AIM:To examine the role of nucleostemin in the growth regulation of gastric cancer, liver cancer and other cancers.

Although solid tumors continuously shed cells, only a very small fraction of the neoplastic cells that enter the blood stream are capable of establishing metastases. In order to be successful these cells must attach, extravasate, proliferate, and induce angiogenesis. Preclinical studies have shown that small-molecule ATP-competitive Src kinase inhibitors can effectively impair metastasis associated tumor cell functions in vitro. However, the impact of these agents on the metastatic cascade in vivo is less well understood. The present studies examined the ability of saracatinib, a dual-specific, orally available inhibitor of Src and Abl protein tyrosine kinases, to interfere with the establishment of lung metastases in mice by tumor cells introduced into the blood stream. The results demonstrated that Src inhibition most effectively interfered with the establishment of secondary tumor deposits when treatments were administered while tumor cells were in the initial phases of dissemination.

Introduction: The metastatic spread of cancer cells remains the principal cause of treatment failure. Src is a non-receptor tyrosine kinase that is frequently over-expressed in malignances, and increased Src activity may be associated with poor patient prognosis. Src tyrosine kinase plays an important role in tumor cell survival, proliferation, migration and invasion. Since these cellular functions are key components of the metastatic cascade, Src may be a novel target for cancer therapy. The present studies were undertaken to investigate whether molecular intervention in Src associated signaling could reduce the metastatic spread of tumor cells. Specifically, the efficacy of saracatinib a potent, selective and orally available Src inhibitor, was evaluated in the highly metastatic rodent KHT sarcoma cell line. Methods: The effect of saracatinib treatment on tumor cell functions, including viability, migration, invasion, and attachment, were examined by clonogenicity, migration/invasion and attachment assays, respectively. To assess saracatinib therapeutic effects on metastatic growth, tumor cells were either pretreated with saracatinib prior to intravenous injection or injected intravenously and then the mice were treated with saracatinib. In the latter case three protocols commencing immediately after tumor cell inoculation were investigated: a single 10 mg/kg dose of saracatinib; four 10 mg/kg doses of saracatinib given at 24 hr intervals; daily 10 mg/kg doses of saracatinib administered over a period of 3 weeks; in all protocols saracatinib was administered p.o. Twenty-one days after cell injection the number of lung metastases were determined. Results: In vitro saracatinib doses ranging from 0.5–5.0 µM significantly reduced Src phosphorylation and functionally inhibited KHT cell proliferation, migration, invasion and adhesion. Pretreating KHT cells with saracatinib (1 or 5 µM, 24 hr) also reduced (2–4-fold) the ability of these cells to form lung metastases when injected into C3H mice via the tail vein. In vivo, daily doses of saracatinib (10 mg/kg) reduced the number of metastases formed at the end of a 3 week period by a factor of ∼2. A similar reduction in lung colonies was achieved with four 10 mg/kg doses of saracatinib given daily commencing immediately after tumor cell injection, or even a single 10 mg/kg treatment administered immediately after tumor cell inoculation. Conclusions: The present studies explored the possibility of utilizing a molecular targeting strategy directed against key aspects of the metastatic cascade. The present findings demonstrate that saracatinib treatment significantly inhibits the ability of the cancer cells to escape the blood stream and invade at a secondary site supporting the notion that Src signal inhibition may hold considerable promise in impairing metastases formation. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B107.