Chemoprevention of mammary carcinogenesis by 1alpha-hydroxyvitamin D5, a synthetic analog of Vitamin D

Organic Synthesis of New Secosteroids from Fucosterol, Its Intestinal Absorption by Caco-2 Cells, and Simulation of the Biological Activities of Vitamin D

We previously examined the cellular uptake of six types of vitamin D in human intestinal Caco-2 cells. Since vitamins D5-D7 were commercially unavailable, we synthesized these compounds organically before studying them. This process led us to understand that new secosteroids could be generated as vitamin D candidates, depending on the sterol used as the starting material. We obtained two new secosteroids-compounds 3 and 4-from fucosterol in the current study. We investigated the intestinal absorption of these compounds using Caco-2 cells cultured in Transwells and compared the results with vitamin D3, a representative secosteroid. The intestinal absorption of compound 4 was comparable to that of vitamin D3. Compound 3 showed similar uptake levels but transported about half as much as vitamin D3. These compounds demonstrated intestinal absorption at the cellular level. Vitamin D is known for its diverse biological activities manifest after intestinal absorption. Using PASS online simulation, we estimated the biological activity of compound 3's activated form. In several items indicated by PASS, compound 3 exhibited stronger biological activity than vitamins D2-D7 and was also predicted to have unique biological activities.

Calcitriol and Calcidiol Can Sensitize Melanoma Cells to Low⁻LET Proton Beam Irradiation

Proton beam irradiation promises therapeutic utility in the management of uveal melanoma. Calcitriol (1,25(OH)₂D₃)—the biologically active metabolite of vitamin D₃—and its precursor, calcidiol (25(OH)D₃), exert pleiotropic effects on melanoma cells. The aim of the study was to evaluate the effect of both calcitriol and calcidiol on melanoma cell proliferation and their response to proton beam irradiation. Three melanoma cell lines (human SKMEL-188 and hamster BHM Ma and BHM Ab), pre-treated with 1,25(OH)₂D₃ or 25(OH)D₃ at graded concentrations (0, 10, 100 nM), were irradiated with 0–5 Gy and then cultured in vitro. Growth curves were determined by counting the cell number every 24 h up to 120 h, which was used to calculate surviving fractions. The obtained survival curves were analysed using two standard models: linear-quadratic and multi-target single hit. Calcitriol inhibited human melanoma proliferation at 10 nM, while only calcidiol inhibited proliferation of hamster lines at 10 and 100 nM doses. Treatment with either 1,25(OH)₂D₃ or 25(OH)D₃ radio sensitized melanoma cells to low doses of proton beam radiation. The strength of the effect increased with the concentration of vitamin D₃. Our data suggest that vitamin D₃ may be an adjuvant that modifies proton beam efficiency during melanoma therapy.

Vitamin D derivatives enhance cytotoxic effects of H2O2 or cisplatin on human keratinocytes

Although the skin production of vitamin D is initiated by ultraviolet radiation type B (UVB), the role vitamin D plays in antioxidative or pro-oxidative responses remains to be elucidated. We have used immortalized human HaCaT keratinocytes as a model of proliferating epidermal cells to test the influence of vitamin D on cellular response to H2O2 or the anti-cancer drug, cisplatin. Incubation of keratinocytes with 1,25(OH)2D3 or its low calcemic analogues, 20(OH)D3, 21(OH)pD or calcipotriol, sensitized cells to ROS resulting in more potent inhibition of keratinocyte proliferation by H2O2 in the presence of vitamin D compounds. These results were supported by cell cycle and apoptosis analyses, and measurement of the mitochondrial transmembrane potentials (MMP), however some unique properties of individual secosteroids were observed. Furthermore, in HaCaT keratinocytes treated with H2O2, 1,25(OH)2D3, 21(OH)pD and calcipotriol stimulated the expression of SOD1 and CAT genes, but not SOD2, indicating a possible role of mitochondria in ROS-modulated cell death. 1,25(OH)2D3 also showed a short-term, protective effect on HaCaT keratinocytes, as exemplified by the inhibition of apoptosis and the maintenance of MMP. However, with prolonged incubation with H2O2 or cisplatin, 1,25(OH)2D3 caused an acceleration in the death of the keratinocytes. Therefore, we propose that lead vitamin D derivatives can protect the epidermis against neoplastic transformation secondary to oxidative or UV-induced stress through activation of vitamin D-signaling. Furthermore, our data suggest that treatment with low calcemic vitamin D analogues or the maintenance of optimal level of vitamin D by proper supplementation, can enhance the anticancer efficacy of cisplatin.

