Enhancement of 1,25-dihydroxyvitamin D3-mediated antitumor activity with dexamethasone

Antiproliferative Effects of 1α-OH-vitD3 in Malignant Melanoma: Potential Therapeutic implications

Early detection and surgery represent the mainstay of treatment for superficial melanoma, but for high risk lesions (Breslow’s thickness >0.75 mm) an effective adjuvant therapy is lacking. Vitamin D insufficiency plays a relevant role in cancer biology. The biological effects of 1α hydroxycholecalciferol on experimental melanoma models were investigated. 105 melanoma patients were checked for 25-hydroxycholecalciferol (circulating vitamin D) serum levels. Human derived melanoma cell lines and in vivo xenografts were used for studying 1α-hydroxycholecalciferol-mediated biological effects on cell proliferation and tumor growth. 99 out of 105 (94%) melanoma patients had insufficient 25-hydroxycholecalciferol serum levels. Interestingly among the six with vitamin D in the normal range, five had a diagnosis of in situ/microinvasive melanoma. Treatment with 1α-hydroxycholecalciferol induced antiproliferative effects on melanoma cells in vitro and in vivo, modulating the expression of cell cycle key regulatory molecules. Cell cycle arrest in G1 or G2 phase was invariably observed in vitamin D treated melanoma cells. The antiproliferative activity induced by 1α-hydroxycholecalciferol in experimental melanoma models, together with the discovery of insufficient 25-hydroxycholecalciferol serum levels in melanoma patients, provide the rationale for using vitamin D in melanoma adjuvant therapy, alone or in association with other therapeutic options.

Vitamin D Signaling Modulators in Cancer Therapy

The antiproliferative and pro-apoptotic effects of 1α,25-dihydroxycholecalciferol (1,25(OH)2D3, 1,25D3, calcitriol) have been demonstrated in various tumor model systems in vitro and in vivo. However, limited antitumor effects of 1,25D3 have been observed in clinical trials. This may be attributed to a variety of factors including overexpression of the primary 1,25D3 degrading enzyme, CYP24A1, in tumors, which would lead to rapid local inactivation of 1,25D3. An alternative strategy for improving the antitumor activity of 1,25D3 involves the combination with a selective CYP24A1 inhibitor. The validity of this approach is supported by numerous preclinical investigations, which demonstrate that CYP24A1 inhibitors suppress 1,25D3 catabolism in tumor cells and increase the effects of 1,25D3 on gene expression and cell growth. Studies are now required to determine whether selective CYP24A1 inhibitors+1,25D3 can be used safely and effectively in patients. CYP24A1 inhibitors plus 1,25D3 can cause dose-limiting toxicity of vitamin D (hypercalcemia) in some patients. Dexamethasone significantly reduces 1,25D3-mediated hypercalcemia and enhances the antitumor activity of 1,25D3, increases VDR-ligand binding, and increases VDR protein expression. Efforts to dissect the mechanisms responsible for CYP24A1 overexpression and combinational effect of 1,25D3/dexamethasone in tumors are underway. Understanding the cross talk between vitamin D receptor (VDR) and glucocorticoid receptor (GR) signaling axes is of crucial importance to the design of new therapies that include 1,25D3 and dexamethasone. Insights gained from these studies are expected to yield novel strategies to improve the efficacy of 1,25D3 treatment.

Glucocorticoids suppress renal cell carcinoma progression by enhancing Na,K-ATPase beta-1 subunit expression

Glucocorticoids are commonly used as palliative or chemotherapeutic clinical agents for treatment of a variety of cancers. Although steroid treatment is beneficial, the mechanisms by which steroids improve outcome in cancer patients are not well understood. Na,K-ATPase beta-subunit isoform 1 (NaK-β1) is a cell-cell adhesion molecule, and its expression is down-regulated in cancer cells undergoing epithelial-to mesenchymal-transition (EMT), a key event associated with cancer progression to metastatic disease. In this study, we performed high-throughput screening to identify small molecules that could up-regulate NaK-β1 expression in cancer cells. Compounds related to the glucocorticoids were identified as drug candidates enhancing NaK-β1 expression. Of these compounds, triamcinolone, dexamethasone, and fluorometholone were validated to increase NaK-β1 expression at the cell surface, enhance cell-cell adhesion, attenuate motility and invasiveness and induce mesenchymal to epithelial like transition of renal cell carcinoma (RCC) cells in vitro. Treatment of NaK-β1 knockdown cells with these drug candidates confirmed that these compounds mediate their effects through up-regulating NaK-β1. Furthermore, we demonstrated that these compounds attenuate tumor growth in subcutaneous RCC xenografts and reduce local invasiveness in orthotopically-implanted tumors. Our results strongly indicate that the addition of glucocorticoids in the treatment of RCC may improve outcome for RCC patients by augmenting NaK-β1 cell-cell adhesion function.

Phase I safety and pharmacodynamic of inecalcitol, a novel VDR agonist with docetaxel in metastatic castration-resistant prostate cancer patients

PURPOSE

We conducted a phase I multicenter trial in naïve metastatic castrate-resistant prostate cancer patients with escalating inecalcitol dosages, combined with docetaxel-based chemotherapy. Inecalcitol is a novel vitamin D receptor agonist with higher antiproliferative effects and a 100-fold lower hypercalcemic activity than calcitriol.

EXPERIMENTAL DESIGN

Safety and efficacy were evaluated in groups of three to six patients receiving inecalcitol during a 21-day cycle in combination with docetaxel (75 mg/m2 every 3 weeks) and oral prednisone (5 mg twice a day) up to six cycles. Primary endpoint was dose-limiting toxicity (DLT) defined as grade 3 hypercalcemia within the first cycle. Efficacy endpoint was ≥30% PSA decline within 3 months.

RESULTS

Eight dose levels (40-8,000 μg) were evaluated in 54 patients. DLT occurred in two of four patients receiving 8,000 μg/day after one and two weeks of inecalcitol. Calcemia normalized a few days after interruption of inecalcitol. Two other patients reached grade 2, and the dose level was reduced to 4,000 μg. After dose reduction, calcemia remained within normal range and grade 1 hypercalcemia. The maximum tolerated dose was 4,000 μg daily. Respectively, 85% and 76% of the patients had ≥30% PSA decline within 3 months and ≥50% PSA decline at any time during the study. Median time to PSA progression was 169 days.

CONCLUSION

High antiproliferative daily inecalcitol dose has been safely used in combination with docetaxel and shows encouraging PSA response (≥30% PSA response: 85%; ≥50% PSA response: 76%). A randomized phase II study is planned.

Vitamin D, steroid hormones, and autoimmunity

The endogenous serum metabolite of vitamin D (calcitriol, 1,25(OH)2 D3 ) is considered a true steroid hormone (D hormone), and like glucocorticoids (GCs) and gonadal hormones, may exert several immunomodulatory activities. Serum vitamin D deficiency (25(OH) D), and therefore reduced 1,25(OH)2 D3 availability, is considered a risk factor for several chronic/inflammatory or autoimmune conditions, including infectious diseases, type 1 diabetes, multiple sclerosis, and especially autoimmune rheumatic diseases (ARD). In ARD in particular, 1,25(OH)2 D3 regulates both innate and adaptive immunity, potentiating the innate response (antimicrobial activity) but reducing adaptive immunity (antigen presentation, T and B cell activities). Regarding a possible synergism between vitamin D and GCs, several studies show that 1,25(OH)2 D3 has significant additive effects on dexamethasone-mediated inhibition of human lymphocyte and monocyte proliferation. Conversely, vitamin D deficiency seems to play a role in increasing autoantibody production by B cells, and seasonal vitamin D declines may trigger flares in ARD, as recently shown. Finally, 1,25(OH)2 D3 seems to reduce aromatase activity and limit the negative effects related to increased peripheral estrogen metabolism (cell proliferation, B cell overactivity).

