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The potential cytotoxic activities of 46 alkaloids isolated from different Strychnos species were tested on different cancer or normal cells cultured in vitro. The authors used a relatively simple microtest which gives good reproducibility. Most of the active compounds belong to the usambarane skeleton but other structure-activity relationships are being discussed.
Bisnordihydrotoxiferine has been isolated as the major alkaloid from the root bark of Strychnos trinervis. This compound shows a wide antimicrobial spectrum against gram-positive, gram-negative and acid-fast microorganisms, filamentous and yeast-like fungi and also phytopathogenic microorganisms. Preliminary studies also reveal some cytotoxic activity in KB cells which was confirmed by tests against sarcoma 180 tumors.
Strychnos henningsii Gilg is used in African traditional medicine for the treatment of various ailments, including rheumatism, gastrointestinal complaints and snake bites. Different preliminary pharmacological experiments are described. The results show that some of the reported folk medicinal applications of S. henningsii can be at least partially explained by the presence of retuline-like alkaloids, whose use could lead to new antinociceptive (antiinflammatory and analgesic) and antispasmodic drugs.
Two new quaternary alkaloids, 9-methoxy-Nb-methylgeissoschizol and guiachrysine together with the known compounds C-alkaloid O, fluorocurine, mavacurine, macusine B and C-profluorocurine, were isolated from Strychnos guianensis stembark. The structures of the compounds were elucidated on the basis of spectroscopic studies.
Two new quaternary indole alkaloids 5',6'-dehydroguiachrysine (1) and 5',6'-dehydroguiaflavine (2) were isolated from Strychnos guianensis stem bark. Their structures were determined by analysis of spectral data. Their inhibitory effects on neuromuscular transmission are also reported and compared to that of other quaternary alkaloids.
The antidiarrhoeal activity of the methanol extract of the dried seeds of Strychnos potatorum (MESP) has been evaluated out in rats using different models (castor oil-induced diarrhoea, effects on gastrointestinal motility and on PGE(2)-induced gastric enteropooling. MESP (100, 200 and 400 mg/kg, p.o.) significantly (P<0.001) inhibited the frequency of defaecation and reduced the wetness of faecal droppings in castor oil-induced diarrhoea, decreased the propulsion of charcoal meal through the gastrointestinal tract, and also reduced the PGE(2)-induced enteropooling.
In this paper, it has been investigated that strychnine, the major active principle in the alcoholic extract of the seeds of Strychnos nux-vomica, is responsible for its antilipid peroxidative property. The mechanism of action of this drug is through the chelation of the free iron in the system. It has also been observed that strychnine does not have any pro-oxidant-property, because it does not convert Fe3+ to Fe2+ and vice versa in the reaction system, as has been observed with several other antioxidants.
Cantleyine, a monoterpene alkaloid isolated from the root bark of Strychnos trinervis, was submitted to a broad spectrum pharmacological screening, in which the principal effect observed was a nonspecific relaxation of isolated smooth muscles. Cantleyine relaxed (IC50 2.1 x 10(-4) M) the guinea-pig trachea, pre-contracted by carbachol and antagonized in a nonspecific manner; carbachol (IC50 2.1 x 10(-4) M) and histamine (IC50 1.4 x 10(-4) M) induced contractions in the guinea-pig ileum; and phenylephrine (IC50 3.8 x 10(-4) M) responses in the rat aorta. Cantleyine antagonized (pD'2, 3.82) cumulative concentration response curves to histamine in the ileum in a noncompetitive, reversible (slope, 4.84) and concentration dependent manner. The tonic contractions induced by histamine and KCl were also inhibited in a concentration-dependent and reversible manner (IC50 7.2 x 10(-5) and 1.8 x 10(-4) M, respectively), suggesting that cantleyine should be acting on voltage-dependent Ca2+ channels. This hypothesis was confirmed by the observation that cantleyine inhibited (pD'2, 3.35), in a concentration dependent manner, the CaCl2 induced contraction in depolarizing medium. These results suggest that cantleyine produces nonspecific spasmolytic effects in smooth muscle and that in guinea-pig ileum this effect is, in part, due to the inhibition of Ca+2 influx through voltage-dependent Ca2+ channels.