Antiproliferative Activity of Double Point Modified Analogs of 1,25-Dihydroxyvitamin D₂ Against Human Malignant Melanoma Cell Lines

Vitamin D is a lipid soluble steroid hormone with pleiotropic biological properties, including regulation of cell proliferation, differentiation and apoptosis. As to these desirable anticancer actions, 1,25-dihydroxyvitamins D and analogs have been reported to inhibit the proliferation and to induce differentiation of a wide variety of cancer cell types, including human malignant melanoma. However, there is a need for novel and more efficacious vitamin D analogs, and how best to design such is still an open issue. A series of double point modified (DPM) analogs of 1,25-dihydroxyvitamin D₂ (1,25(OH)₂D₂) induced differentiation of the vitamin D receptor (VDR) positive A375 and VDR negative SK-MEL 188b human malignant melanoma cell lines. Surprisingly, the dose of 1,25(OH)₂D₂ required to inhibit the proliferation of the A375 melanoma cell line by was several fold lower than that required in the case of 1,25(OH)₂D₃. To evaluate the impact of the modification in the side chain (additional 22-hydroxyl) and in the A-ring (5,6-trans modification), the regular side-chain of vitamin D₂ or D₃ was retained in the structure of our analogs. As expected, 5,6-trans modification was advantageous to enhancing the anti-proliferative activity of analogs, but not as a single point modification (SPM). Very unexpectedly, the additional 22-hydroxyl in the side-chain reduced significantly the anti-proliferative activity of both the natural and 5,6-trans series analogs. Finally, an induction of pigmentation in melanoma SK-MEL 188b cells was observed to sensitized cells to the effect of vitamin D analogs.

Comparative regulation of gene expression by 1,25-dihydroxyvitamin D3 in cells derived from normal mammary tissue and breast cancer

Previous genomic profiling of immortalized, non-tumorigenic human breast epithelial cells identified a set of 1,25-dihydroxyvitamin D3 (1,25D) regulated genes with potential relevance to breast cancer prevention. In this report, we characterized the effect of 1,25D on a subset of these genes in six cell lines derived from mammary tissue and breast cancers. Non-tumorigenic cell lines included hTERT-HME1, HME and MCF10A cells which are often used to model normal breast epithelial cells. Breast cancer cell lines included MCF7 cells (a model of early stage, estrogen-dependent disease), DCIS.com cells (a derivative of MCF10A cells that models in situ breast cancer) and Hs578T cells (a model of metastatic disease). All of these cell lines express the vitamin D receptor (VDR) and exhibit anti-cancer responses to 1,25D such as changes in proliferation, apoptosis, metabolism, or invasion. Our comparative data demonstrate highly variable responses to 1,25D (100nM, 24h) between the cell lines. In both hTERT-HME1 and HME cell lines, CYP24A1, SLC1A1 and ITGB3 were up-regulated whereas KDR, GLUL and BIRC3 were down-regulated in response to 1,25D. In contrast, no changes in SLC1A1, ITGB3 or GLUL expression were detected in 1,25D treated MCF10A cells although KDR and BIRC3 were down-regulated by 1,25D. The effects of 1,25D on these genes in the breast cancer cell lines were blunted, with the DCIS.com cells exhibiting the most similar responses to the immortalized hTERT-HME1 and HME cells. The differences in cellular responses were not due to general impairment in VDR function as robust CYP24A1 induction was observed in all cell lines. Thus, our data indicate that the genomic changes induced by 1,25D are highly cell-type specific even in model cell lines derived from the same tissue. The implication of these findings is that genomic responses to changes in vitamin D status in vivo are likely to be distinct from individual to individual, particularly in neoplastic tissue. This article is part of a Special Issue entitled '17th Vitamin D Workshop'.

