321. Oncolytic Adenovirus Expressing IFN as a Tool To Eliminate Pancreatic Cancer Stem Cells

Abstract

Pancreatic cancer is the 4th leading cause of cancer related death in the US, and curative resection of tumors is the most effective treatment against the disease. Unfortunately, the majority of patients are diagnosed in the advanced stage of the disease, and palliative treatment with Gemcitabine is the therapy of choice. In both cases, curative resection of tumors or chemotherapy, effectiveness can be limited by the presence of pancreatic cancer stem cells. Cancer stem cells (CSC) are correlated with drug resistance, tumor recurrence, and metastasis. CSC are usually located in the hypoxic center of the tumors in a quiescent stage and are not affected by conventional chemotherapeutics that target highly replicating cells, such as Gemcitabine. CSC are also called tumor initiating cells (TIC), and as low as 100 cells are reported to form tumors in pre-clinical models.Inclusion of IFN alpha (IFN) in combination therapy protocols against pancreatic cancer can be highly beneficial to tackle this problem. IFN is reported to be cytotoxic to cancer cells, have antiangiogenic properties, stimulate anti-tumor immunity, and sensitize cancer cells to chemoradiation. In addition, IFN is reported to induce activation of quiescent CSC making them susceptible to chemotherapy drugs that target highly replicating cells. Phase II and III clinical trials combining IFN with 5-FU and radiation in an adjuvant therapy setting reported a 35% increase in the five year overall survival of pancreatic cancer patients. Stimulated by the promising results reported in IFN clinical trials we developed an oncolytic adenovirus expressing IFN (OAd-IFN). Our aim is to use the virus to improve IFN therapeutic effects in combination therapy by restricting high levels of IFN expression to the tumor. In vitro data testing triple combination of OAd-IFN + radiation+ 5-FU using MIA PACA-2 and S2103 pancreatic cancer cells in colony formation assay (CFA) showed that OAd-IFN combination was more efficacious in inhibiting colony formation than triple combination with OAd-LUC, a counterpart of OAd-IFN expressing luciferase. Triple combination with OAd-IFN was also more efficient than double therapies with 5-FU+radiation, OAd-LUC + radiation, and OAd-LUC+5-FU. As CFA is an assay frequently used to access the proliferating capacity of single cells in vitro, our data suggests that IFN expressed virus decreased the number of TIC/CSC. This is supported by our in vivo studies showing that inclusion of OAd-IFN in combination with radiation or with 5-FU+radiation results in superior tumor shrinkage than all therapies not involving IFN or including OAd-LUC. In addition, tumors treated with OAd-IFN combination have a longer recurrence interval compared with all other treatments suggesting reduced levels of TIC.Although further studies are necessary to understand the impact of our OAd-IFN virus in pancreatic cancer stem cells, we believe IFN expressed by our virus made quiescent CSC more susceptible to treatments. Because our virus can express high levels of IFN restricted to the tumor site, we believe that a higher percentage of these cells will be affected by IFN delaying clinical recurrence of tumors, and improving therapy effectiveness.