maxacalcitol and Breast-Neoplasms

Today, it is well established that besides playing a crucial role in the establishment and maintenance of the calcium homeostasis in the body, the active form of vitamin D, 1,25(OH)2D3, also acts an effective regulator of cell growth and differentiation in a number of different cell types, including cancer cells. This has led to an increased interest in using 1,25(OH)2D3 in the treatment or prevention of cancer patients and to a substantial number of studies investigating the effect of 1,25(OH)2D3 on cancer cells. The results are encouraging, but clearly demonstrate that the therapeutic window of 1,25(OH)2D3 is extremely narrow due to the calcemic adverse effects of this compound. Much effort has consequently been directed into identifying vitamin D analogs with potent cell regulatory effects but with weaker effects on the calcium metabolism than those of 1,25(OH)2D3. In an attempt to clarify the mechanisms implicated in the cell regulatory effects of 1,25(OH)2D3 and eventually facilitate the process of developing new specific vitamin D analogs, numerous investigations have been carried out with 1,25(OH)2D3 and its analogs. The present review will focus on the results obtained in these studies and describe some of the synthetic analogs, which have shown to be of particular interest in relation to cancer.

Topics: Animals; Antineoplastic Agents; Apoptosis; Breast Neoplasms; Calcitriol; Cell Cycle; Cell Differentiation; Drug Resistance, Neoplasm; Female; Growth Substances; Humans; Male; Neoplasm Invasiveness; Neoplasm Metastasis; Neoplasms, Experimental; Prostatic Neoplasms; Steroid Hydroxylases; Telomerase; Tumor Cells, Cultured

[3H]thymidine incorporation and DNA content were used to investigate the antiproliferative effects of 1,25(OH)2D3 and four analogues [16-ene-1,25(OH)2D3 (16-ene)]; 16-ene,23-yne-1,25(0H)2,D3; EB1089; and 22 oxa-1,25(OH)2D3] on MCF-7, BT-474, and MDA-MB-453 breast cancer cell lines. 1,25(OH)2D3 and the analogues elicited a biphasic response from MCF-7 and BT-474 estrogen receptor (ER)-positive cells, in the presence of estradiol (E2), with lower doses (between 10(-12) and 10(-10) M) tending to stimulate proliferation and higher doses (between 10(-9) and 10(-6) M) inhibiting proliferation by as much as 65%. In the absence of E2, the stimulatory effect was abrogated. Proliferation of MDA-MB-453, estrogen receptor-negative (ER-) cells, was stimulated by these compounds only at 10(-12) M, and inhibited by all higher doses, by as much as 83%. All three cell lines were shown to be vitamin D receptor (VDR) positive, and 1,25(OH)2D3 and all four analogues bound to the VDR with high affinities in each cell line. The antiestrogen ICI 164,384 inhibited the proliferation of all three cell lines. ICI 164,384 at 10(-8) M in combination with 1,25(OH)2D, or EB1089 converted biphasic response of the ER+ cells to one resembling the response of the ER- cells, by eliminating the stimulatory response elicited by 1,25(OH)2D3 at low doses and enhancing the antiproliferative effects of higher doses by as much as 1000-fold. These data are consistent with the hypothesis that E2 in the ER+ cells blocks the antiproliferative effects of the analogues and suggest the potential usefulness of combined antiestrogen and 1,25(OH)2D3 analogues in ER+ breast tumors, whereas 1,25(OH)2D3 analogues alone might suffice in ER- breast tumors.

Topics: Antineoplastic Agents; Breast Neoplasms; Calcitriol; Cell Division; Drug Screening Assays, Antitumor; Drug Therapy, Combination; Estradiol; Estrogen Antagonists; Female; Humans; Neoplasm Proteins; Polyunsaturated Alkamides; Receptors, Calcitriol; RNA, Messenger; Tumor Cells, Cultured

The steroid hormone 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] has potential to be used as an antitumor agent, but its clinical application is restricted by the strong calcemic activity. Therefore, new vitamin D3 analogues are developed with increased growth inhibitory and reduced calcemic activity. In the present study, we have examined the antiproliferative effects of four novel vitamin D3 analogues (CB966, EB1089, KH1060, and 22-oxa-calcitriol) on breast cancer cells, either alone or in combination with the antiestrogen tamoxifen. The estrogen-dependent ZR-75-1 and estrogen-responsive MCF-7 cell lines were used as a model. It was shown that, with EB1089 and KH1060, the same growth inhibitory effect as 1,25-(OH)2D3 could be reached at up to 100-fold lower concentrations, whereas CD966 and 22-oxa-calcitriol were nearly equipotent with 1,25-(OH)2D3. The growth inhibition by the vitamin D3 compounds could be augmented by combined treatment with tamoxifen. At the maximal effective concentrations of the vitamin D3 compounds, the effect of combined treatment was addictive (MCF-7 cells) or less than additive (ZR-75-1 cells). Tamoxifen increased the sensitivity of the cells to the vitamin D3 compounds 2- to 4000-fold, which was expressed by a shift to lower median effective concentration values. Thereby, the vitamin D3 compounds may be used at even lower dosages in combination therapy with tamoxifen. A major problem of tamoxifen therapy is the development of tamoxifen resistance. We have observed that tamoxifen-resistant clones of ZR-75-1 cells retain their response to the vitamin D3 compounds. Regulation of the growth-related oncogene c-myc (mRNA level) and the estrogen receptor (protein level) were studied but appeared not to be related to the antiproliferative action of the vitamin D3 compounds. Together, our data point to a potential benefit of combination therapy with 1,25-(OH)2D3 or vitamin D3 analogues and tamoxifen for the treatment of breast cancer.

Topics: Antineoplastic Agents; Breast Neoplasms; Calcitriol; Cell Division; Drug Resistance; Drug Screening Assays, Antitumor; Estradiol; Humans; Proto-Oncogene Proteins c-myc; Receptors, Calcitriol; Tamoxifen; Tumor Cells, Cultured

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.

Topics: Animals; Antineoplastic Agents; Breast Neoplasms; Calcitriol; Dose-Response Relationship, Drug; Drug Screening Assays, Antitumor; Drug Synergism; Female; Humans; Mice; Mice, Nude; Neoplasm Transplantation; Neoplasms, Hormone-Dependent; Receptors, Estrogen; Tamoxifen; Tumor Cells, Cultured

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.

Topics: Animals; Breast Neoplasms; Calcitriol; Calcium; Cell Differentiation; Cell Division; Doxorubicin; Humans; Hypercalcemia; Kinetics; Mice; Mice, Nude; Neoplasm Transplantation; Receptors, Estrogen; Serum Albumin; Tumor Cells, Cultured