Extended-Release Calcifediol: A Data Journey From Phase 3 Studies to Real-world Evidence Highlights the Importance of Early Treatment of Secondary Hyperparathyroidism.

BACKGROUND: Early secondary hyperparathyroidism (SHPT) diagnosis and treatment are crucial to delay the progression of SHPT and related complications, in particular, cardiovascular events and bone fractures. Extended-release calcifediol (ERC) has been developed for the treatment of SHPT in patients with stage 3/4 chronic kidney disease (CKD) and vitamin D insufficiency (VDI). SUMMARY: This review compares baseline characteristics and treatment responses of SHPT patients receiving ERC in Phase 3 studies with those treated with ERC in a real-world study. Mean ± standard deviation baseline parathyroid hormone (PTH) levels were 147 ± 56 pg/mL and 148 ± 64 pg/mL in the Phase 3 ERC cohorts, and 181 ± 98 pg/mL in the real-world study. Other baseline laboratory parameters were consistent between the clinical and real-world studies. ERC treatment increased 25-hydroxyvitamin D [25(OH)D] and significantly reduced PTH levels, regardless of baseline CKD stage, in all studies. In the pooled Phase 3 per-protocol populations, 74% of the ERC cohort were up-titrated to 60 µg/day after 12 weeks at 30 µg/day, 97% attained 25(OH)D levels ≥30 ng/mL, and 40% achieved ≥30% PTH reduction. Despite a much lower rate of uptitration in the real-world study, 70% of patients achieved 25(OH)D levels ≥30 ng/mL, and 40% had a ≥30% reduction in PTH. KEY MESSAGES: These data establish a 'continuum' of clinical and real-world evidence of ERC effectiveness for treating SHPT, irrespective of CKD stage, baseline PTH levels, and ERC dose. This evidence supports early treatment initiation with ERC, following diagnosis of SHPT, VDI, and stage 3 CKD, to delay SHPT progression.

Evaluation of Therapies for Secondary Hyperparathyroidism Associated with Vitamin D Insufficiency in Chronic Kidney Disease.

Introduction: Parathyroid hormone-lowering responses after administration of three different therapies capable of raising serum total 25-hydroxyvitamin D (25OHD) were evaluated in patients with secondary hyperparathyroidism (SHPT), vitamin D insufficiency (VDI), and stage 3 or 4 chronic kidney disease (CKD). Methods: Sixty-nine adult subjects with intact parathyroid hormone (iPTH) ≥85 and <500 pg/mL and VDI (25OHD <30 ng/mL) were randomized after ≥4-week washout to 2 months of open-label treatment with: (1) extended-release calcifediol (ERC) 60 µg/day; (2) immediate-release calcifediol (IRC) 266 µg/month; (3) high-dose cholecalciferol (HDC) 300,000 IU/month; or (4) paricalcitol plus low-dose cholecalciferol (PLDC) 1 or 2 µg and 800 IU/day, used as reference hormone replacement therapy. Serum 25OHD, calcium (Ca), phosphorus (P), plasma iPTH, and adverse events were monitored weekly. No clinically significant differences were observed at baseline between treatment groups. Results: Sixty-two subjects completed the study per protocol (PP; 14-17 per group). Mean (SD) 25OHD and iPTH at baseline were 20.6 (6.6) ng/mL and 144.8 (90) pg/mL, respectively. Mean 25OHD increased at end of treatment (EOT) to 82.9 (17.0) ng/mL with ERC (p < 0.001) and 30.8 (11.6) ng/mL with HDC (p < 0.05), but remained unchanged with IRC and PLDC. EOT 25OHD levels reached ≥30 ng/mL in all subjects treated with ERC and in 44% with HDC. All subjects attained EOT 25OHD levels ≥50 ng/mL with ERC versus none with other therapies. iPTH response rates at EOT (≥10, 20 or 30% below baseline) were similar for ERC and PLDC; rates for IRC and HDC were much lower. No significant changes from baseline were observed in ionized or corrected total Ca or P in any group. One episode of hypercalcemia (>10.3 mg/dL) occurred with PLDC. Hyperphosphatemia (>5.5 mg/dL) occurred once with ERC, eight times with HDC, 3 times with IRC, and twice with PLDC. Conclusion: ERC was highly effective in both raising serum 25OHD and decreasing iPTH in patients with SHPT, VDI, and stage 3 or 4 CKD. iPTH-lowering response rates with ERC were similar to daily PLDC, the reference therapy; rates with IRC or HDC were significantly lower. ERC is an attractive alternative to vitamin D hormone therapy in CKD patients.

REsCue trial: Randomized controlled clinical trial with extended-release calcifediol in symptomatic COVID-19 outpatients.

