Antitumor effect of 22-oxa-calcitriol, a noncalcemic analogue of calcitriol, in athymic mice implanted with human breast carcinoma and its synergism with tamoxifen

The antitumor effect of 22-oxa-calcitriol (OCT), a newly developed noncalcemic analogue of calcitriol, was examined in vivo in athymic mice implanted with human breast carcinoma with or without estrogen receptor (ER). In ER-positive MCF-7 tumor, the growth of which was dependent on exogenous estrogen, administration p.o. of OCT as well as the antiestrogen tamoxifen five times a week for 4 weeks suppressed tumor growth in a dose-related fashion. The antitumor effect of 1.0 microgram/kg body weight (BW) OCT (mean +/- SEM of tumor weight in 6 mice: 28 +/- 4% of vehicle-treated group) was comparable to that of 2.0 mg/kg BW tamoxifen (25 +/- 6% of control group). In addition, a synergistic antitumor effect of submaximal doses of OCT and tamoxifen was observed in MCF-7 tumor in vivo as well as in ER-positive breast carcinoma cell lines (MCF-7 and ZR-75-1) in vitro. Administration of OCT p.o. three times a week for 4 weeks also suppressed the growth of ER-negative MX-1 tumor in a dose-dependent manner without raising serum calcium concentrations. The antitumor effect of 1.0 microgram/kg BW OCT (mean +/- SEM of tumor weight in 10 mice: 44 +/- 6% of vehicle-treated group) was greater than that of 500 micrograms/kg BW Adriamycin (71 +/- 6% of control group). These results indicate that OCT suppresses the growth of ER-negative as well as ER-positive breast carcinoma in vivo without causing hypercalcemia and that the antitumor effect of OCT can be enhanced by tamoxifen in an ER-positive tumor. It is suggested that OCT may provide a new strategy, either alone or in combination with other anticancer drugs, for systemic adjuvant therapy of breast carcinoma regardless of ER status.

Differential effects of 1,25-(OH)2D3 and 22-oxacalcitriol on phosphate and calcium metabolism

1,25-dihydroxyvitamin D3 has been used with success in the treatment of secondary hyperparathyroidism associated with chronic renal failure. However, frequently 1,25-(OH)2D3 induces hypercalcemia, especially in those patients ingesting large doses of calcium carbonate, precluding the administration of therapeutic doses of 1,25-(OH)2D3. In addition, control of serum phosphorus is a persistent problem in patients maintained on chronic hemodialysis and 1,25-(OH)2D3 treatment can aggravate the hyperphosphatemia. Thus, ideally an analog of 1,25-(OH)2D3 that can suppress PTH with minor effects on calcium (Ca) and phosphate (PO4) metabolism would be an ideal tool to control secondary hyperparathyroidism. We have shown that 22-oxa-1,25-(OH)2D3 (OCT), an analog of 1,25-(OH)2D3 with little calcemic activity, can suppress PTH mRNA in normal rats and in cultured bovine parathyroid cells with equipotency to 1,25-(OH)2D3. To further characterize the differential effects of 1,25-(OH)2D3 and OCT on Ca and PO4 metabolism we performed several experiments in intact and parathyroidectomized (PTX) rats. In metabolic studies in four groups of normal rats 1,25-(OH)2D3 treatment (8 ng/day) significantly increased the intestinal Ca absorption from 15.2 +/- 2.68% to 30.5 +/- 2.85% (P < 0.01), while the same dose of OCT had no effect. A dose of 200 ng/day of OCT increased intestinal Ca absorption similarly to the 8 ng/day dose of 1,25-(OH)2D3, from 10.6 +/- 2.49% to 24.8 +/- 2.35% (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of two new vitamin D3 derivatives, 22-oxa-1 alpha-25-dihydroxyvitamin D3 (OCT) and 2 beta-(3-hydroxypropoxy)-1 alpha, 25-dihydroxyvitamin D3 (ED-71), on bone metabolism in organ culture

