Phenotypic differentiation-linked growth inhibition in human leukemia cells by active vitamin D3 analogues

Two lineages of immune cells that differentially express the vitamin D receptor

Since 1983 it has been known that monocytes and activated T and B cells expressed the vitamin D receptor (VDR) and are therefore vitamin D targets. New data identified two lineages of immune cells that can be differentiated by the expression of the VDR. Monocytes, macrophages, neutrophils, and hematopoietic stem cells were mostly from VDR positive lineages. T cells, ILC1 and ILC3 were also largely VDR positive, which is consistent with the known effects of vitamin D as regulators of type-1 and type-3 immunity. Activation of the VDR negative T cells did not induce the expression of the VDR reporter, suggesting that perhaps only a subset of the T cells in the periphery express the VDR. When activated, the VDR negative T cells responded as if they were VDR knockout T cells in that they made more IFN-γ and proliferated faster than the VDR positive T cells. The ability of vitamin D to regulate immune function will depend on which cells express the VDR and a better understanding of the signals that regulate VDR expression in immune cells.

Vitamin D receptor-mediated skewed differentiation of macrophages initiates myelofibrosis and subsequent osteosclerosis

Myelofibrosis in myeloproliferative neoplasms (MPNs) with mutations such as JAK2V617F is an unfavorable sign for uncontrollable disease progression in the clinic and is complicated with osteosclerosis whose pathogenesis is largely unknown. Because several studies have revealed that macrophages are an indispensable supporter for bone-forming osteoblasts, we speculated that macrophages might play a significant role in the proliferation of collagen-producing myofibroblasts in marrow fibrotic tissues. Here, we show that myelofibrosis critically depends on macrophages whose differentiation is skewed by vitamin D receptor (VDR) signaling. In our novel myelofibrosis model established by transplantation of VDR^+/+ hematopoietic stem/progenitor cells into VDR^-/- mice, donor-derived F4/80⁺ macrophages proliferated together with recipient-derived α-smooth muscle actin-positive myofibroblasts, both of which comprised fibrotic tissues with an indistinguishable spindle-shaped morphology. Interfering VDR signals, such as low vitamin D diet and VDR deficiency in donor cells as well as macrophage depletion prevented myelofibrosis in this model. These interventions also ameliorated myelofibrosis in JAK2V617F-driven murine MPNs likely in a transforming growth factor-β1- or megakaryocyte-independent manner. These results suggest that VDR and macrophages may be novel therapeutic targets for MPNs with myelofibrosis.

Vitamin D and all-cause mortality among adults in USA: findings from the National Health and Nutrition Examination Survey Linked Mortality Study

BACKGROUND

Whether concentrations of vitamin D are related to mortality remains unresolved. Our objective was to examine the relationship between serum concentrations of 25-hydroxyvitamin D and all-cause mortality in a national sample of US adults.

METHODS

We used data from the National Health and Nutrition Examination Survey Mortality Study from 2001 to 2004 with mortality compiled through 2006. Mortality status was established through a match to the National Death Index.

RESULTS

Of the 7531 participants, 347 died. Median follow-up was 3.8 years. The mean unadjusted concentrations of vitamin D were 54.1 nmol/l (21.7 ng/ml) among participants who died and 60.7 nmol/l (24.3 ng/ml) among participants who survived (P = 0.002). After adjustment for socio-demographic factors, the hazard ratios (HR) for all-cause mortality were 1.65 [95% confidence interval (CI): 95% CI: 1.13-2.40] for participants with a concentration <50 nmol/l (<20 ng/ml) and 1.02 (95% CI: 0.74-1.41) for participants with a concentration of 50 to <75 nmol/l (20 to <30 ng/ml) compared with participants who had a concentration of ≥ 75 nmol/l (≥ 30 ng/ml). After more extensive adjustment, the HRs were 1.28 (95% CI: 0.86-1.90) and 0.91 (95% CI: 0.63-1.33), respectively. The fully adjusted HR per 10 nmol/l of vitamin D was 0.93 (95% CI: 0.86-1.01). The HRs did not vary by gender (P = 0.80) or among the three major racial or ethnic groups (P = 0.46).

CONCLUSIONS

Concentrations of vitamin D were weakly and inversely related to all-cause mortality in this sample of US adults.

The role of transcriptional coactivator TRAP220 in myelomonocytic differentiation

The TRAP220 subunit of the thyroid hormone receptor-associated polypeptide transcription coactivator complex (TRAP/Mediator complex), mammalian counterpart of the yeast Mediator complex, is proposed to act on a variety of major and specific biological events through physical interactions with nuclear receptors. The vitamin D receptor (VDR) and retinoic acid receptor (RAR), coupled with retinoid X receptor (RXR), are nuclear receptors which have important roles for monopoiesis and granulopoiesis, respectively. In this study, we present the functional role of TRAP220 in nuclear receptor-mediated monopoiesis and granulopoiesis. The mouse Trap220(-/-) yolk sac hematopoietic progenitor cells were resistant to 1,25-dihydroxyvitamin D(3)-stimulated differentiation into monocytes/macrophages. Furthermore, flow cytometric analyses showed that HL-60 cells, human promyelocytic leukemia cell line, wherein TRAP220 was down-regulated, did not differentiate efficiently into monocytes and granulocytes by stimulation with 1,25-dihydroxyvitamin D(3) and all-trans retinoic acid, correspondingly. The expression of direct target genes of VDR or RAR, as well as the differentiation marker genes, was low in the knockdown cells. These results indicated a crucial role of TRAP220 in the optimal VDR- and RAR-mediated myelomonocytic differentiation processes in mammalian hematopoiesis.

Casein kinase Iepsilon down-regulates phospho-Akt via PTEN, following genotoxic stress-induced apoptosis in hematopoietic cells

Here, we show a functional role of casein kinase I (CKI) epsilon in hematopoietic cell survival through the modification of phosphatidylinositol 3-kinase (PI3K)/Akt signaling. Introduction of wild-type (WT)-CKIepsilon into interleukin-3 (IL-3)-dependent 32D cells increased the sensitivity to genotoxic stresses, such as gamma-irradiation, etoposide, and IL-3 deprivation, whereas kinase-negative (KN)-CKIepsilon suppressed it. Contrary to KN-CKIepsilon, WT-CKIepsilon attenuated the IL-3-induced activation of Akt with the increase of PTEN activity. Similarly, the increase of Akt activation, as well as PTEN inactivation, was accompanied both by a decrease of CKIepsilon expression induced by all-trans retinoic acid and by the addition of a specific inhibitor for CKIepsilon in HL-60 cells. CKIepsilon seems to activate PTEN by physical interaction. These results suggest that the CKIepsilon-induced down-regulation of PI3K/Akt signaling through PTEN lead to amplified sensitivity to apoptosis. Thus, the suppression of CKIepsilon in many human leukemia cell lines may play a role in the cell immortalization.

