New vitamin D analogs as potential therapeutics in melanoma

Biological Effects of CYP11A1-Derived Vitamin D and Lumisterol Metabolites in the Skin

Novel pathways of vitamin D3, lumisterol 3 (L3), and tachysterol 3 (T3) activation have been discovered, initiated by CYP11A1 and/or CYP27A1 in the case of L3 and T3. The resulting hydroxymetabolites enhance protection of skin against DNA damage and oxidative stress; stimulate keratinocyte differentiation; exert anti-inflammatory, antifibrogenic, and anticancer activities; and inhibit cell proliferation in a structure-dependent manner. They act on nuclear receptors, including vitamin D receptor, aryl hydrocarbon receptor, LXRα/β, RAR-related orphan receptor α/γ, and peroxisome proliferator-activated receptor-γ, with selectivity defined by their core structure and distribution of hydroxyl groups. They can activate NRF2 and p53 and inhibit NF-κB, IL-17, Shh, and Wnt/β-catenin signaling. Thus, they protect skin integrity and physiology.

Malignant Melanoma: An Overview, New Perspectives, and Vitamin D Signaling

Melanoma, originating through malignant transformation of melanin-producing melanocytes, is a formidable malignancy, characterized by local invasiveness, recurrence, early metastasis, resistance to therapy, and a high mortality rate. This review discusses etiologic and risk factors for melanoma, diagnostic and prognostic tools, including recent advances in molecular biology, omics, and bioinformatics, and provides an overview of its therapy. Since the incidence of melanoma is rising and mortality remains unacceptably high, we discuss its inherent properties, including melanogenesis, that make this disease resilient to treatment and propose to use AI to solve the above complex and multidimensional problems. We provide an overview on vitamin D and its anticancerogenic properties, and report recent advances in this field that can provide solutions for the prevention and/or therapy of melanoma. Experimental papers and clinicopathological studies on the role of vitamin D status and signaling pathways initiated by its active metabolites in melanoma prognosis and therapy are reviewed. We conclude that vitamin D signaling, defined by specific nuclear receptors and selective activation by specific vitamin D hydroxyderivatives, can provide a benefit for new or existing therapeutic approaches. We propose to target vitamin D signaling with the use of computational biology and AI tools to provide a solution to the melanoma problem.

Nutritional Interventions for Patients with Melanoma: From Prevention to Therapy-An Update

Melanoma is an aggressive skin cancer, whose incidence rates have increased over the past few decades. Risk factors for melanoma are both intrinsic (genetic and familiar predisposition) and extrinsic (environment, including sun exposure, and lifestyle). The recent advent of targeted and immune-based therapies has revolutionized the treatment of melanoma, and research is focusing on strategies to optimize them. Obesity is an established risk factor for several cancer types, but its possible role in the etiology of melanoma is controversial. Body mass index, body surface area, and height have been related to the risk for cutaneous melanoma, although an 'obesity paradox' has been described too. Increasing evidence suggests the role of nutritional factors in the prevention and management of melanoma. Several studies have demonstrated the impact of dietary attitudes, specific foods, and nutrients both on the risk for melanoma and on the progression of the disease, via the effects on the oncological treatments. The aim of this narrative review was to summarize the main literature results regarding the preventive and therapeutic role of nutritional schemes, specific foods, and nutrients on melanoma incidence and progression.

Knocking out the Vitamin D Receptor Enhances Malignancy and Decreases Responsiveness to Vitamin D3 Hydroxyderivatives in Human Melanoma Cells

Simple Summary

Active forms of vitamin D3, including 1,25(OH)₂D3, 20(OH)D3 and 1,20(OH)₂D3, inhibited cell proliferation, migration rate and the ability to form colonies and spheroids in the wild-type melanoma cell line, while cells with the vitamin D receptor (VDR) silenced showed an increased but not complete resistance to their action. Furthermore, silencing of the VDR in melanoma cells enhanced their proliferation as well as spheroid and colony formation and increased their migration rate. Previous clinicopathological studies have shown an inverse correlation between VDR expression, melanoma progression and poor outcome of the disease. Thus, the expression of VDR is not only necessary for the inhibition of melanoma growth by active forms of vitamin D, but the VDR can also function as a melanoma tumor suppressor gene.

Abstract

Vitamin D3 is not only involved in calcium and phosphate metabolism in humans, but it can also affect proliferation and differentiation of normal and cancer cells, including melanoma. The mechanism of the anti-cancer action of vitamin D3 is not fully understood. The nuclear vitamin D receptor (VDR) is crucial for the phenotypic effects of vitamin D hydroxyderivatives. VDR expression shows an inverse correlation with melanoma progression and poor outcome of the disease. In this study we knocked out the VDR in a human melanoma cell line using CRISPR methodology. This enhanced the proliferation of melanoma cells grown in monolayer culture, spheroids or colonies and their migration. Activated forms of vitamin D, including classical 1,25(OH)₂D3, 20(OH)D3 and 1,20(OH)₂D3, inhibited cell proliferation, migration rate and the ability to form colonies and spheroids in the wild-type melanoma cell line, while VDR KO cells showed a degree of resistance to their action. These results indicate that expression of VDR is important for the inhibition of melanoma growth induced by activated forms of vitamin D. In conclusion, based on our previous clinicopathological analyses and the current study, we suggest that the VDR can function as a melanoma tumor suppressor gene.

