Alexandra Paulo

Indoloquinolines as scaffolds for drug discovery.

Traditional medicines have contributed greatly over the centuries to the discovery and development of new therapeutic agents and indoloquinoline alkaloids may represent a new class of drug leads. Cryptolepine (5-methyl-5Hindolo[3,2-b]quinoline), neocryptolepine (5-methyl-5H-indolo[2,3-b]quinoline), isocryptolepine (5-methyl-5H-indolo[3,2-c]quinoline, extracted from the African medicinal plant Cryptolepis sanguinolenta, and isoneocryptolepine (5-methyl-5Hindolo[2,3-c]quinoline), which has never been found in nature, are isomeric tetracyclic compounds of particular interest due to their broad spectrum of biological activities including antiparasitic, antifungal, antibacterial, cytotoxic, anti-inflammatory and antihyperglycaemic. As a result, in the last 30 years hundreds of indoloquinoline analogues were synthesized and their biological activities evaluated. In this paper, we present an overview of the potential of indoloquinolines as scaffolds in drug discovery by reviewing the in vitro and in vivo biological activities of natural and synthetic analogues, as well as the proposed mechanisms of action and structure-activity relationships.

The flavonoid-rich fraction of Coreopsis tinctoria promotes glucose tolerance regain through pancreatic function recovery in streptozotocin-induced glucose-intolerant rats

AIM OF THE STUDY Infusions of Coreopsis tinctoria Nutt. flowering tops have been used traditionally in Portugal to control hyperglycaemia and a previous study revealed that daily administration of the infusion during a 3-week period promoted the recovery of glucose tolerance by a mechanism different from inhibition of glucose absorption and direct promotion of insulin secretion. We know report the study of the ethyl acetate fraction of Coreopsis tinctoria flowers infusion aiming to confirm flavonoids as bioactive metabolites. To give one step forward into the antihyperglycaemic mechanism of action of this traditionally used plant we also studied the activity of Coreopsis tinctoria flavonoids on the pancreatic function of glucose-intolerant rats. A standard antioxidant, Trolox, was also studied for comparative purposes as the antioxidant mechanism has been frequently purposed as one of the mechanisms mediating antihyperglycaemic effects of flavonoid-rich extracts. MATERIAL AND METHODS Thirteen compounds, mainly of flavanone and chalcone flavonoidal type, have been identified in this fraction by HPLC-DAD-ESI-MS/MS, and the major one (marein) quantified by HPLC-UV. The fraction (125 mg containing 20 mg of marein/kg b.w.) and Trolox (50 mg/kg b.w.) were administered daily by oral gavage to normal and STZ (40 mg/kg b.w.)-induced glucose-intolerant Wistar rats for 3 weeks. Blood glucose levels were measured weekly by Oral Glucose Tolerance Test. Pancreatic function was evaluated by plasma lipase of treated and non-treated glucose-tolerant and- intolerant rats after the 3-week treatment period. RESULTS After 2 weeks oral treatment with Coreopsis tinctoria AcOEt fraction the animals were no longer glucose-intolerant, an effect maintained over the remaining experimental period. Additionally, plasma lipase values of glucose-intolerant animals treated with the AcOEt fraction (13.5 ± 0.84 U/L) showed a clear reduction when compared with the glucose-intolerant group (34.60 ± 1.76 U/L; P<0.001) and normoglycaemic control (8.35 ± 0.69 U/L) demonstrating recovery of pancreatic function. On the other hand, treatment with standard antioxidant Trolox had no effect on glucose homeostasis of glucose-intolerant rats. The oral treatment with Coreopsis tinctoria fraction caused no hepatotoxicity, as determined by blood alanine and aspartate transaminases, and had also no effect on glucose homeostasis and pancreatic function of normal rats. CONCLUSIONS AcOEt fraction, containing the same amount of marein as the infusion, promoted glucose tolerance regain in the rats more quickly, which means that the bioactivity is probably due to the several flavonoids present in Coreopsis tinctoria extracts and not to marein alone. The results also strongly suggest that these compounds act by promoting pancreatic cell function recovery from STZ-induced injury, possibly through a mechanism of action other than merely antioxidant mediated.

In vitro antibacterial screening of Cryptolepis sanguinolenta alkaloids

The ethanol and aqueous crude extracts and five alkaloids isolated from the roots of Crytolepis sanguinolenta (Lindl.) Schlechter were screened for antibacterial activity against 7 reference strains by the twofold serial broth microdilution assay. The ethanol extract and the alkaloids cryptolepine and cryptoheptine inhibited the growth of all strains tested except that of Pseudomonas aeruginosa.

