The sodium/iodide symporter (NIS) mediates iodide uptake in lactating breast tissue and is expressed in some breast cancers. We have previously demonstrated that all-trans retinoic acid (tRA) stimulates NIS gene expression and the selective cytotoxic effect of beta-emitting radioiodide-131 ((131)I) in both in vitro and in vivo MCF-7 breast cancer cell systems. We studied the ability of natural and synthetic retinoids, in combination with other nuclear receptor ligands, to achieve greater and more sustained induction of NIS in MCF-7 cells and enhance (131)I-mediated cytotoxicity. Selective stimulation of retinoic acid receptor (RAR) beta/gamma produced marked NIS induction; and selective stimulation of RARalpha, RARgamma, or retinoid X receptor produced more modest induction. Maximal NIS induction was seen with 9-cis retinoic acid and AGN190168, a RAR beta/gamma-agonist. Dexamethasone (Dex), but not the other nuclear receptor ligands, in combination with tRA synergistically induced iodide uptake and NIS mRNA expression, predominantly by prolonging NIS mRNA half-life. The addition of Dex reduced the EC(50) of tRA for NIS stimulation to approximately 7%, such that 10(-7) m tRA with addition of Dex enhanced iodide uptake and selective cytotoxicity of (131)I greater than 10(-6) m tRA alone. AGN190168 combined with Dex synergistically increased iodide uptake and significantly prolonged induction (5 d) of iodide uptake compared with that induced by the combination of tRA/Dex or 9-cis retinoic acid/Dex. The addition of Dex reduced the effective dose of retinoid and prolonged the induction of NIS, especially with AGN190168, suggesting higher efficacy of (131)I after combination treatment.

ABSTRACT. Four canine melanoma cell lines were established from the subcutaneous, oral gingival and mucosal melanoma tissues at the primary and metastatic sites. These cell lines were designated as CMeC-1, CMeC-2, KMeC and LMeC. The cells were spindles in shape, similar to that of primary tumor cells. The doubling times of these cells ranged from 34.1 ± 5.61 to 57.9 ± 3.28 hr and their chromosome number ranged from 46 to 80. When transplanted into nude mice, CMeC-1 and LMeC produced tumors, whereas CMeC-2 and KMeC did not. The morphology of the tissue formed by xenotransplantation of these cells was similar to their primary tumors.

Iodide uptake in the thyroid and breast is mediated by the sodium/iodide symporter (NIS). NIS activation is used for radioiodide imaging and therapeutic ablation of thyroid carcinoma. NIS is expressed in >70% of breast cancers but at a level insufficient for radioiodine treatment. All-trans retinoic acid (tRA) induces NIS gene expression and functional iodide uptake in human breast cancer cell lines and mouse breast cancer models. tRA usually regulates gene expression by direct interaction of RA receptor (RAR) with a target gene, but it can also act through nongenomic pathways. We report a direct influence of tRA treatment on the phosphoinositide 3-kinase (PI3K) signal transduction pathway that mediates tRA-induced NIS expression in MCF-7 breast cancer cells. MCF-7 cells express all three RAR isoforms, A, B, and ;, and RXRA. We previously identified RARB and RXRA as important for NIS induction by tRA. Treatment with LY294002, the PI3K inhibitor, or p85A knockdown with siRNA abolished tRAinduced NIS expression. Immunoprecipitation experiments and glutathione S-transferase pull-down assay showed a direct interaction between RARB2, RXRA, and p85A. RA also induced rapid activation of Akt in MCF-7 cells. Treatment with an Akt inhibitor or Akt knockdown with siRNA reduced NIS expression. These findings indicate that RA induction of NIS in MCF-7 cells is mediated by rapid activation of the PI3K pathway and involves direct interaction with RAR and retinoid X receptor. Defining these mechanisms should lead to methods to further enhance NIS expression, as well as retinoid targets that influence growth and differentiation of breast cancer. [Cancer Res 2009;69(8):3443-50]