Boron Compounds in the Breast Cancer Cells Chemoprevention and Chemotherapy

Various biological functions of Boron (B) compounds are known (Blevins & Lukaszewski, 1994; Tariq & Mott, 2007; Nielsen, 2008). Boron is found in nuts, vegetables, dried/fresh fruits and red wine (Brown & Shelp, 1997). Boron is also present in bacterial antibiotics, such as tartrolon, borophycin, boromycin and aplasmomycin (Rezanka & Sigler, 2008); in the bacterial quorum sensing molecule auto-inducer AI-2 (Bemd et al., 2002); and in vibrioferrin, a B-containing siderophore produced by particular marine bacteria (Shady et al., 2007). In plants, the rigidity of the cell wall depends on the rhamnogalacturonan II complex (RG-II) formation, a pectic polysaccharide covalently linked by cis-diol bonds to apiosil residues of borate-esters (Ishii & Matsunaga, 1996, 2001). Several articles have provided information about transporters responsible for efficient B uptake by roots, xylem loading and B distribution among leaves. The transporters are required under B limitation for efficient acquisition and utilisation of B. Two types of transporters are involved in these processes: NIPs (nodulin-26-like intrinsic proteins) for boric acid channels and boron exporters encoded by BOR1 (Miwa & Fujiwara, 2010). The expression of the genes encoding these transporters has been shown to be finely regulated in the B availability response to ensure tissue B homeostasis. Furthermore, the tolerance of plants to the stress produced by low B or high B in the environment can be generated by altering the expression of these transporters (Tanaka & Fujiwara, 2007). All of these transporters are involved in boron transport regulation in plants. B is an essential element not only for vascular plants but also for diatoms, cyanobacteria and a number of marine algal flagellate species (Rezanka & Sigler, 2008). Recently, ATR1 has been found to be responsible for the high B tolerance in S. Cerevisiae. ATR1 encodes a multidrug resistance transporter and it is widely distributed in bacteria, archaea and lower eukaryotes (Miwa & Fujiwara, 2010). Animals such as zebra, fish, trout and frogs also require boron (Rowe & Eckert, 1999; Fort et al., 1999). Borate ions activate the mitogen-activated protein kinases pathway and stimulate the growth and the proliferation of human embryonic kidney 293 cells (Park et al., 2005). The B-transporter, NaBCl, controls plasma borate levels in human kidney cells (Park at al., 2004). The fact that B has such a broad range of physiological functions is not surprising. The electron structure of B and its position in the periodic table (adjacent to carbon) make B-containing molecules electrophilic with the trigonal