NUTRITION AND CANCER, 59(2), 192–198 Copyright C  2007, Lawrence Erlbaum Associates, Inc. Insights Into the Mechanisms Involved in Magnesium-Dependent Inhibition of Primary Tumor Growth Jeanette A. M. Maier, Anna Nasulewicz-Goldeman, Matteo Simonacci, Alma Boninsegna, Andrzej Mazur, and Federica I. Wolf Abstract: We have previously shown that a low Magnesium (Mg)-containing diet reversibly inhibits the growth of pri- mary tumors that develop after the injection of Lewis lung carcinoma (LLC) cells in mice. Here we investigate some of the mechanisms responsible for the Mg-dependent regulation of tumor development by studying cell cycle regulation, tu- mor angiogenesis, and gene expression under Mg deficiency. The inhibition of LLC tumor growth in Mg-deficient mice is due to a direct effect of low Mg on LLC cell proliferation and to an impairment of the angiogenic switch. We also observed an increase of nitric oxide synthesis and oxidative DNA dam- age. Complementary DNA arrays reveal that Mg deficiency modulates tumor expression of genes involved in the control of cell cycle, stress response, proteolysis, and adhesion. Our results suggest that Mg has multiple and complex roles in tumor development. Introduction Magnesium (Mg) is involved in the regulation of a large number of biochemical reactions that are crucial to cell pro- liferation, differentiation, apoptosis, and angiogenesis (1). Because it functions as an allosteric modulator of several enzymes or bridges structurally distinct molecules, Mg sta- bilizes DNA, promotes DNA replication and transcription, influences RNA translation, and induces ribosome assem- bly (2). Compelling evidence shows that Mg is required for proliferation in normal diploid and transformed cells (3–5). Recently, the role of Mg in regulating cell proliferation was underscored by studies based on the deletion of the transient receptor potential melastatin (TRPM) 7, which is critical to Mg entry in eukaryotic cells (6). Interestingly, cells in which TRPM 7 was genetically deleted are Mg depleted and growth arrested (6). J. A. M. Maier is affiliated with the Dipartimento di Scienze Precliniche LITA Vialba, Universit` a di Milano, 20157 Milano, Italy. A. Nasulewicz-Goldeman is affiliated with the Institute of Immunology and Experimental Therapy, Polish Academy of Sciences, 53–114 Wroclaw, Poland. M. Simonacci, A. Boninsegna, and F. I. Wolf are affiliated with the Istituto di Patologia Generale, e Centro di Ricerche Oncologiche Giovanni XXIII, Facolt` a di Medicina, Universit` a Cattolica del Sacro Cuore, Largo F. Vito, 100168 Roma, Italy. A. Mazur is affiliated with the INRA, Clermont Ferrand/Theix, Centre de Recherche en Nutrition Humaine d’Auvergne, Unit´ e de Nutrition Humaine, Equipe Stress M´ etabolique et Micronutriments, 63122 Saint-Gen` es-Champanelle, France. The occidental diet is relatively deficient in Mg because of its low content in water and soils and because of the processing of some foods (7). Apart from being associated with a decreased dietary intake, Mg deficiency occurs in diabetes, metabolic syndrome, nephropathies, chronic alco- holism, and other age-associated diseases. In addition, di- uretics and some anticancer drugs promote Mg waste, thus leading to hypomagnesemia (8). Epidemiological studies about the relation between Mg content in drinking water and cancer provided a vast array of results: An inverse relationship was found for breast, prostate, and ovarian cancers; a protective trend for esophageal cancer, but no correlation for other tumors (8). A recent large epi- demiological prospective study on Swedish women demon- strated that the incidence of rectal cancer was inversely re- lated to the levels of Mg in the diet (9). An observational study comparing control subjects to patients affected by dif- ferent kind of tumors (lung, breast, ovary, oropharyngeal, and hypopharyngeal cancers) showed that in cancer patients, serum Mg was lower (P< 0.001) than in controls, and this correlated with the stage of malignancy (10). The contribution of Mg availability to tumor growth is still debated, and both experimental and epidemiological ev- idences are fragmentary and sometimes contradictory. Al- though low serum Mg is detected in tumor-bearing organ- isms, including oncologic patients, Mg content is increased in tumors compared to their normal counterpart both in vivo and in vitro (3,8,11). This observation supports the hypoth- esis that growing tissues require more Mg than resting ones to sustain their proliferation rate. Because tumors are able to maintain high intracellular Mg in spite of decreased ex- tracellular availability, they have been addressed as a very powerful “Mg trap” (3). The capability of tumor cells to sequester and keep up Mg is confirmed by experiments in vitro showing that the proliferation of tumor cells is less