Role of androgen and vitamin D receptors in endothelial cells from benign and malignant human prostate

Forty years ago, Judah Folkman (Folkman. N Engl J Med 285: 1182-1186, 1971) proposed that tumor growth might be controlled by limiting formation of new blood vessels (angiogenesis) needed to supply a growing tumor with oxygen and nutrients. To this end, numerous "antiangiogenic" agents have been developed and tested for therapeutic efficacy in cancer patients, including prostate cancer (CaP) patients, with limited success. Despite the lack of clinical efficacy of lead anti-angiogenic therapeutics in CaP patients, recent published evidence continues to support the idea that prostate tumor vasculature provides a reasonable target for development of new therapeutics. Particularly relevant to antiangiogenic therapies targeted to the prostate is the observation that specific hormones can affect the survival and vascular function of prostate endothelial cells within normal and malignant prostate tissues. Here, we review the evidence demonstrating that both androgen(s) and vitamin D significantly impact the growth and survival of endothelial cells residing within prostate cancer and that systemic changes in circulating androgen or vitamin D drastically affect blood flow and vascularity of prostate tissue. Furthermore, recent evidence will be discussed about the expression of the receptors for both androgen and vitamin D in prostate endothelial cells that argues for direct effects of these hormone-activated receptors on the biology of endothelial cells. Based on this literature, we propose that prostate tumor vasculature represents an unexplored target for modulation of tumor growth. A better understanding of androgen and vitamin D effects on prostate endothelial cells will support development of more effective angiogenesis-targeting therapeutics for CaP patients.

Temporal changes in tissue 1α,25-dihydroxyvitamin D3, vitamin D receptor target genes, and calcium and PTH levels after 1,25(OH)2D3 treatment in mice

The vitamin D receptor (VDR) maintains a balance of plasma calcium and 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], its natural active ligand, by directly regulating the calcium ion channel (TRPV6) and degradation enzyme (CYP24A1), and indirectly regulating the parathyroid hormone (PTH) for feedback regulation of the synthetic enzyme CYP27B1. Studies that examined the intricate relationships between plasma and tissue 1,25(OH)2D3 levels and changes in VDR target genes and plasma calcium and PTH are virtually nonexistent. In this study, we investigated temporal correlations between tissue 1,25(OH)2D3 concentrations and VDR target genes in ileum and kidney and plasma calcium and PTH concentrations in response to 1,25(OH)2D3 treatment in mice (2.5 μg/kg ip, singly or q2d × 4). After a single ip dose, plasma 1,25(OH)2D3 peaked at ∼0.5 h and then decayed biexponentially, falling below basal levels after 24 h and then returning to baseline after 8 days. Upon repetitive ip dosing, plasma, ileal, renal, and bone 1,25(OH)2D3 concentrations rose and decayed in unison. Temporal profiles showed increased expressions of ileal Cyp24a1 and renal Cyp24a1, Mdr1/P-gp, and VDR but decreased renal Cyp27b1 mRNA after a time delay in VDR activation. Increased plasma calcium and attenuated PTH levels and increased ileal and renal Trpv6 expression paralleled the changes in tissue 1,25(OH)2D3 concentrations. Gene changes in the kidney were more sustained than those in intestine, but the magnitudes of change for Cyp24a1 and Trpv6 were lower than those in intestine. The data revealed that 1,25(OH)2D3 equilibrates with tissues rapidly, and VDR target genes respond quickly to exogenously administered 1,25(OH)2D3.

Anticancer steroids: linking natural and semi-synthetic compounds

Steroids, a widespread class of natural organic compounds occurring in animals, plants and fungi, have shown great therapeutic value for a broad array of pathologies. The present overview is focused on the anticancer activity of steroids, which is very representative of a rich structural molecular diversity and ability to interact with various biological targets and pathways. This review encompasses the most relevant discoveries on steroid anticancer drugs and leads through the last decade and comprises 668 references.

Inecalcitol, an analog of 1,25D3, displays enhanced antitumor activity through the induction of apoptosis in a squamous cell carcinoma model system

Epidemiological data suggest an important role of vitamin D signaling in cancer development and progression, and experimental studies demonstrate that the active vitamin D metabolite 1α, 25-dihydroxyvitamin D₃ (1,25D₃) has broad spectrum antitumor activity. Hypercalcemia has often been suggested to limit the clinical application of these data. The 14-epi-analog of 1,25D₃, inecalcitol [19-nor-14-epi-23-yne-1,25-(OH)₂D₃; TX522], was developed to have superagonistic antitumor activities but low hypercalcemia potential. We examined the antitumor activity of inecalcitol and the underlying mechanisms in a murine squamous cell carcinoma (SCC) model system. In vitro, compared with 1,25D₃, inecalcitol showed enhanced vitamin D receptor (VDR)-mediated transcriptional activity. Inecalcitol suppressed SCC cell proliferation in a dose-dependent manner with an IC50 value 30 times lower than that of 1,25D₃. Both inecalcitol and 1,25D₃ induced a comparable level of G0/G₁ cell cycle arrest in SCC cells. The level of apoptosis induced by inecalcitol was markedly higher than that of 1,25D₃. Apoptosis was mediated through the activation of the caspase 8/10- caspase 3 pathway. Further, inecalcitol markedly inhibited the mRNA and protein expression of c-IAP1 and XIAP compared with 1,25D₃. In vivo, inecalcitol inhibits SCC tumor growth in a dose-dependent fashion. Notably, inecalcitol induced a significantly higher level of apoptosis in the SCC xenograft model. While in vitro inecalcitol demonstrates apparent enhanced VDR binding and antiproliferative effects compared to 1,25D₃, in vivo these advantages disappear; at doses of inecalcitol that have equivalent antitumor effects, similar hypercalcemia is seen. This may be explained by the pharmacokinetics of 1,25D₃ vs. inecalcitol and attributed to the much shorter serum half-life of inecalcitol.We show that inecalcitol has potent antitumor activity in the SCC model system, and this is associated with a strong induction of apoptosis. These findings support the further development of inecalcitol in cancer treatment.

Down-regulation of vitamin D receptor in mammospheres: implications for vitamin D resistance in breast cancer and potential for combination therapy

Vitamin D signaling in mammary cancer stem cells (MCSCs), which are implicated in the initiation and progression of breast cancer, is poorly understood. In this study, we examined vitamin D signaling in mammospheres which are enriched in MCSCs from established breast cancer cell lines. Breast cancer cells positive for aldehyde dehydrogenase (ALDH(+)) had increased ability to form mammospheres compared to ALDH(-) cells. These mammospheres expressed MCSC-specific markers and generated transplantable xenografts in nude mice. Vitamin D receptor (VDR) was significantly down-regulated in mammospheres, as well as in ALDH(+) breast cancer cells. TN aggressive human breast tumors as well as transplantable xenografts obtained from SKBR3 expressed significantly lower levels of VDR but higher levels of CD44 expression. Snail was up-regulated in mammospheres isolated from breast cancer cells. Inhibition of VDR expression by siRNA led to a significant change in key EMT-specific transcription factors and increased the ability of these cells to form mammospheres. On the other hand, over-expression of VDR led to a down-regulation of Snail but increased expression of E-cad and significantly compromised the ability of cells to form mammospheres. Mammospheres were relatively insensitive to treatment with 1,25-dihydroxyvitamin D (1,25D), the active form of vitamin D, compared to more differentiated cancer cells grown in presence of serum. Treatment of H-Ras transformed HMLE(HRas) cells with DETA NONOate, a nitric oxide (NO)-donor led to induction of MAP-kinase phosphatase -1 (MKP-1) and dephosphorylation of ERK1/2 in the mammospheres. Combined treatment of these cells with 1,25D and a low-concentration of DETA NONOate led to a significant decrease in the overall size of mammospheres and reduced tumor volume in nude mice. Our findings therefore, suggest that combination therapy using 1,25D with drugs specifically targeting key survival pathways in MCSCs warrant testing in prospective clinical trial for treatment of aggressive breast cancer.

Dexamethasone enhances 1alpha,25-dihydroxyvitamin D3 effects by increasing vitamin D receptor transcription

Calcitriol, the active form of vitamin D, in combination with the glucocorticoid dexamethasone (Dex) has been shown to increase the antitumor effects of calcitriol in squamous cell carcinoma. In this study we found that pretreatment with Dex potentiates calcitriol effects by inhibiting cell growth and increasing vitamin D receptor (VDR) and VDR-mediated transcription. Treatment with actinomycin D inhibits Vdr mRNA synthesis, indicating that Dex regulates VDR expression at transcriptional level. Real time PCR shows that treatment with Dex increases Vdr transcripts in a time- and a dose-dependent manner, indicating that Dex directly regulates expression of Vdr. RU486, an inhibitor of glucocorticoids, inhibits Dex-induced Vdr expression. In addition, the silencing of glucocorticoid receptor (GR) abolishes the induction of Vdr by Dex, indicating that Dex increases Vdr transcripts in a GR-dependent manner. A fragment located 5.2 kb upstream of Vdr transcription start site containing two putative glucocorticoid response elements (GREs) was evaluated using a luciferase-based reporter assay. Treatment with 100 nm Dex induces transcription of luciferase driven by the fragment. Deletion of the GRE distal to transcription start site was sufficient to abolish Dex induction of luciferase. Also, chromatin immunoprecipitation reveals recruitment of GR to distal GRE with Dex treatment. We conclude that Dex increases VDR and vitamin D effects by increasing Vdr de novo transcription in a GR-dependent manner.

