Discovery of Highly Potent Daphnane Diterpenoids Uncovers Importin-ß1 as a Druggable Vulnerability in Castration-Resistant Prostate Cancer.

Importins are overexpressed in many cancers and mediate the abnormal nuclear transport of oncogenic factors. The druggable potential of importins still remains unclear, largely because of the lack of potent inhibitors. Herein, the anti-castration-resistant prostate cancer (CRPC) screening of a Euphorbiaceae diterpenoid library followed by target fishing led to the identification of a highly potent importin-ß1 inhibitor, daphnane diterpenoid DD1. DD1 selectively inhibited the growth and survival of CRPC cells at subnanomolar concentrations and completely blocked tumor growth in preclinical models at an extremely low dosage. Mechanistic studies revealed that targeting of importin-ß1 by DD1 significantly reduced the nuclear accumulation of key CRPC drivers, shutting down their downstream oncogenic signaling. Disruption of the predicted binding sites of DD1 on importin-ß1 abolished this anti-CRPC effect. These findings suggest that importin-ß1 is an effective therapeutic target in CRPC and that DD1 as the most potent importin-ß1 inhibitor to date can be developed as therapeutics for treatment of this disease.

Crotonianoids A-C, Three Unusual Tigliane Diterpenoids from the Seeds of Croton tiglium and Their Anti-Prostate Cancer Activity.

Crotonianoids A-C (1-3), three unusual tigliane diterpenoids, were isolated from the seeds of Croton tiglium. Compound 1 is a 13,14:13,15-diseco-tigliane featuring a unique spiro[bicyclo[5.3.0]decane-2,5'-2'(3'H,4'H)-furanone] core; 2 is a 13,15-seco-tigliane incorporating a rare peroxide bridge between C-13 and C-15; and 3 is the first example of a phorbol ester with a 10R-configuration. Their structures were determined by spectroscopic, computational, and X-ray diffraction methods. Compounds 1 and 2 markedly inhibited the growth and survival of prostate cancer cell C4-2B at micromolar concentrations and induced cell apoptosis. Mechanistic study revealed that 1 and 2 could suppress androgen receptor (AR) signaling pathway by promoting the degradation of AR protein.

Tigliane and rhamnofolane glycosides from Euphorbia wallichii prevent oxidative stress-induced neuronal death in PC-12 cells.

Tigliane and rhamnofolane diterpenoids bearing glycosyl substituents are rarely found in nature. In the current study, seven new tigliane glycosides, euphorwallsides A - G (1-7), and five new rhamnofolane glycosides, euphorwallsides H - L (8-12), were isolated from the whole plants of Euphorbia wallichii. Their structures were elucidated by a combination of spectroscopic, computational, and chemical means. The aglycones of 1-5 represent a rare class of 13-deoxygenated tiglianes, while those of 8-12 represent the first examples of 4-deoxygenated rhamnofolanes. 2, 3, 5, 7, 8, and 12 showed significant neuroprotective effects on sodium nitroprusside (SNP)-induced neuronal death in pheochromocytoma cell line PC-12 at 10 µM, being more active than the clinical drug, edaravone. Mechanistic study revealed that the most active compound, 3, could inhibit reactive oxygen species (ROS) accumulation and restore the mitochondrial membrane potential via modulating the Nrf2 signaling pathway in PC-12 cells.

Salviplenoid A from Salvia plebeia attenuates acute lung inflammation via modulating NF-κB and Nrf2 signaling pathways.

Acute lung injury (ALI) involves series of inflammatory pathologies and cause high morbidity. Salviplenoid A (SA) was a new sesquiterpenoid from the traditional inflammatory herb Salvia plebeia. In our previous study, SA exhibited antiinflammatory activity in RAW264.7 cells. However, the extensive effects of SA in human cells and in vivo and the active mechanisms are unclear. Thus, in this study, we sought to access its effects in vitro and in vivo and to investigate its mechanisms. SA was proved to inhibit the induction of proinflammatory cytokines in human cell types, including pulmonary epithelial cells and endothetial cells. It also depressed monocyte adhesion. Moreover, SA potently attenuated the acute lung inflammation in the LPS-induced mouse model shown by down-regulation of proinflammatory mediators, inhibition of polymorphonuclear neutrophil infiltration, and alleviation of related symptoms like alveolar congestion and mucus secretion. Further evaluation confirmed that SA regulated NF-κB pathway by inhibiting the IκB-α phosphorylation. And it markedly mediated Nrf2/HO-1 pathway by activating the Nrf2/HO-1 expression and promoting Nrf2 nuclear translocation. Therefore, SA could attenuate acute lung inflammation via suppressing NF-κB and activating Nrf2, which provide a theoretical basis for the potential application of SA in clinic.