OBJECTIVES: This double-blind randomized controlled trial investigated raising serum 25-hydroxyvitamin D (25D) with extended-release calcifediol (ERC) on time to symptom resolution in patients with mild to moderate COVID-19. METHODS: COVID-19 outpatients received oral ERC (300 mcg on days 1-3 and 60 mcg on days 4-27) or placebo (NCT04551911). Symptoms were self-reported daily. Primary end points were raising 25D to ≥50 ng/mL and decreasing resolution time for five aggregated symptoms (three respiratory). RESULTS: In all, 171 patients were randomized, 160 treated and 134 (65 ERC, 69 placebo) retained. The average age was 43 y (range 18-71), 59% were women. The mean baseline 25D was 37 ± 1 (SE) ng/mL. In the full analysis set (FAS), 81% of patients in the ERC group achieved 25D levels of ≥50 ng/mL versus 15% in the placebo group (P < 0.0001). In the per-protocol (PP) population, mean 25D increased with ERC to 82 ± 4 (SE) ng/mL (P < 0.0001) by day 7; the placebo group trended lower. Symptom resolution time was unchanged in the FAS by ERC (hazard ratio [HR], 0.983; 95% confidence interval [CI], 0.695-1.390; P = 0.922). In the PP population, respiratory symptoms resolved 4 d faster when 25D was elevated above baseline level at both days 7 and 14 (median 6.5 versus 10.5 d; HR, 1.372; 95% CI, 0.945-1.991; P = 0.0962; Wilcoxon P = 0.0386). Symptoms resolved in both treatment groups to a similar extent by study end. Safety concerns including hypercalcemia were absent with ERC treatment. CONCLUSION: ERC safely raised serum 25D to ≥50 ng/mL in outpatients with COVID-19, possibly accelerating resolution of respiratory symptoms and mitigating the risk for pneumonia. These findings warrant further study.

Real-world assessment: effectiveness and safety of extended-release calcifediol and other vitamin D therapies for secondary hyperparathyroidism in CKD patients.

INTRODUCTION: Extended-release calcifediol (ERC), active vitamin D hormones and analogs (AVD) and nutritional vitamin D (NVD) are commonly used therapies for treating secondary hyperparathyroidism (SHPT) in adults with stage 3-4 chronic kidney disease (CKD) and vitamin D insufficiency (VDI). Their effectiveness for increasing serum total 25-hydroxyvitamin D (25D) and reducing elevated plasma parathyroid hormone (PTH), the latter of which is associated with increased morbidity and mortality, has varied across controlled clinical trials. This study aimed to assess real-world experience of ERC and other vitamin D therapies in reducing PTH and increasing 25D. METHODS: Medical records of 376 adult patients with stage 3-4 CKD and a history of SHPT and VDI from 15 United States (US) nephrology clinics were reviewed for up to 1 year pre- and post-ERC, NVD or AVD initiation. Key study variables included patient demographics, concomitant usage of medications and laboratory data. The mean age of the study population was 69.5 years, with gender and racial distributions representative of the US CKD population. Enrolled patients were grouped by treatment into three cohorts: ERC (n = 174), AVD (n = 55) and NVD (n = 147), and mean baseline levels were similar for serum 25D (18.8-23.5 ng/mL), calcium (Ca: 9.1-9.3 mg/dL), phosphorus (P: 3.7-3.8 mg/dL) and estimated glomerular filtration rate (eGFR: 30.3-35.7 mL/min/1.73m2). Mean baseline PTH was 181.4 pg/mL for the ERC cohort versus 156.9 for the AVD cohort and 134.8 pg/mL (p < 0.001) for the NVD cohort. Mean follow-up during treatment ranged from 20.0 to 28.8 weeks. RESULTS: Serum 25D rose in all cohorts (p < 0.001) during treatment. ERC yielded the highest increase (p < 0.001) of 23.7 ± 1.6 ng/mL versus 9.7 ± 1.5 and 5.5 ± 1.3 ng/mL for NVD and AVD, respectively. PTH declined with ERC treatment by 34.1 ± 6.6 pg/mL (p < 0.001) but remained unchanged in the other two cohorts. Serum Ca increased 0.2 ± 0.1 pg/mL (p < 0.001) with AVD but remained otherwise stable. Serum alkaline phosphatase remained unchanged. CONCLUSIONS: Real-world clinical effectiveness and safety varied across the therapies under investigation, but only ERC effectively raised mean 25D (to well above 30 ng/mL) and reduced mean PTH levels without causing hypercalcemia.

Extended-Release Calcifediol Effectively Raises Serum Total 25-Hydroxyvitamin D Even in Overweight Nondialysis Chronic Kidney Disease Patients with Secondary Hyperparathyroidism.