We have tested two new vitamin D3 derivatives, 22-oxa-1 alpha, 25-dihydroxyvitamin D3 (OCT) and 2 beta-(3-hydroxypropoxy)-1 alpha, 25-dihydroxyvitamin D3 (ED-71), for their effects on bone metabolism compared with 1 alpha, 25-dihydroxyvitamin D3 (1,25(OH)2D3) in two organ-culture systems. In a previous study (Abe et al. 1987), it was reported that OCT had weak activity in stimulating bone resorption in vitro. In the present study, however, OCT stimulated bone resorption in cultured fetal rat long bones and inhibited collagen synthesis in cultured neonatal mouse calvariae in a dose-dependent manner with significant effects at 10(-10) M and maximal responses at 10(-8) M. Its potency and effectiveness were identical to 1,25(OH)2D3. On the other hand, ED-71, which has been found to prevent bone loss in vivo (Okano et al. 1989b), was less active in vitro. The activity of ED-71 at 10(-8) M on bone resorption was similar to 1,25(OH)2D3, but it did not stimulate resorption at 10(-10) M. Its inhibitory effect on collagen synthesis was weaker than for OCT of 1,25(OH)2D3. The activity of all three compounds on bone resorption was not inhibited by indomethacin or cortisol. 1,25(OH)2D3 and OCT significantly inhibited [3H]-thymidine incorporation into mouse calvariae at 10(-9) M, while ED-71 inhibited [3H]-thymidine incorporation only at 10(-8) M. These results indicate that OCT and 1,25(OH)2D3 have similar effects on bone in organ culture. Pharmacokinetic differences may explain the marked difference in response to those two agents in vivo. ED-71 is less potent, particularly in inhibiting bone formation. Such differences may have importance in the development of vitamin D analogs for clinical use.

Metabolism of 22-oxacalcitriol by a vitamin D-inducible pathway in cultured parathyroid cells

Catabolism of 22-oxacalcitriol (OCT) in parathyroid cells was compared to that of the parent hormone, 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Catabolism of both compounds was greatly accelerated by pretreatment of the cells with 1,25-(OH)2D3 or OCT. The rate of degradation of OCT was slightly greater than that of 1,25-(OH)2D3. Excess unlabeled OCT or 1,25-(OH)2D3 inhibited metabolism of both tritiated substrates. Ketoconazole, a cytochrome P450 inhibitor, blocked catabolism of both compounds. The major OCT metabolite appeared to be 1,20-dihydroxy-22,23,24,25,26,27-hexanor-vitamin D3 which was not active in suppressing PTH secretion. We conclude that OCT appears to be metabolized by the same vitamin D-inducible side chain oxidation pathway that catabolizes other vitamin D compounds and that its higher than expected suppression of PTH secretion is not due to slower cellular metabolism.

A new, highly sensitive assay for 1,25-dihydroxyvitamin D not requiring high-performance liquid chromatography: application of monoclonal antibody against vitamin D receptor to radioreceptor assay

A new, highly sensitive radioreceptor assay, which does not require high-performance liquid chromatography, has been developed for the determination of 1,25-dihydroxyvitamin D3 (1,25-(OH2)D3) in serum. The assay involves rapid extraction of serum, Sep Pak silica purification, and addition of 1,25-dihydroxyvitamin D3 receptor, radiolabeled 1,25-dihydroxyvitamin D3, bovine serum albumin, and monoclonal antibody to specifically precipitate the receptor. This method is sensitive to 0.3-0.6 pg/tube, with B50 occurring at 5.8 pg/tube. This sensitivity combined with overall recovery of 1,25-dihydroxyvitamin D3 (81.5 +/- 5.2%, n = 50, mean +/- SD) allows the measurement of serum 1,25-(OH)2D3 in duplicates with only 0.5 ml of serum. Intra- and interassay coefficient of variation were 9.5 and 14.6%, respectively. Dilution analysis, analytical recovery of added 1,25-dihydroxyvitamin D3, and comparison with a standard method using HPLC have been used to validate the assay. Serum 1,25-dihydroxyvitamin D3 level was for normal adults, 36.6 +/- 10.5 pg/ml (n = 14); in primary hyperparathyroidism, 98.9 +/- 19.9 pg/ml (n = 16); in chronic renal failure, 17.8 +/- 5.1 pg/ml (n = 12). This method allows large numbers of samples to be processed at once. Further, the method is rapid and provides an accurate assay using small amounts of serum.