Potent antiproliferative effects of 25-hydroxy-16-ene-23-yne-vitamin D₃ that resists the catalytic activity of both CYP27B1 and CYP24A1

The potency of 25-hydroxyvitamin D3 (25(OH)D3) is increased by several fold through its metabolism into 1α,25-dihydroxyvitamin D3 (1α,25(OH)2D3) by cytochrome P450 27B1 (CYP27B1). Thus, the pivotal role of 1α-hydroxylation in the activation of vitamin D compounds is well known. Here, we examined the metabolism of 25-hydroxy-16-ene-23-yne-vitamin D3 (25(OH)-16-ene-23-yne-D3), a synthetic analog of 25(OH)D3 in a cell-free system and demonstrated that 25(OH)-16-ene-23-yne-D3 is neither activated by CYP27B1 nor inactivated by cytochrome P450 24A1 (CYP24A1). These findings were also confirmed in immortalized normal human prostate epithelial cells (PZ-HPV-7) which are known to express both CYP27B1 and CYP24A1, indicating that the structural modifications featured in 25(OH)-16-ene-23-yne-D3 enable the analog to resist the actions of both CYP27B1 and CYP24A1. To provide intelligible structure-function information, we also performed molecular docking analysis between the analog and CYP27B1. Furthermore, 25(OH)-16-ene-23-yne-D3 was found to suppress the growth of PZ-HPV-7 cells with a potency equivalent to 1α,25(OH)2D3. The antiproliferative activity of 25(OH)-16-ene-23-yne-D3 was found to be vitamin D receptor (VDR)-dependent as it failed to inhibit the growth of mammary tumor cells derived from VDR-knockout mice. Furthermore, stable introduction of VDR into VDR-knockout cells restored the growth inhibition by 25(OH)-16-ene-23-yne-D3. Thus, we identified 25-hydroxy-16-ene-23-yne-vitamin D3 as a novel non-1α-hydroxylated vitamin D analog which is equipotent to 1α,25(OH)2D3 in its antiproliferative activity. We now propose that the low potency of the intrinsic VDR-mediated activities of 25(OH)D3 can be augmented to the level of 1α,25(OH)2D3 without its activation through 1α-hydroxylation by CYP27B1, but by simply preventing its inactivation by CYP24A1.

Decreased expression of CYP27B1 correlates with the increased aggressiveness of ovarian carcinomas

CYP27B1 hydroxylates 25-hydroxyvitamin D3 in position C1α into biologically active 1,25-dihydroxyvitamin D3, calcitriol. CYP27B1 is expressed in normal tissues and tumors. Since calcitriol indicates anticancer activities and CYP27B1 expression can be deregulated during malignant progression, we analyzed its expression in ovarian cancers in relation to pathomorphological features of tumors and overall survival (OS). Expression of CYP27B1 was evaluated in 61 ovarian tumors, 18 metastases and 10 normal ovaries. Normal ovarian epithelium showed the highest levels CYP27B1 with a significant decrease in its expression in ovarian cancers. Both poorly differentiated primary tumors and metastases showed the lowest level of CYP27B1 expression, while non-metastasizing tumors showed a higher CYP27B1 level than tumors that developed metastases. The expression of CYP27B1 was positively correlated with a lower proliferation rate, lower dynamism of tumor growth and tumor infiltrating lymphocyte response. Furthermore, CYP27B1 expression was negatively correlated with tumor cell modeling of their microenvironment. CYP27B1 expression was also associated with longer OS time. In summary, our results suggest that local expression of CYP27B1 in ovarian tumor cells can modify their behavior and promote a less aggressive phenotype by affecting local concentrations of active of vitamin D levels within the tumor microenvironment.

Vitamin D and breast cancer: emerging concepts

The benefit of vitamin D in cancer prevention and to certain extent therapy has been well recognized. The active form of vitamin D, 1,25-dihydroxycholecalciferol (1,25(OH)2 D3) is a natural ligand for vitamin D receptor (VDR). Since 1,25(OH)2D3 exerts toxic effects at a concentration that is beneficial, nearly 1500 analogs of vitamin D have been synthesized and evaluated for their efficacy in a variety of carcinogenesis and human cancer models both in vitro and in vivo. Among these only a handful of them have been approved for evaluation in clinical trials for leukemia, breast, prostate and colon cancers. The mechanism of vitamin D action is mediated by the nuclear VDR and the signaling cascade for its action is extensively reported. In this review we focus on the newer concepts for vitamin D action. These include (1) differential effects of vitamin D in maintaining cell proliferation when the cells are under stress but suppressing cell growth when the cells are transformed; (2) functional significance of VDR polymorphism in potential vitamin D responsiveness; (3) regulation of constitutive splicing of vitamin D target gene, CYP24a, by the hormone and its significance; and (4) regulation of microRNA by vitamin D in breast cancer. It is anticipated that the new work in these selective areas would expand the understanding of vitamin D in breast cancer prevention and therapy.

