[4-Amino-2-[(1-methylsulfonylpiperidin-4-yl)amino]pyrimidin-5-yl](2,3-difluoro-6-methoxyphenyl)methanone(R 547)

R547 is a potent ATP-competitive inhibitor of CDK1/2/4 with Ki of 2 nM/3 nM/1 nM. It is less potent to CDK7 and GSK3α/β, while inactive to other kinases. Phase 1.

R547 identified as a diaminopyrimidine compound, which is a potent and selective ATP-competitive CDK inhibitor. R547 effectively inhibits CDK1/cyclinB, CDK2/cyclinE, and CDK4/cyclinD1(Ki=1-3nM) and is inactive(Ki>5,000nM) against a panel of >120 unrelated kinases. R547 effectively inhibits the proliferation of tumor cell lines independent of multidrug resistant status, histologic type, retinoblastoma protein, or p53 status, with IC50s <0.60 μM. R547 reduces phosphorylation of the cellular retinoblastoma protein at specific CDK phosphorylation sites at the same concentrations that induced cell cycle arrest, suggesting a potential pharmaco dynamics marker for clinical use. R547 inhibits the proliferation of tumor cell lines and is active in all 19 cell lines tested irrespective of tissue of origin, multidrug resistance (MDR), p53, or retinoblastoma status. R547 possessing both 5-and 6-fluoro substitution culminated in an Inhibitor with low, single-digit nanomolar potency against the CDKs(Ki=0.001,0.003,and 0.001 μM for CDK1,CDK2, and CDK4,respectively) and excellent cellular potency (IC50=0.08 μM,HCT116 cell line).

R547 administered with oral and i.v. dosing in multiple established human tumor significantly inhibits tumor activity(P < 0.01). R547 administered orally at dose of 40 mg/kg daily in colon, lung, breast, prostate, and melanoma human tumor xenograft models shows significant TGI (79-99%). R547 is equally efficacious (TGI, 61-95%) when dosed with 40 mg/kg i.v. once weekly. These doses of R547 are not toxic and did not result in body weight loss. R547 does not show signs of overt toxicity during the course of the 3-week study and any gross pathology at necropsies done at the end of the studies.R547 inhibits tumor growth up to 95% in the HCT116 human colorectal tumor xenograft model in nude mice . R547 causes significant TGI in all of the models tested when dosed orally and i.v. at or below the maximum tolerated dose. R547 inhibits phosphorylation of retinoblastoma protein in tumors at the efficacious exposures in tumor xenograft models, providing a pharmacodynamic biomarker for clinical use. R547 reported here suggests that this is a promising molecule for evaluation in the treatment of solid tumors.

Cyclin-dependent kinases (Cdks) are critical positive regulators of cell cycle progression and cellular transcription whose dysregulation can lead to the development of cancer. R547 is a diaminopyrimidine compound that inhibits Cdk1/cyclin B, Cdk2/cyclin E, and Cdk4/cyclin D1 (K_is = 1-3 nM). It is inactive against a panel of more than 120 unrelated kinases (K_is > 5 μM). R547 inhibits tumor cell proliferation (IC₅₀s ≤ 0.6 μM in vitro), inducing cell cycle arrest at G₁ and G₂ phases and apoptosis as well as reducing phosphorylation of the retinoblastoma protein. It also demonstrates antitumor activity in vivo in various human tumor xenograft models.

CDK4/CyclinD1

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