Application of aromatase inhibitors in endocrine responsive breast cancers

The potential therapeutic benefits of vitamin D in the treatment of estrogen receptor positive breast cancer

Calcitriol (1,25-dihydroxyvitamin D(3)), the hormonally active form of vitamin D, inhibits the growth of many malignant cells including breast cancer (BCa) cells. The mechanisms of calcitriol anticancer actions include cell cycle arrest, stimulation of apoptosis and inhibition of invasion, metastasis and angiogenesis. In addition we have discovered new pathways of calcitriol action that are especially relevant in inhibiting the growth of estrogen receptor positive (ER+) BCa cells. Calcitriol suppresses COX-2 expression and increases that of 15-PGDH thereby reducing the levels of inflammatory prostaglandins (PGs). Our in vitro and in vivo studies show that calcitriol decreases the expression of aromatase, the enzyme that catalyzes estrogen synthesis selectively in BCa cells and in the mammary adipose tissue surrounding BCa, by a direct repression of aromatase transcription via promoter II as well as an indirect effect due to the reduction in the levels of PGs, which are major stimulator of aromatase transcription through promoter II. Calcitriol down-regulates the expression of ERα and thereby attenuates estrogen signaling in BCa cells including the proliferative stimulus provided by estrogens. Thus the inhibition of estrogen synthesis and signaling by calcitriol and its anti-inflammatory actions will play an important role in inhibiting ER+BCa. We hypothesize that dietary vitamin D would exhibit similar anticancer activity due to the presence of the enzyme 25-hydroxyvitamin D-1α-hydroxylase (CYP27B1) in breast cells ensuring conversion of circulating 25-hydroxyvitamin D to calcitriol locally within the breast micro-environment where it can act in a paracrine manner to inhibit BCa growth. Cell culture and in vivo data in mice strongly suggest that calcitriol and dietary vitamin D would play a beneficial role in the prevention and/or treatment of ER+BCa in women.

Inhibitory effects of calcitriol on the growth of MCF-7 breast cancer xenografts in nude mice: selective modulation of aromatase expression in vivo

Calcitriol (1,25-dihydroxyvitamin D(3)), 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.

NCCN Task Force Report: Bone Health in Cancer Care

Bone health and maintenance of bone integrity are important components of comprehensive cancer care in both early and late stages of disease. Risk factors for osteoporosis are increased in patients with cancer, including women with chemotherapy-induced ovarian failure, those treated with aromatase inhibitors for breast cancer, men receiving androgen-deprivation therapy for prostate cancer, and patients undergoing glucocorticoid therapy. The skeleton is a common site of metastatic cancer recurrence, and skeletal-related events are the cause of significant morbidity. The National Comprehensive Cancer Network (NCCN) convened a multidisciplinary task force on Bone Health in Cancer Care to discuss the progress made in identifying effective screening and therapeutic options for management of treatment-related bone loss; understanding the factors that result in bone metastases; managing skeletal metastases; and evolving strategies to reduce bone recurrences. This report summarizes presentations made at the meeting.

Molecular targets of breast cancer: AKTing in concert

Despite significant advancement in the diagnosis and treatment of breast cancer, many patients succumb to this disease. The elucidation of aberrant signaling pathways that lead to breast cancer should help develop more effective therapeutic strategies. The Akt signaling pathway plays an important role in the development and progression of breast cancer. Overexpression/activation of Akt has been associated with poor prognosis and resistance to hormonal and chemotherapy. Although mutations in Akt are rare in breast cancer, the activity of Akt is regulated by hormones, growth factors, growth factor receptors, oncogenes and tumor suppressor genes that are often deregulated in breast cancer. The objective of this commentary is to discuss recent literature on how activation of Akt by various signaling pathways contributes to breast cancer and confers resistance to current therapy.