INTRODUCTION: Obesity increases the risk of vitamin D insufficiency, which exacerbates secondary hyperparathyroidism in chronic kidney disease. Recent studies suggest that serum total 25-hydroxyvitamin D (25OHD) levels of ≥50 ng/mL are necessary to produce significant reductions in elevated parathyroid hormone levels in nondialysis patients. Data from real-world and randomized controlled trials (RCTs) involving these patients were examined for (1) relationships between vitamin D treatments and the achieved levels of serum 25OHD and between serum 25OHD and body weight (BW)/body mass index (BMI); and (2) the impact of BW/BMI on achieving serum 25OHD levels ≥50 ng/mL with extended-release calcifediol (ERC) treatment or vitamin D supplementation (cholecalciferol or ergocalciferol). METHODS: Data obtained from nondialysis patients participating in two real-world studies, one conducted in Europe (Study 1) and the other (Study 2) in the USA, and in two US RCTs (Studies 3 and 4) were analyzed for serum 25OHD outcomes after treatment with ERC, vitamin D supplements, or placebo. RESULTS: More than 50% of subjects treated with vitamin D supplements in both real-world studies (Studies 1 and 2) failed to achieve serum 25OHD levels ≥30 ng/mL, a level widely viewed by nephrologists as the threshold of adequacy; only 7.3-7.5% of subjects achieved levels ≥50 ng/mL. Data from the European study (Study 1) showed that serum 25OHD levels had significant and nearly identical inverse relationships with BW and BMI, indicating that high BW or BMI thwarts the ability of vitamin D supplements to raise serum 25OHD. One RCT (Study 3) showed that 8 weeks of ERC treatment (60 µg/day) raised serum 25OHD levels to ≥30 and 50 ng/mL in all subjects, regardless of BW, while cholecalciferol (300,000 IU/month) raised serum 25OHD to these thresholds in 56% and 0% of subjects, respectively. The other RCT (Study 4) showed that ERC treatment (30 or 60 µg/day) successfully raised mean serum 25OHD levels to at least 50 ng/mL for subjects in all BW categories, whereas no increases were observed with placebo treatment. CONCLUSION: Real-world studies conducted in Europe and USA in nondialysis patients (Studies 1 and 2) showed that vitamin D supplements (cholecalciferol or ergocalciferol) were unreliable in raising serum total 25OHD to targets of 30 or 50 ng/mL. In contrast, ERC was demonstrated to be effective in one real-world study (Study 2) and two RCTs (Studies 3 and 4) conducted in US nondialysis patients in raising serum 25OHD to these targeted levels irrespective of BW.

Rationale for Raising Current Clinical Practice Guideline Target for Serum 25-Hydroxyvitamin D in Chronic Kidney Disease.

BACKGROUND: Vitamin D repletion is recommended for secondary hyperparathyroidism (SHPT) and associated vitamin D insufficiency (VDI) in chronic kidney disease (CKD), but optimal levels of serum total 25-hydroxyvitamin D remain undefined. Clinical practice guidelines target sufficiency, whereas recent data indicate that higher levels are required to control the elevation of intact parathyroid hormone (iPTH) as CKD advances. This secondary analysis of 2 randomized controlled trials seeks to identify the minimum level of mean serum 25-hydroxyvitamin D required to control SHPT arising from VDI in stage 3 or 4 CKD. METHODS: Adult subjects (n = 429) with SHPT, VDI, and stage 3 or 4 CKD were stratified by stage and treated daily with either extended-release calcifediol (ERC) or placebo in 2 identical, parallel, randomized, double-blind studies. After treatment for 26 weeks, all subjects were ranked by the level of serum total 25-hydroxyvitamin D and divided into quintiles in order to examine the relationships between the degree of vitamin D repletion and the associated changes in plasma iPTH, serum bone turnover markers, calcium, phosphorus, intact fibroblast growth factor 23 (FGF23) and vitamin D metabolites, estimated glomerular filtration rate (eGFR), and urine calcium:creatinine (Ca:Cr) ratio. RESULTS: Progressive increases in serum 1,25-dihydroxyvitamin D and reductions in plasma iPTH and serum bone turnover markers were observed as mean posttreatment serum 25-hydroxyvitamin D rose from 13.9 ng/mL (in Quintile 1) to 92.5 ng/mL (in Quintile 5), irrespective of CKD stage. Mean serum calcium, phosphorus and FGF23, eGFR, and urine Ca:Cr ratio (collectively "safety parameters") did not significantly change from Quintile 1. Suppression of iPTH and bone turnover markers was not observed until serum 25-hydroxyvitamin D rose to at least 50.8 ng/mL (Quintile 3). CONCLUSION: ERC therapy produced exposure-dependent reductions in plasma iPTH and bone turnover markers only when mean serum total 25-hydroxyvitamin D reached at least 50.8 ng/mL, indicating that current targets for vitamin D repletion therapy in CKD are too low. Gradual elevation of mean serum 25-hydroxyvitamin D to 92.5 ng/mL was not associated with significant adverse changes in safety parameters.

Extended-release calcifediol for secondary hyperparathyroidism in stage 3-4 chronic kidney disease.

INTRODUCTION: Extended-release calcifediol (ERC) 30 µg capsules were recently approved as Rayaldee® by the United States Food and Drug Administration (FDA) for the treatment of secondary hyperparathyroidism (SHPT) in adults with stage 3-4 (not 5) chronic kidney disease (CKD) and vitamin D insufficiency (serum total 25-hydroxyvitamin D < 30 ng/mL). Calcifediol is 25-hydroxyvitamin D3, a prohormone of calcitriol (1,25-dihydroxyvitamin D3), the endogenous active vitamin D hormone. ERC capsules have a lipophilic fill which gradually releases calcifediol, corrects vitamin D insufficiency and increases serum calcitriol and thereby suppresses production of parathyroid hormone (PTH) in CKD patients without perturbing normal vitamin D and mineral metabolism. Areas covered: This review focuses on the chemical, pharmacokinetic, pharmacodynamic and clinical profiles of ERC and describes the product's utility relative to other current treatment options for SHPT. Expert commentary: Randomized clinical trials (RCTs) have demonstrated that nutritional vitamin D is ineffective for treating SHPT whereas vitamin D receptor activators can correct elevated PTH but with increased risk of hypercalcemia and hyperphosphatemia. ERC offers healthcare professionals a new treatment option that has been demonstrated in RCTs to be safe and effective for controlling SHPT without meaningfully increasing serum concentrations of calcium or phosphorus.

