Anti-tumor activity of calcitriol: pre-clinical and clinical studies

Ultraviolet B and incidence rates of leukemia worldwide

BACKGROUND

Recent research has suggested a relationship between vitamin D deficiency and risk of leukemia.

PURPOSE

Using data from the UN cancer database, GLOBOCAN, this study will determine whether a relationship exists for latitude and ultraviolet B (UVB) irradiance with incidence rates of leukemia in 175 countries.

METHODS

Multiple regression was used to analyze the independent association between UVB and age-adjusted incidence rates of leukemia in 139 countries in 2002. This study controlled for dietary data on intake of energy from animal sources and per capita healthcare expenditures. The analyses were performed in 2009.

RESULTS

People residing in the highest-latitude countries had the highest rates of leukemia in both men (R(2)=0.34, p<0.0001) and women (R(2)=0.24, p<0.0001). In men, UVB was independently inversely associated with leukemia incidence rates (p≤0.001), whereas animal energy consumption (p=0.02) and per capita healthcare expenditures (p≤0.0001) were independently positively associated (R(2) for model=0.61, p≤0.0001). In women, UVB adjusted for cloud cover was independently inversely associated with leukemia incidence rates (p≤0.01), whereas animal energy consumption (p≤0.05) and per capita healthcare expenditures (p=0.0002) were independently positively associated (R(2) for model=0.51, p<0.0001).

CONCLUSIONS

Countries with low UVB had higher age-adjusted incidence rates of leukemia. This suggests the possibility that low serum 25-hydroxyvitamin D status, because of lower levels of UVB, somehow might predict the development of leukemia.

Serum 25(OH) vitamin D and risk of breast cancer: a nested case-control study from the French E3N cohort

BACKGROUND

High 25-hydroxyvitamin D [25(OH)D] serum concentrations have been found to be associated with reduced breast cancer risk. However, few studies have further investigated this relationship according to menopausal status, nor have they taken into account factors known to influence vitamin D status, such as dietary and serum calcium, parathyroid hormone, and estradiol serum levels.

METHODS

We designed a nested case-control study within the French E3N cohort. Cases were women diagnosed with incident breast cancer (n = 636). Controls (n = 1,272) were matched with cases on age, menopausal status at blood collection, age at menopause, and center and year of blood collection. Multivariate logistic regression models were established.

RESULTS

We found a decreased risk of breast cancer with increasing 25(OH) vitamin D(3) serum concentrations (odds ratio, 0.73; 95% confidence interval, 0.55-0.96; P trend = 0.02) among women in the highest tertile. We also observed a significant inverse association restricted to women under 53 years of age at blood sampling [odds ratio (T(3) versus T(1)), 0.60; 95% confidence interval, 0.37-0.98; P trend = 0.04]. In premenopausal women, the risk was also decreased, although not significantly.

CONCLUSION

Our findings support a decreased risk of breast cancer associated with high 25(OH) vitamin D(3) serum concentrations, especially in younger women, although we were unable to confirm a direct influence of age or menopausal status.

IMPACT

Randomized intervention trials with vitamin D supplementation are required to confirm its benefits on breast cancer risk, but the maintenance of adequate vitamin D levels should be encouraged by public health policy.

Differential regulation of TP73 isoforms by 1α,25-dihydroxyvitamin D3 and survivin in human colon and breast carcinomas

We evaluate whether 1,25(OH)(2)D(3) downregulates TP73 variants in colon and breast carcinomas, the role of survivin in this context, and the significance of this network in the clinic. Tumor cells were treated/untreated with 1,25(OH)(2)D(3) and transiently transfected with survivin. Levels of survivin and TP73 variants were evaluated by quantitative RT-PCR and Western blotting. In 75 colon and 60 breast cancer patients, the expressions of survivin and TP73 isoforms were determined. Tumor characteristics were examined in each patient. Survivin protein levels were also evaluated in a subgroup of patients and cell lines. Decrease in survivin and TAp73 transcripts and protein and ΔNp73 mRNA was detected after 1,25(OH)(2)D(3) treatment. Ectopic survivin expression led to an increase in the TAp73, ΔNp73, ΔEx2p73, and ΔEx2-3p73 transcripts. In cancer patients, direct correlations were observed between TP73 variants and survivin levels. 1,25(OH)(2)D(3) negatively regulate survivin and TP73 variants in colon and breast cancer cells. Positive regulation of TP73 isoforms by survivin may exist, which reinforces the possibility that the downregulation of TP73 forms by 1,25(OH)(2)D(3) is survivin-dependent.

1α,25-dihydroxyvitamin D3 (vitamin D3) catalyzes suppressive activity on human natural regulatory T cells, uniquely modulates cell cycle progression, and augments FOXP3

Human natural regulatory T cells (nTregs) show great promise for therapeutically modulating immune-mediated disease, but remain poorly understood. One explanation under intense scrutiny is how to induce suppressive function in non-nTregs and increase the size of the regulatory population. A second possibility would be to make existing nTregs more effective, like a catalyst raises the specific activity of an enzyme. The latter has been difficult to investigate due to the lack of a robust short-term suppression assay. Using a microassay described herein we demonstrate that nTregs in distinct phases of cell cycle progression exhibit graded degrees of potency. Moreover, we show that physiological concentrations of 1α,25-dihydroxyvitamin D3 (vitamin D3) boosts nTregs function. The enhanced suppressive capacity is likely due to vitamin D3's ability to uniquely modulate cell cycle progression and elevate FOXP3 expression. These data suggest a role for vitamin D3 as a mechanism for catalyzing potency of nTregs.

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.

1,25D3 enhances antitumor activity of gemcitabine and cisplatin in human bladder cancer models

BACKGROUND

1,25 dihydroxyvitamin D3 (1,25D3) potentiates the cytotoxic effects of several common chemotherapeutic agents. The combination of gemcitabine and cisplatin is a current standard chemotherapy regimen for bladder cancer. The authors investigated whether 1,25D3 could enhance the antitumor activity of gemcitabine and cisplatin in bladder cancer model systems.

METHODS

Human bladder cancer T24 and UMUC3 cells were pretreated with 1,25D3 followed by gemcitabine and cisplatin. Apoptosis was assessed by annexin V staining. Caspase activation was examined by immunoblot analysis and substrate-based caspase activity assay. The cytotoxic effects were examined by using 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) and in vitro clonogenic assay. p73 protein levels were assessed by immunoblot analysis. Knockdown of p73 was achieved by siRNA. The in vivo antitumor activity was assessed by in vivo excision clonogenic assay and tumor regrowth delay in the T24 xenograft model.

RESULTS

1,25D3 pretreatment enhanced gemcitabine and cisplatin-induced apoptosis and the activities of caspases 8, 9, and 3 in T24 and UMUC3 cells. 1,25D3 synergistically reduced gemcitabine and cisplatin-suppressed surviving fraction in T24 cells. 1,25D3, gemcitabine, or cisplatin induced p73 accumulation, which was enhanced by gemcitabine and cisplatin or 1,25D3 and gemcitabine and cisplatin. p73 expression was lower in human primary bladder tumor tissue compared with adjacent normal tissue. Knockdown of p73 increased clonogenic capacity of T24 cells treated with 1,25D3, gemcitabine and cisplatin, or 1,25D3 and gemcitabine and cisplatin. 1,25D3 and gemcitabine and cisplatin combination enhanced tumor regression compared with 1,25D3 or gemcitabine and cisplatin alone.

