DECREASED TUMORIGENICITY OF A HUMAN COLON ADENOCARCINOMA CELL-LINE BYAN ANTISENSE EXPRESSION VECTOR SPECIFIC FOR C-SRC

In greater than 80% of colon tumors and established cell lines, the sp ecific activities of the protein tyrosine kinases pp60(c-src) and pp62 (c-yes) are increased with respect to normal colonic epithelial cells. However, no mutations in either gene have been identified in colon tu mors. Therefore, the possible biological consequences of activations o f these protein tyrosine kinases in colon tumors have been unclear. To determine if pp60(c-src) activation affects growth and tumorigenicity of established colon tumor cell lines, an antisense expression vector that specifically reduces pp60(c-src) expression was constructed. The vector was transfected into HT 29 cells, an established colon tumor c ell line in which both pp60(c-src) and pp62(c-yes) are activated. Two stable subclones were isolated in which pp60(c-src) but pp62(c-yes) ex pression and activity were reduced. These established cell lines proli ferated more slowly than parental cells proportionately to reduction i n pp60(c-src) expression. When injected into nude mice, antisense tran sfected cells formed slow-growing tumors; however, the rate of tumor g rowth was reduced far greater than would be predicted from decreased p roliferation rates in tissue culture. In contrast, stable subclones tr ansfected with a comparable ''sense'' expression vector were unaltered in growth rates in tissue culture and in nude mice with respect to pa rental HT 29 cells. These data demonstrate that the activation of pp60 (c-src) alone contributes to the tumorigenicity of HT 29 cells, a cell line widely used as a model for biological properties of colon carcin oma. Furthermore, because pp60(c-src) and pp62(c-yes) appear redundant to the growth regulation of normal colonic epithelial cells, the data suggest that src-specific inhibitors might be of therapeutic value fo r colon cancer.