The efficacy and safety of biological molecules in cancer therapy, such as peptides and small interfering RNAs (siRNAs), could be markedly increased if high concentrations could be achieved and amplified selectively in tumour tissues versus normal tissues after intravenous administration. This has not been achievable so far in humans. We hypothesized that a poxvirus, which evolved for blood-borne systemic spread in mammals, could be engineered for cancer-selective replication and used as a vehicle for the intravenous delivery and expression of transgenes in tumours. JX-594 is an oncolytic poxvirus engineered for replication, transgene expression and amplification in cancer cells harbouring activation of the epidermal growth factor receptor (EGFR)/Ras pathway, followed by cell lysis and anticancer immunity. Here we show in a clinical trial that JX-594 selectively infects, replicates and expresses transgene products in cancer tissue after intravenous infusion, in a dose-related fashion. Normal tissues were not affected clinically. This platform technology opens up the possibility of multifunctional products that selectively express high concentrations of several complementary therapeutic and imaging molecules in metastatic solid tumours in humans.

Efforts to selectively target and disrupt established tumor vasculature have largely failed to date. We hypothesized that a vaccinia virus engineered to target cells with activation of the ras/MAPK signaling pathway (JX-594) could specifically infect and express transgenes (hGM-CSF, b-galactosidase) in tumor-associated vascular endothelial cells in humans. Efficient replication and transgene expression in normal human endothelial cells in vitro required either VEGF or FGF-2 stimulation. Intravenous infusion in mice resulted in virus replication in tumor-associated endothelial cells, disruption of tumor blood flow, and hypoxia within 48 hours; massive tumor necrosis ensued within 5 days. Normal vessels were not affected. In patients treated with intravenous JX-594 in a phase I clinical trial, we showed dose-dependent endothelial cell infection and transgene expression in tumor biopsies of diverse histologies. Finally, patients with advanced hepatocellular carcinoma, a hypervascular and VEGF-rich tumor type, were treated with JX-594 on phase II clinical trials. JX-594 treatment caused disruption of tumor perfusion as early as 5 days in both VEGF receptor inhibitor-na€ ve and -refractory patients. Toxicities to normal blood vessels or to wound healing were not evident clinically or on MRI scans. This platform technology opens up the possibility of multifunctional engineered vaccinia products that selectively target and infect tumorassociated endothelial cells, as well as cancer cells, resulting in transgene expression, vasculature disruption, and tumor destruction in humans systemically. Cancer Res; 73(4); 1265-75. Ó2012 AACR.

JX-594 is a targeted and granulocyte macrophage-colony stimulating factor (GM-CSF)-expressing oncolytic poxvirus designed to selectively replicate in and destroy cancer cells through viral oncolysis and tumor-specific immunity. In order to study the mechanisms-of-action (MOA) of JX-594 in humans, a mechanistic proof-of-concept clinical trial was performed at a low dose equivalent to ≤10% of the maximum-tolerated dose (MTD) in other clinical trials. Ten patients with previously treated stage IV melanoma were enrolled. Tumors were injected weekly for up to nine total treatments. Blood samples and tumor biopsies were analyzed for evidence of transgene activity, virus replication, and immune stimulation. The β-galactosidase (β-gal) transgene was expressed in all patients as evidenced by antibody induction. Six patients had significant induction of GM-CSF-responsive white blood cell (WBC) subsets such as neutrophils (25-300% increase). JX-594 replication and subsequent shedding into blood was detectable in five patients after cycles 1-9. Tumor biopsies demonstrated JX-594 replication, perivascular lymphocytic infiltration, and diffuse tumor necrosis. Mild flu-like symptoms were the most common adverse events. In sum, JX-594 replication, oncolysis, and expression of both transgenes were demonstrated; replication was still evident after multiple cycles. These findings have implications for further clinical development of JX-594 and other transgene-armed oncolytic viruses.

Oncolytic viruses pose many questions in their use in cancer therapy. In this study, we assessed the potential of mpJX-594 (mouse-prototype JX-594), a replication-competent vaccinia virus administered by intravenous injection, to target the tumor vasculature, produce immune activation and tumor cell killing more widespread than the infection, and suppress invasion and metastasis. These actions were examined in RIP-Tag2 transgenic mice with pancreatic neuroendocrine tumors that developed spontaneously and progressed as in humans. mpJX-594 initially infected tumor vascular endothelial cells, leading to vascular pruning and prolonged leakage in tumors but not in normal organs; parallel effects were observed in U87 gliomas. Viral infection spread to tumor cells, where tumor cell killing was much more widespread than the infection. Widespread tumor cell killing at 5 days was prevented by depletion of CD8 T lymphocytes and did not require GM-CSF, as mpJX-594 variants that expressed human, mouse, or no GM-CSF produced equivalent amounts of killing. The antivascular, antitumor, and antimetastatic effects of mpJX-594 were amplified by concurrent or sequential administration of sunitinib, a multitargeted receptor tyrosine kinase inhibitor. These effects were not mimicked by selective inhibition of VEGFR2 despite equivalent vascular pruning, but were accompanied by suppression of regulatory T cells and greater influx of activated CD8 T cells. Together, our results showed that mpJX-594 targets tumor blood vessels, spreads secondarily to tumor cells, and produces widespread CD8 T-cell-dependent tumor cell killing in primary tumors and metastases, and that these effects can be amplified by coadministration of sunitinib. These findings reveal multiple unrecognized features of the antitumor properties of oncolytic vaccinia viruses, all of which can be amplified by the multitargeted kinase inhibitor sunitinib. .