CYP24A1 inhibition enhances the antitumor activity of calcitriol

High systemic exposures to calcitriol are necessary for optimal antitumor effects. Human prostate cancer PC3 cells are insensitive to calcitriol treatment. Therefore, we investigated whether the inhibition of 24-hydroxylase (CYP24A1), the major calcitriol inactivating enzyme, by ketoconazole (KTZ) or RC2204 modulates calcitriol serum pharmacokinetics and biologic effects. Dexamethasone (Dex) was added to minimize calcitriol-induced hypercalcemia and as a steroid replacement for the KTZ inhibition of steroid biosynthesis cytochrome P450 enzymes. KTZ effectively inhibited time-dependent calcitriol-inducible CYP24A1 protein expression and enzyme activity in PC3 cells and C3H/HeJ mouse kidney tissues. Systemic calcitriol exposure area under the curve was higher in mice treated with a combination of calcitriol and KTZ than with calcitriol alone. KTZ and Dex synergistically potentiated calcitriol-mediated antiproliferative effects in PC3 cells in vitro; this effect was associated with enhanced apoptosis. After treatment with calcitriol and KTZ/Dex, although caspase-9 and caspase-3 were not activated and cytochrome c was not released by mitochondria, caspase-8 was activated and the truncated Bid protein level was increased. Translocation of apoptosis-inducing factor to the nucleus was observed, indicating a role of the apoptosis-inducing factor-mediated and caspase-independent apoptotic pathways. Calcitriol and KTZ/Dex combination suppressed the clonogenic survival and enhanced the growth inhibition observed with calcitriol alone in PC3 human prostate cancer xenograft mouse model. Our results show that the administration of calcitriol in combination with CYP24A1 inhibitor enhances antiproliferative effects, increases systemic calcitriol exposure, and promotes the activation of caspase-independent apoptosis pathway.

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.

Epigenetic silencing of CYP24 in the tumor microenvironment

Calcitriol (1,25 dihydroxycholecalciferol) has significant anti-tumor activity in vitro and in vivo in a number of tumor model systems. We developed a system for isolation of fresh endothelial cells from tumors and Matrigel environments which demonstrate that CYP24, the catabolic enzyme involved in vitamin D signaling, is epigenetically silenced selectively in tumor-derived endothelial cells (TDEC). TDEC maintain phenotypic characteristics which are distinct from endothelial cells isolated from normal tissues and from Matrigel plugs (MDEC). In TDEC, calcitriol induces G(0)/G(1) arrest, modulates p27 and p21, and induces apoptotic cell death and decreases P-Erk and P-Akt. In contrast, endothelial cells isolated from normal tissues and MDEC are unresponsive to calcitriol-mediated anti-proliferative effects despite intact signaling through the vitamin D receptor (VDR). In TDEC, which are sensitive to calcitriol, the CYP24 promoter is hypermethylated in two CpG island regions located at the 5'end; this hypermethylation may contribute to gene silencing of CYP24. The extent of methylation in these two regions is significantly less in MDEC. Lastly, treatment of TDEC with a DNA methyltransferase inhibitor restores calcitriol-mediated induction of CYP24 and resistance to calcitriol. These data suggest that epigenetic silencing of CYP24 modulates cellular responses to calcitriol.

Glucocorticoid regulation of the vitamin D receptor

Many studies indicate calcitriol has potent anti-tumor activity in different types of cancers. However, high levels of vitamin D can produce hypercalcemia in some patients. Glucocorticoids are used to ameliorate hypercalcemia and to enhance calcitriol anti-tumor activity. Calcitriol in combination with the glucocorticoid dexamethasone (Dex) increased vitamin D receptor (VDR) protein levels and ligand binding in squamous cell carcinoma VII (SCC). In this study we found that both calcitriol and Dex induce VDR- and glucocorticoid receptor (GR)-mediated transcription respectively, indicating both hormone receptors are active in SCC. Pre-treatment with Dex increases VDR-mediated transcription at the human CYP24A1 promoter. Whereas, pre-treatment with other steroid hormones, including dihydrotestosterone and R1881, has no effect on VDR-mediated transcription. Real-time PCR indicates treatment with Dex increases Vdr transcripts in a time-dependent manner, suggesting Dex may directly regulate expression of Vdr. Numerous putative glucocorticoid response elements (GREs) were found in the Vdr gene. Chromatin immuno-precipitation (ChIP) assay demonstrated GR binding at several putative GREs located within the mouse Vdr gene. However, none of the putative GREs studied increase GR-mediated transcription in luciferase reporter assays. In an attempt to identify the response element responsible for Vdr transcript regulation, future studies will continue to analyze newly identified GREs more distal from the Vdr gene promoter.

Phase 2 trial of weekly intravenous 1,25 dihydroxy cholecalciferol (calcitriol) in combination with dexamethasone for castration-resistant prostate cancer

BACKGROUND

Preclinical data indicate that there is substantial antitumor activity and synergy between calcitriol and dexamethasone. On the basis of these data, the authors conducted a phase 2 trial of intravenous (iv) calcitriol at a dose of 74 microg weekly (based on a recent phase 1 trial) and dexamethasone in patients with castration-resistant prostate cancer (CRPC).

METHODS

A 2-stage Kepner-Chang design was used. Oral dexamethasone at a dose of 4 mg was given weekly on Days 1 and 2, and iv calcitriol (74 microg over 1 hour) was administered weekly on Day 2 from 4 to 8 hours after the dexamethasone dose in patients with CRPC. Laboratory data were monitored weekly, and renal sonograms, computed tomography scans, and bone scans were obtained every 3 months. Disease response was assessed by using the Response Evaluation Criteria in Solid Tumors (RECIST) and standard criteria for prostate-specific antigen (PSA) response. The calcitriol dose was delineated by from the authors' recent phase 1 trial.

RESULTS

Of 18 evaluable patients, 15 patients were Caucasian (83%). No patients had a complete or partial response by either RECIST or PSA response criteria. Fourteen patients had progressive disease, 2 patients refused to continue treatment (after 64 days and 266 days), and 2 patients remain on the trial (for 306 days and 412 days).The median time to disease progression was 106 days (95% confidence interval, 80-182 days). Fourteen episodes of grade 3 or 4 toxicity were noted in 7 patients (hyperglycemia, hypocalemia, chest pain, dyspnea, hypercalcemia, hypophosphatemia, cardiac arrhythmia, and pain). Only 1 episode of grade 3/ 4 toxicity was related definitely to calcitriol (hypercalcemia). No treatment-related deaths were noted.

CONCLUSIONS

High-dose, iv calcitriol at a dose of 74 microg weekly in combination with dexamethasone was well tolerated but failed to produce a clinical or PSA response in men with CRPC.

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

PURPOSE

The primary objective of this study was to determine the maximum tolerated dose (MTD) of intravenously (i.v.) calcitriol administered in combination with a fixed oral dose of dexamethasone and gefitinib in patients with refractory solid tumors.

METHODS

A fixed oral dose of dexamethasone of 4 mg/day was given every 12 h x 3 doses starting 12 h prior to i.v. calcitriol administration. Calcitriol was administered i.v. over 1 h on weeks 1, 3, and weekly thereafter. The starting calcitriol dose level was 57 microg and escalation occurred in cohorts of three patients until the MTD was defined. Gefitinib was given at a fixed oral daily dose of 250 mg starting at week 2 (day 8). Serum calcitriol PK studies were performed on day 1 (calcitriol + dexamethasone) and on day 15 (calcitriol + dexamethasone + gefitinib).

RESULTS

A total of 20 patients were treated. Dose-limiting hypercalcemia was observed in two out of the four patients receiving 163 mcg/week of calcitriol. Mean (+/-SE) peak serum calcitriol concentration (C (max)) at the MTD (125 microg/week calcitriol) was 11.17 +/- 2.62 ng/ml and the systemic exposure (AUC(0-72 h)) of 53.30 +/- 10.49 ng h/ml. The relationship between calcitriol dose and either C (max) or AUC was linear over the 57-163 microg dose range.