Cellular and molecular effects of vitamin D on carcinogenesis

Epidemiologic data suggest that the incidence and severity of many types of cancer inversely correlates with indices of vitamin D status. The vitamin D receptor (VDR) is highly expressed in epithelial cells at risk for carcinogenesis including those resident in skin, breast, prostate and colon, providing a direct molecular link by which vitamin D status impacts on carcinogenesis. Consistent with this concept, activation of VDR by its ligand 1,25-dihydroxyvitamin D (1,25D) triggers comprehensive genomic changes in epithelial cells that contribute to maintenance of the differentiated phenotype, resistance to cellular stresses and protection of the genome. Many epithelial cells also express the vitamin D metabolizing enzyme CYP27B1 which enables autocrine generation of 1,25D from the circulating vitamin D metabolite 25-hydroxyvitamin D (25D), critically linking overall vitamin D status with cellular anti-tumor actions. Furthermore, pre-clinical studies in animal models has demonstrated that dietary supplementation with vitamin D or chronic treatment with VDR agonists decreases tumor development in skin, colon, prostate and breast. Conversely, deletion of the VDR gene in mice alters the balance between proliferation and apoptosis, increases oxidative DNA damage, and enhances susceptibility to carcinogenesis in these tissues. Because VDR expression is retained in many human tumors, vitamin D status may be an important modulator of cancer progression in persons living with cancer. Collectively, these observations have reinforced the need to further define the molecular actions of the VDR and the human requirement for vitamin D in relation to cancer development and progression.

CARD-024, a vitamin D analog, attenuates the pro-fibrotic response to substrate stiffness in colonic myofibroblasts

Intestinal fibrosis is one of the major complications of Crohn's disease (CD) for which there are no effective pharmacological therapies. Vitamin D deficiency is common in CD, though it is not known whether this is a contributing factor to fibrosis, or simply a consequence of the disease itself. In CD, fibrosis is mediated mainly by activated intestinal myofibroblasts during remodeling of extracellular matrix in response to wound healing. We investigated the effects of CARD-024 (1-alpha-hydroxyvitamin D5), a vitamin D analog with minimal hypercalcemic effects, on the pro-fibrotic response of intestinal myofibroblasts to two fibrogenic stimuli: TGFβ stimulation and culture on a physiologically stiff matrix. TGFβ stimulated a fibrogenic phenotype in Ccd-18co colonic myofibroblasts, characterized by an increase in actin stress fibers and mature focal adhesions, and increased αSMA protein expression, while CARD-024 repressed αSMA protein expression in a dose-dependent manner. Culture of colonic myofibroblasts on physiological high stiffness substrates induced morphological changes with increased actin stress fibers and focal adhesion staining, induction of αSMA protein expression, FAK phosphorylation, induction of fibrogenic genes, and repression of COX-2 and IL-1β. CARD-024 treatment repressed the stiffness-induced morphological features including stellate cell morphology and the maturation of focal adhesions. CARD-024 repressed the stiffness-mediated induction of αSMA protein expression, FAK phosphorylation, and MLCK and ET-1 gene expression. In addition, CARD-024 partially stimulated members of the COX-2/IL-1β inflammatory pathway. In summary, CARD-024 attenuated the pro-fibrotic response of colonic myofibroblasts to high matrix stiffness, suggesting that vitamin D analogs such as CARD-024 may ameliorate intestinal fibrosis.

Dual functions of autophagy in the response of breast tumor cells to radiation: cytoprotective autophagy with radiation alone and cytotoxic autophagy in radiosensitization by vitamin D 3

In MCF-7 breast tumor cells, ionizing radiation promoted autophagy that was cytoprotective; pharmacological or genetic interference with autophagy induced by radiation resulted in growth suppression and/or cell killing (primarily by apoptosis). The hormonally active form of vitamin D, 1,25D 3, also promoted autophagy in irradiated MCF-7 cells, sensitized the cells to radiation and suppressed the proliferative recovery that occurs after radiation alone. 1,25D 3 enhanced radiosensitivity and promoted autophagy in MCF-7 cells that overexpress Her-2/neu as well as in p53 mutant Hs578t breast tumor cells. In contrast, 1,25D 3 failed to alter radiosensitivity or promote autophagy in the BT474 breast tumor cell line with low-level expression of the vitamin D receptor. Enhancement of MCF-7 cell sensitivity to radiation by 1,25D 3 was not attenuated by a genetic block to autophagy due largely to the promotion of apoptosis via the collateral suppression of protective autophagy. However, MCF-7 cells were protected from the combination of 1,25D 3 with radiation using a concentration of chloroquine that produced minimal sensitization to radiation alone. The current studies are consistent with the premise that while autophagy mediates a cytoprotective function in irradiated breast tumor cells, promotion of autophagy can also confer radiosensitivity by vitamin D (1,25D 3). As both cytoprotective and cytotoxic autophagy can apparently be expressed in the same experimental system in response to radiation, this type of model could be utilized to distinguish biochemical, molecular and/or functional differences in these dual functions of autophagy.

