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Experimental Therapeutics |
Departments of Pharmacology [P. A. H., R. A. M., Z. R. S., R. M. R., C. S. J.] and Medicine [D. L. T., C. S. J.] and The University of Pittsburgh Cancer Institute [D. L. T., C. S. J.], University of Pittsburgh, Pittsburgh, Pennsylvania 15213
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ABSTRACT |
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INTRODUCTION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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In vitro, 1,25-D3 promotes the differentiation of myeloid leukemias (4, 5, 6) and inhibits the proliferation of prostatic (7) , breast (8 , 9) , colon (10) , and pancreatic carcinomas (11) . In vivo, 1,25-D3 inhibits tumor cell growth in breast (9) , prostate (7) , colon (12) , and squamous cell (13) animal tumor model systems. The antiproliferative activity of 1,25-D3 in these different systems has been linked to its ability to promote cellular differentiation, cell cycle arrest, and apoptosis (14) . In prostatic carcinoma cell lines, the antiproliferative effects of 1,25-D3 require VDR expression (15 , 16) . 1,25-D3 binding activates the VDR, allowing it to modulate the transcription of target genes with promoters containing a vitamin D response element (17) .
We have demonstrated that 1,25-D3 has significant antitumor activity in vitro and in vivo in the murine SCC model (13) . 1,25-D3 induces SCC to undergo growth arrest with a significant percentage of cells in G0-G1 after 24 h of treatment in vitro (18) . We have also shown that 1,25-D3 activity in SCC is enhanced by concomitant treatment with dex (19) . In SCC tumor-bearing mice, dex increases VDR ligand binding within tumor and kidney, but not in intestine, which may explain its ability to enhance 1,25-D3 antitumor activity while blocking 1,25-D3-induced hypercalcemia (19) .
In hematopoietic cells (5 , 20) and epithelial (11 , 21 , 22) cell lines, 1,25-D3-mediated cell cycle arrest correlates with increased expression of the cdk inhibitors p21Waf1/Cip1 or p27Kip1. These proteins negatively regulate cell cycle progression by binding to and inhibiting cyclin: cdk complexes (23) . Agents promoting G0-G1 arrest and differentiation in HL60 cells, such as 1,25-D3, increase p21 (6 , 24) and p27 (20) expression. 1,25-D3-mediated cell cycle arrest in these cells is associated with decreased cdk2 and cdk6 activity (25) . In U937 cells, 1,25-D3 induces p21 and p27 expression, and this increase is associated with the presence of a vitamin D response element in the p21 promoter (5) . 1,25-D3 antiproliferative activity in pancreatic cancer lines in vitro has also been attributed to increased p21 and p27 expression (11) . These studies describe modulation of p21 and p27 by 1,25-D3 in tissue culture systems, although comparable in vivo studies have not yet been reported. To investigate the basis for 1,25-D3 antiproliferative activity in SCC, studies were undertaken to examine whether p21 or p27 were modulated in vitro and in vivo by 1,25-D3 and whether these effects correlated with tumor growth inhibition.
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MATERIALS AND METHODS |
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Tumor Cells and Model System.
For these studies, the murine SCCVII/SF tumor model was used. SCCVII/SF is a moderately well differentiated SCC derived from a spontaneously arising tumor of the C3H mouse (26)
. SCCVII/SF cells were maintained in female C3H/HeJ mice, 6–10 weeks of age, obtained from The Jackson Laboratory (Bar Harbor, ME), as described previously (13)
. The mice were age- and sex-matched for experimental use. Animals were used in accordance with Institutional Animal Care and Use Committee (IACUC) guidelines. For in vitro studies, SCC cells were grown in RPMI 1640 plus 15% FCS and only passed twice. In vitro studies were initiated by treating subconfluent SCC cultures with 5.0 ml of fresh media containing either 0.004% ethanol vehicle, 10 nM 1,25-D3, 500 nM dex, or 10 nM 1,25-D3 + 500 nM dex/T25 flask.
Preparation of Cell Lysates.
