Vitamin D is not really a vitamin but the precursor to the potent steroid hormone calcitriol, which has widespread actions throughout the body. Calcitriol regulates numerous cellular pathways that ...could have a role in determining cancer risk and prognosis. Although epidemiological and early clinical trials are inconsistent, and randomized control trials in humans do not yet exist to conclusively support a beneficial role for vitamin D, accumulating results from preclinical and some clinical studies strongly suggest that vitamin D deficiency increases the risk of developing cancer and that avoiding deficiency and adding vitamin D supplements might be an economical and safe way to reduce cancer incidence and improve cancer prognosis and outcome.
► Calcitriol, (active form of vitamin D) exerts anticancer effects in breast cancer models. ► Calcitriol inhibits prostaglandin synthesis and exerts anti-inflammatory effects. ► Calcitriol inhibits ...estrogen synthesis and signaling and may be beneficial in ER+breast cancer. ► Dietary vitamin D can be converted to calcitriol in the breast and can exert anticancer effects. ► Calcitriol and dietary vitamin D may be useful in breast cancer treatment and chemoprevention.
Calcitriol (1,25-dihydroxyvitamin D3), the hormonally active form of vitamin D, inhibits the growth of many malignant cells including breast cancer (BCa) cells. The mechanisms of calcitriol anticancer actions include cell cycle arrest, stimulation of apoptosis and inhibition of invasion, metastasis and angiogenesis. In addition we have discovered new pathways of calcitriol action that are especially relevant in inhibiting the growth of estrogen receptor positive (ER+) BCa cells. Calcitriol suppresses COX-2 expression and increases that of 15-PGDH thereby reducing the levels of inflammatory prostaglandins (PGs). Our in vitro and in vivo studies show that calcitriol decreases the expression of aromatase, the enzyme that catalyzes estrogen synthesis selectively in BCa cells and in the mammary adipose tissue surrounding BCa, by a direct repression of aromatase transcription via promoter II as well as an indirect effect due to the reduction in the levels of PGs, which are major stimulator of aromatase transcription through promoter II. Calcitriol down-regulates the expression of ERα and thereby attenuates estrogen signaling in BCa cells including the proliferative stimulus provided by estrogens. Thus the inhibition of estrogen synthesis and signaling by calcitriol and its anti-inflammatory actions will play an important role in inhibiting ER+BCa. We hypothesize that dietary vitamin D would exhibit similar anticancer activity due to the presence of the enzyme 25-hydroxyvitamin d-1α-hydroxylase (CYP27B1) in breast cells ensuring conversion of circulating 25-hydroxyvitamin D to calcitriol locally within the breast micro-environment where it can act in a paracrine manner to inhibit BCa growth. Cell culture and in vivo data in mice strongly suggest that calcitriol and dietary vitamin D would play a beneficial role in the prevention and/or treatment of ER+BCa in women.
Aromatase, the enzyme that catalyzes estrogen synthesis, is critical for the progression of estrogen receptor-positive breast cancer (BCa) in postmenopausal women. We show that calcitriol, the ...hormonally active form of vitamin D, regulates the expression of aromatase in a tissue-selective manner. Calcitriol significantly decreased aromatase expression in human BCa cells and adipocytes and caused substantial increases in human osteosarcoma cells (a bone cell model exhibiting osteoblast phenotype in culture) and modest increases in ovarian cancer cells. Calcitriol administration to immunocompromised mice bearing human BCa xenografts decreased aromatase mRNA levels in the tumors and the surrounding mammary adipose tissue but did not alter ovarian aromatase expression. In BCa cells, calcitriol also reduced the levels of prostaglandins (PGs), major stimulators of aromatase transcription, by suppressing the expression of cyclooxygenase-2 (which catalyzes PG synthesis) and increasing that of 15-hydroxyprostaglandin dehydrogenase (which catalyzes PG degradation). The mechanism of aromatase down-regulation by calcitriol in BCa cells is therefore 2-fold: a direct repression of aromatase transcription via promoter II through the vitamin D-response elements identified in this promoter and an indirect suppression by reducing the levels of PGs. Combinations of calcitriol with three different aromatase inhibitors (AIs) caused enhanced inhibition of BCa cell growth. The combination of calcitriol and an AI may have potential benefits for BCa therapy. In addition to augmenting the ability of AIs to inhibit BCa growth, calcitriol acting as a selective aromatase modulator that increases aromatase expression in bone would reduce the estrogen deprivation in bone caused by the AIs, thus ameliorating the AI-induced side effect of osteoporosis.
In addition to its known anti-cancer effects, calcitriol inhibits estrogen synthesis in breast cancer cells by directly repressing aromatase transcription and indirectly decreasing aromatase expression by reducing prostaglandin levels.
