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 survive in a growth-factor-depleted environment, whereas normal melanocytes die rapidly under such conditions. The increased survival of melanoma cells is due to their production of growth factors for autocrine growth stimulation. Here, we describe a strategy to inhibit pleiotrophin (PTN), a heparin-binding autocrine growth factor for melanoma cells. To target PTN production in melanoma cells, a replication-deficient, recombinant adenovirus was generated to express antisense (AS) PTN at high efficiency. The AS vector induced transcripts that completely inhibited PTN protein production. Melanoma growth was strongly inhibited if the tumor cells were maintained in a three-dimensional environment in soft agar, whereas cell growth was not affected if the tumor cells were grown as a monolayer, suggesting the importance of cell-matrix interactions for the biological activity of this growth factor. The down-regulation of PTN in transduced melanoma cells coincided with the down-regulation of the cell-cycle regulator cyclin E and the up-regulation of the cell-cycle inhibitor p21WAF1/Cip1. Tumor growth in vivo was also delayed by the AS-PTN vector, confirming that PTN is essential for the three-dimensional growth of tumor cells. Our studies demonstrate the importance of assessing potential melanoma antagonists not only on cells grown as monolayers but also in three-dimensional matrices.