Halofuginone inhibits tumor growth in the polyoma middle T antigen mouse via a thrombospondin-1 independent mechanism

• Published in: Cancer biology & therapy 2006-02, Vol.5 (2), p.218-224
• Main Authors: Yee, Karen O., Connolly, Caitlin M., Pines, Mark, Lawler, Jack
• Format: Article
• Language: English
• Subjects: Animals; Antigens, Viral, Tumor - genetics; Antineoplastic Agents - therapeutic use; Binding; Biology; Bioscience; Breast Neoplasms - blood supply; Breast Neoplasms - drug therapy; Breast Neoplasms - genetics; Calcium; Cancer; Cell; Collagen Type I - analysis; Cycle; Landes; Mice; Mice, Transgenic; Neovascularization, Pathologic - drug therapy; Neovascularization, Pathologic - genetics; Organogenesis; Piperidines; Polyomavirus - genetics; Polyomavirus - immunology; Proteins; Quinazolines - therapeutic use; Quinazolinones; Smad2 Protein - antagonists & inhibitors; Smad3 Protein - antagonists & inhibitors; Thrombospondin 1 - genetics; Thrombospondin 1 - metabolism; Transforming Growth Factor beta - metabolism; Tumor Burden - drug effects
• ISSN: 1538-4047; 1555-8576
• DOI: 10.4161/cbt.5.2.2419

Halofuginone inhibits fibrosis by decreasing type I collagen synthesis and tumor growth through an anti-angiogenic mechanism. In vitro data suggested that halofuginone inhibited angiogenesis through upregulating thrombospondin-1(TSP-1) expression and by inhibiting cell proliferation. To determine whether thrombospondin-1 (TSP-1) is necessary for inhibition of tumor growth and angiogenesis by halofuginone, we tested the effect of halofuginone on mammary tumor growth in polyoma middle T antigen, TSP-1 null (TSP-1-/-PyT) transgenic mice. After 30 days of treatment, we found a significant decrease in tumor weight in these mice and the extent of tumor growth inhibition was comparable to that found in TSP-1 expressing PyT mice (TSP-1 +/+PyT). However, no significant difference in tumor weight was observed after 60 days of halofuginone treatment between control and treated mice in both genotypes. Interestingly, type I collagen level was lower in the halofuginone treated TSP-1+/+PyT tumors at 30 days, but this was not observed in the TSP-1-/-PyT mice. Level of type I collagen did not correlate with blood vessel number as a decrease in the number of vessels was observed in the halofuginone treated tumors from both the TSP-1+/+PyT and TSP-1-/-PyT mice as compared to control tumors. Because halofuginone has been shown to inhibit type I collagen synthesis by inhibiting the TGF-? signaling pathway, we measured Smad 2/3 phosphorylation levels and found that halofuginone inhibited Smad 2/3 phosphorylation in cells derived from TSP-1+/+PyT tumors. We also found that it inhibited Smad 2/3 phosphorylation in cells treated with the TGF-? activating sequence of TSP-1, TSR2+RFK. Our data demonstrate that halofuginone inhibits mammary tumor growth in a transgenic mouse model via a TSP-1 independent pathway, by decreasing tumor angiogenesis and by inhibiting TGF-? signaling.