Both primary and acquired resistance to the growth-inhibitory effects of anti-estrogens (e.g., tamoxifen) limits the clinical usefulness of these drugs in the treatment of breast cancer. The new, steroidal anti-estrogen ICI 182,780 was tested for its ability to inhibit the proliferation of a tamoxifen-resistant variant of the parental MCF-7 human breast-cancer cell line. Two cell lines cloned from the MCF-7 line were used for these experiments: a tamoxifen-sensitive line, MCF 5-21, and a tamoxifen-resistant line, MCF 5-23. Compared with tamoxifen, ICI 182,780 appeared to be 150 and 1540 times more effective in inhibiting cell growth in the 5-21 and 5-23 sub-lines respectively. ICI 182,780 completely circumvented tamoxifen resistance at a concentration of (5 to 10) x 10(-9) M in this model. Based on IC50 concentrations, the 5-23 line was 22-fold more resistant to tamoxifen than the 5-21 line, but only 2-fold more resistant to ICI 182,780, reducing relative resistance by 10-fold in the resistant line. There were no differences in ER parameters between the 2 lines. ER numbers/cell were: 40500 and 34800 and the KD 0.48 and 0.15 x 10(-9) M in the 5-21 and 5-23 cells respectively. In the 5-23 cells, the concentrations of ICI 182,780 and tamoxifen resulting in a 50% inhibition of 3H-estradiol binding were 2.3 x 10(-8) M and 1 x 10(-6) M, respectively (cf. estradiol 0.89 x 10(-9) M). Thus, one potential mechanism for the increased effectiveness of ICI 182,780 may relate to the increased affinity of this drug for the estrogen receptor as compared with tamoxifen.

Hormonal activation of cAMP-dependent protein kinase has been studied in cultured cells derived from a rat osteogenic sarcoma and in osteoblast-rich cells grown from newborn rat calvaria. Both cell strains contain adenylate cyclase activities which respond to parathyroid hormone (PTH) and a variety of prostanoids. PTH, prostaglandin E2 (PGE2), and prostacyclin (PGI2) were all capable of activating cAMP-dependent protein kinase(s) in suspensions of the two cell types. Activation was very rapid in all cases, being detectable at 10 sec and maximal between 30-60 sec. Using saturating concentrations of hormones, the protein kinase activity ratio remained elevated (between 0.6-0.9) for up to 35 min after the start of PGE2 stimulation, but declined toward basal activity ratio 5-10 min after stimulation with PTH or PGI2. Each of the hormones caused a dose-dependent increase in activation of cAMP-dependent protein kinase in both cell types. Half-maximal activation of the enzyme occurred at 2 X 10(-9) M bovine PTH for calvarial cells, at 10(-8) M bPTH for osteogenic sarcoma cells, and at 2-4 X 10(-8) M PGE2 and 1-3 X 10(-7) M PGI2 for both cell types. Maximal activation of protein kinase occurred before maximal cAMP accumulated, implying that only a fraction of cAMP is biologically significant. These two cell strains provide a useful means of analyzing postreceptor events in the hormonal regulation of bone cells.

The etiology of non-insulin-dependent diabetes mellitus (NIDDM) is not known. Hyperglycemia is due to increased hepatic glucose production (HGP), decreased glucose uptake, and impaired insulin secretion. It is unknown if these defects are coinherited or if one precedes and causes the others. The aim of this study was to determine the earliest defects in the evolution of the syndrome in the New Zealand obese (NZO) mouse, a polygenic model of NIDDM. NZO and control NZC mice were studied at 4-5 and 20 wk of age. Glucose turnover and glucose uptake in individual tissues were measured basally and during a hyperinsulinemic clamp. First-phase insulin secretion was measured after an intravenous glucose load. HGP was higher in the NZO mice both basally and during the clamp at both ages. At 4-5 wk of age, there was evidence of insulin insensitivity in brown adipose tissue, soleus, diaphragm, red quadriceps, and red gastrocnemius but not in heart, white quadriceps, and white gastrocnemius. In 20-wk-old mice, insulin responsiveness was decreased in white and brown adipose tissue and soleus muscle but not in heart, diaphragm, red and white quadriceps, and red and white gastrocnemius. First-phase insulin secretion (percentage rise above basal) 3 min after the glucose bolus was impaired in NZO mice at both ages. We conclude that hepatic glucose overproduction, brown adipose tissue and skeletal muscle insulin resistance, and impaired first-phase insulin secretion are all early abnormalities in the NZO mouse.

Further studies of insulin secretion from isolated pancreatic islets of the NZO strain of obese hyperglycemic mouse have shown markedly impaired insulin secretory responses to D-glucose in islets from fasted or fed mice. NZO islets at a low glucose concentration (3.3 mM) showed a significant insulin secretory response to 0.5 mM 3-isobutyl-1-methylxanthine (IBMX), a phosphodiesterase inhibitor, but in the presence of this agent showed no significant additional response to increased glucose concentration. This contrasted with the situation in islets from an arbitrarily chosen control strain of mouse (C57Bl) which showed a small or insignificant response to 0.5 mM IBMX at a low glucose concentration, but a greatly enhanced response to glucose in the presence of IBMX. In contrast to the relative refractoriness of the NZO islets to glucose, they showed a large response to D,L-glyceraldehyde, at least equal to that found in the control islets. Glucose utilization was studied by measuring the conversion of D-[5-3H]glucose to [3H]H2O. In islets from both fasted and fed NZO mice, glucose utilization, when calculated on the basis of islet DNA content, was markedly reduced at high glucose concentrations compared to that in islets from the control strain. It is concluded that the relative unresponsiveness of NZO islets to glucose is associated with, and perhaps due to, a decreased rate of glucose utilization. The preserved responsiveness to glyceraldehyde suggests that the reduced glucose utilization may be due to a partial metabolic block before the triose phosphate step in the islet glycolytic pathway.