Total Biosynthesis of the Tubulin-Binding Alkaloid Colchicine.

Colchicine (1) is a bioactive plant alkaloid from Colchicum and Gloriosa species that is used as a pharmaceutical treatment for inflammatory diseases, including gouty arthritis and familial Mediterranean fever. The activity of this alkaloid is attributed to its ability to bind tubulin dimers and inhibit microtubule assembly, which not only promotes anti-inflammatory effects, but also makes colchicine a potent mitotic poison. The biochemical origins of colchicine biosynthesis have been investigated for over 50 years, but only recently has the underlying enzymatic machinery become clear. Here, we report the discovery of multiple pathway enzymes from Gloriosa superba that allows for the reconstitution of a complete metabolic route to 1. This includes three enzymes that process a previously established tropolone-containing intermediate into 1 via tailoring of the nitrogen atom. We further demonstrate the total biosynthesis of enantiopure (-)-1 from primary metabolites via heterologous production in a model plant, thus enabling future efforts for the metabolic engineering of this medicinal alkaloid. Additionally, our results provide insight into the timing and tissue specificity for the late stage modifications required in colchicine biosynthesis, which are likely connected to the biological functions for this class of medicinal alkaloids in native producing plants.

Screening the elite chemotypes of Gloriosa superba L. in India for the production of anticancer colchicine: simultaneous microwave-assisted extraction and HPTLC studies.

BACKGROUND: Gloriosa superba L. (Colchicaceae) is a high-value medicinal plant indigenous to Africa and Southeast Asia. Its therapeutic benefits are well-established in traditional medicines including Ayurveda. It is well known for its natural bioactive compound colchicine which exhibits a wide range of pharmacological activities i.e. rheumatism, gout and was also introduced into clinical practices. The increasing demand as well as its illegal harvesting has brought this valuable plant under threatened category. METHODS: The present investigation describes a microwave assisted extraction (MAE) strategy coupled with a densitometric-high performance thin layer chromatographic (HPTLC) methodology for the analysis of colchicine from 32 different populations of G. superba. A Box-Behnken statistical design (3 level factor) has been employed to optimize MAE, in which power of microwave, time of irradiation, aqueous ethanol and pH were used as independent variables whereas colchicine was used as the dependent variables. Chromatography was carried out on Silica gel 60 F254 TLC plates with toluene: methanol, 85:15 (v/v) being used as solvent system. Densitometric measurement was performed at λ=254 nm following post-derivatization (10% methanolic sulphuric acid). RESULTS: Optimal conditions for extraction to obtain the maximum colchicine yield was found to be 7.51 mg g- 1 which was very close to be predicted response 7.48 mg g- 1 by maintaining microwave power (460 W), irradiation time (6.4 min), aqueous ethanol-30, pH -3. Colchicine content ranged between 2.12-7.58 mg g- 1 among 32 G. superba populations in which only three chemotypes viz. GS- 1, GS- 3, and GS- 2 collected from West Bengal and Sikkim, respectively exhibited maximum yield of colchicine. CONCLUSION: Therefore, this newly developed optimized MAE coupled with HPTLC densitometry methodology not only quantifies colchicine in order to identify elite chemotypes of G. superba, but it also encourages in selecting high yielding populations of the plants for industrial use and economic boost for the farmers. This validated, simple and reproducible HPTLC protocol is being used for the first time to estimate colchicine from natural populations of G. superba obtained from 32 different geographical regions of India.

Puzzling Out the Colchicine Biosynthetic Pathway.

Colchicine is among the oldest plant natural products (NPs) still used for treating a broad spectrum of human diseases including gout and other articular inflammation disorders. This molecule is synthesized by several herbaceous species related to the Liliaceae family, but in very low quantities in whole plants. As for many pharmaceutical compounds from plants, the production of colchicine still depends on the natural resource from which it is extracted. From the past decade, metabolic engineering has progressively become a credible alternative for the cost-effective large-scale production of several valuable NPs. In the same vein, Nett and colleagues recently reported an unprecedented advance in the field for colchicine. By using a combination of transcriptomics, metabolomics and pathway reconstitution, Sattely's group deciphered a near-complete biosynthetic pathway to colchicine without prior knowledge of biosynthetic genes. Besides constituting a benchmark for the elucidation of natural product biosynthetic pathways, it opens unprecedented perspectives regarding metabolic engineering of colchicine biosynthesis.

DNA demethylation overcomes attenuation of colchicine biosynthesis in an endophytic fungus Diaporthe.