CONCLUSIONS

1,25D3 potentiates gemcitabine and cisplatin-mediated growth inhibition in human bladder cancer models in vitro and in vivo, which involves p73 induction and apoptosis.

Vitamin D in combination cancer treatment

As a steroid hormone that regulates mineral homeostasis and bone metabolism, 1α, 25-dihydroxycholecalciferol (calcitriol) also has broad spectrum anti-tumor activities as supported by numerous epidemiological and experimental studies. Calcitriol potentiates the anti-tumor activities of multiple chemotherapeutics agents including DNA-damaging agents cisplatin, carboplatin and doxorubicin; antimetabolites 5-fluorouracil, cytarabine, hydroxyurea, cytarabine and gemcitabine; and microtubule-disturbing agents paclitaxel and docetaxel. Calcitriol elicits anti-tumor effects mainly through the induction of cancer cell apoptosis, cell cycle arrest, differentiation, angiogenesis and the inhibition of cell invasiveness by a number of mechanisms. Calcitriol enhances the cytotoxic effects of gamma irradiation and certain antioxidants and naturally derived compounds. Inhibition of calcitriol metabolism by 24-hydroxylase promotes growth inhibition effect of calcitriol. Calcitriol has been used in a number of clinical trials and it is important to note that sufficient dose and exposure to calcitriol is critical to achieve anti-tumor effect. Several trials have demonstrated that safe and feasible to administer high doses of calcitriol through intermittent regimen. Further well designed clinical trials should be conducted to better understand the role of calcitriol in cancer therapy.

Benefit-risk assessment of vitamin D supplementation

Current intake recommendations of 200 to 600 IU vitamin D per day may be insufficient for important disease outcomes reduced by vitamin D.

INTRODUCTION

This study assessed the benefit of higher-dose and higher achieved 25-hydroxyvitamin D levels [25(OH)D] versus any associated risk.

METHODS AND RESULTS

Based on double-blind randomized control trials (RCTs), eight for falls (n = 2426) and 12 for non-vertebral fractures (n = 42,279), there was a significant dose-response relationship between higher-dose and higher achieved 25(OH)D and greater fall and fracture prevention. Optimal benefits were observed at the highest dose tested to date for 700 to 1000 IU vitamin D per day or mean 25(OH)D between 75 and 110 nmol/l (30-44 ng/ml). Prospective cohort data on cardiovascular health and colorectal cancer prevention suggested increased benefits with the highest categories of 25(OH)D evaluated (median between 75 and 110 nmol/l). In 25 RCTs, mean serum calcium levels were not related to oral vitamin D up to 100,000 IU per day or achieved 25(OH)D up to 643 nmol/l. Mean levels of 75 to 110 nmol/l were reached in most RCTs with 1,800 to 4,000 IU vitamin D per day without risk.

CONCLUSION

Our analysis suggests that mean serum 25(OH)D levels of about 75 to 110 nmol/l provide optimal benefits for all investigated endpoints without increasing health risks. These levels can be best obtained with oral doses in the range of 1,800 to 4,000 IU vitamin D per day; further work is needed, including subject and environment factors, to better define the doses that will achieve optimal blood levels in the large majority of the population.

Vitamin D analogs

Vitamin D has gone through a renaissance with the association of vitamin D deficiency with a wide array of common diseases including breast, colorectal and prostate cancers, cardio-vascular disease, autoimmune conditions and infections. Vitamin D analogs constitute a valuable group of compounds which can be used to regulate gene expression in functions as varied as calcium and phosphate homeostasis, as well as cell growth regulation and cell differentiation of a wide spectrum of cell types. This review will discuss the full range of vitamin D compounds currently available, some of their possible uses, and potential mechanisms of action.

The role of vitamin D in cancer prevention and treatment

Calcitriol (1,25-dihydroxyvitamin D(3)), the hormonally active form of vitamin D, exerts growth inhibitory and prodifferentiating effects on many malignant cells and retards tumor growth in animal models. Calcitriol is being evaluated as an anticancer agent in several human cancers. The mechanisms underlying the anticancer effects of calcitriol include inhibition of cell proliferation, stimulation of apoptosis, suppression of inflammation, and inhibition of tumor angiogenesis, invasion, and metastasis. This review discusses some of the molecular pathways mediating these anticancer actions of calcitriol and the preclinical data in cell culture and animal models. The clinical trials evaluating the use of calcitriol and its analogues in the treatment of patients with cancer are described. The reasons for the lack of impressive beneficial effects in clinical trials compared with the substantial efficacy seen in preclinical models are discussed.

Occupational sunlight exposure and risk of renal cell carcinoma

BACKGROUND

Recent findings indicate that vitamin D obtained from ultraviolet (UV) exposure may reduce the risk of several different cancers. Vitamin D is metabolized to its active form within the kidney, which is the major organ for vitamin D metabolism and activity. Because both the incidence of renal cell carcinoma (RCC) and the prevalence of vitamin D deficiency have increased over the past few decades, in the current study, the authors explored whether occupational UV exposure was associated with RCC risk.

METHODS

A hospital-based, case-control study of 1097 patients with RCC (cases) and 1476 controls was conducted in 4 Central and Eastern European countries. Demographic and occupational information was collected to examine the association between occupational UV exposure and RCC risk.

RESULTS

A significant reduction (24%-38%) in the risk of RCC was observed with increasing occupational UV exposure among men who participated in the study. No association between UV exposure and RCC risk was observed among women who participated. When the analyses were stratified by latitude as another estimate of sunlight intensity, a stronger reduction (71%-73%) in the risk of RCC was observed between UV exposure and cancer risk among men who resided at the highest latitudes.

CONCLUSIONS

The current results suggested that, among men, there is an inverse association between occupational UV exposure and the risk of RCC. Replication studies are warranted to confirm these results.

1alpha,25-Dihydroxyvitamin D(3) triggered vitamin D receptor and farnesoid X receptor-like effects in rat intestine and liver in vivo

1alpha,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), a natural ligand of the vitamin D receptor (VDR), was found to increase the rat ileal Asbt and bile acid absorption. The effects of VDR, whose expression is low in liver, on hepatic transporters and enzymes are unknown. Protein and mRNA levels of target genes in the small intestine, colon and liver after intraperitoneal dosing of 1,25(OH)(2)D(3) (0-2.56 nmol/kg/day for 4 days) to the rat were determined by Western blotting and qPCR, respectively. The 1,25(OH)(2)D(3) treatment increased total Cyp3a protein and Cyp3a1 mRNA expressions in the proximal small intestine, and the short heterodimer partner (SHP), the fibroblast growth factor 15 (FGF15), organic solute transporter (Ostalpha and Ostbeta) mRNA and Asbt protein expressions in the ileum. About 50% higher portal bile acid concentration (65.1+/-14.9 vs 41.9+/-7.8 microm, p<0.05) and elevated expressions of the hepatic farnesoid X receptor (FXR) and SHP mRNA resulted with 1,25(OH)(2)D(3) treatment. Increased Bsep and Ostalpha mRNA expressions in liver and a>50% reduction in the Cyp7a1 protein level (p<0.05) and cholesterol metabolism in rat liver microsomes (p=0.002), likely consequences of the bile acid-FXR-SHP cascade and activation of the signaling pathway for Cyp7a1 inhibition by FGF15, were found. Increased hepatic multidrug resistance-associated protein (Mrp3) and multidrug resistance protein 1a (Mdr1a) mRNA and P-gp protein were also observed. It was concluded that the changes in hepatic transporters and enzymes in the rat were indirect, secondary effects of the liver FXR-SHP cascade due to increased intestinal absorption of bile acids and elevated levels of FGF15, events that led to the activation of FXR.

