Clinical Trials Involving Vitamin D Analogs in Prostate Cancer

A synthetic lethal screen identifies the Vitamin D receptor as a novel gemcitabine sensitizer in pancreatic cancer cells

Overcoming chemoresistance of pancreatic cancer (PCa) cells should significantly extend patient survival. The current treatment modalities rely on a variety of DNA damaging agents including gemcitabine, FOLFIRINOX, and Abraxane that activate cell cycle checkpoints, which allows cells to survive these drug treaments. Indeed, these treatment regimens have only extended patient survival by a few months. The complex microenvironment of PCa tumors has been shown to complicate drug delivery thus decreasing the sensitivity of PCa tumors to chemotherapy. In this study, a genome-wide siRNA library was used to conduct a synthetic lethal screen of Panc1 cells that was treated with gemcitabine. A sublethal dose (50 nM) of the drug was used to model situations of limiting drug availability to PCa tumors in vivo. Twenty-seven validated sensitizer genes were identified from the screen including the Vitamin D receptor (VDR). Gemcitabine sensitivity was shown to be VDR dependent in multiple PCa cell lines in clonogenic survival assays. Sensitization was not achieved through checkpoint override but rather through disrupting DNA repair. VDR knockdown disrupted the cells' ability to form phospho-γH2AX and Rad51 foci in response to gemcitabine treatment. Disruption of Rad51 foci formation, which compromises homologous recombination, was consistent with increased sensitivity of PCa cells to the PARP inhibitor Rucaparib. Thus inhibition of VDR in PCa cells provides a new way to enhance the efficacy of genotoxic drugs.

Vitamin D, intermediary metabolism and prostate cancer tumor progression

Epidemiological data have demonstrated an inverse association between serum vitamin D3 levels, cancer incidence and related mortality. However, the effects of vitamin D on prostate cancer biology and its utility for prevention of prostate cancer progression are not as well-defined. The data are often conflicting: some reports suggest that vitamin D3 induces apoptosis in androgen dependent prostate cancer cell lines, while others suggest that vitamin D3 only induces cell cycle arrest. Recent molecular studies have identified an extensive synergistic crosstalk between the vitamin D- and androgen-mediated mRNA and miRNA expression, adding an additional layer of post-transcriptional regulation to the known VDR- and AR-regulated gene activation. The Warburg effect, the inefficient metabolic pathway that converts glucose to lactate for rapid energy generation, is a phenomenon common to many different types of cancer. This process supports cell proliferation and promotes cancer progression via alteration of glucose, glutamine and lipid metabolism. Prostate cancer is a notable exception to this general process since the metabolic switch that occurs early during malignancy is the reverse of the Warburg effect. This "anti-Warburg effect" is due to the unique biology of normal prostate cells that harbor a truncated TCA cycle that is required to produce and secret citrate. In prostate cancer cells, the TCA cycle activity is restored and citrate oxidation is used to produce energy for cancer cell proliferation. 1,25(OH)2D3 and androgen together modulates the TCA cycle via transcriptional regulation of zinc transporters, suggesting that 1,25(OH)2D3 and androgen maintain normal prostate metabolism by blocking citrate oxidation. These data demonstrate the importance of androgens in the anti-proliferative effect of vitamin D in prostate cancer and highlight the importance of understanding the crosstalk between these two signaling pathways.

Castration-resistant prostate cancer: new science and therapeutic prospects

There is a growing number of new therapies targeting different pathways that will revolutionize patient management strategies in castration-resistant prostate cancer (CRPC) patients. Today there are more clinical trial options for CRPC treatment than ever before, and there are many promising agents in late-stage clinical testing. The hypothesis that CRPC frequently remains driven by a ligand-activated androgen receptor (AR) and that CRPC tissues exhibit substantial residual androgen levels despite gonadotropin-releasing hormone therapy, has led to the evaluation of new oral compounds such as abiraterone and MDV 3100. Their results, coupled with promising recent findings in immunotherapy (eg sipuleucel-T) and with agents targeting angiogenesis (while awaiting the final results of the CALGB trial 90401) will most probably impact the management of patients with CRPC in the near future. Other new promising agents need further development. With our increased understanding of the biology of this disease, further trial design should incorporate improved patient selection so that patient populations are those who may be most likely to benefit from treatment.

