Catharanthine Catharanthine is a terpene indole alkaloid produced by the medicinal plant '' Catharanthus roseus'' and '' Tabernaemontana divaricata''. Catharanthine is derived from strictosidine, but the exact mechanism by which this happens is currently unkn ...

and vindoline are

terpenoid The terpenoids, also known as isoprenoids, are a class of naturally occurring organic compound, organic chemicals derived from the 5-carbon compound isoprene and its derivatives called terpenes, diterpenes, etc. While sometimes used interchangeabl ...

indole Indole is an organic compound with the formula . Indole is classified as an aromatic heterocycle. It has a bicyclic structure, consisting of a six-membered benzene ring fused to a five-membered pyrrole ring. Indoles are derivatives of indole ...

alkaloids Alkaloids are a broad class of naturally occurring organic compounds that contain at least one nitrogen atom. Some synthetic compounds of similar structure may also be termed alkaloids. Alkaloids are produced by a large variety of organisms i ...

naturally produced within the Madagascar periwinkle plant (''Catharanthus roseus'') whose

dimerization In chemistry, dimerization is the process of joining two identical or similar molecular entities by bonds. The resulting bonds can be either strong or weak. Many symmetrical chemical species are described as dimers, even when the monomer is u ...

produces the anti-cancer drugs

vinblastine Vinblastine, sold under the brand name Velban among others, is a chemotherapy medication, typically used with other medications, to treat a number of types of cancer. This includes Hodgkin's lymphoma, non-small-cell lung cancer, bladder canc ...

and

vincristine Vincristine, also known as leurocristine and sold under the brand name Oncovin among others, is a chemotherapy medication used to treat a number of types of cancer. This includes acute lymphocytic leukemia, acute myeloid leukemia, Hodgkin lym ...

. The precursor of catharanthine and vindoline is

strictosidine Strictosidine is a natural chemical compound and is classified as a glucoalkaloid and a vinca alkaloid. It is formed by the Pictet–Spengler condensation reaction of tryptamine with secologanin, catalyzed by the enzyme strictosidine synthase. ...

, the common precursor of all indole alkaloids. Misra, N., Luthra, R., Singh, K. L., & Kumar, S. (1999). Recent advances in biosynthesis of alkaloids. Comprehensive Natural Products Chemistry, 25–59. https://doi.org/10.1016/b978-0-08-091283-7.00127-2 The localization of catharanthine and vindoline within the plant tissue has been heavily studied in recent years with conflicting results. The dimerization of catharanthine and vindoline to form vinblastine and vincristine is catalyzed by a

peroxidase Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzymes which play a role in various biological processes. They are named after the fact that they commonly break up peroxides, and should not be confused with other ...

and a

reductase In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually uti ...

, and includes several intermediate compounds.Li, C., Wood, J. C., Vu, A. H., Hamilton, J. P., Rodriguez Lopez, C. E., Payne, R. M., Serna Guerrero, D. A., Gase, K., Yamamoto, K., Vaillancourt, B., Caputi, L., O’Connor, S. E., & Robin Buell, C. (2023). Single-cell multi-omics in the medicinal plant Catharanthus roseus. Nature Chemical Biology, 19(8), 1031–1041. https://doi.org/10.1038/s41589-023-01327-0

Origin

The compounds catharanthine and vindoline are naturally produced within the leaves of ''C. roseus'' plants. The ''C. roseus'' plant is a member of the

Apocynaceae Apocynaceae (, from '' Apocynum'', Greek for "dog-away") is a family of flowering plants that includes trees, shrubs, herbs, stem succulents, and vines, commonly known as the dogbane family, because some taxa were used as dog poison. Notable mem ...

family, which are flowering plants that are found primarily in tropical and subtropical areas of the world. ''C. roseus'' are poisonous but medically useful plants due to the various terpenoid indole alkaloids (TIAs) they produce in their leaves, roots, and flowers. The precursor of catharanthine and vindoline is strictosidine, formed by the dimerization of

tryptamine Tryptamine is an indolamine metabolite of the essential amino acid tryptophan. The chemical structure is defined by an indole—a fused benzene and pyrrole ring, and a 2-aminoethyl group at the second carbon (third aromatic atom, with the firs ...

and

secologanin Secologanin is a secoiridoid monoterpene synthesized from geranyl pyrophosphate in the mevalonate pathway. Secologanin then proceeds with dopamine or tryptamine to form ipecac and terpene indole alkaloids, respectively. Biosynthesis Secologa ...

. The reaction scheme to form catharanthine and vindoline involves more than 20

enzymes An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...

, of which not all have been isolated and characterized.

