421. Evaluating the Efficacy of Combination Cancer Treatment: Oncolytic Adenovirus and 5FU Chemotherapy

Previous studies have shown that Interferon(IFN)-based chemoradiation therapy can improve survival after resection of pancreas cancer. However, its clinical utility to this point has been limited due to the severe toxicity related to its use systemically. Gene Therapy represents a promising approach to deliver localized treatments that are effective and minimally toxic. Our aim in this study is to evaluate our group's novel oncolytic adenovirus (OAd) which allows targeting IFN treatment to cancer cells while sparing healthy tissue. The OAd, 5/3Cox2DE3ADPIFN, is selectively replicative in Cox2 (+) cell lines, allowing for specificity in therapy. It has also been modified to with a 5/3 chimeric knob to facilitate transduction, an overexpression of the adenoviral death protein, and expresses our IFN gene of interest. This study was conducted to analyze the combination of 5FU chemotherapy and our OAd in vitro in order to assess the interaction of treatments and determine the optimum combined treatment regimen. Treatments were analyzed in pancreatic cancer and esophageal adenocarcinoma cell lines S2013 and OE19. Recombinant OAds expressing luciferase rather than IFN were used in this study to isolate the combination of 5FU and the virus. Two viral models were evaluated: our selective therapeutic virus (Cox2) and a nearly identical but universally replicative virus (wild type). Cells were treated with 0, 1 or 10 viral particles per cell and 0, 5, 10, or 20 uM 5FU. Three timing regimens were used: simultaneous administration, 5FU 4 hours before virus, and virus 48 hours before 5FU. Crystal Violet and MTS Assays were used to measure cell death. Viral Copy number was used to assess viral replication using qPCR with a viral E4 primer. Cell death analysis showed an earlier killing effect from the wild type virus but otherwise similar patterns. 5FU and each virus produced dose dependent cell death independently. There was a significant additive effect seen in cell death from combining treatments when using 5FU before virus in both S2013 and OE19. Simultaneous treatment showed an additive killing effect with the combination in S2013, but a reduced killing by the combination compared to virus alone in OE19. There was also reduced combination killing when using virus before 5FU in S2013. Viral copy experiments in S2013 using simultaneous treatment showed dose dependent inhibition of viral replication, with only the 20uM dose significantly limiting viral replication over time. Our Cox2 OAd shows a killing effect similar to wild type in multiple cancer cell lines. When combined with 5FU treatment the expected summation in overall cell death from the independent treatments varies by timing of administrations as well as by type of cancer cell line. The reduced killing of the combination treatment in the simultaneous and virus before 5FU regimens, as well as the replication inhibition shown by viral copy number, may suggest an inhibition of the virus by 5FU under certain conditions. This also suggests the possibility of a gene therapy treatment regimen with optimal therapeutic effect, which appears to be 5FU before virus based on the results collected. Further studies investigating different chemotherapeutic drugs and regimens should be conducted to examine these trends.