Roles of Nonadiabatic Processes, Reaction Mechanism, and Selectivity in Cu-Catalyzed [2 + 2] Photocycloaddition of Norbornene and Acetone to Oxetane.

Oxetane has been extensively studied for its applications in medicinal chemistry and as a reactive intermediate in synthesis. Experiments report a Cu-catalyzed [2 + 2] photocycloaddition of acetone and norbornene to oxetane, which is proposed to deviate from the conventional Paternò-Büchi reaction. However, its mechanism at the atomic level is not clear. In this study, we used a combination of multistate complete active space second-order perturbation theory (MS-CASPT2) and density functional theory to systematically investigate the reaction mechanism and elucidate the factors contributing to the diastereomeric selectivity. Initially, the formation of the TpCu(Norb) complex is achieved by strong interaction between tris(pyrazolyl)borate Cu(I) (TpCu) and norbornene in the ground state (S0). Upon photoexcitation, TpCu(Norb) eventually decays to the T1 state, in which TpCu(Norb) attacks acetone to initiate subsequent reactions and produces final endo- or exo-oxetane products. All these reactions initially involve the C-C bond formation in the T1 state thereto leading to a ring-opening intermediate. This intermediate then undergoes a nonradiative transition to the S0 state, producing a five-membered ring intermediate, from which the C-O bond is formed, leading to the experimentally dominant exo-product. In contrast, the endo-oxetane formation requires a rearrangement process after the C-C bond is formed because of the large steric effects. As a consequence, the different reaction pathways generating exo- and endo-products exhibit large differences in the free-energy barriers, which results in a diastereomeric selectivity observed experimentally. Additionally, the nonradiative transition is found to play an important role in facilitating these reaction steps. The present computational study provides valuable mechanistic insights into Cu-catalyzed photocycloaddition reactions.

Efficacy and mechanism study of cordycepin against brain metastases of small cell lung cancer based on zebrafish.

BACKGROUND: Small cell lung cancer (SCLC) is an aggressive tumor with high brain metastasis (BM) potential. There has been no significant progress in the treatment of SCLC for more than 30 years. Cordycepin has shown the therapeutic potential for cancer by modulating multiple cellular signaling pathways. However, the effect and mechanism of cordycepin on anti-SCLC BM remain unknown. PURPOSE: In this study, we focused on the anti-SCLC BM effect of cordycepin in the zebrafish model and its potential mechanism. STUDY DESIGN AND METHODS: A SCLC xenograft model based on zebrafish embryos and in vitro cell migration assay were established. Cordycepin was administrated by soaking and microinjection in the zebrafish model. RNA-seq assay was performed to analyze transcriptomes of different groups. Geno Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment were performed to reveal the underlying mechanism. Real-time qPCR was used to verify the effects of cordycepin on the key genes. RESULTS: Cordycepin showed lower cytotoxicity in vitro compared with cisplatin, anlotinib and etoposide, but showed comparable anti-proliferation and anti-BM effects in zebrafish SCLC xenograft model. Cordycepin showed significant anti-SCLC BM effects when administrated by both soaking and microinjection. RNA-seq demonstrated that cordycepin was involved in vitamin D metabolism, lipid transport, and proteolysis in cellular protein catabolic process pathways in SCLC BM microenvironment in zebrafish, and was involved in regulating the expressions of key genes such as cyp24a1, apoa1a, ctsl. The anti-BM effect of cordycepin in SCLC was mediated by reversing the expression of these genes. CONCLUSION: Our work is the first to describe the mechanism of cordycepin against SCLC BM from the perspective of regulating the brain microenvironment, providing new evidence for the anti-tumor effect of cordycepin.

Mechanism of hepatotoxicity of first-line tyrosine kinase inhibitors: Gefitinib and afatinib.

AIMS: Both gefitinib and afatinib are epidermal growth factor tyrosine kinase inhibitors (EGFR-TKI) in the treatment of non-small cell lung cancer (NSCLC). It has been reported that gefitinib and afatinib could cause hepatotoxicity during the clinic treatment, therefore it is critical to investigate their hepatotoxicity systematically. In this study, zebrafish (Danio rerio) were used as model animals to compare the hepatotoxicity and their toxic mechanism. MAIN METHODS: The zebrafish transgenic line [Tg (fabp10a: dsRed; ela3l:EGFP) was used in this study. After larvae developed at 3 days post fertilization (dpf), they were put into different concentrations of gefitinib and afatinib. At 6 dpf, the viability, liver area, fluorescence intensity, histopathology, apoptosis, transaminase reflecting liver function, the absorption of yolk sac, and the expression of relative genes were observed and analyzed respectively. KEY FINDINGS: Both gefitinib and afatinib could induce the larvae hepatotoxicity dose-dependently. Based on the liver morphology, histopathology, apoptosis and function assessments, gefitinib showed higher toxicity, causing more serious liver damage. Both gefitinib and afatinib caused abnormal expressions of genes related to endoplasmic reticulum stress (ERS) pathway and apoptosis. For example, jnk, perk, bip, chop, ire1, bid, caspase3 and caspase9 were up-regulated, while xbp1s, grp78, bcl-2/bax, and caspase8 were down-regulated. The hepatotoxicity difference of gefitinib and afatinib might be due to the different expression level of related genes.

A systematical comparison of anti-angiogenesis and anti-cancer efficacy of ramucirumab, apatinib, regorafenib and cabozantinib in zebrafish model.

AIMS: Gastric cancer (GC) is one of the most common malignant tumors in the world. Anti-angiogenic therapy is a useful strategy for the treatment of advanced GC. This study was aimed to systemically compare the anti-angiogenesis, anti-cancer efficacy, as well as the safety of four known anti-angiogenic drugs, namely ramucirumab, apatinib, regorafenib and cabozantinib. MAIN METHODS: Anti-angiogenic effect was evaluated for the intersegmental vessels (ISVs) and subintestinal veins (SIVs) formation in the Tg (fli-1: EGFP) zebrafish embryos. Anti-cancer efficacy was tested for the in vivo cell proliferation in cell line derived tumor xenograft (CDX) model based on Tg (fli-1: EGFP) zebrafish embryos. KEY FINDINGS: All four drugs exhibited anti-angiogenic abilities and tumor inhibition effects in fli-1: EGFP transgenic zebrafish. Using zebrafish xenografted model, we found that effectiveness of ramucirumab in anti-GC-proliferation is better than apatinib, regorafenib and cabozantinib. The combination of anti-angiogenic drugs and cisplatin showed no significant benefit in tumors. Meanwhile, toxicity assay showed that all tested anti-angiogenic drugs could cause cardiovascular-related side effects. The therapeutic index (LD50/ED50) of cabozantinib is higher than apatinib and regorafenib, suggesting a potential as an anti-GC drug. SIGNIFICANCE: The comparison of GC-related anti-angiogenic drugs was first reported. It was found that cabozantinib had a potential as an anti-GC drug. Zebrafish model was an ideal animal model for the research of anti-angiogenic behaviors.