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Keywords:

  • calcitriol;
  • vitamin D;
  • thrombosis;
  • prostate cancer;
  • thromboembolism

Summary

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

The incidence of venous and arterial thrombosis in a placebo-controlled randomised trial of DN-101 (high dose calcitriol) with docetaxel versus docetaxel was compared. Of the 13 thrombotic events observed in the 250 patients enroled in this study, two occurred in DN-101 and 11 in placebo-treated patients (P = 0·01). This difference remained significant after adjustment for baseline history of thrombosis, atrial fibrillation and use of anti-thrombotic agents. In vitro and vitamin D receptor (VDR) knockout mouse studies predict that nanomolar concentrations of calcitriol may act as an antithrombotic agent. We report the first clinical observation that supports this hypothesis in humans.

Thrombosis is a frequent and important complication of cancer and affects 15–20% of cancer patients. Recently, vitamin D receptor (VDR) ligands have been shown to alter the expression and activity of a number of proteins important for coagulation. Interestingly, these effects consistently serve to reduce the activation of coagulation.

In vitro, VDR ligands upregulate thrombomodulin (Maillard et al, 1993; Koyama et al, 1998; Ohsawa et al, 2000) and downregulate tissue factor (Koyama et al, 1998; Ohsawa et al, 2000). In monocytes, treatment with VDR ligands reverses the procoagulant effects of tumour necrosis factor and oxidised low density lipoprotein on thrombomodulin and tissue factor. Further, VDR ligands increase expression of tissue plasminogen activator (Gyetko et al, 1988) and decrease plasminogen activator inhibitor 1 (PAI-1) expression (Barbosa et al, 2004; Wu-Wong et al, 2006). In in vitro systems, the modulation of the coagulation system occurs at 1,25-dihydroxyvitamin D (calcitriol) concentrations that are significantly above the normal physiological range (Gyetko et al, 1988; Koyama et al, 1998; Ohsawa et al, 2000).

These in vitro observations of reduced coagulation are supported by functional studies in in vivo models. Decreased platelet function in response to VDR ligands was seen in experimental diabetic rats (Katoh et al, 1988). The physiological relevance of these observations was further supported by haemostatic studies in the vitamin D receptor knock-out (VDRKO) mouse (Aihara et al, 2004). These mice showed increased levels of tissue factor gene expression, suppression of thrombomodulin expression, decreased expression and plasma levels of antithrombin and increased platelet aggregation when compared with wild type mice. When these mice were challenged by the injection of lipopolysaccharide (LPS), the VDRKO mice showed increased fibrin deposition in multiple organs compared with wild type mice. Thus, this model not only confirmed and extended the in vitro mechanistic observations, but also demonstrated that these effects of VDR translate into a prothrombotic state.

Weekly high dose calcitriol was recently examined in a prospective, double blinded randomised trial that compared calcitriol plus docetaxel to placebo plus docetaxel in patients with metastatic androgen-independent prostate cancer (AIPC) (Beer, 2005). The rationale and design of this trial, dubbed the AIPC Study of Calcitriol Enhancing Taxotere (ASCENT) study has been published elsewhere (Beer, 2005) and the primary efficacy analyses are submitted for publication.

Methods

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Briefly, 250 patients were randomised 1:1 to docetaxel 36 mg/m2 plus 45 μg DN-101 (calcitriol) weekly or to the same docetaxel regimen plus placebo. This dose of calcitriol produced peak blood calcitriol concentrations of 3·4 ± 0·8 nmol/l (Beer et al, 2005). The primary endpoint was the proportion of patients experiencing a prostate-specific antigen (PSA) response by 6 months. Safety analyses demonstrated an unanticipated reduction in the incidence of serious adverse events in the DN-101 group when compared with the placebo group (27% vs. 41%, P = 0·02). Further exploratory analyses of safety revealed a substantial reduction in thrombotic adverse events. As the first large placebo-controlled trial of high dose calcitriol, ASCENT provided a unique opportunity to examine the thrombosis experience of cancer patients exposed to substantially supraphysiological concentrations of a VDR ligand.

Thrombosis was defined as the composite endpoint of deep venous thrombosis (DVT), pulmonary embolism (PE), myocardial infarction (MI), ischaemic cerebrovascular accident (CVA) and arterial thrombosis (AT) (Levine et al, 1994). Severity grade was assigned according the National Cancer Institutes Common Toxicity Criteria (CTC), version 2.0. The thrombosis experience of both study arms was compared using the Chi-Square test. Pre-enrolment history of thrombosis, atrial fibrillation and use of anti-thrombotic agents was examined. The Cochran–Mantel–Haenszel test was used to adjust for the effect of these baseline factors. P-values < 0·05 were considered significant.

