Inhibition of tumor growth in liver epithelial cells transfected with a transforming growth factor alpha antisense gene.

Transforming growth factor alpha (TGF alpha) overexpression is associated with human hepatocellular carcinoma and with transformation of rat liver epithelial cell lines. In transgenic mice TGF alpha overexpression in the liver induces hepatocyte proliferation and leads to the development of tumors. Using a transformed rat liver epithelial cell line which can give rise to hepatocellular carcinomas, we used antisense genes to examine the importance of TGF alpha in tumor growth. Two different rat TGF alpha complementary DNA fragments were cloned in the antisense orientation into a thymidine kinase minigene downstream of a retroviral long terminal repeat. Cell lines that stably expressed the more effective construct, which contained a fragment that spanned the TGF alpha start codon, exhibited a 4-fold reduction in TGF alpha secretion relative to cell lines that expressed the thymidine kinase minigene alone. Following introduction into nude mice of 2 x 10(5) cells the control cell lines grew rapidly to produce large, highly cellular tumors by 5-6 weeks following injection, whereas with the antisense cell lines tumor growth was delayed so that tumors needed an additional 5 weeks to reach the same size. A high level of growth inhibition was also evident following injection of 2 x 10(6) cells, although the delay in tumor growth from antisense lines was shortened to about 3 weeks. Furthermore, tumors produced by 3 of the 4 antisense cell lines tested were fibrotic and hypocellular relative to those produced by the control cell lines. Growth of tumors from the antisense cell lines was associated with a decline in antisense RNA expression. In contrast, tumors generated from the control cell lines maintained high levels of expression of the control thymidine kinase minigene. These data demonstrate that tumor growth from highly tumorigenic liver cells can be inhibited by disrupting their ability to produce TGF alpha.