CONCLUSIONS

The addition of a low dose of dexamethasone allowed the safe escalation of calcitriol to the MTD of 125 microg/week. This dose level resulted in serum calcitriol concentrations that are associated with pre-clinical antitumor activity. However, no antitumor activity was noted clinically in patients with solid tumors.

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.

In vitro and in vivo evaluation of combined calcitriol and cisplatin in dogs with spontaneously occurring tumors

PURPOSE

Calcitriol potentiates cisplatin-mediated activity in a variety of tumor models. We examine here, the effect of calcitriol and cisplatin pre-clinically and clinically in canine spontaneous tumors through in vitro studies on tumor cells and through a phase I study of calcitriol and cisplatin to identify the maximum-tolerated dosage (MTD) of this combination in dogs with cancer and to characterize the pharmacokinetic disposition of calcitriol in dogs.

METHODS

Canine tumor cells were investigated for calcitriol/cisplatin interactions on proliferation using an MTT assay in a median-dose effect analysis; data were used to derive a combination index (CI). Cisplatin was given at a fixed dosage of 60 mg/m2. Calcitriol was given i.v. and the dosage was escalated in cohorts of three dogs until the MTD was defined. Serum calcitriol concentrations were quantified by radioimmunoassay.

RESULTS

In vitro, CIs < 1.0 were obtained for all combinations of calcitriol/cisplatin examined. The MTD was 3.75 microg/kg calcitriol in combination with cisplatin, and hypercalcemia was the dose-limiting toxicosis. The relationship between calcitriol dosage and either Cmax or AUC was linear. Calcitriol dosages >1.5 microg/kg achieved Cmax > or = 9.8 ng/mL and dosages >1.0 microg/kg achieved AUC > or = 45 h ng/mL.

CONCLUSIONS

Calcitriol and cisplatin have synergistic antiproliferative effects on multiple canine tumor cells and high-dosages of i.v. calcitriol in combination with cisplatin can be safely administered to dogs. Cmax and AUC at the MTD 3.75 microg/kg calcitriol exceed concentrations associated with antitumor activity in a murine model, indicating this combination might have significant clinical utility in dogs.

Differential antiproliferative effects of calcitriol on tumor-derived and matrigel-derived endothelial cells

The most active metabolite of vitamin D, calcitriol, is growth inhibitory for various tumor types in vitro and in vivo and inhibits the growth of endothelial cells freshly isolated from tumors [tumor-derived endothelial cells (TDEC)]. We compared the effects of calcitriol on Matrigel-derived endothelial cells (MDEC) and TDEC isolated from Matrigel plugs and squamous cell carcinoma tumors, respectively. TDEC and MDEC expressed vitamin D receptor (VDR) and responded to calcitriol by increasing VDR protein expression. Although no mutations were found in VDR from either cell type, Scatchard plot analysis revealed a higher ligand-binding affinity in TDEC (K(d), 0.26 nmol/L) than MDEC (K(d), 0.65 nmol/L). The VDR signaling axis in both cells was intact as shown using nuclear translocation and 24-hydroxylase promoter-luciferase reporter assays. However, unlike TDEC, MDEC were resistant to calcitriol-induced growth inhibition. Calcitriol (10 nmol/L) resulted in a 12.3% growth inhibition of MDEC compared with 47% in TDEC. In TDEC, calcitriol resulted in induction of G(0)/G(1) arrest (10.75%) and reduction of S-phase cells (6.8%) with induction of p27 and down-regulation of p21 protein expression. Apoptotic effects, determined by Annexin V staining were also observed in calcitriol-treated TDEC (38.6%). Calcitriol caused reduced expression of p-Erk and p-Akt and an increase of poly(ADP-ribose) polymerase and caspase-3 cleavage in TDEC. By contrast, none of these effects on cell cycle or apoptosis were seen in calcitriol-treated MDEC. These results show that TDEC were more sensitive than MDEC to the antiproliferative effects of calcitriol despite apparently normal VDR content and structure of signaling axis in both cell types.

1,25-dihydroxyvitamin D3 and dexamethasone increase interleukin-10 production in CD4+ T cells from patients with Crohn's disease

BACKGROUND AND AIM

In Crohn's disease (CD), epidemiological data and animal studies suggest that vitamin D (vitD) has protective immune-modulating properties. 1,25-dihydroxyvitamin D3 and dexamethasone (DEX) induce interleukin (IL)-10 productions in healthy controls (HC) T cells. We studied if 1,25-dihydroxyvitamin D3 with and without DEX could induce IL-10 production, downregulate pro-inflammatory Interferon (IFN)-gamma and Tumor Necrosis Factor (TNF)-alpha production, and influence cell kinetics in peripheral CD4+ T cells from CD patients.

METHODS

CD4+ T cells were separated from peripheral blood from CD patients and HC. Cells were activated by anti-CD3 and anti-CD28 in the presence of 1,25-dihydroxyvitamin D3 and/or DEX. Cytokine levels, proliferation, and apoptosis were measured following 7 days of culture.

RESULTS

In T cells from CD patients, 1,25-dihydroxyvitamin D3 and DEX increased IL-10 production from a median of 0.08 ng/ml to 0.2 ng/ml (p<0.01) and downregulated IFN-gamma production from 8.3 ng/ml to 3.1 ng/ml (p<0.01). The induced IL-10 increase in cultures from HC (0.2 ng/ml to 1.0 ng/ml, p<0.01) was significantly higher than in CD patients (p<0.05). In CD cultures, the IL-4 production increased from 0.3 ng/ml to 0.5 ng/ml (p<0.01) and IL-6 production from 2.5 ng/ml to 6.1 ng/ml (p<0.05). Similar changes in cytokine levels were observed with 1,25-dihydroxyvitamin D3 independently of DEX. In addition, 1,25-dihydroxyvitamin D3 and DEX decreased proliferation and reduced viability of T cells.

CONCLUSION

We found that 1,25-dihydroxyvitamin D3 with and without DEX stimulation increased IL-10 and reduced IFN-gamma production. These findings suggest that vitD may play a therapeutic role in CD.

Vitamin D signalling pathways in cancer: potential for anticancer therapeutics

Epidemiological studies indicate that vitamin D insufficiency could have an aetiological role in various human cancers. Preclinical research indicates that the active metabolite of vitamin D, 1alpha,25(OH)2D3, also known as calcitriol, or vitamin D analogues might have potential as anticancer agents because their administration has antiproliferative effects, can activate apoptotic pathways and inhibit angiogenesis. In addition, 1alpha,25(OH)2D3 potentiates the anticancer effects of many cytotoxic and antiproliferative anticancer agents. Here, we outline the epidemiological, preclinical and clinical studies that support the development of 1alpha,25(OH)2D3 and vitamin D analogues as preventative and therapeutic anticancer agents.

Mechanistic and pharmacodynamic studies of a 25-hydroxyvitamin D3 derivative in prostate cancer cells

1,25-Dihydroxyvitamin D(3) (1,25(OH)(2)D(3)), the biologically active form of vitamin D has strong antiproliferative effects in cancer cells. But it is highly toxic at therapeutic doses. We have observed that 25-hydroxyvitamin D(3)-3-bromoacetate (25-OH-D(3)-3-BE), a derivative of 25-hydroxyvitamin D(3), the pro-hormonal form of 1,25(OH)(2)D(3) has strong growth-inhibitory and proapoptotic properties in hormone-sensitive and hormone-refractory prostate cancer cells. In the present investigation we demonstrate that the antiproliferative effect of 25-OH-D(3)-3-BE is predominantly mediated by VDR in ALVA-31 prostate cancer cells. In other mechanistic studies we show that the proapoptotic property of 25-OH-D(3)-3-BE is related to the inhibition of phosphorylation of Akt, a pro-survival protein. Furthermore, we carried out cellular uptake and serum stability studies of 25-OH-D(3)-3-BE to demonstrate potential therapeutic applicability of 25-OH-D(3)-3-BE in hormone-sensitive and hormone-insensitive prostate cancer.

