1. ¹Department of Pathology, University of Illinois at Chicago, College of Medicine, Chicago, IL, USA
2. ²Department of Ophthalmology, University of Illinois at Chicago, College of Medicine, Chicago, IL, USA
3. ³Department of Microbiology and Immunology, University of Illinois at Chicago, College of Medicine, Chicago, IL, USA

Correspondence: Dr T Valyi-Nagy, Department of Pathology, University of Illinois at Chicago, 840 South Wood Street, Room 130 CSN, M/C 847, Chicago, IL 60612, USA. E-mail: tiborv@uic.edu

Received 1 March 2009; Revised 1 June 2009; Accepted 11 July 2009; Published online 6 November 2009.

Abstract

To better understand melanoma resistance to herpes simplex virus type 1 (HSV-1)-mediated oncolysis, traditional two-dimensional (2D) cultures and extracellular matrix (ECM) containing three-dimensional (3D) cultures of OCM1 and C918 uveal melanoma cells were infected with an HSV-1 strain that expresses the green fluorescent protein (GFP) marker during replication. Although 2D cultures were completely destroyed within a few days of HSV-1 inoculation, viable GFP-negative tumor cells remained detectable in 3D cultures for several weeks. Tumor cells with increased resistance to HSV-1 included cells that formed vasculogenic mimicry patterns and multicellular spheroids and cells that invaded Matrigel individually. Mechanisms of tumor resistance against HSV-1 in the 3D environment included impaired virus spread in the ECM and ECM-mediated inhibition of viral replication after viral entry into tumor cells. Observations also suggested that HSV-1 established quiescent infection in some tumor cells present in multicellular spheroids and that this could revert to productive viral infection when the tumor growth pattern changed. These findings indicate that 3D tumor cell cultures can be used to identify distinct tumor cell populations with increased resistance to HSV-1 and to explore mechanisms of ECM-mediated tumor resistance to oncolytic virotherapy.