Use of Extended-Release Calcifediol to Treat Secondary Hyperparathyroidism in Stages 3 and 4 Chronic Kidney Disease.

BACKGROUND/AIMS: Vitamin D insufficiency and secondary hyperparathyroidism (SHPT) are associated with increased morbidity and mortality in chronic kidney disease (CKD) and are poorly addressed by current treatments. The present clinical studies evaluated extended-release (ER) calcifediol, a novel vitamin D prohormone repletion therapy designed to gradually correct low serum total 25-hydroxyvitamin D, improve SHPT control and minimize the induction of CYP24A1 and FGF23. METHODS: Two identical multicenter, randomized, double-blind, placebo-controlled studies enrolled subjects from 89 US sites. A total of 429 subjects, balanced between studies, with stage 3 or 4 CKD, SHPT and vitamin D insufficiency were randomized 2:1 to receive oral ER calcifediol (30 or 60 µg) or placebo once daily at bedtime for 26 weeks. Most subjects (354 or 83%) completed dosing, and 298 (69%) entered a subsequent open-label extension study wherein ER calcifediol was administered without interruption for another 26 weeks. RESULTS: ER calcifediol normalized serum total 25-hydroxyvitamin D concentrations (>30 ng/ml) in >95% of per-protocol subjects and reduced plasma intact parathyroid hormone (iPTH) by at least 10% in 72%. The proportion of subjects receiving ER calcifediol who achieved iPTH reductions of ≥30% increased progressively with treatment duration, reaching 22, 40 and 50% at 12, 26 and 52 weeks, respectively. iPTH lowering with ER calcifediol was independent of CKD stage and significantly greater than with placebo. ER calcifediol had inconsequential impact on serum calcium, phosphorus, FGF23 and adverse events. CONCLUSION: Oral ER calcifediol is safe and effective in treating SHPT and vitamin D insufficiency in CKD.

Modified-release oral calcifediol corrects vitamin D insufficiency with minimal CYP24A1 upregulation.

Vitamin D insufficiency is prevalent in chronic kidney disease (CKD) and associated with secondary hyperparathyroidism (SHPT) and increased risk of bone and vascular disease. Unfortunately, supplementation of stage 3 or 4 CKD patients with currently recommended vitamin D2 or D3 regimens does not reliably restore serum total 25-hydroxyvitamin D to adequacy (≥30ng/mL) or effectively control SHPT. Preclinical and clinical studies were conducted to evaluate whether the effectiveness of vitamin D repletion depends, at least in part, on the rate of repletion. A modified-release (MR) oral formulation of calcifediol (25-hydroxyvitamin D3) was developed which raised serum 25-hydroxyvitamin D3 and calcitriol levels gradually. Single doses of either bolus intravenous (IV) or oral MR calcifediol were administered to vitamin D deficient rats. Bolus IV calcifediol produced rapid increases in serum 25-hydroxyvitamin D3, calcitriol and FGF23, along with significant induction of CYP24A1 in both kidney and parathyroid gland. In contrast, oral MR calcifediol produced gradual increases in serum 25-hydroxyvitamin D3 and calcitriol and achieved similar hormonal exposure, yet neither CYP24A1 nor FGF23 were induced. A 10-fold greater exposure to bolus IV than oral MR calcifediol was required to similarly lower intact parathyroid hormone (iPTH). Single doses of oral MR (450 or 900µg) or bolus IV (450µg) calcifediol were administered to patients with stage 3 or 4 CKD, SHPT and vitamin D insufficiency. Changes in serum 25-hydroxyvitamin D3 and calcitriol and in plasma iPTH were determined at multiple time-points over the following 42 days. IV calcifediol produced abrupt and pronounced increases in serum 25-hydroxyvitamin D3 and calcitriol, but little change in plasma iPTH. As in animals, these surges triggered increased vitamin D catabolism, as evidenced by elevated production of 24,25-dihydroxyvitamin D3. In contrast, MR calcifediol raised serum 25-hydroxyvitamin D3 and calcitriol gradually, and meaningfully lowered plasma iPTH levels. Taken together, these studies indicate that rapid increases in 25-hydroxyvitamin D3 trigger CYP24A1 and FGF23 induction, limiting effective exposure to calcitriol and iPTH reduction in SHPT. They also support further investigation of gradual vitamin D repletion for improved clinical effectiveness. This article is part of a Special Issue entitled "17th Vitamin D Workshop".

Differential effects of oral doxercalciferol (Hectorol) or paricalcitol (Zemplar) in the Cyp27b1-null mouse model of uremia.

