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BackgroundOncolytic reovirus therapy for cancer induces a typical antiviral response to this RNA virus, including neutralizing antibodies. Concomitant treatment with cytotoxic chemotherapies has been hypothesized to improve the therapeutic potential of the virus. Chemotherapy side effects can include immunosuppression, which may slow the rate of the antiviral antibody response, as well as potentially make the patient more vulnerable to viral infection.MethodReovirus neutralizing antibody data were aggregated from separate phase I clinical trials of reovirus administered as a single agent or in combination with gemcitabine, docetaxel, carboplatin and paclitaxel doublet or cyclophosphamide. In addition, the kinetics of individual antibody isotypes were profiled in sera collected in these trials.ResultsThese data demonstrate preserved antiviral antibody responses, with only moderately reduced kinetics with some drugs, most notably gemcitabine. All patients ultimately produced an effective neutralizing antibody response.ConclusionPatients’ responses to infection by reovirus are largely unaffected by the concomitant drug treatments tested, providing confidence that RNA viral treatment or infection is compatible with standard of care treatments.

Purpose: Reovirus type 3 Dearing (RT3D) replicates preferentially in Ras-activated cancers. RT3D shows synergistic in vitro cytotoxicity in combination with platins and taxanes. The purpose of this phase I/II study was to assess RT3D combined with carboplatin/paclitaxel in patients with advanced cancers. Experimental Design: Patients were initially treated in a dose-escalating, phase I trial with intravenous RT3D days 1 to 5, carboplatin [area under curve (AUC) 5, day 1] and paclitaxel (175 mg/m2, day 1) 3-weekly. RT3D was escalated through three dose levels: 3 × 109, 1 × 1010, and 3 × 1010 TCID50 in cohorts of three. Primary endpoints were to define the maximum tolerated dose and dose-limiting toxicity and to recommend a dose for phase II studies. Secondary endpoints included pharmacokinetics, immune response, and antitumor activity. A subsequent phase II study using the 3 × 1010 TCID50 dose characterized the response rate in patients with head and neck cancer. Results: Thirty-one heavily pretreated patients received study therapy. There were no dose-limiting toxicities during dose-escalation and most toxicities were grade I/II. Overall effectiveness rates were as follows: one patient had a complete response (3.8%), six patients (23.1%) had partial response, two patients (7.6%) had major clinical responses clinically evaluated in radiation pretreated lesions which are not evaluable by Response Evaluation Criteria in Solid Tumors (RECIST), nine patients (34.6%) had stable disease, and eight patients (30.8%) had disease progression. Viral shedding was minimal and antiviral immune responses were attenuated compared with previous single-agent data for RT3D. Conclusions: The combination of RT3D plus carboplatin/paclitaxel is well tolerated with evidence of activity in cancer of the head and neck. A randomized phase III study is currently open for recruitment. Clin Cancer Res; 18(7); 2080–9. ©2012 AACR.

Purpose: REOLYSIN (Oncolytics Biotech) consists of a wild-type oncolytic reovirus, which has selective cytotoxicity for tumor cells while sparing normal cells. In a phase I study as a single agent, repeated infusions of reovirus were safe with evidence of antitumor activity. Preclinical studies indicate potential for synergy between reovirus and chemotherapeutic agents. A multicenter, phase I dose escalation study was designed to assess the safety of combining reovirus with docetaxel chemotherapy in patients with advanced cancer. Experimental Design: Patients received 75 mg/m2 docetaxel (day 1) and escalating doses of reovirus up to 3 × 1010 TCID50 (days 1-5) every 3 weeks. Results: Twenty-five patients were enrolled, and 24 patients were exposed to treatment, with 23 completing at least one cycle and 16 suitable for response assessment. Dose-limiting toxicity of grade 4 neutropenia was seen in one patient, but the maximum tolerated dose was not reached. Antitumor activity was seen with one complete response and three partial responses. A disease control rate (combined complete response, partial response, and stable disease) of 88% was observed. Immunohistochemical analysis of reovirus protein expression was observed in posttreatment tumor biopsies from three patients. Conclusion: The combination of reovirus and docetaxel is safe, with evidence of objective disease response, and warrants further evaluation in a phase II study at a recommended schedule of docetaxel (75 mg/m2, three times weekly) and reovirus (3 × 1010 TCID50, days 1-5, every 3 weeks). Clin Cancer Res; 16(22); 5564–72. ©2010 AACR.

