It has been reported that interferon (IFN) can inhibit cell division on both normal and malignant cells. However, the effect of IFN on the cells at different phases of the cell cycle is still uncertain. In this report, we have studied the cytostatic properties of interferon in each phase of cell cycle by treating synchronous cell population with IFN alone and/or 60Co x-irradiation. Human hypernephroma cells ACHN (ATCC no. CRL 1611) originally initiated by Dr. Chang and Dr. Hogan were used in the experiments reported here. The cells were grown in monolayer cultures in MEM supplemented with 10% fetal calf serum. The biological properties of exponential growing cells showed an abnormal karyotype, large vacuoles in the cytoplasm, and a doubling time of 24 h. Cells were synchronized into G1, S, and G2 + M phases by centrifugal elutriation. Autoradiography and flow cytometry data indicated that ≥ 95% G1 cells, ≥ 80% S cells, and ≥ 70% G2 + M cells were obtained by this method. A single dose of 103 U human interferon alpha (HuIFN-α)(Hoffman-La Roche, recombinant leukocyte D interferon (IFN-αD), RO 22-9859) was given to the synchronous cell populations. The cell cycle delay, growth inhibition and cell viability were measured with the Coulter Counter and Channelyzer system, flow cytometry, and colony-forming assay. Preliminary studies showed that IFN inhibited ACHN cell growth to the same extent at each phase of the cell cycle. However, there was no reduction in the clonogenecity of synchronous cells after IFN treatment. The cell age response after single doses of 600 rad 137CS r-irradiation showed that S phase cells were resistant while both G1 and G2 + M cells were sensitive to radiation. The results of combining treatment of IFN and irradiation showed additional cell-killing effect as compared with irradiation alone.
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