Insights into the role of ERp57 in cancer

Endoplasmic reticulum resident protein 57 (ERp57) has a molecular weight of 57 kDa, belongs to the protein disulfide-isomerase (PDI) family, and is primarily located in the endoplasmic reticulum (ER). ERp57 functions in the quality control of nascent synthesized glycoproteins, participates in major histocompatibility complex (MHC) class I molecule assembly, regulates immune responses, maintains immunogenic cell death (ICD), regulates the unfolded protein response (UPR), functions as a 1,25-dihydroxy vitamin D3 (1,25(OH)2D3) receptor, regulates the NF-κB and STAT3 pathways, and participates in DNA repair processes and cytoskeletal remodeling. Recent studies have reported ERp57 overexpression in various human cancers, and altered expression and aberrant functionality of ERp57 are associated with cancer growth and progression and changes in the chemosensitivity of cancers. ERp57 may become a potential biomarker and therapeutic target to combat cancer development and chemoresistance. Here, we summarize the available knowledge of the role of ERp57 in cancer and the underlying mechanisms.

Vitamin D receptor(s): In the nucleus but also at membranes?

The genomic actions of the vitamin D are mediated via its biologically most potent metabolite 1α,25-dihydroxyvitamin D₃ (1,25(OH)₂ D₃ ) and the transcription factor vitamin D receptor (VDR). Activation of VDR by 1,25(OH)₂ D₃ leads to change in the expression of more 1000 genes in various human tissues. Based on (epi)genome, transcriptome and crystal structure data the molecular details of this nuclear vitamin D signalling pathway are well understood. Vitamin D is known for its role on calcium homeostasis and bone formation, but it also modulates energy metabolism, innate and adaptive immunity as well as cellular growth, differentiation and apoptosis. The observation of rapid, non-genomic effects of 1,25(OH)₂ D₃ at cellular membranes and in the cytosol initiated the question, whether there are alternative vitamin D-binding proteins in these cellular compartments. So far, the best candidate is the enzyme PDIA3 (protein disulphide isomerase family A member 3), which is found at various subcellular locations. Furthermore, also VDR seems to play a role in membrane-based responses to vitamin D. In this viewpoint, we will dispute whether these rapid, non-genomic pathways are a meaningful addition to the genome-wide effects of vitamin D.

Antiproliferative activity of side-chain truncated vitamin D analogs (PRI-1203 and PRI-1204) against human malignant melanoma cell lines

Vitamin D compounds are versatile molecules widely considered as promising agents in cancer prevention and treatment, including melanoma. Previously we investigated series of double point modified vitamin D₂ analogs as well as non-calcemic 20S-hydroxyvitamin D₃ and 21-hydroxypregnacalciferol as to their anti-melanoma activity. Surprisingly, short side-chain vitamin D analogs were found to be biologically active compounds. Thus, here we tested novel derivatives of pregnacalciferol with an additional hydroxyl at the end of the truncated side chain, PRI-1203 and PRI-1204, as to their potency against human melanoma A375 and RPMI7951 cell lines. Tested compounds are geometric isomers, with 19-methylene positioned in PRI-1203 like in a calcitriol molecule, but reversed in the PRI-1204 analog to the (5E,7E) geometry (5,6-trans). We noticed a decrease in cells viability exerted by PRI-1203. The antiproliferative effect of PRI-1204 was very low, emphasizing the importance of the natural 19-methylene geometry in the PRI-1203. PRI-1203 was also effective in inhibition of A375 melanoma cells migration. PRI-1203, but not PRI-1204, increased the percentage of A375 and RPMI7951 melanoma cells in the G0/G1 phase of cell cycle, possibly in a p21 and p27 independent manner. Both, analogs have very low effect on the level of CYP24A1 mRNA, in comparison to active form of vitamin D - 1.25(OH)2D3. In addition, both tested compounds failed to elicit VDR translocation to the nucleus. Thus, it could be postulated that side chain shortening strongly affects binding of analogs to VDR and activation of genomic responses, however do not impair their antiproliferative activities.

Vitamin D and its low calcemic analogs modulate the anticancer properties of cisplatin and dacarbazine in the human melanoma A375 cell line

Melanoma represents a significant challenge in cancer treatment due to the high drug resistance of melanomas and the patient mortality rate. This study presents data indicating that nanomolar concentrations of the hormonally active form of vitamin D, 1α,25-dihydroxyvitamin D3 [1α,25(OH)₂D3], its non-calcemic analogues 20S-hydroxyvitamin D3 and 21-hydroxypregnacalciferol, as well as the low-calcemic synthetic analog calcipotriol, modulate the efficacy of the anticancer drugs cisplatin and dacarbazine. It was observed that vitamin D analogs sensitized melanoma A375 cells to hydrogen peroxide used as an inducer of oxidative stress. On the other hand, only 1α,25(OH)₂D3 resulted in a minor, but significant effect on the proliferation of melanoma cells treated simultaneously with dacarbazine, but not cisplatin. Notably, cisplatin (300 µM) exhibited a higher overall antiproliferative activity than dacarbazine. Cisplatin treatment of melanoma cells resulted in an induction of apoptosis as demonstrated by flow cytometry (accumulation of cells at the subG₁ phase of the cell cycle), whereas dacarbazine caused G₁/G₀ cell cycle arrest, with the effects being improved by pre-treatment with vitamin D analogs. Treatment with cisplatin resulted in an initial increase in the level of reactive oxygen species (ROS). Dacarbazine caused transient stimulation of ROS levels and the mitochondrial membrane potential (Δψ_m) (after 1 or 3 h of treatment, respectively), but the effect was not detectable following prolonged (24 h) incubation with the drug. Vitamin D exhibited modulatory effects on the cells treated with dacarbazine, decreasing the half maximal inhibitory concentration (IC₅₀) for the drug, stimulating G₁/G₀ arrest and causing a marked decrease in Δψ_m. Finally, cisplatin, dacarbazine and 1α,25(OH)₂D3 displayed modulatory effects on the expression of ROS and vitamin D-associated genes in the melanoma A375 cells. In conclusion, nanomolar concentrations of 1,25(OH)₂D₃ only had minor effects on the proliferation of melanoma cells treated with dacarbazine, decreasing the relative IC₅₀ value. However, co-treatment with vitamin D analogs resulted in the modulation of cell cycle and ROS responses, and affected gene expression, suggesting possible crosstalk between the signaling pathways of vitamin D and the anticancer drugs used in this study.

