Intravenous Administration of Adenoviruses Targeting Transforming Growth Factor Beta Signaling Inhibits Established Bone Metastases in 4T1 Mouse Mammary Tumor Model in an Immunocompetent Syngeneic Host

We have examined the effect of adenoviruses expressing soluble transforming growth factor receptorII-Fc (sTGFβRIIFc) in 4T1 mouse mammary tumor bone metastasis model in syngeneic BALB/c mice. Infection of 4T1 cells with a non-replicating adenovirus Ad(E1-).sTβRFc, or with two oncolytic adenoviruses Ad.sTβRFc and TAd.sTβRFc expressing sTGFβRIIFc produced sTGFβRIIFc protein. Oncolytic viruses were capable of replicating and induced cytotoxicity in 4T1 cells. 4T1 cells were resistant to the cytotoxic effects of TGFBβ-1 (up to 10 ng/ml). However, TGFβ-1 induced the phosphorylations of SMAD2 and SMAD3, which were inhibited by co-incubation with sTGFβRIIFc protein. TGFβ-1 also induced IL-11, a well know osteolytic factor. Intracardiac injection of 4T1-luc2 cells produced bone metastasis by day 4. Intravenous injection of Ad.sTβRFc (on days 5 and 7) followed by bioluminescence imaging of mice on days 7, 11 and 14 in tumor bearing mice indicated the inhibition of bone metastasis progression (p<0.05). X-ray radiography of mice on day 14 showed a significant reduction of the lesion size by Ad.sTβRFc (p<0.01) and TAd.sTβRFc (p<0.05). However, Ad(E1-).sTβRFc expressing sTGFβRIIFc was not effective in inhibiting bone metastases. Thus, systemic administration of Ad.sTβRFc and TAd.sTβRFc can inhibit bone metastasis in 4T1 mouse mammary tumor model, and can be developed as potential anti-tumor agents for breast cancer.