Protein was extracted from in vitro-treated cells and from tumors harvested from treated animals using lysis buffer [1% Triton X-100, 0.1% SDS, 50 mM Tris (pH 8.0), 150 mM NaCl, 0.6 mM PMSF, and 5 µg/ml leupeptin]. To extract proteins from in vitro cultures, monolayers were washed twice with PBS, and 200 µl of lysis buffer were added/T25 flask. Flasks were rocked for 30 min at 4°C. Lysates were transferred to 1.5-ml Eppendorf tubes and clarified by centrifugation at 13,000 rpm for 10 min at 4°C.
Lysates were also prepared from tumors that were flash frozen in liquid nitrogen immediately at the time of harvest. Frozen tumors were pulverized, then homogenized for 45 s at 4°C in 1.5–3.0 ml of lysis buffer. Homogenates were stored on ice for 30 min and then clarified, as described above. Clarified protein lysates were transferred to fresh tubes and stored at -80°C until use. Protein concentrations were determined in duplicate using the Bio-Rad protein assay (Bio-Rad Laboratories, Hercules, CA), according to manufacturer’s directions.
Western Blot Analysis.
Proteins were resolved on SDS-polyacrylamide gels under denaturing conditions, and then electrophoretically transferred to poly(vinylidene difluoride) membranes (NEN Life Science Products, Boston, MA) overnight at 4°C. At room temperature, membranes were blocked for a minimum of 1 h in a 5% w/v solution of nonfat milk in TBST [10 mM Tris (pH 7.6), 150 mM NaCl, and 0.05% Tween 20], then incubated for 1 h with primary antibody. The blots were washed three times in TBST and subsequently incubated with secondary antibody conjugated with horseradish peroxidase for 1 h. The blots were again washed, and the proteins were detected using Renaissance Western blot chemiluminescence reagents (NEN Life Science Products).
Northern Blot Analysis.
Total RNA was extracted from in vitro-treated cells using the Ultraspec RNA isolation system (Biotecx Laboratories, Houston, TX), according to manufacturer’s directions. RNA was electrophoresed through formaldehyde-agarose gels and transferred to GeneScreen (NEN Life Science Products) overnight at room temperature.
For p21 Northern blots, the EcoRI fragment of the murine p21 cDNA (generously provided by Dr. Bert Vogelstein, Johns Hopkins University, Baltimore, MD) was labeled with 32P-dCTP using the random primed DNA labeling kit from Boehringer Mannheim (Indianapolis, IN). After prehybridization, labeled probe was diluted and incubated with the membrane overnight at 43°C. The blots were washed under standard conditions and exposed to film at -80°C.
For p27 Northern blots, the HindIII-EcoRI fragment of murine p27 was isolated from the plasmid 
Exlox(+)-mp27 (generously provided by Dr. J. Massagué, Memorial Sloan-Kettering Cancer Center, New York, NY). The gel-purified fragment was labeled using the random primer fluorescein labeling kit from NEN Life Sciences Products. The cDNA labeling reaction and subsequent Northern blots were performed according to the manufacturer’s instructions.
Densitometry.
Densitometry of autoradiographs was performed using a Molecular Dynamics personal densitometer equipped with ImageQuant software (Molecular Dynamics, Sunnyvale, CA).
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RESULTS |
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. The upper band (ppRb) corresponds to hyperphosphorylated Rb, whereas the faster migrating species (pRb) results from Rb dephosphorylation. Only the hypophosphorylated form of Rb was detected in cells treated with 1,25-D3 for 24 h, consistent with the observation that 1,25-D3 induces G0-G1 arrest in SCC (Fig. 1)
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. However, at 24 h, treatment with either 1,25-D3 or dex reduced p21 expression 2- to 3-fold compared with ethanol, and p21 was reduced 10-fold after treatment with 1,25-D3 + dex. Although dex had no effect on p27 expression, 1,25-D3 treatment resulted in an 
2-fold increase in p27 expression at 24 h, which was not further enhanced by concomitant dex exposure (Fig. 2B)
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. At the 2-h time point, p27 transcripts were expressed at a comparable level in all treatment groups. By 24 h, p27 transcripts increased nearly 2-fold after treatment with either 1,25-D3 or dex and increased 4-fold after 1,25-D3 + dex treatment (Fig. 3B)
. Thus, alterations in p21 and p27 transcript levels may contribute to the changes in p21 and p27 protein levels observed after 24 h of 1,25-D3 treatment.