Cryptolepis sanguinolenta activity against diarrhoeal bacteria

Cryptolepine is the main alkaloid of Cryptolepis sanguinolenta (Lindl.) Schlechter, a plant used in traditional medicine in West Africa. The minimal inhibitory concentrations (MICs) of cryptolepine, ethanol and aqueous extracts of Cryptolepis sanguinolenta root were determined for 65 strains of Campylobacter jejuni, 41 strains of Campylobacter coli isolated from sporadic cases of gastroenteritis in Portugal and 86 strains of Vibrio cholerae isolated from patients with enteric infections in Angola, Brazil and Portugal. The ethanol extract activity against Campylobacter strains (MIC90% = 25 micrograms/ml) is higher than that of co-trimoxazole and sulfamethoxazole and Campylobacter strains susceptibility for cryptolepine (MIC90% = 12.5 micrograms/ml) is equal for ampicillin. The ethanol extract and cryptolepine show some activity against the Vibrio cholerae strains, although their activities are lower than that of tetracycline. The results suggest that these roots could be a therapeutic alternative for bacterial etiologic diarrhoea in West Africa.

Cryptolepine analogues containing basic aminoalkyl side-chains at C-11: Synthesis, antiplasmodial activity, and cytotoxicity

A series of cryptolepine derivatives has been synthesized through the incorporation of short basic side-chains in the C-11 position of the 10H-indolo[3,2-b]quinoline scaffold. Their antiplasmodial activity was evaluated in vitro against the chloroquine resistant Plasmodium falciparum W2 strain, showing IC(50) values between 22 and 184 nM, while their cytotoxicity was assessed using HUVEC cells, revealing three compounds with a selectivity ratio higher than 10. The most selective of these derivatives, 4d, with a selectivity ratio of 46, was also the least cytotoxic of the series.

Cytoprotective effect of Coreopsis tinctoria extracts and flavonoids on tBHP and cytokine-induced cell injury in pancreatic MIN6 cells

ETHNOPHARMACOLOGICAL RELEVANCE [corrected] Coreopsis tinctoria flowering tops infusion is traditionally used in Portugal for treating the symptoms of diabetes. Recent studies have revealed its antihyperglycemic activity when administered for 3 weeks to a STZ-induced glucose intolerance model in the rat and glucose tolerance regain was even clearer and pancreatic function recovery was achieved when administering Coreopsis tinctoria flavonoid-rich AcOEt fraction. In this study we aimed to evaluate the protective effect of Coreopsis tinctoria flowering tops aqueous extract, AcOEt fraction and the pure compounds marein and flavanomarein, against beta-cell injury, in a mouse insulinoma cell line (MIN6) challenged with pro-oxidant tert-butyl-hydroperoxide (tBHP) or cytokines. MATERIALS AND METHODS The protective effects of Coreopsis tinctoria flowering tops extracts and pure compounds were evaluated through pre-incubating MIN6 cells with samples followed by treatment with tBHP (400 μM for 2 h) after which viability was determined through ATP measurements. In order to assess whether plant extracts were involved in decreasing reactive oxygen species, superoxide anion production was determined through a lucigenin-enhanced chemiluminescent method. Lastly, the direct influence of Coreopsis tinctoria extracts and main compounds on cell survival/apoptosis was determined measuring caspase 3 and 7 cleavage induced by cytokines. RESULTS Coreopsis tinctoria flowering tops extracts (25-100 μg/mL) and pure compounds (200-400 μM), when pre-incubated with MIN6 cells did not present any cytotoxicity, instead they increased cell viability in a dose dependent manner when challenged with tBHP. Treatment with this pro-oxidant also showed a rise in superoxide radical anion formation in MIN6 cells. This increase was significantly reduced by treatment with superoxide dismutase enzyme (SOD) but not by pre-treatment with Coreopsis tinctoria flowering tops extracts. Caspase 3/7 activation measurements show that Coreopsis tinctoria flowering tops extracts, as well as marein and flavanomarein, significantly inhibit apoptosis. CONCLUSIONS Coreopsis tinctoria extracts and pure compounds show cytoprotection that seems to be due to inhibition of the apoptotic pathway, and not through a decrease on superoxide radical production.

Comparative in vitro and in vivo antimalarial activity of the indole alkaloids ellipticine, olivacine, cryptolepine and a synthetic cryptolepine analog