Suppression of PTH and decreased action on bone are partially responsible for the low calcemic activity of 22-oxacalcitriol relative to 1,25-(OH)2D3

We previously showed that OCT, an analog of 1,25-(OH)2D3 with little calcemic activity, can decrease PTH mRNA levels in normal rats and inhibit PTH secretion in cultured bovine parathyroid cells with the same potency as 1,25-(OH)2D3 and that in normal rats fed a normal calcium diet, administration of OCT (500 ng) for 5 days did not increase plasma Ca. Thus, to determine if PTH suppression by OCT contributes to its lack of calcemic activity and to further characterize the effects of OCT on Ca metabolism, we performed several studies in parathyroidectomized (PTX) rats. PTX rats, maintained on a normal diet (0.9% Ca), received daily injections of vehicle, 1,25-(OH)2D3 (200 ng/day), or OCT (200 ng/day) for 6 days. Plasma Ca was measured daily. Plasma Ca in control rats stayed between 6.60 and 7.40 mg/dl, whereas Ca increased to 12.9 +/- 0.42 mg/dl in 1,25-(OH)2D3-treated rats and to 9.53 +/- 0.35 mg/dl in OCT-treated rats after 6 days. With a Ca-deficient diet, control rats maintained a plasma Ca between 4.25 and 4.60 mg/dl, but Ca increased to 13.7 +/- 0.24 mg/dl with 1,25-(OH)2D3 and to 7.29 +/- 0.17 mg/dl with OCT. Since the elevation in Ca by OCT was similar with both diets, OCT appears to act primarily on bone. PTX rats were infused with PTH (1.84 micrograms/kg/day) via an Alzet pump to achieve normal plasma Ca and then treated daily with either vehicle or OCT (200 ng/day). After 6 days, OCT increased serum Ca to 10.7 +/- 0.21 mg/dl over a control value of 8.58 +/- 0.29 mg/dl.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of administration of thyroxine on the risk of postpartum recurrence of hyperthyroid Graves' disease

In our previous study, we reported that the administration of T4 to patients with Graves' disease who were under treatment with methimazole (MMI) decreased the level of antibodies to thyroid-stimulating hormone (TSH) receptors and the rate of recurrence of hyperthyroidism. In this study, the effect of T4 administration on the rate of postpartum recurrence of hyperthyroidism was examined. Seventy-eight patients with Graves' disease had been treated with MMI for 1-3 yr before pregnancy, and MMI was discontinued 5-6 months after the onset of pregnancy because the levels of antibodies to TSH receptors decreased during early pregnancy. The patients were then divided into two groups. Group A (n = 40) was given T4 (100 micrograms/day) and group B (n = 38) was not given any drugs from 5 months after the onset of pregnancy until 1 yr after delivery. The levels of the antibodies to TSH receptors and serum concentrations of thyroxine-binding globulin (TBG) and T4 were not different between the two groups before and during pregnancy, although a transient increase in serum T4 and TBG concentrations were observed during the pregnancy in both groups. After delivery, levels of antibodies to TSH receptors increased in both groups. The rate of increase, however, was more rapid in group B than in group A. The levels were significantly higher in group B than A at 3, 6, 9, and 12 months after delivery. Serum T4 and TBG concentrations decreased after delivery in both groups. Serum concentrations of T4 increased after delivery in group B but not in group A. The concentration of T4 was significantly higher in group B than in group A at 9 and 12 months after delivery. Postpartum recurrence of hyperthyroidism was 5.0% in group A and 31.6% in group B, respectively, during the first year after delivery. These results suggest that administration of T4 during pregnancy and after delivery is effective in decreasing the level of antibodies to TSH receptors and to prevent the postpartum recurrence of hyperthyroidism.

A case of autoimmune insulin antibody syndrome associated with polymyositis, empty sella and apparent high urinary output of immunoreactive insulin

Patients with autoimmune insulin antibody are characterized by hypoglycemic attacks and antibodies to insulin in serum without prior insulin administration. In the present report, a patient with hypoglycemia due to autoimmune insulin antibody associated with primary empty sella syndrome and polymyositis appeared to have high urinary immunoreactive insulin (IRI) in the face of normal urinary C peptide. Consequently, the urinary IRI/C peptide ratio was apparently high. The amelioration of hypoglycemic attacks and polymyositis by prednisolone treatment was accompanied by the disappearance of the antibodies and complete normalization of the urinary IRI and IRI/C peptide ratio. No comparable rise in the urinary IRI and IRI/C peptide ratio was observed in the patients with other disorders studied. Glucose clamp and glucose tolerance study showed decreased sensitivity to exogenous or newly secreted insulin, prolonged half disappearance time of serum insulin, and normal disappearance of blood glucose. These results were consistent with the idea that autoantibodies buffered the effect of exogenous or newly secreted insulin and maintained a relatively constant level of serum free insulin which was not high enough when a large amount of glucose was loaded, but was too high after prolonged fasting, which eventually caused hypoglycemic attacks.

