Current progress and novel strategies that target CDK12 for drug discovery

Discovery of novel imidazo[1,2-b]pyridazine derivatives as potent covalent inhibitors of CDK12/13

Triple-negative breast cancer (TNBC) is widely recognized as the most aggressive subtype of breast cancer, and treatment options for patients with TNBC remain highly limited. Recently, cyclin-dependent kinases 12/13 (CDK12/13) have been identified as promising therapeutic targets for TNBC. In our study, we report the design and synthesis of novel imidazo[1,2-b]pyrazine-based covalent inhibitors of CDK12/13, which exhibit potent inhibitory activity against TNBC cells. Among these compounds, compound 24 emerged as the most potent inhibitor, with CDK12 IC50 of 15.5 nM and CDK13 IC50 of 12.2 nM. Compound 24 forms a covalent bond with Cys1039 of CDK12 and effectively suppresses the proliferation of TNBC cell lines MDA-MB-231 and MDA-MB-468, with EC50 values of 5.0 nM and 6.0 nM, respectively. Compound 24 demonstrated superior efficacy to the currently known CDK12/13 covalent inhibitor, THZ531. These findings suggest compound 24 may be a promising lead for developing CDK12/13-targeted therapies for treating TNBC.

Emerging molecular phenotypes and potential therapeutic targets in esophageal and gastric adenocarcinoma unearthed by whole genome and transcriptome analyses

BACKGROUND

Adenocarcinoma of the esophagus and stomach demands a deeper molecular understanding to advance treatment strategies and improve patient outcomes. Here, we profiled the genome and transcriptome landscape of these cancers, explored molecular characteristics that are undetectable by other sequencing platforms, and analyzed their potential clinical ramifications.

METHODS

Our study employed state-of-the-art integrative analyses of whole genome and transcriptome sequencing on 51 matched tumor and germline samples from 46 patients. Mutations and rearrangements in clinically relevant cancer genes were investigated and correlated with OncoKB, a knowledge-based precision oncology database, to identify treatment implications. Genome-wide signatures and manually curated molecular profiles were also determined.

RESULTS

The analyses revealed 90 targetable oncogenic mutations and fusions in 63 % of the patients, including novel NTRK, NRG1, ALK, and MET fusions, and structural variants in cancer genes like RAD51B. Also, molecular signatures associated with mismatch repair and homologous recombination deficiency were elucidated. Notably, we identified CDK12-type genomic instability associated with CDK12 fusions.

CONCLUSIONS

Our findings support the potential of whole genome and transcriptome sequencing analyses as a comprehensive approach to identify treatment targets in adenocarcinoma of the stomach and the esophagus, and their application in precision oncology.

Quest for discovering novel CDK12 inhibitor

CDK12 is essential for cellular processes like RNA processing, transcription, and cell cycle regulation, inhibiting cancer cell growth and facilitating macrophage invasion. CDK12 is a significant oncogenic factor in various cancers, including HER2-positive breast cancer, Anaplastic thyroid carcinoma, Hepatocellular carcinoma, prostate cancer, and Ewing sarcoma. It is also regarded as a potential biomarker, emphasizing its broader significance in oncology. Targeting CDK12 offers a promising strategy to develop therapy. Various monoclonal antibodies have drawn wide attention, but they are expensive compared to small-molecule inhibitors, limiting their accessibility and affordability for patients. Consequently, this research aims to identify effective CDK12 inhibitors using comprehensive high-throughput virtual screening. RASPD protocol has been employed to screen three different databases against the target followed by drug-likeness, molecular docking, ADME, toxicity, Consensus molecular docking, MD Simulation, and in-vitro studies MTT assay. The research conducted yielded one compound ZINC11784547 has demonstrated robust binding affinity, favorable ADME features, less toxicity, remarkable stability, and cytotoxic effect. The identified compound holds promise for promoting cancer cell death through CDK12 inhibition.

Targeting cyclin-dependent kinases: From pocket specificity to drug selectivity

The development of selective modulators of cyclin-dependent kinases (CDKs), a kinase family with numerous members and functional variations, is a significant preclinical challenge. Recent advancements in crystallography have revealed subtle differences in the highly conserved CDK pockets. Exploiting these differences has proven to be an effective strategy for achieving excellent drug selectivity. While previous reports briefly discussed the structural features that lead to selectivity in individual CDK members, attaining inhibitor selectivity requires consideration of not only the specific structures of the target CDK but also the features of off-target members. In this review, we summarize the structure-activity relationships (SARs) that influence selectivity in CDK drug development and analyze the pocket features that lead to selectivity using molecular-protein binding models. In addition, in recent years, novel CDK modulators have been developed, providing more avenues for achieving selectivity. These cases were also included. We hope that these efforts will assist in the development of novel CDK drugs.

