Imaging approaches to assess mechanism-of-action and response in patients with advanced hepatocellular carcinoma treated with the novel oncolytic poxvirus JX-594.

210 Background: The novel oncolytic virus JX-595 has demonstrated anti-cancer mechanisms of action, as defined in preclinical models, which includes cytolysis, intra-tumoral vascular disruption, and immune-mediated tumor targeting. Methods: To determine whether mechanism(s) of action (MOA) of the novel anti-cancer oncolytic virus JX-594 could be demonstrated by MRI imaging in patients with advanced hepatocellular carcinoma (HCC), dynamic contrast-enhanced MRI of the liver was performed at baseline, day 5, and week 8 following intra-tumoral injection. Images were evaluated by a central reviewer blinded to treatment and dose using both modified RECIST and Choi response criteria. 17/30 subjects underwent day 5 (D5) post-treatment imaging; 28/30 had week 8 (W8) imaging. Results: Choi responses correlated more reliably than RECIST with JX-594 MOA. Evidence of intra-tumoral vascular shutdown, manifest by areas of reduced or non-enhancement (Choi response), was observed in 6 of 17 subjects on D5 5 MRI scans. Day 5 Choi responses were a predictor of week 8 Choi responses in all but 1 subject. Of the 11/17 D5 Choi non-responders, 3 were Choi responders at 8 weeks. Increase in size at D5 of small lesions present at baseline (“unmasking”) is compatible with oncolytic flare due to intra-tumoral edema contributed to by cell lysis and immune infiltration. RECIST criteria tumor measurements did not identify MOA of JX-594, and resulted in the appearance of pseudoprogression at D5 in some subjects. Conclusions: Hyperacute MRI post-therapy can be used to detect activity of the JX-594, a novel oncolytic anti-cancer therapy. Day 5 Choi responses were a predictor of subsequent response at week 8. Clinical trial information: NCT00554372.