A Review on Phytochemicals of the Genus Maytenus and Their Bioactive Studies.

The genus Maytenus is a member of the Celastraceae family, of which several species have long been used in traditional medicine. Between 1976 and 2021, nearly 270 new compounds have been isolated and elucidated from the genus Maytenus. Among these, maytansine and its homologues are extremely rare in nature. Owing to its unique skeleton and remarkable bioactivities, maytansine has attracted many synthetic endeavors in order to construct its core structure. In this paper, the current status of the past 45 years of research on Maytenus, with respect to its chemical and biological activities are discussed. The chemical research includes its structural classification into triterpenoids, sesquiterpenes and alkaloids, along with several chemical synthesis methods of maytansine or maytansine fragments. The biological activity research includes activities, such as anti-tumor, anti-bacterial and anti-inflammatory activities, as well as HIV inhibition, which can provide a theoretical basis for the better development and utilization of the Maytenus.

Are Microbial Endophytes the 'Actual' Producers of Bioactive Antitumor Agents?

For millenia, plants have been a major source of medications against human and animal diseases. In the case of anticancer agents, a significant number of current agents can trace their source back to nominally plant secondary metabolites, with examples being taxol, vinca alkaloids, camptothecin (CPT), and their modified derivatives. However, it is now becoming apparent that these and other plant-derived materials, plus similar agents from marine sources may well have a microbe in their background. In this short Opinion, evidence for such claims are presented for some of the agents currently in use or in preclinical and clinical trials against cancer.

LC-HRMS quantitation of intact antibody drug conjugate trastuzumab emtansine from rat plasma.

AIM: Compared with small molecules, LC-MS quantitation of larger biotherapeutic proteins such as antibodies and antibody-drug conjugates at the intact level presents many challenges in both LC and MS due to their higher molecular weight, bigger size, structural complexity and heterogeneity. RESULTS & CONCLUSION: In this study, quantitation of an intact lysine-linked antibody-drug conjugate, trastuzumab emtansine is presented. Trastuzumab emtansine was extracted from rat plasma using bead-based immunoaffinity capture; after elution from the beads, it was directly analyzed on a LC-HRMS system. Quantitation using both extracted ion chromatogram and deconvoluted mass peaks was evaluated. A limit of quantitation was approximately 20 ng on column with a linear dynamic range from 5 to 100 µg/ml. In addition, the reproducibility and distribution of the drug-to-antibody ratio at different trastuzumab emtansine concentrations were discussed.

Occurrence and spatial distribution of maytansinoids in Putterlickia pyracantha, an unexplored resource of anticancer compounds.

Maytansinoids possess remarkable antibiotic activities along with high cytotoxicity, many of which are currently used (or in clinical trials) in the treatment of breast cancer. Celastraceous plants and their associated microorganisms serve as an important resource of maytansinoids. Here, we report the occurrence and structural elucidation of several maytansinoids in Putterlickia pyracantha plants bioprospected in South Africa. In addition to maytansine, which is already known to be present in this species, we show the presence of maytanprine, maytanbutine, maytanvaline, normaytancyprine and an abundant maytansine precursor in different tissues using high-resolution mass spectrometry. Furthermore, we identified two new hydroxylated maytansinoids by HRMS(2) analyses. We also employed MALDI-imaging-HRMS to study the spatial distribution and localization of the maytansinoids within the different plant tissues. On the one hand, the fragmentation pathways of the maytansinoids we report herein using HRMS(n) will allow quick identification of these compounds in the future without isolating from the natural resources. On the other hand, MALDI-imaging-HRMS revealed insights into the plausible ecological roles and biosynthetic pathways of these compounds in P. pyracantha plants.

Endophytes are hidden producers of maytansine in Putterlickia roots.

Several recent studies have lent evidence to the fact that certain so-called plant metabolites are actually biosynthesized by associated microorganisms. In this work, we show that the original source organism(s) responsible for the biosynthesis of the important anticancer and cytotoxic compound maytansine is the endophytic bacterial community harbored specifically within the roots of Putterlickia verrucosa and P. retrospinosa plants. Evaluation of the root endophytic community by chemical characterization of their fermentation products using HPLC-HRMS(n), along with a selective microbiological assay using the maytansine-sensitive type strain Hamigera avellanea revealed the endophytic production of maytansine. This was further confirmed by the presence of AHBA synthase genes in the root endophytic communities. Finally, MALDI-imaging-HRMS was used to demonstrate that maytansine produced by the endophytes is typically accumulated mainly in the root cortex of both plants. Our study, thus, reveals that maytansine is actually a biosynthetic product of root-associated endophytic microorganisms. The knowledge gained from this study provides fundamental insights on the biosynthesis of so-called plant metabolites by endophytes residing in distinct ecological niches.

A study of the bacterial community in the root system of the maytansine containing plant Putterlickia verrucosa.

Maytansinoid compounds are ansa antibiotics occurring in the bacterium Actinosynnema pretiosum, in mosses and in higher plants such as Putterlickia verrucosa (E. Meyer ex Sonder) Szyszyl. The disjunct occurrence of maytansinoids has led to the consideration that plant-associated bacteria may be responsible for the presence of maytansinoids in P. verrucosa plants. Investigation of the bacterial community of this plant by molecular methods led to the observation that A. pretiosum, a maytansine-producing bacterium, is likely to be an inhabitant of the rhizosphere and the endorhiza of P. verrucosa.

An isolable acyclic hemiacetal of ansamitocin P-3.

