The Tumor-selective Somatostatin Analog, TT2-32 Induces a Biphasic Activation of Phosphotyrosine Phosphatase Activity in Human Colon Tumor Cell Line, SW620

Somatostatin has been demonstrated to activate phosphotyrosine phosphatases (PTPases) in pancreatic cells. In this work we studied the effect of a tumor-selective somatostatin structural derivative, TT2-32, on the PTPase activity in the SW620 human colon tumor cell line. TT2-32 caused a strong inhibition of cell proliferation. In response to TT2-32 we found a rapid and sustained increase (5-30 min) in PTPase activity showing two maxima at 0.1 and 30 microM concentrations, respectively. During short-term incubation tyrosine kinase activity was much less affected by TT2-32. TT2-32-induced activation of PTPases may be an important early step in the signaling cascade in the inhibition of cell proliferation in colon carcinomas.