Oncolytic viruses designed to attack malignant cells can in addition infect and destroy tumor vascular endothelial cells. We show here that this expanded tropism of oncolytic vaccinia virus to the endothelial compartment is a consequence of VEGF-mediated suppression of the intrinsic antiviral response. VEGF/VEGFR2 signaling through Erk1/2 and Stat3 leads to upregulation, nuclear localization, and activation of the transcription repressor PRD1-BF1/Blimp1. PRD1-BF1 does not contribute to the mitogenic effects of VEGF, but directly represses genes involved in type I interferon (IFN)-mediated antiviral signaling. In vivo suppression of VEGF signaling diminishes PRD1-BF1/Blimp1 expression in tumor vasculature and inhibits intravenously administered oncolytic vaccinia delivery to and consequent spread within the tumor.

Histone deacetylase inhibitors (HDI) dampen cellular innate immune response by decreasing interferon production and have been shown to increase the growth of vesicular stomatitis virus and HSV. As attenuated tumour-selective oncolytic vaccinia viruses (VV) are already undergoing clinical evaluation, the goal of this study is to determine whether HDI can also enhance the potency of these poxviruses in infection-resistant cancer cell lines. Multiple HDIs were tested and Trichostatin A (TSA) was found to potently enhance the spread and replication of a tumour selective vaccinia virus in several infection-resistant cancer cell lines. TSA significantly decreased the number of lung metastases in a syngeneic B16F10LacZ lung metastasis model yet did not increase the replication of vaccinia in normal tissues. The combination of TSA and VV increased survival of mice harbouring human HCT116 colon tumour xenografts as compared to mice treated with either agent alone. We conclude that TSA can selectively and effectively enhance the replication and spread of oncolytic vaccinia virus in cancer cells.

In this study, we show that several microtubule-destabilizing agents used for decades for treatment of cancer and other diseases also sensitize cancer cells to oncolytic rhabdoviruses and improve therapeutic outcomes in resistant murine cancer models. Drug-induced microtubule destabilization leads to superior viral spread in cancer cells by disrupting type I IFN mRNA translation, leading to decreased IFN protein expression and secretion. Furthermore, microtubule-destabilizing agents specifically promote cancer cell death following stimulation by a subset of infection-induced cytokines, thereby increasing viral bystander effects. This study reveals a previously unappreciated role for microtubule structures in the regulation of the innate cellular antiviral response and demonstrates that unexpected combinations of approved chemotherapeutics and biological agents can lead to improved therapeutic outcomes.

d Attenuated Semliki Forest virus (SFV) may be suitable for targeting malignant glioma due to its natural neurotropism, but its replication in brain tumor cells may be restricted by innate antiviral defenses. We attempted to facilitate SFV replication in glioma cells by combining it with vaccinia virus, which is capable of antagonizing such defenses. Surprisingly, we found parenchymal mouse brain tumors to be refractory to both viruses. Also, vaccinia virus appears to be sensitive to SFV-induced antiviral interference. Brain tumors are particularly life-threatening due to their sensitive anatomical location. Recently, temozolomide plus radiotherapy has provided a measurable survival benefit to a subset of patients (1), but more effective therapies are still needed. In this regard, oncolytic viruses (OVs) seem particularly promising, as they display higher tumor specificity and possibly fewer side effects than standard therapies (2). One of our OV candidates, attenuated Semliki Forest virus (SFV), was able to fully eradicate orthotopic U87 xenografts in 100% of treated nude mice following a single systemic injection (3). However, in other models, we and others have identified limitations to oncolytic virotherapy; in particular, innate antiviral defenses limit virus replication in tumor cells (4,5).In order to probe further and overcome the mechanisms of glioma resistance to oncolytic SFV, we combined it with oncolytic vaccinia virus (VV), which itself has shown promise in glioma targeting and also has the capacity to facilitate replication of type I interferon (IFN)-sensitive OVs by antagonizing innate antiviral defenses (6)(7)(8). First, we demonstrate efficient killing of DBT mouse glioma cells in vitro but not in vivo by SFV alone, mirroring the results we observed in our previous rat model (4) (Fig. 1A and B). Lack of efficacy could not be explained simply by the immune competence of the animals, as SFV successfully eradicated another type of syngeneic tumor (CT26LacZ) at a similar dose (not shown). Next, we observed that SFV limits its own spread in DBT cells under spatially restrictive conditions (under agarose) and that this limitation could be lifted by coinfecting cells with VV or neutralizing type I IFN using polyclonal antibody (anti-beta interferon [IFN-␤]) or recombinant vaccinia virus-encoded B18R protein (Fig. 1C). Facilitation of SFV spread in DBT cells by VV is dependent on B18R, as we did not see enhancement when B18R-deleted VV was used. While the spread of SFV under agarose was enhanced when SFV was combined with VV, replication of VV itself was strongly inhibited (Fig. 1C), which was also confirmed by quantifying virus output from coinfected DBT cells in free culture (Fig. 1D). DBT cell killing by the virus combinations was synergistic, as calculated by the Chou-Talalay method (Fig. 1E). However, combination of SFV with VV in an orthotopic DBT model did not provide statistically significant improvement in survival compared to the next best therapy, VV alone, by either systemic injection or d...