309. Oncolytic Efficacy and Enhanced Safety of Measles Virus Activated by Tumor-Secreted Matrix-Metalloproteases

INTRODUCTION. Cancer cells secrete matrix-metalloproteases (MMP) that degrade the extracellular matrix and are responsible for some hallmarks of malignant cancer. Many viruses, including a few currently used in oncolytic virotherapy clinical trials, depend on intracellular proteases to process their proteins and activate their particles. We show here for measles virus (MV) that particle activation can be made dependent of proteases secreted by cancer cells. RESULTS. MV depends on the intracellular protease furin to process and activate its envelope fusion (F) protein. To make F protein activation cancer cell-specific we introduced hexameric sequences recognized by an MMP, and identified the mutant proteins most effective in fusing MMP-expressing human fibrosarcoma cells (HT1080). We showed that an MMP-inhibitor interferes with syncytia formation elicited by mutant F proteins, and confirmed MMP-dependent cleavage by Edman degradation sequence analysis. We generated recombinant MVs expressing the modified F proteins in place of furin-activated F. These viruses spread only in cells secreting MMP. In nude mice, an MMP-activated MV retarded HT1080 xenograft growth as efficiently as the furin-activated MV vaccine strain. In MV-susceptible mice, the furin-activated virus caused lethal encephalitis upon intracerebral inoculation, whereas the MMP-activated did not. DISCUSSION. We took advantage of the tumor microenvironment to activate viral particles in situ, augmenting selectivity and enhancing safety. This study opens the perspective of combining targeting at the particle activation, receptor recognition, and selective replication levels to improve the therapeutic index of MV in ongoing clinical trials of oncolysis. Conditional activation by tumor-specific proteases can be engineered in other oncolytic viruses.