Calcitriol (1,25-dihydroxyvitamin D3), the hormonally active metabolite of vitamin D, exerts its anti-proliferative activity in breast cancer (BCa) cells by multiple mechanisms including the ...downregulation of the expression of estrogen receptor α (ER). We analyzed an ∼3.5 kb ER promoter sequence and demonstrated the presence of two potential negative vitamin D response elements (nVDREs), a newly identified putative nVDRE upstream at -2488 to -2473 bp (distal nVDRE) and a previously published sequence (proximal nVDRE) at -94 to -70 bp proximal to the P1 start site. Transactivation analysis using ER promoter deletion constructs and heterologous promoter-reporter constructs revealed that both nVDREs functioned to mediate calcitriol transrepression. In the electrophoretic mobility shift assay, the vitamin D receptor (VDR) showed strong binding to both nVDREs in the presence of calcitriol, and the chromatin immunoprecipitation assay demonstrated the recruitment of the VDR to the distal nVDRE site. Mutations in the 5' hexameric DNA sequence of the distal nVDRE resulted in the loss of calcitriol-mediated transrepression and the inhibition of protein-DNA complex formation, demonstrating the importance of these nucleotides in VDR DNA binding and transrepression. A putative nuclear factor-Y (NFY) binding site, identified within the distal nVDRE, led to the findings that NFY bound to the distal nVDRE site interfered with the binding of the VDR at the site and reduced calcitriol-mediated transrepression. In conclusion, the ER promoter region contains two negative VDREs that act in concert to bind to the VDR and both nVDREs are required for the maximal inhibition of ER expression by calcitriol. The suppression of ER expression and estrogen-mediated signaling by calcitriol in BCa cells suggests that vitamin D may be useful in the treatment of ER+ BCa.
Calcitriol exhibits antiproliferative and pro-differentiation effects in prostate cancer. Our goal is to further define the mechanisms underlying these actions. We studied established human prostate ...cancer cell lines and primary prostatic epithelial cells and showed that calcitriol regulated the expression of genes involved in the metabolism of prostaglandins (PGs), known stimulators of prostate cell growth. Calcitriol significantly repressed the mRNA and protein expression of prostaglandin endoperoxide synthase/cyclooxygenase-2 (COX-2), the key PG synthesis enzyme. Calcitriol also up-regulated the expression of 15-hydroxyprostaglandin dehydrogenase, the enzyme initiating PG catabolism. This dual action was associated with decreased prostaglandin E2 secretion into the conditioned media of prostate cancer cells exposed to calcitriol. Calcitriol also repressed the mRNA expression of the PG receptors EP2 and FP, providing a potential additional mechanism of suppression of the biological activity of PGs. Calcitriol treatment attenuated PG-mediated functional responses, including the stimulation of prostate cancer cell growth. The combination of calcitriol with nonsteroidal anti-inflammatory drugs (NSAIDs) synergistically acted to achieve significant prostate cancer cell growth inhibition at approximately 2 to 10 times lower concentrations of the drugs than when used alone. In conclusion, the regulation of PG metabolism and biological actions constitutes a novel pathway of calcitriol action that may contribute to its antiproliferative effects in prostate cells. We propose that a combination of calcitriol and nonselective NSAIDs might be a useful chemopreventive and/or therapeutic strategy in men with prostate cancer, as it would allow the use of lower concentrations of both drugs, thereby reducing their toxic side effects.
