Investigation of the Potential Targets behind the Promising and Highly Selective Antileishmanial Action of Synthetic Flavonoid Derivatives

Leishmaniases are among the neglected tropical diseases that still cause devastating health, social, and economic consequences to more than 350 million people worldwide. Despite efforts to combat these vector-borne diseases, their incidence does not decrease. Meanwhile, current antileishmanial drugs are old and highly toxic, and safer presentations are unaffordable to the most severely affected human populations. In a previous study by our research group, we synthesized 17 flavonoid derivatives that demonstrated impressive inhibition capacity against rCPB2.8, rCPB3, and rH84Y. These cysteine proteases are highly expressed in the amastigote stage, the target form of the parasite. However, although these compounds have been already described in the literature, until now, the amastigote effect of any of these molecules has not been proven. In this work, we aimed to deeply analyze the antileishmanial action of this set of synthetic flavonoid derivatives by correlating their ability to inhibit cysteine proteases with the action against the parasite. Among all the synthesized flavonoid derivatives, 11 of them showed high activity against amastigotes of Leishmania amazonensis, also providing safety to mammalian host cells. Furthermore, the high production of nitric oxide by infected cells treated with the most active cysteine protease B (CPB) inhibitors confirms a potential immunomodulatory response of macrophages. Besides, considering flavonoids as multitarget drugs, we also investigated other potential antileishmanial mechanisms. The most active compounds were selected to investigate another potential biological pathway behind their antileishmanial action using flow cytometry analysis. The results confirmed an oxidative stress after 48 h of treatment. These data represent an important step toward the validation of CPB as an antileishmanial target, as well as aiding in new drug discovery studies based on this protease.

Metabolomics Approach Expands the Classification of Propolis Samples from Midwest Brazil

Propolis samples collected from five areas in Mato Grosso do Sul state, Midwest Brazil, comprising portions of the Cerrado, Pantanal, and Atlantic Forest ecosystems, were investigated for metabolomic profiles and evaluated for antioxidant and antitumor potential. Chemical profiles were determined by HPLC-DAD-MS/MS data and evaluated using principal component analysis and hierarchical clustering analysis to discern chemical composition patterns. Based on phytogeographical origin and chemical composition, 20 potential markers were identified and five groups were distinguished: (I) Cerrado/Central, (II) Atlantic Forest/South, (III) Cerrado-Pantanal transition area/Northwest, (IV) Cerrado/North, and (V) Pantanal/West. Drawing on HPLC-DAD-MS/MS and NMR data, 47 compounds were successfully or tentatively identified, including prenylated phenylpropanoids, flavonoids, isoflavonoids, and di- and triterpenoids, among other constituents. Isoflavonoids, typically found in red propolis from Northeast Brazil, are being reported for the first time in a propolis sample from the Midwest. A new prenylated aromatic compound, (E)-3-[4-hydroxy-3-(2-hydroxy-3-methylbut-3-en-1-yl)-5-(3-methylbut-2-en-1-yl)phenyl]propenoic acid, was obtained. Samples in group II exhibited promising antitumor potential against prostate and breast carcinoma cells, as did samples in groups III and IV against the latter cell line. The sample in group I, despite containing the highest amount of total phenolic compounds and being the only sample to exhibit scavenging activity against DPPH, was not the most cytotoxic against the cell lines tested.

S-(4-Methoxyphenyl)-4-methoxybenzenesulfonothioate as a Promising Lead Compound for the Development of a Renal Carcinoma Agent

Organosulfur compounds show cytotoxic potential towards many tumor cell lines. Disulfides and thiosulfonates act through apoptotic processes, inducing proteins associated with apoptosis, endoplasmic reticulum stress, and the unfolded protein response. Three p-substituted symmetric diaryl disulfides and three diaryl thiosulfonates were synthesized and analyzed for inhibition of tubulin polymerization and for human cancer cell cytotoxic activity against seven tumor cell lines and a non-tumor cell line. S-(4-methoxyphenyl)-4-methoxybenzenesulfonothioate (6) exhibited inhibition of tubulin polymerization and showed the best antiproliferative potential, especially against the 786-0 cell line, being six times more selective as compared with the non-tumor cell line. In addition, compound 6 was able to activate caspase-3 after 24 and 48 h treatments of the 786-0 cell line and induced cell-cycle arrest in the G2/M stage at the highest concentration evaluated at 24 and 48 h. Compound 6 was able to cause complete inhibition of proliferation, inducing the death of 786-0 cells, by increasing the number of cells at G2/M and greater activation of caspase-3.

