Abstract 5221: Development of TGN-1076, a selective and reversible small molecule inhibitor of CDK7
Authors: Thode Trason , Li Zhaoliang , Weston Alexis , Dana Srikanta , Ampanattu Sherin Daniel , Soldi Raffaella , Kaadige Mohan Rao , Vankayalapti Hariprasad , Chung Vincent , Chao Joseph , Von Hoff Daniel D , Sharma Sunil 
Published: September 2020

Abstract
Purpose: Tumor genetic heterogeneity can lead to dysregulation of transcriptional programs and cause cancer cells to become highly dependent on certain regulators of gene expression. Super-enhancers (SEs) are a class of regulatory regions that are associated with a strong enrichment of transcriptional coactivators (MED1, BRD4) and chromatin marks (H3K27Ac). It has been shown that tumor cells can acquire SEs at oncogenic driver genes (MYC, TERT, BCL2, GFI1, MED1, OCT4, and SOX2), activate their expression, and induce transcriptional reprogramming. Importantly, the majority of super-enhancers depend on the ability of cyclin-dependent kinase 7 (CDK7) to initiate transcription by phosphorylating the C-terminal domain of RNA Pol II. Recent reports have shown that high level of CDK7 is associated with poor prognosis in breast, gastric, ovarian, pancreatic, SCLC, ATC, and AML cancers. We have embarked on developing a novel therapeutic that specifically targets the CDK7 catalytic ATP pocket. Previously, we reported the discovery of TGN-1062 as a potent inhibitor of CDK7. In this study, we report the development of TGN-1076, an analog of TGN-1062, as a selective and reversible inhibitor of CDK7 due to its ideal candidate criteria.
Methods: With structure-guided and iterative medicinal chemistry approaches, the previous lead candidate TGN-1062 was further optimized to improve potency, target selectivity, and desirable drug-like properties. In vitro kinase assays were performed using ADP-GloTM kinase assay kit (Promega). Cell viability assays were performed in a panel of cancer cell lines using CellTiter-Glo assay kit (Promega). RNA Pol II phosphorylation and total MYC protein levels were determined by Western Blotting.
Results: TGN-1076 inhibited CDK7 activity with an IC50 of 20 nM and showed 10-500 fold selectivity against the closest members of the CDK family. TGN-1076 blocked growth of multiple cancer cells, among these pancreatic cancer cells were most sensitive with an GI50 of &lt;0.6 µM. More importantly, phosphorylation of RNA Pol II and super-enhancer dependent expression of MYC as well as it's downstream target MCL-1 were significantly reduced in TGN-1076 treated MiaPaca2 pancreatic cancer cells. TGN-1076 showed high micromolar activity (&gt;5 µM) against hERG and multiple P450 isozymes. The results from these studies along with ADME-Tox and pharmacokinetics will be presented.
Conclusion: In summary, we have developed a novel selective and reversible inhibitor of CDK7. Our current efforts are focused on further optimization and nomination of a preclinical candidate for ADME-Tox and tumor efficacy studies.
Citation Format: Trason Thode, Zhaoliang Li, Alexis Weston, Srikanta Dana, Sherin Daniel Ampanattu, Raffaella Soldi, Mohan Rao Kaadige, Hariprasad Vankayalapti, Vincent Chung, Joseph Chao, Daniel D Von Hoff, Sunil Sharma. Development of TGN-1076, a selective and reversible small molecule inhibitor of CDK7 [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5221.