Vitamin d and its role in cancer and immunity: a prescription for sunlight

Vitamin D has been recognized for more than a century as essential for the normal development and mineralization of a healthy skeleton. More extensive roles for vitamin D were suggested by the discovery of the vitamin D receptor (VDR) in tissues that are not involved in calcium and phosphate metabolism. VDR has been discovered in most tissues and cells in the body and is able to elicit a wide variety of biologic responses. These observations have been the impetus for a reevaluation of the physiologic and pharmacologic actions of vitamin D. Here, we review the role of vitamin D in regulation of the immune system and its possible role in the prevention and treatment of cancer and immune-mediated diseases.

Calcitriol (1,25-Dihydroxycholecalciferol) Selectively Inhibits Proliferation of Freshly Isolated Tumor-Derived Endothelial Cells and Induces Apoptosis

Calcitriol (1,25-dihydroxycholecalciferol) has antiproliferative and/or proapoptotic effects on many cell types and the glucocorticoid dexamethasone enhances these effects. We have shown that calcitriol modulates several key signaling proteins involved in differentiation, proliferation and apoptosis in tumor-derived murine endothelial cells (TDEC) and that these effects were not seen with endothelial cells isolated similarly from normal tissues. In the present study, TDEC and mouse embryonic yolk sac endothelial cells (MYSEC) were treated with calcitriol and followed over time for an effect. MYSEC were utilized as 'normal' control endothelial cells because they were more primitive, being isolated from a highly neovascular tissue, and had a similar morphology without the stimulus of the tumor microenvironment. The vitamin D receptor (VDR) is present in TDEC and MYSEC, and was upregulated in calcitriol-treated TDEC and MYSEC; dexamethasone further increased VDR expression following 48 h of treatment. The modulatory effects on signaling proteins were maximal by treatment for 48 h; phospho-Erk, phospho-Akt, p21 and bcl-2 were decreased in treated TDEC with the induction of p27 but there were no effects on MYSEC. After 48 h increased apoptosis was seen in treated TDEC by annexin V labeling with caspase-3 cleavage and decreased levels of poly(ADP-ribose) polymerase, but no effects were seen in MYSEC. Cell cycle analysis showed increased G(0)/G(1) arrest and an increase in the apoptotic sub-G(1) peak in treated TDEC but similar effects were not seen in MYSEC following 48-hour treatment. Proliferation assays were utilized and TDEC demonstrated decreased proliferation compared to normal endothelial cells at 48 h. To determine whether or not the VDR signaling was impaired in MYSEC, we performed the 24-hydroxylase (CYP24) promoter-luciferase reporter assay. CYP24 is a key enzyme involved in the breakdown of vitamin D. VDR signaling was intact in both cell types and calcitriol induced CYP24 mRNA expression in MYSEC but not in TDEC. Taken together, despite similar levels of VDR expression and intact signaling in both cell types, calcitriol selectively inhibits proliferation and induces apoptosis in TDEC with no effect on MYSEC. Thus calcitriol exerts differential effects on TDEC compared to normal cells.

Phase I study of weekly DN-101, a new formulation of calcitriol, in patients with cancer

BACKGROUND

DN-101 is a new, high-dose, oral formulation of calcitriol under investigation for the treatment of cancer. We sought to evaluate the tolerability and pharmacokinetics (PK) of weekly doses of DN-101 in patients with advanced cancer.

METHODS

Patients who completed a previously reported single dose escalation study of DN-101 [Beer et al. (2005) Clin Cancer Res 11:7794-7799] were eligible for this continuation weekly dosing study. Cohorts of 3-10 patients were treated at doses of 15, 30, 45, 60, and 75 microg calcitriol. Once 45 microg was established as the maximum tolerated dose (MTD), this cohort was expanded to include 18 patients. Dose limiting toxicity (DLT) was defined as > or =grade 2 hypercalcemia or > or =grade 3 persistent treatment-related toxicities.

RESULTS

Thirty-seven patients were recruited. DLT of transient reversible grade 2 hypercalcemia (serum calcium of 11.6-12.5 mg/dL) occurred in two of six patients treated with 60 microg of DN-101. No DLT was observed in the 18 patients who received DN-101 weekly at 45 microg. Overall, DN-101 was well tolerated. The most frequent adverse events were fatigue (27%), hypercalcemia (19%, including five grade 1, two grade 2, and no grade 3 or 4 events), and grade 1 nausea (16%). PK parameters following repeat dosing were comparable to those for the initial dose (n = 4).

CONCLUSION

The MTD for weekly DN-101 was established as 45 mug. The DLTs observed were two episodes of rapidly reversible grade 2 hypercalcemia in two of the six patients treated at 60 microg weekly. Repeat doses of DN-101 at 45 microg weekly are well tolerated and this dose is suitable for studies of weekly DN-101 in cancer patients.

A phase II trial of dexamethasone, vitamin D, and carboplatin in patients with hormone-refractory prostate cancer

BACKGROUND

A Phase II prospective trial was performed to study the efficacy of combination therapy with dexamethasone, calcitriol (1,25-dihydroxyvitamin D3), and carboplatin in patients with hormone-refractory prostate cancer (HRPC). Preclinical data from prostate cancer cell lines suggested a synergistic effect of these therapies.

METHODS

All patients had pathologically confirmed prostate cancer with at least 2 consecutive increases in prostate-specific antigen (PSA). Treatment started with 1 mg of oral dexamethasone given daily with 0.5 mcg of daily calcitriol added at the start of Week 5. Carboplatin (area under the concentration time curve = 2) was started at the beginning of Week 7. Initially, carboplatin was given weekly; however, the protocol was changed later to give carboplatin for the first 4 weeks of a 6-week cycle. Of 40 patients who consented to participate, 6 patients were ineligible or declined to start therapy, leaving 34 treated patients. The median follow-up was 80.7 weeks (range, 11.5-260 weeks).

RESULTS

A formal PSA response was seen in 13 of 34 treated patients (38.2%; 95% confidence interval [95% CI], 22.2-56.4%). The median overall survival was 97.7 weeks (95% CI, 61-114 weeks). Significant adverse events that were observed during the trial period included 2 deaths (myocardial infarction and cardiogenic shock), 4 patients with Grade 3 neutropenia (according to the National Cancer Institute Common Toxicity Criteria, version 2.0), 2 patients with thrombosis, 2 patients with inflammatory bowel symptoms, and 2 patients with new-onset diabetes mellitus.

CONCLUSIONS

The novel combination of dexamethasone, calcitriol, and carboplatin for patients with HRPC produced a PSA response in 13 of 34 patients and had an acceptable side-effect profile.

Pharmacokinetics and tolerability of a single dose of DN-101, a new formulation of calcitriol, in patients with cancer

BACKGROUND

Intermittent administration allows substantial dose escalation of calcitriol but limited bioavailability of the commercially available formulations at high doses is limiting. In this dose escalation study, we sought to evaluate the tolerability and pharmacokinetics of a single oral dose of DN-101, a high-dose calcitriol formulation.

METHODS

DN-101 doses were escalated in sequential groups of three to six patients with advanced solid tumors. Dose-limiting toxicity was defined as grade > or =2 hypercalcemia or grade > or =3 persistent treatment-related toxicities. Single-dose administration of 15, 30, 60, 75, 90, 105, 135, and 165 mug was tested.

RESULTS

Thirty-eight patients were enrolled in 2002 and 2003. The median age was 70 years (range, 44-91 years). Dose escalation was stopped at the 165 microg level when the number of capsules required at one time reached 11. No dose-limiting toxicities occurred. Transient and self-limited grade 3 toxicities were hyponatremia (2) and proteinuria (1). A dose-proportional increase in peak concentration (C(max)) and area under the concentration curve (AUC) was seen across the full range of DN-101 doses tested. At the 165 microg dose, C(max) was 6.21 +/- 1.99 ng/mL, AUC(0-24) was 41.3 +/- 9.77 ng h/mL, AUC(0-infinity) was 55.4 +/- 8.44, and half-life (T(1/2)) was 16.2 hours.

CONCLUSIONS

At doses between 15 and 165 microg, DN-101 exhibits linear pharmacokinetics. At 165 microg, DN-101 achieves systemic exposure that is 5- to 8-fold higher than that achieved with commercial formulations of calcitriol, which makes DN-101 comparable to that required for antitumor activity in vivo in a murine squamous cell carcinoma model.