Indole alkaloids ellipticine (1), cryptolepine triflate (2a), rationally designed 11-(4-piperidinamino)cryptolepine hydrogen dichloride (2b) and olivacine (3) (an isomer of 1) were evaluated in vitro against Plasmodium falciparum and in vivo in Plasmodium berghei-infected mice. 1-3 inhibited P. falciparum (IC₅₀≤1.4 μM, order of activity: 2b>1>2a>3). In vitro toxicity to murine macrophages was evaluated and revealed selectivity indices (SI) of 10-12 for 2a and SI>2.8×10² for 1, 2b and 3. 1 administered orally at 50mg/kg/day was highly active against P. berghei (in vivo inhibition compared to untreated control (IVI)=100%, mean survival time (MST)>40 days, comparable activity to chloroquine control). 1 administered orally and subcutaneously was active at 10 mg/kg/day (IVI=70-77%; MST=27-29 days). 3 exhibited high oral activity at ≥50 mg/kg/day (IVI=90-97%, MST=23-27 days). Cryptolepine (2a) administered orally and subcutaneously exhibited moderate activity at 50mg/kg/day (IVI=43-63%, MST=24-25 days). At 50 mg/kg/day, 2b administered subcutaneously was lethal to infected mice (MST=3 days) and moderately active when administered orally (IVI=45-55%, MST=25 days). 1 and 3 are promising compounds for development of antimalarials.

KRAS oncogene repression in colon cancer cell lines by G-quadruplex binding indolo[3,2- c ]quinolines

KRAS is one of the most frequently mutated oncogenes in human cancer, yet remaining undruggable. To explore a new therapeutic strategy, a library of 5-methyl-indolo[3,2-c]quinoline derivatives (IQc) with a range of alkyldiamine side chains was designed to target DNA and RNA G-quadruplexes (G4) in the promoter and 5′-UTR mRNA of the KRAS gene. Biophysical experiments showed that di-substituted IQc compounds are potent and selective KRAS G4 stabilizers. They preferentially inhibit the proliferation of KRAS mutant cancer cell lines (0.22 < IC50 < 4.80 μM), down-regulate KRAS promoter activity in a luciferase reporter assay, and reduce both KRAS mRNA and p21KRAS steady-state levels in mutant KRAS colon cancer cell lines. Additionally, IQcs induce cancer cell death by apoptosis, explained in part by their capacity to repress KRAS expression. Overall, the results suggest that targeting mutant KRAS at the gene level with G4 binding small molecules is a promising anticancer strategy.

Recovery of oral glucose tolerance by wistar rats after treatment with Coreopsis tinctoria infusion

Infusions of Coreopsis tinctoria flowering tops have traditionally been used in Portugal to control hyperglycaemia but no pharmacological or toxicological studies have been reported until now. The chalcones marein and okanin were isolated from the aqueous extract, together with the 2S‐3′,4′,7,8‐tetrahydroxyflavanone. The content of marein in extracts was determined by HPLC‐UV and the radical scavenging capacity evaluated by the DPPH method (EC50 = 21 µg/mL). Glucose intolerance was induced by a single intraperitoneal injection of streptozotocin in saline (40 mg/Kg). After three weeks of oral treatment with C. tinctoria extract (500 mg/Kg/day) the animals were no longer glucose‐intolerant (p > 0.05). Additionally, this oral treatment caused no hepatotoxicity in the rats, as determined by blood alanine and aspartate transaminases. A single administration of extract had no effect on oral glucose tolerance in normal Wistar rats. The extract also had no effect on insulin secretion by MIN6 cells. In conclusion, C. tinctoria infusion is able to abolish the streptozotocin‐induced glucose‐intolerance in rats after three weeks of oral treatment by a mechanism other than induction of insulin secretion. The recovery of β‐pancreatic function mediated by an antioxidant mechanism is a possibility that deserves further investigation. Copyright

Synthesis, G‐Quadruplex Stabilisation, Docking Studies, and Effect on Cancer Cells of Indolo[3,2‐b]quinolines with One, Two, or Three Basic Side Chains

G‐quadruplex (G4) DNA structures in telomeres and oncogenic promoter regions are potential targets for cancer therapy, and G4 ligands have been shown to modulate telomerase activity and oncogene transcription. Herein we report the synthesis and G4 thermal stabilisation effects, determined by FRET melting assays, of 20 indolo[3,2‐b]quinolines mono‐, di‐, and trisubstituted with basic side chains. Molecular modelling studies were also performed in an attempt to rationalise the ligands′ binding poses with G4. Overall, the results suggest that ligand binding and G4 DNA thermal stabilisation increase with an N5‐methyl or a 7‐carboxylate group and propylamine side chains, whereas selectivity between G4 and duplex DNA appears to be modulated by the number and relative position of basic side chains. From all the indoloquinoline derivatives studied, the novel trisubstituted compounds 3 d and 4 d, bearing a 7‐(aminoalkyl)carboxylate side chain, stand out as the most promising compounds; they show high G4 thermal stabilisation (ΔTm values between 17 and 8 °C) with an inter‐G4 ΔTm trend of Hsp90A>KRas21R≈F21T>c‐Kit2, 10‐fold selectivity for G4 over duplex DNA, and 100‐fold selectivity for the HCT116 cancer cell line (IC50 and IC90: <10 μM) over primary rat hepatocytes. Compounds 3 d and 4 d also decreased protein expression levels of Hsp90 and KRas in HCT116 cancer cells.