Vitamin D in older population: new roles for this 'classic actor'?

Vitamin D is a group of lipophilic hormones with pleiotropic actions. It has been traditionally related to bone metabolism, although several studies in the last decade have suggested its role in muscle strength and falls, cardiovascular and neurological diseases, insulin-resistance and diabetes, malignancies, autoimmune diseases and infections. Vitamin D appears to be a hormone with several actions and is fundamental for many biological systems including bone, skeletal muscle, brain and heart. The estimated worldwide prevalence of vitamin D deficiency of 50% in elderly subjects underlines the importance of vitamin D deficiency for public health. In this review, we will describe changes in vitamin D levels with age in both sexes, cut off values to define Vitamin D status, the impact of vitamin D deficiency in age-related disease and finally different therapeutic options available to treat Vitamin D deficiency in older populations.

Vitamin D pathway gene variants and prostate cancer prognosis

BACKGROUND

Observational studies linking vitamin D deficiency with increased prostate cancer (PCa) mortality and the pleiotropic anticancer effects of vitamin D in malignant prostate cell lines have initiated trials examining potential therapeutic benefits of vitamin D metabolites. There have been some successes but efforts have been hindered by risk of inducing hypercalcemia. A limited number of studies have investigated associations between variants in vitamin D pathway genes with aggressive forms of PCa. Increased understanding of relevant germline genetic variation with disease outcome could aid in the development of vitamin-D-based therapies.

METHODS

We undertook a comprehensive analysis of 48 tagging single-nucleotide polymorphisms (tagSNPs) in genes encoding for vitamin D receptor (VDR), vitamin D activating enzyme 1-alpha-hydroxylase (CYP27B1), and deactivating enzyme 24-hydroxylase (CYP24A1) in a cohort of 1,294 Caucasian cases with an average of 8 years of follow-up. Disease recurrence/progression and PCa-specific mortality risks were estimated using adjusted Cox proportional hazards regression.

RESULTS

There were 139 cases with recurrence/progression events and 57 cases who died of PCa. Significantly altered risks of recurrence/progression were observed in relation to genotype for two VDR tagSNPs (rs6823 and rs2071358) and two CYP24A1 tagSNPs (rs927650 and rs2762939). Three VDR tagSNPs (rs3782905, rs7299460, and rs11168314), one CYP27B1 tagSNP (rs3782130), and five CYP24A1 tagSNPs (rs3787557, rs4809960, rs2296241, rs2585428, and rs6022999) significantly altered risks of PCa death.

CONCLUSIONS

Genetic variations in vitamin D pathway genes were found to alter both risk of recurrence/progression and PCa-specific mortality.

Curcumin: a novel nutritionally derived ligand of the vitamin D receptor with implications for colon cancer chemoprevention