Antiproliferative Activity of Extracts of Campomanesia adamantium (Cambess.) O. Berg and Isolated Compound Dimethylchalcone Against B16-F10 Murine Melanoma

Campomanesia adamantium, a native species of the Brazilian Cerrado, is characterized as a natural source of phenolic compounds and has known potential anticancer activities. This study aimed to evaluate the chemical profile of dichloromethane extracts of pulp (DEGPU) and peel (DEGPE) from the fruits of C. adamantium and to identify compounds with antiproliferative effects in vitro against melanoma cells by sulforhodamine B (SRB) assay, apoptosis induction assay, caspase-3 activation assay, nitric oxide (NO) release in coculture of B16-F10 cells and murine peritoneal macrophages. The chemical profiles of DEGPU and DEGPE were analyzed by high performance liquid chromatography coupled to diode array detector and mass spectrometer using the electrospray ionization interface (HPLC-DAD-ESI-MS/MS). Thirteen compounds were identified in both extracts and the chromatographic study of the most active extract in SRB assay DEGPU (GI₅₀ of 16.17 μg/mL) resulted in the isolation of seven compounds. The isolated compound dimethylchalcone (DMC) had the highest antiproliferative activity against B16-F10 with a GI₅₀ of 7.11 μg/mL. DEGPU extract activated caspase-3 in 29% of cells at 25 μg/mL and caused a 50% decrease in NO release in coculture. DEGPU can be characterized as a source of bioactive compounds such as DMC, as seen from its antiproliferative effect in vitro by inducing B16-F10 cells to undergo apoptosis, essential feature in the search for new anticancer drugs.

Rubiaceae-Type Cyclopeptides from Galianthe thalictroides

Two Rubiaceae-type cyclopeptides, 6-O-methylbouvardin (1) and the new cyclopeptide 5β-hydroxy-RA-III (2), were isolated from the roots of Galianthe thalictroides. Employing the sulforhodamine B assay, compounds 1 and 2 were tested in vitro against three cancer cell lines--786-0 (kidney carcinoma), PC-3 (prostate carcinoma), and HT-29 (colon carcinoma)--and showed GI50 values ranging from 0.06 to 1.80 μg mL(-1). This is the first report on the isolation of Rubiaceae-type cyclopeptides from a genus other than Rubia or Bouvardia.

Synthesis and evaluation of diaryl sulfides and diaryl selenide compounds for antitubulin and cytotoxic activity

We have devised a procedure for the synthesis of analogs of combretastatin A-4 (CA-4) containing sulfur and selenium atoms as spacer groups between the aromatic rings. CA-4 is well known for its potent activity as an inhibitor of tubulin polymerization, and its prodrugs combretastatin A-4 phosphate (CA-4P) and combretastatin A-1 phosphate (CA-1P) are being investigated as antitumor agents that cause tumor vascular collapse in addition to their activity as cytotoxic compounds. Here we report the preparation of two sulfur analogs and one selenium analog of CA-4. All synthesized compounds, as well as several synthetic intermediates, were evaluated for inhibition of tubulin polymerization and for cytotoxic activity in human cancer cells. Compounds 3 and 4 were active at nM concentration against MCF-7 breast cancer cells. As inhibitors of tubulin polymerization, both 3 and 4 were more active than CA-4 itself. In addition, 4 was the most active of these agents against 786, HT-29 and PC-3 cancer cells. Molecular modeling binding studies are also reported for compounds 1, 3, 4 and CA-4 to tubulin within the colchicine site.

A new cytotoxic β-carboline alkaloid from Galianthe thalictroides

A cytotoxicity-guided fractionation of the roots of Galianthe thalictroides afforded a new β-carboline alkaloid, 1-(hydroxymethyl)-3-(2-hydroxypropan-2-yl)-2-(5-methoxy-9H- β-carbolin-1-yl)cyclopentanol, which exhibited strong cytotoxic activity against three human cancer cell lines (MCF-7, 786-0, and UACC62). Its structure was established on the basis of 1D- and 2D-NMR spectroscopic techniques supported by HRMS data.