Antiproliferative Activity of Non-Calcemic Vitamin D Analogs on Human Melanoma Lines in Relation to VDR and PDIA3 Receptors

Vitamin D is a precursor for secosteroidal hormones, which demonstrate pleiotropic biological activities, including the regulation of growth and the differentiation of normal and malignant cells. Our previous studies have indicated that the inhibition of melanoma proliferation by a short side-chain, low calcemic analog of vitamin D—21(OH)pD is not fully dependent on the expression of vitamin D receptor (VDR). We have examined the effects of classic vitamin D metabolites, 1,25(OH)₂D₃ and 25(OH)D₃, and two low calcemic vitamin D analogs, (21(OH)pD and calcipotriol), on proliferation, mRNA expression and vitamin D receptor (VDR) translocation in three human melanoma cell lines: WM98, A375 and SK-MEL-188b (subline b of SK-MEL-188, which lost responsiveness to 1,25(OH)₂D₃ and became VDR^−/−CYP27B1^−/−). All tested compounds efficiently inhibited the proliferation of WM98 and A375 melanoma cells except SK-MEL-188b, in which only the short side-chain vitamin D analog—21(OH)pD was effective. Overall, 21(OH)pD was the most potent compound in all three melanoma cell lines in the study. The lack of responsiveness of SK-MEL-188b to 1,25(OH)₂D₃, 25(OH)D₃ and calcipotriol is explained by a lack of characteristic transcripts for the VDR, its splicing variants as well as for vitamin D-activating enzyme CYP27B1. On the other hand, the expression of VDR and its splicing variants and other vitamin D related genes (RXR, PDIA3, CYP3A4, CYP2R1, CYP27B1, CYP24A1 and CYP11A1) was detected in WM98 and A375 melanomas with the transcript levels being modulated by vitamin D analogs. The expression of VDR isoforms in WM98 cells was stimulated strongly by calcipotriol. The antiproliferative activities of 21(OH)pD appear not to require VDR translocation to the nucleus, which explains the high efficacy of this noncalcemic pregnacalciferol analog in SK-MEL-188b melanoma, that is, VDR^−/−. Therefore, we propose that 21(OH)pD is a good candidate for melanoma therapy, although the mechanism of its action remains to be defined.

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.

On the role of classical and novel forms of vitamin D in melanoma progression and management

Melanoma represents a significant clinical problem affecting a large segment of the population with a relatively high incidence and mortality rate. Ultraviolet radiation (UVR) is an important etiological factor in malignant transformation of melanocytes and melanoma development. UVB, while being a full carcinogen in melanomagenesis, is also necessary for the cutaneous production of vitamin D3 (D3). Calcitriol (1,25(OH)2D3) and novel CYP11A1-derived hydroxyderivatives of D3 show anti-melanoma activities and protective properties against damage induced by UVB. The former activities include inhibitory effects on proliferation, plating efficiency and anchorage-independent growth of cultured human and rodent melanomas in vitro, as well as the in vivo inhibition of tumor growth by 20(OH)D3 after injection of human melanoma cells into immunodeficient mice. The literature indicates that low levels of 25(OH)D3 are associated with more advanced melanomas and reduced patient survivals, while single nucleotide polymorphisms of the vitamin D receptor or the D3 binding protein gene affect development or progression of melanoma, or disease outcome. An inverse correlation of VDR and CYP27B1 expression with melanoma progression has been found, with low or undetectable levels of these proteins being associated with poor disease outcomes. Unexpectedly, increased expression of CYP24A1 was associated with better melanoma prognosis. In addition, decreased expression of retinoic acid orphan receptors α and γ, which can also bind vitamin D3 hydroxyderivatives, showed positive association with melanoma progression and shorter disease-free and overall survival. Thus, inadequate levels of biologically active forms of D3 and disturbances in expression of the target receptors, or D3 activating or inactivating enzymes, can affect melanomagenesis and disease progression. We therefore propose that inclusion of vitamin D into melanoma management should be beneficial for patients, at least as an adjuvant approach. The presence of multiple hydroxyderivatives of D3 in skin that show anti-melanoma activity in experimental models and which may act on alternative receptors, will be a future consideration when planning which forms of vitamin D to use for melanoma therapy.