Fungal endophytes, a major component of the plant host microbiome, are known to synthesize plant-derived metabolites in vitro. However, attenuation of metabolite production upon repeated sub-culturing is a major drawback towards utilizing them as an alternative for plant-derived metabolites. In this study, we isolated Diaporthe perseae, a fungal endophyte from Gloriosa superba tubers, which showed the production of colchicine in axenic cultures. Mass spectrometry, Nuclear Magnetic Resonance spectroscopy, and tubulin polymerization assays confirmed the compound to be colchicine. Repeated sub-culturing of the endophyte for 10 generations led to a reduction in the yield of the metabolite from 55.25 µg/g to 2.32 µg/g of mycelial dry weight. Treatment of attenuated cultures with DNA methylation inhibitor 5-azacytidine resulted in increased metabolite concentration (39.68 µg/g mycelial dry weight) in treated samples compared to control (2.61 µg/g mycelial dry weight) suggesting that 5-azacytidine can induce demethylation of the fungal genome to overcome the phenomenon of attenuation of metabolite synthesis. Reduced levels of global methylation were observed upon 5-azacytidine treatment in attenuated cultures (0.41 % of total cytosines methylated) as compared to untreated control (0.78 % of total cytosines methylated). The results provide a significant breakthrough in utilizing fungal endophytes as a veritable source of plant-derived metabolites from critically endangered plants.

Discovery and engineering of colchicine alkaloid biosynthesis.

Few complete pathways have been established for the biosynthesis of medicinal compounds from plants. Accordingly, many plant-derived therapeutics are isolated directly from medicinal plants or plant cell culture1. A lead example is colchicine, a US Food and Drug Administration (FDA)-approved treatment for inflammatory disorders that is sourced from Colchicum and Gloriosa species2-5. Here we use a combination of transcriptomics, metabolic logic and pathway reconstitution to elucidate a near-complete biosynthetic pathway to colchicine without prior knowledge of biosynthetic genes, a sequenced genome or genetic tools in the native host. We uncovered eight genes from Gloriosa superba for the biosynthesis of N-formyldemecolcine, a colchicine precursor that contains the characteristic tropolone ring and pharmacophore of colchicine6. Notably, we identified a non-canonical cytochrome P450 that catalyses the remarkable ring expansion reaction that is required to produce the distinct carbon scaffold of colchicine. We further used the newly identified genes to engineer a biosynthetic pathway (comprising 16 enzymes in total) to N-formyldemecolcine in Nicotiana benthamiana starting from the amino acids phenylalanine and tyrosine. This study establishes a metabolic route to tropolone-containing colchicine alkaloids and provides insights into the unique chemistry that plants use to generate complex, bioactive metabolites from simple amino acids.

Biotransformation of colchicinoids into their corresponding 3-O-glucosyl derivatives by selected strains of Bacillus megaterium.

Natural colchicinoids and their semisynthetic derivatives are important active ingredients for pharmaceutical applications. Thiocolchicoside (3-demethoxy-3-glucosyloxythiocolchicine) is used in several countries as standard therapy for the treatment of diseases of the muscle-skeletal system, due to its potent antiinflammatory and myorelaxant properties. Manufacturing of thiocolchicoside requires a key step, the regioselective demethylation and glucosylation of chemically derivative thiocolchicine. High selectivity and efficiency of this transformation cannot be achieved in a satisfactory way with a chemical approach. In particular, the chemical demethylation, a part from requiring toxic and aggressive reagents, generates a complex mixture of products with no industrial usefulness. We report herein an efficient, direct and green biotransformation of thiocolchicine into thiocolchicoside, performed by a specific strain of Bacillus megaterium. The same process, with minor modifications, can be used to convert the by-product 3-O-demethyl-thiocolchicine into thiocolchicoside. In addition, we describe the B. megaterium strain selection process and the best conditions for this effective double biotransformation. The final product has a pharmaceutical quality, and the process has been industrialised.

Chemical mechanisms involved during the biosynthesis of tropolones.

Tropolones are seven-membered aromatic rings which feature in the core of several important bioactive natural products including colchicine and stipitatic acid. Studies of their biosynthesis over nearly 70 years have revealed four parallel routes from polyketide, terpene, alkaloid and shikimate precursors, but the key steps all involve ring expansion of an alkylated 6-membered ring. Recent studies in fungi have revealed details of the individual chemical steps at the molecular level, but detailed molecular biosynthetic pathways in other organisms remain obscure.