Phosphatidylinositol 3-kinase regulates PMA-induced differentiation and superoxide production in HL-60 cells

Treatment of the human promyelocytic leukemia cell line HL-60 with phorbol myristate acetate (PMA) is associated with induction of monocytic or myelocytic differentiation. Since phosphatidylinositol 3-kinase (PI3-kinase) is a critical player in cell proliferation, survival, and differentiation, we studied the role of PI3-kinase during induction of the differentiated monocytic phenotype and superoxide production. In treatment of HL-60 cells with PMA, the PI3-kinase inhibitors LY294002 and wortmannin inhibited cell adhesion and spreading and phagocytic activity. LY294002 and wortmannin also inhibited the proliferation of HL-60 cells. During PMA-induced monocytic differentiation, LY294002 induced apoptosis in a dose dependent manner. The phosphorylation of p85alpha derived from PMA-stimulated HL-60 cells was shown in the time dependent manner. However, p70 S6 kinase inhibitor, rapamycin, did not inhibit PMA-induced monocytic differentiation. During PMA-induced monocytic differentiation, LY294002 inhibited c-jun protein expression and decrease of c-myc protein level. In contrast, LY294002 induced production of superoxide in the HL-60 cells stimulated with forskolin. Moreover, staurosporine and H7, PKC inhibitors, enhanced superoxide production in dibutyryl cAMP-induced HL-60 cells. These results suggest that PI3-kinase may regulate PMA-induced differentiation signal and provide a crucial link between PKC and cAMP in HL-60 cells.

Metabolism of 1alpha,25-dihydroxyvitamin D(3) in human promyelocytic leukemia (HL-60) cells: in vitro biological activities of the natural metabolites of 1alpha,25-dihydroxyvitamin D(3) produced in HL-60 cells

The secosteroid hormone, 1alpha,25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)], induces differentiation of the human promyelocytic leukemia (HL-60) cells into monocytes/macrophages. At present, the metabolic pathways of 1alpha,25(OH)(2)D(3) and the biologic activity of its various natural intermediary metabolites in HL-60 cells are not fully understood. 1alpha,25(OH)(2)D(3) is metabolized in its target tissues via modifications of both the side chain and the A-ring. The C-24 oxidation pathway, the main side chain modification pathway initiated by hydroxylation at C-24 leads to the formation of the end product, calcitroic acid. The C-23 and C-26 oxidation pathways, the minor side chain modification pathways initiated by hydroxylations at C-23 and C-26 respectively together lead to the formation of the end product, 1alpha,25(OH)(2)D(3)-lactone. The C-3 epimerization pathway, the newly discovered A-ring modification pathway is initiated by epimerization of the hydroxyl group at C-3 to form 1alpha,25-dihydroxy-3-epi-vitamin-D(3). We performed the present study first to examine in detail the metabolism of 1alpha,25(OH)(2)D(3) in HL-60 cells and then to assess the ability of the various natural intermediary metabolites of 1alpha,25(OH)(2)D(3) in inducing differentiation and in inhibiting clonal growth of HL-60 cells. We incubated HL-60 cells with [1beta-(3)H] 1alpha,25(OH)(2)D(3) and demonstrated that these cells metabolize 1alpha,25(OH)(2)D(3) mainly via the C-24 oxidation pathway and to a lesser extent via the C-23 oxidation pathway, but not via the C-3-epimerization pathway. Three of the natural intermediary metabolites of 1alpha,25(OH)(2)D(3) derived via the C-24 oxidation pathway namely, 1alpha,24(R),25-trihydroxyvitamin D(3), 1alpha,25-dihydroxy-24-oxovitamin D(3) and 1alpha,23(S),25-trihydroxy-24-oxovitamin D(3) [1alpha,23(S),25(OH)(3)-24-oxo-D(3)] were almost as potent as 1alpha,25(OH)(2)D(3) in terms of their ability to differentiate HL-60 cells into monocytes/macrophages. We then selected 1alpha,23(S),25(OH)(3)-24-oxo-D(3) which has the least calcemic activity among all the three aforementioned natural intermediary metabolites of 1alpha,25(OH)(2)D(3) to examine further its effects on these cells. Our results indicated that 1alpha,23(S),25(OH)(3)-24-oxo-D(3) was also equipotent to its parent in inhibiting clonal growth of HL-60 cells and in inducing expression of CD11b protein. In summary, we report that 1alpha,25(OH)(2)D(3) is metabolized in HL-60 cells into several intermediary metabolites derived via both the C-24 and C-23 oxidation pathways but not via the C-3 epimerization pathway. Some of the intermediary metabolites derived via the C-24 oxidation pathway are found to be almost equipotent to 1alpha,25(OH)(2)D(3) in modulating growth and differentiation of HL-60 cells. In a previous study, the same metabolites when compared to 1alpha,25(OH)(2)D(3) were found to be less calcemic. Thus, the findings of our study suggest that some of the natural metabolites of 1alpha,25(OH)(2)D(3) may be responsible for the final expression of the noncalcemic actions that are presently being attributed to their parent, 1alpha,25(OH)(2)D(3).

The effects of 1alpha,24(S)-dihydroxyvitamin D(2) analog on cancer cell proliferation and cytokine expression