H2O2-dependent translocation of TCTP into the nucleus enables its interaction with VDR in human keratinocytes: TCTP as a further module in calcitriol signalling

Translationally controlled tumour protein (TCTP) is an evolutionarily highly conserved molecule implicated in many processes related to cell cycle progression, proliferation and growth, to the protection against harmful conditions including apoptosis and to the human allergic response. We are showing here that after application of mild oxidative stress, human TCTP relocates from the cytoplasm to the nuclei of HaCaT keratinocytes where it directly associates with the ligand-binding domain of endogenous vitamin D(3) receptor (VDR) through its helical domain 2 (AA 71-132). Interestingly, the latter harbours a putative nuclear hormone receptor coregulatory LxxLL-like motif which seems to be involved in the interaction. Moreover, we demonstrate that VDR transcriptionally induces the expression of TCTP by binding to a previously unknown VDR response element within the TCTP promotor. Conversely, ectopically overexpressed TCTP downregulates the amount of VDR on both mRNA as well as protein level. These data, to conclude, suggest a kind of feedback regulation between TCTP and VDR to regulate a variety of (Ca(2+) dependent) cellular effects and in this way further underscore the physiological relevance of this novel protein-protein interaction.

Vitamin d pathway genes, diet, and risk of renal cell carcinoma

Mediated by binding to the high-affinity vitamin D receptor (VDR), vitamin D forms a heterodimer complex with the retinoid-X-receptor (RXR). Variation in both genes has been shown to modify renal cell carcinoma (RCC) risk. Therefore, we investigated whether VDR and RXRA polymorphisms modify associations between RCC risk and frequency of dietary intake of vitamin D and calcium rich foods, and occupational ultraviolet exposure among 777 RCC case and 1035 controls from Central and Eastern Europe. A positive association was observed in this population between increasing dietary intake frequency of yogurt, while an inverse association was observed with egg intake frequency. RXRA polymorphisms, located 3' of the coding sequence, modified associations between specific vitamin D rich foods and RCC risk, while RXRA polymorphisms, located in introns 1 and 4, modified associations with specific calcium rich foods. Results suggest that variants in the RXRA gene modified the associations observed between RCC risk and calcium and vitamin D intake.

Vitamin D: considerations in the continued development as an agent for cancer prevention and therapy

Considerable preclinical and epidemiologic data suggest that vitamin D may play a role in the pathogenesis, progression, and therapy for cancer. Numerous epidemiologic studies support the hypothesis that individuals with lower serum vitamin D levels have a higher risk of a number of cancers. Measures of vitamin D level in such studies include both surrogate estimates of vitamin D level (residence in more northern latitudes, history of activity, and sun exposure) as well as measured serum 25(OH) cholecalciferol levels. Perhaps, the most robust of these epidemiologic studies is that of Giovannucci et al, who developed and validated an estimate of serum 25(OH) cholecalciferol level and reported that among >40,000 individuals in the Health Professionals Study, an increase in 25(OH) cholecalciferol level of 62.5 ng/mL was associated with a reduction in the risk of head/neck, esophagus, pancreas cancers, and acute leukemia by >50%. Unfortunately, very limited data are available to indicate whether or not giving vitamin D supplements reduces the risk of cancer. Many preclinical studies indicate that exposing cancer cells, as well as vascular endothelial cells derived from tumors, to high concentrations of active metabolites of vitamin D halts progression through cell cycle, induces apoptosis and will slow or stop the growth of tumors in vivo. There are no data that one type of cancer is more or less susceptible to the effects of vitamin D. Vitamin D also potentiates the antitumor activity of a number of types of cytotoxic anticancer agents in in vivo preclinical models. Vitamin D analogues initiate signaling through a number of important pathways, but the pathway(s) essential to the antitumor activities of vitamin D are unclear. Clinical studies of vitamin D as an antitumor agent have been hampered by the lack of a suitable pharmaceutical preparation for clinical study. All commercially available formulations are inadequate because of the necessity to administer large numbers of caplets and the poor "bioavailability" of calcitriol (the most carefully studied analogue) at these high doses. Preclinical data suggest that high exposures to calcitriol are necessary for the antitumor effects. Clinical data do indicate that high doses of calcitriol (>100 mcg weekly, intravenously, and 0.15 microg /kg weekly, orally) can be given safely. The maximum tolerated dose of calcitriol is unclear. While a 250-patient trial in men with castration-resistant prostate cancer comparing docetaxel (36 mg/sqm weekly) +/- calcitriol 0.15 microg/kg indicated that calcitriol was very safe may have reduced to death rate, an adequately powered (1000 patients) randomized study of weekly docetaxel + calcitriol versus q3 week docetaxel was negative. The limitations of this trial were the unequal chemotherapy arms compared in this study and the failure to use an optimal biologic dose or maximum-tolerated dose of calcitriol. In view of the substantial preclinical and epidemiologic data supporting the potential role of vitamin D in cancer, careful studies to evaluate the impact of vitamin D replacement on the frequency of cancer and the impact of an appropriate dose and schedule of calcitriol or other active vitamin D analogue on the treatment of established cancer are indicated.

Vitamin D, nervous system and aging

This is a mini-review of vitamin D(3), its active metabolites and their functioning in the central nervous system (CNS), especially in relation to nervous system pathologies and aging. The vitamin D(3) endocrine system consists of 3 active calcipherol hormones: calcidiol (25OHD(3)), 1alpha-calcitriol (1alpha,25(OH)2D(3)) and 24-calcitriol (24,25(OH)2D(3)). The impact of the calcipherol hormone system on aging, health and disease is discussed. Low serum calcidiol concentrations are associated with an increased risk of several chronic diseases including osteoporosis, cancer, diabetes, autoimmune disorders, hypertension, atherosclerosis and muscle weakness all of which can be considered aging-related diseases. The relationship of many of these diseases and aging-related changes in physiology show a U-shaped response curve to serum calcidiol concentrations. Clinical data suggest that vitamin D(3) insufficiency is associated with an increased risk of several CNS diseases, including multiple sclerosis, Alzheimer's and Parkinson's disease, seasonal affective disorder and schizophrenia. In line with this, recent animal and human studies suggest that vitamin D insufficiency is associated with abnormal development and functioning of the CNS. Overall, imbalances in the calcipherol system appear to cause abnormal function, including premature aging, of the CNS.

