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Actions of cis-Diamminedichloroplatinum on Cell Surface Nucleic Acids in Cancer Cells as Determined by Cell Electrophoresis Techniques¹

Department of Biophysics, Michigan State University, East Lansing, Michigan 48824

Whole-cell electrophoresis determinations, using a null technique to measure a cloud of cells, were made on a variety of tumor cell suspensions in order to examine the charged groups on the cell surfaces. We report here evidence, derived from these measurements, which indicates the presence of nucleic acids on the surfaces of the tumor cells. Cells of the ascitic and solid forms of the Sarcoma 180 mouse tumor, grown in ICR mice, showed a decrease of 10 to 20% in electrophoretic mobility when incubated with nucleases. One variant, S-180, exhibited sensitivity to RNase only; another variant was sensitive to both RNase and DNase, while different tumor lines were shown to be sensitive to DNase only. Treatment of tumorbearing animals with a therapeutic dose of cisplatin resulted in a loss of tumor cell mobility identical to that produced by the nuclease incubations of the control cells. Incubation of the cisplatin-treated tumor cells with nucleases produced no change in mobility. The isoelectric points of these cells were determined and are consistent with the loss of a group with a low pK value, such as the phosphates of RNA and DNA, in both cisplatin-treated cells and nuclease-incubated cells. Using the S-180 tumor sensitive to both RNase and DNase, the rates of the two enzymes were additive, but the mobility decreased to the same level regardless of whether the enzymes were used alone or together. This suggests that both enzymes act on the same site. RNase and DNase immobilized on agarose beads were capable of lowering the mobility of the cells upon incubation, confirming the surface location of these nucleic acid residues. S-180 tumor cells were also placed in a tissue culture medium at 37° for up to 22 hr and were treated in vitro with cisplatin and other metabolic inhibitors. Nucleic acid or protein synthesis inhibitors produced a loss of the cell surface nucleic acids. In another in vitro experiment, the nucleic acids were first removed by nucleases, and, when the cells were incubated at 37°, the nucleic acids reappeared. Disappearance with the inhibitors or reappearance after digestion exhibited a half-time of about 2 hr. Surface nucleic acids were detected by this electrophoresis technique on all of several types of tumor cells but not on any normal cells examined.

¹ Research supported by Grant CA-11349 from the National Cancer Institute and by fellowships from Engelhard Industries; The International Nickel Co., Inc.; and Matthey Bishop, Inc.

² Present address: Department of Biological Chemistry, St. Jude Children's Research Hospital, 332 N. Lauderdale, P. O. Box 318, Memphis, Tenn. 38101.

³ To whom requests for reprints should be addressed.

Received 8/24/81. Accepted 6/ 7/82.

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