Anne Myrthue

CCL2 is induced by chemotherapy and protects prostate cancer cells from docetaxel-induced cytotoxicity.

Metastatic prostate cancer is either inherently resistant to chemotherapy or rapidly acquires this phenotype after chemotherapy exposure. In this study, we identified a docetaxel‐induced resistance mechanism centered on CCL2.

The Iroquois Homeobox Gene 5 Is Regulated by 1,25-Dihydroxyvitamin D3 in Human Prostate Cancer and Regulates Apoptosis and the Cell Cycle in LNCaP Prostate Cancer Cells

1,25-Dihydroxyvitamin D3 [1,25(OH)2D3], the most active metabolite of vitamin D3, has significant antitumor activity in a broad range of preclinical models of cancer. In this study, we show that the Iroquois homeobox gene 5 (Irx5) is down-regulated by 1,25(OH)2D3 in human prostate cancer samples from patients randomly assigned to receive weekly high-dose 1,25(OH)2D3 or placebo before radical prostatectomy. Down-regulation of Irx5 by 1,25(OH)2D3 was also shown in the human androgen-sensitive prostate cancer cell line LNCaP and in estrogen-sensitive MCF-7 breast cancer cells. Knockdown of Irx5 by RNA interference showed a significant reduction in LNCaP cell viability, which was accompanied by an increase in p21 protein expression, G2-M arrest, and an increase in apoptosis. The induced apoptosis was partially mediated by p53, and p53 protein expression was increased as a result of Irx5 knockdown. Cell survival was similarly reduced by Irx5 knockdown in the colon cancer cell line HCT 116 and in MCF-7 breast cancer cells, each being derived from clinical tumor types that seem to be inhibited by 1,25(OH)2D3. Overexpression of Irx5 led to a reduction of p21 and p53 expression. This is the first report that Irx5 is regulated by 1,25(OH)2D3 in humans and the first report to show that Irx5 is involved in the regulation of both the cell cycle and apoptosis in human prostate cancer cells. Irx5 may be a promising new therapeutic target in cancer treatment.

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

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

ID1 Enhances Docetaxel Cytotoxicity in Prostate Cancer Cells through Inhibition of p21

To identify potential mechanisms underlying prostate cancer chemotherapy response and resistance, we compared the gene expression profiles in high-risk human prostate cancer specimens before and after neoadjuvant chemotherapy and radical prostatectomy. Among the molecular signatures associated with chemotherapy, transcripts encoding inhibitor of DNA binding 1 (ID1) were significantly upregulated. The patient biochemical relapse status was monitored in a long-term follow-up. Patients with ID1 upregulation were found to be associated with longer relapse-free survival than patients without ID1 increase. This in vivo clinical association was mechanistically investigated. The chemotherapy-induced ID1 upregulation was recapitulated in the prostate cancer cell line LNCaP. Docetaxel dose-dependently induced ID1 transcription, which was mediated by ID1 promoter E-box chromatin modification and c-Myc binding. Stable ID1 overexpression in LNCaP increased cell proliferation, promoted G(1) cell cycle progression, and enhanced docetaxel-induced cytotoxicity. These changes were accompanied by a decrease in cellular mitochondria content, an increase in BCL2 phosphorylation at serine 70, caspase-3 activation, and poly(ADP-ribose) polymerase cleavage. In contrast, ID1 siRNA in the LNCaP and C42B cell lines reduced cell proliferation and decreased docetaxel-induced cytotoxicity by inhibiting cell death. ID1-mediated chemosensitivity enhancement was in part due to ID1 suppression of p21. Overexpression of p21 in LNCaP-ID1-overexpressing cells restored the p21 level and reversed ID1-enhanced chemosensitivity. These molecular data provide a mechanistic rationale for the observed in vivo clinical association between ID1 upregulation and relapse-free survival. Taken together, it shows that ID1 expression has a novel therapeutic role in prostate cancer chemotherapy and prognosis.

Effect of Calcitriol on Prostate-Specific Antigen In vitro and in Humans

Background: Calcitriol, the natural ligand for the vitamin D receptor, has significant potential in prostate cancer treatment. Measurement of its antineoplastic activity in prostate cancer clinical trials may be complicated by effects of calcitriol on prostate-specific antigen (PSA) production. We examined the effects of calcitriol at similar concentration on cell proliferation, androgen receptor (AR) expression, and PSA production in vitro and on PSA concentrations in prostate cancer patients. Experimental Design: LNCaP prostate cancer cell proliferation was examined by cell counts 6 days after exposure to a range of concentrations of calcitriol. AR and PSA protein was quantified in LNCaP cells over 96 hours after exposure to 1 nmol/L calcitriol. Serum PSA and free PSA was serially measured by immunoassay over a period of 8 days in patients with hormone-naïve prostate cancer after a single dose of 0.5 μg/kg calcitriol. Results: Calcitriol treatment resulted in dose-dependent growth inhibition of LNCaP with ∼50% growth inhibition at the clinically achievable concentration of 1 nmol/L. Time-dependent up-regulation of AR expression and of PSA production in LNCaP cells was shown at the same concentration. No significant change in serum PSA or free PSA over 8 days was seen in eight subjects treated with a single dose of 0.5 μg/kg calcitriol. The analysis was powered to detect a 1.23-fold change between the baseline and day 8 serum PSA. Conclusions: At clinically achievable concentrations, calcitriol inhibits growth and induces AR and PSA expression in LNCaP cells. We did not detect similar changes in serum PSA or free PSA in patients exposed to similar concentrations of calcitriol. Thus, a PSA flare, predicted by preclinical systems, is unlikely to occur in patients and therefore unlikely to complicate interpretation of clinical trial outcomes.