Isolation and absolute configuration of SMTP-0, a simplest congener of the SMTP family nonlysine-analog plasminogen modulators

Amine-Regulated pri-SMTP Oxidation in SMTP Biosynthesis in Stachybotrys: Possible Implication in Nitrogen Acquisition

SMTP (the name SMTP is derived from Stachybotrys microspora triprenyl phenol) is a family of triprenyl phenol secondary metabolites from a black mold, Stachybotrys microspora. Some SMTP congeners exhibit anti-inflammatory and profibrinolytic activities that, in combination, contribute to the treatment of ischemic stroke. The final step in the SMTP biosynthesis is a non-enzymatic amine conjugation with an o-phthalaldehyde moiety of the precursor pre-SMTP, which can form adducts with proteins and nucleic acids. Thus, pre-SMTP formation should be a precisely regulated, rate-limiting step in the SMTP biosynthesis. To address the mechanism backing this regulation, we purified a metabolite that rapidly disappeared following amine feeding, identifying a novel compound, pri-SMTP. Furthermore, an enzyme, designated as pri-SMTP oxidase, responsible for pri-SMTP conversion to pre-SMTP, was purified. The formation of pri-SMTP, which is regulated by nitrogen and carbon nutrients, occurred in particular septate mycelia. Although pri-SMTP oxidase was expressed constitutively, the consumption of pri-SMTP was accelerated only when a primary amine was fed. Thus, SMTP biosynthesis is regulated by at least three mechanisms: (i) pri-SMTP formation affected by nutrients, (ii) the compartmentalization of pri-SMTP formation/storage, and (iii) amine-regulated pri-SMTP oxidation. Amine-regulated SMTP formation (i.e., amine-capturing with pre-SMTP) may play a role in the nitrogen acquisition/assimilation strategy in S. microspora, since pri-SMTP synthesis occurs on non-preferred nitrogen.

Progress in Isoindolone Alkaloid Derivatives from Marine Microorganism: Pharmacology, Preparation, and Mechanism

Compound 1 (SMTP-7, also FGFC1), an isoindolone alkaloid from marine fungi Starchbotrys longispora FG216 and fungi Stachybotrys microspora IFO 30018, possessed diverse bioactivities such as thrombolysis, anti-inflammatory and anti-oxidative properties, and so on. It may be widely used for the treatment of various diseases, including cerebral infarction, stroke, ischemia/reperfusion damage, acute kidney injury, etc. Especially in cerebral infarction, compound 1 could reduce hemorrhagic transformation along with thrombolytic therapy, as the traditional therapies are accompanied with bleeding risks. In the latest studies, compound 1 selectively inhibited the growth of NSCLC cells with EGFR mutation, thus demonstrating its excellent anti-cancer activity. Herein, we summarized pharmacological activities, preparation of staplabin congeners—especially compound 1—and the mechanism of compound 1, with potential therapeutic applications.

Absolute configuration determination of SMTP-7 via microcrystal electron diffraction (MicroED)

The absolute configuration of a clinically important drug candidate, SMTP-7, with only micron-sized powders available, is directly obtained via microcrystal electron diffraction (MicroED) analysis.

Natural Compounds Isolated from Stachybotrys chartarum Are Potent Inhibitors of Human Protein Kinase CK2

A large number of secondary metabolites have been isolated from the filamentous fungus Stachybotrys chartarum and have been described before. Fourteen of these natural compounds were evaluated in vitro in the present study for their inhibitory activity towards the cancer target CK2. Among these compounds, stachybotrychromene C, stachybotrydial acetate and acetoxystachybotrydial acetate turned out to be potent inhibitors with IC₅₀ values of 0.32 µM, 0.69 µM and 1.86 µM, respectively. The effects of these three compounds on cell proliferation, growth and viability of MCF7 cells, representing human breast adenocarcinoma as well as A427 (human lung carcinoma) and A431 (human epidermoid carcinoma) cells, were tested using EdU assay, IncuCyte^® live-cell imaging and MTT assay. The most active compound in inhibiting MCF7 cell proliferation was acetoxystachybotrydial acetate with an EC₅₀ value of 0.39 µM. In addition, acetoxystachybotrydial acetate turned out to inhibit the growth of all three cell lines completely at a concentration of 1 µM. In contrast, cell viability was impaired only moderately, to 37%, 14% and 23% in MCF7, A427 and A431 cells, respectively.