Androgen Receptor regulation of Vitamin D receptor in response of castration-resistant prostate cancer cells to 1α-Hydroxyvitamin D5 - a calcitriol analog

Calcitriol (1,25(OH)(2)D3) is cytostatic for prostate cancer (CaP), but had limited therapeutic utility due to hypercalcemia-related toxicities, leading to the development of low-calcemic calcitriol analogs. We show that one analog, 1-α-Hydroxyvitamin-D5 (1α(OH)D5), induced apoptosis in castration-sensitive LNCaP prostate cancer cells, but unlike calcitriol, did not increase androgen receptor (AR) transcriptional activity. LNCaP-AI, a castrate-resistant (CRCaP) LNCaP subline, was resistant to 1α(OH)D5 in the presence of androgens; however, androgen withdrawal (AWD), although ineffective by itself, sensitized LNCaP-AI cells to 1α(OH)D5. Investigation of the mechanism revealed that the vitamin D receptor (VDR), which mediates the effects of 1α(OH)D5, is downregulated in LNCaP-AI cells compared to LNCaP in the presence of androgens, whereas AWD restored VDR expression. Since LNCaP-AI cells expressed higher AR compared to LNCaP and AWD decreased AR, this indicated an inverse relationship between VDR and AR. Further, AR stimulation (by increased androgen) suppressed VDR, while AR downregulation (by ARsiRNA) stimulated VDR levels and sensitized LNCaP-AI cells to 1α(OH)D5 similar to AWD. Another cell line, pRNS-1-1, although isolated from a normal prostate, had lost AR expression in culture and adapted to androgen-independent growth. These cells expressed the VDR and were sensitive to 1α(OH)D5, but restoration of AR expression suppressed VDR levels and induced resistance to 1α(OH)D5 treatment. Taken together, these results demonstrate negative regulation of VDR by AR in CRCaP cells. This effect is likely mediated by prohibitin (PHB), which was inhibited by AR transcriptional activity and stimulated VDR in CRCaP, but not castrate-sensitive cells. Therefore, in castration sensitive cells, although the AR negatively regulates PHB, this does not affect VDR expression, whereas in CRCaP cells, negative regulation of PHB by the AR results in concomitant negative regulation of the VDR by the AR. These data demonstrate a novel mechanism by which 1α(OH)D5 prolong the effectiveness of AWD in CaP cells.

Cancer chemoprevention by natural products: how far have we come?

Since ancient times, natural products, herbs and spices have been used for preventing several diseases, including cancer. The term chemoprevention was coined in the late 1970s and referred to the prevention of cancer by selective use of phytochemicals or their analogs. The field utilizes experimental carcinogenesis models to examine the efficacy of chemopreventive agents in a stage-specific manner. The concept of using naturally derived chemicals as potential chemopreventive agents has advanced the field dramatically. Throughout the years, a vast number of chemopreventive agents present in natural products have been evaluated using various experimental models. A number of them have progressed to early clinical trials. More recently, the focus has been directed towards molecular targeting of chemopreventive agents to identify mechanism(s) of action of these newly discovered bioactive compounds. Moreover, it has been recognized that single agents may not always be sufficient to provide chemopreventive efficacy, and, therefore, the new concept of combination chemoprevention by multiple agents or by the consumption of "whole foods" has become an increasingly attractive area of study. Novel technologies, such as nanotechnology, along with a better understanding of cancer stem cells, are certain to continue the advancement of the field of cancer chemoprevention in years to come.

Cancer chemoprevention by natural products: how far have we come?

Since ancient times, natural products, herbs and spices have been used for preventing several diseases, including cancer. The term chemoprevention was coined in the late 1970s and referred to the prevention of cancer by selective use of phytochemicals or their analogs. The field utilizes experimental carcinogenesis models to examine the efficacy of chemopreventive agents in a stage-specific manner. The concept of using naturally derived chemicals as potential chemopreventive agents has advanced the field dramatically. Throughout the years, a vast number of chemopreventive agents present in natural products have been evaluated using various experimental models. A number of them have progressed to early clinical trials. More recently, the focus has been directed towards molecular targeting of chemopreventive agents to identify mechanism(s) of action of these newly discovered bioactive compounds. Moreover, it has been recognized that single agents may not always be sufficient to provide chemopreventive efficacy, and, therefore, the new concept of combination chemoprevention by multiple agents or by the consumption of "whole foods" has become an increasingly attractive area of study. Novel technologies, such as nanotechnology, along with a better understanding of cancer stem cells, are certain to continue the advancement of the field of cancer chemoprevention in years to come.

