Ferrozoles: Ferrocenyl derivatives of letrozole with dual effects as potent aromatase inhibitors and cytostatic agents

In the treatment of hormone-dependent cancers, aromatase inhibitors (AI) are receiving increased attention due to some undesirable effects such as the risk of endometrial cancer and thromboembolism of SERMs (selective estrogen receptor modulators). Letrozole is the most active AI with 99% aromatase inhibition. Unfortunately, this compound also exhibits some adverse effects such as hot flashes and fibromyalgias. Therefore, there is an urgent need to explore new types of AIs that retain the same-or even increased-antitumor ability. Inspired by the letrozole structure, a set of new derivatives has been synthesized that include a ferrocenyl moiety and different heterocycles. The derivative that contains a benzimidazole ring, namely compound 6, exhibits a higher aromatase inhibitory activity than letrozole and it also shows potent cytostatic behavior when compared to other well-established aromatase inhibitors, as demonstrated by dose-response, cell cycle, apoptosis and time course experiments. Furthermore, 6 promotes the inhibition of cell growth in both an aromatase-dependent and -independent fashion, as indicated by the study of A549 and MCF7 cell lines. Molecular docking and molecular dynamics calculations on the interaction of 6 or letrozole with the aromatase binding site revealed that the ferrocene moiety increases the van der Waals and hydrophobic interactions, thus resulting in an increase in binding affinity. Furthermore, the iron atom of the ferrocene fragment can form a metal-acceptor interaction with a propionate fragment, and this results in a stronger coupling with the heme group-a possibility that is consistent with the strong aromatase inhibition of 6.

Effect of the aniline fragment in Pt(II) and Pt(IV) complexes as anti-proliferative agents. Standard reduction potential as a more reliable parameter for Pt(IV) compounds than peak reduction potential

The problems of resistance and side effects associated with cisplatin and other chemotherapeutic drugs have boosted research aimed at finding new compounds with improved properties. The use of platinum(IV) prodrugs is one alternative, although there is some controversy regarding the predictive ability of the peak reduction potentials. In the work described here a series of fourteen chloride Pt(II) and Pt(IV) compounds was synthesised and fully characterised. The compounds contain different bidentate arylazole heterocyclic ligands. Their cytotoxic properties against human lung carcinoma (A549), human breast carcinoma (MCF7) and human colon carcinoma (HCT116 and HT29) cell lines were studied. A clear relationship between the type of ligand and the anti-proliferative properties was found, with the best results obtained for the Pt(II) compound that contains an aniline fragment, (13), thus evidencing a positive effect of the NH₂ group. Stability and aquation studies in DMSO, DMF and DMSO/water mixtures were carried out on the active complexes and an in-depth analysis of the two aquation processes, including DFT analysis, of 13 was undertaken. It was verified that DNA was the target and that cell death occurred by apoptosis in the case of 13. Furthermore, the cytotoxic derivatives did not exhibit haemolytic activity. The reduction of the Pt(IV) compounds whose Pt(II) congeners were active was studied by several techniques. It was concluded that the peak reduction potential was not useful to predict the ability for reduction. However, a correlation between the cytotoxic activity and the standard reduction potential was found.

Role of the non-canonical notch ligand delta-like protein 1 in hormone-producing cells of the adult male mouse pituitary

To better understand the role of the non-canonical Notch ligand delta-like protein 1 (DLK1), in hormone-producing cells, we studied the cell distribution and subcellular localisation of DLK1 in the pituitary of male adult 129/SvJ mice, and analysed the variations in the hormone-producing cells associated with the lack of this gene in Dlk1 knockout mice. The results obtained showed the presence of DLK1-immunoreactive (ir) cells in all hormone-producing cells of the anterior pituitary. Immunoelectron microscopy showed DLK1-ir in the rough endoplasmic reticulum and inside secretory vesicles, suggesting that DLK1 is released together with pituitary hormones. Moreover, we found that prolactin (PRL)-DLK1-ir cells are in intimate contact with follicle-stimulating hormone (FSH)-ir-DLK1-negative cells. In Dlk1 knockout mice, we detected a significantly lower number of gowth hormone (GH)-ir cells, a reduction in the FSH and PRL immunostaining intensity, and a significant decrease in FSH mRNA expression compared to wild-type mice. An increase in pituitary GH mRNA expression and serum leptin levels was also found. These findings provide evidence supporting several regulatory functions of DLK1 in the pituitary gland.

Specific regions of the extracellular domain of dlk, an EGF-like homeotic protein involved in differentiation, participate in intramolecular interactions

The level of expression of dlk, an EGF-like protein possessing six EGF-like repeats in its extracellular region, is critical for 3T3-L1 fibroblasts to differentiate into adipocytes in response to IGF1. The mechanism of action of dlk is not well understood, but its localization on the cell membrane suggests that dlk may function as a receptor, as a ligand or as a regulatory protein modulating the binding, the signaling, or the expression of other molecules involved in cell differentiation and growth. In this work, we demonstrate, by using the Yeast Two-Hybrid system, that dlk interacts with itself through specific regions of its extracellular domain. The strongest interactions were observed between specific EGF-like repeats and between a non EFG-like region where unknown proteases act to generate soluble forms of dlk. These observations suggest that the interaction between two membrane dlk molecules belonging to the same or to different cells, or the interaction between soluble and membrane dlk variants, may be important to regulate dlk function.