Vitamin D and melanoma: state of the art and possible therapeutic uses

Despite the presence of several studies in literature, the real connection between vitamin D serological levels, vitamin D receptor and melanoma remains unclear, probably because of the complex correlation between vitamin D and melanoma. Indeed, UV radiations are not reported as the main risk factor for melanoma in non-sun-exposed, while systemic immunosuppression, anatomical and physiological features may contribute to malignancy. Therefore, the correlation between melanoma cells in sun-exposed areas and vitamin D, as well as vitamin D receptor could be different from the one in melanoma of sun-shielded sites. These differences may also explain the controversial results reported in the literature regarding the correlation between melanoma and vitamin D, as well as the different outcomes in melanoma patients treated with vitamin D as adjuvant therapy. The aim of this review is to highlight the most recent findings about vitamin D and melanoma, focusing on the anatomic site of the primary tumor as well as on the possible therapeutic uses of vitamin D in melanoma patients.

Vitamin D signaling and melanoma: role of vitamin D and its receptors in melanoma progression and management

Ultraviolet B (UVB), in addition to having carcinogenic activity, is required for the production of vitamin D3 (D3) in the skin which supplies >90% of the body's requirement. Vitamin D is activated through hydroxylation by 25-hydroxylases (CYP2R1 or CYP27A1) and 1α-hydroxylase (CYP27B1) to produce 1,25(OH)₂D3, or through the action of CYP11A1 to produce mono-di- and trihydroxy-D3 products that can be further modified by CYP27B1, CYP27A1, and CYP24A1. The active forms of D3, in addition to regulating calcium metabolism, exert pleiotropic activities, which include anticarcinogenic and anti-melanoma effects in experimental models, with photoprotection against UVB-induced damage. These diverse effects are mediated through an interaction with the vitamin D receptor (VDR) and/or as most recently demonstrated through action on retinoic acid orphan receptors (ROR)α and RORγ. With respect to melanoma, low levels of 25(OH)D are associated with thicker tumors and reduced patient survival. Furthermore, single-nucleotide polymorphisms of VDR and the vitamin D-binding protein (VDP) genes affect melanomagenesis or disease outcome. Clinicopathological analyses have shown positive correlation between low or undetectable expression of VDR and/or CYP27B1 in melanoma with tumor progression and shorter overall (OS) and disease-free survival (DFS) times. Paradoxically, this correlation was reversed for CYP24A1 (inactivating 24-hydroxylase), indicating that this enzyme, while inactivating 1,25(OH)₂D3, can activate other forms of D3 that are products of the non-canonical pathway initiated by CYP11A1. An inverse correlation has been found between the levels of RORα and RORγ expression and melanoma progression and disease outcome. Therefore, we propose that defects in vitamin D signaling including D3 activation/inactivation, and the expression and activity of the corresponding receptors, affect melanoma progression and the outcome of the disease. The existence of multiple bioactive forms of D3 and alternative receptors affecting the behavior of melanoma should be taken into consideration when applying vitamin D management for melanoma therapy.

Analysis of the interaction of calcitriol with the disulfide isomerase ERp57

Calcitriol, the active form of vitamin D3, can regulate the gene expression through the binding to the nuclear receptor VDR, but it can also display nongenomic actions, acting through a membrane-associated receptor, which has been discovered as the disulfide isomerase ERp57. The aim of our research is to identify the binding sites for calcitriol in ERp57 and to analyze their interaction. We first studied the interaction through bioinformatics and fluorimetric analyses. Subsequently, we focused on two protein mutants containing the predicted interaction domains with calcitriol: abb'-ERp57, containing the first three domains, and a'-ERp57, the fourth domain only. To consolidate the achievements we used the calorimetric approach to the whole protein and its mutants. Our results allow us to hypothesize that the interaction with the a' domain contributes to a greater extent than the other potential binding sites to the dissociation constant, calculated as a Kd of about 10-9 M.

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.

Steroid biosynthesis in adipose tissue

Tissue-specific expression of steroidogenic enzymes allows the modulation of active steroid levels in a local manner. Thus, the measurement of local steroid concentrations, rather than the circulating levels, has been recognized as a more accurate indicator of the steroid action within a specific tissue. Adipose tissue, one of the largest endocrine tissues in the human body, has been established as an important site for steroid storage and metabolism. Locally produced steroids, through the enzymatic conversion from steroid precursors delivered to adipose tissue, have been proven to either functionally regulate adipose tissue metabolism, or quantitatively contribute to the whole body's steroid levels. Most recently, it has been suggested that adipose tissue may contain the steroidogenic machinery necessary for the initiation of steroid biosynthesis de novo from cholesterol. This review summarizes the evidence indicating the presence of the entire steroidogenic apparatus in adipose tissue and discusses the potential roles of local steroid products in modulating adipose tissue activity and other metabolic parameters.

