Data from Chemoprevention Activity of 25-Hydroxyvitamin D in the MMTV-PyMT Mouse Model of Breast Cancer

Abstract

<div>Abstract<p>Development of oncologic conditions is often accompanied by inadequate vitamin D status. The chemoprevention ability of this molecule is of high interest for breast cancer, the most common malignancy in women worldwide. Because current effective vitamin D analogues, including the naturally occurring active metabolite 1,25-dihydroxycholecalciferol (1,25(OH)<sub>2</sub>D), frequently cause hypercalcemia at pharmacologic doses, the development of safer molecules for clinical chemopreventive use is essential. This study examines whether exogenously supplied prohormone 25-hydroxycholecalciferol (25(OH)D) can delay tumor progression <i>in vivo</i> without hypercalcemic effects. A low vitamin D diet (25 IU/kg) in the non-immunodeficient MMTV-PyMT mouse model of metastatic breast cancer revealed a significant acceleration of mammary neoplasia compared with normal diet (1,000 IU/kg). Systemic perfusion of MMTV-PyMT mice with 25(OH)D or 1,25(OH)<sub>2</sub>D delayed tumor appearance and significantly decreased lung metastasis, and both metabolites reduced Ki-67, cyclin D1, and ErbB2 levels in tumors. Perfusion with 25(OH)D caused a 50% raise in tumor 1,25(OH)<sub>2</sub>D levels, indicating good tumor penetration and effective activation. Importantly, in contrast with 1,25(OH)<sub>2</sub>D, perfusion with 25(OH)D did not cause hypercalcemia. <i>In vitro</i> treatment of cultured MMTV-PyMT mammary tumor cells with 25(OH)D inhibited proliferation, confirming local activation of the prohormone in this system. This study provides an <i>in vivo</i> demonstration in a non-immunodeficient model of spontaneous breast cancer that exogenous 25(OH)D delays neoplasia, tumor growth, and metastasis, and that its chemoprevention efficacy is not accompanied by hypercalcemia. <i>Cancer Prev Res; 8(2); 120–8. ©2014 AACR.</i></p></div>