Discovery of novel anti-angiogenesis agents. Part 9: Multiplex inhibitors suppressing compensatory activations of RTKs

Recent advances and future directions on small molecule VEGFR inhibitors in oncological conditions

"A journey of mixed emotions" is a quote that best describes the progress chart of vascular endothelial growth factor receptor (VEGFR) inhibitors as cancer therapeutics in the last decade. Exhilarated with the Food and Drug Administration (FDA) approvals of numerous VEGFR inhibitors coupled with the annoyance of encountering the complications associated with their use, drug discovery enthusiasts are on their toes with an unswerving determination to enhance the rate of translation of VEGFR inhibitors from preclinical to clinical stage. The recently crafted armory of VEGFR inhibitors is a testament to their growing dominance over other antiangiogenic therapies for cancer treatment. This review perspicuously underscores the earnest attempts of the researchers to extract the antiproliferative potential of VEGFR inhibitors through the design of mechanistically diverse structural assemblages. Moreover, this review encompasses sections on structural/molecular properties and physiological functions of VEGFR, FDA-approved VEGFR inhibitors, and hurdles restricting the activity range/clinical applicability of VEGFR targeting antitumor agents. In addition, tactics to overcome the limitations of VEGFR inhibitors are discussed. A clear-cut viewpoint transmitted through this compilation can provide practical directions to push the cart of VEGFR inhibitors to advanced-stage clinical investigations in diverse malignancies.

Discovery of novel PROTACs based on multi-targeted angiogenesis inhibitors

Anti-angiogenesis has been proved to be an effective strategy for the treatment of tumors. Anti-angiogenic drugs had achieved certain therapeutic effects. However, drug resistance also gradually emerged and limited the application of angiogenesis inhibitors. Proteolysis Targeting Chimeras (PROTACs) are bifunctional molecules capable of degrading proteins through the ubiquitin-proteasome system (UPS). Compared with traditional inhibitors, they displayed advantages of less dosage, lower toxicity and less resistance. In this study, we designed and synthesized a series of novel PROTACs based on our recently reported multi-targeted angiogenesis inhibitor S5. Preliminary biological evaluation of title PROTACs was carried out in various cell lines. The results indicated that these novel bifunctional PROTACs displayed potential in degrading BRAF protein. Their degradation mechanism showed that the degradation of BRAF by PROTAC-1 was dependent on binding to target proteins and E3 ubiquitin ligase. Our findings provided further evidence that these novel PROTACs could be considered in further application in overcome of clinical resistance of traditional angiogenesis inhibitors.

Tumor-microenvironmental-response Bi-functional molecules for efficient imaging and anti-tumor activity therapy

To improve the visualization and potency of anticancer agents, the diagnosis and treatment integration bi-functional molecules were constructed based on active candidate BD7, approved drug Linifanib, and monoclonal antibody Bevacizumab. Commercial available Rhodamine B was inducted to realize imaging-aided diagnosis and target efficiency monitoring for cancer cells. In order to maintain the anticancer activity of drugs, disulfide bond was incorporated as releasable group based on tumor microenviroment. After design, synthesis and structure characterization of title compounds, various biological evaluation and cancer cell imaging analysis were carried out. The results indicated that these title diagnosis and treatment integration bi-functional molecules exhibited comparable potency with that of corresponding parent drug. Meanwhile, these agents afforded good performance in cell imaging and could be used to differentiate cancer cells from normal ovarian cells in real time. Further optimization of these bi-functional molecules is ongoing to improve the potency and precision and will be reported in due course. Our findings are expected to achieve efficient screening and real-time prognostic monitoring under the premise of high anti-tumor activity for clinical application.

Design, synthesis, and biological evaluation of novel Bcr-AblT315I inhibitors incorporating amino acids as flexible linker

Despite the success of imatinib in CML therapy through Bcr-Abl inhibition, acquired drug resistance occurs over time in patients. In particular, the resistance caused by T315I mutation remains a challenge in clinic. Herein, we embarked on a structural optimization campaign aiming at discovery of novel Bcr-Abl inhibitors toward T315I mutant based on previously reported dibenzoylpiperazin derivatives. We proposed that incorporation of flexible linker could achieve potent inhibition of Bcr-Abl^T315I by avoiding steric clash with bulky sidechain of Ile315. A library of 28 compounds with amino acids as linker has been developed and evaluated. Among them, compound AA2 displayed the most potent activity against Bcr-Abl^WT and Bcr-Abl^T315I, as well as toward Bcr-Abl driven K562 and K562R cells. Further investigations indicated that AA2 could induce apoptosis of K562 cells and down regulate phosphorylation of Bcr-Abl. In summary, the compounds with amino acid as novel flexible linker exhibited certain antitumor activities, providing valuable hints for the discovery of novel Bcr-Abl inhibitors to overcome T315I mutant resistance, and AA2 could be considered as a candidate for further optimization.

