Anticancer evaluation of structurally diverse Amaryllidaceae alkaloids and their synthetic derivatives

Plants of the Amaryllidaceae family have been under intense scrutiny for the presence of the specific metabolites responsible for the medicinal properties associated with them. The study began in 1877 with the isolation of alkaloid lycorine from Narcissus pseudonarcissus and since then more than 100 alkaloids, exhibiting diverse biological activities, have been isolated from the Amaryllidaceae plants. Based on the present scientific evidence, it is likely that isocarbostyril constituents of the Amaryllidaceae, such as narciclasine, pancratistatin and their congeners, are the most important metabolites responsible for the therapeutic benefits of these plant species in the folk medical treatment of cancer. Notably, Narcissus poeticus L., used by the ancient Greek physicians, is now known to contain about 0.12 g of narciclasine per kg of fresh bulbs. The focus of the present research work is the chemistry and biology of these compounds as specifically relevant to their potential use in medicine. In particular, the anticancer evaluation of lycorine, narciclasine as well as of other Amaryllidaceae alkaloids and their synthetic derivatives are presented in this paper. The structure–activity relationships among some groups of Amaryllidaceae alkaloids will be discussed.     

C1,C2-ether derivatives of the Amaryllidaceae alkaloid lycorine: Retention of activity of highly lipophilic analogues against cancer cells

As a continuation of the studies aimed at the development of new anticancer agents derived from the Amaryllidaceae alkaloid lycorine, 35 C1,C2-ether analogues of this natural product were synthesized. The compounds were evaluated for antiproliferative activities in vitro in a panel of tumor cell lines with varied levels of apoptosis resistance. A strong correlation between the compound lipophilicity and anticancer activity was observed, indicating that cell permeability properties must be an important determinant in the design of lycorine-based anticancer agents. A theoretical docking model, consistent with the experimental observations, is presented.     

Alkaloid patterns in Leucojum aestivum shoot culture cultivated at temporary immersion conditions

The alkaloid patterns in Leucojum aestivum L. shoot culture cultivated at temporary immersion conditions were investigated using gas chromatography-mass spectrometry. 18 alkaloids were identified, and galanthamine, hamayne and lycorine were dominant. The L. aestivum 80 shoot culture, cultivated at temporary immersion conditions, is a prospective biological matrix for obtaining wide range Amaryllidaceae alkaloids, showing valuable biological and pharmacological activities. The temperature of cultivation influenced enzyme activities, catalyzing phenol oxidative coupling of 4′-O-methylnorbelladine and formation of the different groups Amaryllidaceae alkaloids. Decreasing the temperature of cultivation of L. aestivum 80 shoot culture led to activation of para-ortho’ phenol oxidative coupling (formation of galanthamine type alkaloids) and inhibited ortho-para’ and para-para’ phenol oxidative coupling (formation of lycorine and haemanthamine types alkaloids).     

Acetylcholinesterase inhibitory activity of some Amaryllidaceae alkaloids and Narcissus extracts

Amaryllidaceous plants produce pharmacologically active alkaloids, galanthamine being the most interesting for its use in the treatment of Alzheimer's disease as a cholinesterase inhibitor. The aim of this work was to test 23 pure Amaryllidaceae alkaloids and 26 extracts from different species of the genus Narcissus for their acetylcholinesterase inhibitory activity using galanthamine as a reference. Only seven alkaloids, belonging to the galanthamine and lycorine skeleton types, exhibited such an effect, sanguinine being the most active, even more than galanthamine. All the extracts with the highest acetylcholinesterase inhibitory activity contained galanthamine except that of N. assoanus, a lycorine type alkaloid-bearing species.     

LED Light Quality Affect Growth,Alkaloids Contents,and Expressions of Amaryllidaceae Alkaloids Biosynthetic Pathway Genes in Lycoris longituba

Journal of Plant Growth Regulation - Lycoris longituba is an important ornamental and medicinal plant and contains various Amaryllidaceae alkaloids such as galanthamine (GAL), lycorine (LYC), and...     

Alkaloids biosynthesis by <Emphasis Type="Italic">Pancratium maritimum</Emphasis> L. shoots in liquid culture

The process of alkaloid biosynthesis by Pancratium maritimum shoot culture, cultivated under submerged conditions, was investigated. Twenty-two compounds of different structural types of the Amaryllidaceae alkaloids (tyramine, narciclasine, galanthamine, haemanthamine, lycorine, pancracine, tazettine and homolycorine types) were detected in the studied samples from biomass and cultural liquid. Dominant compounds in the shoots were of tyramine, lycorine and haemanthamine types, whereas in the culture media were found mainly lycorine type compounds. Based on the multi-metabolic estimation of the alkaloid metabolism and physiological peculiarities, liquid cultures of P. maritimum shoots could be defined as prospective biological systems for producing bioactive molecules with acetylcholinesterase inhibitory and apoptotic activities.     

