1. ¹Department of Surgery, University Medical Center Utrecht, Utrecht, The Netherlands
2. ²Virus and Stem Cell Biology Laboratory, Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
3. ³Department of Pathology, University Medical Center Utrecht, Utrecht, The Netherlands

Correspondence: Dr O Kranenburg, Department of Surgery, University Medical Center Utrecht, PO Box 85500, Utrecht 3508 GA, The Netherlands. E-mail: o.kranenburg@umcutrecht.nl

⁴These authors contributed equally to this work

Received 16 June 2007; Revised 11 October 2007; Accepted 10 November 2007; Published online 8 February 2008.

Abstract

Reovirus T3D preferentially kills tumor cells expressing Ras oncogenes and has shown great promise as an anticancer agent in various preclinical tumor models. Here, we investigated whether reovirus can infect and kill tumor cell cultures and tissue fragments isolated from resected human colorectal tumors, and whether this was affected by the presence of endogenous oncogenic KRAS. Tissue fragments and single-cell populations isolated from human colorectal tumor biopsies were infected with reovirus virions or with intermediate subviral particles (ISVPs). Reovirus virions were capable of infecting neither single-cell tumor cell populations nor small fragments of intact viable tumor tissue. However, infection of tumor cells with ISVPs resulted in transient viral protein synthesis, irrespective of the presence of oncogenic KRAS, but this did not lead to the production of infectious virus particles, and tumor cell viability was largely unaffected. ISVPs failed to infect intact tissue fragments. Thermolysin treatment of tumor tissue liberated single cells from the tissue and allowed infection with ISVPs, but this did not result in the production of infectious virus particles. Immunohistochemistry on tissue microarrays showed that junction adhesion molecule 1, the major cellular reovirus receptor, was improperly localized in the cytoplasm of colorectal tumor cells and was expressed at very low levels in liver metastases. This may contribute to the observed resistance of tumor cells to reovirus T3D virions. We conclude that infection of human colorectal tumor cells by reovirus T3D requires processing of virions to ISVPs, but that oncolysis is prevented by a tumor cell response that aborts viral protein synthesis and the generation of infectious viral particles, irrespective of KRAS mutation status.