Dinaciclib (SCH727965)

Dinaciclib is a potent cyclin-dependent kinase (CDK) inhibitor with IC50s for CDK2, CDK5, CDK1 and CDK9 at 1 nM, 1 nM, 3 nM, and 4 nM, respectively. [1] It is in phase I or II clinical trials for various cancers.

Dinaciclib interacts with the acetyl-lysine recognition site of bromodomains. [2] Inhibition of CDK 1 suppresses Rb phosphorylation, leading to cell cycle arrest and apoptosis. [3]

Dinaciclib is active against a broad spectrum of human tumor cell lines in vitro and in vivo. It has great potential to improve cancer chemotherapy.

References:
[1]Parry D., et al. (2010). Dinaciclib (SCH 727965), a Novel and Potent Cyclin-Dependent Kinase Inhibitor. Mol Cancer Ther (9): 2344- 2353.
[2]Martin, M. P., et al. (2013). Cyclin-dependent kinase inhibitor dinaciclib interacts with the acetyl-lysine recognition site of bromodomains. ACS Chemical Biology 8 (11): 2360–5.
[3]Payton M., et al. (2006). Discovery and Evaluation of Dual CDK1 and CDK2 Inhibitors. Cancer Res 66: 4299-4308.

Cyclin-dependent kinase inhibitor Dinaciclib (SCH727965) inhibits pancreatic cancer growth and progression in murine xenograft models.[Pubmed:21768779]

Cancer Biol Ther. 2011 Oct 1;12(7):598-609. Epub 2011 Oct 1.

Pancreatic cancer is one of the most lethal of human malignancies, and potent therapeutic options are lacking. Inhibition of cell cycle progression through pharmacological blockade of cyclin-dependent kinases (CDK) has been suggested as a potential treatment option for human cancers with deregulated cell cycle control. Dinaciclib (SCH727965) is a novel small molecule multi-CDK inhibitor with low nanomolar potency against CDK1, CDK2, CDK5 and CDK9 that has shown favorable toxicity and efficacy in preliminary mouse experiments, and has been well tolerated in Phase I clinical trials. In the current study, the therapeutic efficacy of SCH727965 on human pancreatic cancer cells was tested using in vitro and in vivo model systems. Treatment with SCH727965 significantly reduced in vitro cell growth, motility and colony formation in soft agar of MIAPaCa-2 and Pa20C cells. These phenotypic changes were accompanied by marked reduction of phosphorylation of Retinoblastoma (Rb) and reduced activation of RalA. Single agent therapy with SCH727965 (40 mg/kg i.p. twice weekly) for 4 weeks significantly reduced subcutaneous tumor growth in 10/10 (100%) of tested low-passage human pancreatic cancer xenografts. Treatment of low passage pancreatic cancer xenografts with a combination of SCH727965 and gemcitabine was significantly more effective than either agent alone. Gene Set Enrichment Analysis identified overrepresentation of the Notch and Transforming Growth Factor-beta (TGF-beta) signaling pathways in the xenografts least responsive to SCH727965 treatment. Treatment with the cyclin-dependent kinase inhibitor SCH727965 alone or in combination is a highly promising novel experimental therapeutic strategy against pancreatic cancer.

Dinaciclib (SCH727965) inhibits the unfolded protein response through a CDK1- and 5-dependent mechanism.[Pubmed:24362465]

Mol Cancer Ther. 2014 Mar;13(3):662-74.

Evidence implicating dysregulation of the IRE1/XBP-1s arm of the unfolded protein response (UPR) in cancer pathogenesis (e.g., multiple myeloma) has prompted the development of IRE1 RNase inhibitors. Here, effects of cyclin-dependent kinase (CDK) inhibitor SCH727965 (dinaciclib) on the IRE1 arm of the UPR were examined in human leukemia and myeloma cells. Exposure of cells to extremely low (e.g., nmol/L) concentrations of SCH727965, a potent inhibitor of CDKs 1/2/5/9, diminished XBP-1s and Grp78 induction by the endoplasmic reticulum (ER) stress-inducers thapsigargin and tunicamycin, while sharply inducing cell death. SCH727965, in contrast to IRE1 RNase inhibitors, inhibited the UPR in association with attenuation of XBP-1s nuclear localization and accumulation rather than transcription, translation, or XBP-1 splicing. Notably, in human leukemia cells, CDK1 and 5 short hairpin RNA (shRNA) knockdown diminished Grp78 and XBP-1s upregulation while increasing thapsigargin lethality, arguing for a functional role for CDK1/5 in activation of the cytoprotective IRE1/XBP-1s arm of the UPR. In contrast, CDK9 or 2 inhibitors or shRNA knockdown failed to downregulate XBP-1s or Grp78. Furthermore, IRE1, XBP-1, or Grp78 knockdown significantly increased thapsigargin lethality, as observed with CDK1/5 inhibition/knockdown. Finally, SCH727965 diminished myeloma cell growth in vivo in association with XBP-1s downregulation. Together, these findings demonstrate that SCH727965 acts at extremely low concentrations to attenuate XBP-1s nuclear accumulation and Grp78 upregulation in response to ER stress inducers. They also highlight a link between specific components of the cell-cycle regulatory apparatus (e.g., CDK1/5) and the cytoprotective IRE1/XBP-1s/Grp78 arm of the UPR that may be exploited therapeutically in UPR-driven malignancies.