Analysis of SNPs and haplotypes in vitamin D pathway genes and renal cancer risk

In the kidney vitamin D is converted to its active form. Since vitamin D exerts its activity through binding to the nuclear vitamin D receptor (VDR), most genetic studies have primarily focused on variation within this gene. Therefore, analysis of genetic variation in VDR and other vitamin D pathway genes may provide insight into the role of vitamin D in renal cell carcinoma (RCC) etiology. RCC cases (N = 777) and controls (N = 1,035) were genotyped to investigate the relationship between RCC risk and variation in eight target genes. Minimum-p-value permutation (Min-P) tests were used to identify genes associated with risk. A three single nucleotide polymorphism (SNP) sliding window was used to identify chromosomal regions with a False Discovery Rate of <10%, where subsequently, haplotype relative risks were computed in Haplostats. Min-P values showed that VDR (p-value = 0.02) and retinoid-X-receptor-alpha (RXRA) (p-value = 0.10) were associated with RCC risk. Within VDR, three haplotypes across two chromosomal regions of interest were identified. The first region, located within intron 2, contained two haplotypes that increased RCC risk by approximately 25%. The second region included a haplotype (rs2239179, rs12717991) across intron 4 that increased risk among participants with the TC (OR = 1.31, 95% CI = 1.09-1.57) haplotype compared to participants with the common haplotype, TT. Across RXRA, one haplotype located 3' of the coding sequence (rs748964, rs3118523), increased RCC risk 35% among individuals with the variant haplotype compared to those with the most common haplotype. This study comprehensively evaluated genetic variation across eight vitamin D pathway genes in relation to RCC risk. We found increased risk associated with VDR and RXRA. Replication studies are warranted to confirm these findings.

RRR-alpha-vitamin E succinate potentiates the antitumor effect of calcitriol in prostate cancer without overt side effects

PURPOSE

To determine the antitumor efficacy of using calcitriol combined with RRR-alpha-vitamin E succinate (VES) on prostate cancer.

EXPERIMENTAL DESIGN

The effects of VES or VES in combination with calcitriol on the calcitriol target genes were evaluated by Western blot and real-time PCR. The antiproliferation effect of the combination in prostate cancer cells was evaluated by the combination index method. The role of the vitamin D(3) receptor (VDR) in the enhanced antitumor effects of the combination was confirmed by small interfering RNA knockdown strategy. Xenograft-bearing mice were used to reaffirm the antitumor efficacy of this combination. Pathohistology analyses and expressions of VDR and its target genes were analyzed in untreated and treated tumors.

RESULTS

VES selectively increased VDR protein in different prostate cancer cells. Low doses of calcitriol combined with VES were significantly superior to the additive effect of individual treatments against prostate cancer cell proliferation. The expression of VDR target genes involved in antiproliferation were further sensitized in the presence of VES. Knockdown of VDR expression abolished the combination benefits in LNCaP and PC3 cells. Consistently, in prostate cancer xenograft models, VES enhanced the therapeutic efficacy of a tolerated dose of calcitriol yet without overt evidence of systemic toxicity and hypercalcemia. This notable in vivo effect was also accompanied by up-regulation of VDR target genes.

CONCLUSIONS

Low-dose calcitriol combined with vitamin E analogue could be a solution to the calcemic side effect. The demonstration of superior antitumor activity of low-dose calcitriol plus VES provides the preclinical basis for developing a useful therapeutic strategy for prostate cancer.

1Alpha,25-dihydroxyvitamin D3 reduces c-Myc expression, inhibiting proliferation and causing G1 accumulation in C4-2 prostate cancer cells

There is an inverse correlation between exposure to sunlight (the major source of vitamin D) and the risk for prostate cancer, the most common noncutaneous cancer and second most common cause of death from cancer in American men. The active metabolite of vitamin D, 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] acting through the vitamin D receptor decreases prostate cancer cell growth and invasiveness. The precise mechanisms by which 1,25(OH)(2)D(3) inhibits growth in prostate cancer have not been fully elucidated. Treatment with 1,25(OH)(2)D(3) causes an accumulation in the G(0)/G(1) phase of the cell cycle in several prostate cancer cell lines. One potential target known to regulate the G(0)/G(1) to S phase transition is c-Myc, a transcription factor whose overexpression is associated with a number of cancers including prostate cancer. We find that 1,25(OH)(2)D(3) reduces c-Myc expression in multiple prostate epithelial cell lines, including C4-2 cells, an androgen-independent prostate cancer cell line. Reducing c-Myc expression to the levels observed after 1,25(OH)(2)D(3) treatment resulted in a comparable decrease in proliferation and G(1) accumulation demonstrating that down-regulation of c-Myc is a major component in the growth-inhibitory actions of 1,25(OH)2D(3). Treatment with 1,25(OH)(2)D(3) resulted in a 50% decrease in c-Myc mRNA but a much more extensive reduction in c-Myc protein. Treatment with 1,25(OH)(2)D(3) decreased c-Myc stability by increasing the proportion of c-Myc phosphorylated on T58, a glycogen synthase kinase-3beta site that serves as a signal for ubiquitin-mediated proteolysis. Thus, 1,25(OH)(2)D(3) reduces both c-Myc mRNA levels and c-Myc protein stability to inhibit growth of prostate cancer cells.

Covalent labeling of nuclear vitamin D receptor with affinity labeling reagents containing a cross-linking probe at three different positions of the parent ligand: structural and biochemical implications

Structure-functional characterization of vitamin D receptor (VDR) requires identification of structurally distinct areas of VDR-ligand-binding domain (VDR-LBD) important for biological properties of 1alpha,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)). We hypothesized that covalent attachment of the ligand into VDR-LBD might alter 'surface structure' of that area influencing biological activity of the ligand. We compared anti-proliferative activity of three affinity alkylating derivatives of 1,25(OH)(2)D(3) containing an alkylating probe at 1,3 and 11 positions. These compounds possessed high-affinity binding for VDR; and affinity labeled VDR-LBD. But, only the analog with probe at 3-position significantly altered growth in keratinocytes, compared with 1,25(OH)(2)D(3). Molecular models of these analogs, docked inside VDR-LBD tentatively identified Ser237 (helix-3: 1,25(OH)(2)D(3)-1-BE), Cys288 (beta-hairpin region: 1,25(OH)(2)D(3)-3-BE,) and Tyr295 (helix-6: 1,25(OH)(2)D(3)-11-BE,) as amino acids that are potentially modified by these reagents. Therefore, we conclude that the beta-hairpin region (modified by 1,25(OH)(2)D(3)-3-BE) is most important for growth inhibition by 1,25(OH)(2)D(3), while helices 3 and 6 are less important for such activity.

