Inhibition of phosphodiestrase 9 induces cGMP accumulation and apoptosis in human breast cancer cell lines, MCF-7 and MDA-MB-468.

OBJECTIVES: Phosphodiesterase 9 (PDE9) is a major isoform of phosphodiesterase hydrolysing cGMP and plays a key role in proliferation of cells, their differentiation and apoptosis, via intracellular cGMP signalling. The study described here was designed to investigate expression, activity and apoptotic effect of PDE9 on human breast cancer cell lines, MCF-7 and MDA-MB-468. MATERIALS AND METHODS: Activity and expression of PDE9 were examined using colorimetric cyclic nucleotide phosphodiesterase assay and real-time RT-PCR methods respectively; cGMP concentration was also measured. MTT viability test, annexin V-FITC staining, Hoechst 33258 staining and caspase3 activity assay were used to detect apoptosis. RESULTS: Treatment of both cell lines with BAY 73-6691 lead to reduction in PDE9 mRNA expression, PDE9 cGMP-hydrolytic activity and elevation of the intracellular cGMP response. BAY 73-6691 significantly reduced cell proliferation in a dose- and time-dependent manner and caused marked increase in apoptosis through caspase3 activation. CONCLUSION: Our results revealed that BAY 73-6691 induced apoptosis in these breast cancer cell lines through the cGMP pathway. These data suggest that BAY 73-6691 could be utilized as an agent in treatment of breast cancer.

Adenosine and deoxyadenosine induces apoptosis in oestrogen receptor-positive and -negative human breast cancer cells via the intrinsic pathway.

In this study we have examined the cytotoxic effects of different concentrations of adenosine (Ado) and deoxyadenosine (dAdo) on human breast cancer cell lines. Ado and dAdo alone had little effect on cell cytotoxicity. However, in the presence of adenosine deaminase (ADA) inhibitor, EHNA, adenosine and deoxyadenosine led to significant growth inhibition of cells of the lines tested. Ado/EHNA and dAdo/EHNA-induced cell death was significantly inhibited by NBTI, an inhibitor of nucleoside transport, and 5'-amino-5'-deoxyadenosine, an inhibitor of adenosine kinase, but the effects were not affected by 8-phenyltheophylline, a broad inhibitor of adenosine receptors. The Ado/EHNA combination brought about morphological changes consistent with apoptosis. Caspase-9 activation was observed in MCF-7 and MDA-MB468 human breast cancer cell lines on treatment with Ado/EHNA or dAdo/EHNA, but, as expected, caspase-3 activation was only observed in MDA-MB468 cells. The results of the study, thus, suggest that extracellular adenosine and deoxyadenosine induce apoptosis in both oestrogen receptor-positive (MCF-7) and also oestrogen receptor-negative (MDA-MB468) human breast cancer cells by its uptake into the cells and conversion to AMP (dAMP) followed by activation of nucleoside kinase, and finally by the activation of the mitochondrial/intrinsic apoptotic pathway.

Competition of tamoxifen with thyroxine for TBG binding: ligand binding assay and computational data.

OBJECTIVE: Tamoxifen, a nonesteroidal antiesterogen, is widely used in the treatment of breast cancer. Recently, the effect of tamoxifen on thyroid function has caused considerable concern, yet the results of different studies are controversial and the precise mechanism of such influence is obscure. In view of the fact that some drugs such as furosemide, diclofenac and mefenamic acid, based on the structural similarities to thyroxine could compete for binding to thyroxine binding globulin (TBG) and appears that there are some structural similarities between tamoxifen and thyroxine, one can hypothesize that tamoxifen is also able to compete for TBG binding and thereby affecting thyroid function tests. DESIGN AND METHODS: In this study, we designed an in vitro binding assay as well as computational methods using MOPAC 7 package for evaluation of competitive potency of tamoxifen for TBG binding in comparison with well-known TBG competitors (including furosemide, mefenamic acid and diclofenac). RESULTS: The result of competition assay and Scatchard analysis revealed that tamoxifen does not bind to TBG at the T4 binding site, thus it is not a thyroxine competitor. Computational results also indicated that structural characteristics of tamoxifen are significantly different from those of T4 and its well-known competitors. CONCLUSION: In conclusion, the probability of competition between tamoxifen and T4 is ruled out by these results.