Gemini vitamin D analogues inhibit estrogen receptor-positive and estrogen receptor-negative mammary tumorigenesis without hypercalcemic toxicity

Numerous preclinical, epidemiologic, and clinical studies have suggested the benefits of vitamin D and its analogues for the prevention and treatment of cancer. However, the hypercalcemic effects have limited the use of 1alpha,25(OH)(2)D(3), the hormonally active form of vitamin D. To identify vitamin D analogues with better efficacy and low toxicity, we have tested >60 novel Gemini vitamin D analogues with a unique structure of two side chains for growth inhibition of breast cancer cells. Our initial studies found that some Gemini analogues are 5-15 times more active than 1alpha,25(OH)(2)D(3) in growth inhibition assay. In vivo experiments were designed to study the inhibitory effect of selected Gemini vitamin D analogues against mammary carcinogenesis by using (a) an N-methyl-N-nitrosourea-induced estrogen receptor (ER)-positive mammary tumor model and (b) an MCF10DCIS.com xenograft model of ER-negative mammary tumors. Among vitamin D analogues we tested, Gemini 0072 [1alpha,25-dihydroxy-20S-21(3-trideuteromethyl-3-hydroxy-4,4,4-trideuterobutyl)-23-yne-26,27-hexafluoro-19-nor-cholecalciferol] and Gemini 0097 [1alpha,25-dihydroxy-20R-21(3-trideuteromethyl-3-hydroxy-4,4,4-trideuterobutyl)-23-yne-26,27-hexafluoro-19-nor-cholecalciferol] administration inhibited by 60% the NMU-induced mammary tumor burden compared with the NMU-treated control group, but these compounds were devoid of hypercalcemia toxicity. In an ER-negative xenograft model, Gemini 0097 significantly suppressed tumor growth without hypercalcemia toxicity. We found that the inhibitory effect of Gemini 0097 was associated with an increased level of cyclin-dependent kinase inhibitor p21 and the insulin-like growth factor binding protein 3 in both ER-positive and ER-negative mammary tumors. Our results suggest that Gemini vitamin D analogues may be potent agents for the prevention and treatment of both ER-positive and ER-negative breast cancer without hypercalcemia toxicity.

Vitamin D, vitamin D analogs (deltanoids) and prostate cancer

'Vitamin D' is a generic term for a family of secosteroids, members of which bind to the vitamin D receptor. Calcitriol, the active form of vitamin D, has antiproliferative effects on many tumor cells. However, clinical use of calcitriol in cancer prevention or therapy is limited because it induces hypercalcemia at the necessary supraphysiological doses. The anti-tumor effects of vitamin D analogs (deltanoids) have been researched extensively; more than 3000 deltanoids have now been described. Prostate cancer is more common in northern geographic regions; mortality decreases with exposure to sunlight. As UV light is necessary for vitamin D synthesis in the skin, it has long been dogma that vitamin D is involved. This review concerns deltanoids that have been assessed for use in treating or preventing prostate cancer.

Toxicity and antitumor activity of the vitamin D analogs PRI-1906 and PRI-1907 in combined treatment with cyclophosphamide in a mouse mammary cancer model

PURPOSE

Active and less toxic vitamin D analogs could be useful for clinical applications. In the present study, we evaluated the toxicity and antitumor effect of two new synthetic analogs of vitamin D, namely PRI-1906 [(24E)-24a-Homo-(1S)-1,25-dihydroxyergocalciferol] and its side-chain unsaturated homo analog PRI-1907.

METHODS

The toxicity and calcemic activity, as well as antitumor effect of calcitriol analogs was investigated in vivo. The studies were performed in a mouse mammary 16/C cancer model. Since calcitriol and its analogs inhibited 16/C tumor growth only slightly, we applied them in the combined therapy with cyclophosphamide (CY). Moreover, cell cycle analysis and VDR and p27 expression were investigated.