Vitamin D and aging

Recent studies using genetically modified mice, such as FGF23-/- and Klotho-/- mice that exhibit altered mineral homeostasis due to a high vitamin D activity showed features of premature aging that include retarded growth, osteoporosis, atherosclerosis, ectopic calcification, immunological deficiency, skin and general organ atrophy, hypogonadism and short lifespan. The phenotype reversed by normalizing vitamin D and/or mineral homeostasis. Thus, hypervitaminosis D due to an increased 1alpha-hydroxylase activity seems to be a cause of the premature aging. In several studies, we have described that a complete or partial lack of vitamin D action (VDR-/- mice and CYP27B1-/-) show almost similar phenotype as FGF23-/- or Klotho-/- mice. VDR mutant mice have growth retardation, osteoporosis, kyphosis, skin thickening and wrinkling, alopecia, ectopic calcification, progressive loss of hearing and balance as well as short lifespan. CYP27B1-/- mice do not show alopecia nor balance deficit, which might be apoVDR-dependent or calcidiol-dependent. The features are typical to premature aging. The phenotype is resistant to a normalization of the mineral homeostasis by a rescue diet containing high calcium and phosphate. Taken together, aging shows a U-shaped dependency on hormonal forms of vitamin D suggesting that there is an optimal concentration of vitamin D in delaying aging phenomena. Our recent study shows that calcidiol is an active hormone. Since serum calcidiol but not calcitriol is fluctuating in physiological situations, calcidiol might determine the biological output of vitamin D action. Due to its high serum concentration and better uptake of calcidiol-DBP by the target cells through the cubilin-megalin system, calcidiol seems to be an important circulating hormone. Therefore, serum calcidiol might be associated with an increased risk of aging-related chronic diseases more directly than calcitriol. Aging and cancer seem to be tightly associated phenomena. Accumulation of damage on DNA and telomeres cause both aging and cancer, moreover the signalling pathways seem to converge on tumour suppressor protein, p53, which seems to be regulated by vitamin D. Also, the insulin-like growth factor signalling pathway (IGF-1, IGFBPs, IGFR) and fibroblast growth factor-23 (FGF-23) regulate growth, aging and cancer. Vitamin D can regulate these signalling pathways, too. Also NF-kappaB and telomerase reverse transcriptase (TERT) might be molecular mechanisms mediating vitamin D action in aging and cancer. Calcidiol serum concentrations show a U-shaped risk of prostate cancer suggesting an optimal serum concentration of 40-60 nmol/L for the lowest cancer risk. Therefore, it is necessary to study several common aging-associated diseases such as osteoporosis, hypertension and diabetes known to be vitamin D-dependent before any recommendations of an optimal serum concentration of calcidiol are given.

Menthol Enhances an Antiproliferative Activity of 1alpha,25-Dihydroxyvitamin D(3) in LNCaP Cells

1α,25-dihydroxyvitamin D₃ [1α,25(OH)₂D₃], the most active form of vitamin D₃, and its analogues have therapeutic benefits for prostate cancer treatment. However, the development of hypercalcemia is an obstacle to clinical applications of 1α,25(OH)₂D₃ for cancer therapy. In this study, we provide evidence that menthol, a key component of peppermint oil, increases an anti-proliferation activity of 1α,25(OH)₂D₃ in LNCaP prostate cancer cells. We found that menthol per se does not exhibit antiproliferative activity, but it is able to enhance 1α,25(OH)₂D₃-mediated growth inhibition in LNCaP cells. Fluorometric assays using Fura-2 showed that 1α,25(OH)₂D₃ does not induce acute Ca²⁺ response, whereas menthol evokes an increase in [Ca²⁺]_i, which suggests that cross-talks of menthol-induced Ca²⁺ signaling with 1α,25(OH)₂D₃-mediated growth inhibition pathways. In addition, Western blot analysis revealed that 1α,25(OH)₂D₃ and menthol cooperatively modulate the expression of bcl-2 and p21 which provides the insight into the molecular mechanisms underlying the enhanced 1α,25(OH)₂D₃-mediated growth inhibition by menthol. Thus, our findings suggest that menthol may be a useful natural compound to enhance therapeutic effects of 1α,25(OH)₂D₃.

Novel Gemini vitamin D(3) analogs have potent antitumor activity

The active form of vitamin D(3), 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], modulates proliferation and induces differentiation of many cancer cells. A new class of analogs of vitamin D(3) has been synthesized, having two side-chains attached to carbon-20 (Gemini) and deuterium substituted on one side-chain. We have examined six of these analogs for their ability to inhibit growth of myeloid leukemia (HL-60), prostate (LNCaP, PC-3, DU145), lung (H520), colon (HT-29), and breast (MCF-7) cancer cell lines. Dose-response clonogenic studies showed that all six analogs had greater antiproliferative activities against cancer cells than 1,25(OH)(2)D(3). Although they had similar potency, the most active of these analogs was BXL-01-0120. BXL-01-0120 was 529-fold more potent than 1,25(OH)(2)D(3) in causing 50% clonal growth inhibition (ED(50)) of HL-60 cells. Pulse-exposure studies demonstrated that exposure to BXL-01-120 (10(-9)M, 48h) resulted in 85% clonal inhibition of HL-60 growth. BXL-01-0120 (10(-11)M, 4 days) induced the differentiation marker, CD11b. Also, morphologically differentiation was more prominent compared to 1,25(OH)(2)D(3). Annexin V assay showed that BXL-01-0120 (10(-10)M, 4 days) induced significantly (p<0.05) more apoptosis than 1,25(OH)(2)D(3). In summary, these analogs have a unique structure resulting in extremely potent inhibition of clonal proliferation of various types of cancer cells, especially HL-60 cells.

A novel SNP in a vitamin D response element of the CYP24A1 promoter reduces protein binding, transactivation, and gene expression

The active form of vitamin D (1alpha,25(OH)(2)D(3)) is known to have antiproliferative effects and has been implicated in cancers of the colon, breast, and prostate. These cancers occur more frequently among African Americans than Caucasians, and individuals with African ancestry are known to have approximately twofold lower levels of serum vitamin D (25(OH)D) compared with individuals of European ancestry. However, epidemiological studies of the vitamin D receptor (VDR) have shown inconsistent associations with cancer risk, suggesting that differences in other genes in the pathway may be important. We sought to identify functionally significant polymorphic variants in CYP24A1, a gene that is highly inducible by 1alpha,25(OH)(2)D(3) and that encodes the primary catabolic enzyme in the pathway. Here we report the identification of six novel SNPs in the human CYP24A1 promoter, including one at nucleotide -279 occurring within the distal vitamin D response element (VDRE2). Our experiments demonstrate that the VDRE2 variant results in decreased protein binding and transactivation in vitro, and reduced expression of CYP24A1 in cultured primary human lymphocytes provides evidence for an effect in vivo. This variant was only observed in our African American population, and represents a first step toward understanding differences in disease risk among racial/ethnic groups.