Anti-inflammatory Ingenane Diterpenoids from the Roots of Euphorbia kansui.

Bioassay-guided fractionation of the ethanolic extract of the roots of Euphorbia kansui led to the isolation of two new ingenane diterpenoids, euphorkans A (1: ) and B (2: ), together with 16 known analogues (3:  - 18: ). Their structures were determined by combined spectral and chemical methods. All the isolates were evaluated for their inhibitory effects on lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophage cells. Compounds 1:  - 6: and 10:  - 13: exhibited pronounced inhibitory activity with IC50 values in the range of 2.78 - 10.6 µM, and were more potent than the positive control, quercetin (IC50 = 15.8 µM). Compounds 1: and 5: were selected for further assays toward the key inflammation mediators TNF-α and IL-6, and showed a significant inhibition in a dose-dependent manner. The preliminary mechanistic study revealed that 1: and 5: inhibited NF-κB activity, which may exert a role in their anti-inflammatory activity.

New halimane and clerodane diterpenoids from Croton cnidophyllus.

Three new halimane furanoditerpenoids (1-3) and three new clerodane furanoditerpenoids (4-6), along with seven known terpenoids including four pimarane diterpenoids (7-10) and three norisoprenoids (11-13) were isolated from the 95% EtOH extracts of the plants of Croton cnidophyllus. The 2D structures including absolute configuration of new furanoditerpenoids (1-6) were elucidated by analysis of their HRMS and NMR data as well as comparison of experimental and calculated ECD curves. Bioassay revealed that two compounds (8 and 9) possessed certain inhibitory effects against NO production stimulated by LPS, with IC50 values of 19.00 ± 1.76 and 21.61 ± 1.11 µM, respectively.

Discovery of the First Raptor (Regulatory-Associated Protein of mTOR) Inhibitor as a New Type of Antiadipogenic Agent.

Raptor, a regulatory-associated protein of mTOR, has been genetically proved to be an important regulator in lipogenesis. However, its druggable potential is rarely investigated, largely due to the lack of an inhibitor. In this study, the antiadipogenic screening of a daphnane diterpenoid library followed by target fishing led to the identification of a Raptor inhibitor, 1c (5/7/6 carbon ring with orthoester and chlorine functionalities). Pharmacodynamic studies verified that 1c is a potent and tolerable antiadipogenic agent in vitro and in vivo. Mechanistic studies revealed that the targeting of Raptor by 1c could block the formation of mTORC1 and then downregulate the downstream S6K1- and 4E-BP1-mediated C/EBPs/PPARγ signaling, eventually retarding adipocyte cell differentiation at the early stage. These findings suggest that Raptor can be explored as a novel therapeutic target for obesity and its related complications, and 1c as the first Raptor inhibitor may provide a new therapeutic option for these conditions.

Diversity of sesquiterpenoids from Stellera chamaejasme with neuroprotective effects.

Chromatographic fractionation of the 95% EtOH extract of the roots of Stellera chamaejasme yielded 20 sesquiterpenoids of four different types, guaiane-, carotane-, sesquicarane-, and alpiniane-types. Among them, sesquistrachanoids A-F were previously undescribed ones, whose structures including absolute configurations were elucidated by spectroscopic methods, the Mo2(OAc)4-induced ECD experiment, and analysis of experimental and calculated 1D NMR and ECD data. Sesquistrachanoid A is a 2,3-seco-guaiane-type sesquiterpenoid with a α-pyrone core and sesquistrachanoid B is the first example of 8,9-seco-guaiane-type sesquiterpenoid featured with an 1,8-δ-lactone core. Sesquistrachanoid C is a guaiane sesquiterpenoid characterized by a peroxide bridge between C-8 and C-10. All sesquiterpenoids were evaluated for their neuroprotective effects on cell damage induced by sodium nitroprusside in PC-12 cells. The bioassay results showed that six compounds at 10 µM could restore the cell viability, being comparable to that of the positive control edaravone. The mechanistic study on the most pronounced activity compound, stelleraguaianone B, demonstrated that it played a neuroprotective role by promoting the mRNA expression of antioxidant enzymes to reduce oxidative stress.

Discovery of a highly potent and orally available importin-ß1 inhibitor that overcomes enzalutamide-resistance in advanced prostate cancer.