Antitumor effects of vitamin D analogs on hamster and mouse melanoma cell lines in relation to melanin pigmentation

Deregulated melanogenesis is involved in melanomagenesis and melanoma progression and resistance to therapy. Vitamin D analogs have anti-melanoma activity. While the hypercalcaemic effect of the active form of Vitamin D (1,25(OH)₂D₃) limits its therapeutic use, novel Vitamin D analogs with a modified side chain demonstrate low calcaemic activity. We therefore examined the effect of secosteroidal analogs, both classic (1,25(OH)₂D₃ and 25(OH)D₃), and novel relatively non-calcemic ones (20(OH)D₃, calcipotriol, 21(OH)pD, pD and 20(OH)pL), on proliferation, colony formation in monolayer and soft-agar, and mRNA and protein expression by melanoma cells. Murine B16-F10 and hamster Bomirski Ab cell lines were shown to be effective models to study how melanogenesis affects anti-melanoma treatment. Novel Vitamin D analogs with a short side-chain and lumisterol-like 20(OH)pL efficiently inhibited rodent melanoma growth. Moderate pigmentation sensitized rodent melanoma cells towards Vitamin D analogs, and altered expression of key genes involved in Vitamin D signaling, which was opposite to the effect on heavily pigmented cells. Interestingly, melanogenesis inhibited ligand-induced Vitamin D receptor translocation and ligand-induced expression of VDR and CYP24A1 genes. These findings indicate that melanogenesis can affect the anti-melanoma activity of Vitamin D analogs in a complex manner.

Vitamin D: Implications for ocular disease and therapeutic potential

Vitamin D is a multifunctional hormone that is now known to play a significant role in a variety of biological functions in addition to its traditional role in regulating calcium homeostasis. There are a large number of studies demonstrating that adequate vitamin D levels are important in maintaining health and show that vitamin D is able to be utilized at local tissue sites. In the eye, we have increasing evidence of the association between disease and vitamin D. In this narrative review, we summarize recent findings on vitamin D and its relationship to various ocular pathologies and the therapeutic potential for some of these, as well as examine the basic science studies that demonstrate that vitamin D is biologically relevant in the eye.

The role of CYP11A1 in the production of vitamin D metabolites and their role in the regulation of epidermal functions

Research over the last decade has revealed that CYP11A1 can hydroxylate the side chain of vitamin D3 at carbons 17, 20, 22 and 23 to produce at least 10 metabolites, with 20(OH)D3, 20,23(OH)2D3, 20,22(OH)2D3, 17,20(OH)2D3 and 17,20,23(OH)3D3 being the main products. However, CYP11A1 does not act on 25(OH)D3. The placenta, adrenal glands and epidermal keratinocytes have been shown to metabolize vitamin D3 via this CYP11A1-mediated pathway that is modified by the activity of CYP27B1, with 20(OH)D3 (the major metabolite), 20,23(OH)2D3, 1,20(OH)2D3, 1,20,23(OH)3D3 and 17,20,23(OH)3D3 being detected, defining these secosteroids as endogenous regulators/natural products. This is supported by the detection of a mono-hydroxyvitamin D3 with the retention time of 20(OH)D3 in human serum. In new work presented here we demonstrate that the CYP11A1-initiated pathways also occurs in Caco-2 colon cells. Our previous studies show that 20(OH)D3 and 20,23(OH)2D3 are non-calcemic at pharmacological doses, dependent in part on their lack of a C1α hydroxyl group. In epidermal keratinocytes, 20(OH)D3, 20(OH)D2 and 20,23(OH)2D3 inhibited cell proliferation, stimulated differentiation and inhibited NF-κB activity with potencies comparable to 1,25(OH)2D3, acting as partial agonists on the VDR. 22(OH)D3 and 20,22(OH)2D3, as well as secosteroids with a short or no side chain, showed antiproliferative and prodifferentiation effects, however, with lower potency than 20(OH)D3 and 20,23(OH)2D3. The CYP11A1-derived secosteroids also inhibited melanocyte proliferation while having no effect on melanogenesis, and showed anti-melanoma activities in terms of inhibiting proliferation and the ability to grow in soft agar. Furthermore, 20(OH)D3 and 20,23(OH)2D3 showed anti-fibrosing effects in vitro, and also in vivo for the former. New data presented here shows that 20(OH)D3 inhibits LPS-induced production of TNFα in the J774 line, TNFα and IL-6 in peritoneal macrophages and suppresses the production of proinflammatory Th1/Th17-related cytokines, while promoting the production of the anti-inflammatory cytokine IL-10 in vivo. In summary, CYP11A1 initiates new pathways of vitamin D metabolism in a range of tissues and products could have important physiological roles at the local or systemic level. In the skin, CYP11A1-derived secosteroids could serve both as endogenous regulators of skin functions and as excellent candidates for treatment of hyperproliferative and inflammatory skin disorders, and skin cancer. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.

Cytochromes p450 and skin cancer: role of local endocrine pathways

Skin is the largest body organ forming a metabolically active barrier between external and internal environments. The metabolic barrier is composed of cytochromes P450 (CYPs) that regulate its homeostasis through activation or inactivation of biologically relevant molecules. In this review we focus our attention on local steroidogenic and secosteroidogenic systems in relation to skin cancer, e.g., prevention, attenuation of tumor progression and therapy. The local steroidogenic system is composed of locally expressed CYPs involved in local production of androgens, estrogens, gluco- and mineralo-corticosteroids from cholesterol (initiated by CYP11A1) or from steroid precursors delivered to the skin, and of their metabolism and/or inactivation. Cutaneous 7-hydroxylases (CYP7A1, CYP7B1 and CYP39) potentially can produce 7-hydroxy/oxy-steroids/sterols with modifying effects on local tumorigenesis. CYP11A1 also transforms 7-dehydrocholesterol (7DHC)→22(OH)7DHC→20,22(OH)2-7DHC→7-dehydropregnenolone, which can be further metabolized to other 5,7- steroidal dienes. These 5,7-dienal intermediates are converted by ultraviolet radiation B (UVB) into secosteroids which show pro-differentiation and anti-cancer properties. Finally, the skin is the site of activation of vitamin D3 through two alternative pathways. The classical one involves sequential hydroxylation at positions 25 and 1 to produce active 1,25(OH)2D3, which is further inactivated through hydroxylation at C24. The novel pathway is initiated by CYP11A1 with predominant production of 20(OH)D3 which is further metabolized to biologically active but non-calcemic D3-hydroxyderivatives. Classical and non-classical (novel) vitamin D analogs show pro-differentiation, anti-proliferative and anticancer properties. In addition, melatonin is metabolized by local CYPs. In conclusion cutaneously expressed CYPs have significant effects on skin physiology and pathology trough regulation of its chemical milieu.