It is well established that 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)), the active metabolite of vitamin D, plays a role in regulating proliferation and differentiation of cells, in addition to its classic function in mineral homeostasis. Recent studies have also provided evidence for the involvement of 1alpha,25(OH)(2)D(3) in regulating the immune system. However, therapeutic application of 1alpha,25(OH)(2)D(3) to hyperproliferative diseases such as cancer, or for immunologic purposes, is thwarted by its hypercalcemic activity. In order to overcome this obstacle, analogs of 1alpha,25(OH)(2)D(3) have been produced that exhibit decreased hypercalcemic activity while retaining the growth and immunologic regulating properties. In the present study, the efficacy of 1alpha,24(S)-dihydroxyvitamin D(2) (1alpha,24(S)(OH)(2)D(2)), a vitamin D(2) analog, in restraining cell proliferation was compared to that of 1alpha,25(OH)(2)D(3). In parallel studies, cancer cell lines were grown in increased concentrations (10(-10)-10(-7) M) of each compound for various incubation periods (1-4 days). Growth was assessed by measuring [(3)H]thymidine incorporation. The results revealed that 1alpha,24(S)(OH)(2)D(2) significantly inhibits proliferation to an extent similar to that observed for 1alpha,25(OH)(2)D(3). Moreover, incubating the human leukemia cell line, HL-60, with 1alpha,24(S)(OH)(2)D(2) resulted in an induction of differentiation of these promyelomonocyte cells into monocyte-macrophage-like cells, in a manner similar to that observed with 1alpha,25(OH)(2)D(3). Using a Western procedure, it was also shown that 1alpha,24(S)(OH)(2)D(2) like 1alpha,25(OH)(2)D(3) enhances the expression of vitamin D receptors (VDR) in the rat osteosarcoma cell line, ROS 17/2.8. The expression of tumor necrosis factor (TNF) alpha (TNF-alpha) in human peritoneal macrophages (HPM) obtained from uremic patients treated with continuous ambulatory peritoneal dialysis (CAPD) was found to be regulated by 1alpha,25(OH)(2)D(3) as well as by 1alpha,24(S)(OH)(2)D(2). Incubations of HPM with 1alpha,25(OH)(2)D(3) or 1alpha,24(S)(OH)(2)D(2), have inhibited the expression of TNF-alpha on both mRNA and protein levels. These results suggest that 1alpha,25(OH)(2)D(3) has a role in controlling the rate of inflammation in the peritoneal cavity of CAPD treated patients. Since 1alpha,24(S)(OH)(2)D(2) does not cause hypercalcemia, the present results encourage the possible use of this vitamin D(2) analog in the treatment of cancer and hyper-inflammatory diseases.

Synthesis and biological activities of the two C(23) epimers of 1alpha,23,25-trihydroxy-24-oxo-19-nor-vitamin D(3): novel analogs of 1alpha,23(S),25-trihydroxy-24-oxo-vitamin D(3), a natural metabolite of 1alpha,25-dihydroxyvitamin D(3)

In a previous report, we indicated that 1alpha,23(S), 25-trihydroxy-24-oxovitamin D(3) [1alpha,23(S), 25(OH)(3)-24-oxo-D(3)], a natural metabolite of 1alpha, 25-dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] is almost equipotent to 1alpha,25(OH)(2)D(3) in suppressing parathyroid hormone (PTH) secretion (Lee et al., 1997. Biochemistry 36, 9429-9437). Also, 1alpha,23(S),25(OH)(3)-24-oxo-D(3) has been shown to possess only weak in vivo calcemic actions. Thus, vitamin D(3) analogs structurally related to 1alpha,23(S),25(OH)(3)-24-oxo-D(3) may have therapeutic value. Furthermore, biologic activity studies of various synthetic analogs of 1alpha,25(OH)(2)D(3) showed that the removal of carbon-19 (C-19) reduces the calcemic activity of 1alpha, 25(OH)(2)D(3.) Therefore, in an attempt to produce vitamin D(3) analogs with a better therapeutic index, we synthesized C(23) epimers of 1alpha,23,25(OH)(3)-24-oxo-19-nor-vitamin D(3) [1alpha,23, 25(OH)(3)-24-oxo-19-nor-D(3)]. The two epimers were compared to 1alpha,25(OH)(2)-19-nor-D(3) and 1alpha,25(OH)(2)D(3) in their ability to generate biologic activities in several in vitro assay systems. In the assay measuring the suppression of parathyroid hormone (PTH) secretion in bovine parathyroid cells, 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3) was as potent as 1alpha, 25(OH)(2)-19-nor-D(3) but was less potent than 1alpha,25(OH)(2)D(3). In the same assay 1alpha,23(R),25(OH)(3)-24-oxo-19-nor-D(3) exhibited greater potency than 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3). In the assays measuring the ability of vitamin D compounds to inhibit clonal growth and to induce differentiation of human promyelocytic leukemia (HL-60) cells, 1alpha,23(S),25(OH)(3)-24-oxo-19-nor-D(3) was less potent than 1alpha,25(OH)(2)-19-nor-D(3) but was equipotent to 1alpha, 25(OH)(2)D(3). More importantly, in the same assays, 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3) was more potent than 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3) and was equipotent to 1alpha, 25(OH)(2)-19-nor-D(3). Also, the vitamin D receptor-mediated transcriptional activity of 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3) was almost equal to that of 1alpha, 25(OH)(2)-19-nor-D(3), but higher than that of 1alpha,23(S), 25(OH)(3)-24-oxo-19-nor-D(3). This finding explains in part the greater in vitro biologic activities of 1alpha,23(R), 25(OH)(3)-24-oxo-19-nor-D(3). In summary, our results indicate that 1alpha,23(R),25(OH)(3)-24-oxo-19-nor-D(3) and to a lesser extent 1alpha,23(S),25(OH)(3)-24-oxo-19-nor-D(3) are potent 19-nor vitamin D(3) analogs, which suppress PTH secretion in bovine parathyroid cells and strongly inhibit clonal growth and induce differentiation of HL-60 cells in vitro.

Isolation and identification of 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3: metabolites of 1alpha,24(R)-dihydroxyvitamin D3 produced in rat kidney

1alpha,24(R)-Dihydroxyvitamin D3 [1alpha,24(R)(OH)2D3], a synthetic vitamin D3 analog, has been developed as a drug for topical use in the treatment of psoriasis. At present, the target tissue metabolism of 1alpha,24(R)(OH)2D3 is not understood completely. In our present study, we investigated the metabolism of 1alpha,24(R)(OH)2D3 in the isolated perfused rat kidney. The results indicated that 1alpha,24(R)(OH)2D3 is metabolized in rat kidney into several metabolites, of which 1alpha,24(R),25-trihydroxyvitamin D3, 1alpha,25-dihydroxy-24-oxovitamin D3, 1alpha,23(S),25-trihydroxy-24-oxovitamin D3, and 1alpha,23-dihydroxy-24,25,26,27-tetranorvitamin D3 are similar to the previously known metabolites of 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3]. In addition to these aforementioned metabolites, we also identified two new metabolites, namely 1alpha-hydroxy-24-oxovitamin D3 and 1alpha,23-dihydroxy-24-oxovitamin D3. The two new metabolites do not possess the C-25 hydroxyl group. Thus, the metabolism of 1alpha,24(R)(OH)2D3 into both 25-hydroxylated and non-25-hydroxylated metabolites suggests that 1alpha,24(R)(OH)2D3 is metabolized in the rat kidney through two pathways. The first pathway is initiated by C-25 hydroxylation and proceeds further via the C-24 oxidation pathway. The second pathway directly proceeds via the C-24 oxidation pathway without prior hydroxylation at the C-25 position. Furthermore, we demonstrated that rat kidney did not convert 1alpha-hydroxyvitamin D3 [1alpha(OH)D3] into 1alpha,25(OH)2D3. This finding indicates that the rat kidney does not possess the classical vitamin D3-25-hydroxylase (CYP27) activity. However, from our present study it is apparent that prior hydroxylation of 1alpha(OH)D3 at the C-24 position in the 'R' orientation allows 25-hydroxylation to occur. At present, the enzyme responsible for the C-25 hydroxylation of 1alpha,24(R)(OH)2D3 is unknown. Our observation that the side chain of 1alpha,24(R)(OH)2D3 underwent 24-ketonization and 23-hydroxylation even in the absence of the C-25 hydroxyl group suggests that 1alpha,25(OH)2D3-24-hydroxylase (CYP24) can perform some steps of the C-24 oxidation pathway without prior C-25 hydroxylation. Thus, we speculate that CYP24 may be playing a dual role in the metabolism of 1alpha,24(R)(OH)2D3.

