413. Effect of Adenoviral Death Protein on NIS-Based Iodine Therapy and Imaging for Pancreatic Cancer

Abstract

In this study, we assess our novel Oncolytic Adenovirus (OAd) expressing a dual function therapeutic and imaging transgene, the sodium-iodide symporter (NIS) as a promising alternative for pancreatic cancer treatment. We hypothesized that NIS expression in pancreatic cancer will induce uptake of radioiodine and allow noninvasive SPECT/CT imaging with 123I. We designed our OAd-NIS to overcome the low efficacy of previous vectors. These viruses have a modified Ad5/Ad3 fiber-knob shown to improve the poor transduction of pancreatic cancer cells. Viral replication is controlled under the Cox2 promoter allowing specific delivery of viral genes, and most of adenoviral E3 genes are deleted and replaced with NIS and Adenovirus Death Protein (ADP) genes. We have previously demonstrated significantly improved ability of ADP-overexpressing OAds to enhance viral release and cytolytic activity. Although improved oncolysis enhances viral release and improve the therapeutic effect in solid tumors, it can potentially reduce radioiodide tracer uptake. To test this possibility we designed and compared identical vectors with ADP (OAd-NIS-ADP) and without ADP (OAd-NIS-noADP) in vitro and in vivo. We first compared virus killing ability in pancreatic cancer cell lines. The ADP+ vector was significantly more cytolytic that no-ADP counterpart and showed improved viral replication and spread. Cox2-controlled OAd did not produce cell death in Cox2-negative control, confirming selectivity. We next assessed OAds ability to induce NIS protein expression and radioiodine uptake. NIS-OAds efficiently produce glycosylated NIS multimers as early as 2-days post infection. Infection with no-ADP vectors resulted in a significantly greater radioiodine uptake (125I) compared to ADP+ viruses. Importantly, ex vivo uptake test in human patient tissues confirmed the high level of NIS in pancreatic adenocarcinoma samples, and revealed no 125I uptake in normal pancreas. We further assessed the ability of our vectors to visualize human pancreatic cancer xenografts in a mouse model by monitoring 99mTcO4− accumulation with SPECT-CT. The OAd-NIS-noADP showed an earlier and more sustained radioisotope uptake when compared to ADP+ supporting its use as a more sensitive diagnostic tool for pancreatic cancer. Of contrary, the ADP+ vector significantly outperformed OAd-NIS-noADP in tumor shrinkage. These results suggest that while OAd-NIS-noADP produces a greater radiotracer uptake and can be used as a diagnostic tool, its ADP+ counterpart results in a better therapeutic effect when applied as a monotherapy. It is now essential to estimate the therapeutic ability of both vectors upon combination with I-131 (ongoing study). Further investigation will include the imaging and therapeutic studies in patient-derived xenografts. Ultimately, the goal of our research is to design a multimodal therapy with radiation and oncolytic virus for diagnosis and therapy of cancers.