Novel vitamin D photoproducts and their precursors in the skin

Novel metabolic pathways initiated by the enzymatic action of CYP11A1 on 7DHC (7-dehydrocholesterol), ergosterol, vitamins D3 and D2 were characterized with help of chemical synthesis, UV and mass spectrometry and NMR analyses. The first pathway follows the sequence 7DHC→22(OH)7DHC → 20,22(OH)27DHC → 7DHP (7-dehydropregnenolone), which can further be metabolized by steroidogenic enzymes. The resulting 5,7-dienes can be transformed by UVB to corresponding, biologically active, secosteroids. Action of CYP11A1 on vitamin D3 and D2 produces novel hydroxyderivatives with OH added at positions C17, C20, C22, C23 and C24, some of which can be hydroxylated by CYP27B1 and/or by CYP27A1 and/ or by CYP24A1.The main products of these pathways are biologically active with a potency related to their chemical structure and the target cell type. Main products of CYP11A1-mediated metabolism on vitamin D are non-calcemic and non-toxic at relatively high doses and serve as partial agonists on the vitamin D receptor. New secosteroids are excellent candidates for therapy of fibrosing, inflammatory or hyperproliferative disorders including cancers and psoriasis.

Decreased VDR expression in cutaneous melanomas as marker of tumor progression: new data and analyses

BACKGROUND

Vitamin D3, acting via vitamin D receptor (VDR) affects a wide range of biological activities, including inhibition of proliferation and angiogenesis, with net antitumor effects. VDR expression is disturbed in many tumors, including melanomas.

AIM

To find correlation between VDR expression in melanomas and prognostic biomarkers.

MATERIALS AND METHODS

VDR was analyzed immunohistochemically in 69 cutaneous melanomas in relation to prognostic factors.

RESULTS

Less advanced melanomas showed significantly higher VDR expression than the advanced stages. The presence of other markers such as ulceration and lack or non-brisk tumor infiltrating lymphocytes (TILs) was accompanied by significantly lower VDR expression. VDR expression also affected overall survival (OS) with most noticeable effect in the cases without ulceration.

CONCLUSION

High VDR expression determines a less malignant phenotype and is related to better prognosis. Loss of VDR expression affects melanoma tumor behavior, allowing for progression of disease. VDR expression can also serve as a prognostic marker in routine histopathology evaluation.

Vitamin D receptor regulates TGF-β signalling in systemic sclerosis

BACKGROUND

Vitamin D receptor (VDR) is a member of the nuclear receptor superfamily. Its ligand, 1,25-(OH)2D, is a metabolically active hormone derived from vitamin D3. The levels of vitamin D3 are decreased in patients with systemic sclerosis (SSc). Here, we aimed to analyse the role of VDR signalling in fibrosis.

METHODS

VDR expression was analysed in SSc skin, experimental fibrosis and human fibroblasts. VDR signalling was modulated by siRNA and with the selective agonist paricalcitol. The effects of VDR on Smad signalling were analysed by reporter assays, target gene analyses and coimmunoprecipitation. The effects of paricalcitol were evaluated in the models of bleomycin-induced fibrosis and fibrosis induced by overexpression of a constitutively active transforming growth factor-β (TGF-β) receptor I (TBRI(CA)).

RESULTS

VDR expression was decreased in fibroblasts of SSc patients and murine models of SSc in a TGF-β-dependent manner. Knockdown of VDR enhanced the sensitivity of fibroblasts towards TGF-β. In contrast, activation of VDR by paricalcitol reduced the stimulatory effects of TGF-β on fibroblasts and inhibited collagen release and myofibroblast differentiation. Paricalcitol stimulated the formation of complexes between VDR and phosphorylated Smad3 in fibroblasts to inhibit Smad-dependent transcription. Preventive and therapeutic treatment with paricalcitol exerted potent antifibrotic effects and ameliorated bleomycin- as well as TBRI(CA)-induced fibrosis.

CONCLUSIONS

We characterise VDR as a negative regulator of TGF-β/Smad signalling. Impaired VDR signalling with reduced expression of VDR and decreased levels of its ligand may thus contribute to hyperactive TGF-β signalling and aberrant fibroblast activation in SSc.

