With breast cancer, early detection and proper staging are critical, influencing both the treatment regimen and therapeutic outcome for a patient. Improvements in these areas will play a profound role in reducing mortality due to this disease. We therefore aim to develop a targeted adenoviral based gene therapy vector that can be used in the detection and staging of metastatic breast cancer. We did this through application of the two-step transcriptional amplification system (TSTA). This system was developed in our lab, and has shown the ability to greatly augment the activity of weak promoters, while still maintaining tissue specificity. We incorporated the tumor specific promoter Mucin1 into the TSTA system to successfully target breast tumor models. Studies carried out in vitro have demonstrated that this MUC1 TSTA vector is able to achieve efficiency of up to 250 fold over basal promoter levels, without loss of specificity. Moreover, when incorporated into an adenoviral vector to express firefly luciferase (AdMUC1-TSTA-fl), it exhibits higher reporter gene expression than a AdCMV-fl virus at the same multiplicity of infection (MOI). Biodistribution studies have shown that, depending upon the initial route of administration, this system holds great potential for use in the detection of lymph node metastais, as well as distant metastases. This vector has shown low off target expression following intravenous injection into non-tumor bearing mice. Through use of in vivo xenograft models of breast cancer, we have shown the ability to target and detect both lymph node metastais, as well as liver metastasis using our AdMUC1 TSTA-fl reporter virus in combination with in vivo optical imaging. Based on these results, we believe that this system holds strong promise for clinical application. A critical aspect of this project will be the incorporation of cytotoxic genes for therapeutic studies. At the same time, the ability to express imaging reporter genes for bioluminescent imaging or PET (positron emission tomography) is highly desirable, allowing for efficient, non-invasive monitoring of pharmacokinetics of transgene expression in real time. To address this issue, we developed a MUC-1 driven TSTA amplification scheme able to simultaneously express two separate transgenes, the firefly luciferase and the herpes simplex virus thymidine kinase (HSV-tk sr39tk) gene. This bi-directional reporter TSTA construct has shown strong efficiency, and specificity, and is currently being evaluated for use in therapeutic application of breast tumors in vivo. This approach holds great promise for the treatment and diagnosis of metastatic breast cancer.
Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 6022.
Thirty-first San Antonio Breast Cancer Symposium Dec 10-14, 2008; San Antonio, TX