Phytotoxicity of secondary metabolites isolated from Flourensia oolepis S.F.Blake

Predictive power of the Triticum root elongation test for the assessment of novel anti‑proliferative therapies

The use of alternative techniques to reduce the number of animals used in anticancer research is an issue of current interest. The aim of this study was to validate the use of a simple and efficient alternative tool for the assessment of the potential of novel anti‑proliferative agents. A set of 20 compounds with various mechanisms were tested in the Triticum aestivum root elongation assay, using aminophylline as negative control. Hierarchical cluster analyses were performed using the furthest neighbor method based on Euclidean distance measure, and the compounds were statistically analyzed in reference to their anti‑proliferative pattern registered in the NCI60 human tumor cell line anticancer drug screen. A correlation between the Triticum test results and the NCI60 anti‑proliferative profile was made for a number of human cells that we defined as the Triticum cell panel. Linear equations were computed that can be used to transform the inhibitory effect measured in any future Triticum assay in order to predict the effect on particular human cells. Of the tested anti‑proliferative agents, methotrexate, colchicine, cantharidin, cisplatin and verapamil produced a growth inhibition over 50%. On the whole, the findings of this study suggest that the Triticum test can be used to detect several types of anti‑proliferative mechanisms, particularly those targeting tubulin, rendering it a useful tool with which to identify novel mitotic spindle inhibitors.

Mechanism Underlying the Reversal of Drug Resistance in P-Glycoprotein-Expressing Leukemia Cells by Pinoresinol and the Study of a Derivative

P-glycoprotein (P-gp) is a membrane protein associated with multidrug resistance (MDR) due to its key role in mediating the traffic of chemotherapeutic drugs outside cancer cells, leading to a cellular response that hinders efforts toward successful therapy. With the aim of finding agents that circumvent the MDR phenotype mediated by P-gp, 15 compounds isolated from native and naturalized plants of Argentina were screened. Among these, the non-cytotoxic lignan (±) pinoresinol successfully restored sensitivity to doxorubicin from 7 μM in the P-gp overexpressed human myelogenous leukemia cells, Lucena 1. This resistance-reversing effect was confirmed by competitively increasing the intracellular doxorubicin accumulation and by significantly inhibiting the efflux of doxorubicin and, to a lesser extent, that of rhodamine 123. The activity obtained was similar to that observed with verapamil. No such results were observed in the sensitive parental K562 cell line. To gain deeper insight into the mode of action of pinoresinol, its effect on P-gp function and expression was examined. The docking simulations indicated that the lignan bound to P-gp at the apex of the V-shaped transmembrane cavity, involving transmembrane helices 4, 5, and 6, and partially overlapped the binding region of tariquidar, which was used as a positive control. These results would shed some light on the nature of its interaction with P-gp at molecular level and merit further mechanistic and kinetic studies. In addition, it showed a maximum 29% activation of ATP hydrolysis and antagonized verapamil-stimulated ATPase activity with an IC₅₀ of 20.9 μM. On the other hand, pinoresinol decreased the presence of P-gp in the cell surface. Derivatives of pinoresinol with improved activity were identified by docking studies. The most promising one, the non-cytotoxic 1-acetoxypinoresinol, caused a reversion of doxorubicin resistance from 0.11 μM and thus higher activity than the lead compound. It also caused a significant increase in doxorubicin accumulation. Results were similar to those observed with verapamil. The results obtained positioned these compounds as potential candidates for effective agents to overcome P-gp-mediated MDR, leading to better outcomes for leukemia chemotherapy.

The Natural Flavonoid Pinocembrin: Molecular Targets and Potential Therapeutic Applications

Pinocembrin is a natural flavonoid compound extracted from honey, propolis, ginger roots, wild marjoram, and other plants. In preclinical studies, it has shown anti-inflammatory and neuroprotective effects as well as the ability to reduce reactive oxygen species, protect the blood-brain barrier, modulate mitochondrial function, and regulate apoptosis. Considering these pharmaceutical characteristics, pinocembrin has potential as a drug to treat ischemic stroke and other clinical conditions. In this review, we summarize its pharmacologic characteristics and discuss its mechanisms of action and potential therapeutic applications.

Distribution of (-)-Hamanasic Acid A in South American Species of Flourensia and Phytotoxic Effects of Leaf Aqueous Extracts

The presence of the phytotoxic sesquiterpene (-)-hamanasic acid A {(-)HAA; 7-carboxy-8-hydroxy-1(2), 12(13)-dien-bisabolene} isolated from Flourensia campestris ( FC), was investigated in the South American species of the genus, together with the evaluation of the phytotoxic activity of their leaf aqueous extracts. (-)HAA was identified and isolated from F. fiebrigii ( FF) and F. oolepis ( FO), being chemically (GC-MS, NMR, [α]D) and biologically (bioassayed on lettuce) indistinguishable from that of FC, while no (-)HAA was found in F. hirta ( FH), F. riparia ( FR) and F. niederleinii ( FN). Its leaf content in FF was similar to that found in FC (ca. 15 mg g−1 WT) and significantly higher than in FO (0.8 mg g−1 WT). The screening for the presence of (-)HAA in other species of Flourensia communities showed that its natural occurrence is restricted only to Flourensia species. No (-)HAA could be detected in any of the 37 -most representative- species of these communities (26 natives, 11 exotics), despite many of them belong to the same family and tribe as Flourensia spp. Leaf aqueous extracts of all Flourensia species exhibited strong inhibitory effects on lettuce germination and on root and shoot growth, regardless of the presence and content of (-)HAA. These results strongly suggest the existence of other powerful phytotoxic compounds in those Flourensia spp lacking (-)HAA. Our results clearly show that (-)HAA only pertains to some species of the genus Flourensia. Relative to previous exomorphologic groupings of the genus, our chemotaxonomic data would give support to the close link described between FC and FF, but not with FR. In addition, the fact that (-)HAA was also found in FO, which belongs to a second different line, also points out that species position in this lineage would deserve to be revisited. The restricted production of (-)HAA by Flourensia in their communities suggests its special link with the genus, and sustains its putative allelochemical role.