TaqI polymorphism of VDR gene contributes to breast cancer risk

Previous studies on the association of Vitamin D receptor (VDR) TaqI gene polymorphism with breast carcinogenesis have yielded inconsistent and inconclusive findings. The current meta-analysis was performed to provide a more precise assessment on the role of VDR TaqI polymorphism in breast cancer risk. 20 eligible case-control studies involving 9,055 cases and 10,516 controls were identified after a comprehensive literature search of the PubMed, Embase, Web of Science, and Wanfang databases. The pooled odds ratio (OR) with corresponding 95% confidence interval (95% CI) was calculated. Stratified analyses by ethnicity and study quality were conducted for further estimation. All statistical analyses were conducted by use of STATA (STATA Corporation, College Station, TX, Version 11.0). The overall ORs showed that the variant t allele and tt genotype were related to an increased risk of breast cancer (OR(t vs. T) = 1.05, 95% CI 1.01-1.10, P(OR) = 0.025; OR(tt vs. TT) = 1.12, 95% CI 1.03-1.23, P(OR) = 0.011; OR(tt vs. Tt + TT) = 1.10, 95% CI 1.01-1.20, P(OR) = 0.023). Stratified analyses of studies in Caucasians and with high-quality further confirmed the results. However, no significant relationship was observed among Asians. This meta-analysis suggests that the VDR TaqI polymorphism confers risk effect on the breast cancer development, particularly in Caucasians.

Factors significantly increasing or inhibiting early stages of malignant melanoma (M.M.) and non-invasive evaluation of new treatment by ingestion and external application of optimal doses of the most effective anti-M.M. substances: haritaki, cilantro, vitamin D3, nori, EPA with DHA, & application of special (+) solar energy stored paper, which reduced the M.M. active area & asbestos rapidly

Sterilizing the pre-cancer skin of malignant melanoma (M.M.) with 70% Isopropyl alcohol intensified malignancy & the malignant response extended to surrounding normal looking skin, while sterilizing with 80% (vodka) or 12% (plum wine) ethyl alcohol completely inhibited M.M. in the area (both effects lasted for about 90 minutes initially). Burnt food (bread, vegetables, meat, and fish), a variety of smoked & non-smoked fish-skin, many animal's skin, pepper, Vitamin C over 75 mg, mango, pineapple, coconut, almond, sugars, Saccharine & Aspartame, garlic, onion, etc & Electromagnetic field from cellular phones worsened M.M. & induced abnormal M.M. response of surrounding skin. We found the following factors inhibit early stage of M.M. significantly: 1) Increasing normal cell telomere, by taking 500 mg Haritaki, often reached between 400-1150 ng& gradually diminished, but the M.M. response was completely inhibited until normal cell telomeres are reduced to 150 ng, which takes 6-8 hours. More than 70 mg Vitamin C, Orange Juice, & other high Vitamin C containing substances shouldn't be taken because they completely inhibit the effects of Haritaki. 2) We found Chrysotile asbestos & Tremolite asbestos (% of the Chrysotile amount) coexist. A special Cilantro tablet was used to remove asbestos & some toxic metals. 3) Vitamin D3 400 I.U. has a maximum inhibiting effect on M.M. but 800 I.U. or higher promotes malignancy. 4) Noricontaining Iodine, etc., was used. 5) EPA 180 mm with DHA 120 mg was most effectively used after metastasis to the surrounding skin was eliminated. When we combined 1 Cilantro tablet & Vitamin D3 400 I.U. withsmall Nori pieces & EPA with DHA, the effect of complete inhibition of M.M. lasted 9-11 hours. When these anti-M.M.substances (Haritaki, Vitamin D3, Cilantro, Nori, EPA. with DHA) were taken together, the effect lasted 12-14 hoursand M.M. involvement in surrounding normal-looking skin disappeared rapidly & original dark brown or black are as satisfying "ABCD" of M.M. completely fell off. Both oral & frequent external application of mixed solution of plum wine & the same combination of anti-M.M. substances can be used as very effective treatment by taking 2-3 times daily. Additional application of special (+) Solar Energy Stored Paper reduced asbestos & accelerated reduction of M.M. positive area rapidly. This method with individualized optimal doses has also been successfully applied to treat several other types of malignancies.

Hydroxylation of CYP11A1-derived products of vitamin D3 metabolism by human and mouse CYP27B1

CYP11A1 can hydroxylate vitamin D3 at carbons 17, 20, 22, and 23, producing a range of secosteroids which are biologically active with respect to their ability to inhibit proliferation and stimulate differentiation of various cell types, including cancer cells. As 1α-hydroxylation of the primary metabolite of CYP11A1 action, 20S-hydroxyvitamin D3 [20(OH)D3], greatly influences its properties, we examined the ability of both human and mouse CYP27B1 to 1α-hydroxylate six secosteroids generated by CYP11A1. Based on their kcat/Km values, all CYP11A1-derived metabolites are poor substrates for CYP27B1 from both species compared with 25-hydroxyvitamin D3. No hydroxylation of metabolites with a 17α-hydroxyl group was observed. 17α,20-Dihydroxyvitamin D3 acted as an inhibitor on human CYP27B1 but not the mouse enzyme. We also tested CYP27B1 activity on 20,24-, 20,25-, and 20,26-dihydroxyvitamin D3, which are products of CYP24A1 or CYP27A1 activity on 20(OH)D3. All three compounds were metabolized with higher catalytic efficiency (kcat/Km) by both mouse and human CYP27B1 than 25-hydroxyvitamin D3. CYP27B1 action on these new dihydroxy derivatives was confirmed to be 1α-hydroxylation by mass spectrometry and nuclear magnetic resonance analyses. Both 1,20,25- and 1,20,26- trihydroxyvitamin D3 were tested for their ability to inhibit melanoma (SKMEL-188) colony formation, and were significantly more active than 20(OH)D3. This study shows that CYP11A1-derived secosteroids are 1α-hydroxylated by both human and mouse CYP27B1 with low catalytic efficiency, and that the presence of a 17α-hydroxyl group completely blocks 1α-hydroxylation. In contrast, the secondary metabolites produced by subsequent hydroxylation of 20(OH)D3 at C24, C25, or C26 are very good substrates for CYP27B1.