Impact of SMTP Targeting Plasminogen and Soluble Epoxide Hydrolase on Thrombolysis, Inflammation, and Ischemic Stroke

Stachybotrys microspora triprenyl phenol (SMTP) is a large family of small molecules derived from the fungus S. microspora. SMTP acts as a zymogen modulator (specifically, plasminogen modulator) that alters plasminogen conformation to enhance its binding to fibrin and subsequent fibrinolysis. Certain SMTP congeners exert anti-inflammatory effects by targeting soluble epoxide hydrolase. SMTP congeners with both plasminogen modulation activity and anti-inflammatory activity ameliorate various aspects of ischemic stroke in rodents and primates. A remarkable feature of SMTP efficacy is the suppression of hemorrhagic transformation, which is exacerbated by conventional thrombolytic treatments. No drug with such properties has been developed yet, and SMTP would be the first to promote thrombolysis but suppress disease-associated bleeding. On the basis of these findings, one SMTP congener is under clinical study and development. This review summarizes the discovery, mechanism of action, pharmacological activities, and development of SMTP.

Enzymology and biosynthesis of the orsellinic acid derived medicinal meroterpenoids

The advent of synthetic biology has yielded fruitful studies on orsellinic acid-derived meroterpenoids, which reportedly possess important biological activities. Genomics and transcriptomics have significantly accelerated the discovery of the biosynthetic genes for orsellinic acid-derived fungal and plant meroterpenoids. Subsequently, a well-developed heterologous host provides a convenient platform to generate a supply of useful natural products. Furthermore, in vitro reconstitution and genome editing tools have been increasingly employed as efficient means to fully understand the enzyme reaction mechanisms. With the knowledge of the biosynthetic machinery, combinatorial and engineered biosyntheses have yielded novel molecules with improved bioactivities. These studies will lay the foundation for the production of meroterpenoids with novel medicinal properties.

Confirmation of the absolute configuration of Stachybotrin C using single-crystal X-ray diffraction analysis of its 4-bromobenzyl ether derivative

The absolute configuration of Stachybotrin C was confirmed in this study. After synthesizing the dimethyl ethers of Stachybotrin C, the C-8 epimer was analyzed by 1D NOESY. However, the stereochemistry determination was difficult through the NOE correlations. Instead, the di(4-bromobenzyl) ether of Stachybotrin C was derived and used for X-ray diffraction analysis, because its single crystal was easier to obtain than that of the original Stachybotrin C. The stereochemistry of Stachybotrin C was determined to be (8S, 9R). This derivatization approach may also be used to prepare single crystals of the analogues.

Stachybotrychromenes A-C: novel cytotoxic meroterpenoids from Stachybotrys sp

In the course of gaining new insights into the secondary metabolite profile of various Stachybotrys strains, in particular concerning triprenyl phenol-like compounds, so far, unknown metabolites with analogous structural features were discovered. Three novel meroterpenoids containing a chromene ring moiety, namely stachybotrychromenes A–C, were isolated from solid culture of the filamentous fungus Stachybotrys chartarum DSMZ 12880 (chemotype S). Their structures were elucidated by means of comprehensive spectroscopic analysis (1D and 2D NMR, ESI-HRMS, and CD) as well as by comparison with spectroscopic data of structural analogues described in literature. Stachybotrychromenes A and B exhibited moderate cytotoxic effects on HepG2 cells after 24 h with corresponding IC₅₀ values of 73.7 and 28.2 μM, respectively. Stachybotrychromene C showed no significant cytotoxic activity up to 100 μM. Moreover, it is noteworthy that stachybotrychromenes A–C are produced not only by S. chartarum chemotype S but also S. chartarum chemotype A and Stachybotrys chlorohalonata.

Isoindolone-Containing Meroperpenoids from the Endophytic Fungus Emericella nidulans HDN12-249

Six isoindolone containing meroterpenoids, emericellolides A-C (1-3) and emeriphenolicins E-G (4-6), were isolated from a plant endophytic fungus Emericella nidulans HDN12-249. Emericellolides A-C (1-3) feature the unprecedented macrolide skeleton composed of an unusual l-glutamate fragment, an isoindolone unit, and a sesquiterpene moiety, while structures of emeriphenolicins E-G (4-6) with two farnesyl groups attached to one isoindolone unit are rare in isoindolone-derived meroterpenoids. These structures including the absolute configurations were established on the basis of MS, NMR, Mo2(AcO)4-induced ECD, Marfey's method, and chemical conversion. Compound 4 exhibited cytotoxicity against HeLa cells with IC50 value of 4.77 μM.