Purpose: To determine the safety and feasibility of combining intratumoral reovirus and radiotherapy in patients with advanced cancer and to assess viral biodistribution, reoviral replication in tumors, and antiviral immune responses. Experimental Design: Patients with measurable disease amenable to palliative radiotherapy were enrolled. In the first stage, patients received radiotherapy (20 Gy in five fractions) plus two intratumoral injections of RT3D at doses between 1 × 108 and 1 × 1010 TCID50. In the second stage, the radiotherapy dose was increased (36 Gy in 12 fractions) and patients received two, four, or six doses of RT3D at 1 × 1010 TCID50. End points were safety, viral replication, immunogenicity, and antitumoral activity. Results: Twenty-three patients with various solid tumors were treated. Dose-limiting toxicity was not seen. The most common toxicities were grade 2 (or lower) pyrexia, influenza-like symptoms, vomiting, asymptomatic lymphopenia, and neutropenia. There was no exacerbation of the acute radiation reaction. Reverse transcription-PCR (RT-PCR) studies of blood, urine, stool, and sputum were negative for viral shedding. In the low-dose (20 Gy in five fractions) radiation group, two of seven evaluable patients had a partial response and five had stable disease. In the high-dose (36 Gy in 12 fractions) radiation group, five of seven evaluable patients had partial response and two stable disease. Conclusions: The combination of intratumoral RT3D and radiotherapy was well tolerated. The favorable toxicity profile and lack of vector shedding means that this combination should be evaluated in newly diagnosed patients receiving radiotherapy with curative intent. Clin Cancer Res; 16(11); 3067–77. ©2010 AACR.

In the last 50 years, there have been a number of anecdotal reports of viral infections causing transient cancer remissions in patients with advanced disease. However, during the last decade, these reports have been supplemented by data indicating the potential antitumor effect of a number of viruses. As a consequence, there has been increasing interest in the development of oncolytic viruses—viruses that selectively destroy cancer cells—as cancer therapeutics. They can be divided into two groups: natural tumor-selective wild-type viruses and genetically engineered tumor-selective viruses; both present advantages and disadvantages. The use of oncolytic viruses as anticancer agents still represents a major challenge and many obstacles need to be overcome: issues of systemic toxicity, tumor selectivity, immune response, and manufacture are added to the inconvenience of genetic manipulation. Reovirus is an inherently selective wild-type virus that seems to fulfill many of the above criteria for an oncolytic virus. Reovirus selectively replicates in Ras-activated cells and has been shown to possess antitumor activity both in vitro and in vivo. Since many tumors have an activated Ras pathway, the potential for using reovirus as an effective anticancer agent is substantial. Ongoing studies have demonstrated its safety when administered to cancer patients.

Purpose: This study combined systemic administration of the oncolytic reovirus type 3 Dearing (reovirus) with chemotherapy in human subjects. We aimed to determine the safety and feasibility of combining reovirus administration with gemcitabine and to describe the effects of gemcitabine on the antireoviral immune response. Experimental Design: Patients received reovirus in various doses, initially we dosed for five consecutive days but this was poorly tolerated. We amended the protocol to administer a single dose and administered up to 3 × 1010 TCID50. Toxicity was assessed by monitoring of clinical and laboratory measurements. We assessed antibody response by cytotoxicity neutralization assay. Results: Sixteen patients received 47 cycles of reovirus. The two initial patients and one patient in the final cohort experienced dose limiting toxicity (DLT). The DLTs consisted of two asymptomatic grade 3 liver enzyme rises and one asymptomatic grade 3 troponin I rise. Common toxicities consisted of known reovirus and gemcitabine associated side effects. Further analysis showed a potential interaction between reovirus and gemcitabine in causing liver enzyme rises. Grade 3 rises in liver enzymes were associated with concomitant aminocetophen use. Importantly, the duration of the liver enzyme rise was short and reversible. Neutralizing antibody responses to reovirus were attenuated both in time-to-occurrence and peak height of the response. Conclusions: Reovirus at the dose of 1 × 1010 TCID50 can be safely combined with full dose gemcitabine. Combination of reovirus with gemcitabine affects the neutralizing antibody response and this could impact both safety and efficacy of this treatment schedule. Clin Cancer Res; 17(3); 581–8. ©2010 AACR.

