Post-translational modifications of CDK5 and their biological roles in cancer.

Post-translational modifications (PTMs) of Cyclin-dependent kinase 5 (CDK5) have emerged as important regulatory mechanisms that modulate cancer development in patients. Though CDK5 is an atypical member of the cyclin-dependent kinase family, its aberrant expression links to cell proliferation, DNA damage response, apoptosis, migration and angiogenesis in cancer. Current studies suggested that, new PTMs on CDK5, including S-nitrosylation, sumoylation, and acetylation, serve as molecular switches to control the kinase activity of CDK5 in the cell. However, a majority of these modifications and their biological significance in cancer remain uncharacterized. In this review, we discussed the role of PTMs on CDK5-mediated signaling cascade, and their possible mechanisms of action in malignant tumors, as well as the challenges and future perspectives in this field. On the basis of the newly identified regulatory signaling pathways of CDK5 related to PTMs, researchers have investigated the cancer therapeutic potential of chemical compounds, small-molecule inhibitors, and competitive peptides by targeting CDK5 and its PTMs. Results of these preclinical studies demonstrated that targeting PTMs of CDK5 yields promising antitumor effects and that clinical translation of these therapeutic strategies is warranted.

Structure-based discovery of neoandrographolide as a novel inhibitor of Rab5 to suppress cancer growth.

Rab5 is a small GTPase that plays a crucial role in oncogenic signal transduction, which was considered as an attractive target for cancer therapy. Rapid GDP/GTP exchange in the packet of Rab5 sustains its high activity for promoting cancer progression. However, Rab5 currently remains undruggable due to the lack of specific inhibitor. Herein, we reported the discovery of a novel Rab5 inhibitor, neoandrographolide (NAP), by using high-throughput virtual screening with a natural product library containing 7459 compounds, which can occupy the surface groove of Rab5, competing with GDP/GTP for the binding. Ser34 is the most important residue in the groove of Rab5, as it forms most hydrogen-bond interactions with GDP/GTP or NAP, and in silico mutation of Ser34 decreased the stabilization of Rab5. Moreover, fluorescence titration experiment and isothermal titration calorimetry (ITC) assay revealed a direct binding between NAP and Rab5. Biochemical and cell-based assays showed that NAP treatment not only diminished the activity of Rab5, but also suppressed cell growth of cancer cell. This finding firstly identifies NAP as a novel inhibitor of Rab5, which directly binds with Rab5 by occupying the GDP/GTP binding groove to suppress its functions, highlighting a great potential of NAP to be developed as a chemotherapeutic agent in cancer therapy.

Curcumol Overcomes TRAIL Resistance of Non-Small Cell Lung Cancer by Targeting NRH:Quinone Oxidoreductase 2 (NQO2).

Resistance to tumor-necrosis-factor-related apoptosis-inducing ligand (TRAIL) of cancer cell remains a key obstacle for clinical cancer therapies. To overcome TRAIL resistance, this study identifies curcumol as a novel safe sensitizer from a food-source compound library, which exhibits synergistic lethal effects in combination with TRAIL on non-small cell lung cancer (NSCLC). SILAC-based cellular thermal shift profiling identifies NRH:quinone oxidoreductase 2 (NQO2) as the key target of curcumol. Mechanistically, curcumol directly targets NQO2 to cause reactive oxygen species (ROS) generation, which triggers endoplasmic reticulum (ER) stress-C/EBP homologous protein (CHOP) death receptor (DR5) signaling, sensitizing NSCLC cell to TRAIL-induced apoptosis. Molecular docking analysis and surface plasmon resonance assay demonstrate that Phe178 in NQO2 is a critical site for curcumol binding. Mutation of Phe178 completely abolishes the function of NQO2 and augments the TRAIL sensitization. This study characterizes the functional role of NQO2 in TRAIL resistance and the sensitizing function of curcumol by directly targeting NQO2, highlighting the potential of using curcumol as an NQO2 inhibitor for clinical treatment of TRAIL-resistant cancers.