erved when combining DOX with the potently redox active Dp44mT-Cu complex . However, it does not explain why the combination of the Dp44mT-Fe complex that displays redox activity and DOX led to nearly additive activity, while Dp44mT and DOX resulted in synergism. The administration of Fe chelators has also been suggested following high-dose cyclophosphamide chemotherapy to manage increased serum non-transferrin-bound Fe that may be deleterious to health. The active cyclophosphamide metabolite, 4HC, covalently get DMXB-A attaches alkyl groups to the guanine N7 position and forms cross-links both between and within DNA strands. Our results for the combinations of all chelators with 4HC ranged from synergism at lower Fa values to antagonism at higher Fa values. Clearly, the most effective combinations in this study were observed with TMX. All of the chelators were synergistic using MCF-7 cells, except DFO, which showed antagonistic effects. Furthermore, TMX showed relatively constant dependence of CI on Fa and displayed increasing synergism on two estrogen receptor-expressing cell lines with increasing dose of SIH, NHAPI or Dp44mT. The combination of NHAPI and Dp44mT with TMX using the estrogen receptor negative MDA-MB-231 cell line was constantly PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19638209 antagonistic throughout the entire Fa scale, potentially due to the lack of the TMX target in these cells. Importantly, TMX is mostly indicated in breast cancer patients as a chemopreventive agent during the post-treatment period to prevent recurrence, as it competes with estradiol for estrogen receptor binding. TMX also decreases the production of transforming growth factor b and insulin-like growth factor 1 that can act to stimulate oncogenesis. Interestingly, MCF-7 cells have been reported to synthesize their own transferrin in an estrogen-dependent manner that may act in an autocrine fashion to stimulate Fe uptake by tumor cells, and thus, proliferation. Hence, the synergism between TMX and Fe chelators may be caused by potentiation of Fe depletioninduced by TMX blocking estrogen-induced Tf synthesis and also direct Fe-binding by the ligands. Synergism between TMX and inositol hexaphosphate, a naturally-occurring polyphosphorylated carbohydrate with Fe-chelating properties, has also been previously reported in MCF-7 cells. Of the combinations of chelators with chemotherapeutics examined in the current study, the most promising combination particularly in terms of maximizing efficacy and minimizing 
the PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19640190 problem of cardiotoxicity, was considered to be NHAPI or its Fe complex with TMX. This combination was utilized due to the marked synergism observed and that NHAPI in contrast to Dp44mT does not appear to result in cardiotoxicity. The combinations of NHAPI or the NHAPI-Fe complex with TMX resulted in G1-S cell cycle arrest, and their synergism was further confirmed by the cellular morphology analyses and DYm measurements. In regard to these latter studies on mitochondrial membrane potential, it is notable that mitochondria are of central importance in apoptotic cell death as well as the major sites of Fe metabolism, being critical for heme and iron-sulfur cluster synthesis. Hence, the marked effect of the NHAPI and TMX combination on this latter organelle was important to assess and demonstrated that it was potently affected. Further detailed studies on the effect of these agents on mitochondrial metabolism are critical to further investigate, as it appears to be a key target. In conclusion, this is the fi