K.W. Colston

POSSIBLE ROLE FOR VITAMIN D IN CONTROLLING BREAST CANCER CELL PROLIFERATION

By means of an immunocytochemical method the 1.25-dihydroxyvitamin D [1.25(OH)2D] receptor status of tumours from 136 patients with primary carcinoma of the breast was determined. Patients with receptor-positive tumours had significantly longer disease-free survival than those with receptor-negative tumours (Chi2 = 4.01, p less than 0.05). 1.25(OH)2D3 inhibits the proliferation of several established human breast cancer cell lines in vitro. Effects of 1.25(OH)2D3 on breast tumour growth in vitro were assessed by means of the nitrosomethylurea-induced rat mammary tumour model of hormone-responsive breast cancer. Treatment of tumour-bearing animals with 0.1 microgram of the synthetic analogue, 1 alpha-hydroxyvitamin D3, three times weekly produced significant inhibition of tumour progression. Taken together, these studies suggest that the levels of 1.25(OH)2D occurring in vivo may exert an inhibitory effect on receptor-positive tumours. Further studies are required to evaluate the role of vitamin D metabolites in the treatment of human malignant disease.

Leukemia cell differentiation: cellular and molecular interactions of retinoids and vitamin D.

1. The conventional approach to treatment of acute myeloid leukemia has been the use of chemotherapy, which although being cytotoxic to malignant clones, is also cytodestructive to normal cells. In addition, some leukemia cells develop resistance to chemotherapy and are therefore difficult to eradicate. 2. Differentiation therapy, whereby immature cells are induced to attain a mature phenotype by differentiation agents, has provided an alternative strategy in the treatment of hyperproliferative disorders. This has been highlighted by the use of all-trans retinoic acid (ATRA) in the treatment of acute promyelocytic leukemia (APL). 3. Another differentiation agent, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), directs monocytic maturation of normal and leukemic cells. Cellular studies have revealed that combinations of vitamin D derivatives and retinoids such as ATRA and 9-cis retinoic acid (9-cis RA) exhibit cooperative effects on differentiation in established leukemia cell lines such as HL-60, U937, and NB4. Furthermore, vitamin D compounds, although not able to induce apoptosis when used alone, potentiate apoptosis induced by 9-cis RA in HL-60 cells and differentially regulate the expression of the apoptosis-related gene products bcl-2 and bax. The molecular mechanisms involved in regulating differentiation and apoptosis by these agents are mediated through the interactions of the nuclear receptors for vitamin D (VDR), ATRA (RAR), and 9-cis RA (RXR), which are able to form homo- or heterodimeric complexes and transcriptionally activate or repress target gene expression. 4. There is evidence to suggest that nitric oxide may also play a role in leukemic cell differentiation and that 1,25(OH)2D3 may influence endogenous nitric oxide production either by directly increasing tumor necrosis factor-alpha (TNF-alpha) or through a secondary mediator such as the C-type lectin CD23.

Interaction of vitamin D derivatives and granulocyte-macrophage colony-stimulating factor in leukaemic cell differentiation

The ability of the physiologically active form of vitamin D, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and two novel vitamin D analogues, EB1089 and KH1060 to induce the differentiation of the U937 and HL-60 leukaemic cell lines was evaluated, alone or in combination with granulocyte–macrophage colony-stimulating factor (GM-CSF). Studies revealed that following 96 h treatment, the vitamin D derivatives inhibited the proliferation, and induced the differentiation of U937 and HL-60 cells in a dose-dependent manner, as determined by cell counts and nitroblue tetrazolium (NBT) reduction assays, respectively. EB1089 and KH1060 were found to be more effective than 1,25(OH)2D3 in exhibiting their antiproliferative and differentiative effects. In contrast, induction of leukaemic cell differentiation with 1 ng/ml GM-CSF after 96 h was less effective when compared with the vitamin D derivatives used individually. Fluorescence activated cell scanning (FACS) analyses indicated that the vitamin D derivatives readily induced the expression of the monocyte-associated cell surface antigen, CD14, and also the β 2-integrins, CD11b and CD18 in both cell lines after 48 h and 96 h treatment. The ability of EB1089 and KH1060 to induce these antigens was achieved with greater efficacy relative to the native hormone. When U937 and HL-60 cell cultures were cotreated for 48 h with the vitamin D compounds and GM-CSF and analysed by FACS, enhanced effects on CD14 and CD11b induction were observed compared to those of the compounds alone. These co-operative effects may occur as a consequence of molecular events which involve the transcription by vitamin D receptors (VDR) of genes required for the responsiveness of immature cells to factors such as GM-CSF, and place these and other related vitamin D analogues as potential therapeutic agents in the treatment of leukaemia.

The use of nasal calcitonin spray in the treatment of hypercalcaemia of malignancy

Hypercalcaemia is a frequent metabolic complication of advanced malignant disease. Calcitonin has been shown to be effective both in controlling malignant hypercalcaemia [10] and in reducing pain in patients with bone metastases [9]. A number of other treatments are also effective in reducing serum calcium levels in malignant disease, including mithramycin [5], intravenous phosphate infusions [2] and bisphosphonates [1]. All effective preparations currently used in managing acute malignant hypercalcaemia require parenteral administration. Synthetic salmon calcitonin has recently been formulated as a nasal spray, and we report on its use in the treatment o f hypercalcaemia of malignancy.