The effect of 22-oxacalcitriol on serum calcitriol

1,25-Dihydroxyvitamin D3 (1,25D) regulates its own levels in circulation by affecting its rates of synthesis and degradation, 22-Oxacalcitriol (OCT), a vitamin D analog with low calcemic activity, decreases circulating PTH levels, one of the regulators of renal 1 alpha-hydroxylase, and stimulates vitamin D degradation in vitro. The purpose of this study was to examine the effects of OCT administration on serum levels of 1,25D. In normal rats, OCT administration (4-200 ng, ip, daily for 5 days) caused a dose-dependent reduction in serum calcitriol levels. At a dose of 200 ng, OCT reduced serum 1,25D from 34.5 +/- 2.7 to 10.9 +/- 0.7 pg/ml (P less than or equal to 0.01) without significant changes in ionized Ca or phosphorus levels. The contribution of the suppression of PTH by OCT to the reduction of serum 1,25D was examined by administering OCT to parathyroidectomized (PTX) rats. Two hundred nanograms of OCT, ip, daily for 5 days significantly reduced serum calcitriol from 29.7 +/- 7.6 to 9.1 +/- 0.5 pg/ml (P less than or equal to 0.01) in rats fed a normal calcium diet. Because OCT increased total calcium (TCa) in this group from 7.4 +/- 0.1 to 9.5 +/- 0.3 mg/dl, similar doses of OCT were given to PTX rats fed a calcium-deficient diet. OCT decreased 1,25D from 58.9 +/- 8.9 to 10.3 +/- 0.4 pg/ml and increased TCa from 4.8 +/- 0.2 to 7.4 +/- 0.1 mg/dl. Comparison of serum 1,25D for identical TCa levels in PTX rats (normal calcium diet controls vs. calcium-deficient diet, OCT-treated) clearly indicates that OCT per se reduced serum 1,25D. Further support for a direct effect of OCT was provided by studies in PTX rats fed a low phosphorus diet. OCT decreased serum 1,25D from 125.8 +/- 15.6 to 10.9 +/- 0.6 pg/ml without significant changes in TCa. To further characterize the mechanisms involved in this effect, similar studies were performed in six normal dogs. Intravenous administration of 0.75 micrograms OCT every other day for 1 week decreased serum calcitriol from 25.4 +/- 3.2 to 12.2 +/- 1.3 pg/ml (P less than or equal to 0.002). Ionized Ca and phosphorus remained unchanged. Despite the short half-life of OCT in the circulation, 1,25D levels returned to basal concentrations 96 h after the last dose of OCT.(ABSTRACT TRUNCATED AT 400 WORDS)

22-oxacalcitriol suppresses 25-hydroxycholecalciferol-1 alpha-hydroxylase in rat kidney

22-oxacalcitriol can decrease the serum level of 1,25-dihydroxycholecalciferol by increasing its metabolic clearance rate and decreasing its production rate. To determine whether 22-oxacalcitriol suppressed the renal 25-hydroxycholecalciferol-1 alpha- hydroxylase we treated rats with 200 ng of 22-oxacalcitriol daily for 1 week. Enzyme activity was measured in vitro by measurement of production of 1,25-dihydroxycholecalciferol by renal slices incubated with 25-hydroxycholecalciferol. 22-oxacalcitriol significantly decreased the 25-hydroxycholecalciferol-1 alpha-hydroxylase activity from 797 +/- 208 pg of 1,25-dihydroxycholecalciferol/g of kidney/h in the control group to 257 +/- 150 pg of 1,25-dihydroxycholecalciferol/g of kidney/h (p less than 0.05). This is the first demonstration of suppression of the renal 25-hydroxycholecalciferol-1 alpha-hydroxylase by the vitamin D3 analog, 22-oxacalcitriol.

Regulation of rat hepatic peroxisomal enoyl-CoA hydratase-3-hydroxyacyl-CoA dehydrogenase bifunctional enzyme by thyroid hormone

Rat hepatic t protein that is negatively regulated by thyroid hormone in nuclear globulin extract was characterized by the antibodies. The following evidence indicated that t protein is a peroxisomal enoyl-CoA hydratase-3-hydroxyacyl-CoA dehydrogenase bifunctional enzyme (bifunctional enzyme). 1. Both proteins had an identical molecular size, and were immunologically indistinguishable from each other. 2. The t protein was abundant in mitochondrial fraction which contained abundant peroxisomes. 3. The amount of the t protein was increased by a peroxisomal proliferator. 4. The activity of the peroxisomal bifunctional enzyme corresponded to the t protein in CM-Sephadex column chromatography. The amount of peroxisomal bifunctional enzyme was increased by thyroidectomy and decreased by 3,5,3'- triiodo-L-thyronine treatment in the whole homogenate of rat liver. These results indicate that the levels of peroxisomal bifunctional enzyme were regulated by thyroid hormone in vivo.