Down regulation of NM23.H1, NM23.H2 and c-myc genes during differentiation induced by 1,25 dihydroxyvitamin D3

The NM23 gene, involved in the negative regulation of metastatic progression, has been found to be highly homologous to developmentally regulated genes such as the awd gene in Drosophila melanogaster and the Gip17 gene in Dyctiostelium discoideum. To ascertain whether the NM23 genes are involved in the differentiation processes of human cell lines, the NM23.H1 and NM23.H2 expression level has been determined during the monocyte-macrophage differentiation of HL-60 and U-937 cell lines induced by vitamin D3. In both lines, vitamin D3 produced induction of differentiative markers, inhibition of cell proliferation and a decrease of the NM23.H1, NM23.H2 and c-myc genes, behaving both as a differentiative and an antiproliferative agent. The fact that the c-myc transcriptional factor PuF is identical to the NM23.H2 gene and that NM23 protein could be a transcriptional factor suggests that the regulatory action exerted by vitamin D3 on c-myc transcription is mediated by NM23.H2.

Effects of protein kinase modulators on transferrin receptor expression in human leukaemic HL-60 cells

The mRNA of transferrin receptor (TfR) is constitutively expressed in proliferating human leukaemic HL-60 cells. Treatment of HL-60 cells with phorbol 12-myristate 13-acetate (PMA), a protein kinase C (PKC) activator, or dibutyryl-cyclic AMP (dbcAMP), a protein kinase A (PKA) activator, resulted in a 90% decrease in the level of TfR mRNA. Inhibition of TfR mRNA expression induced by 10 nM PMA and 100 microM dbcAMP was abolished by prior incubation of cells with 0.1-1.0 microM GF109203X, a PKC-specific inhibitor, and 1-10 microM H-89, a PKA-specific inhibitor, respectively. The blocking effects of GF109203X and H-89 were dose-dependent and complete at the highest concentrations of the inhibitors used. Although treatment of cells with GF109203X or H-89 alone did not alter the constitutive expression of TfR mRNA, incubation of cells with 30-100 nM staurosporine, a wide-spectrum protein kinase inhibitor, resulted in suppression of the constitutive expression of TfR mRNA in a dose-dependent manner. These results suggest that (i) the down-regulation of TfR mRNA expression during the differentiation of HL-60 cells can be mediated by activation of either PKC or PKA; (ii) the constitutive expression of TfR mRNA in proliferating HL-60 cells is staurosporine-sensitive and is probably maintained by protein kinase(s) other than PKC and PKA.

Expression of cell surface antigens during the differentiation of HL-60 cells induced by 1,25-dihydroxyvitamin D3, retinoic acid and DMSO

HL-60 cells were induced to differentiate by 1,25-dihydroxyvitamin D3, retinoic acid or DMSO. In order to investigate to which extent this maturation mimics the in vivo monocytic or myeloid differentiation, we compared induced HL-60 cells with peripheral blood monocytes and granulocytes by using a panel of mAbs directed against myeloid cell surface antigens. Upon exposure to 1,25-(OH)2D3, HL-60 cells acquired a differentiation phenotype close to that of mature monocytes. The changes in myeloid cell surface antigens induced by retinoic acid or DMSO paralleled the expression pattern of these molecules in normal granulopoiesis, although maturation was not achieved and partially defective.

Novel vitamin D3 derivatives, 26-homo-delta 22-dehydro-1 alpha,25(S)-dihydroxyvitamin D3 and 26-homo-delta 22-dehydro-1 alpha,25(R)-dihydroxyvitamin D3: preferential activity in c-myc mRNA production and in induction of phenotypic differentiation of HL-60 cells

Novel vitamin D3 derivatives, 26-homo-delta 22-1 alpha,25(S)-dihydroxyvitamin D3 and 26-homo-delta 22-1 alpha,25(R)-dihydroxyvitamin D3 were compared with the native hormone, 1,25-dihydroxyvitamin D3, and with other vitamin D3 derivatives, in inhibition of cell growth, induction of phenotypic differentiation, and c-myc mRNA reduction of HL-60 cells. The degree of inhibition in cell growth caused by 26-homo-delta 22-1 alpha,25(S)-(OH)2D3 was the greatest followed by 26-homo-delta 22-1 alpha,25(R)-(OH)2D3. The ability to reduce NBT was parallel to that to inhibit cellular proliferation. 26-homo-delta 22-1 alpha,25(S)-(OH)2D3, 26-homo-delta 22-1 alpha,25(R)-(OH)2D3, 24-homo-24-F2-1 alpha,25-(OH)2D3, and 1 alpha,24(R)-(OH)2-26-Cl-D3 were more active than 1 alpha,25-(OH)2D3 in the induction of OK-M1+ and OK-Mo-2+ HL-60 cells. Using two color flow cytometric analysis, the percentages of OK-M5(+)- and OK-DR(+)-HL-60 cells were 33% in the treatment with 26-homo-delta 22-1 alpha,25(S)-(OH)2D3 plus interferon-gamma (IFN-gamma) but 14% in the treatment with 1 alpha,25-(OH)2D3 plus IFN-gamma. 26-Homo-delta 22-1 alpha,25(S)-(OH)2D3 has an inhibitory effect on c-myc reduction in treated HL-60 cells. These results suggest that the novel vitamin D3 derivatives, 26-homo-delta 22-1 alpha,25(S)-(OH)2D3 and 26-homo-delta 22-1 alpha,25(R)-(OH)2D3, have preferential activity in inducing phenotypic differentiation and in inducing cell proliferation related c-myc mRNA activity.

