FIRST-IN-CLASS CDK7 INHIBITOR, INDUCES ROBUST APOPTOSIS IN ACUTE MYELOID LEUKEMIA AND DEMONSTRATES DURABLE IN VIVO EFFICACY
Author(s): ,
Yoon Jong Choi
Affiliations:
Biology,Syros Pharmaceuticals,Cambridge,United States
,
Shanhu Hu
Affiliations:
Biology,Syros Pharmaceuticals,Cambridge,United States
,
Nan Ke
Affiliations:
Biology,Syros Pharmaceuticals,Cambridge,United States
,
Yixuan Ren
Affiliations:
Biology,Syros Pharmaceuticals,Cambridge,United States
,
Jeremy Lopez
Affiliations:
Biology,Syros Pharmaceuticals,Cambridge,United States
,
Sofija Milijovska
Affiliations:
Computational Biology,Syros Pharmaceuticals,Cambridge,United States
,
David Orlando
Affiliations:
Computational Biology,Syros Pharmaceuticals,Cambridge,United States
,
Darby Schmidt
Affiliations:
Chemistry,Syros Pharmaceuticals,Cambridge,United States
,
Michael Bradley
Affiliations:
Biology,Syros Pharmaceuticals,Cambridge,United States
,
Kevin Sprott
Affiliations:
Chemistry,Syros Pharmaceuticals,Cambridge,United States
,
Christian Fritz
Affiliations:
Biology,Syros Pharmaceuticals,Cambridge,United States
Eric Olson
Affiliations:
Biology,Syros Pharmaceuticals,Cambridge,United States
(Abstract release date: May 19, 2016) EHA Learning Center. Choi Y. Jun 11, 2016; 133446
Yoon Jong Choi
Yoon Jong Choi

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Abstract: P558

Type: Poster Presentation

Presentation during EHA21: On Saturday, June 11, 2016 from 17:30 - 19:00

Location: Poster area (Hall H)

Background
CDK7 acts bi-functionally as a CDK-activating kinase (CAK) controlling proliferation and as a transcriptional kinase phosphorylating the P-CTD-RNAPol II, thereby driving efficient transcriptional processes. CDK7 has recently emerged as an attractive gene control target in cancers driven by transcriptional dependencies and regulated by Super-enhancers (SEs) (Kwiatkowski et al., 2014; Chipumuro et al., 2014; Christensen 2014; Wang 2015). Acute Myeloid Leukemias (AML) harbor mutations in genes controlling gene expression, and as a consequence, are exquisitely sensitive to CDK7 inhibition. Employing our SE-platform technology we reveal mechanistic insights underlying the vulnerability of AML to gene control modulation via selective CDK7 inhibition.

Aims
Evaluate CDK7 as an anti-cancer target in AML, using our covalent, potent and highly selective CDK7 inhibitor. Investigate the cellular and mechanistic consequences of targeting CDK7 in AML underlying their susceptibility to CDK7-dependent transcriptional control.

Methods
Characterize CDK7 inhibition in vitro and in vivo to evaluate potency and efficacy in AML cell lines and xenografts (cell line derived xenografts, CDXs and patient derived xenografts, PDXs). We employ our SE-platform technology and next-generation sequencing to identify key mechanisms targeted in AML with our selective CDK7 inhibitor.

Results
Here we report a first-in-class CDK7 inhibitor that covalently targets a cysteine outside the kinase domain, resulting in sustained, highly selective inhibition. Syros compound, SY-1365, exhibits significant biochemical potency (Ki = 17 ± 7nM) and selectivity when profiled against >450 other kinases. In a cancer cell line panel, acute leukemias emerged among the most sensitive to CDK7 inhibition. Moreover, AML cell lines undergo rapid and robust apoptosis within 24 hours. This is preceded by >90% CDK7 target engagement and concomitant loss of P-CTD-RNAPol II suggesting the primary consequence of targeting CDK7 is the impaired transcriptional activity dependent on CDK7. Further investigation of the transcriptional consequences of CDK7 inhibition point to a reliance on key disease relevant transcriptional aberrations including translocations and SE-genes (e.g. MLL fusions, MYB, HOX10A and MYC).Given the covalent mechanism of SY-1365 and PK profile, we evaluated intermittent treatments in vitro with subsequent washout of free drug to model dosing regimens in vivo. We demonstrate that brief drug exposures maintain a robust irreversible apoptotic response in leukemia cells. In contrast, treated non-transformed cells recover from a transient G2/M arrest followed by re-synthesis of free CDK7 and no apoptosis/cell death. We have extended these findings to in vivo experiments whereby intermittent dosing in AML patient derived xenograft models (PDX, AM7577) maintains efficacy (reducing human CD45+ leukemia cells to <1%) with a significant survival advantage. We have established a PD assay by measuring target engagement of CDK7 both in mouse xenografts and human PBMCs to support: 1) establishing a PK-PD-efficacy relationship 2) quantifying target engagement during dose escalation in a Ph1 clinical trial.

Conclusion
In summary, we describe our first-in-class CDK7 inhibitor, SY-1365 that is potent, highly selective and leads to durable, complete responses in xenograft models of AML. These data support the rationale for advancing compounds with this profile toward clinical development.

Session topic: Acute myeloid leukemia - Biology 3

Keyword(s): Acute myeloid leukemia, Cancer, Kinase inhibitor, Transcriptional regulation
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