The nuclear vitamin D receptor (VDR) mediates the actions of 1,25-dihydroxyvitamin D(3) (1,25D) to regulate gene transcription. Recently, the secondary bile acid, lithocholate (LCA), was recognized as a novel VDR ligand. Using reporter gene and mammalian two-hybrid systems, immunoblotting, competitive ligand displacement and quantitative real-time PCR, we identified curcumin (CM), a turmeric-derived bioactive polyphenol, as a likely additional novel ligand for VDR. CM (10(-5) M) activated transcription of a luciferase plasmid containing the distal vitamin D responsive element (VDRE) from the human CYP3A4 gene at levels comparable to 1,25D (10(-8) M) in transfected human colon cancer cells (Caco-2). While CM also activated transcription via a retinoid X receptor (RXR) responsive element, activation of the glucocorticoid receptor (GR) by CM was negligible. Competition binding assays with radiolabeled 1,25D confirmed that CM binds directly to VDR. In mammalian two-hybrid assays employing transfected Caco-2 cells, CM (10(-5) M) increased the ability of VDR to recruit its heterodimeric partner, RXR, and steroid receptor coactivator-1 (SRC-1). Real-time PCR studies revealed that CM-bound VDR can activate VDR target genes CYP3A4, CYP24, p21 and TRPV6 in Caco-2 cells. Numerous studies have shown chemoprotection by CM against intestinal cancers via a variety of mechanisms. Small intestine and colon are important VDR-expressing tissues where 1,25D has known anticancer properties that may, in part, be elicited by activation of CYP-mediated xenobiotic detoxification and/or up-regulation of the tumor suppressor p21. Our results suggest the novel hypothesis that nutritionally-derived CM facilitates chemoprevention via direct binding to, and activation of, VDR.

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

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

Prostate-derived Ets transcription factor as a favorable prognostic marker in ovarian cancer patients

We have previously shown that ovarian tumors express prostate-derived Ets transcription factor (PDEF). However, the precise role of PDEF in the prognosis of ovarian cancer is unknown. In our study, we report for the first time that expression of PDEF in tumor lesions of patients with ovarian cancer is associated with favorable prognosis. Evaluation of samples from 40 patients with ovarian cancer showed that early stage (IA) and borderline (IIB, III) ovarian tumors expressed higher levels of PDEF mRNA and protein and lower levels of survivin compared to late stage ovarian tumors (IIIC and IV, p < 0.05). Normal ovarian tissues expressed the highest levels of PDEF mRNA and protein when compared to tumor tissues (p < 0.05). A Log-Rank test showed that overall survival of patients with PDEF-positive and survivin-negative ovarian tumors was significantly longer than those with PDEF-negative and survivin-positive tumors (p < 0.01). Forced expression of PDEF in PDEF-negative ovarian tumor cells inhibited tumor cell growth, induced apoptosis, downregulated survivin expression and its promoter activity. Furthermore, treatment of ovarian cancer cells with vitamin D or a selenium compound resulted in re-expression of PDEF, downregulation of survivin, induction of apoptosis and inhibition of tumor cell growth when compared to untreated controls (p < 0.05). Together, these observations showed an inverse correlation between PDEF and survivin expression and suggested that increased PDEF expression along with reduced survivin was associated with prolonged survival of patients with ovarian cancer.

Vitamin D and intervention trials in prostate cancer: from theory to therapy

Studies of vitamin D and prostate cancer have advanced rapidly from the hypothesis that vitamin D deficiency increases the risk of prostate cancer to intervention trials of vitamin D administration in clinical cancer. The hormonal form of vitamin D, 1,25(OH)(2)D, exerts prodifferentiating, antiproliferative, anti-invasive, and antimetastatic effects on prostate cells. Moreover, normal prostate cells synthesize 1,25(OH)(2)D from serum levels of the prohormone, 25-hydroxyvitamin D. The autocrine synthesis of 1,25(OH)(2)D by prostatic cells provides a biochemical mechanism whereby vitamin D may prevent prostate cancer. Many prostate cancer cells have lost the ability to synthesize 1,25(OH)(2)D but still possess 1,25(OH)(2)D receptors. This suggests that whereas vitamin D (e.g., cholecalciferol) might prevent prostate cancer, existing prostate tumors likely would require treatment with 1,25(OH)(2)D and/or its analogs. The major obstacle to the use of 1,25(OH)(2)D in patients therapeutically is the risk of hypercalcemia. Several maneuvers to reduce this risk, including pulse dosing and the use of less calcemic 1,25(OH)(2)D analogs, have been explored in Phase I-III clinical trials. Once merely a promise, vitamin D-based therapies for prostate cancer may soon be medical practice.