Diaphyseal long bone cortical tissue from 30 patients with lethal perinatal Sillence II and progressively deforming Sillence III osteogenesis imperfecta (OI) has been studied at multiple levels of ...structural resolution. Interpretation in the context of woven to lamellar bone formation by mesenchymal osteoblasts (MOBLs) and surface osteoblasts (SOBLs) respectively demonstrates lamellar on woven bone synthesis as an obligate self-assembly mechanism and bone synthesis following the normal developmental pattern but showing variable delay in maturation caused by structurally abnormal or insufficient amounts of collagen matrix. The more severe the variant of OI is, the greater the persistence of woven bone and the more immature the structural pattern; the pattern shifts to a structurally stronger lamellar arrangement once a threshold accumulation for an adequate scaffold of woven bone has been reached. Woven bone alone characterizes lethal perinatal variants; variable amounts of woven and lamellar bone occur in progressively deforming variants; and lamellar bone increasingly forms rudimentary and then partially compacted osteons not reaching full compaction. At differing levels of microscopic resolution: lamellar bone is characterized by short, obliquely oriented lamellae with a mosaic appearance in progressively deforming forms; polarization defines tissue conformations and localizes initiation of lamellar formation; ultrastructure of bone forming cells shows markedly dilated rough endoplasmic reticulum (RER) and prominent Golgi bodies with disorganized cisternae and swollen dispersed tubules and vesicles, structural indications of storage disorder/stress responses and mitochondrial swelling in cells with massively dilated RER indicating apoptosis; ultrastructural matrix assessments in woven bone show randomly oriented individual fibrils but also short pericellular bundles of parallel oriented fibrils positioned obliquely and oriented randomly to one another and in lamellar bone show unidirectional fibrils that deviate at slight angles to adjacent bundles and obliquely oriented fibril groups consistent with twisted plywood fibril organization. Histomorphometric indices, designed specifically to document woven and lamellar conformations in normal and OI bone, establish ratios for: i) cell area/total area X 100 indicating the percentage of an area occupied by cells (cellularity index) and ii) total area/number of cells (pericellular matrix domains). Woven bone is more cellular than lamellar bone and OI bone is more cellular than normal bone, but these findings occur in a highly specific fashion with values (high to low) encompassing OI woven, normal woven, OI lamellar and normal lamellar conformations. Conversely, for the total area/number of cells ratio, pericellular matrix accumulations in OI woven are smallest and normal lamellar largest. Since genotype-phenotype correlation is not definitive, interposing histologic/structural analysis allowing for a genotype-histopathologic-phenotype correlation will greatly enhance understanding and clinical management of OI.
•Mosaic appearance of lamellar bone composed of short lamellae at oblique angles•Histomorphometry establishes new cellularity indices for woven and lamellar bone.•Golgi bodies by TEM show irregular dispersed cisternae and swollen tubulo-vesicles.•Changes in matrix conformation along woven to lamellar continuum reflect OI severity.
Bone metastases are a common complication of breast cancer. We have demonstrated that intermittent administration of parathyroid hormone (PTH1-34) reduces the incidence of bone metastases in murine ...models of breast cancer by acting on osteoblasts to alter the bone microenvironment. Here, we examined the role of signaling mediated by PTH 1 receptor (PTH1R) in both osteoblasts and breast cancer cells in influencing bone metastases. In mice with impaired PTH1R signaling in osteoblasts, intermittent PTH did not reduce bone metastasis. Intermittent PTH also did not reduce bone metastasis when expression of PTH1R was knocked down in 4T1 murine breast cancer cells by shRNA. In 4T1 breast cancer cells, PTH decreased expression of PTH-related protein (PTHrP), implicated in the vicious cycle of bone metastases. Knockdown of PTHrP in 4T1 cells significantly reduced migration toward MC3T3-E1 osteoblasts, and migration was further inhibited by treatment with intermittent PTH. Conversely, overexpression of PTHrP in 4T1 cells increased migration toward MC3T3-E1 osteoblasts, and this was not inhibited by PTH. In conclusion, PTH1R expression is crucial in both osteoblasts and breast cancer cells for PTH to reduce bone metastases, and in breast cancer cells, this may be mediated in part by suppression of PTHrP.
In a search for improved therapies for prostate cancer, we investigated the effect of genistein in combination with 1alpha-25-dihydroxyvitamin D3 1,25(OH)2D3, on the growth of DU145 human prostate ...cancer cells. DU145 cells were very resistant to the growth inhibitory action of 1,25(OH)2D3 or genistein when administered individually. However, the combination caused a significant growth inhibition seen at lower concentrations of both agents. 1,25(OH)2D3 induces the expression of the CYP24 gene, which codes for the enzyme that initiates the catabolism of 1,25(OH)2D3. We showed for the first time that genistein at low doses (50-100 nM) directly inhibited CYP24 at the enzyme level. Addition of genistein to mitochondrial preparations inhibited CYP24 enzyme activity in a noncompetitive manner. CYP24 inhibition by genistein increased the half-life of 1,25(OH)2D3 thereby augmenting the homologous up-regulation of the vitamin D receptor (VDR) both at the mRNA and protein levels. Genistein co-treatment enhanced 1,25(OH)2D3-mediated transactivation of the vitamin D responsive reporters OC-Luc and OP-Luc transfected into DU145 cells. Consistent with the growth inhibition due to the combination treatment, significant changes in the expression of genes involved in growth arrest and apoptosis were seen. We conclude that genistein potentiates the antiproliferative actions of 1,25(OH)2D3 in DU145 cells by two mechanisms: (i) an increase in the half-life of 1,25(OH)2D3 due to the direct inhibition of CYP24 enzyme activity and (ii) an amplification of the homologous up-regulation of VDR. Together these two effects lead to a substantial enhancement of the cellular responses to the growth inhibitory and pro-apoptotic signaling by 1,25(OH)2D3.
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