A reinvestigation of Strychnos icaja roots has resulted in the isolation of two tertiary quasi-symmetric bisindole alkaloids named strychnogucines A (1) and B (2). Their structures were identified by means of spectroscopic data interpretation. Compound 2 was highly active in vitro and compound 1 moderately active against four strains of Plasmodium falciparum. Strychnogucine B (2) was more active against a chloroquine-resistant strain than against a chloroquine-sensitive one (best CI(50), 80 nM against the W2 strain). In addition, this compound showed a selective antiplasmodial activity with 25-180 times greater toxicity toward P. falciparum, relative to cultured human cancer cells (KB) or human fibroblasts (WI38).
From the stem bark of Strychnos decussata (Pappe) Gilg (Loganiaceae), five tertiary indole alkaloids have been isolated and identified. Previously known alkaloids, but new to this plant, were: akagerine (1) and 17-O-methylakagerine (2), while alkaloids newly found in nature were 10-hydroxy-21-O-methylkribine (3a), 10-hydroxyepi-21-O-methylkribine (3b) and 10-hydroxy-17-O-methylakagerine (4). Structures have been ascribed to the new compounds on the basis of their spectral, particularly nmr, data. The pharmacological activity of the alkaloids is also discussed.
The major quaternary alkaloid from Strychnos angolensis was isolated, and its structure was determined by its spectral data as 11-methoxy-macusine A. The alkaloid showed muscle-relaxant activity.
From the leaves of Strychnos pseudoquina (Loganiaceae), isorhamnetin (1) and a new biflavone (2) named strychnobiflavone were isolated together with the alkaloids diaboline and 11-methoxydiaboline.
The reinvestigation of Strychnos nux-vomica resulted in the isolation of a colored monoquaternary bisindole alkaloid from the roots. The structure of this new orange substance, strychnochrysine (1), was defined by detailed spectroscopic methods.
Reinvestigation of Strychnos usambarensis Gilg resulted in the isolation of a tertiary phenolic bisindole alkaloid, 10'-hydroxyusambarensine (1), which was identified by detailed spectroscopic methods. Compound 1 was moderately active against two strains of Plasmodium falciparum in vitro.
A reinvestigation of Strychnos guianensis resulted in the isolation of a colored quaternary bisindole alkaloid from the stem bark. The structure of this new substance, guiaflavine (1), was defined by detailed spectroscopic methods and comparison with model compounds.
Reinvestigation of Strychnos icaja Baillon resulted in the isolation of vomicine, isostrychnine and of three new sungucine derivatives, named isosungucine (8), 18-hydroxy-sungucine (9) and 18-hydroxy-isosungucine (10). They were identified by detailed spectroscopic methods. The complete 1H- and 13C-NMR study of sungucine was also realized. Some of these compounds were highly active against Plasmodium falciparum in vitro and more particularly against the chloroquine-resistant strain. Compound 10 showed a selective antiplasmodial activity, with > 100-fold greater toxicity towards Plasmodium falciparum, relative to cultured human cancer cells (KB and HeLa lines) or fibroblasts (WI38).
Sungucine and isosungucine are two bisindole alkaloids isolated from the roots of the African plant Strychnos icaja Baillon. They both exhibit antiplasmodial activities but also show cytotoxic effects against human cancer cell lines. In order to elucidate their mechanism of action, we have investigated the interaction of the alkaloids with DNA and their capacity to inhibit nucleic acids and protein synthesis in the human HL-60 promyelocytic leukemia cell line. Cell treatment with both sungucine and isosungucine leads to the appearance of a hypo-diploid DNA content peak. Western blotting analysis reveals that the two alkaloids induce cleavage of the poly(ADP-ribose) polymerase (PARP) and promote the cleavage of a caspase-3 DEVD peptide substrate. The activation of the caspase cascade is accompanied with a fragmentation of DNA in cells, as revealed by the TUNEL assay. Altogether, the results shed light on the mechanism of action of these two plant alkaloids and identify signaling factors involved in (iso)sungucine-induced apoptosis in HL-60 cells.
Seven alkaloids isolated from Strychnos usambarensis have been assessed for in vitro activities against Entamoeba histolytica and Plasmodium falciparum and for in vivo activity against Plasmodium berghei in mice. Strychnopentamine and 3',4'-dihydrousambarensine were highly active against P. falciparum in vitro, but were inactive and non-toxic against P. berghei in vivo. Usambarensine, usambarine, and 18,19-dihydrousambarine were highly active against E. histolytica in vitro, but were less active against P. falciparum in vitro. Nb-Methylusambarensine was less active against both protozoa than was usambarensine, and akagerine possessed little antiprotozoal activity. Structure-activity relationships are discussed in the context of the reported cytotoxic and pharmacological properties of these alkaloids.