Insulin-like growth factor (IGF-I) is associated with autocrine and paracrine stimulation for cell growth and development of brain tumor cells. The function of IGF-I in the brain metastatic variant of human lung cancer cells is investigated. The cells used here were derived in vivo with intracarotid injection of human non-small cell lung carcinoma NCI-H226. The tumor was developed as a cultured cell line, H226Br. Unlike the parental cells, H226Br was tumorigenic in nu/nu nude mice. Reverse transcriptase-polymerase chain reaction showed that IGF-I transcript of H226Br is increased compared to that of parental cells. The amount of IGF-I secreted in cultured medium of H226Br is higher than that of cultured parental cells. The IGF-I receptor-specific antibody, αIR3, inhibits H226Br growth in serum-free culture. The results established that IGF-I is an autocrine growth regulator for human non-small cell lung cancer cells that progressed to brain.
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