Cyclin-dependent kinase 9 (CDK9), a member of the cyclin-dependent protein kinase (CDK) family, is involved in transcriptional elongation of several target genes. CDK9 is ubiquitously expressed and has been shown to contribute to a variety of malignancies such as pancreatic, prostate and breast cancers. Here we report the development of a heterobifunctional small molecule proteolysis targeting chimera (PROTAC) capable of cereblon (CRBN) mediated proteasomal degradation of CDK9. In HCT116 cells, it selectively degrades CDK9 while sparing other CDK family members. This is the first example of a PROTAC that selectively degrades CDK9.
The neurotoxicity of amyloid-b protein (Ab) is widely regarded as one of the fundamental causes of neurodegeneration in Alzheimer's disease (AD). This toxicity is related to Ab aggregation into oligomers, protofibrils and fibrils. Recent studies suggest that intracellular Ab, which causes profound toxicity, could be one of the primary therapeutic targets in AD. So far, no compounds targeting intracellular Ab have been identified. We have investigated the toxicity induced by intracellular Ab in a neuroblastoma MC65 line and found that it was closely related to intracellular accumulation of oligomeric complexes of Ab (Ab-OCs). We further identified a cell-permeable tricyclic pyrone named CP2 that ameliorates this toxicity and significantly reduces the levels of Ab-OCs. In aqueous solution, CP2 attenuates Ab oligomerization and prevents the oligomer-induced death of primary cortical neurons. CP2 analogs represent a new class of promising compounds for the amelioration of Ab toxicities within both intracellular and extracellular sites.
Cyclin dependent kinase (CDK) inhibitors
have been the topic of intense research for nearly 2 decades due to
their widely varied and critical functions within the cell. Recently
CDK9 has emerged as a druggable target for the development of cancer
therapeutics. CDK9 plays a crucial role in transcription regulation;
specifically, CDK9 mediated transcriptional regulation of short-lived
antiapoptotic proteins is critical for the survival of transformed
cells. Focused chemical libraries based on a plethora of scaffolds
have resulted in mixed success with regard to the development of selective
CDK9 inhibitors. Here we review the regulation of CDK9, its cellular
functions, and common core structures used to target CDK9, along with
their selectivity profile and efficacy in vitro and in vivo.
The discovery of small molecule inhibitors of cytotoxicity induced by amyloid-β (Aβ) oligomers, either applied extracellularly or accumulated intraneuronally, is an important goal of drug development for Alzheimer's disease (AD), but has been limited by the lack of efficient screening methods. Here we describe our approach using two cell-based methods. The first method takes advantage of the unique ability of extracellularly applied Aβ oligomers to rapidly induce the exocytosis of formazan formed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). We employed a short protocol to quantify this toxicity, and quickly identified two novel inhibitors, code-named CP2 and A5, from two compound libraries. A second independent screen of the same libraries using our previously published MC65 protection assay, which identifies inhibitors of toxicity related to intracellular Aβ oligomers, also selected the same two leads, suggesting that both assays select for the same anti-Aβ oligomer properties displayed by these compounds. We further demonstrated that A5 attenuated the progressive aggregation of existing Aβ oligomers, reduced the level of intracellular Aβ oligomers, and prevented the Aβ oligomer-induced death of primary cortical neurons, effects similar to those demonstrated by CP2. Our results suggest that, when combined, the two methods would generate fewer false results and give a high likelihood of identifying leads that show promises in ameliorating Aβ oligomer-induced toxicities within both intraneuronal and extracellular sites. Both assays are simple, suitable for rapid screening of a large number of medicinal libraries, and amenable for automation.
Development of selective kinase inhibitors that target the ATP binding site continues to be a challenge largely due to similar binding pockets. Palbociclib is a cyclin-dependent kinase inhibitor that targets the ATP binding site of CDK4 and CDK6 with similar potency. The enzymatic function associated with the kinase can be effectively probed using kinase inhibitors however the kinase independent functions cannot. Herein, we report a palbociclib based PROTAC that selectively degrades CDK6 while sparing the homolog CDK4. We used competition studies to characterize the binding and mechanism of CDK6 degradation.
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