Inhibitory Effects of Calcitriol on the Growth of MCF-7 Breast Cancer Xenografts in Nude Mice: Selective Modulation of Aromatase Expression in vivo

Abstract

Calcitriol (1,25-dihydroxyvitamin D3), the hormonally active metabolite of vitamin D, exerts many anticancer effects in breast cancer (BCa) cells. We have previously shown using cell culture models that calcitriol acts as a selective aromatase modulator (SAM) and inhibits estrogen synthesis and signaling in BCa cells. We have now examined calcitriol effects in vivo on aromatase expression, estrogen signaling, and tumor growth when used alone and in combination with aromatase inhibitors (AIs). In immunocompromised mice bearing MCF-7 xenografts, increasing doses of calcitriol exhibited significant tumor inhibitory effects (~50% to 70% decrease in tumor volume). At the suboptimal doses tested, anastrozole and letrozole also caused significant tumor shrinkage when used individually. Although the combinations of calcitriol and the AIs caused a statistically significant increase in tumor inhibition in comparison to the single agents, the cooperative interaction between these agents appeared to be minimal at the doses tested. Calcitriol decreased aromatase expression in the xenograft tumors. Importantly, calcitriol also acted as a SAM in the mouse, decreasing aromatase expression in the mammary adipose tissue, while increasing it in bone marrow cells and not altering it in the ovaries and uteri. As a result, calcitriol significantly reduced estrogen levels in the xenograft tumors and surrounding breast adipose tissue. In addition, calcitriol inhibited estrogen signaling by decreasing tumor ERα levels. Changes in tumor gene expression revealed the suppressive effects of calcitriol on inflammatory and growth signaling pathways and demonstrated cooperative interactions between calcitriol and AIs to modulate gene expression. We hypothesize that cumulatively these calcitriol actions would contribute to a beneficial effect when calcitriol is combined with an AI in the treatment of BCa.

Temporal changes in tissue 1α,25-dihydroxyvitamin D3, vitamin D receptor target genes, and calcium and PTH levels after 1,25(OH)2D3treatment in mice

“…For in vivo pharmacokinetic studies in male, C57BL/6 mice (8 wk old), doses of either 0 or 2.5 g/kg (or 0.05 g/mouse or 120 pmol) 1,25(OH) 2D3, dissolved in sterile corn oil (5 l/g), were given ip on days 0, 2, 4, and 8 at 9 AM. The dose was based on a series of published reports, with doses ranging from 0.1 to 5 g/mouse or 0.25 to 5 g/kg for ip or oral administration, daily or every other day in mice (1,2,27,37,39,42,47,55). In humans, doses of 1,25(OH) 2D3 (0.5 g/kg or 38 g) furnished a similar clearance and exposure with minimal toxicity when used intermittently (8,38).…”

Staying a Step Ahead of Cancer

“…Besides anti-proliferative, pro-apoptotic, and prodifferentiating actions on various malignant cells and decreasing tumor growth in vivo, calcitriol also exhibits several anti-inflammatory effects including suppression of prostaglandin action, inhibition of p38 stress kinase signaling, and the subsequent production of pro-inflammatory cytokines and inhibition of NF-κB signaling . Calcitriol also decreases the expression of aromatase, the enzyme that catalyzes estrogen synthesis in breast cancer, both by a direct transcriptional repression and indirectly by reducing prostaglandins, which are major stimulators of aromatase transcription , Swami et al 2011, Zanatta et al 2011). Other important effects include the suppression of tumor angiogenesis, invasion, and metastasis , So et al 2010, Chung et al 2009, Ma, Trump and Johnson 2010.…”

Transrepression of the estrogen receptor promoter by calcitriol in human breast cancer cells via two negative vitamin D response elements

“…Interestingly, our studies reveal that in ERC BCa cells calcitriol inhibits both estrogen synthesis and signaling, leading to a significant attenuation of estrogen stimulation of cell growth (Krishnan et al 2010a). We have shown that calcitriol acts as a selective aromatase modulator (SAM) and decreases estrogen synthesis in BCa cells and the surrounding mammary adipose tissue by suppressing aromatase expression (Krishnan et al 2010b, Swami et al 2011. Furthermore, calcitriol and its analogs also downregulate ER expression in BCa cells (James et al 1994, Simboli-Campbell et al 1997, Swami et al 2000, thereby causing a significant inhibition of estrogenic bioresponses in these cells, including the suppression of estrogenstimulated cell growth (Demirpence et al 1994, Swami et al 2000.…”