Relationships between the cell cycle and the expression of c-myc and transferrin receptor genes during induced myeloid differentiation

We examined the relationship of cellular oncogene c-myc and transferrin receptor (TfR) gene expression to cell proliferation and cell cycle progression during myeloid differentiation in the HL-60 myeloid leukemia cell line. In order to determine levels of mRNA for these genes in HL-60 cells induced to differentiate along the myeloid pathway, RNA was isolated from HL-60 cells incubated with retinoic acid for 24 h and Northern blots were probed with labeled cDNAs for c-myc and TfR. c-myc mRNA decreased within 3 h of retinoic acid addition, and TfR mRNA decreased after 9 h; both mRNAs continued to decrease over 24 h. RNA was also isolated from HL-60 cells separated by centrifugal elutriation into cell cycle phases. TfR and c-myc cDNA probes hybridized equally to RNA from uninduced cells in all phases of the cell cycle. However, after 24 h incubation with the differentiation inducer retinoic acid, TfR mRNA was expressed substantially less in the G1 stage, whereas c-myc mRNA was still expressed equally in all cell cycle phases. These data indicate that, although TfR and c-myc expression are both associated with cell proliferation in the HL-60 line, TfR is down-regulated specifically in G1 upon induction of terminal differentiation whereas c-myc expression is disassociated from cell cycle control in these cells.

Hypercalcemia and vitamin D metabolism in Hodgkin's disease. Is there an underlying immunoregulatory relationship?

Hypercalcemia is not common in Hodgkin's disease, but in reported cases is often unassociated with bone involvement. A case is presented demonstrating a mechanism involving elevated levels of 1,25-dihydroxy vitamin D3 (calcitriol). Similar cases in the literature are reviewed. Data implicating calcitriol as a hematolymphoid regulatory hormone are discussed as they may relate to lymphomas, leukemias, and paraneoplastic lymphocyte and monocyte/macrophage activity.

Stimulatory effect of 1,25-dihydroxyvitamin D3 on the glucose-6-phosphate dehydrogenase activity in the MCF-7 human breast cancer cell line

Human breast cancer cell lines have been shown to possess high affinity receptors for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) and their growth is inhibited by this steroid. The present study examines the effect of 1,25(OH)2D3 on the activity of glucose-6-phosphate dehydrogenase (G6PD) in cells of a human breast cancer cell line MCF-7. G6PD, an enzyme which controls the hexose monophosphate shunt, is elevated and sensitive to 17 beta-estradiol in breast tumors. G6PD activity was stimulated by 1,25(OH)2D3 in a dose-dependent manner at very low concentrations of steroid (10(-10)-10(-12) M). 1,25(OH)2D3 increased maximum velocity without modifying the affinity constant of the enzyme for glucose-6-phosphate.

Cooperative effects of tumor necrosis factor-alpha and 1,25-dihydroxyvitamin D3 on growth inhibition, differentiation, and c-myc reduction in human promyelocytic leukemia cell line HL-60

The simultaneous addition of recombinant human tumor necrosis factor-alpha (rTNF-alpha) and 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) synergistically induced growth inhibition and differentiation of the human promyelocytic leukemia cell line HL-60. A significantly greater reduction in c-myc mRNA level was also observed after a 20-h combined treatment with rTNF-alpha and 1,25-(OH)2D3 than was observed following administration of either agent alone. These results suggest that rTNF-alpha and 1,25-(OH)2D3 induce HL-60 cell growth inhibition through different molecular mechanisms, and that their simultaneous administration could provide a new approach to the treatment of cancer.

Cell cycle-related expression of surface antigens on myelomonocytic leukemia cells

We investigated the relationship between the expression of surface antigens and the cell cycle phase in leukemic cells from cell lines and one patient using two-color flow cytometry, in order to determine the reason for the uneven expression of some markers which frequently leads to equivocal results as to leukemic phenotyping. As a result, it was demonstrated that monocyte-related differentiation markers, including I2, My4, Mo1 and Mo2, on monocytoid leukemic cells are preferentially expressed at the G0/G1 phase. Consequently, it is expected that the positivities for such markers vary with the proliferation status of the leukemic cells.

Effect of prostaglandin E2 on gamma-interferon and 1,25(OH)2D3 vitamin D3-induced c-myc reduction during HL-60 cell differentiation

The effect of prostaglandin E2 (PGE2) on the reduction of c-myc expression during the differentiation of the human leukemic cell line, HL-60, was examined. PGE2, a potent inducer of intracellular cyclic AMP (cAMP) in HL-60 cells, augmented monocyte-associated cell surface antigens induced by human gamma-interferon (IFN-gamma) or 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3) in these cells. The elevation of intracellular cAMP was induced dose-dependently by PGE2, but not by IFN-gamma or 1,25(OH)2D3. Changes were also seen in functional differentiation, such as, the increase of phagocytic capability and superoxide generation. PGE2 also enhanced the reduction of c-myc expression and the down-regulation of transferrin receptor by IFN-gamma or 1,25(OH)2D3, whereas PGE2 alone did not induce these phenotypic changes. These data suggest that IFN-gamma and 1,25(OH)2D3 reduce c-myc expression of HL-60 cells by a mechanism other than the augmentation of intracellular cAMP.

Metabolism of the vitamin D3 derivative (24R)-hydroxycalcidiol by human promyelocytic leukemia cells (HL-60). Isolation and identification of (5Z) and (5E)-(24R)-19-nor-10-oxo-24-hydroxycalcidiol

Human promyelocytic leukemia cells (HL-60 cells) incubated with (24R)-hydroxy[26,27-methyl-3H]calcidiol (0.2 microCi) or non-radioactive (24R)-hydroxycalcidiol (370 micrograms) produced significant quantities of two new vitamin D3 (calciol) metabolites. The metabolites were isolated from HL-60 cell culture media by methanol/chloroform extraction and a series of chromatographic procedures. The two new metabolites were identified as (5Z)- and (5E)-(24R)-19-nor-10-oxo-24-hydroxycalcidiol by HPLC analysis, ultraviolet absorption spectrophotometry, mass spectrometry and Fourier-transform infrared spectrophotometry. According to the isolation and purification procedures, the total amounts of 3.04 micrograms (5Z)-(24R)-19-nor-10-oxo-24-hydroxycalcidiol (lambda max = 310 nm, epsilon = 17070 M-1 cm-1) and 8.89 micrograms (5E)-(24R)-19-nor-10-oxo-24-hydroxycalcidiol (lambda max = 312 nm, e = 24,500 M-1 cm-1) were calculated, assuming an Mr of 418. The activity of 19-nor-10-oxo-(24R)-hydroxycalcidiol to promote HL-60 cell differentiation was higher than the activity of the precursor (24R)-hydroxycalcidiol suggesting a possible biological action of this metabolite in HL-60 cells.