Enhancement by dexamethasone of the therapeutic benefits of cisplatin via regulation of tumor angiogenesis and cell cycle kinetics in a murine tumor paradigm

We have investigated in the current study, the possible modulatory effects of dexamethasone on cisplatin cytotoxicity in Ehrlich ascites carcinoma (EAC)-bearing female Swiss albino mice. Cisplatin (3.5mg/kg) was injected IP for 3 consecutive days in mice previously inoculated SC with EAC cells in the right flank. Dexamethasone (2.5mg/kg) was administered SC alone or 24h ahead of cisplatin challenge, and these regimens were given for 3 consecutive days. Dexamethasone enhanced the anti-tumor effects of cisplatin, clearly demonstrated by the increased mean tumor growth time (TGT) and tumor growth delay time (TGDT) values compared to cisplatin alone. The effects of dexamethasone on tumor angiogenesis and cell cycle distribution of EAC cells have been addressed as possible mechanisms, whereby the glucocorticoid could probably augment cisplatin cell-kill. Indeed, dexamethasone enhanced the angiostatic activity of cisplatin by 52.5%. The glucocorticoid also synchronized the EAC cells in the G2/M phase, secondary to its regulatory role on the transcriptional and translational activity in these cells, thus, exposing them to the dramatic cytotoxic potential of cisplatin. One could conclude that dexamethasone enhanced the anti-tumor effects of cisplatin via augmenting its angiostatic activity and modulating cell cycle kinetics. Also, dexamethasone did not alter cisplatin-induced nephrotoxicity, thus demonstrating an improved therapeutic potential.

Phase II trial of high-dose, intermittent calcitriol (1,25 dihydroxyvitamin D3) and dexamethasone in androgen-independent prostate cancer

BACKGROUND

Data suggest that vitamin D plays a role in the treatment and prevention of prostate cancer. The combination of high-dose, intermittent calcitriol (1,25 dihydroxyvitamin D3) plus dexamethasone was studied based on evidence that dexamethasone potentiates the antitumor effects of calcitriol and ameliorates hypercalcemia.

METHODS

Oral calcitriol was administered weekly, Monday, Tuesday, and Wednesday (MTW), at a dose of 8 microg, for 1 month, at a dose of 10 microg every MTW for 1 month, and at a dose of 12 microg every MTW thereafter. Dexamethasone at a dose of 4 mg was administered each Sunday, and MTW weekly. Calcium and creatinine were determined weekly and radiographs of the urinary tract were performed every 3 months. All patients were considered evaluable for toxicity.

RESULTS

Forty-three men with androgen-independent prostate cancer were entered; 37 received at least 1 month of calcitriol given at a dose of 12 microg every day x 3 per week. The majority of patients had bone metastases and rising prostate-specific antigen (PSA) levels. All had an Eastern Cooperative Oncology Group performance status of 0 or 1. Eight patients (19%) experienced partial responses by PSA criterion (PSA decline of > or =50%, persisting for > or = 28 days). Subjective clinical improvement occurred in some patients. Toxicity was minimal: urinary tract stones in 2 patients; and a readily reversible, CTC (v.3.0) Grade <2 creatinine increase in 4 patients. Throughout the study only 4 patients ever had a serum calcium level >11.0 mg/dL and no patient had a calcium level >12.0 mg/dL.

CONCLUSIONS

The response rate reported in the current study (19%) was not found to be clearly higher than expected with dexamethasone alone. High-dose intermittent calcitriol plus dexamethasone appears to be safe, feasible, and has antitumor activity.

Cooperation between antioxidants and 1,25-dihydroxyvitamin D3 in induction of leukemia HL60 cell differentiation through the JNK/AP-1/Egr-1 pathway

Vitamin D derivatives have demonstrated anti-cancer activity, but their clinical use is precluded by hypercalcemia. Previously, we found that carnosic acid potentiates differentiation of human leukemia cells induced by low concentrations of 1alpha,25-dihydroxyvitamin D(3) (1,25D(3)). In this study, we investigated if this effect is a general property of antioxidants, and whether there is a common mechanism whereby antioxidants potentiate monocytic differentiation. We found that all antioxidants tested enhanced differentiation-related cell cycle arrest induced by a low (1 nM) concentration of 1,25D(3). Addition of antioxidants to 1,25D(3) activated the JNK pathway as indicated by increased phosphorylation of c-jun and ATF-2, although each compound alone had a minimal effect. Antioxidants also enhanced the 1,25D(3)-induced AP-1 DNA binding and transactivation ability. Expression of Egr-1 and c-fos was increased by combinations of antioxidants and 1,25D(3), in parallel with the activation of the JNK pathway. The potentiation of differentiation by antioxidants was inhibited by JNK inhibitor SP600125 and a dominant negative JNK 1/2 construct, and Egr-1 and c-fos expression was proportionally decreased, suggesting that JNK pathway regulates these transcription factors. While potentiating the prodifferentiation effect of 1,25D(3), antioxidants did not promote the elevation of basal levels of intracellular calcium by 1,25D(3). The results indicate that JNK-AP1 pathway has an important role in the potentiation of 1,25D(3)-induced differentiation by antioxidants, and regulates expression of Egr-1 and c-fos. Combinations of antioxidants with 1,25D(3) should be further evaluated for use in cancer chemoprevention and therapy.

Vitamin D compounds in leukemia

The biologically active form of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)(2)D3,] possess in vitro multiple anti-cancer activities including growth arrest, induction of apoptosis and differentiation of a variety of different types of malignant cells. However, its use as a therapeutic agent is hindered by its calcemic effects. Analogs of 1,25(OH)(2)D3 have enhanced anti-tumor activity, with reduced calcemic effects. However, limited clinical studies using vitamin D compounds have not yet achieved major clinical success. Nevertheless, pre-clinical studies suggest that the combination of either 1,25(OH)(2)D3 or its analogs with other agents can have additive or synergistic anti-cancer activities, suggesting future clinical studies.

ASCENT: The androgen-independent prostate cancer study of calcitriol enhancing taxotere

ASCENT, the Androgen-Independent Prostate Cancer (AIPC) Study of Calcitriol Enhancing Taxotere, is a double-blind, placebo-controlled randomized clinical trial designed to determine if DN-101, a high-dose oral formulation of calcitriol designed for cancer therapy, significantly increases the proportion of patients who have > 50% reduction in serum prostate-specific antigen (PSA) levels in response to docetaxel. The secondary goals of ASCENT are to evaluate the effect of DN-101 combined with docetaxel on PSA progression-free survival, tumour response rate in measurable disease, tumour progression-free survival, skeletal morbidity-free survival, clinical progression-free survival, and overall survival, and to examine the safety and tolerability of DN-101 combined with docetaxel. ASCENT builds on phase I work showing that weekly dosing allows substantial dose-escalation of calcitriol, the natural ligand for the vitamin D receptor, and on phase II work that suggested that adding weekly high-dose 'pulse' calcitriol may enhance the activity of weekly docetaxel in patients with AIPC. The preclinical rationale for calcitriol and its combination with docetaxel for prostate cancer therapy is reviewed, as are the key clinical trials that led to the development of ASCENT. The ASCENT design and its strengths and limitations are presented.

Pharmacokinetics of liquid calcitriol formulation in advanced solid tumor patients: comparison with caplet formulation

The non linear relationship between calcitriol (1,25-D(3)) dose and AUC in cancer patients suggests that the commercially available caplet 1,25-D(3) formulation (Rocaltrol) cannot achieve the high systemic exposure associated with antitumor activity in animal models. The primary objective of this analysis was to determine whether a liquid 1,25-D(3) formulation had a more favorable pharmacokinetic profile. This analysis was based on the results obtained in 2 phase I clinical studies seeking to determine the maximum tolerated dose of 1,25-D(3) administered in combination with either dexamethasone or paclitaxel daily for three consecutive days weekly. Data were available for 12 patients treated with the caplet formulation at doses ranging from 12 microg to 21 microg, and for 16 patients treated with the liquid formulation at doses ranging from 13 microg to 36 microg; data for 19 patients were available at doses for which both formulations were used. There were no differences in C(max) and AUC(0-24 h) between the two formulations (P > 0.17) As was noted with the caplet formulation, dose-related proportional increases in C(max) and AUC(0-24 h) were not observed with liquid 1,25-D(3) at doses > or = 13 microg (P > 0.83). We conclude that the commercially available liquid 1,25-D(3) formulation offers no PK advantage over caplet formulation.

