We have investigated three prostatic cancer cell lines, PC-3, DU-145, and LNCa.FGC, and found that all three cell lines can grow in serum-free medium without the addition of exogenous growth factors. All three cell lines produce substantial amounts of insulin-like growth factor 1 (IGF-1) that is secreted in the medium and they all display constitutively autophosphorylated IGF-1 receptors; two of the cell lines overexpress IGF-1 receptor RNA. The growth of all three cell lines is inhibited by an antisense oligodeoxynucleotide to IGF-1 receptor RNA or by peptide analogues of IGF-1 that compete with IGF-1 for binding to its receptor. Our results indicate that these three cell lines grow by an autocrine loop in which the overproduced IGF-1 activates its receptor. Interference with the activation of the receptor leads to cessation of growth.
This work was supported by NIH Grants GM 33694 and CA 56309.