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.

Antineoplastic agents target the 25-hydroxyvitamin D3 24-hydroxylase messenger RNA for degradation: implications in anticancer activity

Calcitriol or 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)] has antitumor activity and hence its levels in patients may play an important role in disease outcome. Here, we report that the antineoplastic agents, daunorubicin hydrochloride, etoposide, and vincristine sulfate inhibited the ability of 1,25(OH)(2)D(3) to cause the accumulation of mRNA for kidney 25-hydroxyvitamin D(3) 24-hydroxylase (CYP24), an enzyme which catabolizes this hormone. This was not due to a drug-induced cytotoxic effect, reduction in the expression of the vitamin D receptor or inhibition of the vitamin D receptor-mediated activation of the mitogen-activated protein kinases or CYP24 promoter activity. Interestingly, there was selective degradation of CYP24 mRNA in the presence of the drugs. This was accompanied by an enhancement in the levels of 1,25(OH)(2)D(3) in cells incubated with 25-hydroxy vitamin D(3). These data identify a novel mechanism of action of some commonly used antineoplastic agents which by decreasing the stability of CYP24 mRNA would prolong the bioavailability of 1,25(OH)(2)D(3) for anticancer actions.

Clair DK, Josson S, Sompol P, Spasojevic I, St. Clair WH. Suppression of RelB-mediated manganese superoxide dismutase expression reveals a primary mechanism for radiosensitization effect of 1alpha,25-dihydroxyvitamin D(3) in prostate cancer cells

Nuclear factor-kappaB provides an adaptive response to protect cancer cells against cytotoxicity induced by redox active therapeutics. RelB is uniquely expressed at a high level in prostate cancer with high Gleason scores. Recently, we showed that the level of RelB rapidly increases in androgen-independent prostate cancer cells after exposure to ionizing radiation (IR), leading to a reduction in intrinsic radiosensitivity. Here, we show that interaction of 1alpha,25-dihydroxyvitamin D(3) [1alpha,25-(OH)(2)D(3)] with the vitamin D receptor significantly enhances radiosensitivity of prostate cancer cells at clinically relevant radiation doses. The radiosensitization effect of 1alpha,25-(OH)(2)D(3) is mediated, at least in part, by selectively suppressing IR-mediated RelB activation, leading to a reduced expression of its target gene MnSOD, a primary antioxidant enzyme in mitochondria. These results suggest that suppression of manganese superoxide dismutase is a mechanism by which 1alpha,25-(OH)(2)D(3) exerts its radiosensitization effect and that 1alpha,25-(OH)(2)D(3) may serve as an effective pharmacologic agent for selectively sensitizing prostate cancer cells to IR via suppression of antioxidant responses in mitochondria.

Antitumor properties of diastereomeric and geometric analogs of vitamin D3

Analogs of 1,25-dihydroxyvitamin D3 with a reversed configuration at C-1 or C-24 and E or Z geometry of the double bond at C-22 in the side chain or at C-5 in the triene system were examined for their antiproliferative activity in vitro against a spectrum of various human cancer cell lines. The analogs coded PRI-2201 (calcipotriol), PRI-2202 and PRI-2205, such as calcitriol and tacalcitol (used as a referential agents), revealed antiproliferative activity against human HL-60, HL-60/MX2, MCF-7, T47D, SCC-25 and mouse WEHI-3 cancer cell lines. The toxicity studies in vivo showed that PRI-2202 and PRI-2205 are less toxic than referential agents. Even at total doses of 2.5-5.0 mg/kg distributed during 5 successive days, no changes in body weight were observed. Calcitriol and tacalcitol showed toxicity in the same protocol at 100 times lower doses. Calcipotriol was lethal to all mice after administration of a total dose of 5.0 mg/kg. The analog PRI-2205 appeared to be more active in mouse Levis lung cancer tumor growth inhibition than calcitriol, calcipotriol or PRI-2202. This analog did not reveal calcemic activity at doses which inhibit tumor growth in vivo nor at higher doses.

