SPH3643: A novel cyclin-dependent kinase 4/6 inhibitor with good anticancer efficacy and strong blood-brain barrier permeability.

The cyclin-dependent kinase (CDK)4/6-cyclin D1-Rb-p16/ink4a pathway is responsible for regulating cell progression past the G1 restriction point during the cell cycle. The development of a majority of human tumors is associated with dysregulation of this pathway, resulting in increased cancer cell proliferation. Both CDK4 and CDK6, well-validated cancer drug targets, function primarily as catalytic enzymes that mediate the phosphorylation of retinoblastoma protein (Rb). Here, we determined that SPH3643 is a novel potent antiproliferative agent that inhibits CDK4/6 kinase activity. In biochemical assays, SPH3643 showed more potent inhibition of both CDK4 and CDK6 than did 2 published CDK4/6 inhibitors, LY2835219 and palbociclib, and had better selectivity than LY2835219. Further in vitro study revealed that SPH3643 blocked Cdk/Rb signaling by inhibiting the phosphorylation of RbSer780 and arrested the MCF-7 cancer cells at G0 /G1 phase, resulting in marked inhibition of the proliferation of Rb-positive cancer cell lines. In vivo SPH3643 treatment in mice bearing xenograft tumor models of breast cancer, colon cancer, acute myelocytic leukemia, and glioblastoma resulted in significant decreases in tumor growth. SPH3643 was able to particularly strongly inhibit glioblastoma (U87-MG) cell growth in the brains of orthotopic carcinoma xenograft mice due to its high degree of intracerebral penetration and significant persistence in this setting. Together these results revealed that SPH3643 is a potent, orally active small-molecule inhibitor of CDK4/6 with robust anticancer efficacy and a high degree of blood-brain barrier permeability.

Liao X ，Hong Y ，Mao Y ，Chen N ，Wang Q ，Wang Z ，Zhang L ，Wang L ，Shi C ，Shi W ，Ge H ，Li A ，Li X ，Xia G ，Liu Y ... -  《-》

Preclinical characterization of the CDK4/6 inhibitor LY2835219: in-vivo cell cycle-dependent/independent anti-tumor activities alone/in combination with gemcitabine.

Gelbert LM ，Cai S ，Lin X ，Sanchez-Martinez C ，Del Prado M ，Lallena MJ ，Torres R ，Ajamie RT ，Wishart GN ，Flack RS ，Neubauer BL ，Young J ，Chan EM ，Iversen P ，Cronier D ，Kreklau E ，de Dios A ... -  《-》

Preclinical characterization of SHR6390, a novel CDK 4/6 inhibitor, in vitro and in human tumor xenograft models.

Inhibition of the cyclin-dependent kinase (CDK) 4/6-retinoblastoma (RB) pathway is an effective therapeutic strategy against cancer. Here, we performed a preclinical investigation of the antitumor activity of SHR6390, a novel CDK4/6 inhibitor. SHR6390 exhibited potent antiproliferative activity against a wide range of human RB-positive tumor cells in vitro, and exclusively induced G1 arrest as well as cellular senescence, with a concomitant reduction in the levels of Ser780-phosphorylated RB protein. Compared with the well-known CDK4/6 inhibitor palbociclib, orally administered SHR6390 led to equivalent or improved tumor efficacy against a panel of carcinoma xenografts, and produced marked tumor regression in some models, in association with sustained target inhibition in tumor tissues. Furthermore, SHR6390 overcame resistance to endocrine therapy and HER2-targeting antibody in ER-positive and HER2-positive breast cancer, respectively. Moreover, SHR6390 combined with endocrine therapy exerted remarkable synergistic antitumor activity in ER-positive breast cancer. Taken together, our findings indicate that SHR6390 is a novel CDK4/6 inhibitor with favorable pharmaceutical properties for use as an anticancer agent.

Long F ，He Y ，Fu H ，Li Y ，Bao X ，Wang Q ，Wang Y ，Xie C ，Lou L ... -  《-》

CDK4/6 inhibitor-SHR6390 exerts potent antitumor activity in esophageal squamous cell carcinoma by inhibiting phosphorylated Rb and inducing G1 cell cycle arrest.

Wang J ，Li Q ，Yuan J ，Wang J ，Chen Z ，Liu Z ，Li Z ，Lai Y ，Gao J ，Shen L ... -  《-》

Design of a brain-penetrant CDK4/6 inhibitor for glioblastoma.

CDK4 and CDK6 are kinases with similar sequences that regulate cell cycle progression and are validated targets in the treatment of cancer. Glioblastoma is characterized by a high frequency of CDKN2A/CCND2/CDK4/CDK6 pathway dysregulation, making dual inhibition of CDK4 and CDK6 an attractive therapeutic approach for this disease. Abemaciclib, ribociclib, and palbociclib are approved CDK4/6 inhibitors for the treatment of HR+/HER2- breast cancer, but these drugs are not expected to show strong activity in brain tumors due to poor blood brain barrier penetration. Herein, we report the identification of a brain-penetrant CDK4/6 inhibitor derived from a literature molecule with low molecular weight and topological polar surface area (MW = 285 and TPSA = 66 Å2), but lacking the CDK2/1 selectivity profile due to the absence of a basic amine. Removal of a hydrogen bond donor via cyclization of the pyrazole allowed for the introduction of basic and semi-basic amines, while maintaining in many cases efflux ratios reasonable for a CNS program. Ultimately, a basic spiroazetidine (cpKa = 8.8) was identified that afforded acceptable selectivity over anti-target CDK1 while maintaining brain-penetration in vivo (mouse Kp,uu = 0.20-0.59). To probe the potency and selectivity, our lead compound was evaluated in a panel of glioblastoma cell lines. Potency comparable to abemaciclib was observed in Rb-wild type lines U87MG, DBTRG-05MG, A172, and T98G, while Rb-deficient cell lines SF539 and M059J exhibited a lack of sensitivity.

Bronner SM ，Merrick KA ，Murray J ，Salphati L ，Moffat JG ，Pang J ，Sneeringer CJ ，Dompe N ，Cyr P ，Purkey H ，Boenig GL ，Li J ，Kolesnikov A ，Larouche-Gauthier R ，Lai KW ，Shen X ，Aubert-Nicol S ，Chen YC ，Cheong J ，Crawford JJ ，Hafner M ，Haghshenas P ，Jakalian A ，Leclerc JP ，Lim NK ，O'Brien T ，Plise EG ，Shalan H ，Sturino C ，Wai J ，Xiao Y ，Yin J ，Zhao L ，Gould S ，Olivero A ，Heffron TP ... -  《-》