP2 for treatment of human patients with advanced ovarian cancer.

Novel approaches to treatment of malignant glioma, the most frequently occurring primary brain tumor, have included the use of a wide range of oncolytic viral vectors. These vectors, either naturally tumor-selective, or engineered as such, have shown promise in the handful of phase I and phase II clinical trials conducted in recent years. The strategies developed for each of the different viruses currently being studied and the history of their development are summarized here. In addition, the results of clinical trials in patients and their implication for future trials are also discussed.

New therapies for metastatic breast cancer patients are urgently needed. The long-term survival rates remain unacceptably low for patients with recurrent disease or disseminated metastases. In addition, existing therapies often cause a variety of debilitating side effects that severely impact quality of life. Oncolytic viruses constitute a developing therapeutic modality in which interest continues to build due to their ability to spare normal tissue while selectively destroying tumor cells. A number of different viruses have been used to develop oncolytic agents for breast cancer, including herpes simplex virus, adenovirus, vaccinia virus, measles virus, reovirus, and others. In general, clinical trials for several cancers have demonstrated excellent safety records and evidence of efficacy. However, the impressive tumor responses often observed in preclinical studies have yet to be realized in the clinic. In order for the promise of oncolytic virotherapy to be fully realized for breast cancer patients, effectiveness must be demonstrated in metastatic disease. This review provides a summary of oncolytic virotherapy strategies being developed to target metastatic breast cancer.

Herpes simplex virus type 1 (HSV-1) mutants lacking the γ134.5 neurovirulence loci are promising agents for treating malignant glioma. Arming oncolytic HSV-1 (oHSV) to express immunostimulatory genes may potentiate therapeutic efficacy. We have previously demonstrated improved pre-clinical efficacy, biodistribution, and safety of M002, a γ134.5-deleted HSV-1 engineered to express murine IL-12. Herein, we describe the safety and biodistribution of M032, a γ134.5-deleted HSV-1 virus that expresses human IL-12 after intracerebral administration to non-human primates (NHPs), Aotus nancymae. Cohorts were administered vehicle, 106, or 108 pfu of M032 on Day 1 and subjected to detailed clinical observations performed serially over a 92-day trial. Animals were sacrificed on Days 3, 31, and 91 for detailed histopathologic assessments of all organs and to isolate and quantify virus in all organs. With the possible exception of one animal euthanized on Day 16, neither adverse clinical signs nor sex- or dose-related differences were attributed to M032. Elevated white blood cell and neutrophil counts were observed in virus-injected groups on Day 3, but no other significant changes were noted in clinical chemistry or coagulation parameters. Minimal to mild inflammation and fibrosis detected, primarily in meningeal tissues, in M032-injected animals on Days 3 and 31had mostly resolved by Day 91. The highest viral DNA levels were detected at the injection site and motor cortex on Day 3 but decreased in CNS tissues over time. These data demonstrate the requisite safety of intracerebral M032 administration for consideration as a therapeutic for treating malignant brain tumors.

The purpose of this study was to improve the efficacy of oncolytic herpes simplex virus (HSV) against metastatic breast cancer by combining treatment with histone deacetylase (HDAC) inhibitors. Metastatic breast cancer continues to be a significant clinical challenge as the survival rates remain below 25%, illustrating the dire need for newly developed therapeutic strategies. Oncolytic viruses selectively replicate in cancer cells but not in normal cells and are an exciting potential therapy being evaluated in patients with breast cancer. HSV is a well-studied oncolytic virus that has been employed in clinical trials for several cancers. These trials have demonstrated safety, but HSV has generally lacked sufficient potency to yield durable tumor responses. In part, this is due to low viral replication and persistence. For tumor-selective replication, oncolytic HSV (oHSV) typically lack the diploid viral γ134.5 gene, which encodes a multifunctional protein that also contributes to viral evasion of host interferon response. Because γ134.5-deleted HSVs are particularly sensitive to interferon, reducing this response may be an effective means of enhancing oncolytic HSV therapy while maintaining deficiency of replication in normal cells. HDAC inhibitors have been shown to reduce the expression of interferon-stimulated genes. Therefore, we hypothesized that oHSV replication and efficacy could be improved by treatment with particular HDAC inhibitors. We tested a panel of HDAC inhibitors with distinct inhibition profiles and selectivity towards different classes of HDACs. Cell viability assays were used to establish lethal dose 50 (LD50) values for each compound and each was tested for its ability to modulate the replication of a γ134.5-deleted oncolytic HSV. The inhibitors were tested at three different dose levels: low (non-lethal), middle (partially lethal), and high (lethal), and two different treatment schedules: prior to viral infection (pre-treatment) or immediately following viral infection (co-treatment). The cell lines selected for this study included the metastatic breast cancer line MDA-MB-231 that was previously shown to be oHSV replication-competent and the oHSV replication-resistant cell lines: immortalized but otherwise normal breast epithelial cell line MCF10A and metastatic murine mammary carcinoma 4T1. Although pre-treatment did not affect viral replication and co-treatment actually reduced it at a high multiplicity of infection (MOI), at a low MOI, significantly enhanced viral replication was observed with both pre- and co-treatment in MDA-MB-231 cells (magnitude of increase dependent on particular HDAC inhibitor), but not in MCF10A. Interestingly, the oHSV-resistant 4T1 cells were rendered permissive by HDAC-inhibitor treatment as significant increases in oHSV replication were noted. These studies demonstrate that HDAC inhibitors can be used to induce viral replication depending on the particular compound and MOI of the virus. Furthermore, these results suggest that HDAC inhibitors could prove useful in combination with oHSV as a novel treatment strategy for metastatic breast cancer. Citation Format: James J. Cody, James M. Markert, Douglas R. Hurst. Treatment of breast cancer cells with histone deacetylase inhibitors increases the replication of an oncolytic herpes simplex virus. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr B54.