Selective cytochrome P450 3A4 inhibitory activity of Amaryllidaceae alkaloids

A library of natural and semi-synthetic Amaryllidaceae alkaloids was screened for cytochrome P450 3A4 (CYP3A4) inhibitory activity. Of the crinane, lycorane and galanthamine representatives examined two semi-synthetic silylated lycorane analogues, accessed via a chemoselective silylation strategy from lycorine, and the natural compound narciclasine exhibited low micromolar activities. Important pharmacological features uncovered include the lack of CYP3A4 inhibitory activity seen for galanthamine and the selective activity that is seen with narciclasine over pancratistatin.     

Further experiments on structure-activity relationships among the lycorine alkaloids

Synthetic lycorine analogues, five Amaryllidaceae alkaloids and narciclasine, all structurally related to lycorine, were tested for their ability to inhibit ascorbic acid biosynthesis in vivo. The highest potency observed was displayed by narciclasine followed by compounds having an aromatic C-ring. Derivatives modified at C-1 and/or C-2 were inactive, while the compound with a double bond between these positions is a weak inhibitor. Also lutessine and its deacetyl derivative having an α-methoxyl group bonded to C-4 of the D-ring appeared completely inactive. These results confirm that the presence of an appropriately substituted C-ring is a necessary requirement for optimal ‘response-triggering’ contact between the lycorine derivatives and the specific receptor. Functional groups jutting out from the α-side of the molecule do not allow a good fit with the binding sites.     

CGC-MS of alkaloids in Leucojum aestivum plants and their in vitro cultures

Underivatised alkaloid mixtures extracted from intact plants and in vitro cultures of Leucojum aestivum (Amaryllidaceae) were investigated by capillary GC-MS. Excellent peak resolution for the alkaloids was exhibited and isomers of galanthamine and N-formylnorgalanthamine were well separated. Fourteen alkaloids of galanthamine, lycorine and crinane types were identified, 11 in the intact plants and eight in the in vitro cultures.     

The Amaryllidaceae alkaloids haemanthamine,haemanthidine and their semisynthetic derivatives as potential drugs

Plants of the Amaryllidaceae family, have a wide distribution through both tropical and sub-tropical regions of the world. They have also a long and notable place in the history of traditional and Western medicine. Amaryllidaceae alkaloids are a structurally diverse group of plant metabolites with a wide range of biological properties including antimalarial, antitumor, antimicrobial, antiviral, enzyme inhibitory, antioxidant, anticonvulsant and antifungal activities. Among them, the haemanthamine-type alkaloids, which have the 5,10b-ethanophenanthridine skeleton as the core structure, represented by haemanthamine and haemanthidine, have received considerable attention, since they have been reported to possess antitumor properties. The present review aims to summarize comprehensively the research that has been published on the Amaryllidaceae alkaloids haemanthamine and haemanthidine.

     

New skeletons and new concepts in Amaryllidaceae alkaloids

The Amaryllidaceae alkaloids, represent a group of isoquinoline alkaloids, which are produced almost solely by members of the Amaryllidaceae family. The alkaloids of this family have attracted considerable amount of interest due to some important pharmacological activities they were shown to possess. In the last decade, our phytochemical studies on four Galanthus (Amaryllidaceae) species of Turkish origin have yielded quite a number of new alkaloids with diverse structures. Among these alkaloids, gracilines and plicamines constitute two new subgroups for the Amaryllidaceae alkaloids. The gracilines contain an incorporated 10b,4a-ethanoiminodibenzo[b,d]pyrane skeleton. The plicamines are dinitrogenous compounds, where the oxygen atom in position 7 of a tazettine skeleton is replaced by a nitrogen atom substituted by a pendant 4-hydroxyphenethyl moiety. One of the new alkaloids, galanthindole, which possesses a nonfused indole ring, unlike the already known subgroups of Amaryllidaceae alkaloids, may be considered as the prototype of a third new subgroup of the Amaryllidaceae alkaloids. Additionally, two known isoquinoline alkaloids which do not possess one of the established skeletons of the Amaryllidaceae alkaloids, namely ( − )-capnoidine and (+)-bulbocapnine, have been isolated from a Turkish Galanthus species. Totally, 21 new, 20 known alkaloids and 2 known lignans have been characterized. In this review, the isolation and structure elucidation of these compounds with interesting chemical structures are described.     

