Jeong Youngtae, Swami Srilatha, Krishnan Aruna V, Williams Jasmaine D, Martin Shanique, Horst Ronald L, Albertelli Megan A, Feldman Brian J, Feldman David, Diehn Maximilian
Stanford Cancer Institute, Stanford University School of Medicine, Stanford, California. Institute for Stem Cell Biology and Regenerative Medicine, Stanford University School of Medicine, Stanford, California.
Department of Medicine, Division of Endocrinology, Gerontology, and Metabolism, Stanford University School of Medicine, Stanford, California.
Mol Cancer Ther. 2015 Aug;14(8):1951-61. doi: 10.1158/1535-7163.MCT-15-0066. Epub 2015 May 1.
The anticancer actions of vitamin D and its hormonally active form, calcitriol, have been extensively documented in clinical and preclinical studies. However, the mechanisms underlying these actions have not been completely elucidated. Here, we examined the effect of dietary vitamin D and calcitriol on mouse breast tumor-initiating cells (TICs, also known as cancer stem cells). We focused on MMTV-Wnt1 mammary tumors, for which markers for isolating TICs have previously been validated. We confirmed that these tumors expressed functional vitamin D receptors and estrogen receptors (ER) and exhibited calcitriol-induced molecular responses including ER downregulation. Following orthotopic implantation of MMTV-Wnt1 mammary tumor cells into mice, calcitriol injections or a vitamin D-supplemented diet caused a striking delay in tumor appearance and growth, whereas a vitamin D-deficient diet accelerated tumor appearance and growth. Calcitriol inhibited TIC tumor spheroid formation in a dose-dependent manner in primary cultures and inhibited TIC self-renewal in secondary passages. A combination of calcitriol and ionizing radiation inhibited spheroid formation more than either treatment alone. Further, calcitriol significantly decreased TIC frequency as evaluated by in vivo limiting dilution analyses. Calcitriol inhibition of TIC spheroid formation could be overcome by the overexpression of β-catenin, suggesting that the inhibition of Wnt/β-catenin pathway is an important mechanism mediating the TIC inhibitory activity of calcitriol in this tumor model. Our findings indicate that vitamin D compounds target breast TICs reducing tumor-initiating activity. Our data also suggest that combining vitamin D compounds with standard therapies may enhance anticancer activity and improve therapeutic outcomes.
维生素D及其激素活性形式骨化三醇的抗癌作用已在临床和临床前研究中得到广泛记载。然而，这些作用背后的机制尚未完全阐明。在此，我们研究了饮食中维生素D和骨化三醇对小鼠乳腺肿瘤起始细胞（TICs，也称为癌症干细胞）的影响。我们重点关注MMTV-Wnt1乳腺肿瘤，此前已验证了分离TICs的标志物。我们证实这些肿瘤表达功能性维生素D受体和雌激素受体（ER），并表现出骨化三醇诱导的分子反应，包括ER下调。将MMTV-Wnt1乳腺肿瘤细胞原位植入小鼠后，注射骨化三醇或补充维生素D的饮食会显著延迟肿瘤出现和生长，而缺乏维生素D的饮食则会加速肿瘤出现和生长。骨化三醇在原代培养中以剂量依赖性方式抑制TIC肿瘤球形成，并在传代培养中抑制TIC自我更新。骨化三醇与电离辐射联合使用比单独使用任何一种治疗方法更能抑制球状体形成。此外，通过体内极限稀释分析评估，骨化三醇显著降低了TIC频率。β-连环蛋白的过表达可克服骨化三醇对TIC球状体形成的抑制作用，这表明抑制Wnt/β-连环蛋白通路是介导骨化三醇在该肿瘤模型中TIC抑制活性的重要机制。我们的研究结果表明，维生素D化合物靶向乳腺TICs，降低肿瘤起始活性。我们的数据还表明，将维生素D化合物与标准疗法联合使用可能增强抗癌活性并改善治疗效果。
