BRD4 in physiology and pathology: ''BET'' on its partners.

Bromodomain-containing 4 (BRD4), a member of Bromo and Extra-Terminal (BET) family, recognizes acetylated histones and is of importance in transcription, replication, and DNA repair. It also binds non-histone proteins, DNA and RNA, contributing to development, tissue growth, and various physiological processes. Additionally, BRD4 has been implicated in driving diverse diseases, ranging from cancer, viral infection, inflammation to neurological disorders. Inhibiting its functions with BET inhibitors (BETis) suppresses the progression of several types of cancer, creating an impetus for translating these chemicals to the clinic. The diverse roles of BRD4 are largely dependent on its interaction partners in different contexts. In this review we discuss the molecular mechanisms of BRD4 with its interacting partners in physiology and pathology. Current development of BETis is also summarized. Further understanding the functions of BRD4 and its partners will facilitate resolving the liabilities of present BETis and accelerate their clinical translation.

Wogonin induces cellular senescence in breast cancer via suppressing TXNRD2 expression.

Cellular senescence contributes to tumor regression through both cell autonomous and non-autonomous mechanisms. Drugs inducing cancer cell senescence and modulating senescence-associated secretory phenotype (SASP) render advantage to the cancer treatment. Breast cancer remains the second most cause of female cancer mortality, among which triple-negative breast cancer (TNBC) has a more aggressive clinical course. Our study showed that in TNBC cell lines including MDA-MB-231 and 4T1 cells, moderate concentrations of wogonin (5, 7-dihydroxy-8-methoxy-2-phenyl-4h-1-benzopyran-4-one) (50-100 µM) not only induced permanent proliferation inhibition, but also increased P16 expression, ß-galactosidase activity, senescence-associated heterochromatin foci and SASP, which are the typical characteristics of cellular senescence. Moreover, results showed that wogonin-induced senescence was partially attributed to the reactive oxygen species (ROS) accumulation upon wogonin treatment in MDA-MB-231 cells, since elimination of ROS by N-acetylcysteine (NAC) was able to repress wogonin-induced ß-galactosidase activity. Mechanistically, wogonin reduced the expression of TXNRD2, an important antioxidant enzyme in controlling the levels of cellular ROS, by altering the histone acetylation at its regulatory region. In addition, senescent MDA-MB-231 cells induced by wogonin exhibited activated NF-κB and suppressed STAT3, which were recognized as regulators of SASP. SASP from these senescent cells suppressed tumor cell growth, promoted macrophage M1 polarization in vitro and increased immune cell infiltration in xenografted tumors in vivo. These results reveal another mechanism for the anti-breast cancer activity of wogonin by inducing cellular senescence, which suppresses tumor progression both autonomously and non-autonomously.

Discovery of a highly selective FLT3 inhibitor with specific proliferation inhibition against AML cells harboring FLT3-ITD mutation.

FLT3 is often over-expressed in AML, and FLT3 mutants, especially FLT-ITD, are closely related to the poor prognosis in AML patients. Thus, FLT3 has become an attractive target for AML therapy. A series of FLT3 inhibitors have been evaluated in various clinical trials, one of which was approved for AML. However, current FLT3 inhibitors still faced the challenges of kinase selectivity and drug resistance due to concurrent FLT3-ITD-TKD mutations. In this work, a new FLT3 inhibitor (compound 1) with simple structure was discovered through virtually screening an in-house molecule database which contains numerous compounds with kinase-inhibition activity. Compound 1 was identified with potent inhibitory activity against several FLT3 mutants and high FLT3 selectivity over other kinases. Moreover, its anti-growth effects on tumor cells in vitro were dependent on the expression of FLT3-ITD, and it showed little cytotoxicity to MV4-11 and human normal cells. Mechanism studies illustrated that compound 1 blocked FLT3 pathway, caused cell cycle arrest and induced apoptosis in MV4-11 cells. Finally, the binding mode of compound 1 was studied by molecular dynamics simulations, which provides insights into key residues involved in intermolecular binding and further structural optimization strategy. Compound 1 can thus serve as a good starting point for the research on FLT3 inhibitors towards the kinase selectivity and potential to overcome drug resistance.

Chemical Space of FLT3 Inhibitors as Potential Anti-AML Drugs.

BACKGROUND: FLT3 is a member of receptor tyrosine kinase III family, mainly expressed in hematopoietic cells. The aberrant expression and function of FLT3 are strongly related to leukemia, especially acute myeloid leukemia. Its varieties of amino-acid residues mutations, such as FLT3-ITDs and -TKDs, can induce constant proliferation of hematological tumor cells with poor prognosis. Hence FLT3 serves as a promising target in AML chemotherapy. OBJECTIVE: This review focused on the progress of FLT3 inhibitors study including those that have entered clinical trials or were reported in numerous patents all over the world. Thus, we provided a useful reference for the development of new anti-leukemia drugs. METHOD: Through a comprehensive retrospective study, FLT3 inhibitors in several patent applications were identified and classified into five categories, including quinolone-related, indole-related, ureas, pyrimidines and other compounds. RESULTS: For each category of compounds, the structural feature, SAR, biological activity and current research status were thoroughly reviewed and analyzed. CONCLUSION: Although some of those compounds expressed potent bioactivities and have reached the advanced clinical trials for the treatment of leukemia, there are still several problems need to be faced before they enter the market eventually, especially the drug resistance issue. The improvement of therapeutic potency for FLT3 inhibitors might depend on the useful combination therapy and further refinement of the intrinsic properties of FLT3 inhibitors.