Inhibition of tumor cell proliferation in vitro and in vivo by exogenous p110RB, the retinoblastoma tumor suppressor protein.

Reconstitution of retinoblastoma gene (RB) deficient tumor cells with RB generally leads to growth suppression in vitro and/or reduced tumorigenicity in nude mice. An alternate approach to gene replacement is the delivery of the RB gene product (p110RB) into cells lacking its expression. In this report we demonstrate that exogenously added p110RB is taken up by and localized to the nucleus of cultured cells and has growth suppression properties similar to endogenous RB. RB-negative (RBneg) tumor cells are preferentially growth inhibited while most RB-positive (RBpos) tumor cells and normal cells are much less sensitive. We have extended these studies to relevant nude mouse xenograft models for human lung cancer. Local or systemic administration of p110RB inhibits tumor growth in treated animals. These results represent the first use of a tumor suppressor protein as a potential cancer therapeutic.