Heterologous expression of the Phycomyces blakesleeanus phytoene dehydrogenase gene (carB) in Mucor circinelloides

A phytoene dehydrogenase-deficient mutant of Mucor circinelloides accumulating only phytoene was transformed with the gene encoding the corresponding enzyme (carB gene) of Phycomyces blakesleeanus. Carotenoids derived from phytoene were detected in the transformants showing that the P. blakesleeanus carB gene complements the M. circinelloides carB mutation. These newly formed carotenoids accumulated in low quantities, indicating that functional complementation was poor. carB mRNA molecules correctly transcribed were detected in the transformants, but they represented a small proportion of the total population of carB-derived mRNAs, mostly constituted by truncated transcripts and by transcripts longer than the transcript that is functional in Phycomyces. These results showed that the P. blakesleeanus carB gene was expressed in M. circinelloides and suggested that the poor complementation observed was owing, at least in part, to the lack of specificity in the recognition of the transcription initiation and termination signals of the P. blakesleeanus carB gene by the M. circinelloides transcriptional machinery.

Notch-1 expression levels in 3T3-L1 cells influence ras signaling and transformation by oncogenic ras

Notch proteins participate in interactions between several cell types involved on the specification of numerous cell fates during development. We previously showed that enforced downregulation of Notch-1 expression prevented adipogenesis of 3T3-L1 cells. Since adipogenesis of 3T3-L1 cells can be induced by oncogenic ras, we studied whether this was also the case in 3T3-L1 cells with decreased levels of Notch-1 expression. We found that oncogenic ras induces transformation and not differentiation of 3T3-L1 cells with diminished levels of Notch-1. This result suggests that Notch-1 is implicated in the interpretation of signals leading to activation of p21 Ras.

Adipocyte differentiation is modulated by secreted delta-like (dlk) variants and requires the expression of membrane-associated dlk

Previous studies demonstrate that the delta-like (dlk) and preadipocyte factor 1 (Pref-1) genes encode similar proteins. Pref-1 is downregulated during adipocyte differentiation, and expression of ectopic Pref-1 inhibits adipogenesis. We explored whether dlk functions similarly to Pref-1 and studied the role of alternately spliced dlk variants encoding membrane-associated or -secreted forms. We also studied whether enforced downregulation of dlk/Pref-1 may enhance the differentiation response of non-committed cells. Ectopic expression of a potentially secreted dlk variant, conditioned media from dlk expressing cells or several individual epidermal-growth-factor-dlk peptides inhibited 3T3-L1 differentiation. This demonstrates that dlk and Pref-1 are functionally equivalent. dlk gene mRNA encoding for secreted variants decreased much faster than total dlk gene mRNA during differentiation of 3T3-L1 cells. In fact, total dlk or membrane-associated dlk protein expression increased during the first hours of differentiation. Cells sorted for lowest levels of dlk protein diminished or lost their ability to differentiate. These data suggest that membrane and secreted dlk protein variants play opposite roles in the control of adipogenesis. In addition, enforced downregulation of dlk protein expression in the weakly adipogenic Balb/c 3T3 cell line dramatically enhanced adipogenesis in response to insulin. These results indicate that dlk protein not only participates in processes leading to inhibition of adipogenesis but that the control of its expression and different spliced variants is essential for the adipogenic response to extracellular signals.

Modulated expression of the epidermal growth factor-like homeotic protein dlk influences stromal-cell-pre-B-cell interactions, stromal cell adipogenesis, and pre-B-cell interleukin-7 requirements

A close relationship exists between adipocyte differentiation of stromal cells and their capacity to support hematopoiesis. The molecular basis for this is unknown. We have studied whether dlk, an epidermal growth factor-like molecule that intervenes in adipogenesis and fetal liver hematopoiesis, affects both stromal cell adipogenesis and B-cell lymphopoiesis in an established pre-B-cell culture system. Pre-B-cell cultures require both soluble interleukin-7 (IL-7) and interactions with stromal cells to promote cell growth and prevent B-cell maturation or apoptosis. We found that BALB/c 3T3 fibroblasts express dlk and function as stromal cells. Transfection of these cells with antisense dlk decreased dlk expression and increased insulin-induced adipocytic differentiation. When antisense transfectants were used as stroma, IL-7 was no longer required to support the growth of pre-B cells and prevent maturation or apoptosis. Antisense dlk transfectants of S10 stromal cells also promoted pre-B-cell growth in the absence of IL-7. These results show that modulation of dlk on stromal cells can influence their adipogenesis and the IL-7 requirements of the pre-B cells growing in contact with them. These results indicate that dlk influences differentiation signals directed both to the stromal cells and to the lymphocyte precursors, suggesting that dlk may play an important role in the bone marrow hematopoietic environment.