Oxocrinine and other alkaloids from Crinum americanum

From bulbs of Crinum americanum oxocrinine, an intermediate in the biosynthesis of Amaryllidaceae alkaloids, was isolated for the first time. In addition, the plant contains crinine, flexinine, O-acetylcrinine, lycorine, hippadine, pratorinine, pratorimine, pratosine, ungeremine and trisphaeridine. The alkaloids were identified by spectroscopic evidence, chemical transformations and partial syntheses.     

In search of a cytostatic agent derived from the alkaloid lycorine: synthesis and growth inhibitory properties of lycorine derivatives

As a continuation of our studies aimed at the development of a new cytostatic agent derived from an Amaryllidaceae alkaloid lycorine, we synthesized 32 analogues of this natural product. This set of synthetic analogues included compounds incorporating selective derivatization of the C1 versus C2 hydroxyl groups, aromatized ring C, lactamized N6 nitrogen, dihydroxylated C3-C3a olefin functionality, transposed olefin from C3-C3a to C2-C3 or C3a-C4, and C1 long-chain fatty esters. All synthesized compounds were evaluated for antiproliferative activities in vitro in a panel of tumor cell lines including those exhibiting resistance to proapoptotic stimuli and representing solid cancers associated with dismal prognoses, such as melanoma, glioblastoma, and non-small-cell lung cancer. Most active analogues were not discriminatory between cancer cells displaying resistance or sensitivity to apoptosis, indicating that these compounds are thus able to overcome the intrinsic resistance of cancer cells to pro-apoptotic stimuli. 1,2-Di-O-allyllycorine was identified as a lycorine analogue, which is 100 times more potent against a U373 human glioblastoma model than the parent natural product. Furthermore, a number of synthetic analogues were identified as promising for the forthcoming in vivo studies.     

Structure-activity studies on the lycorine pharmacophore: A potent inducer of apoptosis in human leukemia cells

The direct chemoselective differential functionalization of the ring-C hydroxyl groups present in the Amaryllidaceae alkaloid lycorine is described allowing for selective manipulation of the 1,2-hydroxyl groups. A mini-library comprised of synthetic and natural lycorane alkaloids was prepared and their apoptosis-inducing activity investigated in human leukemia (Jurkat) cells. Further insights into the nature of this interesting apoptosis-inducing pharmacophore are described, including the requirement of both free hydroxyl groups in ring-C.     

Two non-hydroxylated alkaloids in Crinum augustum

Several alkaloids were isolated from Crinum augustum grown in Assiut, Egypt. Two were identified as lycorine and buphanisine. In addition two new non-hydroxylated alkaloids of identical molecular formula C₁₇H₁₉NO₄ were investigated by spectroscopic methods. The gross structure of the first, termed augustine, belongs to the 1,2-epoxy-5, 10-b-ethanophenanthridine-type. In contrast the second could not be related to any of the known alkaloid types of the Amaryllidaceae.     

Cytotoxic activities of Amaryllidaceae alkaloids against gastrointestinal cancer cells

The treatment of many diseases is highly dependent on natural products and natural products can also be used as design templates for future anticancer drugs. Thirteen Amaryllidaceae alkaloids possessing α-crinane, β-crinane, galantamine, lycorine and tazettine-type skeleton have been isolated in our laboratory, and their cytotoxicity against p53-mutated gastrointestinal cancer cells were evaluated. At the same time, healthy small intestine cells were used to determine overall toxicity against noncancerous cells. In this study, we demonstrated that haemanthamine, haemanthidine and lycorine showed strong cytotoxicity against p53-mutated Caco-2 and HT-29 colorectal adenocarcinoma cells as quantified in terms of IC₅₀ values. We for the first time observed approximately 20 times higher IC₅₀values against normal intestine epithelial cells FHs-74 Int after haemanthamine and lycorine treatment when compared with Caco-2 and HT-29 cancer cells. In conclusion, our data indicate that α-C2 bridged haemanthamine may be perspective anticancer drug candidate for further semisynthetic modification and structure-activity relationship study.     

Antibacterial constituents of the plant family Amaryllidaceae

There is a pressing need in antibiotic drug discovery for new drugs to counterbalance the effects of multidrug resistance. Plants represent a viable platform for such endeavors owing to their traditional relevance in infectious disease therapies as well as their vast chemical resources. As many as fifty different species of the Amaryllidaceae are discernible with such functions in traditional medicine, thirty-nine of which have been subjected to pharmacological evaluations. Submicromolar antibacterial activities for several of these plants have been the driving force behind studies targeting their active constituents. This review accounts for close to a hundred of such entities, mainly isoquinoline alkaloids, which have been the focus in assays of thirty different bacterial pathogens. Promising activities were detected in several instances, although disappointingly the submicromolar level could not be breached. Also considered are structure–activity relationships which have emerged within the various groups of Amaryllidaceae alkaloids.