Jakub Chlebek

Isoquinoline alkaloids as a novel type of AKR1C3 inhibitors

AKR1C3 is an important human enzyme that participates in the reduction of steroids and prostaglandins, which leads to proliferative signalling. In addition, this enzyme also participates in the biotransformation of xenobiotics, such as drugs and procarcinogens. AKR1C3 is involved in the development of both hormone-dependent and hormone-independent cancers and was recently demonstrated to confer cell resistance to anthracyclines. Because AKR1C3 is frequently upregulated in various cancers, this enzyme has been suggested as a therapeutic target for the treatment of these pathological conditions. In this study, nineteen isoquinoline alkaloids were examined for their ability to inhibit a recombinant AKR1C3 enzyme. As a result, stylopine was demonstrated to be the most potent inhibitor among the tested compounds and exhibited moderate selectivity towards AKR1C3. In the follow-up cellular studies, stylopine significantly inhibited the AKR1C3-mediated reduction of daunorubicin in intact cells without considerable cytotoxic effects. This inhibitor could therefore be used as a model AKR1C3 inhibitor in research or evaluated as a possible therapeutic anticancer drug. Furthermore, based on our results, stylopine can serve as a model compound for the design and future development of structurally related AKR1C3 inhibitors.

Flavones Inhibit the Activity of AKR1B10, a Promising Therapeutic Target for Cancer Treatment.

AKR1B10 is an NADPH-dependent reductase that plays an important function in several physiological reactions such as the conversion of retinal to retinol, reduction of isoprenyl aldehydes, and biotransformation of procarcinogens and drugs. A growing body of evidence points to the important role of the enzyme in the development of several types of cancer (e.g., breast, hepatocellular), in which it is highly overexpressed. AKR1B10 is regarded as a therapeutic target for the treatment of these diseases, and potent and specific inhibitors may be promising therapeutic agents. Several inhibitors of AKR1B10 have been described, but the area of natural plant products has been investigated sparingly. In the present study almost 40 diverse phenolic compounds and alkaloids were examined for their ability to inhibit the recombinant AKR1B10 enzyme. The most potent inhibitors-apigenin, luteolin, and 7-hydroxyflavone-were further characterized in terms of IC50, selectivity, and mode of action. Molecular docking studies were also conducted, which identified putative binding residues important for the interaction. In addition, cellular studies demonstrated a significant inhibition of the AKR1B10-mediated reduction of daunorubicin in intact cells by these inhibitors without a considerable cytotoxic effect. Although these compounds are moderately potent and selective inhibitors of AKR1B10, they constitute a new structural type of AKR1B10 inhibitor and may serve as a template for the development of better inhibitors.

In Vitro Inhibitory Effects of 8-O-Demethylmaritidine and Undulatine on Acetylcholinesterase and Their Predicted Penetration across the Blood-Brain Barrier.

Alzheimers disease is the most common cause of dementia. Currently, acetylcholinesterase (AChE) inhibition is the most widely used therapeutic treatment. A large number of naturally occurring compounds have been found to inhibit AChE. In this report the mechanism of AChE inhibition of two Amaryllidaceae alkaloids, 8-O-demethylmaritidine (1) and undulatine (2), and their possible penetration across the blood-brain barrier have been studied. Both compounds act via a mixed inhibition mechanism. Based on the parallel artificial permeation assay (PAMPA) for the prediction of blood-brain barrier (BBB) penetration, only 2 should be able to cross the BBB by passive permeation.

Isoquinoline alkaloids as prolyl oligopeptidase inhibitors.

Prolyl oligopeptidase is a cytosolic serine peptidase that hydrolyses proline-containing peptides at the carboxy terminus of proline residues. It has been associated with schizophrenia, bipolar affective disorder, and related neuropsychiatric disorders and therefore may have important clinical implications. Thirty-one isoquinoline alkaloids of various structural types, previously isolated in our laboratory, were screened for their ability to inhibit prolyl oligopeptidase. Promising results have been showed by alkaloids californidine (IC50=55.6±3.5 μM), dihydrosanquinarine (IC50=99.1±7.6 μM), corypalmine (IC50=128.0±10.5 μM) and N-methyllaurotetanine (IC50=135.0±11.7 μM).

Natural products as potential human ether-a-go-go-related gene channel inhibitors - screening of plant-derived alkaloids.

Inhibition of the cardiac human ether-a-go-go-related gene channel is a problematic off-target pharmacological activity and, hence, a major safety liability in clinical practice. Several non-cardiac drugs have been restricted in their use, or even removed from the market due to this potentially fatal adverse effect. Comparatively little is known about the human ether-a-go-go-related gene inhibitory potential of plant-derived compounds. In the course of an ongoing human ether-a-go-go-related gene in vitro study, a total of 32 structurally diverse alkaloids of plant origin as well as two semi-synthetically obtained protoberberine derivatives were screened by means of an automated Xenopus oocyte assay. Protopine, (+)-bulbocapnine, (+)-N-methyllaurotetanine, (+)-boldine, (+)-chelidonine, (+)-corynoline, reserpine, and yohimbine reduced the human ether-a-go-go-related gene current by ≥ 50% at 100 µM, and were submitted to concentration-response experiments. Our data show that some widely occurring plant-derived alkaloids carry a potential risk for human ether-a-go-go-related gene toxicity.