Results

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

As shown in Table I, the DN-101 arm showed a significant reduction in thrombotic adverse events when compared with the placebo arm. Specifically, any grade thrombosis, grade 3 or 4 thrombosis, and thrombosis classified as a serious adverse event were reduced. Both venous and arterial thromboses were less frequent in patients treated with DN-101. Not unexpectedly, the risk of thrombosis correlated with the patients’ performance status. The overall incidence of thrombosis in Eastern Cooperative Oncology Group (ECOG) performance status (PS) 0 patients was 3·4% for placebo-treated patients and 0% for DN-101 treated patients. 13·6% of placebo-treated and 5·2% of DN-101 treated patients who had an ECOG PS of 1 or 2 had a thrombotic of adverse event.

Table I.   Thrombosis in AIPC Study of Calcitriol Enhancing Taxotere (ASCENT)
 DN-101 (%)Placebo (%)P-value*P-value†
  1. DVT, deep venous thrombosis; PE, pulmonary embolism; CVA, ischaemic cerebrovascular accident; MI, myocardial infarction; AT, arterial thrombosis.

  2. *Chi-Square.

  3. †Cochran–Mantel–Haenszel adjusted for prior history of thrombosis, atrial fibrillation and prior use of antithrombotic agents.

All serious adverse events27410·020·05
Serious adverse events due to thrombosis1·67·20·030·04
Grade 3 and 4 thrombosis1·68·00·020·03
Any grade thrombosis1·68·80·010·02
All venous thrombosis (DVT/PE)1·65·60·090·08
All arterial thrombosis (CVA/MI/AT)0·03·20·040·10

In the ASCENT study, patients were randomised without regard to prior history of thrombosis or prior use of anti-thrombotic agents. Therefore, we examined the possibility that a chance imbalance between the two groups with regard to these factors might explain the apparent reduction in the thrombosis seen with DN-101. As shown in Table II, more placebo patients (16%) than DN-101 treated patients (10%) entered the study on anti-thrombotic agents and more placebo patients (15·2%) than DN-101 treated patients (7·2%) had a history of prior thrombosis or atrial fibrillation.

Table II.   Patient characteristics
 Placebo +  DocetaxelDN-101 +  Docetaxel
  1. ECOG, Eastern Cooperative Oncology Group; PSA, prostate-specific antigen; LMW, low molecular weight; DVT, deep venous thrombosis; PE, pulmonary embolism; CVA, ischaemic cerebrovascular accident; MI, myocardial infarction.

Randomised (n)125125
Age, median (range), years70 (47–92)68 (45–87)
ECOG performance status (%)
 04754
 14743
 263
Site of metastatic disease (%)
 Bone8590
 Lymph node4435
 Liver58
PSA, median (range), ng/ml91 (5–6288)123 (4–4453)
Haemoglobin, median (range), g/dl12·5 (8·1–15·5)12·5 (8·0–15·2)
Platelet Count, median (range), ×109/l250 (106–516)248 (108–467)
Antithrombotic use at enrolment (%)
 All1610
 Aspirin42
 Clopidogrel41
 Warfarin108
 Heparin or LMW heparin11
Prior history
 DVT42
 PE30
 MI63
 CVA43
 Arterial thrombosis00
 Atrial fibrillation33

The observed reduction in thrombosis in the DN-101 arm remained significant after adjustment for prior history of thrombosis, atrial fibrillation or use of anti-thrombotic drugs (Table I). Interestingly, 10 of the 13 thrombotic events seen in the ASCENT study occurred in patients with no prior history of thrombosis.

Discussion

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Our observation suggests that targeting the VDR with high dose calcitriol may reduce thromboembolic events. This finding is consistent with studies of renal dialysis patients that demonstrated reduced cardiovascular mortality when activated VDR ligands were administered during dialysis (Shoji et al, 2004). Our observation is further supported by a strong biological rationale. Both in vitro and in vivo experiments demonstrated several mechanisms by which calcitriol or other VDR ligands would be expected to reduce the activation of coagulation that is commonly seen in cancer patients.

This observation emerged from an exploratory analysis and should be prospectively tested and confirmed. The recently activated phase III clinical trial that compares docetaxel with DN-101 to docetaxel with prednisone (ASCENT-2) will prospectively examine the thrombotic experience of both arms. If confirmed, this activity of high dose calcitriol could offer an important benefit to cancer patients by safely reducing the burden of thrombosis and its complications.

Acknowledgements

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Oregon Health & Science University (OHSU) and Dr. Beer have a significant financial interest in Novacea, Inc. a company that has a commercial interest in the results of this research and technology. This potential conflict was reviewed and a management plan approved by the OHSU Conflict of Interest in Research Committee and the Integrity Program Oversight Council was implemented. This study was supported by Novacea, Inc and by Sanofi-Aventis.

References

  1. Top of page
  2. Summary
  3. Methods
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
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