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. A similar low level of PARP cleavage (5–9%) was observed among all treatment groups at each of the time points examined (Fig. 4)
. Thus, although SCC cells express this marker of apoptosis at a low level, the level of PARP cleavage is not modulated significantly by 1,25-D3, dex, or the combination. The inability of 1,25-D3 to induce apoptosis in SCC was confirmed in flow cytometric studies, in which only a low level of annexin binding activity was detected in control cultures and cultures treated with 1,25-D3 (data not shown).
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, SCC tumor volumes increased 3-fold over a 96-h period in control, saline-injected animals. Tumors from animals treated with a single dose of 1,25-D3 showed only a 1.5-fold increase in volume over the same time course, indicating that a single injection of 1,25-D3 was sufficient to slow tumor growth significantly. However, none of the tumors from animals treated with the single dose therapy shrunk to below pretreatment volume. In contrast, a decrease in tumor volume was observed in 8 of 10 animals receiving a daily dose of 1,25-D3 for 3 days, resulting in a statistically significant decrease in fractional tumor volume at 96 h.
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, repeated administration of 1,25-D3 in vivo was associated with a statistically significant decrease in p21 expression within tumors. Relative to saline-injected controls, p21 expression was decreased at 4, 8, and 24 h in tumors harvested from animals receiving three injections of 1,25-D3. p21 expression was not similarly down-modulated at 4 h or at 8 h after treatment in tumors harvested from animals receiving a single injection of 1,25-D3; p21 levels did decline slightly in these samples after 24 h of treatment. Unlike p21, p27 expression was comparable in tumors harvested from control animals and animals treated with 1,25-D3 at each of the time points examined. Thus, a 1,25-D3 treatment that resulted in SCC tumor regression was associated with a decrease in p21 expression, but no change in p27 expression. In animals treated with either one or multiple doses of 1,25-D3, tumor cell expression of VDR was elevated 4 h and 8 h after treatment and declined to control levels within 24 h. This modulation of VDR expression confirms delivery of 1,25-D3 to the tumors.
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DISCUSSION |
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. These data suggest that the in vitro antitumor activity of 1,25-D3 in SCC results from inhibition of cell cycle progression. Loss of Rb phosphorylation in response to 1,25-D3 treatment is associated with an 2-fold increase in expression of the cdk inhibitor p27 and a nearly 3-fold decrease in expression of the related cdk inhibitor p21. In vivo, administration of 1,25-D3 (0.75 µg/day for 3 days) to SCC tumor-bearing mice resulted in a reduction in tumor volume that was associated with a statistically significant decrease in p21 expression within tumors. However, intratumoral p27 levels were not modulated by 1,25-D3 treatment. These experiments, which represent the first investigation of in vivo modulation of cdk inhibitors in response to 1,25-D3 administration, suggest that the growth inhibitory effects of 1,25-D3 in SCC either require or result in p21 down-modulation.
In vitro, evidence of 1,25-D3-mediated G0-G1 arrest in SCC is observed as early as 24 h after treatment (Fig. 1
and Ref. 18
). At this time point, p27 expression is increased and p21 expression is decreased within 1,25-D3-treated cells (Fig. 2, A and B)
. Thus, changes in one or both of these molecules may be important for the in vitro antitumor activity of 1,25-D3. Dex, which acts synergistically with 1,25-D3 to inhibit SCC proliferation in vitro and in vivo (19)
, enhances 1,25-D3-induced down-modulation of p21 without affecting the ability of 1,25-D3 to up-modulate p27 (Fig. 2, A and B)
. These data may indicate that the changes in p21 are most critical to the antitumor activity of 1,25-D3. This hypothesis is further supported by our finding that 1,25-D3 mediates p21 reduction in vivo without modulating p27.
