Project description:The design of selective small-molecules is often stymied by similar ligand binding pockets. Here we report the first cyclin-dependent kinase 6 (CDK6) degrader, BSJ-03-123, that uses phthalimide-conjugation to exploit protein-interface determinants to achieve proteome-wide degradation selectivity. Pharmacologic CDK6 degradation targets a selective dependency of acute myeloid leukemia cells, and coupling acute degradation with transcriptomics and phosphoproteomics enabled dynamic mapping of the immediate role of CDK6 in coordinating signaling and transcription.
Project description:Cyclin-dependent kinase 6 (CDK6) represents a novel therapeutic target for the treatment of certain subtypes of acute myeloid leukemia (AML). CDK4/6 kinase inhibitors have been widely studied in many cancer types and their effects may be limited by primary and secondary resistance mechanisms. CDK4/6 degraders, which eliminate kinase dependent and kinase independent effects, have been suggested as alternative therapeutic option. We show that efficacy of the CDK6 specific protein degrader BSJ-03-123 varies among AML subtypes and depends on low expression of the INK4 proteins p16INK4A and p18INK4C. INK4 protein levels are significantly elevated in MLL-AF9+ compared to AML1-ETO+ cells, contributing to the different CDK6 degradation efficacy. We demonstrate that CDK6 complexes containing p16INK4A or p18INK4C are protected from BSJ-mediated degradation and that INK4 levels define the proliferative response to CDK6 degradation. These findings define INK4 proteins as predictive marker for CDK6 degradation – targeted therapies in AML.
Project description:We describe a critical role for Cdk6 in JAK2V617F+ MPN evolution. The absence of Cdk6 ameliorates clinical symptoms and prolongs survival of JAK2V617F fl/+ vav-Cre mice. The Cdk6 protein interferes with three hallmarks of disease: besides regulating malignant stem cell quiescence, it promotes NFkB signaling and contributes to cytokine production while inhibiting apoptosis. The treatment with palbociclib did not mirror these effects, showing that the functions of Cdk6 in MPN pathogenesis are largely kinase-independent.
Project description:By selective and reversible inhibition of CDK4/CDK6, we have developed a strategy to both inhibit proliferation and enhance cytotoxic killing of cancer cells. Induction of prolonged early-G1 arrest (pG1) by CDK4/CDK6 inhibition halts gene expression in early-G1 and prevents expression of genes programmed for other cell cycle phases. S-phase synchronization upon removal of the early-G1 block (pG1-S) fails to completely restore scheduled gene expression. Consequently, coordinate loss of IRF4 and gain of Bim and Noxa expression sensitize myeloma tumor cells to bortezomib-induced apoptosis in pG1 and more profoundly in pG1-S in vitro. Induction of pG1 and pG1-S by CDK4/CDK6 inhibition augments tumor-specific bortezomib killing in myeloma xenografts. Inhibition of CDK4/CDK6 in combination therapy thus represents a novel mechanism-based cancer therapy. PD 0332991 (PD) is the only known specific and reversible CDK4/CDK6 inhibitor. Gene expression was measured in myeloma MM1.S cells treated with PD (0.25 uM) in triplicate for 12, 24 or 36 h, or in cells released from G1, induced by 24hPD, for 4 or 18 h.
Project description:The cyclin-dependent kinases (CDK) CDK6 and CDK4 have redundant functions in regulating cell-cycle progression. We describe a novel role for CDK6 in hematopoietic and leukemic stem cells (HSCs and LSCs) that exceeds its function as cell-cycle regulator. Although hematopoiesis appears regular under steady state conditions Cdk6-/- HSCs do not efficiently repopulate upon competitive transplantation and Cdk6-deficient mice are significantly more susceptible to 5-fluorouracil (5-FU) treatment. We find that activation of HSCs requires CDK6, which interferes with transcription of key regulators including Egr1. The central role of Egr1 is supported by transcriptional profiling of HSCs. The impaired repopulation capacity extends to BCR-ABLp210+ leukemic stem cells. Transplantation with BCR-ABLp210+-infected bone marrow (BM) from Cdk6-/- mice fails to induce disease although recipient mice do harbor LSCs. Egr1 knock-down in cdk6-/- BCR-ABLp210+ LSKs significantly enhances colony formation underlining the importance of the Cdk6-Egr1 axis. Our findings define CDK6 as an important regulator of stem cell activation and as essential component of a transcriptional complex that suppresses Egr1 in HSCs and LSCs. Four-condition experiment, Untreated or polyI:C-treated CDK6-/- cells versus untreated or polyI:C-treated wild-type cells. Biological replicates: 3 untreated replicates, 3 polyI:C-treated replicates.
Project description:CDK6 induces a complex transcriptional program to block p53 in hematopoietic cells. CDK6 binds to the promoters of genes including p53-antagonists. Cells lacking CDK6 kinase function are required to mutate p53 to achieve a fully transformed immortalized state.