RESULTS

The LD50 values after five daily subcutaneous (s.c.) injections were 7.8, 10.0 and 2.4 microg/kg per day for calcitriol, PRI-1906 and PRI-1907, respectively. The serum calcium level increased to 40, 23 and 63% over the control for these compounds. We also compare the antitumor activity of the PRI-1906 with the calcitriol and previously studied PRI-2191 (1,24-dihydroxyvitamin D3, tacalcitol). Statistically significant inhibition of tumor growth by calcitriol up to the eighth day was observed in all schedules applied. PRI-1906 inhibited the tumor growth at doses 1 and 5 microg/kg per day, and PRI-2191 only at the dose 5 microg/kg per day.

CONCLUSION

Addition of vitamin D analogs increased the antitumor effect of CY. PRI-1906 exhibited toxicity higher than PRI-2191 but lower than calcitriol and antitumor activity similar to both PRI-2191 and calcitriol. This new analog seems to be a good candidate for the combined treatment of mammary cancer.

Translational approaches for the prevention of estrogen receptor-negative breast cancer

Breast cancer prevention has focused heavily on endocrine interventions using selective estrogen receptor modulators and aromatase inhibitors. Tamoxifen, the stereotypical selective estrogen receptor modulator, significantly reduces the breast cancer incidence in high-risk women. Selective estrogen receptor modulators and aromatase inhibitors, however, only prevent the development of estrogen receptor-positive breast cancer and have no effect in reducing the risk of estrogen receptor-negative breast cancer, which has poor prognosis. Thus, preventive therapies for estrogen receptor-negative breast cancer are clearly needed. Recently, a number of novel chemopreventive agents targeting nonendocrine pathways have been developed and shown to prevent estrogen receptor-negative mammary tumorigenesis in animal models. These agents include rexinoids, selective cyclooxygenase-2 inhibitors, tyrosine kinase inhibitors, and others. In this review, we discuss the effects of selective estrogen receptor modulators and aromatase inhibitors, as well as novel agents targeting nonendocrine pathways. We also discuss the promise of combining these agents for the effective prevention of all forms of breast cancer.

25(OH)D3 and 1,25(OH)2D3 serum concentration and breast tissue expression of 1alpha-hydroxylase, 24-hydroxylase and Vitamin D receptor in women with and without breast cancer

1,25(OH)2D3 is an antiproliferative agent that may inhibit proliferation of breast cancer (BC) cells in vitro and BC development in animals. Epidemiological studies have shown a high incidence of BC in people less exposed to solar rays. To unravel the role of Vitamin D3 in BC patients, we have investigated serum levels of 25(OH)D3 and its active form 1,25(OH)2D3 as well as tissue expression of 1alpha-hydroxylase, 24-hydroxylase, and Vitamin D-receptor (VDR), determined by semiquantitative RT-PCR, in 88 Brazilian BC patients and 35 women without cancer (submitted to mammoplasties or resection of benign lesions). Median age of women with and without cancer was 51 and 46 years, respectively, and the majority of BC patients were classified as clinical stage II (67%). Although no differences in 25(OH)D3 serum concentration were found, 1,25(OH)2D3 (40+/-21 pg/ml) levels in BC patients were lower than in women without cancer (53+/-23). Our results indicate that 24-hydroxylase, VDR and 1alpha-hydroxylase mRNA tissue expression is similar in both groups and no correlation between 24-hydroxylase, 1alpha-hydroxylase, and VDR expression in breast tumors was found. A low 1,25(OH)2D3 serum concentration seems to be associated to breast cancer, however, the mechanism involved in this regulation is still unclear.

Human mammary epithelial cells express CYP27B1 and are growth inhibited by 25-hydroxyvitamin D-3, the major circulating form of vitamin D-3

1alpha,25-dihydroxycholecalciferol [1alpha,25(OH)2D3], the active form of cholecalciferol, is a negative growth regulator of breast cancer cells. CYP27B1 is a cytochrome P450-containing hydroxylase expressed in kidney and other tissues that generates 1alpha,25(OH)2D3 from an inactive vitamin D precursor 25-hydroxycholecalciferol [25(OH)D3]. In these studies, we tested the hypothesis that mammary cells express CYP27B1 and locally produce 1alpha,25(OH)2D3, which acts in an autocrine manner to regulate cell turnover. Using Western blot and quantitative real-time PCR, CYP27B1 mRNA and protein were detected in immortalized, nontumorigenic human mammary epithelial cell (HMEC) cultures. Furthermore, HMEC cultures were dose dependently growth inhibited by physiological concentrations of 25(OH)D3, suggesting that CYP27B1 converts this precursor cholecalciferol metabolite to 1alpha,25(OH)2D3, the ligand for the vitamin D receptor (VDR). In support of this suggestion, both 1alpha,25(OH)2D3 and 25(OH)D3 transactivated VDR in HMEC cultures, as measured by induction of a vitamin D responsive reporter gene and upregulation of CYP24, an endogenous VDR target gene. No induction of CYP24 by 25(OH)D3 was observed in mammary cells derived from CYP27B1 null mice. Similar results were observed in 2 independently derived immortalized HMEC lines as well as in primary cultures derived from human breast epithelium. These are the first studies to demonstrate that nontransformed human mammary cells express CYP27B1, that they are growth inhibited by physiologically relevant concentrations of 25(OH)D3, and that they provide a biological mechanism linking vitamin D status to breast cancer risk.