p21 promotes cell cycle arrest in G0-G1 by binding to G1 cyclin:cdk complexes and inhibiting their activity, which is required for entry into S phase (23) . Enforced overexpression of p21 in tumor cells using an adenoviral vector (32) or a tetracycline-inducible system (33) results in tumor growth inhibition in vitro and in vivo, indicating that p21 possesses tumor suppressor activity. Moreover, p21 induction by 1,25-D3 correlates with growth inhibition in pancreatic (11) and prostate cancer cell lines (21) . It was, therefore, initially surprising that the antiproliferative activity of 1,25-D3 in SCC is associated with p21 reduction rather than p21 induction. In contrast to these earlier studies, our findings suggest that p21 has growth and/or survival-promoting activities in SCC that can be overcome by 1,25-D3 administration; such unique roles for p21 have been described recently (34 , 35) .
How might reduced p21 levels lead to SCC growth inhibition? We previously reported that 1,25-D3 caused prominent morphological changes in SCC in vitro (increased cell size and cytoplasmic spreading), consistent with cellular differentiation (13)
. Similar changes in cell morphology and p21 expression were observed in vitro in human SCC cells induced to differentiate by stable RXR
expression (36)
. Inhibition of p21 expression was also recently shown to be necessary for keratinocytes to complete terminal differentiation when cultured in low calcium medium (37)
. These results support the hypothesis that the in vitro antiproliferative activity of 1,25-D3 results from its ability to induce SCC differentiation, which may require p21 reduction for its completion.
Loss of p21 might also lead to SCC growth inhibition by triggering an apoptotic cascade. In endothelial cells deprived of growth factors, proteolytic cleavage of p21 results in inappropriate cdk2 activation and apoptosis (38)
. Although these data suggest that loss of p21 expression itself can act as a trigger for cell death, we find no evidence that 1,25-D3 induces SCC apoptosis in vitro, at a time when p21 expression is reduced. It is possible that 1,25-D3-treated SCC cells do not undergo apoptosis in response to p21 down-modulation in vitro due to a compensating increase in p27 expression, which itself has been shown to protect certain cells against apoptosis (39)
. However, a different situation may exist in vivo, where 1,25-D3 decreases p21 expression without increasing p27 (Table 2)
. In this case, loss of p21 may result in cdk2 activation and apoptosis. Consistent with such a hypothesis, we find that 1,25-D3 induces a potent apoptotic response in MLL cells, in which both p21 and p27 are down-modulated in response to treatment.4
Initiation of an apoptotic response in vivo would account for the reduction in tumor volume that is observed after three daily injections of 1,25-D3.
p21 has been reported to protect cells from apoptosis, and loss of p21 has been shown to sensitize cells to both DNA- (40) and microtubule-damaging agents (34) . In a human xenograft model, HT116 tumors harboring homozygous deletion of p21 regressed after radiation therapy while parental HT116 tumors progressed, further supporting the notion that p21 must be eliminated before cells become susceptible to apoptosis (40) . HT116 cells deficient in p21 expression also displayed increased susceptibility to cisplatin and nitrogen mustard in vivo (41) . We have previously demonstrated that SCC cells are rendered significantly more susceptible to the cytotoxic effects of cisplatin by pretreatment with the 1,25-D3 analogue Ro23-7553 (18) . Given our current findings, it is tempting to speculate that the enhanced cytotoxicty of cisplatin in SCC observed after Ro23-7553 treatment is due to 1,25-D3-mediated down-modulation of p21 expression in these cells. Experiments to test this hypothesis are now in progress.
