Paracrine and autocrine functions of PDGF in malignant disease

Abstract: Growth factors and their receptors are frequently activated by mutations in human cancer. Platelet-derived growth factor (PDGF)-B and its tyrosine kinase receptor, the PDGF ?-receptor, have been implicated in autocrine transformation as well as paracrine stimulation of tumor growth. The availability of clinically useful antagonists motivates evaluation of PDGF inhibition in these diseases.In chronic myelomonocytic leukemia with t(5;12), parts of the transcription factor TEL and the PDGF ?-receptor are fused, generating a constitutively signaling protein. Oligomerization and unique phosphorylation pattern of TEL-PDGF?R was demonstrated, as well as the transforming activity of TEL-PDGF?R, which was sensitive to PDGF ?-receptor kinase inhibition.Dermatofibrosarcoma protuberans (DFSP) is characterized by a translocation involving the collagen I?1 and PDGF B-chain genes. The COLIA1-PDGFB fusion protein was processed to mature PDGF-BB and transformed fibroblasts in culture. The PDGF antagonist STI571 inhibited growth of COLIA1-PDGFB transfected cells and primary DFSP cells in vitro and in vivo through induction of apoptosis.Paracrine effects of PDGF-DD, a ligand for the PDGF ?-receptor, were evaluated in a murine model of malignant melanoma. PDGF-DD production accelerated tumor growth and altered the vascular morphology in experimental melanomas.A validated immunohistochemical procedure for PDGF ?-receptor detection was established and applied to normal tissues and more than 280 tumor biopsies. Perivascular and stromal expression was detected in 90% and 50%, respectively, of human tumors.Recently, non-transformed cells in the tumor microenvironment have emerged as targets in cancer therapy. Selective sensitization of tumor fibroblasts to paclitaxel by STI571 was evaluated in vitro and in a xenograft model. Whereas neither drug alone caused growth inhibition, combination of the two significantly reduced tumor growth, suggesting anti-stromal therapy as a possible treatment modality in solid tumors.