Abstract 5319: Noninvasive reporter gene imaging for optimization of HSV-1 oncolysis in hepatic metastases

Abstract

Abstract Background: Liver metastases account for over 70% of deaths resulting from colorectal cancer. Apart from surgical resection other treatments are palliative. Herpes simplex virus l (HSV-1) oncolysis is a novel therapeutic option where cancer cells are destroyed by replicating viruses. HSV-1 mutants (eg:HSV-Luc) have been created by inactivating the ribonucleotide reductase (RR) gene responsible for virus replication. The abundance of nucleotide pools in mitotically active cancer cells substitute for the absence of viral RR enabling its replication within cancer cells rather than in normal cells. Viral oncolysis treatment requires close monitoring of the virus. In an effort to develop methods to image viral oncolysis of liver tumors we used bioluminescence to provide a benchmark for subsequent PET reporter correlation. We present the detection of HSV-Luc expression in relation to virus dose, replication, and route of delivery. Methods: Focal liver metastases were created in balb/c mice by inserting a piece of tumor (1mm3) subcapsularly. Once tumors reached 3-4mm3 varying doses of HSV-Luc (1×103, 3×104, 1×105, 1×106, or 1×107pfu) was injected directly into the tumor or into the spleen. The conditionally replicating HSV-Luc has the LacZ and firefly luciferase genes enabling its detection in vivo and in vitro. Virus expression in vivo was determined by bioluminescence imaging over a week with luciferin, beginning at 6 hrs and expressed as net signal intensity (NSI) corrected for background. Data are presented as the mean±SD. Results: The intensity of bioluminescence is reflective of the degree of virus expression. A high virus dose (1×107pfu) injected directly into the tumor generates an intense signal (NSI 7,000) detected as early as 6hrs. The signal peaks at 24hrs (NSI 82,000) and declines by day6. Tumor destruction is evident by the reduction in tumor volume from 39.8+13.9mm3 to 27.7+22.9mm3 by day7. A low virus dose initially expresses a less intense signal that intensifies over time as the virus replicates in the tumor. A virus dose of 1×106pfu is detected initially at 24hrs with a NSI of 5,000 which peaks by 96hrs (NSI 228,000). This signal gradually declines by day6. Tumor volume decreases from 21.3+8.0mm3 to 16.3+5.8mm3 by day7. The lowest virus dose detectable after intra-tumor injection is 3×104pfu. Virus expression post entry into the portal circulation has a timely distribution. Both virus doses above when injected into the spleen circulates through the liver (peak signal at 18hrs) to be cleared by 24hrs. The signal from then onwards is from the tumor where the virus replicates. Conclusion: The intensity of bioluminescence is reflective of the degree of virus expression related to dose, time, and route of delivery. This data is crucial to locate and quantify virus infection in tumor cells and as such it can serve as a benchmark for PET reporter correlation in our ongoing clinical trials of HSV-1 oncolysis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5319. doi:10.1158/1538-7445.AM2011-5319