1alpha,25-Dihydroxyvitamin D3 potentiates cisplatin antitumor activity by p73 induction in a squamous cell carcinoma model

1alpha,25-Dihydroxyvitamin D3 (1,25D3) exhibits antitumor activity in a variety of cancers including squamous cell carcinoma (SCC). Intrinsic resistance of SCC cells to cisplatin was observed and led to the investigation into whether 1,25D3 sensitizes SCC cells to cisplatin. Pretreatment with 1,25D3 followed by cisplatin enhanced growth inhibition in SCC cells compared with 1,25D3 alone as assessed by cytotoxicity and in vitro clonogenic assays. In addition, 1,25D3 sensitized SCC cells to cisplatin-mediated apoptosis. Treatment of tumor-bearing C3H mice with 1,25D3 before cisplatin reduced clonogenic survival using in vivo excision clonogenic assay. These results were not observed in a 1,25D3-resistant SCC variant, indicating the critical role of 1,25D3 in sensitizing SCC cells to cisplatin. Further, a marked decrease in fractional tumor volume was observed when SCC tumor-bearing mice were treated with 1,25D3 before cisplatin compared with either agent administered alone. Cisplatin has been shown to modulate p73 protein level in certain cancer cells. Our data showed that p73 level was not affected by cisplatin but increased by 1,25D3 in SCC cells. Knocking down p73 by small interfering RNA protected SCC cells against 1,25D3 and cisplatin-mediated clonogenic cell kill and apoptosis. Increasing p73 protein level by knocking down UFD2a, which mediates p73 degradation, promoted 1,25D3 and cisplatin-mediated clonogenic cell kill. These results suggest that 1,25D3 potentiates cisplatin antitumor activity in vitro and in vivo in a SCC model system possibly through p73 induction and apoptosis. The combination treatment may provide a more effective therapeutic regimen in cancer treatment.

Circulating 25-hydroxyvitamin D, VDR polymorphisms, and survival in advanced non-small-cell lung cancer

PURPOSE

We showed previously that in early-stage non-small-cell lung cancer (NSCLC), serum vitamin D levels and VDR polymorphisms were associated with survival. We hypothesized that vitamin D levels and VDR polymorphisms may also affect survival among patients with advanced NSCLC.

PATIENTS AND METHODS

We evaluated the relationship between circulating 25-hydroxyvitamin D levels; VDR polymorphisms, including Cdx-2 G>A (rs11568820), FokI C>T (rs10735810), and BsmI C>T (rs144410); and overall survival among patients with advanced NSCLC. Analyses of survival outcomes were performed using the log-rank test and Cox proportional hazards models, adjusting for sex, stage, and performance status.

RESULTS

There were 294 patients and 233 deaths, with median follow-up of 42 months. We found no difference in survival by circulating vitamin D level. The C/C genotype of the FokI polymorphism was associated with improved survival: median survival for C/C was 21.4 months, for C/T was 12.1 months, and for T/T was 15.6 months (log-rank P = .005). There were no significant effects on survival by the Cdx-2 or BsMI polymorphism. However, having increasing numbers of protective alleles was associated with improved survival (adjusted hazard ratio for two or more v zero to one protective alleles, 0.57; 95% CI, 0.41 to 0.79; P = .0008). On haplotype analysis, the G-T-C (Cdx-2-FokI-BsmI) haplotype was associated with worse survival compared with the most common haplotype of G-C-T (adjusted hazard ratio, 1.61; 95% CI, 1.21 to 2.14; P = .001).

CONCLUSION

There was no main effect of vitamin D level on overall survival in the advanced NSCLC population. The T allele of the VDR FokI>T polymorphism and the G-T-C (Cdx-2-FokI-BsmI) haplotype were associated with worse survival.

Vitamin D receptor expression in normal, premalignant, and malignant human lung tissue

BACKGROUND

There is a strong interest in identifying chemopreventive agents that might help decrease the burden of lung cancer. The active metabolite of vitamin D, 1,25-dihydroxycholecalciferol (calcitriol), has been shown to have antiproliferative effects in several tumor types, mediated by the vitamin D receptor (VDR). This is the first comprehensive survey of VDR expression in a series of human lung tissues, including normal and premalignant central airway biopsies and lung tumors.

METHODS

Immunohistochemical expression of nuclear and cytoplasmic VDR was examined in 180 premalignant or malignant bronchial biopsies from bronchoscopy of 78 high-risk individuals at the Roswell Park Cancer Institute and also in 63 tumor samples from 35 lung cancer patients from the University of Chicago Hospitals. Associations between clinicopathologic data and VDR expression were examined.

RESULTS

VDR expression was present in many samples. In biopsies, VDR was commonly detected throughout the full epithelial layer. Most histologically normal (60%, 53 of 88) and metaplastic (61%, 39 of 64) samples had moderate to high nuclear intensity; dysplastic samples mostly had low nuclear intensity (10 of 18, 55%). In tumor samples, 62% (38 of 61) were lacking cytoplasmic VDR, with nuclear expression present in 79%(49 of 62). Analysis of all samples revealed a positive linear trend between proportion of samples with greater nuclear than cytoplasmic intensity and increasing histologic grade (P < 0.01).

CONCLUSIONS

VDR expression spanned the lung carcinogenesis spectrum. Nuclear expression was similar across various histologies, whereas cytoplasmic expression decreased with increasing histologic grade. These results indicate that there is potential for the use of calcitriol as a chemopreventive agent against the development of lung cancer.

Vitamin D insufficiency in a multiethnic cohort of breast cancer survivors

BACKGROUND

Little is known about vitamin D status in breast cancer survivors. This issue is important because vitamin D influences pathways related to carcinogenesis.

OBJECTIVE

The objective of this report was to describe and understand vitamin D status in a breast cancer survivor cohort.

DESIGN

Data are from the Health, Eating, Activity, and Lifestyle study. With the use of a cross-sectional design, we examined serum concentrations of 25-hydroxyvitamin D [25(OH)D] in 790 breast cancer survivors from western Washington state, New Mexico, and Los Angeles County. Cancer treatment data were obtained from Surveillance, Epidemiology, and End Results registries and medical records. Fasting blood, anthropometry, and lifestyle habits were collected after diagnosis and treatment. We examined distributions of 25(OH)D by race-ethnicity, season, geography, and clinical characteristics. Multivariate regression tested associations between 25(OH)D and stage of disease.

RESULTS

Five hundred ninety-seven (75.6%) of the women had low serum 25(OH)D, suggesting vitamin D insufficiency or frank deficiency. The overall mean (+/-SD) was 24.8 +/- 10.4 ng/mL, but it was lower for African Americans (18.1 +/- 8.7 ng/mL) and Hispanics (22.1 +/- 9.2 ng/mL). Women with localized (n = 424) or regional (n = 182) breast cancer had lower serum 25(OH)D than did women with in situ disease (n = 184) (P = 0.05 and P = 0.03, respectively). Multivariate regression models controlled for age, body mass index (in kg/m(2)), race-ethnicity, geography, season, physical activity, diet, and cancer treatments showed that stage of disease independently predicted serum 25(OH)D (P = 0.02).

CONCLUSIONS

In these breast cancer survivors, the prevalence of vitamin D insufficiency was high. Clinicians might consider monitoring vitamin D status in breast cancer patients, together with appropriate treatments, if necessary.