Rapid transcriptional down-regulation of c-myc expression during cyclic adenosine monophosphate-promoted differentiation of leukemic cells

Pharmacologic elevation of cyclic AMP (cAMP) promotes growth arrest and differentiation in a variety of transformed mammalian cells, including the HL-60 human promyelocytic leukemia cell line. However, mechanisms underlying this phenomenon are poorly understood. Because cellular oncogenes play a pivotal role in regulating proliferation and differentiation, we examined whether cAMP-promoted differentiation of HL-60 was preceded by a decrease in the expression of c-myc, a cellular oncogene both amplified and constitutively expressed in HL-60. We find that cyclic AMP elevation in HL-60 caused by three different pharmacologic regimens is followed by an abrupt, greater than 90% decrease in steady state c-myc mRNA levels within 3 h, well before detectable changes in proliferation and differentiation. This decrease, which occurs despite protein synthetic blockade, is attributable to transcriptional down-regulation of c-myc and is accompanied by changes in chromatin structure near c-myc promoter sites. Our findings establish that cAMP, a ubiquitous intracellular regulatory messenger previously known only to enhance gene transcriptional activity in higher eukaryotic cells, can also suppress transcription of a cellular oncogene, thereby suggesting a potential mechanism for cAMP-promoted differentiation.

Treatment of four patients with myelodysplastic syndrome with a small dose of aclacinomycin-A

The effect of a small dose of aclacinomycin-A (ACR) was examined in two patients with refractory anemia (RA) and two with refractory anemia with excess of blasts in transformation (RAEB-t). ACR (7 or 14 mg/m2) was given for 10 days in a 2-h per day drip infusion. Clinical symptoms and laboratory data improved in 3 of these 4 patients. In a patient with RA, marked increase in reticulocytes and elevation of the hemoglobin level from 6 to 9 g/dl was observed after two courses of ACR therapy. In two with RAEB-t, Auer's rod bearing cells disappeared in the bone marrow and megaloblastic change of the erythroblasts was diminished in one patient. Hemoglobin levels rose from 4.7 to 10 g/dl in one, and platelets and WBC increased in another. No effect was seen in a patient with RA. The cytoreductive effect of ACR was minor compared to the therapy with small dose of cytosine arabinoside (Ara-C). Therefore, ACR warrants further consideration for the treatment of patients with MDS.

Differentiated HL-60 promyelocytic leukaemia cells produce a factor inducing differentiation

The bipotential human promyelocytic leukaemia cell line HL-60 can be induced to differentiate into monocytic or granulocytic cells by treatment with 1,25 dihydroxyvitamin D3 (1,25(OH)2D3) or dimethylsulphoxide (DMSO) respectively. Conditioned media (CM) from 1,25(OH)2D3- or DMSO-treated cells were able to induce monocytic differentiation in fresh HL-60 cells as measured by induction of non-specific esterase and macrophage surface markers. CM from 1,25(OH)2D3-treated cells also led to a dose dependent loss of proliferative capacity in soft agar colony assays. These effects were not due to a toxic effect of the CM or to residual inducer present in the CM. gamma-interferon and GM-CSF were apparently not responsible for these effects. CM from the human histiocytic lymphoma cell line U937 led to only a low level of induction of macrophage differentiation in fresh HL-60 cells. The defect in HL-60 leukaemic cells may therefore be at the level of induction of an autonomously-produced differentiation factor.

Mandibular growth and histologic changes in condylar cartilage of rats intoxicated with vitamin D3 or 1,25(OH)2D3 and pair-fed (undernourished) rats

The mandibular condyles of 1,25(OH)2D3 or Vitamin D3 intoxicated rats were studied and compared with those of normal as well as pair-fed controls. Experimental animals were injected with either Vitamin D3 (2 mg/kg/day) or 1,25(OH)2D3 (400 ng/kg/day) for 19 days. Controls were given the solvent only, while pair-fed animals were restricted in their food intake for the same period of time, so that they exhibited a weight-curve similar to that of the experimental rats. The length of the mandibular ramus was measured in lateral radiographs of all mandibles. Demineralized coronal sections were obtained from all mandibular condyles and were stained with Mallory's connective tissue stain. The width of each zone within the condylar cartilage was measured. Experimental animals showed significant reduction in width of all layers within the condylar cartilage, with total lack of distinction between the maturation and hypertrophic zones. They also exhibited a significant retardation in growth of the mandible. Pair-fed animals had a normal width of the chondroprogenitor layer but significantly smaller maturation + hypertrophic zones (vs. controls). They also exhibited a significant retardation in mandibular growth but not to the same degree as did the intoxicated animals. Reduction in growth attributed to 1,25(OH)2D3 or Vitamin D3 intoxication is partly caused by undernutrition, which is a by-product of this condition. A further kinetic study is indicated to elucidate the mechanism of growth retardation and the differential effect on the various cartilage layers.

Metabolism of 25-hydroxycholecalciferol in human promyelocytic leukemia cells (HL-60). Isolation and identification of (5Z)- and (5E)-19-nor-10-oxo-25-hydroxycholecalciferol

Human promyelocytic leukemia cells incubated with 25-hydroxy[26,27-methyl-3H] cholecalciferol (1 microCi) or non-radioactive 25-hydroxycholecalciferol (550 micrograms) produced significant quantities of two vitamin D3 metabolites. The two metabolites were isolated and purified by methanol chloroform extraction and a series of chromatographic procedures. The metabolite purification and elution positions on these columns were followed by radioactivity and their ultraviolet absorption at 310 nm. The two metabolites have been unequivocally identified as (5Z)- and (5E)-19-nor-10-oxo-25-hydroxycholecalciferol by ultraviolet absorption spectrophotometry, mass spectrometry, Fourier-transform infrared spectrophotometry and co-chromatography with synthetic compounds on a high-performance liquid chromatograph. (5E)- but not (5Z)-19-nor-10-oxo-25-hydroxycholecalciferol was able to induce HL-60 cell phenotypic and functional differentiation. However, these two metabolites of 25-hydroxycholecalciferol did not bind specifically to the chick intestinal 3.7 S. receptor protein for 1 alpha,25-dihydroxycholecalciferol. The precise biological role of these metabolites is as yet unclear.

