Hyaluronidase expression by an oncolytic adenovirus enhances its intratumoral spread and supresses tumor growth

Successful virotherapy requires efficient virus spread within tumors. We tested whether the expression of hyaluronidase, an enzyme which dissociates the extra-cellular matrix (ECM), could enhance the intratumoral distribution of an oncolytic adenovirus and improve its therapeutic activity. As a proof of concept, we demon-strated that intratumoral coadministration of hyaluroni-dase in mice-bearing tumor xenografts improves the antitumor activity of an oncolytic adenovirus. Next, we constructed a replication-competent adenovirus express-ing a soluble form of the human sperm hyaluronidase (PH20) under the control of the major late promoter (MLP) (AdwtRGD-PH20). Intratumoral treatment of human melanoma xenografts with AdwtRGD-PH20 resulted in degradation of hyaluronan (HA), enhanced viral distribution, and induced tumor regression in all treated tumors. Finally, the PH20 cDNA was inserted in an oncolytic adenovirus that selectively kills pRb pathway-defective tumor cells. The antitumoral activ-ity of the novel oncolytic adenovirus expressing PH20 (ICOVIR17) was compared to that of the parental virus ICOVIR15. ICOVIR17 showed more antitumor efficacy following intratumoral and systemic administration in mice with prestablished tumors, along with an improved spread of the virus within the tumor. Importantly, a single intravenous dose of ICOVIR17 induced tumor regression in 60% of treated tumors. These results indicate that ICOVIR17 is a promising candidate for clinical testing.