Thioredoxin reductase (TrxR) catalyzes the reduction of thioredoxin (Trx) with NADPH as a co-factor. Trx, and in multiple cases also TrxR, are over-expressed in many tumors, leading to increased cell proliferation. In this regard, Turunen et al. (2004) found that 122 of 221 (55%) breast invasive tumors showed immunoreactivity to TrxR in the cytoplasm, as assessed by immunohistochemistry. Furthermore, HeLa cells that over-express TrxR have higher growth rates, altered cell cycle profile, decreased apoptosis, and are refractory to cytotoxic agents that induce oxidative stress. Therefore, the TrxR/Trx system has been identified as a valuable target for novel anti-cancer therapies. The crystal structure of human TrxR, indicates two redox-active sites, one with a Cys-Cys and one with a Cys-SeCys couple, which are excellent targets for structure-based inhibitor design. We hypothesized that rational-designed molecules containing a cyclic 1,2-disulfide unit as a pharmacophoric group will selectively block TrxR activity and will inhibit tumor growth in breast cancer. We synthesized a library of 40 cyclic disulfides derivatives connected to a variety of core structural units. We tested their inhibitory effects on the growth of the non-malignant breast cancer cell line MCF12A and a panel of breast cancer cell lines that included the non-tumorigenic cell line T47D, the tumorigenic cell lines MCF-7, ZR-75-1, BT-20, MDA-MB-468, SkBr-3 and the metastatic breast cancer cell lines BT-474 and MDA-MB-231. Each cell line was grown in its corresponding culture media and plated in 96-well plates. Afterward, cells were treated (in quadruplicates) with 10 μM of each compound for a 72 hour period. In order to measure toxicity, MTT assay was used. Our results showed that six of the forty compounds tested proved to inhibit cell proliferation in the eight breast cancer cell lines used. For instance, the cyclic disulfide SED-087 inhibited by 55 to 86% the cell proliferation of breast cancer cell lines tested. Moreover, five of the thiosulfinates decreased by more than 65% the cell growth of the breast cancer cell lines used in the screening: CPV-161 (74-94%), CPV-154 (73-93%), CPV-159 (80-99%), CPV-156 (72-95%) and CPV-164 (67-99%). However, only the thiosulfinate CPV-159 did not affect cell proliferation of the non-malignant cell line MCF-12A (3% growth inhibition), while all other compounds had cytotoxic effects on this cell line. We also determined the levels of TrxR in all cell lines using western blot analysis. Our results demonstrated that all cell lines used expressed TrxR. Our data strongly suggest that CPV-159 may be a novel candidate for further testing as anti-neoplastic agent. Current efforts are directed toward the elucidation of the mechanisms involved in the cellular response as a consequence of TrxR inhibition by thiosulfinate derivatives. Supported by RCMI #G12RR0305.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3714.