Annual review of PROTAC degraders as anticancer agents in 2022

Following nearly two decades of development, significant advancements have been achieved in PROTAC technology. As of the end of 2022, more than 20 drugs have entered clinical trials, with ARV-471 targeting estrogen receptor (ER) showing remarkable progress by entering phase III clinical studies. In 2022, significant progress has been made on multiple targets. The first reversible covalent degrader designed to target the KRASG12C mutant protein, based on cyclopropionamide, has been reported. Additionally, the activity HDCA1 degrader surpassed submicromolar levels during the same year. A novel FEM1B covalent ligand called EN106 was also discovered, expanding the range of available ligands. Furthermore, the first PROTAC drug targeting SOS1 was reported. Additionally, the first-in-class degraders that specifically target BRD4 isoforms (BRD4 L and BRD4 S) have recently been reported, providing a valuable tool for further investigating the biological functions of these isoforms. Lastly, a breakthrough was also achieved with the first degrader targeting both CDK9 and Cyclin T1. In this review, we aimed to update the PROTAC degraders as potential anticancer agents covering articles published in 2022. The design strategies, degradation effects, and anticancer activities were highlighted, which might provide an updated sight to develop novel PROTAC degraders with great potential as anticancer agents as well as favorable drug-like properties.

Design principles for cyclin K molecular glue degraders

Molecular glue degraders are an effective therapeutic modality, but their design principles are not well understood. Recently, several unexpectedly diverse compounds were reported to deplete cyclin K by linking CDK12-cyclin K to the DDB1-CUL4-RBX1 E3 ligase. Here, to investigate how chemically dissimilar small molecules trigger cyclin K degradation, we evaluated 91 candidate degraders in structural, biophysical and cellular studies and reveal all compounds acquire glue activity via simultaneous CDK12 binding and engagement of DDB1 interfacial residues, in particular Arg928. While we identify multiple published kinase inhibitors as cryptic degraders, we also show that these glues do not require pronounced inhibitory properties for activity and that the relative degree of CDK12 inhibition versus cyclin K degradation is tuneable. We further demonstrate cyclin K degraders have transcriptional signatures distinct from CDK12 inhibitors, thereby offering unique therapeutic opportunities. The systematic structure-activity relationship analysis presented herein provides a conceptual framework for rational molecular glue design.

Gluing the pieces together

Illuminating the path to degrading troublesome proteins.

Research progress of anticancer drugs targeting CDK12

Cyclin-dependent kinase 12 (CDK12) is a transcription-associated CDK that plays key roles in transcription, translation, mRNA splicing, the cell cycle, and DNA damage repair. Research has identified that high expression of CDK12 in organs such as the breast, stomach, and uterus can lead to HER2-positive breast cancer, gastric cancer and cervical cancer. Inhibiting high expression of CDK12 suppresses tumor growth and proliferation, suggesting that it is both a biomarker for cancer and a potential target for cancer therapy. CDK12 inhibitors can competitively bind the CDK12 hydrophobic pocket with ATP to avoid CDK12 phosphorylation, blocking subsequent signaling pathways. The development of CDK12 inhibitors is challenging due to the high homology of CDK12 with other CDKs. This review summarizes the research progress of CDK12 inhibitors, their mechanism of action and the structure-activity relationship, providing new insights into the design of CDK12 selective inhibitors.

Targeting pre-mRNA splicing in cancers: roles, inhibitors, and therapeutic opportunities

Accumulating evidence has indicated that pre-mRNA splicing plays critical roles in a variety of physiological processes, including development of multiple diseases. In particular, alternative splicing is profoundly involved in cancer progression through abnormal expression or mutation of splicing factors. Small-molecule splicing modulators have recently attracted considerable attention as a novel class of cancer therapeutics, and several splicing modulators are currently being developed for the treatment of patients with various cancers and are in the clinical trial stage. Novel molecular mechanisms modulating alternative splicing have proven to be effective for treating cancer cells resistant to conventional anticancer drugs. Furthermore, molecular mechanism-based combination strategies and patient stratification strategies for cancer treatment targeting pre-mRNA splicing must be considered for cancer therapy in the future. This review summarizes recent progress in the relationship between druggable splicing-related molecules and cancer, highlights small-molecule splicing modulators, and discusses future perspectives of splicing modulation for personalized and combination therapies in cancer treatment.

A practical "preTACs-cytoblot" platform accelerates the streamlined development of PROTAC-based protein degraders

With the growing importance of PROTAC-mediated protein degradation in drug discovery, robust synthetic methodologies and rapid screening assays are urgently needed. By harnessing the improved alkene hydroazidation reaction, we developed a novel strategy to introduce azido groups into the linker-E3 ligand conjugates and effectively created a range of prepacked terminal azide-labeled "preTACs" as PROTAC toolkit building blocks. Moreover, we demonstrated that preTACs are ready to conjugate to ligands targeting a protein of interest to generate libraries of chimeric degraders, which are subsequently screened for effective protein degradation directly from cultured cells with a cytoblot assay. Our study exemplifies that this practical "preTACs-cytoblot" platform allows efficient PROTAC assembly and rapid activity assessments. It may help industrial and academic investigators to accelerate their streamlined development of PROTAC-based protein degraders.