Vitamin D compounds. Effect on clonal proliferation and differentiation of human myeloid cells

We examined the effect of 1 alpha,25-dihydroxyvitamin D3 (1 alpha,25(OH)2D3) and a variety of vitamin D analogs on proliferation and differentiation of normal and leukemic myeloid clonogenic cells. Only cells from myeloid leukemic lines that contained relatively mature cells (HL-60, U937, THP, HEL, M1) were induced to differentiate and were inhibited in their clonal growth by exposure to 1 alpha,25(OH)2D3 (50% inhibition, 3 X 10(-8)-8 X 10(-10) M). A fluorinated analog of vitamin D was 5-10-fold more potent than 1 alpha,25(OH)2D3. Cells from a human myeloblast line (KG-1) and normal human granulocyte-monocyte stem cells (GM-CFC), both of which depend on colony-stimulating factor (CSF) for clonal growth, were stimulated in their clonal proliferation by 1 alpha,25(OH)2D3 in the presence of suboptimal concentrations of CSF. Leukemic cells from 10 of 14 patients with myeloid leukemia, but not normal GM-CFC from 12 patients in remission, were markedly inhibited in their clonal proliferation by 1 alpha,25(OH)2D3. Our results suggest that 1 alpha,25(OH)2D3 may be a cofactor in hematopoiesis and that vitamin D analogs may have a differential effect on normal versus leukemic growth.

A computerized histomorphometric study of the effects of intoxication with vitamin D3 or 1,25 (OH)2D3 on growth and dentin production of impeded and unimpeded rat incisors

The effects of Vitamin D3 and 1,25(OH)2D3 intoxication on growth and dentinogenesis were studied in impeded and unimpeded rat incisors. Animals were intoxicated either with Vitamin D3 (2 mg/kg/day) or 1,25(OH)2D3 (400 ng/kg/day) for 19 days. Undecalcified transverse sections were obtained from all lower incisors. The outlines of all dental tissues were traced and fed into a computer which depicted the changes in all variables measured (circumference and cross-sectional area of tooth, pulp and dentin, width of dentin, CEJ [cemento-enamel junction] diameter and maximal labio-lingual diameter). Eruption rates, which had been recorded previously every 48 h, were used to compute the physiological age of each tooth site, so that only areas of similar age be compared. Growth. External dimensions of all intoxicated teeth decreased as the experiment progressed in contrast with control incisors which continued to increase in size. This effect was more pronounced in unimpeded incisors and may be due to the inhibitory influence of 1,25(OH)2D3 on cellular proliferation at the apical progenitor end. Dentinogenesis. 1,25(OH)2D3 intoxication had no significant effect on the rate of eruption and dentin formation in both impeded and unimpeded incisors. The same was true for impeded incisors intoxicated with Vitamin D3 but, both eruption and dentin production rates were impaired in Vitamin D3 unimpeded incisors.

Inhibitors of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced multinucleated cell formation and HTLV-I p19 antigen expression in HTLV-I-infected T-cell line KH-2Lo

To elucidate the biological mechanisms of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced phenotypic changes in HTLV-I virus-infected human T-cell line KH-2Lo cells, inhibitors of TPA-induced ornithine decarboxylase (ODC), protein kinases and calmodulin were examined for their effects on TPA-induced multinucleated cell formation and HTLV-I p19 antigen expression. Among the inhibitors of TPA-induced ODC activity, alpha-difluoromethyl ornithine (DFMO), 1,25(OH)2D3 and its analogues, and retinoic acid were tested. As inhibitors of protein kinases, 1-(5-isoquinolinyl-sulfonyl)-2-methylpiperazine (H-7), N-[2-(methylamino)ethyl]-5-isoquinoline-sulfonamide (H-8) and 1,(5-isoquinolynylsulfonyl)-2,3-dimethylpiperazine (H-5) were used. In addition, a calmodulin inhibitor, N-(4-aminobutyl)-5-chlor-2-naphthalenesulfonamide (W13) and its inactive analogue, N-(4-aminobutyl)-2-naphthalenesulfonamide (W12) were also tested. 1,25(OH)2D3 and its active analogues inhibited both TPA-induced HTLV-I p19 antigen expression and multinucleated cell formation after 4 days of culture with TPA. On the other hand, an inhibitor of ODC, DFMO, the protein kinase inhibitors, the calmodulin inhibitor and retinoic acid suppressed TPA-induced HTLV-I p19 expression but did not suppress multinucleated cell formation.

Interactions of 1,25-dihydroxyvitamin D3 and the immune system

A series of recent discoveries indicate that the hormonal form of vitamin D3, namely, 1,25(OH)2D3 plays a role in the regulation of the immune system. Cells of the monocyte/macrophage lineage possess receptors for 1,25(OH)2D3 regardless of their activation stage; cells of the lymphoid lineage also express these receptors but only at certain stages of their differentiation pathway and upon activation. Further, 1,25(OH)2D3 promotes the differentiation of monocyte precursors towards monocyte/macrophages and enhances monocyte function in antigen presentation. In addition 1,25(OH)2D3 is a potent inhibitor of interleukin-2 (IL-2) and suppresses effector functions of both T and B lymphocytes via IL-2-dependent as well as via IL-2-independent mechanisms. The theoretical and clinical implications of these discoveries are discussed.

Effect of 1,25-dihydroxyvitamin D3 on cytokine-induced thymocyte proliferation

To clarify the mechanism of the inhibitory effect of 1,25(OH)2D3 on lymphocyte proliferation, the effect of 1,25(OH)2D3 on murine thymocyte proliferation induced by interleukin 1 (IL-1), or 2 (IL-2) was examined. Physiological concentrations of 1,25(OH)2D3 inhibited thymocyte proliferation induced by IL-1 and IL-2 in similar fashion suggesting an inhibition of the response to IL-2 by this hormone. In addition, cortisone-resistant thymocytes (including a majority of medullary thymocytes), which proliferate more vigorously in response to IL-1 than do untreated thymocytes, were more sensitive to 1,25(OH)2D3 inhibition. Therefore, the inhibition of IL-2 production of the mature medullary thymocyte by this hormone was also suggested.

Transferrin receptor regulation is coupled to intracellular ferritin in proliferating and differentiating HL60 leukemia cells

Cultured myeloid leukemia cells display transferrin receptors but decrease receptor display after differentiation induction or accumulation of intracellular iron. To determine whether regulation of transferrin receptors and ferritin were linked under these disparate conditions, serum-free and fetal bovine serum (FBS) cultures of HL60 promyelocytic leukemia cells were used to investigate relationships between transferrin receptor display and intracellular ferritin. Using 125I-transferrin binding and immunofluorescence staining for transferrin receptors, HL60 cells cultured in serum-free, transferrin-free medium expressed fewer transferrin receptors and contained increased ferritin when compared to cells cultured with FBS or transferrin supplemented, serum-free medium. When placed in medium containing transferrin, cells previously grown in transferrin-free medium rapidly re-expressed transferrin receptors and decreased their ferritin content. HL60 cells induced to differentiate into granulocytes or macrophages also decreased transferrin receptor display and increased their ferritin content. Transferrin receptor display and ferritin content in both proliferating and differentiating myeloid leukemia cells are inversely related and their regulation is closely linked. Regulation of transferrin receptor display and ferritin synthesis may be important events regulating myeloid cell growth and differentiation.

