Monitoring of Biodistribution and Persistence of Conditionally Replicative Adenovirus in a Murine Model of Ovarian Cancer Using Capsid-Incorporated mCherry and Expression of Human Somatostatin Receptor Subtype 2 Gene

Abstract

A significant limiting factor to the human clinical application of conditionally replicative adenovirus (CRAd)-based virotherapy is the inability to noninvasively monitor these agents and their potential persistence. To address this issue, we proposed a novel imaging approach that combines transient expression of the human somatostatin receptor (SSTR) subtype 2 reporter gene with genetic labeling of the viral capsid with mCherry fluorescent protein. To test this dual modality system, we constructed the Ad5/3Δ24pIXcherry/SSTR CRAd and validated its capacity to generate fluorescent and nuclear signals in vitro and following intratumoral injection. Analysis of 64Cu-CB-TE2A-Y3-TATE biodistribution in mice revealed reduced uptake in tumors injected with the imaging CRAd relative to the replication-incompetent, Ad-expressing SSTR2 but significantly greater uptake compared to the negative CRAd control. Optical imaging demonstrated relative correlation of fluorescent signal with virus replication as determined by viral genome quantification in tumors. Positron emission tomography/computed tomography studies demonstrated that we can visualize radioactive uptake in tumors injected with imaging CRAd and the trend for greater uptake by standardized uptake value analysis compared to control CRAd. In the aggregate, the plasticity of our dual imaging approach should provide the technical basis for monitoring CRAd biodistribution and persistence in preclinical studies while offering potential utility for a range of clinical applications.

Perspective on Adenoviruses: Epidemiology, Pathogenicity, and Gene Therapy

“…HAdV vectors are used for virotherapy and gene therapy for cancer [101,106,107,108]. The application of HAdVs for cancer therapy dates back to the 1950s when wild-type Ad was used to treat cervical cancer.…”

Adenoviral-mediated imaging of gene transfer using a somatostatin receptor-cytosine deaminase fusion protein

“…In this regard, we have previously utilized the human somatostatin receptor subtype 2 (SSTR2) for imaging of gene transfer using gamma camera imaging and PET imaging. 15 – 19 Somatostatin receptors are members of the G protein-coupled receptor (GPCR) family that have seven transmembrane domains consisting of three extracellular loops, termed E1, E2, and E3. 18 SSTR2 is expressed on brain, spleen, and kidney tissues and overexpressed in a variety of tumor types, leading to the development of tumor imaging agents.…”