High-dose calcitriol and carboplatin in metastatic androgen-independent prostate cancer

Calcitriol acts synergistically with carboplatin in preclinical models of adenocarcinoma of the prostate. The authors sought to test high-dose oral calcitriol in combination with carboplatin in patients with metastatic androgen-independent prostate cancer. Seventeen patients received oral calcitriol (0.5 microg/kg) on day 1 and intravenous carboplatin (AUC 7 or AUC 6 in patients with prior radiation) on day 2, repeated every 4 weeks. PSA response was the primary end point and was defined as a 50% reduction confirmed 4 weeks later. Palliative response (2-point reduction or normalization of pain on the present pain intensity [PPI] scale without increased analgesic consumption) was also examined. One of 17 patients (6%, 95% CI, 0-28) achieved a confirmed PSA response. Four patients (24%, 95% CI, 7-49) had PSA reductions ranging from 24 to 38%. Of the 15 patients with a PPI > or = 1 point on entry, 3 (18%, 95% CI, 4-48) met criteria for palliative response. Treatment-related toxicity was mild and generally similar to that expected with single-agent carboplatin. Despite encouraging preclinical evidence, the addition of oral calcitriol to carboplatin in this study was not associated with an increase in the response rate when compared with the reported activity of carboplatin alone.

Rationale for the development and current status of calcitriol in androgen-independent prostate cancer

Calcitriol, the principal active metabolite of vitamin D, has significant antineoplastic activity in pre-clinical models of prostate cancer and many other tumor types. Reported mechanisms of activity include inhibition of proliferation and cell cycle arrest, induction of apoptosis, and reduction of invasiveness and angiogenesis. Different mechanisms may be responsible in different tumor types and under different experimental conditions. Importantly, preclinical data suggest that calcitriol acts in a synergistic and/or additive manner when combined with antineoplastic agents that are relevant to prostate cancer, including dexamethasone and several classes of cytotoxic agents. The antineoplastic effects of calcitriol occur at concentrations that substantially exceed the normal physiologic range and cannot be safely achieved with conventional daily dosing. Intermittent administration of calcitriol has allowed significant dose escalation. In combination with weekly docetaxel, the agent produced encouraging results in a single-institution phase II study. An international placebo-controlled randomized trial that is currently under way will provide more robust information about the safety and efficacy of this combination.

Interaction of nuclear receptor ligands with the Vitamin D signaling pathway in prostate cancer

A number of hormonal ligands and/or the nuclear receptors that mediate their actions have been targeted for prostate cancer therapy. Androgens, the ligands for the androgen receptor (AR), are critical for the growth of prostate cancer. Inhibition of androgen production has been the mainstay of treatment for advanced prostate cancer for decades. Other more recently tested targets include retinoid receptors (RAR and RXR), glucocorticoid receptors (GR), estrogen receptors (ER) and peroxisome proliferator-activated receptors (PPAR). Calcitriol, acting through the Vitamin D receptor (VDR), has many tumor suppressive activities in the prostate, including inhibition of proliferation, induction of apoptosis and/or differentiation, and reduction of cellular invasion. Because of these properties, calcitriol and its less hypercalcemic analogs are being evaluated as agents to prevent or treat prostate cancer. Androgens, retinoids, glucocorticoids, estrogens and agonists of PPAR directly or indirectly impact Vitamin D signaling pathways, and vice versa. In order to design the most effective strategies to use calcitriol to prevent or treat prostate cancer, the interactions of other nuclear receptors and their ligands with the Vitamin D signaling pathway need to be considered.

Enhancement by other compounds of the anti-cancer activity of vitamin D(3) and its analogs

Differentiation therapy holds promise as an alternative to cytotoxic drug therapy of cancer. Among compounds under scrutiny for this purpose is the physiologically active form of vitamin D(3), 1,25-dihydroxyvitamin D(3), and its chemically modified derivatives. However, the propensity of vitamin D(3) and its analogs to increase the levels of serum calcium has so far precluded their use in cancer patients except for limited clinical trials. This article summarizes the range of compounds that have been shown to increase the differentiation-inducing and antiproliferative activities of vitamin D(3) and its analogs, and discusses the possible mechanistic basis for this synergy in several selected combinations. The agents discussed include those that have differentiation-inducing activity of their own that is increased by combination with vitamin D(3) or analogs, such as retinoids or transforming growth factor-beta and plant-derived compounds and antioxidants, such as curcumin and carnosic acid. Among other compounds discussed here are dexamethasone, nonsteroidal anti-inflammatory drugs, and inhibitors of cytochrome P450 enzymes, for example, ketoconazole. Thus, recent data illustrate that there are extensive, but largely unexplored, opportunities to develop combinatorial, differentiation-based approaches to chemoprevention and chemotherapy of human cancer.

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

1,25-Dihydroxycholecalciferol (calcitriol) is recognized widely for its effects on bone and mineral metabolism. Epidemiological data suggest that low Vitamin D levels may play a role in the genesis of prostate cancer and perhaps other tumors. Calcitriol is a potent anti-proliferative agent in a wide variety of malignant cell types. In prostate, breast, colorectal, head/neck and lung cancer as well as lymphoma, leukemia and myeloma model systems calcitriol has significant anti-tumor activity in vitro and in vivo. Calcitriol effects are associated with an increase in G0/G1 arrest, induction of apoptosis and differentiation, modulation of expression of growth factor receptors. Glucocorticoids potentiate the anti-tumor effect of calcitriol and decrease calcitriol-induced hypercalcemia. Calcitriol potentiates the antitumor effects of many cytotoxic agents and inhibits motility and invasiveness of tumor cells and formation of new blood vessels. Phase I and II trials of calcitriol either alone or in combination with carboplatin, taxanes or dexamethasone have been initiated in patients with androgen dependent and independent prostate cancer and advanced cancer. Data indicate that high-dose calcitriol is feasible on an intermittent schedule, no dose-limiting toxicity has been encountered and optimal dose and schedule are being delineated. Clinical responses have been seen with the combination of high dose calcitriol+dexamethasone in androgen independent prostate cancer (AIPC) and apparent potentiation of the antitumor effects of docetaxel have been seen in AIPC. These results demonstrate that high intermittent doses of calcitriol can be administered to patients without toxicity, that the MTD is yet to be determined and that calcitriol has potential as an anti-cancer agent.

Novel approaches to treat asymptomatic, hormone-naive patients with rising prostate-specific antigen after primary treatment for prostate cancer

Biochemical-only recurrent prostate cancer presents the ideal setting for assessing novel agents or approaches for prostate cancer treatment. There is no clear evidence that delay in initiation of more definitive androgen-deprivation therapy is harmful, and a simple blood test--the prostate-specific antigen (PSA) level--is readily available to screen for potential antineoplastic activity. Current novel approaches include vaccines, cyclooxygenase-2 (COX-2) inhibitors, selective apoptotic antineoplastic drugs, endothelin-A receptor antagonists, chemotherapy, vitamin D, and peroxisome proliferator-activated receptor-gamma agonists. In this screening process, certain therapies have emerged as delaying PSA progression or decelerating PSA velocity. These therapies, such as the COX-2 inhibitors, will need to proceed to phase 3 trials to answer the more important question of whether this change in PSA dynamics translates into improved survival. Patients enrolling in these trials need to be clearly informed of the limited expectations of these novel exploratory approaches.

Pretreatment with Dexamethasone Increases Antitumor Activity of Carboplatin and Gemcitabine in Mice Bearing Human Cancer Xenografts

PURPOSE

The present study was undertaken to determine the effects of dexamethasone (DEX) pretreatment on antitumor activity and pharmacokinetics of the cancer chemotherapeutic agents carboplatin and gemcitabine.

EXPERIMENTAL DESIGN

Antitumor activities of carboplatin and gemcitabine with or without DEX pretreatment were determined in six murine-human cancer xenograft models, including cancers of colon (LS174T), lung (A549 and H1299), and breast (MCF-7 and MDA-MB-468) and glioma (U87-MG). Effects of DEX on plasma and tissue pharmacokinetics of carboplatin and gemcitabine were also determined by using the LS174T, A549, and H1299 models.

RESULTS

Although DEX alone showed minimal antitumor activity, DEX pretreatment significantly increased the efficacy of carboplatin, gemcitabine, or a combination of both drugs by 2-4-fold in all xenograft models tested. Without DEX treatment, the tumor exposure to carboplatin, measured by the area under the curve, was markedly lower than normal tissues. However, DEX pretreatment significantly increased tumor carboplatin levels, including 200% increase in area under the curve, 100% increase in maximum concentration, and 160% decrease in clearance. DEX pretreatment similarly increased gemcitabine uptake in tumors.

