ABSTRACT
Advanced prostate cancer is not curable by current treatment strategies indicating a significant need for new chemotherapeutic options. Highly substituted ansa-titanocene compounds have shown promising cytotoxic activity in a range of cancers. The objectives of this study are to examine the effects of these titanocene compounds on prostate cancer cells. Prostate cell lines were treated with three novel titanocene compounds and compared to titanocene dichloride and cisplatin. Percent apoptosis, viability and cell cycle were assessed using propidium iodide DNA incorporation with flow cytometry. Cytochrome C was assessed by western blotting of mitochondrial and cytoplasmic fractions. Apoptosis Inducing Factor was assessed by confocal microscopy. These novel compounds induced more apoptosis compared to cisplatin in a dose dependent manner. Compound Y had the most significant effect on cell cycle and apoptosis. Despite the release of cytochrome C from the mitochondrial fraction there was no inhibition of apoptosis with the pan caspase inhibitor, ZVAD-FMK. AIF was shown to translocate from the cytosol to the nucleus mediating a caspase independent cell death. Bcl-2 over expressing PC-3 cells, which were resistant to cisplatin induced apoptosis, underwent apoptosis following treatment with all the titanocene compounds. This study demonstrates possible mechanisms by which these novel titanocene compounds can mediate their apoptotic effect in vitro. The fact that they can induce more apoptosis than cisplatin in advanced cancer cell lines would confer an advantage over cisplatin. They represent exciting new agents with future potential for the treatment of advanced prostate cancer.
Subject(s)
Antineoplastic Agents/pharmacology , Apoptosis/drug effects , Organometallic Compounds/pharmacology , Amino Acid Chloromethyl Ketones/pharmacology , Antineoplastic Agents/chemistry , Apoptosis Inducing Factor/metabolism , Blotting, Western , Cell Cycle/drug effects , Cell Line, Tumor , Cell Proliferation/drug effects , Cell Survival/drug effects , Cisplatin/pharmacology , Cysteine Proteinase Inhibitors/pharmacology , Cytochromes c/metabolism , Humans , Male , Molecular Structure , Organometallic Compounds/chemistry , Prostatic Neoplasms/metabolism , Prostatic Neoplasms/pathology , Proto-Oncogene Proteins c-bcl-2/genetics , Proto-Oncogene Proteins c-bcl-2/metabolism , TransfectionABSTRACT
Nitrogen monoxide (nitric oxide) generated endogenously has a variety of different properties. Among others it regulates blood pressure and transmission of nerve impulses, and has been shown to exert specific toxic effects, but also, paradoxically, to protect against various toxic substances. Recent studies suggest that NO* can serve as an antioxidant of the highly oxidizing ferryl myoglobin (MbFe(IV)=O), which has been proposed to be at least in part responsible for the oxidative damage caused by the reperfusion of ischemic tissues. In the present work we have determined the rate constant for the reaction between MbFe(IV)=O and NO* [(17.9+/-0.5)x10(6)M(-1)s(-1) at pH 7.5 and 20 degrees C] and we have shown that this reaction proceeds via the intermediate nitrito-metmyoglobin complex MbFe(III)ONO. Our results imply that this reaction is very likely to take place in vivo and might indeed represent a detoxifying pathway for both MbFe(IV)=O as well as NO*. Moreover, we have found that the rate of reaction of MbFe(IV)=O with nitrite is significantly lower (16+/-1 M(-1) s(-1) at pH 7.5 and 20 degrees C). Thus, this reaction probably plays a role only when NO* has been consumed completely and large concentrations of nitrite are still present. In contrast to the protecting role of NO*, the reaction with nitrite generates nitrogen dioxide which can contribute to tyrosine nitration. Indeed, we have demonstrated that nitrite can nitrate added tyrosine in the presence of iron(III) myoglobin and hydrogen peroxide.