Nuclear transporter importin-ß1 is emerging as an attractive target by virtue of its prevalence in many cancers. However, the lack of druggable inhibitors restricts its therapeutic proof of concept. In the present work, we optimized a natural importin-ß1 inhibitor DD1 to afford an improved analog DD1-Br with better tolerability (>25 folds) and oral bioavailability. DD1-Br inhibited the survival of castration-resistant prostate cancer (CRPC) cells with sub-nanomolar potency and completely prevented tumor growth in resistant CRPC models both in monotherapy (0.5 mg/kg) and in enzalutamide-combination therapy. Mechanistic study revealed that by targeting importin-ß1, DD1-Br markedly inhibited the nuclear accumulation of multiple CRPC drivers, particularly AR-V7, a main contributor to enzalutamide resistance, leading to the integral suppression of downstream oncogenic signaling. This study provides a promising lead for CRPC and demonstrates the potential of overcoming drug resistance in advanced CRPC via targeting importin-ß1.

Euphopanes A-C, three new diterpenoids from Euphorbia pekinensis.

Three new diterpenoids, euphopanes A-C (1-3), including one ent-isopimarane (1), one ent-abietane (2) and one cembrane (3), along with five known compounds (4-8) were isolated from the roots of Euphorbia pekinensis. Their structures were elucidated by extensive spectroscopic analysis, and the absolute configurations of compounds 1-3 were determined by ECD calculations. All the isolates were screened for the cytotoxicity against three cancer cell lines (C4-2B, C42B/ENZR, and MDA-MB-231), and compounds 1, 2, and 4 showed significant cytotoxicity against human prostate cancer cells C4-2B with IC50 values of 14.3, 16.9, and 15.3 µM, respectively.

A new tigliane-type diterpenoid from Euphorbia tirucalli.

Five tigliane (1-5) and one ingenane (6) diterpenoids were isolated from the ethanol extract of Euphorbia tirucalli. The structures of these compounds were identified based on analysis of their spectroscopic data. Among them, compound 12-O-(2E,4E,6E,8E-tetradecatetraenoyl)-13-O-isobutyroyl-4ß-deoxyphorbol (1) was a new tigliane. The Rho123 effluxion assay showed that tiglianes with a trans-fused 5/7 ring system such as compounds 1, 2, and 4 had potent inhibitory activity against P-glycoprotein in HepG2/ADR cells.

Jolkinolide B sensitizes bladder cancer to mTOR inhibitors via dual inhibition of Akt signaling and autophagy.

The monotherapy of mTOR inhibitors (mTORi) in cancer clinical practice has achieved limited success due to the concomitant activation of compensatory pathways, such as Akt signaling and cytoprotective autophagy. Thus, the combination of mTORi and the inhibitors of these pro-survival pathways has been considered a promising therapeutic strategy. Herein, we report the synergistic effects of a natural anti-cancer agent Jolkinolide B (JB) and mTORi (temsirolimus, rapamycin, and everolimus) for the effective treatment of bladder cancer. A mechanistic study revealed that JB induced a dual inhibition of Akt feedback activation and cytoprotective autophagy, potentiating the anti-proliferative efficacy of mTORi in both PTEN-deficient and cisplatin-resistant bladder cancer cells. Meanwhile, mTORi augmented the pro-apoptotic and pro-paraptotic effects of JB by reinforcing JB-activated endoplasmic reticulum stress and MAPK pathways. These synergistic mechanisms were related to cellular reactive oxygen species accumulation. Our study suggests that dual inhibition of Akt feedback activation and cytoprotective autophagy is an effective strategy in mTORi-based therapy, and JB + mTORi combination associated with multiple anti-cancer mechanisms and good tolerance in mouse models may serve as a promising treatment for bladder cancer.

Discovery of 8,9-seco-ent-Kaurane Diterpenoids as Potential Leads for the Treatment of Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) is a lethal malignancy without safe and effective therapeutic drugs. In this study, the anti-TNBC bioassay-guided isolation of the medicinal plant Croton kongensis followed by the structural modification led to the construction of a small ent-kaurane diterpenoid library (1-25). With subsequent biological screening, 20 highly potent compounds (IC50s < 3 µM) were identified. Among them, 8,9-seco-ent-kaurane 6 displayed comparable activity (IC50s ∼ 80 nM) to doxorubicin but with better selectivity. The analysis of structure-activity relationships suggested that the cleavage of the C8-C9 bond and the presence of α,ß-unsaturated ketone moiety were essential for the activity. The mechanistic study revealed that 6 induced apoptosis, autophagy, and metastasis suppression in TNBC cells via inhibition of Akt. In vivo, 6 significantly suppressed the TNBC tumor growth without causing side effects. All these results suggested that 6 may serve as a promising lead for the development of novel anti-TNBC agents in the future.

