An antisense strategy for inhibition of human melanoma growth targets the growth factor pleiotrophin

A major biological characteristic of metastatic melanomas is their ability to sur,ive in a growth-factor-depleted environment, whereas normal melanocy tes die rapidly under such conditions. The increased survival of melanoma c ells is due to their production of growth factors for autocrine growth stim ulation, Here, we describe a strategy to inhibit pleiotrophin (PTN), a hepa rin-binding autocrine growth factor for melanoma cells, To target PTN produ ction in melanoma cells, a replication-deficient? recombinant adenovirus wa s generated to er;press antisense (AS) PTN at high efficiency. The AS vecto r induced transcripts that completely inhibited PTN protein production. Mel anoma growth was strongly inhibited if the tumor cells were maintained in a three-dimensional environment in soft agar, whereas cell growth was not af fected if the tumor cells were grown as a monolayer, suggesting the importa nce of cell-matrix interactions for the biological activity of this growth factor. The down-regulation of PTN in transduced melanoma cells coincided w ith the down-regulation of the cell-cycle regulator cyclin E and the up-reg ulation of the cell-cycle inhibitor p21(WAF1/Cip1). Tumor growth in vivo wa s also delayed by the AS-PTN vector, confirming that PTN is essential for t he three-dimensional growth of tumor cells. Our studies demonstrate the imp ortance of assessing potential melanoma antagonists not only on cells grown as monolayers but also in three-dimensional matrices.