Attenuation of Ras signaling restores androgen sensitivity to hormone-refractory C4-2 prostate cancer cells.

Progression of prostate cancer to androgen-refractory disease is correlated with increased expression of growth factors and receptors capable of establishing autocrine and/or paracrine growth-stimulatory loops. Many of these growth factor receptors engage Ras as part of their normal signaling activities, raising the possibility that activation of endogenous c-Ras could be a common mechanism for prostate cancer progression. Here we demonstrate that inducible expression of a dominant negative form of Ras restores androgen sensitivity to a hormone-refractory prostate cancer cell line. We show that expression of RasN17 in the hormone-refractory C4-2 cell line enhances in vitro sensitivity to the growth-inhibitory action of the antiandrogen Casodex and inhibits anchorage-independent cell growth. Moreover, although induction of RasN17 by itself has no observable effect on the growth of C4-2 xenografts in intact male mice, it restores androgen dependence to the C4-2 xenografts so that they dramatically regress after surgical androgen ablation.