Calcif Tissue Int (1985) 37:519-525 Calcified Tissue International 9 1985 by Springer-Verlag Inhibitory Effects of Parathyroid Hormone on Growth of Osteogenic Sarcoma Cells Nicola C. Partridge,* Anne Louise Opie, Rebecca T. Opie, and T. John Martin University of Melbourne, Department of Medicine, Repatriation General Hospital, Heidelberg, Victoria, Australia Summary. The effects of the bone resorbing hor- mone, parathyroid hormone (PTH), on the growth of malignant osteoblastic cells have been examined. The malignant osteoblastic cells were a clonal line (UMR 106) derived from a transplantable rat osteo- genic sarcoma. The predominant effect of PTH at doses above 10 -1~ M was an inhibition of replica- tion and DNA synthesis. Replication was decreased by PTH in both the presence or absence of serum and at various cell seeding densities. Both bovine PTH (1-84) and the synthetic hormone, human PTH (1-34), inhibited replication, but with bovine hormone being an order of magnitude more potent. The effects could be observed in as short a time as 6 hours with DNA synthesis and 24 hours with rep- lication. Key words: Osteoblast -- Parathyroid hormone -- Replication -- DNA synthesis. In vivo studies of the effects of parathyroid hor- mone (PTH) on bone formation have yielded varied results. In one investigation, the hormone was shown to stimulate bone apposition independent of resorption [1], while in another, bone turnover was increased but not bone formation alone [2]. The latter authors noted that the effects of PTH could have been mediated through the increased circu- lating levels of 1,25(OH) 2 vitamin D 3, caused by PTH administration. Net effects of PTH on bone formation are likely to be influenced by changes in the number of active osteoblasts. Although there is little information on the regulation of osteoblast * Present address: Pediatric Research Institute, Cardinal Glennon Children's Hospital and St. Louis University, 3662 Park Avenue, St. Louis, Missouri 63110. Send reprint requests to Prof. T. J. Martin, University of Mel- bourne, Dept. of Medicine, Repatriation General Hospital, Hei- delberg, Victoria, Australia, 3081. proliferation by PTH, some studies have indicated an inhibitory effect of the hormone. For example, in one study, in vivo administration of the hormone was shown to depress uptake of RNA precursors and [3H]-thymidine into these cells [3]. Similarly, a later detailed morphologic study reported that in vitro, PTH inhibited membrane ruffling and prolif- eration of osteoblasts [4]. We have induced and characterized a transplant- able rat osteogenic sarcoma that, together with the clonal lines derived from it, is a hormonally re- sponsive tumor showing activation of adenylate cy- clase and cAMP-dependent protein kinase by PTH [5-11]. The cells, which are phenotypically osteo- blastic, have much in common with osteoblasts pre- pared from newborn rat calvaria [8, 10]. The present work examines the effects of PTH on the growth of the most osteoblast-like clone (UMR 106) derived from the sarcoma. Materials and Methods Materials Bovine parathyroid hormone (bPTH), a generous gift from Dr. E Barling, Department of Biochemistry, University of Auckland, New Zealand, had a potency of 3000 U/mg. Synthetic human parathyroid hormone hPTH (1-34), 5000 U/mg, was obtained from Beckman Pty. Ltd., Palo Alto, CA, USA. [6-3H]-thymidine or [methyl-3H]-thymidinewere purchased from the Radiochem- ical Centre, Amersham, Bucks, UK. Fetal calf serum (FCS) was purchased from Grand Island Biological Co. Laboratories, Mel- bourne, Victoria, Aust. All other tissue culture reagents and plastic ware were obtained from Flow Laboratories Australia Pty. Ltd., Mt. Waverley, Victoria, Aust. Cells The establishment of the clonal osteogenic sarcoma cell line, UMR 106, has been reported previously [7, 10]. The experiments