BACKGROUND/AIMS: Kidney disease patients experience declining calcitriol levels and develop secondary hyperparathyroidism (SHPT). Animal models of uremia based on 5/6 nephrectomy (NTX) do not consistently reproduce this calcitriol deficiency. We developed an animal model, the NTX Cyp27b1-null mouse, which completely lacks endogenous calcitriol, and examined the suitability of this model for evaluation of treatment with vitamin D analogs in uremia. METHODS: NTX was performed at 2 months of age. One week post-NTX, animals were treated for 4 weeks with vehicle; doxercalciferol at 30, 100 or 300 pg/g body weight (b.w.); or paricalcitol at 100, 300 or 1,000 pg/g b.w. by gavage 3 times per week. RESULTS: Serum blood urea nitrogen and creatinine were elevated. Vehicle-treated NTX null mice had hypocalcemia and SHPT. Doxercalciferol at 100 or 300 pg/g b.w. normalized serum calcium and parathyroid hormone (PTH) levels. Paricalcitol at 300 or 1,000 pg/g normalized serum calcium, but PTH levels remained elevated. Osteomalacia was corrected by 100 pg/g b.w. of doxercalciferol or 1,000 pg/g b.w. of paricalcitol. The highest dose of doxercalciferol, but not of paricalcitol, significantly reduced osteitis fibrosa. CONCLUSION: Our results reveal the differential efficacy of doxercalciferol and paricalcitol in this novel animal model incorporating both calcitriol deficiency and renal insufficiency.

Comparison of active vitamin D compounds and a calcimimetic in mineral homeostasis.

The differential effects between cinacalcet and active vitamin D compounds on parathyroid function, mineral metabolism, and skeletal function are incompletely understood. Here, we studied cinacalcet and active vitamin D compounds in mice expressing the null mutation for Cyp27b1, which encodes 25-hydroxyvitamin D-1α-hydroxylase, thereby lacking endogenous 1,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)]. Vehicle-treated mice given high dietary calcium had hypocalcemia, hypophosphatemia, and marked secondary hyperparathyroidism. Doxercalciferol and 1,25(OH)(2)D(3) each normalized these parameters and corrected both the abnormal growth plate architecture and the diminished longitudinal bone growth observed in these mice. In contrast, cinacalcet suppressed serum parathyroid hormone (PTH) cyclically and did not correct the skeletal abnormalities and hypocalcemia persisted. Vehicle-treated mice given a "rescue diet" (high calcium and phosphorus, 20% lactose) had normal serum calcium and PTH levels; cinacalcet induced transient hypocalcemia and mild hypercalciuria. The active vitamin D compounds and cinacalcet normalized the increased osteoblast activity observed in mice with secondary hyperparathyroidism; cinacalcet, however, increased the number and activity of osteoclasts. In conclusion, cinacalcet reduces PTH in a cyclical manner, does not eliminate hypocalcemia, and does not correct abnormalities of the growth plate. Doxercalciferol and 1,25(OH)(2)D(3) reduce PTH in a sustained manner, normalize serum calcium, and improve skeletal abnormalities.

Long-term therapeutic effect of vitamin D analog doxercalciferol on diabetic nephropathy: strong synergism with AT1 receptor antagonist.

The intrarenal renin-angiotensin system (RAS) plays a key role in the development of diabetic nephropathy. Recently, we showed that combination therapy with an AT(1) receptor blocker (ARB) and an activated vitamin D analog produced excellent synergistic effects against diabetic nephropathy, as a result of blockade of the ARB-induced compensatory renin increase. Given the diversity of vitamin D analogs, here we used a pro-drug vitamin D analog, doxercalciferol (1alpha-hydroxyvitamin D(2)), to further test the efficacy of the combination strategy in long-term treatment. Streptozotocin-induced diabetic DBA/2J mice were treated with vehicle, losartan, doxercalciferol (0.4 and 0.6 microg/kg), or losartan and doxercalciferol combinations for 20 wk. Vehicle-treated diabetic mice developed progressive albuminuria and glomerulosclerosis. Losartan alone moderately ameliorated kidney injury, with renin being drastically upregulated. A similar therapeutic effect was seen with doxercalciferol alone, which markedly suppressed renin and angiotensinogen expression. The losartan and doxercalciferol combination most effectively prevented albuminuria, restored glomerular filtration barrier structure, and dramatically reduced glomerulosclerosis in a dose-dependent manner. These effects were accompanied by blockade of intrarenal renin upregulation and ANG II accumulation. These data demonstrate an excellent therapeutic potential for doxercalciferol in diabetic renal disease and confirm the concept that blockade of the compensatory renin increase enhances the efficacy of RAS inhibition and produces synergistic therapeutic effects in combination therapy.

Hepatic activation and inactivation of clinically-relevant vitamin D analogs and prodrugs.