Exposure of SCC cells to 1,25-D3 for 24 h in vitro resulted in an 2-fold decrease in p21 transcripts (Fig. 3A)
. This may account, in part, for the 3-fold reduction in p21 protein levels observed after 1,25-D3 administration (Fig. 2A)
. Although 1,25-D3 has previously been shown to activate p21 transcription in U937 cells (5)
, the VDR has been reported to repress the transcription of certain genes, including interleukin-2 (42)
and granulocyte macrophage colony-stimulating factor (43)
. It is, therefore, theoretically possible that the transcript reduction we observe is due to a direct, inhibitory effect of 1,25-D3 on p21 transcription initiation. However, it is likely that p21 levels are regulated by additional posttranscriptional mechanisms in SCC because treatment with 1,25-D3 in combination with dex results in only a 2-fold decrease in p21 transcripts, but a nearly 10-fold decrease in p21 protein levels (Figs. 2A
and 3A
). Recent studies indicate that p21 is degraded by a proteosome-dependent pathway (44)
; 1,25-D3 treatment may activate this endogenous mechanism and, thereby, indirectly down-modulate p21.
Our data are consistent with a model in which 1,25-D3 exerts antiproliferative activity in SCC by modulating expression of the cdk inhibitors p21 and p27. Significantly, modulation of p21 by 1,25-D3 occurs both in tumor cells treated in tissue culture and in tumors isolated from treated mice. In vitro, 1,25-D3 administration results in G0-G1 arrest that is associated with increased expression of p27 and decreased expression of p21. In vivo, 1,25-D3 administration results in tumor regression (presumably via the induction of cell death) that is associated with decreased expression of p21 and no change in p27 expression. On the basis of these data, we propose that the mechanism by which 1,25-D3 exerts antiproliferative activity in SCC may differ in vitro and in vivo and that the decision between cell cycle arrest or cell death may depend critically on the balance between p21 and p27 expression.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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1 Funded by NIH/National Cancer Institute Grant CA67267 (to C. S. J.). 
2 To whom requests for reprints should be addressed, at University of Pittsburgh, Department of Pharmacology, W1002 Biomedical Science Tower, Pittsburgh, PA 15213. Phone: (412) 648-2344; Fax: (412) 648-9856; E-mail: pah13+{at}pitt.edu
3 The abbreviations used are: 1,25-D3, 1,25-dihydroxycholecalciferol; dex, dexamethasone; SCC, squamous cell carcinoma; PARP, poly(ADP-ribose) polymerase; VDR, vitamin D receptor; cdk, cyclin-dependent kinase; Rb, retinoblastoma.
4 R. Modzelewski, 1,25-Dihydroxycholecalciferol effects in prostatic adenocarcinoma models, manuscript in preparation.
Received 12/ 1/98. Accepted 4/ 2/99.
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REFERENCES |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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,25-dihydroxyvitamin D3 are mediated exclusively through the genomic signaling pathway. Endocrinology, 137: 1554-1561, 1996.[Abstract]
,25-dihydroxyvitamin D3 in the human prostatic carcinoma cell line ALVA-31. J. Steroid Biochem. Mol. Biol., 58: 277-288, 1996.[Medline]
-mediated transcriptional down-regulation of the cyclin-dependent kinase inhibitor p21Cip1/Waf1 correlates with terminal differentiation of squamous cell carcinoma lines. Cell Growth Differ., 9: 619-627, 1998.[Abstract]
,25-dihydroxyvitamin D3-mediated effects. J. Immunol., 160: 209-218, 1998.This article has been cited by other articles:
