Abstract
BackgroundReovirus type 3 Dearing (T3D) has demonstrated oncolytic activity in vitro, in in vivo murine models and in early clinical trials. However the true potential of oncolytic viruses may only be realized fully in combination with other modalities such as chemotherapy, targeted therapy and radiotherapy. In this study, we examine the oncolytic activity of reovirus T3D and chemotherapeutic agents against human prostate cancer cell lines, with particular focus on the highly metastatic cell line PC3 and the chemotherapeutic agent docetaxel. Docetaxel is the standard of care for metastatic prostate cancer and acts by disrupting the normal process of microtubule assembly and disassembly. Reoviruses have been shown to associate with microtubules and may require this association for efficient viral replication.MethodsThe effects of reovirus and chemotherapy on in vitro cytotoxicity were investigated in PC3 and Du 145 cells and the interactions between agents were assessed by combination index analysis. An Annexin V/propidium iodide fluorescence-activated cell sorting-based assay was used to determine mode of cell death. The effects of reovirus and docetaxel administered as single agent or combination therapy were tested in vivo in a murine model. The effects of docetaxel and reovirus, alone and together, on microtubule stabilisation were investigated by Western blot analysis.ResultsVariable degrees of synergistic cytotoxicity were observed in PC3 and Du 145 cells exposed to live reovirus and several chemotherapy agents. Combination of reovirus infection with docetaxel exposure led to increased late apoptotic/necrotic cell populations. Reovirus/docetaxel combined therapy led to reduced tumour growth and increased survival in a PC3 tumour bearing mouse model. Microtubule stabilization was enhanced in PC3 cells treated with reovirus/docetaxel combined therapy compared to other reovirus/chemotherapy combinations.ConclusionsThe co-administration of a variety of chemotherapeutic agents with live reovirus was able to enhance cytotoxicity synergistically in vitro. The combination of docetaxel with reovirus also delayed tumour growth and improved survival in vivo. Enhanced microtubule stabilisation following this combination treatment may, in part, explain the mechanism of synergy. These results provide evidence to support the ongoing clinical trials using these agents.
Highlights
Reovirus type 3 Dearing (T3D) has demonstrated oncolytic activity in vitro, in in vivo murine models and in early clinical trials
Reovirus cytotoxicity in PC3, Du 145 and LNCaP cell lines The effect of reovirus infection over 48 h was assessed in three human prostate cancer cell lines
Administration in combination with other modalities such as chemotherapy, targeted therapy and radiotherapy may be necessary in order to realize the full potential of reovirus, and other oncolytic viruses
Summary
Reovirus type 3 Dearing (T3D) has demonstrated oncolytic activity in vitro, in in vivo murine models and in early clinical trials. We examine the oncolytic activity of reovirus T3D and chemotherapeutic agents against human prostate cancer cell lines, with particular focus on the highly metastatic cell line PC3 and the chemotherapeutic agent docetaxel. Reoviruses are ubiquitous, nonpathogenic viruses that have innate oncolytic activity in a wide range of human and murine tumour cells. This property correlates with the transformed state of the cell [1,2] as transformation of immortalized cells which were not tumorigenic in vivo with oncogenes such as Ras, Sos, v-erb and c-myc rendered them susceptible to reovirus oncolysis [3,4,5]. In order to maximise the efficiency of tumour kill, combination therapy with other treatment modalities such as radiation or chemotherapy is likely
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