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Cyclin-dependent kinase 9 (CDK9) is a serine/threonine kinase involved in the regulation of transcription elongation. An inhibition of CDK9 downregulates a number of short-lived proteins responsible for tumor maintenance and survival, including the antiapoptotic BCL-2 family member MCL-1. As pan-CDK inhibitors under development have faced dosing and toxicity challenges in the clinical setting, we generated selective CDK9 inhibitors that could be amenable to an oral administration. Here, we report the lead optimization of a series of azaindole-based inhibitors. To overcome early challenges with promiscuity and cardiovascular toxicity, carboxylates were introduced into the pharmacophore en route to compounds such as 14 and 16 . These CDK9 inhibitors demonstrated a reduced toxicity, adequate pharmacokinetic properties, and a robust in vivo efficacy in mice upon oral dosing., Competing Interests: The authors declare the following competing financial interest(s): I'm an employee and stock holder of Abbvie., (© 2021 American Chemical Society.)

BCL-X L , an antiapoptotic member of the BCL-2 family of proteins, drives tumor survival and maintenance and thus represents a key target for cancer treatment. Herein we report the rational design of a novel series of selective BCL-X L inhibitors exemplified by A-1293102. This molecule contains structural elements of selective BCL-X L inhibitor A-1155463 and the dual BCL-X L /BCL-2 inhibitors ABT-737 and navitoclax, while representing a distinct pharmacophore as assessed by an objective cheminformatic evaluation. A-1293102 exhibited picomolar binding affinity to BCL-X L and both efficiently and selectively killed BCL-X L -dependent tumor cells. X-ray crystallographic analysis demonstrated a key hydrogen bonding network in the P2 binding pocket of BCL-X L , while the bent-back moiety achieved efficient occupancy of the P4 pocket in a manner similar to that of navitoclax. A-1293102 represents one of the few distinct structural series of selective BCL-X L inhibitors, and thus serves as a useful tool for biological studies as well as a lead compound for further optimization., Competing Interests: The authors declare the following competing financial interest(s): AbbVie participated in interpretation of data and review and approval of publication. Z-F.T., X.W., J.C., J.P.I., S.J., R.A.J., P.J.K., C.S., B.D.W., L.Z., H.Z., S.W.E., D.C.P., A.S.J., J.D.L., and A.J.S. are employees of AbbVie; C.P. was an employee of AbbVie at the time of the study., (© 2021 American Chemical Society.)

Herein we describe the discovery of A-1331852, a first-in-class orally active BCL-X L inhibitor that selectively and potently induces apoptosis in BCL-X L -dependent tumor cells. This molecule was generated by re-engineering our previously reported BCL-X L inhibitor A-1155463 using structure-based drug design. Key design elements included rigidification of the A-1155463 pharmacophore and introduction of sp 3 -rich moieties capable of generating highly productive interactions within the key P4 pocket of BCL-X L . A-1331852 has since been used as a critical tool molecule for further exploring BCL-2 family protein biology, while also representing an attractive entry into a drug discovery program., Competing Interests: The authors declare the following competing financial interest(s): AbbVie and Genentech participated in interpretation of data and review and approval of publication. L.W., G.A.D., A.S.J., Z-F.T., T. M. H., R.R.F., X.S., M.B., A.R.K., X.W., M.D.W., N.D.C., S.S., D.C.P., R.A.J., P.N., M.L.S., S.K.T., Y.X., J.X., H.Z., P.N.L., M.J.M., E.R.B., W.G., P.K., S.W.E., J.D.L., and A.J.S. are employees of AbbVie, Inc. C.H.P. was an employee of AbbVie, Inc at the time of the study. E.C. and W.J.F. are employees of Genentech, Inc. J.A.F., D.D., and D.S. were employees of Genentech, Inc. at the time of the study.

A-1155463, a highly potent and selective BCL-XL inhibitor, was discovered through nuclear magnetic resonance (NMR) fragment screening and structure-based design. This compound is substantially more potent against BCL-XL-dependent cell lines relative to our recently reported inhibitor, WEHI-539, while possessing none of its inherent pharmaceutical liabilities. A-1155463 caused a mechanism-based and reversible thrombocytopenia in mice and inhibited H146 small cell lung cancer xenograft tumor growth in vivo following multiple doses. A-1155463 thus represents an excellent tool molecule for studying BCL-XL biology as well as a productive lead structure for further optimization.

Because of the promise of BCL-2 antagonists in combating chronic lymphocytic leukemia (CLL) and non-Hodgkin's lymphoma (NHL), interest in additional selective antagonists of antiapoptotic proteins has grown. Beginning with a series of selective, potent BCL-XL antagonists containing an undesirable hydrazone functionality, in silico design and X-ray crystallography were utilized to develop alternative scaffolds that retained the selectivity and potency of the starting compounds.