Like most pharmaceutical agents, vitamin D analogs are subject to hepatic metabolism by a variety of cytochrome P450 (CYP)-based systems. Metabolism can involve activation as well as inactivation of the vitamin D analog and one of the more successful families includes the 1alpha-hydroxyvitamin D prodrugs (1alpha-OH-D2, 1alpha-OH-D3, 1alpha-OH-D4, 1alpha-OH-D5), that all require a step of activation. Some of these prodrugs are in use or clinical trial because they have a therapeutic advantage over calcitriol. However, the nature of the activation of these molecules is poorly understood, particularly with regard to the CYP isoform involved. Various transfected CYPs and hepatic cell lines combined with tandem LC-MS analysis were used to investigate the metabolism of a spectrum of vitamin D analogs, including 1alpha-OH-Ds and the topical analog, calcipotriol. In the case of the 1alpha-OH-Ds, evidence was found of multiple sites of side-chain hydroxylation consistent with the generation of more than one active form. The potential involvement of CYP27A and other putative 25-hydroxylases in 1alpha-OH-D activation was also shown, as well as the potential for CYP24 activation and inactivation. In the case of calcipotriol, the respective roles of non-vitamin D-related CYPs and CYP24 in the catabolism of this anti-psoriatic drug were dissected out using cell lines with or without CYP24 expression, allowing us to demonstrate the potential contribution of CYP24 to "vitamin D resistance". The implications of hepatic metabolism in the context of other facets thought to play a role in the mechanism of action of anticancer and antiproliferative vitamin D analogs are discussed.

Evidence for the activation of 1alpha-hydroxyvitamin D2 by 25-hydroxyvitamin D-24-hydroxylase: delineation of pathways involving 1alpha,24-dihydroxyvitamin D2 and 1alpha,25-dihydroxyvitamin D2.

While current dogma argues that vitamin D prodrugs require side-chain activation by liver enzymes, recent data suggest that hydroxylation may also occur extrahepatically. We used keratinocytes and recombinant human enzyme to test if the 25-hydroxyvitamin D-24-hydroxylase (CYP24A1) is capable of target cell activation and inactivation of a model prodrug, 1alpha-hydroxyvitamin D2 (1alpha(OH)D2) in vitro. Mammalian cells stably transfected with CYP24A1 (V79-CYP24A1) converted 1alpha(OH)D2 to a series of metabolites similar to those observed in murine keratinocytes and the human cell line HPK1A-ras, confirming the central role of CYP24A1 in metabolism. Products of 1alpha(OH)D2 included the active metabolites 1alpha,24-dihydroxyvitamin D2 (1alpha,24(OH)2D2) and 1alpha,25-dihydroxyvitamin D2 (1alpha,25(OH)2D2); the formation of both indicating the existence of distinct activation pathways. A novel water-soluble metabolite, identified as 26-carboxy-1alpha,24(OH)2D2, was the presumed terminal degradation product of 1alpha(OH)D2 synthesized by CYP24A1 via successive 24-hydroxylation, 26-hydroxylation and further oxidation at C-26. This acid was absent in keratinocytes from Cyp24a1 null mice. Slower clearance rates of 1alpha(OH)D2 and 1alpha,24(OH)2D2 relative to 1alpha,25(OH)2D2 and 1alpha,25(OH)2D3 were noted, arguing for a role of 24-hydroxylated metabolites in the altered biological activity profile of 1alpha(OH)D2. Our findings suggest that CYP24A1 can activate and inactivate vitamin D prodrugs in skin and other target cells in vitro, offering the potential for treatment of hyperproliferative disorders such as psoriasis by topical administration of these prodrugs.

The vitamin D prodrugs 1alpha(OH)D2, 1alpha(OH)D3 and BCI-210 suppress PTH secretion by bovine parathyroid cells.

BACKGROUND: Active vitamin D compounds are widely used in the treatment of secondary hyperparathyroidism associated with renal failure. These compounds reduce PTH secretion through vitamin D receptor (VDR)-dependent repression of PTH gene transcription. In previous studies, 1alpha(OH)D3, a vitamin D prodrug, inhibited PTH secretion in cultured bovine parathyroid cells, but it was unclear whether 1alpha(OH)D3 itself or an active metabolite produced this inhibition. METHODS: We determined the effectiveness of the vitamin D prodrugs 1alpha(OH)D3, 1alpha(OH)D2 and 1alpha(OH)-24(R)-methyl-25-ene-D2 (BCI-210) at inhibiting PTH secretion in bovine parathyroid cell cultures, and examined the metabolism of [3H]1alpha(OH)D2 in these cells. RESULTS: All three prodrugs suppressed PTH secretion with approximately 10% of the activity of 1,25(OH)2D3; much higher activity than expected based on the VDR affinities of these prodrugs (0.25% of 1,25(OH)2D3). Parathyroid cells activated [3H]1alpha(OH)D2 to both 1,25(OH)2D2 and 1,24(OH)2D2. 1,24(OH)2D2 was detectable at 4 h, increased to a maximum at 8 h, and then decreased. In contrast, 1,25(OH)2D2 levels increased linearly with time, suggesting the presence of constitutively active vitamin D-25-hydroxylase not previously reported in parathyroid cells. The cytochrome P-450 inhibitor ketoconazole (50 microM) reduced 1alpha(OH)D2 metabolism to below detectable levels, but did not significantly affect suppression of PTH by 1alpha(OH)D2. CONCLUSIONS: The vitamin D prodrugs 1alpha(OH)D3, 1alpha(OH)D2 and BCI-210 suppressed PTH production by cultured parathyroid cells. The ability of 1alpha(OH)D2 to reduce PTH despite inhibition of its metabolism suggests a direct action of this 'prodrug' on the parathyroid gland, but the mechanism underlying this activity is not yet known.