During impurity analysis of maytansinol (2), produced from the reduction of ansamitocin P-3 (AP-3, 1), a surprisingly stable acyclic hemiacetal (4) was isolated. A combination of 1D and 2D NMR experiments, along with liquid chromatography-mass spectrometry data was used to confirm the structure. Comparison of NMR data to the previously reported bridged acetal (3), a by-product of AP-3 reduction, supports reassignment of the latter to the former. Additionally, ROESY data, in conjunction with minimum energy calculations, support intramolecular hydrogen bonding that is involved in stabilizing the hemiacetal. This report adds another example to the very short list of isolable acyclic hemiacetals.

Preparative isolation and purification of anti-tumor agent ansamitocin P-3 from fermentation broth of Actinosynnema pretiosum using high-performance counter-current chromatography.

Ansamitocin P-3 is a potent anti-tumor maytansinoid found in Actinosynnema pretiosum. However, due to the complexity of the fermentation broth of Actinomycete, how to effectively separate ansamitocin P-3 is still a challenge. In this study, both analytical and preparative high-performance counter-current chromatography were successfully used to separate and purify ansamitocin P-3 from fermentation broth. A total of 28.8 mg ansamitocin P-3 with purity of 98.4% was separated from 160 mg crude sample of fermentation broth in less than 80 min with the two-phase solvent system of hexane-ethyl acetate-methanol-water (0.6:1:0.6:1, v/v/v/v). The purity and structural identification were determined by HPLC, (1)H NMR, (13)C NMR and mass spectroscopy.

Amide N-glycosylation by Asm25, an N-glycosyltransferase of ansamitocins.

Ansamitocins are potent antitumor maytansinoids produced by Actinosynnema pretiosum. Their biosynthesis involves the initial assembly of a macrolactam polyketide, followed by a series of postpolyketide synthase (PKS) modifications. Three ansamitocin glycosides were isolated from A. pretiosum and fully characterized structurally as novel ansamitocin derivatives, carrying a beta-D-glucosyl group attached to the macrolactam amide nitrogen in place of the N-methyl group. By gene inactivation and complementation, asm25 was identified as the N-glycosyltransferase gene responsible for the macrolactam amide N-glycosylation of ansamitocins. Soluble, enzymatically active Asm25 protein was obtained from asm25-expressing E. coli by solubilization from inclusion bodies. Its optimal reaction conditions, including temperature, pH, metal ion requirement, and Km/Kcat, were determined. Asm25 also showed broad substrate specificity toward other ansamycins and synthetic indolin-2-ones. To the best of our knowledge, this represents the first in vitro characterization of a purified antibiotic N-glycosyltransferase.

The ansacarbamitocins: polar ansamitocin derivatives.

The ansacarbamitocins are a new family of maytansinoids that are unusually substituted with a glucose subunit and two carbamate functional groups and exhibit modest activity against some agricultural fungal disease organisms. Ansacarbamitocins A-F ( 1- 6) all consist of the same macrocyclic core as the ansamitocins, with variation occurring on the glucose unit, while ansacarbamitocins A1 and B1 ( 7, 8) additionally lack the epoxide group on C-4 and C-5.

Cytotoxic activity of maytanprine isolated from Maytenus diversifolia in human leukemia K562 cells.

We examined the cytotoxic effect of maytanprine isolated from the methanol extract of Maytenus diversifolia on human leukemia K562 cells using a flow cytometer and compared its cytotoxicity with that of maytansine, a potent cytotoxic maytansinoid. Maytanprine at concentrations of 0.03 nM or more (up to 1 nM) attenuated cell growth with decreasing cell viability and increased the population of shrunken cells in a concentration-dependent manner. Complete inhibition of growth by maytanprine was observed at concentrations of 0.3 nM or more. The compound at 0.03 nM markedly decreased the population at G0G1 phase in the cell cycle, but only slightly decreased that in the G2M phase, suggesting the possibility that it inhibits or delays cell division, and increased the population of cells with hypodiploidal DNA (apoptotic cells). The potency of maytanprine in inhibiting cell growth was greater than that of maytansine, although the inhibitory action of maytanprine was similar to that of maytansine. The results suggest that maytanprine exerts a potent inhibitory action on the growth of human leukemia K562 cells. M. diversifolia is one natural source of maytanprine, which is more cytotoxic than maytansine.

Antitumor agents, 112. Emarginatine B, a novel potent cytotoxic sesquiterpene pyridine alkaloid from Maytenus emarginata.

A new sesquiterpene pyridine alkaloid, emarginatine B [2] has been isolated, along with maytansine [3], from Maytenus emarginata. Emarginatine B showed potent cytotoxicity against human KB cells (ED50 = 0.4 micrograms/ml). Spectral correlations established its structure as a 9-benzoate and C-8 epimer of emarginatine A [1]. The conformational aspect of the latter compound was elucidated by nmr studies, including the use of 2D-nmr techniques and difference nOe methods.

Ansamitocin P-3, a maytansinoid, from Claopodium crispifolium and Anomodon attenuatus or associated actinomycetes.

Guided by cytotoxicity, ansamitocin P-3, a maytansinoid, was isolated in very low yield from two members of the moss family Thuidiaceae, Claopodium crispifolium (Hook.) Ren. & Card. and Anomodon attenuatus (Hedw.) Hueb. Ansamitocin P-3 showed potent cytotoxicity against the human solid tumor cell lines A-549, HT-29. A possible basis for the occurrence of this compound in mosses is discussed.

Antitumor principles in mosses: the first isolation and identification of maytansinoids, including a novel 15-methoxyansamitocin P-3.

A novel 15-methoxyansamitocin P-3 [2], in company with three known maytansinoids 1, 3, and 4, was isolated for the first time from two Japanese mosses, Isothecium subdiversiforme and Thamnobryum sandei. All are potent cytotoxic compounds.