Colchicine semisynthetics: chemotherapeutics for cancer?

Nitrogen-containing bioactive alkaloids of plant origin play a significant role in human health and medicine. Several semisynthetic antimitotic alkaloids are successful in anticancer drug development. Gloriosa superba biosynthesizes substantial quantities of colchicine, a bioactive molecule for gout treatment. Colchicine also has antimitotic activity, preventing growth of cancer cells by interacting with microtubules, which could lead to the design of better cancer therapeutics. Further, several colchicine semisynthetics are less toxic than colchicine. Research is being conducted on effective, less toxic colchicine semisynthetic formulations with potential drug delivery strategies directly targeting multiple solid cancers. This article reviews the dynamic state of anticancer drug development from colchicine semisynthetics and natural colchicine production and briefly discusses colchicine biosynthesis.

Statistical optimization of process variables for the production of an anticancer drug (colchicine derivatives) through fermentation: at scale-up level.

Effect of various nutritional components and fermentation parameters on biotransformation of colchicine using Bacillus megaterium ACBT03 to produce 3-demethylated colchicine (3-DMC) has been investigated. Initially, Plackett-Burman (PB) design was used to evaluate the 11 nutritional variables to screen medium component that significantly influences the 3-demethylated colchicine (3-DMC) production. Three most statistically significant nutrients that is starch, glycerol and yeast extract were identified. Response surface methodology was used to optimize fermenter operational factors pH, temperature, impeller tip velocity and aeration rate for high 3-DMC production. The predicted results of 3-DMC yield (7689.13mg/l) were obtained at 5-l-jar fermenter after optimization of pH 6.8, temperature 28°C, impeller tip velocity 4650cm/min, and aeration rate 2.0vvm. The validity of model was confirmed; and the optimum medium designed led a maximum 3-DMC yield of 7335mg/l, which had 3-4% variation with predicted results. Furthermore, the experiment was scaled up in the 70-l fermenter.

Microsome-mediated transformation of O-methylandrocymbine to demecolcine and colchicine.

Microsomal preparations from immature seeds of Colchicum autumnale L. catalyse the ring expansion reaction of O-methylandrocymbine to demecolcine in the presence of NADPH and O2. In addition evidence is given for further transformation of demecolcine to colchicine in the presence of acetyl-CoA and NADPH.

Radioimmunoassay for colchicine: synthesis and properties of three haptens.

For the development of radioimmunoassay procedures for colchicine, three haptens, N-ethylamino-colchiceinamide, 4-formylchochicine - (O-carboxymethyl) oxime and 4-hydroxymethylcolchicine O-hemisuccinic acid were synthetized and characterized by mass and proton magnetic resonance spectrometries. The conjugates obtained by coupling the haptens to bovine serum albumin were employed to immunize rabbits and goats.

Ideas and experiments in biosynthesis.

During the past 25 years or so, there has been almost undreamed of progress in understanding the pathways by which living systems synthesize the remarkable range of substances they contain. This progress could not have been made had not isotopes of carbon, nitrogen, hydrogen and oxygen become available in quantity at a time when the intellectual climate was right for their penetrating application in biosynthetic research. It was by his generation of far-reaching ideas about biosynthesis that Sir Robert Robinson made such a major contribution to establishing this right climate. His thinking pointed the way for many studies on living systems. Several examples will be discussed which were of particular interest to Sir Robert, such as the biosynthesis of morphine and colchicine, and another topic which is currently at a fascinating stage of development, the biosynthesis of natural porphyrins. New equipment and techniques, especially 13C n.m.r. spectroscopy and high-pressure liquid chromatography, have helped in a borad study of the biochemical conversion of porphobilinogen into uroporphyrinogen-III which must be formed by some rearrangement process. It is established that a single intramolecular rearrangement occurs and that this step comes at the end of the assembly of four porphobilinogen units which forms the unrearranged bilane.

Distribution of porcine fecal coliflora throughout a barn.

Three hundred and seventy strains of fecal Escherichia coli were isolated from pigs in one barn and 475, 539 and 490 strains were isolated at each of three successive samplings in another barn. The majority of the E. coli isolates obtained at any one sampling belonged to a small number of E. coli types. Three repeated samplings in one barn indicated that the dominant E. coli types harboured by pigs in this barn were constantly changing. The results also suggested that, within a particular barn, a successive batch of pigs could experience the same sequence of E. coli types. Colicin production appeared to be associated with dominant strains and the proportion of colicin producers in different investigations ranged from 36 to 68%.