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Effects of Streptozotocin-induced Diabetes and Insulin on Phospholipid Content of R3230AC Mammary Tumor Cells¹

Department of Biochemistry [U. N., J. A. R., R. H.] and University of Rochester Cancer Center [U.N., R. H.], University of Rochester School of Medicine and Dentistry, Rochester, New York 14642

The influence of diabetes and insulin treatment on the phospholipid content of R3230AC mammary tumors, a hormonally responsive neoplasm, was studied. Diabetes was induced by administration of streptozotocin 3 days prior to tumor implantation. Protamine zinc insulin, 3 IU/rat twice daily, was administered to tumor-bearing rats for 3 days. Enzymatically dissociated tumor cells from diabetic animals showed significant increases in phosphatidyl choline, lysophosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositol, and phosphatidic acid, compared to controls. Diabetic animals treated with insulin displayed reductions in phosphatidyl choline, lysophosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositol, and phosphatidic acid to levels approximating those found in intact (control) animals. However, neither diabetes nor insulin treatment altered sphingomyelin levels. Mammary tumor cells from diabetic animals showed a 21% increase in DNA content compared to that in intact controls and treatment of diabetic animals with insulin lowered DNA level significantly. The responsiveness of both phospholipids and DNA content to changes in the insulin milieu of the host suggest that phospholipids may play an important role in mediating the effects of insulin on growth of R3230AC tumors.

¹ Supported by USPHS Grant CA 16660 from the NIH.

² Supported by USPHS Grant 5T32 CA 0936305 from the NIH.

³ To whom requests for reprints should be addressed, at Department of Biochemistry, Box 607, University of Rochester Medical Center, 601 Elmwood Ave., Rochester, NY 14642.

Received 3/22/85. Revised 7/ 3/85. Accepted 7/12/85.