Recognition of a 56 kDa protein in partially purified rat hepatic nuclear thyroid hormone receptor by anti-human c-erb A beta antibody

Human beta thyroid hormone receptor (c-erb A beta protein) produced by an Escherichia coli expression system was purified by sequential column chromatography followed by electroelution from an electrophoresis gel and an antibody was prepared. The antibody recognized a 56 kDa protein band in a partially purified rat hepatic nuclear thyroid hormone receptor fraction on Western blotting. Although multiple bands appeared on Western blotting of crude rat hepatic receptor preparations, a 56 kDa band was the most prominent and preadsorption of the antibody by purified c-erb A protein resulted in almost complete disappearance of the 56 kDa band, indicating that the 56 kDa band was formed by a specific antigen-antibody interaction. Furthermore, the 56 kDa protein appeared to co-elute with 3, 5, 3'-triiodo-L-thyronine binding activity in hydroxylapatite, Sephacryl S-200, and DNA-cellulose column chromatography of rat hepatic nuclear receptor, and sequential column purification resulted in selective enrichment of the 56 kDa band. These results suggest that the 56 kDa protein may be the major component of the rat hepatic thyroid hormone receptor.

Heat shock decreases nuclear transport of 3,5,3'-triiodo-L-thyronine in clone 9 cells

Thyroid hormone, T3, enters cells through an energy-dependent, saturable process and/or passive diffusion. Although the nucleus is the primary site of T3 action, exact mechanisms by which T3 is transported to nucleus are uncertain. In this report, initial cellular and nuclear uptake of T3 was determined using a rat liver cell line (clone 9), in which energy-dependent cellular T3 uptake was demonstrable. One to 5 mM sodium butyrate enhanced cellular T3 uptake with a concomitant increase in nuclear T3 uptake after 30 h. Increased cellular T3 uptake was associated with the increase in the maximum velocity of saturable cellular T3 uptake systems without affecting the Michaelis-Menten constant. Sodium butyrate, however, elicited a reduction in nuclear thyroid hormone receptor levels. On the other hand, heat shock (42 C for 60 min) reduced nuclear T3 uptake without affecting the Michaelis-Menten constant and maximum velocity of saturable cellular T3 uptake. Although nuclear receptor levels were reduced transiently after the heat shock, decreased nuclear T3 transport was not caused by the changes in the receptor levels. NADPH-dependent cytosolic T3 binding protein was undetectable in clone 9 cells before and after butyrate treatment or heat shock. In conclusion, sodium butyrate enhanced nuclear T3 uptake through the increase in cellular T3 uptake that is prerequisite to nuclear T3 transport. However, nuclear T3 uptake mechanisms independent of the cellular uptake system exist and are sensitive to heat shock. Nuclear receptors and cytosolic T3 binding proteins do not seem to be involved in the alteration of nuclear T3 uptake after sodium butyrate or heat shock. These findings suggest intracellular regulatory mechanisms of thyroid hormone transport.

A synthetic analogue of vitamin D3, 22-oxa-1,25-dihydroxy-vitamin D3, stimulates the production of prostacyclin by vascular tissues

We investigated the effect of 22-oxa-1,25-dihydroxyvitamin D3, a synthetic analogue of vitamin D3, on the production of prostacyclin by vascular tissues using rat aortic rings and A7r5 cells derived from fetal rat aortic smooth muscle. Prostacyclin synthesis by aortic rings of rats treated with 22-oxa-1,25-dihydroxyvitamin D3 was much higher than that of non-treated controls, but did not cause any significant hypercalcemia. Treatment with 22-oxa-1,25-dihydroxyvitamin D3 significantly increased the production of prostacyclin by A7r5 cells for 48 hours in a dose-dependent manner. In time-course studies, cells incubated with 22-oxa-1,25-dihydroxyvitamin D3 or 1,25-dihydroxyvitamin D3 produced prostacyclin progressively over a period of 48 hours. The shortest period of incubation that produced a significant amount of prostacyclin compared with control cultures was 24 hours. We observed that treatment with 22-oxa-1,25-dihydroxyvitamin D3 induced cyclooxygenase mRNA in A7r5 cells. Our data suggest that 22-oxa-1,25-dihydroxyvitamin D3 may possibly be a protective substance against the development of atherosclerosis by modulating prostaglandin metabolism.

