Interferon-induced nuclear DNA alterations in malignant carcinoid tumors in vivo

Tumor cell specimens were obtained by ultrasonically guided percutaneous needle liver biopsy from 23 patients with metastatic small intestinal carcinoid tumors. The patients were admitted to the hospital for antitumor therapy (streptozocin, 5-fluorouracil, and leukocyte interferon). The tumor cell samples were used for DNA cytofluorometry. All tumors (12 cases) from untreated patients exhibited diploid DNA stem lines with low proliferative activity. The mean number of tetraploid cells was 8%. Altered nuclear DNA records were obtained in tumors of 8 patients, all of which were treated with leukocyte interferon at 3-6 X 10(6) IU/day for 4-32 months. The DNA records in these tumors varied, but they were mainly in the range between diploid and tetraploid values. In some cases several nuclear DNA peaks were observed within the limits for the cell cycle. It is assumed that the interferon treatment was responsible for the development of altered DNA cell lines because: 1) all untreated tumors yielded regular diploid DNA histograms, 2) interferon was the only drug administered to all patients with tumors displaying altered DNA records, and 3) modal diploid DNA values were observed prior to the interferon treatment in some patients. It is suggested that interferon in vivo blocked carcinoid tumor cell populations in different phases of the cell cycle. This result might explain the nuclear DNA profiles registered in the treated patients as well as the therapeutic effect obtained by interferon.