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  R. J. Menezes, R. T. Cheney, A. Husain, M. Tretiakova, G. Loewen, C. S. Johnson, V. Jayaprakash, K. B. Moysich, R. Salgia, and M. E. Reid Vitamin D Receptor Expression in Normal, Premalignant, and Malignant Human Lung Tissue Cancer Epidemiol. Biomarkers Prev., May 1, 2008; 17(5): 1104 - 1110. [Abstract] [Full Text] [PDF]
|
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|
|
 |
|
 I. Chung, A. R. Karpf, J. R. Muindi, J. M. Conroy, N. J. Nowak, C. S. Johnson, and D. L. Trump Epigenetic Silencing of CYP24 in Tumor-derived Endothelial Cells Contributes to Selective Growth Inhibition by Calcitriol J. Biol. Chem., March 23, 2007; 282(12): 8704 - 8714. [Abstract] [Full Text] [PDF]
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|
 |
|
 M. G. Fakih, D. L. Trump, J. R. Muindi, J. D. Black, R. J. Bernardi, P. J. Creaven, J. Schwartz, M. G. Brattain, A. Hutson, R. French, et al. A Phase I Pharmacokinetic and Pharmacodynamic Study of Intravenous Calcitriol in Combination with Oral Gefitinib in Patients with Advanced Solid Tumors Clin. Cancer Res., February 15, 2007; 13(4): 1216 - 1223. [Abstract] [Full Text] [PDF]
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Q.-P. Li, X. Qi, R. Pramanik, N. M. Pohl, M. Loesch, and G. Chen Stress-induced c-Jun-dependent Vitamin D Receptor (VDR) Activation Dissects the Non-classical VDR Pathway from the Classical VDR Activity J. Biol. Chem., January 19, 2007; 282(3): 1544 - 1551. [Abstract] [Full Text] [PDF]
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 I. Chung, M. K. Wong, G. Flynn, W.-d. Yu, C. S. Johnson, and D. L. Trump Differential Antiproliferative Effects of Calcitriol on Tumor-Derived and Matrigel-Derived Endothelial Cells. Cancer Res., September 1, 2006; 66(17): 8565 - 8573. [Abstract] [Full Text] [PDF]
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Y. Ma, W.-D. Yu, R.-X. Kong, D. L. Trump, and C. S. Johnson Role of Nongenomic Activation of Phosphatidylinositol 3-Kinase/Akt and Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase Kinase/Extracellular Signal-Regulated Kinase 1/2 Pathways in 1,25D3-Mediated Apoptosis in Squamous Cell Carcinoma Cells Cancer Res., August 15, 2006; 66(16): 8131 - 8138. [Abstract] [Full Text] [PDF]
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 W. Liu, S. L. Asa, and S. Ezzat 1{alpha},25-Dihydroxyvitamin D3 Targets PTEN-Dependent Fibronectin Expression to Restore Thyroid Cancer Cell Adhesiveness Mol. Endocrinol., September 1, 2005; 19(9): 2349 - 2357. [Abstract] [Full Text] [PDF]
|
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 A. P. B. Dackiw, S. Ezzat, P. Huang, W. Liu, and S. L. Asa Vitamin D3 Administration Induces Nuclear p27 Accumulation, Restores Differentiation, and Reduces Tumor Burden in a Mouse Model of Metastatic Follicular Thyroid Cancer Endocrinology, December 1, 2004; 145(12): 5840 - 5846. [Abstract] [Full Text] [PDF]
|
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|
 |
|
 T. M. Beer and A. Myrthue Calcitriol in cancer treatment: From the lab to the clinic Mol. Cancer Ther., March 1, 2004; 3(3): 373 - 381. [Abstract] [Full Text]
|
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|
|
R. Lin, T. T. Wang, W. H. Miller Jr., and J. H. White Inhibition of F-Box Protein p45SKP2 Expression and Stabilization of Cyclin-Dependent Kinase Inhibitor p27KIP1 in Vitamin D Analog-Treated Cancer Cells Endocrinology, March 1, 2003; 144(3): 749 - 753. [Abstract] [Full Text] [PDF]