Purification of human c-erb A beta protein

Human thyroid hormone receptor (c-erb A protein) produced by Escherichia coli expression vector plasmid was purified sequentially using polyethylenimine precipitation of DNA, hydroxylapatite column chromatography, ammonium sulphate precipitation, Sephacryl S-300 gel filtration and mono Q-Sepharose column chromatography. These column procedures resulted in 41.3-fold purification of 3,5,3'-tri-iodo-L-thyronine (T3) binding activity over the initial E. coli extract. Purified protein as well as crude preparation showed high-affinity binding to T3. The c-erb A protein enriched by column purification was further purified by electroelution after electrophoresis. Rabbit antibody against the c-erb A protein was prepared and used for the Western blotting analysis. The antibody recognized c-erb A protein but not the bacterial proteins in crude E. coli extract. When partially purified rat hepatic nuclear thyroid hormone receptor was analysed, a 56 kDa receptor was specifically recognized by the antibody.

The activity of 22-oxacalcitriol in osteoblast-like (ROS 17/2.8) cells

22-Oxacalcitriol (OCT), a synthetic vitamin D analog, can mimic the ability of 1,25-dihydroxyvitamin D3[1,25-(OH)2D3] to differentiate leukemia and skin cells, to enhance the immune response and to suppress PTH secretion, but has much less calcemic activity. The mechanism for this selective action is not understood. OCT has been shown to have a diminished ability to mobilize calcium from bone in vivo, but in vitro findings are contradictory. Little is known about the effect of OCT on bone forming cells. Therefore, the present studies were designed to investigate the actions of OCT at the molecular level in the osteoblast-like cell line, ROS 17/2.8. 3H-OCT was bound to the vitamin D receptor (VDR) in intact cells at the same rate as 3H-1,25-(OH)2D3. As previously found for 1,25-(OH)2D3, the time course of specific binding of OCT was biphasic, with an initial plateau at 1 h and a further increase from 2-8 h. Scatchard analysis demonstrated that exposure to 3H-1,25-(OH)2D3 increased VDR from 24 fmol/mg protein at 2 h to 85 fmol/mg protein at 8 h. Exposure to 3H-OCT increased VDR from 22 to 76 fmol/mg protein, indicating that OCT is also capable of up-regulating the VDR in ROS 17/2.8 cells. In contrast to the lower affinity of OCT for VDR reported for chick intestine and HL-60 cells, the Kd for OCT in intact ROS 17/2.8 cells was identical to that for 1,25-(OH)2D3. The effect of OCT on osteocalcin secretion and alkaline phosphatase (ALP) activity in ROS 17/2.8 cells was also determined. Pretreatment for 24 h with either 1,25-(OH)2D3 or OCT resulted in a dose-dependent enhancement of osteocalcin secretion. A 2-fold stimulation by both compounds was observed with 10(-7)M. ALP activity was measured after a 72-h incubation with 10(-7)M 1,25-(OH)2D3 or OCT. Both compounds increased ALP activity to the same extent. Stimulation by OCT of VDR levels, ALP activity, and osteocalcin secretion were inhibited by the addition of 5 microM cycloheximide, indicating that these actions of OCT require new protein synthesis. Thus, OCT, like 1,25-(OH)2D3, up-regulates the vitamin D receptor, stimulates osteocalcin secretion, and increases ALP activity in ROS 17/2.8 cells, suggesting that the analog may be as active as 1,25-(OH)2D3 in stimulating bone formation in vivo. The low activity of OCT in mobilizing calcium from bone in vivo does not appear to be due to an inability of this compound to act on osteoblasts.

A novel vitamin D3 analog, 22-oxa-1,25-dihydroxyvitamin D3, inhibits the growth of human breast cancer in vitro and in vivo without causing hypercalcemia