Notch-1 controls the expression of fatty acid-activated transcription factors and is required for adipogenesis

Notch, a transmembrane receptor member of the homeotic epidermal growth factor-like family of proteins, participates in cell-to-cell signaling to control cell fate during development. Activated Notch-1 constructs lacking the extracellular region prevent differentiation of several mammalian cells in vitro. This effect, however, bypasses the normal mechanisms of cell-to-cell interactions in which Notch-1 participates. We investigated the role of Notch-1 in the hormone-induced adipocyte differentiation of 3T3-L1 fibroblasts, a paradigmatic model of adipogenesis that requires cell-to-cell contact. Unlike other differentiation models, Notch-1 expression and function were necessary conditions for adipogenesis. Impaired Notch-1 expression by antisense Notch-1 constructs prevented adipocyte differentiation. Strategies aimed at blocking putative Notch/ligand interactions also blocked adipogenesis, implicating Notch as a critical molecule in cell-to-cell signaling necessary for differentiation. Inhibition of Notch-1 expression or function decreased the expression of peroxisomal proliferator-activated receptors delta and gamma, transcription factors that control adipocyte differentiation and that are up-regulated at cell confluence. These results implicate Notch in the commitment of 3T3-L1 cells to undergo adipogenesis by controlling the expression of the principal regulators of this process.

Complementation analysis of carotenogenic mutants of Mucor circinelloides

Mutants of the filamentous fungus Mucor circinelloides altered in the synthesis of beta-carotene (genotype car) have been isolated by direct inspection of the color shown by the colonies derived from mutagenized spores. The mutants were analyzed for the carotenoid content in darkness and light and studied with respect to complementation in heterokaryons made by spheroplast fusion. The results revealed the existence of at least four complementation groups. The carB mutants are white and accumulate phytoene. The carR mutants are red and accumulate lycopene. The carP mutants are most likely disturbed in the synthesis of phytoene: two of them are white and do not accumulate carotenoids; another carP mutant is yellowish, probably because it is leaky. There are three yellowish mutants which belong to one or more complementation groups different from carB, carR, and carP. Two white mutants obtained in a single mutagenization step failed to complement with the carR and the carP mutants. The wild-type and the carB and carR mutants tested for M. circinelloides showed similar photoinduction.

The phytoene dehydrogenase gene of Phycomyces: regulation of its expression by blue light and vitamin A

By using a polymerase chain reaction based cloning strategy we isolated the gene (carB) encoding the enzyme phytoene dehydrogenase from Phycomyces blakesleeanus. The deduced protein, a 583 residue polypeptide, showed great similarity to carotenoid dehydrogenases from other fungi and bacteria, especially in the amino-terminal region. The main conserved regions found in other phytoene dehydrogenases, which are thought to be essential for the enzymatic activity, are present in the sequence from Phycomyces. Heterologous expression of the Phycomyces gene in Escherichia coli showed that, as in other fungi and bacteria, a single polypeptide catalyzes the four dehydrogenations that convert phytoene to lycopene. RNA measurements indicated that the level of expression of the phytoene dehydrogenase gene in wild-type mycelia increased in response to blue light. The kinetics of this increase in transcription of the gene after blue light induction (0.1 and 0.4 W/m2) exhibit a two-step (biphasic) dependence on fluence rate, suggesting that there could be two separate components involved in the reception of the low and high blue light signal. The presence of vitamin A in the medium stimulated transcript accumulation in the wild type and in some carotenogenic mutant strains. Diphenylamine, a phytoene dehydrogenase inhibitor, did not affect the level of transcription of this gene.

Carotenoid biosynthesis in wild type and mutant strains of Mucor circinelloides

Carotenoid biosynthesis in wild type Mucor circinelloides has been investigated and the biochemical characterisation of the MS1 and MS9 mutant strains, impaired in carotenoid formation, carried out. In liquid cultures, all strains produced carotenoids (mainly beta-carotene, but also xi-carotene, lycopene and gamma-carotene) at the onset of stationary phase of growth. Carotenogenesis was light dependent. In liquid cultures carotenoid formation in wild type was affected by diphenylamine, which prevented desaturation, nicotine, resulting in reduced carotenoid levels, but CPTA caused an increase in the total carotenoid content but a reduced beta-carotene level, with the accumulation of lycopene and gamma-carotene. The mutant strains MS1 and MS9 contained only 5.0 and 11.5% of wild type carotenoid levels, respectively. Cell extracts of light-grown mycelia, incubated with 3(R)-[2-14C] mevalonic acid, produced beta-carotene, but incorporations into carotenoids were substantially reduced in the cell extracts of MS1 and MS9. Analysis of prenyl diphosphate intermediates indicated that, compared to wild type, geranylgeranyl diphosphate accumulated in MS1. MS9 extracts produced a larger amount of prenyl phosphates and a more even distribution of radioactivity from mevalonic acid into farnesyl and geranylgeranyl diphosphates. Squalene and long chain prenyl phosphates were formed by the cell extracts of all strains. It is proposed that the MS1 strain possesses a mutation in a gene responsible for phytoene formation, whilst a regulatory mutation, affecting prenyl transferase activities has occurred in MS9.