Prostate cancer, serum parathyroid hormone, and the progression of skeletal metastases

Bony metastases from prostate cancer are a significant cause of morbidity and mortality. These metastases are predominantly blastic (bone-forming) and commonly cause increased serum levels of parathyroid hormone (PTH) as calcium ions are transferred from serum into blastic bone. The epidemiologic and clinical significance of secondary hyperparathyroidism in advanced prostate cancer have not been widely appreciated. Prostate cancer bony metastases show increased expression of the PTH receptor (PTH-IR) and PTH promotes the growth and invasiveness of prostate cancer cells in bone. Thus, blastic metastases appear to induce a "vicious cycle" in which PTH resorbs normal bone to support the growth of blastic bone. Recognition of the potential role of PTH in the progression of skeletal metastases suggests novel opportunities for prostate cancer secondary prevention. In particular, we propose that suppressing serum PTH in advanced prostate cancer may reduce morbidity by decreasing fractures and pain caused by bone resorption and may reduce mortality by retarding the progression of metastatic disease.

Calcium metabolism in birds

Calcium is one of the most important plasma constituents in mammals and birds. It provides structural strength and support (bones and eggshell) and plays vital roles in many of the biochemical reactions in the body. The control of calcium metabolism in birds is highly efficient and closely regulated in a number of tissues, primarily parathyroid gland, intestine, kidney, and bone. The hormones with the greatest involvement in calcium regulation in birds are parathyroid hormone, 1,25-dihydroxyvitamin D(3) (calcitriol), and estrogen, with calcitonin playing a minor and uncertain role. The special characteristics of calcium metabolism in birds, mainly associated with egg production, are discussed, along with common clinical disorders secondary to derangements in calcium homeostasis.

The vitamin D receptor

The vitamin D endocrine system is known for its essential role in calcium homeostasis and bone metabolism, and induces cell differentiation, inhibits cell growth, controls other hormonal systems, and modulates the immune response. Vitamin D(3) is a prohormone that is taken up by diet or synthesized in ultraviolet radiation-exposed skin and metabolically converted to the active metabolite, 1alpha,25-dihydroxyvitamin D(3). This nuclear hormone binds with high affinity the nuclear receptor vitamin D receptor. More than 3000 synthetic analogs of 1alpha,25(OH)(2)D(3) are known. This review aims to provide an overview on vitamin D signaling from the skin perspective.

Role of nongenomic activation of phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase 1/2 pathways in 1,25D3-mediated apoptosis in squamous cell carcinoma cells

Vitamin D is a steroid hormone that regulates calcium homeostasis and bone metabolism. The active form of vitamin D [1 alpha,25-dihydroxyvitamin D(3) (1,25D3)] acts through both genomic and nongenomic pathways. 1,25D3 has antitumor effects in a variety of cancers, including colorectal, prostate, breast, ovarian, and skin cancers. 1,25D3 exerts growth-inhibitory effects in cancer cells through the induction of apoptosis, cell cycle arrest, and differentiation. The mechanisms regulating 1,25D3-induced apoptosis remain unclear. We investigated the role of nongenomic signaling in 1,25D3-mediated apoptosis in squamous cell carcinoma (SCC) cells. 1,25D3 induced rapid and sustained activation of phosphatidylinositol 3-kinase/Akt and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) 1/2 pathways in SCC cells. These effects were nongenomic: they occurred rapidly and were not inhibited by cycloheximide or actinomycin D. To examine whether the nongenomic activation of Akt and ERK1/2 plays a role in 1,25D3-mediated apoptosis, the expression of Akt or ERK1/2 was reduced by small interfering RNA (siRNA). siRNA-Akt significantly enhanced 1,25D3-induced apoptosis as indicated by increased levels of Annexin V-positive cells and increased sub-G(1) population and DNA fragmentation. In contrast, siRNA-ERK1/2 had no effects on 1,25D3-induced apoptosis. In addition, siRNA-Akt transfection followed by 1,25D3 treatment induced apoptosis much sooner than 1,25D3 alone. siRNA-Akt and 1,25D3 induced caspase-10 activation, suppressed the expression of c-IAP1 and XIAP, and promoted 1,25D3-induced caspase-3 activation. These results support a link between 1,25D3-induced nongenomic signaling and apoptosis. 1,25D3 induces the activation of phosphatidylinositol 3-kinase/Akt, which suppresses 1,25D3-mediated apoptosis and prolongs the survival of SCC cells.

A phase I pharmacokinetic and pharmacodynamic study of intravenous calcitriol in combination with oral gefitinib in patients with advanced solid tumors

PURPOSE

In preclinical models, calcitriol and the tyrosine kinase inhibitor gefitinib are synergistic and modulate extracellular signal-regulated kinase (Erk) and Akt pathways. Therefore, we conducted a phase I study of calcitriol and gefitinib to determine the maximum tolerated dose (MTD) of this combination.

EXPERIMENTAL DESIGN

Calcitriol was given i.v. over 1 h on weeks 1, 3, and weekly thereafter. Gefitinib was given at a fixed oral daily dose of 250 mg starting at week 2 (day 8). Escalation occurred in cohorts of three patients until the MTD was defined. Pharmacokinetic studies were done for calcitriol and gefitinib. Serial skin biopsies were done to investigate epidermal growth factor receptor (EGFR) pathway pharmacodynamic interactions.

RESULTS

Thirty-two patients were treated. Dose-limiting hypercalcemia was noted in two of four patients receiving 96 mug/wk of calcitriol. One of seven patients developed dose-limiting hypercalcemia at the MTD 74 mug/wk calcitriol dose level. The relationship between calcitriol dose and peak serum calcitriol (C(max)) and systemic exposure (AUC) was linear. Mean (+/-SD) serum calcitriol C(max) at the MTD was 6.68 +/- 1.42 ng/mL. Gefitinib treatment inhibited EGFR, Akt, and Erk phosphorylation in the skin. Calcitriol did not have consistent effects on skin EGFR or its downstream elements. The combination of gefitinib and calcitriol did not modulate tumor EGFR pathway in patients with serial tumor biopsies.

CONCLUSIONS

High doses of weekly i.v. calcitriol can be administered safely in combination with gefitinib. Calcitriol concentrations achieved at the MTD 74 mug calcitriol exceed in vivo concentrations associated with antitumor activity in preclinical models.

Vitamin D3and the immune system: maintaining the balance in health and disease

1,25-Dihydroxyvitamin D3(1,25(OH)2D3), the active form of vitamin D3, is a central player in Ca and bone metabolism. More recently, important immunomodulatory effects have been attributed to this hormone. By binding to its receptor, the vitamin D receptor, 1,25(OH)2D3regulates the expression of various genes and consequently affects the behaviour of different cell types within the immune system. 1,25(OH)2D3can potently inhibit pathogenic T cells and gives rise to elevated numbers of regulatory T cells via the induction of tolerogenic dendritic cells. These immunomodulatory activities of 1,25(OH)2D3have also been proven usefulin vivo: administration of 1,25(OH)2D3in several animal models can prevent or cure different autoimmune diseases and graft rejection. To overcome the dose-limiting side effects of 1,25(OH)2D3on Ca and bone, less calcaemic structural analogues (alone or in combination with synergistically acting drugs or bone-resorption inhibitors) have been successfully used in animal models. Furthermore, as 1,25(OH)2D3also contributes to host defence against infectious agents by the induction of antimicrobial responses, this molecule might provide a new strategy to deal with drug-resistant infections. According to the pleiotropic effects of 1,25(OH)2D3in the immune system, increasing epidemiological data underline the importance of adequate vitamin D intakes in reducing the risk of several autoimmune diseases and infections such as tuberculosis.