CONCLUSIONS

To our knowledge, this is the first report that DEX significantly enhances the antitumor activity of carboplatin and gemcitabine and increases their accumulation in tumors. These results provide a basis for further evaluation of DEX as a chemosensitizer in patients.

Calcitriol in cancer treatment: From the lab to the clinic

1,25-Dihydroxyvitamin D (calcitriol), the most active metabolite of vitamin D, has significant antineoplastic activity in preclinical models. Several mechanisms of activity have been proposed. These include inhibition of proliferation associated with cell cycle arrest and, in some models, differentiation, reduction in invasiveness and angiogenesis, and induction of apoptosis. Proposed mechanisms differ between tumor models and experimental conditions, and no unifying hypothesis about the mechanism of antineoplastic activity has emerged. Synergistic and/or additive effects with cytotoxic chemotherapy, radiation, and other cancer drugs have been reported. Significantly supraphysiological concentrations of calcitriol are required for antineoplastic effects. Such concentrations are not achievable in patients when calcitriol is dosed daily due to predictable hypercalcemia and hypercalcuria; however, phase I trials have demonstrated that intermittent dosing allows substantial dose escalation and has produced potentially therapeutic peak calcitriol concentrations. Recently, a phase II study reported encouraging levels of activity for the combination of high-dose calcitriol and docetaxel administered on a weekly schedule in patients with androgen-independent prostate cancer. This regimen is now under study in a placebo-controlled randomized trial in androgen-independent prostate cancer and in phase II studies in several other tumor types. Further work is needed to elucidate the molecular mechanisms of antineoplastic activity and optimal clinical applications of calcitriol in cancer.

High-dose calcitriol, zoledronate, and dexamethasone for the treatment of progressive prostate carcinoma

BACKGROUND

Preclinical and clinical data have suggested that high-dose calcitriol (1,25-dihydroxycholecalciferol) has activity against prostate carcinoma. Pulse-dosed calcitriol and dexamethasone may maximize tolerability and efficacy. The authors examined the toxicity of pulse-dosed calcitriol with zoledronate and with the addition of dexamethasone at the time of disease progression.

METHODS

Patients with progressive prostate carcinoma were eligible for the current study. In cohorts of 3-6 patients, calcitriol was administered for 3 consecutive days per week, starting at a dose of 4 microg per day. Doses were escalated to 30 microg per day. Intravenous zoledronate (4 mg) was administered monthly. Dexamethasone could be added to the regimen at disease progression. Toxicities, markers of bone turnover, plasma calcitriol levels, and clinical outcomes were recorded.

RESULTS

Thirty-one patients were treated in cohorts that were defined by the calcitriol dose administered (4, 6, 8, 10, 14, 20, 24, or 30 microg). Seven patients received dexamethasone. Three patients had their doses reduced due to calcium-related laboratory findings. Patients tolerated therapy well, even in the 30 microg cohort; therefore, a maximum tolerated dose was not defined. Peak plasma levels observed in the 24 microg and 30 microg cohorts ranged from 391 to 968 pg/mL. Minimal antitumor effects were observed.

CONCLUSIONS

Calcitriol was well tolerated at doses up to and including 30 microg 3 times per week in combination with intravenous zoledronate 4 mg monthly, with or without dexamethasone, in patients with progressive prostate carcinoma. Peak plasma levels in the 24 microg and 30 microg cohorts were greater than the levels associated with antitumor effects preclinically. Due to the cumbersome dosing schedule and the lack of significant activity observed, Phase II trials of this regimen are not planned.

Role of Vitamin D receptor gene in radiation-induced neoplastic transformation of human breast epithelial cell

1 Alpha,25-(OH)(2)-Vitamin D(3), the physiologically active metabolite of Vitamin D is known for its pro-differentiating and antiproliferative activity on various cancer cell lines. It exerts its growth-regulatory effects through binding to the Vitamin D recepter (VDR), a member of the steroid/thyroid/retinoic acid receptor family, which functions as a ligand-dependent transcription factor. There is accumulating evidence that Vitamin D may be an important determinant of both the occurrence and progression of breast cancer. Since radiation is an important etiological factor for breast cancer progression, it is important to study the role of VDR gene in radiation-induced breast carcinogenesis. This study is focused on a human breast tumor model developed by irradiating the spontaneously immortalized MCF-10F cell line with graded doses of high-linear energy transfer (LET) radiation followed by treatment with estrogen. Study of VDR gene by restriction digestion with ApaI, BsmI and TaqI detected no polymorphism but direct sequencing analyses identified few single-base mutations within intron 8 and exon 9 of the gene. Over-expression of the VDR gene was noticed in irradiated and tumorigenic cell lines compared with control. Likewise, immunohistochemical data indicated a significant increase in VDR intensity in irradiated and tumorigenic cell lines. Considering all these evidence, it is likely that VDR can be used as a prognostic marker of tumor progression in radiation- and estrogen-induced breast carcinogenesis.

Development of weekly high-dose calcitriol based therapy for prostate cancer

Calcitriol, the principal biologically active ligand of the Vitamin D receptor (VDR), has been shown to inhibit cancer cell proliferation in in vitro and in vivo models of prostate cancer and a wide range of other neoplasms. In addition, calcitriol's activity appears to be additive, and in some experimental systems, synergistic with dexamethasone and several cytotoxic chemotherapy agents. While effects on progression through the cell cycle, induction of apoptosis, inhibition of angiogenesis, and reduction in tumor invasiveness have been demonstrated, the exact mechanisms of VDR-mediated antineoplastic activity remain incompletely understood. Antineoplastic activity of calcitriol requires substantially supraphysiologic concentrations of this compound. Dose escalation of calcitriol administered daily was severely limited by predictable hypercalcemia and/or hypercalcuria. This limitation has been overcome with intermittent dosing of calcitriol. At Oregon Health & Science University, weekly oral administration of calcitriol allowed the attainment of peak serum calcitriol concentrations well above 1 nM, a concentration that inhibits prostate cancer proliferation by more than 50% in vitro. Weekly high-dose calcitriol was then combined with weekly docetaxel in a Phase II clinical trial carried out in men with metastatic androgen-independent prostate cancer. Treatment resulted in PSA response (defined as a confirmed 50% reduction) in 81% of patients. This level of activity, as well as the median time to progression of 11.4 months and median survival of 19.5 months, compared favorably to results with docetaxel alone and led to the development of a recently initiated randomized trial of docetaxel with calcitriol or placebo in the same patient population.

A limited sampling method for the estimation of serum calcitriol area under the curve in cancer patients

Pharmacokinetic (PK) data from 34 cancer patients receiving 2 to 10 micrograms of calcitriol subcutaneously (s.c.) were used to develop a limited sampling method for predicting serum calcitriol area under curve (AUC) based on three samples instead of the full complement of 12 to 16 samples. Serum calcitriol levels were measured by 1, 25-dihydroxyvitamin D3-[I125] radioimmunoassay. Individual patient-corrected serum calcitriol AUC0-12 h was calculated by the trapezoidal rule after subtracting the pretreatment serum calcitriol level. PK data were split into "training" and "evaluation" sets based on calcitriol dose and chronological order of enrollment. Linear regression models of log-corrected AUC0-12 h versus individual log calcitriol serum levels in the hour 1, 2, 3, 4, 6, and 8 samples were established using the training data set of 17 patients. The fit was tested on the evaluation data set of 17 patients using mean squared error (MSE) as the fit criterion. The best single time point predictor of log AUC0-12 h was the log serum (calcitriol) at hour 6 (MSE = 0.0061). The best prediction of log AUC0-12 h using two time points was found to involve hour 6 and hour 2 (MSE = 0.0018). The prediction equation for the latter model was as follows: Log AUC = 1.125 + 0.3756.log (calcitriol) at hour 2 + 0.5859.log (calcitriol) at hour 6. This limited sampling method was further evaluated in 83 cancer patients treated with 4 to 38 micrograms of oral (p.o.) calcitriol; observed and predicted calcitriol AUC0-12 h were highly correlated (r > or = 0.90, p = 0.0001). These results show that serum calcitriol AUC0-12 h after s.c. and p.o. calcitriol administration is accurately estimated using pretreatment and 2- and 6-hour blood samples.