1,24(S)-dihydroxyvitamin D2, an endogenous vitamin D2 metabolite, inhibits growth of breast cancer cells and tumors.

BACKGROUND: 1,24-Dihydroxyvitamin D2 (1,24(OH)2D2) is a naturally occurring metabolite of vitamin D2 with low calcemic activity and potent antiproliferative activity. We evaluated the activity of 1,24(OH)2D2 in breast cancer models. MATERIALS AND METHODS: The antiproliferative activity of 1,24(OH)2D2 was quantitated against human and murine breast cancer cell lines. The antitumor activity of 1,24(OH)2D2 was quantitated using MCF-7 xenografts in nude mice. RESULTS: 1,24(OH)2D2 inhibited growth of vitamin D receptor (VDR)-positive, but not VDR-negative, breast cancer cells. 1,24(OH)2D2 (10 microg/kg or 50 microg/kg) reduced MCF-7 xenograft growth by 50% after five weeks. Tumor morphology in treated animals was consistent with replacement of epithelial cells by stromal tissue. Mice treated with 1,24(OH)2D2 showed no loss of body weight, hypercalcemia or kidney calcification. CONCLUSION: 1,24(OH)2D2 inhibits growth of breast cancer cells via VDR-dependent mechanisms; its complete lack of toxicity and significant antitumor activity supports further development for chemotherapeutic applications.

Tissue distribution and activity studies of 1,24-dihydroxyvitamin D2, a metabolite of vitamin D2 with low calcemic activity in vivo.

The active vitamin D compound 1alpha,24(S)-dihydroxyvitamin D(2) (1,24(OH)(2)D(2)) is under development as a therapy for disorders including cancer and secondary hyperparathyroidism. 1,24(OH)(2)D(2) is a potent inhibitor of cell proliferation in vitro and, relative to calcitriol (1,25(OH)(2)D(3)), has reduced calcemic activity in vivo. To examine the mechanisms underlying this reduced calcemic activity, we studied the tissue distribution in rats of radiolabeled 1,24(OH)(2)D(2) or 1,25(OH)(2)D(3) over 24h. Serum levels of 1,24(OH)(2)D(2) were lower than those of 1,25(OH)(2)D(3) at all time points; however, tissue levels of radiolabeled compounds followed different patterns. In duodenum and kidney, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) rose to similar levels at early time points; 1,24(OH)(2)D(2) levels then declined more rapidly. In bone marrow, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were present at similar levels at all time points. In liver, 1,24(OH)(2)D(2) levels were two-fold higher than 1,25(OH)(2)D(3) at 1h post-injection, declining to similar levels by 8h. In vitamin D-deficient rats, doses of 1,24(OH)(2)D(2) 30-fold higher than 1,25(OH)(2)D(3) were required to produce equal stimulation of intestinal calcium absorption. In the same deficient animals, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were nearly equipotent at stimulating bone calcium mobilization. In cultured bone cells, 1,24(OH)(2)D(2) and 1,25(OH)(2)D(3) were equipotent at stimulating osteoclast formation and bone resorption. In summary, the reduced calcemic activity of 1,24(OH)(2)D(2) may result from altered pharmacokinetics relative to 1,25(OH)(2)D(3), resulting in relatively rapid decreases in 1,24(OH)(2)D(2) levels and activity in target organs such as intestine. Further studies will be necessary to confirm these findings and to confirm the clinical utility of 1,24(OH)(2)D(2).

Effectiveness of 1alpha-hydroxyvitamin D2 in inhibiting tumor growth in a murine transgenic pigmented ocular tumor model.

OBJECTIVE: To study the effectiveness of the vitamin D analogue 1alpha-hydroxyvitamin D(2) (1alpha-OH-D(2)) in inhibiting ocular tumor growth in transgenic "Tyr-Tag" mice that developed pigmented ocular tumors produced with the simian virus 40 T and t antigens under the control of the mouse tyrosinase gene. These animals develop pigmented intraocular tumors primarily from the retinal pigment epithelium that closely resemble the histologic features and growth pattern of human choroidal melanoma. METHODS: A total of 73 Tyr-Tag transgenic mice between 6 and 7 weeks old were randomly assigned by sex and litter to 3 treatment groups to receive 0.05 microg/d, 0.1 microg/d, or 0.2 microg/d of 1alpha-OH-D(2); a control group received vehicle (coconut oil). The drug was administered by oral gavage 5 times a week for 5 weeks. The animals were then euthanized and their eyes were enucleated and processed histologically. Three serial sections from each eye were examined microscopically and the mean tumor area measured using Optimus software version 6.5 (Media Cybernetics LP, Silver Spring, Md). Toxic adverse effects were assessed on the basis of mortality, weight loss, and serum calcium levels. RESULTS: The mean tumor size in the 0.1- microg/d and 0.2- microg/d dose groups was smaller than in the controls (P<.001). No significant difference was seen between the 0.05- microg/d dose group and the control group (P =.64). Survival for the 0.1- microg/d and 0.2- microg/d dose groups was lower than for the controls (95% in the controls vs 85.7% and 73.7%, respectively; P<.01). CONCLUSION: In the Tyr-Tag transgenic mouse, 1alpha-OH-D(2) inhibits pigmented ocular tumor growth at moderate drug levels with relatively low mortality. Clinical Relevance Vitamin D analogues merit further preclinical study in the treatment of ocular melanoma.