Research Progress and Application of Bioorthogonal Reactions in Biomolecular Analysis and Disease Diagnosis

Bioorthogonal reactions are rapid, specific and high yield reactions that can be performed in in vivo microenvironments or simulated microenvironments. At present, the main biorthogonal reactions include Staudinger ligation, copper-catalyzed azide alkyne cycloaddition, strain-promoted [3 + 2] reaction, tetrazine ligation, metal-catalyzed coupling reaction and photo-induced biorthogonal reactions. To date, many reviews have reported that bioorthogonal reactions have been used widely as a powerful tool in the field of life sciences, such as in target recognition, drug discovery, drug activation, omics research, visualization of life processes or exogenous bacterial infection processes, signal transduction pathway research, chemical reaction dynamics analysis, disease diagnosis and treatment. In contrast, to date, few studies have investigated the application of bioorthogonal reactions in the analysis of biomacromolecules in vivo. Therefore, the application of bioorthogonal reactions in the analysis of proteins, nucleic acids, metabolites, enzyme activities and other endogenous molecules, and the determination of disease-related targets is reviewed. In addition, this review discusses the future development opportunities and challenges of biorthogonal reactions. This review presents an overview of recent advances for application in biomolecular analysis and disease diagnosis, with a focus on proteins, metabolites and RNA detection.

Effective and transient mapping of protein-protein interactions: Application of novel releasable photoaffinity linkers

Herein, two novel multifunctional releasable photoaffinity linkers were developed for effective and transient tracking interacting proteins with the overall objective of understanding their in vivo biological functions in real-time. These linkers could be used for the chemical modification of protein under moderate experimental conditions to form protein photoaffinity probes. These probes incorporated with both photoaffinity labels and tag-transfer, enable photo-crosslinking of bait proteins along with the release of unrelated groups. These photoaffinity linkers can be utilized to construct probes for disease markers, which could enable rapid diagnosis in a clinical setting at minimal interference with normal physiology.

Recent advances in, and challenges of, anti-angiogenesis agents for tumor chemotherapy based on vascular normalization

A major problem associated with cancer treatment is resistance-prone chemotherapeutic drugs. An increasing number of studies have documented that the occurrence of resistance tends to be associated with abnormal blood vessels. In 2001, Jain proposed the vascular normalization theory, which was recently applied to the drug-resistant treatment of tumors in the clinic. Through the intervention of angiogenesis inhibitors, remodeling the structure and function of abnormal vessels can maximize the efficacy of chemotherapeutic drugs. In this review, we systematically describe the occurrence and progress of tumor angiogenesis, as well as the pathological characteristics of tumor blood vessels. Moreover, druggable targets for vascular normalization and the development of related inhibitors are also outlined.

C-H Bond Arylation of Pyrazoles at the β-Position: General Conditions and Computational Elucidation for a High Regioselectivity

Direct arylation of most five-membered ring heterocycles are generally easily accessible and strongly favored at the α-position using classical palladium-catalysis. Conversely, regioselective functionalization of such heterocycles at the concurrent β-position remains currently very challenging. Herein, we report general conditions for regioselective direct arylation at the β-position of pyrazoles, while C-H α-position is free. By using aryl bromides as the aryl source and a judicious choice of solvent, the arylation reaction of variously N-substituted pyrazoles simply proceeds via β-C-H bond functionalization. The β-regioselectivity is promoted by a ligand-free palladium catalyst and a simple base without oxidant or further additive, and tolerates a variety of substituents on the bromoarene. DFT calculations revealed that a protic solvent such as 2-ethoxyethan-1-ol significantly enhances the acidity of the proton at β-position of the pyrazoles and thus favors this direct β-C-H bond arylation. This selective pyrazoles β-C-H bond arylation was successfully applied for the straightforward building of π-extended poly(hetero)aromatic structures via further Pd-catalyzed combined α-C-H intermolecular and intramolecular C-H bond arylation in an overall highly atom-economical process.