Vitamin D receptor (VDR) ablation alters carcinogen-induced tumorigenesis in mammary gland, epidermis and lymphoid tissues

The Vitamin D receptor (VDR) and its ligand, 1,25(OH)(2)D(3), regulate cell proliferation, differentiation and apoptosis in vitro, yet the physiological significance of this regulation is unclear. In these studies, we used VDR knockout (VDRKO) mice to examine the impact of VDR on chemical carcinogen-induced tumorigenesis in vivo. Wild type (WT) and VDRKO littermates were fed a high calcium diet to prevent disturbances in calcium homeostasis and were gavaged with dimethylbenzanthracence (DMBA) using a protocol designed to induce mammary tumors. Compared to WT littermates, VDRKO mice exhibited an increased incidence of mammary gland hyperplasia and a higher percentage of hormone independent tumors with squamous differentiation. VDR ablation also significantly enhanced tumor development in epidermis and lymphoid tissues, but did not affect tumor development in ovary, uterus, lung or liver. These data indicate that VDR ablation alters susceptibility to DMBA-induced carcinogenesis in a tissue specific fashion, and provide support that optimal VDR signaling may act to suppress tumorigenesis.

Toxicity and antineoplastic effect of (24R)-1,24-dihydroxyvitamin D3 (PRI-2191)

Many efforts have been made to obtain active and less toxic Vitamin D analogs for new clinical applications. The results of previous studies demonstrated the efficacy and safety of topical treatment of psoriasis with one of these analogs, 1,24-dihydroxyvitamin D(3), tacalcitol (1,24-(OH)(2)D(3)). In the present study, we evaluated the toxicity and antitumor effect of this analog. Lethal toxicity of 1,24-(OH)(2)D(3) after s.c. injection was significantly lower than that of calcitriol. No significant differences were observed in the toxicity of the analogs when administered p.o. Calcium levels in the serum of mice treated with calcitriol were significantly higher (111%) than those in mice treated with 1,24-(OH)(2)D(3) (89%) at 5 day after the first s.c. (10 microg/kg/day) administration in comparison to the control (healthy, untreated animals). Oral administration increased the calcium level by 78% for calcitriol and only to 47% over the control for 1,24-(OH)(2)D(3). Parallel administration of clodronate prevented the calcitriol- and 1,24-(OH)(2)D(3)-induced lethal toxicity and also prevented increase in calcium levels. Single therapy with calcitriol did not affect tumor growth in the 16/C mouse mammary cancer model. In contrary, 1,24-(OH)(2)D(3) alone reduced tumor volume to 41% of control. Cisplatin alone did not affect growth of 16/C tumor in these conditions. The growth of tumors in the presence of cisplatin was inhibited by 1,24-(OH)(2)D(3) but not by calcitriol. Interestingly, the inhibition of tumor growth in cisplatin-treated mice by 1,24-(OH)(2)D(3) was greater, than that observed in mice treated with this analog alone. In conclusion, 1,24-(OH)(2)D(3) revealed higher antitumor and lower calcemic activity and toxicity than calcitriol. Application of biphosphonates along with Vitamin D analogs is sufficient to overcome the calcemic and toxic side effects of the proposed treatment.

Dietary and medicinal antimutagens and anticarcinogens: molecular mechanisms and chemopreventive potential--highlights of a symposium

Antimutagens and anticarcinogens are common amongst many traditional herbal remedies and dietary therapies. With increased understanding of the mechanistic basis of cancer development and cancer prevention, we are now better aware of ways in which some of these traditional remedies may act at the cellular or subcellular levels. This special issue features some of the highlights of the conference on this topic that was held in Seoul on October 17-19, 2001.