Latitude and incidence of ocular melanoma

We investigated the associations between latitude and the incidence of two different types of ocular melanoma, external ocular melanoma (exposed to sunlight) and internal melanoma (not exposed to sunlight), separately. Using 1992-2002 data from the Surveillance, Epidemiology, and End Results (SEER) Program of National Cancer Institute, we identified 2142 ocular melanoma cases in non-Hispanic whites, and then regressed the incidences of various types of ocular melanomas with latitude. Our analysis indicated that the higher the latitude (away from the equator, the less sun exposure), the lower the risk of external ocular melanoma (eyelid and conjunctival melanomas) among non-Hispanic whites (P for trend = 0.018). The incidence increased 2.48 fold from 47-48 degrees to 20-22 degrees. This trend is very similar to that of skin melanoma. The incidence of internal ocular melanoma (uveal melanoma) increased significantly with increasing latitudes (the less sun exposure, P for trend < 0.0001), it increased 4.91 fold from 20-22 degrees to 47-48 degrees. The latitudinal patterns of ocular melanomas may reflect the dual effects of sunlight exposure, i.e. a mutagenic effect of direct solar radiation on external ocular melanomas and a protective effect for internal uveal melanoma, which is similar to the sun radiation protective effects for various internal malignant tumors that are not exposed to the sunlight.

The cell cycle hypothesis of Alzheimer's disease: Suggestions for drug development

The cell cycle of hypothesis of neural dysfunction in chronic neurodegenerative conditions such as Alzheimer's disease (AD) offers a unified approach to understanding both existing and novel strategies for drug development. At the present time, a ligand based approach is a pragmatic solution for identifying new chemical leads on which to base future discovery and optimisation. We have pursued a ligand based approach on the basis of public domain data to identify existing compounds capable of abrogating the cell cycle at the G0-G1 interface. Selected on this basis, irrespective of the tissue under study, we identified several classes of compounds as potential chemical leads. Of these compounds, at least ten have already been shown to be neuroprotective in animal models of acute neurodegeneration. Such compounds could form the basis of a screening exercise after development of suitable screening tools. Progressing of chemical leads through such an approach will be more efficient if future leads display relevant "drug-like" properties. Further, drug development in this arena should take account of the special concerns raised by targeting an elderly population. This will involve accounting for frequent polypharmacy in the aging population, and age-related alterations in physiology.

Controlling the chromatin organization of vitamin D target genes by multiple vitamin D receptor binding sites

An essential prerequisite for the direct modulation of transcription by 1alpha,25-dihydroxy vitamin D(3) (1alpha,25(OH)(2)D(3)) is the location of at least one activated vitamin D receptor (VDR) protein close to the transcription start site of the respective primary 1alpha,25(OH)(2)D(3) target gene. This is achieved through the specific binding of VDR to a 1alpha,25(OH)(2)D(3) response element (VDRE). Although these elements are well characterized in vitro, the function of VDREs in living cells in the context of chromatin is still largely unknown. To resolve this issue, approximately 8kB of the promoter regions of the primary 1alpha,25(OH)(2)D(3) target genes CYP24, cyclin C and p21((Waf1/Cip1)) were screened by chromatin immunoprecipitation (ChIP) assays for VDR binding sites using antibodies against VDR and its partner proteins. This approach identified three to four functional VDREs per gene promoter. In parallel, in silico screening of the extended gene areas (i.e. 10kB of promoter, introns, exons and 10kB of the downstream region) of all six members of the insulin-like growth factor binding protein (IGFBP) gene family was performed. Gel shift, reporter gene and ChIP assays identified in total 10 functional VDREs in the genes IGFBP1, IGFBP3 and IGFBP5. Taken together, both screening approaches suggest that a reasonable proportion of all VDR target genes, if not all, are under the control of multiple VDREs.

Expression of splice variants of 1alpha-hydroxylase in mcf-7 breast cancer cells

1,25-Dihydroxyvitamin D(3) (calcitriol) is the most active natural metabolite of Vitamin D(3). It has strong antiproliferative and differentiating effects on various cell types including breast cancer cells. 25-Hydroxyvitamin D(3)-1alpha-hydroxylase (1alpha-hydroxylase, CYP27B1) is one of the key enzymes in the formation of calcitriol. It has been found in breast cancer cells suggesting an autocrine regulation of formation of calcitriol in these cells. Alternative splicing of the encoding genes for this enzyme can possibly play a role in regulating the enzyme level and can explain tissue specific variations of 1alpha-hydroxylase activity. Splice variants containing intron 1 may encode for truncated proteins with deletion of protein domains which are essential for its enzymatic activity. In order to obtain more information on the abundance of 1alpha-hydroxylase splice variants, we performed a highly specific nested touchdown PCR in MCF-7 cells. The full-length sequence of 1alpha-hydroxylase and two different splice variants of this enzyme containing intron 1 were isolated. By Western blot technique we then confirmed the protein products of the full-length enzyme and its splice variants. We hypothesize that that the expression of splice variants can lead to a quantitatively lower expression of the mRNA of the full-length enzyme. The abundance of less active 1alpha-hydroxylase protein variants can alter the local synthesis of calcitriol in the cells and may explain variations of enzymatic activity in different cells and tissues.

A two-phase strategy for treatment of oxidant-dependent cancers

In many cancers, a chronic increase in oxidant stress - associated with elevated levels of hydrogen peroxide - contributes to the increased proliferative rate, diminished apoptosis, increased angiogenic and metastatic capacity, and chemoresistance that often characterize advanced malignancies. This oxidant stress often reflects up-regulation of expression and activity of NADPH oxidase, and/or decreased activity of catalase, which functions as suppressor gene in oxidant-dependent cancers. These characteristics of oxidant-dependent cancers suggest a dual strategy for treatment of these cancers. Since ascorbate can react spontaneously with molecular oxygen to generate hydrogen peroxide, high-dose intravenous ascorbate should be selectively toxic to tumors that are low in catalase activity - as suggested by numerous cell culture studies. Measures which concurrently improve the oxygenation of hypoxic tumor regions would be expected to boost the efficacy of such therapy; calcitriol and high-dose selenium might also be useful in this regard. Secondly, during the intervals between sessions of ascorbate therapy, administration of agents which can safely inhibit NADPH oxidase would be expected to slow the proliferation and spread of surviving tumor cells - while providing selection pressure for a further decline in catalase activity. In effect, cancers treated in this way would be whipsawed between lethally excessive and inadequately low oxidant stress. An additional possibility is that ascorbate-induced oxidant stress in tumors might potentiate the cell kill achieved with concurrently administered cytotoxic drugs, inasmuch as oxidant mechanisms appear to play a mediating role in the apoptosis induced by many such drugs, largely via activation of c-Jun NH(2)-terminal kinase; cell culture studies would be useful for evaluating this possibility.