The phosphorylated prodrug FTY720 is a histone deacetylase inhibitor that reactivates ERα expression and enhances hormonal therapy for breast cancer.

Estrogen receptor-α (ERα)-negative breast cancer is clinically aggressive and does not respond to conventional hormonal therapies. Strategies that lead to re-expression of ERα could sensitize ERα-negative breast cancers to selective ER modulators. FTY720 (fingolimod, Gilenya), a sphingosine analog, is the Food and Drug Administration (FDA)-approved prodrug for treatment of multiple sclerosis that also has anticancer actions that are not yet well understood. We found that FTY720 is phosphorylated in breast cancer cells by nuclear sphingosine kinase 2 and accumulates there. Nuclear FTY720-P is a potent inhibitor of class I histone deacetylases (HDACs) that enhances histone acetylations and regulates expression of a restricted set of genes independently of its known effects on canonical signaling through sphingosine-1-phosphate receptors. High-fat diet (HFD) and obesity, which is now endemic, increase breast cancer risk and have been associated with worse prognosis. HFD accelerated the onset of tumors with more advanced lesions and increased triple-negative spontaneous breast tumors and HDAC activity in MMTV-PyMT transgenic mice. Oral administration of clinically relevant doses of FTY720 suppressed development, progression and aggressiveness of spontaneous breast tumors in these mice, reduced HDAC activity and strikingly reversed HFD-induced loss of estrogen and progesterone receptors in advanced carcinoma. In ERα-negative human and murine breast cancer cells, FTY720 reactivated expression of silenced ERα and sensitized them to tamoxifen. Moreover, treatment with FTY720 also re-expressed ERα and increased therapeutic sensitivity of ERα-negative syngeneic breast tumors to tamoxifen in vivo more potently than a known HDAC inhibitor. Our work suggests that a multipronged attack with FTY720 is a novel combination approach for effective treatment of both conventional hormonal therapy-resistant breast cancer and triple-negative breast cancer.

L-myo-Inositol 1-phosphate synthase from Entamoeba histolytica.

L-myo-Inositol 1-phosphate synthase (I-1-P synthase) catalyses the primary reaction for the synthesis of inositol in a variety of prokaryotes, eukaryotes and in the chloroplasts of algae and higher plants. Inositol is a precursor of essential macromolecules like membrane phospholipids, GPI anchor proteins and lipophosphoglycans, which play a determinant role in the pathogenesis of protozoan parasites such as Leishmania and Entamoeba. However, there is no report of I-1-P synthase or its gene from these organisms. The gene INO1 coding for this enzyme was first cloned from Saccharomyces cerevisiae and subsequently from several plants. Using molecular cloning techniques we have isolated and characterised the INO1 gene coding for the enzyme I-1-P synthase from Entamoeba histolytica. Simultaneously, we have purified and characterised the native enzyme from E. histolytica trophozoites and the cloned gene product from Escherichia coli. The gene product and the purified enzyme were both shown to be recognised by a heterologous anti-I-1-P synthase antibody from the phytoflagellate Euglena gracilis. Phylogenetic analysis of I-1-P synthase sequences from different eukaryotes suggest that it is highly conserved across species and the origin of this enzyme precedes the evolutionary divergence of modern eukaryotes.

L-myo-lnositol 1-Phosphate Synthase from Plant Sources (Characteristics of the Chloroplastic and Cytosolic Enzymes).

L-myo-inositol 1-phosphate synthase (EC 5.5.1.4) from cyanobacterial (Spirulina platensis), algal (Euglena gracilis), and higher plant (Oryza sativa, Vigna radiata) sources was purified to electrophoretic homogeneity, biochemically characterized, and compared. Both chloroplastic and cytosolic forms of the enzyme were detected in E. gracilis, O. sativa, and V. radiata, whereas only the cytosolic form was detected in streptomycin-bleached or chloroplastic mutants of E. gracilis and in S. platensis. Both the chloroplastic and cytosolic forms from different sources could be purified following the same three-step chromatographic protocol. L-myo-inositol 1-phosphate synthases purified from these different sources do not differ significantly with respect to biochemical and kinetic parameters except for the molecular mass of the chloroplastic and cytosolic native holoenzymes, which appear to be homotetrameric and homotrimeric associations of their constituent subunits, respectively. Monovalent and divalent cations, sugar alcohols, and sugar phosphates are inhibitory to the enzyme activity. N-ethylmaleimide inhibition of synthase activity could be protected by the combined presence of the substrate glucose-6-phosphate and cofactor NAD+. Antibody raised against the cytosolic enzyme from E. gracilis immunoprecipitates and cross-reacts with both chloroplastic and cytosolic forms from the other sources studied.