Autophagy is a catabolic process that is tightly regulated during normal cell growth, development, and homeostasis. Although it may be death inducing, it is also an important survival mechanism for cells in stressful environments, including hypoxia, nutrient deprivation, chemical or physical pressure, or detachment from colonies. Considering the stress associated with the process of metastasis, we hypothesized that autophagy may play a role in the ability of breast cancer cells to survive and metastasize. To test this, we first compared cell proliferation after autophagic induction between metastatic breast cancer cell lines (MDA-MB-231 and -435), a non-metastatic breast cancer cell line (MDA-MB-436), and a ‘normal’ breast epithelial cell line (MCF10A). Both metastatic cell lines continued to proliferate following induction of autophagy; however, the non-metastatic and normal cell lines were growth-inhibited. Autophagy was also more rapidly induced by rapamycin in the metastatic cell lines as demonstrated by an increase in LC3II expression. To test the different survival capabilities between metastatic and normal cells, we selected cells through five rounds of starvation with Earle's balanced salt solution (EBSS) and compared their ability to induce autophagy. Although both the normal and metastatic cells maintained their ability to proliferate under normal conditions, the MDA-MB-231 cells that survived starvation (231-EB5) proliferated more rapidly than the parental population following induction of autophagy. In contrast, both MCF10A and MCF10A-EB5 cells were growth-inhibited. The 231-EB5 cells induced autophagy more rapidly than the parental population as demonstrated by increased expression of LC3II (analyzed by immunoblot) and increased LC3 puncta (analyzed by immunofluorescence). Migration of parental 231 cells was inhibited by rapamycin; however, there was no change in the ability of 231-EB5 cells to migrate after treatment with rapamycin. Growth in three dimensions also was significantly altered. MCF10A-EB5 cells were more extended compared to the spherical growth of the parental MCF10A cells. Protrusions emitted from the 231-EB5 cells were more rounded compared to the extended spikes of the parental 231 cells. Altogether, these results demonstrate that select populations derived from metastatic breast cancer cells have different abilities to survive, proliferate, and migrate following induction of autophagy, suggesting that autophagy may be a key mechanism for tumor progression and metastasis. Citation Format: Yi Li, Monica J. Lewis, Jianzhong Liu, James J. Cody, Douglas R. Hurst. Metastatic breast cancer cell phenotype is regulated by autophagy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1678. doi:10.1158/1538-7445.AM2013-1678

The majority of patients with advanced breast cancer develop osteolytic metastases in the skeleton, which lead to such complications as pain, fractures, hypercalcemia and a general decrease in the quality of life. Current therapies for bone metastases are not curative in nature. Thus, new treatments are needed for osteolytic bone metastasis of breast cancer. Conditionally replicating adenoviruses (CRADs) are a new class of anti-cancer agents that offer the potential ability to infect and lyse all the cells of a tumor. In clinical trials, replicating adenoviruses have exhibited safety but not the desired level of efficacy, demonstrating a need for improvement. One approach to enhance the efficacy of a CRAD is to arm it with a therapeutic transgene. Osteoprotegerin (OPG), the recently described inhibitor of osteoclastic bone resorption, represents a promising candidate with which to arm a replicating adenovirus designed to treat osteolytic bone metastasis. We hypothesize that a replicating adenovirus armed with a gene for OPG will be able to inhibit breast cancer bone metastasis and reduce the tumor burden in the bone through two actions: direct lysis of the tumor cells by replication of the virus and inhibition of bone resorption by the production of OPG.