Phase I trial of gene-mediated cytotoxic immunotherapy in combination with chemoradiation for locally advanced pancreatic cancer.

Abstract

195 Background: More than 80% of patients with pancreatic cancer present with locally advanced or metastatic disease and have a median survival of only 6 months. Immunotherapy approaches may improve outcomes. Gene Mediated Cytotoxic Immunotherapy (GMCI) is an approach that generates a systemic anti-tumor vaccine effect through intra-tumoral delivery of an adenoviral vector expressing the HSV-thymidine kinase gene (AdV-tk) followed by anti-herpetic prodrug and synergy with chemoradiation. The mechanisms of action involve tumor cytotoxicity, activation of antigen presenting cells and stimulation of systemic anti-tumor T-cell immunity. Safety with potential efficacy has been demonstrated in multiple clinical studies. This is the first application of GMCI in pancreatic cancer. Methods: This study evaluated 4 dose levels of AdV-tk (3x1010 to 1x1012 vector particles) injected into locally advanced tumors via EUS or CT-guidance before and during week 3 of standard 5-FU-chemoradiation. Valacyclovir (Valtrex, GSK) prodrug was given for 14 days after each of 2 AdV-tk injections. Results: The study completed accrual with 13 patients enrolled and 12 completing therapy with 3 at each of the 4 dose levels. One patient refused further participation during course 1 after recovering from azotemia. Median age was 64 years (range 55-81) and median baseline CA19-9 was 1634 U/ml. No dose limiting toxicities and no injection related complications occurred. Possibly related grade 3-4 toxicities, all of which were transient, included dehydration, azotemia and worsening elevation of bilirubin and AST. Kaplan-Meier estimated median survival is 12.2 months with 6 patients still alive at 8-20 months. Two patients achieved a partial response by RECIST criteria. One occurred in week 6 despite discontinuing 5-FU/radiation during week 1. The other had gradual decrease of a 7 cm tumor over 11 months. Serum CA19-9 levels decreased in 8/8 evaluable patients by 32-91% at 3 months after treatment initiation. Conclusions: AdV-tk can be safely injected into pancreatic tumors and combined with standard chemoradiation. Early results are highly encouraging and justify further evaluation in a phase II study. [Table: see text]