1,25-Dihydroxyvitamin D3 regulates proliferation of activated T-lymphocyte subsets

The biologically active vitamin D metabolite, 1,25-(OH) 2D3 suppressed phytohaemagglutinin (PHA)-induced lymphocyte proliferation dose-dependently (0.1 nM-100 nM), and decreased the OKT4+/OKT8+ ratio and transferrin-receptor-positive (OKT9+) cells. A possible parallelism between expression of 1,25-(OH) 2D3 receptors and interleukin 2 (IL2)-receptors recognized by anti-Tac antibody was not confirmed in this study. However, the addition of exogenous IL2 abolished the inhibitory effects of 1,25-(OH) 2D3 on PHA-stimulated T-cell proliferation, and the decrease of OKT4+ and OKT9+ T-cell in this population. Among various vitamin D3 analogues examined, 1,25-(OH) 2D3 was the most potent anti-proliferative effect, followed in order by 1,24S-(OH) 2D3, 1 alpha OH D3, 25 OH D3 and 24,25-(OH) 2D3.

Role of transferrin, Fe, and transferrin receptors in myeloid leukemia cell growth. Studies with an antitransferrin receptor monoclonal antibody

In previous studies, antitransferrin receptor antibody 42/6 inhibited growth of normal granulocyte/macrophage progenitors and some malignant myeloid cells. In these studies, leukemia cell lines cultured without serum and fresh leukemia cells were used to investigate the roles of Fe, transferrin receptors, and transferrin in leukemia cell growth, and mechanisms of 42/6 inhibition and resistance. HL60 and KG-1 leukemia cells grown in serum-free medium were inhibited by 42/6. In contrast to results in fetal calf serum (FCS), soluble Fe (ferric nitriloacetate) reversed 42/6 growth inhibition of serum-free HL60 cells. When HL60 cells were adapted for growth in serum-free, transferrin-free medium, they became refractory to 42/6 growth inhibition. By using radiolabeled transferrin and 42/6, HL60 cells cultured in FCS and transferrin displayed similar quantities of transferrin receptors (29,000-30,000/cell) and similar Kd's (3.8-4.9 X 10(-9) M). Cells grown in transferrin-free medium showed a similar Kd (3.1 X 10(-9) M), but fewer transferrin binding sites (5,000/cell). Transferrin-independent cells contained a log higher concentration of intracellular ferritin. For both FCS and serum-free HL60 cells, calculated affinities for 42/6 were lower (5.7-10.0 X 10(-9) M), but the number of binding sites was three- to fourfold higher. To investigate further the relationship between receptor display and antibody inhibition in proliferating normal and malignant myeloid cells, simultaneous immunofluorescence was used to determine the cell cycle status of transferrin receptor-positive cells. Malignant cells in S + G2/M displayed approximately 50% of the amount of transferrin receptors detected in normal dividing colony-stimulating factor-stimulated marrow cells. Receptor display by dividing cells from two patients with acute nonlymphocytic leukemia was variable. When HL60 cells were exposed to dimethyl sulfoxide, transferrin receptor display decreased, and 42/6 growth inhibition was abrogated or greatly diminished. The presence of 42/6 did not prevent dimethyl sulfoxide-induced HL60 differentiation in serum-containing or serum-free cultures. We conclude that human leukemia cells require Fe for growth and that 42/6 inhibits transferrin-dependent cells by Fe deprivation. Some dividing normal and differentiating malignant cells display reduced transferrin receptors, and can also escape antibody inhibition. The increased ferritin levels and decreased transferrin receptors in transferrin-independent HL60 cells confirm the inverse relationship between cell ferritin content and transferrin receptor display. These studies indicate a critical role for Fe in leukemia cell growth and possible roles in cellular differentiation.

Dormant tumor cells in liver and brain. An autopsy study on metastasizing tumors

In 96 of 100 autopsy cases with metastasizing tumor diseases single disseminated tumor cells were detected in liver or brain tissues. These tumor cells appear to be in a resting state. Most of the resting or dormant tumor cells (dtc) are distinguishable from tumor cells within metastasis (mtc) by morphological criteria such as cell size or density, shape and size of the nucleus. These observations suggest that disseminated cells from many primary tumors might pass through a resting (Go) state before they eventually initiate malignant cell growth and give rise to metastatic colonies. Most likely the dtc are not affected by systemic chemotherapy.

In vitro drug testing using hemopoietic cells: goals and limitations

In vitro drug sensitivity is one of many biologic variables which may predict in vivo drug response. Even if in vitro assays provide relevant data, for some tumors, variable levels of stem-cell origin, differentiation, tumor heterogeneity, or self renewal may be more important than cytotoxicity to proliferating cells. Although ANLL has been used here frequently as a model, it may not be the most appropriate tumor for study. Unlike many cancers, in ANLL, primary drug resistance is unusual, and in relapse, secondary drug resistance is usually incomplete. It has been suggested that in vitro drug sensitivity predicts remissions for patients who do not die of infection or remain aplastic during induction therapy. However, for the majority of patients, this argument acknowledges the overriding importance of biologic variables other than in vitro drug cytotoxicity. For rapidly growing tumors, such as Burkitt's lymphoma, rapid emergence of drug resistance related to disease burden may be the most important response determinant. Perhaps in other tumors, in vitro drug sensitivity will be an independent variable of overriding importance. To determine the role of in vitro drug testing, trials examining in vitro drug sensitivity must meet stringent criteria. The assays should use well-defined and reproducible cultures and drug exposures. The trials must be large enough, contain homogenously treated patients, and use carefully defined response and survival endpoints. Decision rules derived from such trials must be further tested by prospective evaluation. Investigators conducting these trials must be prepared to search for important in vitro results reflecting tumor biology and to analyze in vitro drug sensitivity as only one continuous variable determining in vivo responses. Such trials will be difficult to conduct and expensive. In the final analysis, in vitro assays may find their most important roles as preclinical drug screens and models for in vitro drug resistance. Further insights into molecular genetics of malignant transformation and drug resistance may make such assays obsolete, but for the present, they provide important insights into tumor variability and mechanisms of drug response.