Gerardo Burton

Development of β-Lapachone Prodrugs for Therapy Against Human Cancer Cells with Elevated NAD(P)H:Quinone Oxidoreductase 1 Levels

β-Lapachone, an o-naphthoquinone, induces a novel caspase- and p53-independent apoptotic pathway dependent on NAD(P)H:quinone oxidoreductase 1 (NQO1). NQO1 reduces β-lapachone to an unstable hydroquinone that rapidly undergoes a two-step oxidation back to the parent compound, perpetuating a futile redox cycle. A deficiency or inhibition of NQO1 rendered cells resistant to β-lapachone. Thus, β-lapachone has great potential for the treatment of specific cancers with elevated NQO1 levels (e.g., breast, non–small cell lung, pancreatic, colon, and prostate cancers). We report the development of mono(arylimino) derivatives of β-lapachone as potential prodrugs. These derivatives are relatively nontoxic and not substrates for NQO1 when initially diluted in water. In solution, however, they undergo hydrolytic conversion to β-lapachone at rates dependent on the electron-withdrawing strength of their substituent groups and pH of the diluent. NQO1 enzyme assays, UV-visible spectrophotometry, high-performance liquid chromatography-electrospray ionization-mass spectrometry, and nuclear magnetic resonance analyses confirmed and monitored conversion of each derivative to β-lapachone. Once converted, β-lapachone derivatives caused NQO1-dependent, μ-calpain-mediated cell death in human cancer cells identical to that caused by β-lapachone. Interestingly, coadministration of N-acetyl-l-cysteine, prevented derivative-induced cytotoxicity but did not affect β-lapachone lethality. Nuclear magnetic resonance analyses indicated that prevention of β-lapachone derivative cytotoxicity was the result of direct modification of these derivatives by N-acetyl-l-cysteine, preventing their conversion to β-lapachone. The use of β-lapachone mono(arylimino) prodrug derivatives, or more specifically a derivative converted in a tumor-specific manner (i.e., in the acidic local environment of the tumor tissue), should reduce normal tissue toxicity while eliciting tumor-selective cell killing by NQO1 bioactivation.

Live Cell Imaging Unveils Multiple Domain Requirements for In Vivo Dimerization of the Glucocorticoid Receptor

The glucocorticoid receptors oligomerization state is revealed to not correlate with its activity; this challenges the current prevailing view that this state defines its transcriptional activity.

Antiproliferative activity of synthetic naphthoquinones related to lapachol. First synthesis of 5-hydroxylapachol

A series of 5-hydroxy-1,4-naphthoquinones analogues was synthesized from juglone (6) and their antiproliferative activity against a representative panel of six human solid tumor cell lines has been investigated. The 2,5-dihydroxy-3-(3-methylbut-2-enyl)naphthalene-1,4-dione (4) and 2,3-dihydro-5-hydroxy-2-(prop-1-en-2-yl)naphtho[2,3-b]furan-4,9-dione (27) were the most potent antiproliferative agents with GI(50) values of 0.42-8.1 and 0.80-2.2microM, respectively. The results provide insight into the correlation between some structural properties of 5-hydroxynaphthoquinones and their antiproliferative activity.

Withanolides and Related Steroids

Since the isolation of the first withanolides in the mid-1960s, over 600 new members of this group of compounds have been described, with most from genera of the plant family Solanaceae. The basic structure of withaferin A, a C28 ergostane with a modified side chain forming a δ-lactone between carbons 22 and 26, was considered for many years the basic template for the withanolides. Nowadays, a considerable number of related structures are also considered part of the withanolide class; among them are those containing γ-lactones in the side chain that have come to be at least as common as the δ-lactones. The reduced versions (γ and δ-lactols) are also known. Further structural variations include modified skeletons (including C27 compounds), aromatic rings and additional rings, which may coexist in a single plant species. Seasonal and geographical variations have also been described in the concentration levels and types of withanolides that may occur, especially in the Jaborosa and Salpichroa genera, and biogenetic relationships among those withanolides may be inferred from the structural variations detected. Withania is the parent genus of the withanolides and a special section is devoted to the new structures isolated from species in this genus. Following this, all other new structures are grouped by structural types.

Thyroid autoregulation. Inhibition of goiter growth and of cyclic AMP formation in rat thyroid by iodinated derivatives of arachidonic acid

Thyroid autoregulation has been related to intraglandular content of an unknown putative iodocompund. Data from different laboratories have shown that the thyroid is capable of producing different iodolipids, including iodinated derivatives of arachidonic acid; such as 5-hydroxy-6-iodo-8, 11, 14-eicosatrienoic-δ-lactone (IL-δ). Previous results from our laboratory showed that a semi-purified preparation of iodinated arachidonic acid exerts an inhibitory action in vitro on calf thyroid. In the present studies three purified iodinated derivatives of arachidonic acid were synthetized: IL-δ; 14-io-do-15-hydroxy-5, 8, 11-eicosatrienoic acid (I-OH-A) and its corresponding ω-lactone (IL-ω). Their action on MMI-induced goiter was studied in rats. Administration of MMI to rats during 10 days increased thyroid weight by 124%. This effect was significantly inhibited by the simultaneous injection of 5 μg/day of I-OH-A (57% inhibition of MMI action), IL-W (39%), IL-δ (33%) and T3 (95%), while arachidonic acid was without action. No inhibition was found with 1.25 μg/day KI, a dose equivalent to that which could be originated from total dehalogenation of the iodocompounds. These results support the idea that these iodocompounds have an intrinsic biologic activity and that there is a correlation between action and chemical structure. Serum TSH was increased around 15–20 fold after MMI administration. Chronic or acute injection of I-OH-A failed to alter TSH levels, indicating that this iodocompound exerts its action directly on the gland, without altering TSH concentration. Serum T3 and T4 were significantly decreased by MMI and addition of I-OH-A, did not change these values. Thyroidal cyclic AMP content was measured in the rats. Treatment with MMI increased cAMP, while injection of I-OH-A significantly decreased this action. These data suggest that this iodocompound acts at the step of cyclic AMP formation. Dose-response studies showed parallel decreases in gland weight, DNA and cAMP contents after I-OH-A treatment. The lowest effective dose was 3 μg/day. The present data demonstrate, for the first time, that some iodinated derivatives or arachidonic acid mimic the action of iodine on thyroid growth and cyclic AMP production and support the hypothesis that they may play a role in the autoregulatory mechanism.