Application of BACE1 immobilized enzyme reactor for the characterization of multifunctional alkaloids from Corydalis cava (Fumariaceae) as Alzheimer's disease targets

In our ongoing study focused on Corydalis cava (Fumariaceae), used in folk medicine in the treatment of memory dysfunctions, we have investigated fifteen previously isolated alkaloids for their potential multifunctional activity on Alzheimers disease (AD) targets. Determination of ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) inhibition was carried out using a BACE1-Immobilized Enzyme Reactor (IMER) by validating the assay with a multi-well plate format Fluorescence Resonance Energy Transfer (FRET) assay. Seven alkaloids out of fifteen were found to be active, with (-)-corycavamine (3) and (+)-corynoline (5) demonstrating the highest BACE1 inhibition activity, in the micromolar range, in a concentration dependent manner. BACE1-IMER was found to be a valid device for the fast screening of inhibitors and the determination of their potency. In a permeation assay (PAMPA) for the prediction of blood-brain barrier (BBB) penetration, the most active compounds, (-)-corycavamine (3) and (+)-corynoline (5), were found to be able to cross the BBB. Not all compounds showed activity against glycogen synthase kinase-3β (GSK-3β) and casein kinase-1δ (CK-1δ). On the basis of the reported results, we found that some C. cava alkaloids have multifunctional activity against AD targets (prolyl oligopeptidase, cholinesterases and BACE1). Moreover, we tried to elucidate the treatment effectivity (rational use) of its extract in memory dysfunction in folk medicine.

Isoquinoline Alkaloids from Fumaria officinalis L. and Their Biological Activities Related to Alzheimer's Disease

Two new isoquinoline alkaloids, named fumaranine (2) and fumarostrejdine (10), along with 18 known alkaloids were isolated from aerial parts of Fumaria officinalis. The structures of the isolated compounds were elucidated on the basis of spectroscopic analyses and by comparison with literature data. The absolute configuration of the new compound 2 was determined by comparing its circular dichroism spectra with those of known analogs. Compounds isolated in sufficient amounts were evaluated for their acetylcholinesterase, butyrylcholinesterase, prolyl oligopeptidase (POP), and glycogen synthase kinase‐3β inhibitory activities. Parfumidine (8) and sinactine (15) exhibited potent POP inhibition activities (IC50 99±5 and 53±2 μM, resp.).

Isolation of Amaryllidaceae alkaloids from Nerine bowdenii W. Watson and their biological activities

Twenty-two isoquinoline alkaloids (1–22) were isolated from fresh bulbs of Nerine bowdenii (Amaryllidaceae) by standard chromatographic methods. The chemical structures were elucidated by MS, and 1D and 2D NMR spectroscopic analyses, and by comparison with literature data. 6-O-Demethylbelladine (11) and 4′-O-demethylbelladine (12) are reported here for the first time. Compounds isolated in sufficient amounts were evaluated for their acetylcholinesterase, and butyrylcholinesterase inhibition activity using Ellmans method. In the prolyl oligopeptidase assay, Z-Gly-Pro-p-nitroanilide was used as substrate. Untested alkaloids were also screened for their cytotoxic activity against p53-mutated Caco-2 and HT-29 colorectal adenocarcinoma cells. At the same time, healthy small intestine cells FH-74 Int were used to determine overall toxicity against noncancerous cells. The crinine-type alkaloid buphanisine (7) demonstrated interesting cytotoxicity against both tested cancer cell lines with IC50 values of 8.59 ± 0.15 μM for Caco-2 and 5.32 ± 1.70 μM for HT-29.

Tannins and their Influence on Health

Abstract Natural polyphenols are a wide class of secondary plant metabolites and represent an abundant antioxidant component of human diet. An important, but often neglected, group of natural polyphenols are tannins. This review offers a general description of chemistry of hydrolysable and condensed tannins (proanthocyanidins), and phlorotannins, the mechanisms of their antioxidation action, like free radical scavenging activity, chelation of transition metals, inhibition of prooxidative enzymes and lipid peroxidation. The mechanisms of action of inhibition of various enzyme systems, antibacterial, antiviral, antiprotozoal, anticarcinogenic, antidiabetic, hepatoprotective, cardiovascular system preventing, immunomodulation, antiallergic and anti-inflammatory effects as well as the absorption, metabolic fate and positive in vivo effects of tannins are enclosed.

Scoulerine affects microtubule structure, inhibits proliferation, arrests cell cycle and thus culminates in the apoptotic death of cancer cells

Scoulerine is an isoquinoline alkaloid, which indicated promising suppression of cancer cells growth. However, the mode of action (MOA) remained unclear. Cytotoxic and antiproliferative properties were determined in this study. Scoulerine reduces the mitochondrial dehydrogenases activity of the evaluated leukemic cells with IC50 values ranging from 2.7 to 6.5 µM. The xCELLigence system revealed that scoulerine exerted potent antiproliferative activity in lung, ovarian and breast carcinoma cell lines. Jurkat and MOLT-4 leukemic cells treated with scoulerine were decreased in proliferation and viability. Scoulerine acted to inhibit proliferation through inducing G2 or M-phase cell cycle arrest, which correlates well with the observed breakdown of the microtubule network, increased Chk1 Ser345, Chk2 Thr68 and mitotic H3 Ser10 phosphorylation. Scoulerine was able to activate apoptosis, as determined by p53 upregulation, increase caspase activity, Annexin V and TUNEL labeling. Results highlight the potent antiproliferative and proapoptotic function of scoulerine in cancer cells caused by its ability to interfere with the microtubule elements of the cytoskeleton, checkpoint kinase signaling and p53 proteins. This is the first study of the mechanism of scoulerine at cellular and molecular level. Scoulerine is a potent antimitotic compound and that it merits further investigation as an anticancer drug.