Biosynthesis of LL-Z1272β: Discovery of a New Member of NRPS-like Enzymes for Aryl-Aldehyde Formation

LL-Z1272β (1) is a prenylated aryl-aldehyde produced by several fungi; it also serves as a key pathway intermediate for many fungal meroterpenoids. Despite its importance in the biosynthesis of natural products, the molecular basis for the biosynthesis of 1 has yet to be elucidated. Here we identified the biosynthetic gene cluster for 1 from Stachybotrys bisbyi PYH05-7, and elucidated the biosynthetic route to 1. The biosynthesis involves a polyketide synthase, a prenyltransferase, and a nonribosomal peptide synthetase (NRPS)-like enzyme, which is responsible for the generation of the aldehyde functionality. Interestingly, the NRPS-like enzyme only accepts the farnesylated substrate to catalyze the carboxylate reduction; this represents a new example of a substrate for adenylation domains.

Total synthesis and stereochemical revision of xiamenmycin A

The relative and absolute configurations of xiamenmycin A, a benzopyran compound isolated from Streptomyces xiamenensis 318 with a highly potent anti-fibrotic activity, have been characterized through the total synthesis.

Structure-activity relationships of the plasminogen modulator SMTP with respect to the inhibition of soluble epoxide hydrolase

A family of fungal metabolites, SMTP, is a small-molecule plasminogen modulator that enhances plasminogen activation, leading to thrombolysis. We recently demonstrated that SMTP-7 effectively treats ischemic stroke due to its thrombolytic activity as well as anti-inflammatory action, which is attributable to soluble epoxide hydrolase (sEH) inhibition. In this paper, we studied detailed structure-activity relationships of plasminogen modulation and sEH inhibition using 25 SMTP congeners including six newly synthesized ones. The results clearly demonstrate that the structure of the N-linked side chain of SMTP congeners markedly affect their activities toward plasminogen modulation and inhibitions of the two activities of sEH (C-terminal epoxide hydrolase and N-terminal phosphatase). A slight change in the N-linked side chain results in affording selectivity of SMTP congeners. Many congeners, which lacked plasminogen modulation activity, differently inhibited the two sEH activities depending on the structures of the N-linked side chain. Some congeners were active in plasminogen modulation and inhibition of both activities of sEH. These results help comprehensive understanding of ideal design of a drug useful for ischemic diseases that are associated with inflammation, such as stroke.

Soluble epoxide hydrolase as an anti-inflammatory target of the thrombolytic stroke drug SMTP-7

Although ischemic stroke is a major cause of death and disability worldwide, only a small fraction of patients benefit from the current thrombolytic therapy due to a risk of cerebral hemorrhage caused by inflammation. Thus, the development of a new strategy to combat inflammation during thrombolysis is an urgent demand. The small molecule thrombolytic SMTP-7 effectively treats ischemic stroke in several animal models with reducing cerebral hemorrhage. Here we revealed that SMTP-7 targeted soluble epoxide hydrolase (sEH) to suppress inflammation. SMTP-7 inhibited both of the two sEH enzyme activities: epoxide hydrolase (which inactivates anti-inflammatory epoxy-fatty acids) and lipid phosphate phosphatase. SMTP-7 suppressed epoxy-fatty acid hydrolysis in HepG2 cells in culture, implicating the sEH inhibition in the anti-inflammatory mechanism. The sEH inhibition by SMTP-7 was independent of its thrombolytic activity. The simultaneous targeting of thrombolysis and sEH by a single molecule is a promising strategy to revolutionize the current stroke therapy.

SMTP-7, a novel small-molecule thrombolytic for ischemic stroke: a study in rodents and primates

SMTP-7 (Stachybotrys microspora triprenyl phenol-7), a small molecule that promotes plasminogen activation through the modulation of plasminogen conformation, has excellent therapeutic activity against cerebral infarction in several rodent models. Detailed evaluations of SMTP-7 in a primate stroke model are needed for effective, safe drug development. Here we evaluated SMTP-7 in a monkey photochemical-induced thrombotic middle cerebral artery (MCA) occlusion model (n=6), in which MCA occlusion was followed by recanalization/reocclusion. SMTP-7 (10 mg/kg, intravenous infusion) significantly increased the postinfusion MCA recanalization rate (32.5-fold, P=0.043) and ameliorated the post-24-h neurologic deficit (by 29%, P=0.02), cerebral infarct (by 46%, P=0.033), and cerebral hemorrhage (by 51%, P=0.013) compared with the vehicle control animals. In normal monkeys, SMTP-7 did not affect general physiologic or hemostatic variables, including coagulation and platelet parameters. Investigations in rodent models of transient and permanent focal cerebral ischemia, as well as arterial thrombosis and bleeding tests, suggest a role for SMTP-7's regulated profibrinolytic action and neuroprotective properties in the monkey MCA occlusion model. In conclusion, SMTP-7 is effective in treating thrombotic stroke in monkeys. SMTP-7 is thus a promising candidate for the development of alternative therapy for ischemic stroke.