Although 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] has been shown to inhibit the growth of certain malignant cells, its hypercalcemic effect has prevented clinical application. We have recently developed a novel vitamin D3 analog, 22-oxa-1,25-(OH)2D3 (OCT), that is capable of promoting differentiation and inhibiting proliferation without inducing hypercalcemia. The present study was undertaken to determine whether OCT could be applied for the treatment of breast cancer with or without estrogen receptor (ER). OCT inhibited the proliferation of both ER-positive (MCF-7, T-47D, and ZR-75-1) and ER-negative breast cancer cells (MDA-MB-231 and BT-20) in vitro in a time- and dose-dependent manner, as determined by cell number and [3H]thymidine uptake. The antiproliferative effect was observed with a concentration as low as 10(-11) M OCT, and treatment of MCF-7 cells with 10(-8) M OCT for 8 days caused more than a 50% reduction in cell number compared with that of vehicle-treated cells. OCT was approximately 1 order of magnitude more potent than 1,25-(OH)2D3 in inhibiting the proliferation of MCF-7 cells. The in vivo effect of OCT was examined in athymic mice implanted with ER-negative MX-1 tumor, which was established as the xenograft derived from human breast carcinoma. Intratumor administration of OCT three times a week remarkably delayed the growth of MX-1 tumor in a time- and dose-dependent manner. The antitumor effect of 1 microgram/kg BW OCT was greater than that of 500 microgram/kg BW adriamycin, and the relative tumor weights in each group on day 26 were 29.7% and 50.5% of that in the vehicle-treated group, respectively. The effects of OCT and adriamycin were additive, and the relative tumor weight after 26 days of combined treatment was 21.7% of that in the vehicle-treated group. Oral administration of OCT was also effective, and the relative tumor weight in the OCT-treated group (1 microgram/kg BW) was 54.6 +/- 0.1% (mean +/- SEM) of that in the vehicle-treated group. Neither intratumor nor oral administration of OCT raised the serum calcium level in these animals. These results demonstrate that OCT is a potent inhibitor of the proliferation of breast cancer cells with or without ER and that OCT inhibits the growth of breast cancer in vivo without inducing hypercalcemia. We suggest that OCT may provide a new strategy for the treatment of breast carcinoma regardless of ER status.

Purification and characterization of thyroid hormone-responsive rat hepatic proteins

Bernal et al. identified two proteins in rat hepatic nuclear extract, t- and n-proteins, that were enriched by thyroidectomy or T3 treatment, respectively. We purified these proteins, raised monospecific antibodies, and characterized them by Western blotting. Anti-n and anti-t-protein antibodies did not recognize t- and n-proteins, respectively. The n-protein was present in nuclear and cytosolic fractions, was present at low levels in the microsomal fraction, and was absent in the mitochondrial fraction of rat liver. The t-protein was more abundant in mitochondrial and microsomal fractions than in the nuclear fraction. The t-protein had the same molecular mass and shared immunological properties with peroxisomal enoyl-coenzyme-A (CoA) hydratase-3-hydroxyacyl-CoA dehydrogenase bifunctional enzyme. The total cellular amount of n-protein increased 12 h after the administration of 1 microgram T3/100 g BW to thyroidectomized rats. Induction was obvious at 0.1 microgram T3/100 g BW after 24 h. Maximal induction was observed at 0.3 microgram T3/100 g BW. The n-protein was induced when thyroidectomized rat liver was perfused with 10(-7) M T3 for 6 h, excluding the possibility that the effect of T3 was mediated by an extrahepatic factor. The n-protein was detected in liver and brain, but not in kidney, heart, testis, or spleen. However, the amount of n-protein in brain was not thyroid hormone dependent. Hepatic n-protein does not correspond to any other T3-responsive protein in terms of its molecular mass and intracellular localization and may be a novel T3-responsive protein.

Disassociation of the macrophage-maturational effects of vitamin D from respiratory burst priming

During the process of enhancing monocytic differentiation of the human leukemia line HL-60, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) also "primes" the cell for respiratory burst by increasing the uptake of Ca2+ across the plasma membrane (Hruska, K.A., Bar-Shavit, Z., Malone, J.D., and Teitelbaum, S.L. (1988) J. Biol. Chem. 263, 16039-16044). The present study asked if the maturational effect of vitamin D is dependent upon this "priming" phenomenon. To this end, we exposed HL-60 to either 1,25(OH)2D3 or its synthetic analogue (1 alpha, 3 beta, 5Z, 7E)-9-10-Secocholesta-5,7,10(19)-triene-1, 3, 25-triol (22-oxa). We found that 22-oxa induced HL-60 maturation as effectively as does the natural steroid. As expected, 48 h of 1,25(OH)2D3 exposure more than doubles (p less than 0.005) HL-60 basal cytosolic Ca2+ and increases inositol triphosphate-sensitive Ca2+ stores approximately 4-fold (p less than 0.01). 22-oxa in contrast alters neither Ca(2+)- nor inositol triphosphate-mobilizable deposits. Moreover, 1,25(OH)2D3 treatment prompts a transient Ca2+ "spike" in response to formyl-methionyl-leucyl-phenylalanine (fMLP) and a marked increase in superoxide (O-2) generation when exposed to the chemotactic peptide (p less than 0.01) or phorbol ester (p less than 0.02). Treatment with 22-oxa does not enable HL-60 to respond to fMLP with a Ca2+ spike or prime the cell for respiratory burst unless it is co-incubated with the Ca2+ ionophore, ionomycin. Similarly, phorbol ester impacts more profoundly on O-2 generation by 1,25(OH)2D3 than 22-oxa preincubated cells (p less than 0.02), unless the latter is added with ionomycin. Our findings indicate that the maturational effects of vitamin D sterols are independent of their capacity to prime cells for respiratory burst and that the Ca2+ ionophoretic effects of 1,25(OH)2D3 play a major role in such priming.