Effectiveness of vitamin D analogues in treating large tumors and during prolonged use in murine retinoblastoma models.

OBJECTIVE: To investigate the effectiveness of the vitamin D analogues 1,25-(OH)(2)-16-ene-23-yne vitamin D(3) (16,23-D(3)) and 1alpha-hydroxyvitamin D(2) (1alpha-OH-D(2)) in inhibiting retinoblastoma growth in large tumors in a xenograft model and with prolonged use in a transgenic model. METHODS: For the large-tumor study, the xenograft athymic mouse/human retinoblastoma cell (Y-79) model was used. Subcutaneous tumors were allowed to grow to an average volume of 1600 mm(3). Systemic treatment with 1 of the vitamin D analogues or with vehicle (control groups) was carried out for 5 weeks. For the long-term study, transgenic beta-luteinizing hormone-large T antigen (LHbeta-Tag) mice were systemically treated with 1 of the 2 compounds or vehicle (control groups) for up to 15 weeks. Tumor size and signs of toxicity were assessed. RESULTS: In the large-tumor study, tumor volume ratios for the 1alpha-OH-D(2) and 16,23-D(3) groups were significantly lower than those for controls (P<.002). No significant differences in tumor volume were seen between the 1alpha-OH-D(2) and 16,23-D(3) groups (P =.15). In the long-term study, the 1alpha-OH-D(2) group showed significantly smaller tumor size compared with its control (P<.001). No significant difference was seen between the 16,23-D(3) group and its control. Some toxic effects related to hypercalcemia were seen in both studies. CONCLUSIONS: In athymic mice in the large-tumor study, both 1alpha-OH-D(2) and 16,23-D(3) were effective in inhibiting tumor growth compared with controls. In the long-term study, 1alpha-OH-D(2) inhibited tumor growth but 16,23-D(3) did not. Effective doses of both compounds caused hypercalcemia and a significant increase in mortality. Clinical Relevance Use of 1alpha-OH-D(2) inhibited tumor growth in large tumors and with long-term treatment compared with controls. Because of hypercalcemia-related toxic effects seen in the present experiments, in clinical trials, serum calcium levels should be carefully monitored. This analogue may require use with drugs that lower serum calcium levels or use of relatively lower doses or skipped doses. The ideal alternative solution would be to identify vitamin D analogues that retain the antineoplastic action without the calcemic activity.

Effects of vitamin D compounds on renal and intestinal Ca2+ transport proteins in 25-hydroxyvitamin D3-1alpha-hydroxylase knockout mice.

BACKGROUND: Vitamin D compounds are used clinically to control secondary hyperparathyroidism (SHPT) due to renal failure. Newer vitamin D compounds retain the suppressive action of 1,25(OH)(2)D(3) on the parathyroid glands and may have less Ca(2+)-mobilizing activity, offering potentially safer therapies. METHODS: This study investigated the effect of a single dose of compound (1,25(OH)(2)D(3), 1,24(OH)(2)D(2), or 1alpha(OH)D(2)) on renal and intestinal Ca(2+) transport proteins, including TRPV5 and TRPV6, and serum Ca(2+), in a novel SHPT model, the 25-OH-D(3)-1alpha-hydroxylase knockout mouse, which lacks endogenous 1,25(OH)(2)D(3) and is severely hypocalcemic. Animals were injected intraperitoneally with compound (100 ng/mouse). RESULTS: Serum levels of 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2) peaked at four hours post-injection (pi), then declined rapidly. 1,25(OH)(2)D(2) generated from 1alpha(OH)D(2) peaked at 12 hours pi and then remained stable. Serum Ca(2+) was increased to near-normal within four hours by 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2), and within 12 hours by 1alpha(OH)D(2). 1,25(OH)(2)D(3) and 1,24(OH)(2)D(2) up-regulated duodenal TRPV5 and TRPV6 mRNA to a similar degree within four hours; mRNA levels decreased by 12 hours after 1,24(OH)(2)D(2) treatment, and by 24 hours after 1,25(OH)(2)D(3) treatment. 1,25(OH)(2)D(3) increased kidney levels of TRPV5, calbindin-D(28K), and calbindin-D(9K) mRNA within four hours; 1,24(OH)(2)D(2) did not change kidney TRPV5 levels and modestly increased calbindin D(9K) by 48 hours. 1alpha(OH)D(2) produced later-onset effects, increasing duodenal TRPV6 and calbindin-D(9K) mRNA levels by 12 hours and TRPV5 by 48 hours. CONCLUSION: In kidney, 1alpha(OH)D(2) increased TRPV5, calbindin-D(28K), and calbindin-D(9K) mRNA levels by 12 hours. This study indicates that Ca(2+) transport proteins, including TRPV5 and TRPV6, are differentially up-regulated by vitamin D compounds.