| Successful treatment of breast cancer directly correlates with tumor stage and grade at diagnosis. Early diagnosis leads to a five-year relative survival rate of 96.8% as opposed to only a 22.5% five-year survival rate when diagnosed at late stage. Cancer-specific mechanisms need to be extended to enable cancer detection in an individual patient, in particular, the metastatic burden that currently cannot be assessed by conventional imaging. This approach for cancer detection would remove the biases of patient characteristics, permit immediate diagnostic feedback, improve sensitivity for early detection of small metastatic lesions, and be cost effective. Toward this goal, the cancer-specific diagnostic adenovirus (Ad) vector (Ad5/3-Id1-SEAP-Id1-mCherry) was produced that includes a human secreted embryonic alkaline phosphatase (SEAP) reporter for blood-based screening and a fluorescent reporter (mCherry) for localized imaging. Importantly, the cancer-specific promoter Id1 was selected to drive both reporters due to the correlation between aggressive cancer phenotypes and high Id1 expression. Safety and efficacy issues have limited the use of recombinant Ad for routine clinical applications. To overcome this impediment, ultrasound microbubbles (MB) were developed to improve Ad delivery to the tumor vasculature. This was achieved by targeting the Ad packaged MB to receptors overexpressed in the tumor, namely alphaVbeta3 integrin, P-selectin, and VEGFR2. During in vitro assessment, both SEAP and mCherry reporter expression was shown to correlate with cancer cell phenotype. In a tumor-bearing mouse model, SEAP reporter expression was found to be 14-fold over background when as little as 2.5% of tumor cells were infected. Triple-targeted MBs displayed enhanced affinity for tumor vasculature when assessed in vitro and in vivo. Packaging of the targeted MBs with diagnostic Ad was confirmed and the approach was tested in a tumor-bearing mouse model. Groups receiving the targeted Ad packaged MBs displayed a 4-fold increase in SEAP reporter expression over groups receiving equivalent unpackaged Ad dosing. In addition, the mCherry fluorescence reporter was localized in the tumor. Safe delivery of a non-invasive diagnostic reporter system using FDA approved MBs has the potential for immediate application, allowing this diagnostic system to impact populations currently in need of more advanced and sensitive detection modalities.;Keywords: breast cancer, screening, gene therapy, microbubbles, ultrasound contrast agent, adenovirus delivery. |