Purpose: To test combination treatment schedules of reovirus and radiation in human and murine tumor cells in vitro and in vivo. Experimental Design: In vitro cytotoxicity and cell cycle effects of reovirus given alone and combined with radiotherapy were assessed by colorimetric, tissue culture infectious dose 50, and fluorescence-activated cell sorting–based assays. Interactions between the agents were evaluated using combination index analysis. The effect of different schedules of reovirus and radiotherapy on viral replication and cytotoxicity was tested in vitro and the combination was assessed in three tumor models in vivo. Results: Characterization of reovirus cytotoxicity in a panel of cell lines yielded a range of sensitivities. Combined reovirus and radiotherapy yielded statistically significantly increased cytotoxicity, particularly in cell lines with moderate susceptibility to reovirus alone. The enhanced cytotoxicity of the combination occurred independently of treatment sequence or schedule. Radiation did not affect viral replication and only reduced reoviral cytotoxicity after clinically irrelevant single doses (>50 Gy). Combination index analysis revealed synergy between radiation (3-10 Gy) and reovirus at multiplicities of infection between 0.001 and 1. Combination treatment significantly increased apoptosis in tumor cells relative to either single-agent treatment. In vivo studies using xenograft and syngeneic tumors showed enhanced activity of the combination relative to reovirus or radiation alone (P < 0.001). Conclusions: Combining reovirus and radiotherapy synergistically enhances cytotoxicity in a variety of tumor cells in vitro and in vivo. These results offer strong support for translational clinical trials of reovirus plus radiotherapy that have been initiated in the clinic.

Purpose: The purpose of the present study was to investigate whether it is possible to achieve truly systemic delivery of oncolytic reovirus, in immunocompetent hosts, using cyclophosphamide to overcome some of the barriers to effective intratumoral delivery and replication of i.v. injected virus. Experimental Design: I.v. delivery of reovirus was combined with different regimens of i.p. administered cyclophosphamide in C57Bl/6 mice bearing established s.c. B16 tumors. Intratumoral viral replication, tumor size, and survival were measured along with levels of neutralizing antibody (NAb) in the blood. Finally, differential toxicities of the virus/cyclophosphamide regimens were monitored through viral replication in systemic organs, survival, and cardiac damage. Results: Repeated i.v. injection of reovirus was poorly effective at seeding intratumoral viral replication/oncolysis. However, by combining i.v. virus with cyclophosphamide, viral titers of between 107 and 108 plaque-forming units per milligram were recovered from regressing tumors. Doses of cyclophosphamide that ablated NAb were associated with severe toxicities, characterized by viral replication in systemic organs—toxicities that are mirrored by repeated reovirus injections into B-cell knockout mice. Next, we restructured the dosing of cyclophosphamide and i.v. virus such that a dose of 3 mg cyclophosphamide was administered 24 h before reovirus injection, and this schedule was repeated every 6 days. Using this protocol, high levels of intratumoral viral access and replication (∼107 plaque-forming units per milligram tumor) were maintained along with systemically protective levels of NAb and only very mild, non–life-threatening toxicity. Conclusion: NAb to oncolytic viruses play a dual role in the context of systemic viral delivery; on one hand, they hinder repeated administration of virus but on the other, they provide an important safety mechanism by which virus released from vigorous intratumoral replication is neutralized before it can disseminate and cause toxicity. These data support the use of cyclophosphamide to modulate, but not ablate, patient NAb, in development of carefully controlled clinical trials of the systemic administration of oncolytic viruses.