Abstract 2828: Rapid identification of potent and highly selective, oral PTEFb Inhibitor BAY 1143572 with first in class potential
Authors: Luecking Ulrich TJ , Scholz Arne , Lienau Philip , Siemeister Gerhard , Kosemund Dirk , Bohlmann Rolf , Eis Knut , Gnoth Mark , Terebesi Ildiko , Meyer Kirstin , Prelle Katja , Valencia Ray , Ince Stuart , von Nussbaum Franz , Mumberg Dominik , Ziegelbauer Karl , Klebl Bert , Choidas Axel , Nussbaumer Peter , Baumann Matthias , Schultz-Fademrecht Carsten , Ruehter Gerd , Eickhoff Jan , Brands Michael 
Published: August 2015

Abstract
PTEFb (positive transcription elongation factor b) is a heterodimer of the transcriptional control kinase CDK9 (Cyclin-dependent kinase 9) and Cyclin T. PTEFb phosphorylates and activates RNA polymerase II. PTEFb inhibition causes rapid depletion of short-lived mRNA transcripts and their associated protein products involved in proliferation and survival like Myc, or Mcl-1 which results in cell death of addicted tumor cells.
We previously disclosed the profile of the lead compound PTEFb BAY1, a nanomolar PTEFb inhibitor with 50-fold selectivity within the CDK family and cellular potency of about 1 μM in proliferation assays on various human tumor cell lines [1]. PTEFb BAY1 also revealed in vivo efficacy in a human acute myeloid leukemia (AML) xenograft model in nude mice. However, the lead compound also displayed certain limitations in ADME properties like low aqueous solubility and a strong recognition by efflux transporters in the Caco2 assay.
Based on these findings, extensive lead optimisation efforts led to the rapid identification of BAY 1143572 which is a more potent and highly selective, orally available PTEFb inhibitor with first-in-class potential. BAY 1143572 has a high aqueous solubility, reduced drug efflux and a moderate oral bioavailability across species that allows daily as well as intermittent dosing schedules in animal models. BAY 1143572 revealed strong in vitro and in vivo anti-tumor efficacy with various cell-lines.
BAY 1143572 is currently being evaluated in a Phase I study to determine the safety, tolerability, pharmacokinetics and initial pharmacodynamic biomarker response in patients with advanced cancer.
This presentation will highlight the key learnings from our PTEFb lead optimization program.
[1]: AACR, April 5-9, 2014, San Diego, Poster Presentation, Abstract 4538, Cancer Res October 1, 2014, 74:4538; doi:10.1158/1538-7445.AM2014-4538
Citation Format: Ulrich TJ Luecking, Arne Scholz, Philip Lienau, Gerhard Siemeister, Dirk Kosemund, Rolf Bohlmann, Knut Eis, Mark Gnoth, Ildiko Terebesi, Kirstin Meyer, Katja Prelle, Ray Valencia, Stuart Ince, Franz von Nussbaum, Dominik Mumberg, Karl Ziegelbauer, Bert Klebl, Axel Choidas, Peter Nussbaumer, Matthias Baumann, Carsten Schultz-Fademrecht, Gerd Ruehter, Jan Eickhoff, Michael Brands. Rapid identification of potent and highly selective, oral PTEFb Inhibitor BAY 1143572 with first in class potential. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2828. doi:10.1158/1538-7445.AM2015-2828