Jolkinolide B targets thioredoxin and glutathione systems to induce ROS-mediated paraptosis and apoptosis in bladder cancer cells.

Bladder cancer is a clinically heterogeneous disease with a poor prognosis. In the current study, anti-proliferation assay of a Euphorbiaceae diterpenoid library led to the identification of an anti-bladder cancer agent Jolkinolide B (JB). JB showed significant cytotoxicity against a panel of bladder cancer cell lines and suppressed the growth of cisplatin (CDDP)-resistant bladder cancer xenografts in single or combination treatments. Mechanistic study revealed that, besides inducing mitogen-activated protein kinase (MAPK)-related apoptosis, JB could trigger the paraptosis via activation of reactive oxygen species (ROS)-mediated endoplasmic reticulum (ER) stress and extracellular signal-regulated kinase (ERK) pathway. The excessive production of ROS could be induced by JB via inhibition of thioredoxin reductase 1 (TrxR1) and depletion of glutathione (GSH). Collectively, JB that targets thioredoxin and GSH systems to induce two distinct cell death modes may serve as a promising candidate in future anti-bladder cancer drug development.

Toonapolyynes A-D, new polyynes from Toona ciliata.

Phytochemical investigation on the leaves and twigs of Toona ciliata has led to the isolation of four new polyynes (1-4) and two knowns (5 and 6). Their structures were determined by extensive spectroscopic analysis (MS, UV, IR, and NMR) and Mosher's method. All compounds were evaluated for their inhibitory activities against HepG2 human tumor cell line but were inactive.

Jatrogricaine A: a new diterpenoid with a 5/6/6/4 carbon ring system from the stems of Jatropha podagrica.

Jatrogricaine A (1), a new diterpenoid possessing a 5/6/6/4 carbon ring system, together with eight known diterpenoids (2-9) were isolated from the stems of Jatropha podagrica. Their structures were elucidated by extensive spectroscopic methods and the absolute configuration of 1 was determined by single crystal X-ray diffraction analysis. All compounds were evaluated for their anti-inflammatory activities in vitro, and compound 3 showed significant inhibitory effects against nitric oxide (NO) production in lipopolysaccharide (LPS)-induced RAW264.7 macrophage cells with an IC50 of 13.44 ± 0.28 µmol·L-1, being comparable to the positive control, quercetin (IC50 17.00 ± 2.10 µmol·L-1).

Euphonoids A-G, cytotoxic diterpenoids from Euphorbia fischeriana.

Seven previously undescribed polycyclic diterpenoids, euphonoids A-G, including four ent-abietanes, two ent-atisanes, and one ent-kaurene, along with 26 known analogues were isolated from the roots of Euphorbia fischeriana. The structures of the undescribed compounds were elucidated by spectroscopic analysis, ECD calculations, and single crystal X-ray diffraction. Besides, the structure of a previously reported ent-abietane diterpenoid, fischeriabietane A, was revised. All the isolates were screened for the cytotoxicities against five cancer cell lines. Euphonoid A, fischeriabietane A, 11-oxo-ebracteolatanolide B, caudicifolin, jolkinolide B, and methyl-8,11-3-dihydroxy-12-oxo-ent-abietadi-13,15(17)-ene-16-oate showed significant inhibitory activities against human prostate cancer C4-2B and C4-2B/ENZR cell lines, with IC50 values being less than 10 µM. The brief structure-activity relationships (SARs) of these diterpenoids were also discussed.

Bioactive diterpenoids from Croton laevigatus.

Eight previously undescribed diterpenoids, crolaevinoids A-H, including two halimanes, four clerodanes, and two laevinanes, along with six known analogues were isolated from the twigs of Croton laevigatus. The structures of the previously undescribed were elucidated by spectroscopic analysis, and their absolute configurations were determined by combination of a single crystal X-ray diffraction and CD analysis (exciton chirality and Rh2(OCOCF3)4-induced methods). Crolaevinoids A and B represent the first halimane diterpenoids with a unique lactone bridge between C-12 and C-17. All compounds were evaluated for their inhibitory effects on the nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW264.7 macrophage cells. Furocrotinsulolide A and 3,4,15,16-diepoxy-cleroda-13(16),14-diene-12,17-olide exhibited pronounced inhibition of NO production with IC50 values of 10.4 ± 0.8 and 6.0 ± 1.0 µM, respectively, being more potent than the positive control, quercetin (IC50 = 13.1 ± 1.9 µM).