Vitamin D inhibits the formation of prostatic intraepithelial neoplasia in Nkx3.1;Pten mutant mice

PURPOSE

Epidemiologic studies have shown that reduced levels of vitamin D represent a major risk factor for prostate cancer. In this report, we have examined the efficacy of 1alpha,25-dihydroxyvitamin D(3) (1,25 D(3)) as a chemopreventive agent using Nkx3.1; Pten mutant mice, which recapitulate stages of prostate carcinogenesis from prostate intraepithelial neoplasia (PIN) to adenocarcinoma.

EXPERIMENTAL DESIGN

1,25 D(3) (or vehicle) was delivered continuously to Nkx3.1; Pten mutant or control mice for a 4-month period beginning before (precancerous cohort) or after (cancerous cohort) these mice developed PIN. At the conclusion of the study, the mice were analyzed for the occurrence of PIN and/or cancer phenotypes by histologic analyses and immunostaining using known markers of cancer progression in these mice.

RESULTS

We found that sustained delivery of 1,25 D(3) to the Nkx3.1; Pten mutant mice resulted in a significant reduction in the formation of PIN while having no apparent effect on the control mice. Furthermore, 1,25 D(3) was maximally effective when delivered before, rather than subsequent to, the initial occurrence of PIN. We further show that this 1,25 D(3)-mediated inhibition of PIN was coincident with up-regulation of vitamin D receptor expression in the prostatic epithelium of the mutant mice, as well as in CASP prostate epithelial cell lines developed from these mice, while having no effect on androgen receptor expression or androgen receptor signaling.

CONCLUSION

Our findings show the value of chemoprevention studies using Nkx3.1; Pten mutant mice, particularly for evaluating the efficacy and underlying mechanisms of potential agents and to gain insights about the optimal timing of their delivery. In particular, our study predicts that vitamin D may have differential effects during early-stage versus late-stage disease and that it is more likely to be beneficial if delivered either before the overt manifestation of clinically detectable disease or during the earliest disease stages, rather than in advanced disease. Thus, our findings support the assessment of vitamin D analogues for chemoprevention in clinical trials targeting patients with early-stage disease and also establish molecular markers that can be used in such trials to determine biological activity and to optimize further clinical trials.

New drugs in prostate cancer

PURPOSE OF REVIEW

The survival of hormone-refractory metastatic prostate cancer patients has improved with the use of docetaxel-based chemotherapy. The survival benefits, however, are modest suggesting that rationally designed therapeutic approaches are needed. We discuss recent developments in the therapeutic approach to advanced metastatic hormone-refractory prostate cancer, including molecularly targeted therapy, signal transduction inhibitors, stem-cell targeted therapy, anti-angiogenic compounds, vaccines and immunomodulating agents, differentiation agents, cytotoxics, and pro-apoptotic agents.

RECENT FINDINGS

Over 200 compounds have entered clinical development for use in advanced prostate cancer, alone or in combination with cytotoxic agents such as docetaxel, or in other combinations. This article will review the results of emerging targets since the approval of docetaxel in 2004, concentrating on some of those compounds that, in our opinion, have the greatest potential and rationale for use.

SUMMARY

The growing field of targeted molecular therapy of prostate cancer has opened up numerous opportunities for therapeutic impact. Knowledge of the molecular determinants of progression, relapse after local therapy, chemotherapeutic resistance, and hormone refractoriness remains essential in the rational design of clinical trials of these agents. Given the complexity, heterogeneity, and crosstalk of molecular pathways and the molecular lesions in prostate cancer, combination or sequential therapy may be a necessary step towards significant therapeutic progress. Novel translational clinical trial methodologies may assist in a more rapid identification of active compounds at biologically active doses for phase-III testing.