A new series of the SMTP plasminogen modulators with a phenylamine-based side chain

SMTPs are a family of small-molecule plasminogen modulators that enhance plasminogen activation. SMTP-7, one of the most potent congeners, is effective in treating thrombotic cerebral infarction. The SMTP molecule consists of a tricyclic γ-lactam moiety, a geranylmethyl group, and an N-linked side chain. The presence of both an aromatic group and a negatively ionizable group in the N-linked side chain is crucial for activity. Investigations of the congeners with a phenylglycine-based side chain suggest that a phenolic hydroxy group affects potency. In this study, we isolate and characterize a series of novel SMTP congeners with a phenylamine-based N-linked side chain. Of the 11 congeners isolated, SMTP-19 (with a 4-phenylcarboxylic acid moiety), SMTP-22 (with a 3-hydroxyphenyl-4-carboxylic acid moiety) and SMTP-25 (with a 2-hydroxyphenyl-3-carboxylic acid moiety) are as potent as SMTP-7 in plasminogen-modulating activity. Their isomers with a carboxylic acid group and/or a phenolic hydroxy group at different positions have <40% of the activity of these congeners. Both SMTP-22 and SMTP-25 have >1.7 times more oxygen radical absorbance capacity as compared with SMTP-7.

SMTP (Stachybotrys microspora triprenyl phenol) enhances clot clearance in a pulmonary embolism model in rats

Background

Stachybotrys microspora triprenyl phenols (SMTPs) are a novel family of small molecules that enhance both activation and fibrin-binding of plasminogen. While their effects on fibrinolysis have been characterized in vitro, little is known about their activity in vivo with respect to plasminogen activation and blood clot clearance.

Results

To select a potent SMTP congener for the evaluation of its action in vitro and in vivo, we tested several SMTP congeners with distinct structural properties for their effects on plasminogen activation. As a result, SMTP-7 (orniplabin) was found to have distinguished activity. Several lines of biochemical evidence supported the idea that SMTP-7 acted as a plasminogen modulator. SMTP-7 elevated plasma level of plasmin-α₂-antiplasmin complex, an index of plasmin formation in vivo, 1.5-fold in mice after the intravenous injections at doses of 5 and 10 mg kg^-1. In a rat pulmonary embolism model, SMTP-7 (5 mg kg^-1) enhanced the rate of clot clearance ~3-fold in the absence of exogenous plasminogen activator. Clot clearance was enhanced further by 5 mg kg^-1 of SMTP-7 in combination with single-chain urokinase-type plasminogen activator.

Conclusions

Our results show that SMTP-7 is a superior plasminogen modulator among the SMTP family compounds and suggest that the agent enhances plasmin generation in vivo, leading to clearance of thrombi in a model of pulmonary embolism.

Structure-activity relationships of 11 new congeners of the SMTP plasminogen modulator

The fungal metabolite Stachybotrys microspora triprenyl phenols (SMTPs) are small-molecule plasminogen modulators that enhance plasminogen activation. The SMTP molecule consists of a tricyclic γ-lactam moiety, an isoprene side-chain and an N-linked side-chain. Previous investigations have demonstrated that the N-linked side-chain is crucial for its activity. In this study, we have isolated 11 new SMTP congeners with a variety of N-linked side-chain structures, to investigate structure-activity relationships. Active compounds included congeners with a carboxyl or a sulfonic acid group in the N-linked side-chain, whereas not all the congeners with a carboxyl group were active. Of these congeners, that with methionine or tyrosine as the N-linked side-chain moiety was more active than that with an aliphatic amino acid. Congeners without ionizable group in the N-linked side-chain were essentially inactive.

Small-molecule modulators of zymogen activation in the fibrinolytic and coagulation systems

The coagulation and fibrinolytic systems are central to the hemostatic mechanism, which works promptly on vascular injury and tissue damage. The rapid response is generated by specific molecular interactions between components in these systems. Thus, the regulation mechanism of the systems is programmed in each component, as exemplified by the elegant processes in zymogen activation. This review describes recently identified small molecules that modulate the activation of zymogens in the fibrinolytic and coagulation systems.