A ring-D aromatic withanolide from Salpichroa origanifolia

Abstract From Salpichroa origanifolia plants, a new withanolide (20 S ,22 R ,24 S ,25 S ,26 R )-5,6α: 22,26: 24,25-triepoxy-26-hydroxy-17(13 → 18) abeo -5α-ergosta-2,13,15,17-tetraen-1-one was isolated and characterized by spectroscopic and chemical methods.

β-Lapachone analogs with enhanced antiproliferative activity

In this study, we describe the synthesis of a series of α- and β-lapachone containing hydroxyl or methoxyl groups on the benzene ring, by means of the selective acid promoted cyclization of the appropriate lapachol analog. The evaluation of the antiproliferative activity in human solid tumor cell lines provided 7-hydroxy-β-lapachone as lead with enhanced activity over the parent drug β-lapachone. Cell cycle studies, protein expression experiments, and reactive oxygen species analysis revealed that, similarly to β-lapachone, ROS formation and DNA damage are critical factors in the cellular toxicity of 7-hydroxy-β-lapachone.

Insights on Glucocorticoid Receptor Activity Modulation through the Binding of Rigid Steroids

Background The glucocorticoid receptor (GR) is a transcription factor that regulates gene expression in a ligand-dependent fashion. This modular protein is one of the major pharmacological targets due to its involvement in both cause and treatment of many human diseases. Intense efforts have been made to get information about the molecular basis of GR activity. Methodology/Principal Findings Here, the behavior of four GR-ligand complexes with different glucocorticoid and antiglucocorticoid properties were evaluated. The ability of GR-ligand complexes to oligomerize in vivo was analyzed by performing the novel Number and Brightness assay. Results showed that most of GR molecules form homodimers inside the nucleus upon ligand binding. Additionally, in vitro GR-DNA binding analyses suggest that ligand structure modulates GR-DNA interaction dynamics rather than the receptors ability to bind DNA. On the other hand, by coimmunoprecipitation studies we evaluated the in vivo interaction between the transcriptional intermediary factor 2 (TIF2) coactivator and different GR-ligand complexes. No correlation was found between GR intranuclear distribution, cofactor recruitment and the homodimerization process. Finally, Molecular determinants that support the observed experimental GR LBD-ligand/TIF2 interaction were found by Molecular Dynamics simulation. Conclusions/Significance The data presented here sustain the idea that in vivo GR homodimerization inside the nucleus can be achieved in a DNA-independent fashion, without ruling out a dependent pathway as well. Moreover, since at least one GR-ligand complex is able to induce homodimer formation while preventing TIF2 coactivator interaction, results suggest that these two events might be independent from each other. Finally, 21-hydroxy-6,19-epoxyprogesterone arises as a selective glucocorticoid with potential pharmacological interest. Taking into account that GR homodimerization and cofactor recruitment are considered essential steps in the receptor activation pathway, results presented here contribute to understand how specific ligands influence GR behavior.

Sesquiterpene lactone variability in Parthenium hysterophorus L.

A population of Parthenium hysterophorus collected in Salta Argentina afforded two ambrosanolides, 2beta-hydroxycoronopilin and 1alpha,2beta,4beta-trihydroxypseudoguaian-6beta,12-olide, as well as five known others. Plants of the fructification from those transplanted from the Puna Argentina at 1200 m over the sea level produced hymenin.

Chemistry and bioactivity of withanolides from south american Solanaceae

Since the isolation of withaferin A in 1965 over 300 withanolides have been described, largely from genera belonging to the Solanaceae. Although until the mid eighties most of the withanolides appeared to adhere to the basic structure of withaferin A, nowadays a considerable number of withanolides and withanolide related compounds are known, which present modified skeletons, aromatic rings, additional rings, etc., posing challenging problems of structure elucidation. Many of these structures coexist in the plants with “normal” withanolides and thus allow us to infer the biogenetic relationships among them and the transformations they suffer in the plant. As a further bonus, several species show marked seasonal and geographical variations in the amount and type of withanolides present, thus adding to the structural diversity. The latter is particularly noteworthy in (but not restricted to) species of the Jaborosa and Salpichroa genera. In recent years these genera, both native to South America, have rendered several novel withanolide types. Exodeconus, Dunalia, Deprea and Vassobia are other southamerican genera where unusual structures have also been found. Recently, some of the withanolides isolated from these plants have shown interesting biological activities as cancer chemopreventive agents (inductors of quinone reductase), as feeding deterrants for several insects, and displaying selective phytotoxicity towards monocotiledoneous and dicotiledoneous species. Trypanocidal and leishmanicidal activities have also been reported.