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F. Galbiati, L. Polastri, S. Gregori, M. Freschi, M. Casorati, U. Cavallaro, P. Fiorina, F. Bertuzzi, A. Zerbi, G. Pozza, et al. Antitumorigenic and Antiinsulinogenic Effects of Calcitriol on Insulinoma Cells and Solid {beta}-Cell Tumors Endocrinology, October 1, 2002; 143(10): 4018 - 4030. [Abstract] [Full Text] [PDF]
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W. N. Wade, M. C. Willingham, C. Koumenis, and S. D. Cramer p27Kip1 Is Essential for the Antiproliferative Action of 1,25-Dihydroxyvitamin D3 in Primary, but Not Immortalized, Mouse Embryonic Fibroblasts J. Biol. Chem., September 27, 2002; 277(40): 37301 - 37306. [Abstract] [Full Text] [PDF]
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P. A. Hershberger, T. F. McGuire, W.-D. Yu, E. G. Zuhowski, J. H. M. Schellens, M. J. Egorin, D. L. Trump, and C. S. Johnson Cisplatin Potentiates 1,25-Dihydroxyvitamin D3-induced Apoptosis in Association with Increased Mitogen-activated Protein Kinase Kinase Kinase 1 (MEKK-1) Expression Mol. Cancer Ther., August 1, 2002; 1(10): 821 - 829. [Abstract] [Full Text] [PDF]
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R. J. Bernardi, C. S. Johnson, R. A. Modzelewski, and D. L. Trump Antiproliferative Effects of 1{alpha},25-Dihydroxyvitamin D3 and Vitamin D Analogs on Tumor-Derived Endothelial Cells Endocrinology, July 1, 2002; 143(7): 2508 - 2514. [Abstract] [Full Text] [PDF]
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R. Lin, Y. Nagai, R. Sladek, Y. Bastien, J. Ho, K. Petrecca, G. Sotiropoulou, E. P. Diamandis, T. J. Hudson, and J. H. White Expression Profiling in Squamous Carcinoma Cells Reveals Pleiotropic Effects of Vitamin D3 Analog EB1089 Signaling on Cell Proliferation, Differentiation, and Immune System Regulation Mol. Endocrinol., June 1, 2002; 16(6): 1243 - 1256. [Abstract] [Full Text] [PDF]
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 W. Liu, S. L. Asa, I. G. Fantus, P. G. Walfish, and S. Ezzat Vitamin D Arrests Thyroid Carcinoma Cell Growth and Induces p27 Dephosphorylation and Accumulation through PTEN/Akt-Dependent and -Independent Pathways Am. J. Pathol., February 1, 2002; 160(2): 511 - 519. [Abstract] [Full Text] [PDF]
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R. J. Bernardi, D. L. Trump, W.-D. Yu, T. F. McGuire, P. A. Hershberger, and C. S. Johnson Combination of 1{alpha},25-Dihydroxyvitamin D3 with Dexamethasone Enhances Cell Cycle Arrest and Apoptosis: Role of Nuclear Receptor Cross-Talk and Erk/Akt Signaling Clin. Cancer Res., December 1, 2001; 7(12): 4164 - 4173. [Abstract] [Full Text] [PDF]
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N. Akutsu, R. Lin, Y. Bastien, A. Bestawros, D. J. Enepekides, M. J. Black, and J. H. White Regulation of Gene Expression by 1{{alpha}},25-Dihydroxyvitamin D3 and Its Analog EB1089 under Growth-Inhibitory Conditions in Squamous Carcinoma Cells Mol. Endocrinol., July 1, 2001; 15(7): 1127 - 1139. [Abstract] [Full Text] [PDF]
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 J. Prudencio, N. Akutsu, N. Benlimame, T. Wang, Y. Bastien, R. Lin, M. J. Black, M. A. Alaoui-Jamali, and J. H. White Action of Low Calcemic 1{{alpha}},25-Dihydroxyvitamin D3 Analogue EB1089 in Head and Neck Squamous Cell Carcinoma J Natl Cancer Inst, May 16, 2001; 93(10): 745 - 753. [Abstract] [Full Text] [PDF]
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P. A. Hershberger, W.-D. Yu, R. A. Modzelewski, R. M. Rueger, C. S. Johnson, and D. L. Trump Calcitriol (1,25-Dihydroxycholecalciferol) Enhances Paclitaxel Antitumor Activity in Vitro and in Vivo and Accelerates Paclitaxel-induced Apoptosis Clin. Cancer Res., April 1, 2001; 7(4): 1043 - 1051. [Abstract] [Full Text]
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