Screening and prevention measures for melanoma: is there a survival advantage?

Controversy has emerged over the past decades regarding the value and impact of melanoma screening to detect early stage disease for improved prognosis. Those questioning the benefits of prevention efforts base their arguments on the absence of prospective, randomized studies demonstrating decreased melanoma mortality to justify the cost associated with screening and educational campaigns. For those in favor of melanoma screening, the lack of proven survival benefit is not a justification to abandon this approach, but rather a reflection of the lack of resources necessary to conduct a long-term trial. In 2009, the US Preventive Services Task Force (USPSTF)report did not recommend routine primary care screening for the general population given the absence of evidence. However, since the USPSTF report, a series of new studies are available, which support the potential benefit of screening and have the potential to significantly impact current policies regarding skin cancer screening, particularly for melanoma.

Vitamin D and overall mortality

Vitamin D is a steroid molecule, mainly produced in the skin that regulates the expression of a large number of genes. Several meta-analyses of epidemiological studies support the evidence that low vitamin D serum level, which is highly prevalent worldwide, could be a 'new' risk factor for many chronic diseases including cancer, and for all-cause mortality. A meta-analysis in healthy subjects suggested that current doses of vitamin D supplements could be associated with decrease in total mortality rates. However, these associations are insufficient to establish causality between vitamin D and all-cause mortality. Furthermore, long-term health effects of high doses of vitamin D, that is, prolonged supplementation and association with different baseline vitamin D levels, remain to be investigated. Several trials are ongoing but population-based, placebo-controlled randomized trials with total mortality as the main endpoint should be planned to confirm a real beneficial effect of vitamin D for non-skeletal diseases and to prove causality.

Rat CYP24A1 acts on 20-hydroxyvitamin D(3) producing hydroxylated products with increased biological activity

20-Hydroxyvitamin D(3) (20(OH)D(3)), the major product of CYP11A1 action on vitamin D(3), is biologically active and is produced in vivo. As well as potentially having important physiological actions, it is of interest as a therapeutic agent due to its lack of calcemic activity. In the current study we have examined the ability of CYP24A1, the enzyme that inactivates 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), to metabolize 20(OH)D(3). Rat CYP24A1 was expressed in Escherichia coli, purified by Ni-affinity chromatography and assayed with substrates incorporated into phospholipid vesicles which served as a model of the inner mitochondrial membrane. In this system CYP24A1 metabolized 1,25(OH)(2)D(3) with a catalytic efficiency 1.4-fold higher than that seen for 25-hydroxyvitamin D(3) (25(OH)D(3)). CYP24A1 hydroxylated 20(OH)D(3) to several dihydroxy-derivatives with the major two identified by NMR as 20,24-dihydroxyvitamin D(3) (20,24(OH)(2)D(3)) and 20,25-dihydroxyvitamin D(3) (20,25(OH)(2)D(3)). The catalytic efficiency of CYP24A1 for 20(OH)D(3) metabolism was more than 10-fold lower than for either 25(OH)D(3) or 1,25(OH)(2)D(3) and no secondary metabolites were produced. The two major products, 20,24(OH)(2)D(3) and 20,25(OH)(2)D(3), caused significantly greater inhibition of colony formation by SKMEL-188 melanoma cells than either 1,25(OH)(2)D(3) or the parent 20(OH)D(3), showing that CYP24A1 plays an activating, rather than an inactivating role on 20(OH)D(3).

Novel vitamin D hydroxyderivatives inhibit melanoma growth and show differential effects on normal melanocytes

BACKGROUND/AIMS

To test the activity of novel hydroxyvitamin D(3) analogs (20(OH)D(3), 20,23(OH)(2)D and 1,20(OH)(2)D(3)) on normal and malignant melanocytes in comparison to 1,25(OH)(2)D(3).

MATERIALS AND METHODS

Human epidermal melanocytes and human and hamster melanoma cells were used to measure effects on proliferation and colony formation in monolayer and soft agar. Cell morphology and melanogenesis were also analyzed. QPCR was used to measure gene expression.

RESULTS

Novel secosteroids inhibited proliferation and colony formation by melanoma cells in a similar fashion to 1,25(OH)(2)D(3), having no effect on melanogenesis. These effects were accompanied by ligand-induced translocation of VDR to the nucleus. In normal melanocytes 1α-hydroxyderivatives (1,25(OH)(2)D(3) and 1,20(OH)(2)D(3)) had stronger anti-proliferative effects than 20(OH)D(3) and 20,23(OH)(2)D(3), and inhibited dendrite formation. The cells tested expressed genes encoding VDR and enzymes that activate or inactivate vitamin D(3).

CONCLUSION

Novel secosteroids show potent anti-melanoma activity in vitro with 20(OH)D(3) and 20,23(OH)(2)D(3) being excellent candidates for pre-clinical testing.