Immunocytochemical localization of synapsin I in the adrenal medulla of rats

The localization of synapsin I in the rat adrenal medulla was studied using the light- and electronmicroscopic immunohistochemistry. By light microscopy, many dot-like reaction products for synapsin I were recognized to be distributed throughout the medullary tissue. The immunoelectron microscopy clearly revealed that gold particles for synapsin I accumulated in abundance in the nerve terminals forming synapses with the chromaffin cell, while the particles were not localized in the chromaffin cells at all. In the nerve terminal, the gold particles were localized exclusively in the region occupied by synaptic vesicles except for the region just beneath the presynaptic plasma membrane. The synaptic vesicles were frequently linked with the adjacent ones by filamentous structures implicated in synapsin I. It is concluded morphologically that synapsin I is a highly-specific protein for the genuine neuron, and is not detected even in the chromaffin cell which originates from the neural crest.

On the mechanisms for the selective action of vitamin D analogs

A variety of analogs of 1,25-(OH)2D3 with less calcemic activity and lower receptor binding affinity than 1,25-(OH)2D3 have been developed. However, these compounds have equal or greater ability to differentiate leukemia cells and psoriatic fibroblasts and to suppress PTH synthesis and secretion. The mechanism for this selectivity has not been elucidated. Because the lower potency of ergocalciferol compared to cholecalciferol in preventing or curing rickets in chicks was associated with a lower affinity of the avian vitamin D binding protein (DBP) for vitamin D2, we tested five analogs with low calcemic activity including 22-oxa-1,25-(OH)2D3 (OCT), MC903, 1,25-(OH)2-16 ene-23-yne D3, 1,25-(OH)2-26,27 dihomo-22-ene-D3, and 1,25-(OH)2-24-trihomo-22-ene-D3 for their affinity for rat serum DBP. All analogs had a low affinity for DBP, ranging from 50-3000 times less than that of 1,25-(OH)2D3. OCT also bound with low affinity to dog and human serum DBP. We tested with OCT the possible consequences of its low affinity for serum DBP. One of the functions of DBP is to prolong the lifetime of 1,25-(OH)2D3 in circulation. Quantification of the metabolic clearance rate (MCR) of OCT in 8 normal dogs using a single bolus injection technique showed that OCT was cleared at a rate of 48.2 +/- 7.5 ml/min, approximately 6-7 times more rapidly than 1,25-(OH)2D3 (6.8 +/- 0.4 ml/min). The estimated half-life of OCT in the circulation was 2.5 +/- 0.3 h compared to 7.0 +/- 0.6; n = 7 for 1,25-(OH)2D3. As our primary interest is the potential of OCT in treating the secondary hyperparathyroidism of CRF, we also measured the MCR of OCT in 5/6 nephrectomized dogs. Uremia does not affect the rate of clearance of OCT from the circulation (MCR: 56.8 +/- 4.5; t1/2 = 2.1 +/- 0.2 n = 4). Despite its shorter half-life, OCT suppressed PTH secretion in vivo in uremic dogs. The effects of low binding to DBP on the percentage uremic dogs. The effects of low binding to DBP on the percentage of free sterol were determined using an ultrafiltration procedure. We compared the proportion of free (unbound) OCT and 1,25-(OH)2D3 in 0.1% BSA-PBS with concentrations of human serum ranging from 0-25%. The proportion of OCT in the free form was significantly higher than that of 1,25-(OH)2D3 for every serum concentration tested. The physiological relevance of a higher percentage of free OCT was tested in normal human macrophages.(ABSTRACT TRUNCATED AT 400 WORDS)