Localization

Catharanthine and vindoline are located predominately in the leaf tissue of ''C. roseus'' plants. In 1996-1998, three studies headed by Mariana Sottomayor from the University of Porto, Portugal localized catharanthine and vindoline in the

vacuoles A vacuole () is a membrane-bound organelle which is present in plant and fungal cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic mo ...

of the plant's cells. This claim was supported by a study in 2008.Costa MM, Hilliou F, Duarte P, Pereira LG, Almeida I, Leech M, Memelink J, Barceló AR, Sottomayor M. Molecular cloning and characterization of a vacuolar class III peroxidase involved in the metabolism of anticancer alkaloids in Catharanthus roseus. Plant Physiol. 2008 Feb;146(2):403-17. doi: 10.1104/pp.107.107060. Epub 2007 Dec 7. PMID 18065566; PMCID: PMC2245823 However, in 2015, a paper compiled data on the localization of TIAs within ''C. roseus'' cells from several studies reported that catharanthine is located in the upper

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...

cells of the leaf and vindoline is located in the

laticifer A laticifer is a type of elongated secretory cell found in the leaves and/or stems of plants that produce latex and rubber as secondary metabolites. Laticifers may be divided into: *Articulated laticifers, i.e., composed of a series of cells joine ...

cells of the leaf.Qu, Y., Easson, M. L., Froese, J., Simionescu, R., Hudlicky, T., & De Luca, V. (2015). Completion of the seven-step pathway from Tabersonine to the Anticancer Drug Precursor Vindoline and its assembly in yeast. Proceedings of the National Academy of Sciences, 112(19), 6224–6229. https://doi.org/10.1073/pnas.1501821112 This conclusion was both confirmed and contradicted by a recent study that used single-cell multi-omics to locate catharanthine and vindoline. This study, published in 2023, discovered the enzyme that produces catharanthine in epidermis cells and catharanthine molecules in idioblast cells. The study also discovered vindoline in idioblast cells.

Reaction scheme

The coupling reaction of catharanthine and vindoline begins with the activation of catharanthine by a peroxidase. This peroxidase was identified, characterized, and named ''CrPrx1'' by the Costa group in 2008. ''CrPrx1'' is dependent on the

hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid that is slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usua ...

naturally present in the leaf tissue to activate catharanthine. Once activated, catharanthine reacts with vindoline to form an

iminium In organic chemistry, an iminium cation is a polyatomic ion with the general structure . They are common in synthetic chemistry and biology. Structure Iminium cations adopt alkene-like geometries: the central C=N unit is nearly coplanar with a ...

intermediate compound. A reductase reduces this compound to form alpha-3’,4’- anhydrovinblastine (AHVB).Sottomayor M, Ros Barceló A. Peroxidase from Catharanthus roseus (L.) G. Don and the biosynthesis of alpha-3',4'-anhydrovinblastine: a specific role for a multifunctional enzyme. Protoplasma. 2003 Sep;222(1-2):97-105. doi: 10.1007/s00709-003-0003-9. PMID 14513315. The reductase is theorized to be a tetrahydroalstonine

synthase In biochemistry, a synthase is an enzyme that catalyses a synthesis process. Note that, originally, biochemical nomenclature distinguished synthetases and synthases. Under the original definition, synthases do not use energy from nucleoside trip ...

called ''THAS''. AHVB reacts further to form vinblastine and vincristine, although this reaction scheme is yet to be fully understood.

Limiting factors

The dimerization of catharanthine and vindoline produces the anti-cancer drugs vinblastine and vincristine.Anamika Paul, Krishnendu Acharya, Nilanjan Chakraborty, Biosynthesis, extraction, detection and pharmacological attributes of vinblastine and vincristine, two important chemotherapeutic alkaloids of Catharanthus roseus (L.) G. Don: A review, South African Journal of Botany, Volume 161, 2023, Pages 365-376, ISSN 0254-6299, https://doi.org/10.1016/j.sajb.2023.08.034. The natural concentrations of catharanthine and vindoline are much higher than the concentrations of vinblastine and vincristine, which suggests that the reaction between catharanthine and vindoline is a

rate-limiting step In chemical kinetics, the overall rate of a reaction is often approximately determined by the slowest step, known as the rate-determining step (RDS or RD-step or r/d step) or rate-limiting step. For a given reaction mechanism, the prediction of the ...

in the two anti-cancer drugs’ production. It has been theorized that the dimerization of catharanthine and vindoline is limited by multiple factors, two being the availability of hydrogen peroxide and the localization of the TIAs. The synthesis of hydrogen peroxide is heavily regulated within the leaves of ''C. roseus'', which means that there is a natural lack of hydrogen peroxide that may limit the amount of catharanthine activated by ''CrPrx1''. The location of catharanthine and vindoline has been heavily investigated and debated, with studies finding the TIAs in the vacuoles, epidermis cells, idioblast cells, and laticifer cells. These studies show that some level of cellular separation between the alkaloids limits their ability to interact and react to produce vinblastine and vincristine.

References

{{reflist Dimers (chemistry)