Abstract PTEFb/CDK9 mediated transcription of short-lived anti-apoptotic survival proteins like MYC, a key oncogene in multiple tumors, plays a critical role in cancer cell growth and survival. In addition, these survival proteins exhibit important functions in the development of resistance to chemotherapy. In contrast to pan-CDK inhibitors which are currently evaluated in Phase I and II clinical trials, to our knowledge PTEFb selective inhibitors have not been explored for clinical utility. We report for the first time the preclinical profile and structure of BAY 1143572, a novel selective PTEFb/CDK9 inhibitor currently being investigated in a Phase I clinical trial. BAY 1143572 had potent and highly selective PTEFb-kinase inhibitory activity in the low nanomolar range against PTEFb/CDK9 and an at least 50-fold selectivity against other CDKs in enzymatic assays. Furthermore, BAY 1143572 showed a favorable selectivity against a panel of non-CDK kinases in vitro. The potent enzymatic activity on PTEFb translated into broad antiproliferative activity against a panel of tumor cell lines with sub-micromolar IC-50 values. In line with the proposed mode of action, a concentration-dependent inhibition of the phosphorylation of the RNA polymerase II and downstream reduction of MYC mRNA and protein levels was observed in vitro. This inhibition was accompanied by an induction of apoptosis in cellular assays. BAY 1143572 also showed single agent in vivo efficacy at tolerated doses in various xenograft tumor models in mice and rats upon once daily oral administration. Potent anti-tumor activity characterized with partial or even complete remissions could be documented in models showing different MYC gene alterations like amplifications and translocations. Treatment with BAY 1143572 resulted in a transient inhibition of intratumoral MYC mRNA and protein levels and an induction of apoptosis in these models. The inhibition of MYC mRNA was also observed in blood cells of BAY 1143572-treated rats indicating the potential clinical utility of MYC in blood cells as a pharmacodynamic marker in clinical development. The in vivo efficacy of BAY 1143572 was significantly enhanced in combination with several chemotherapeutics in different solid tumor models. These pharmacology data provided the rationale for the initiation of clinical development of BAY 1143572 in advanced cancer patients (NCT01938638). In conclusion, our data provide preclinical proof of concept for BAY 1143572 as a potent and highly selective inhibitor of PTEFb/CDK9 with first-in-class potential. Further clinical evaluation of BAY 1143572 for the treatment of cancers dependent on the transcription of the key oncogene MYC and other short-lived survival proteins is warranted. Citation Format: Arne Scholz, Ulrich Luecking, Gerhard Siemeister, Philip Lienau, Ulf Boemer, Peter Ellinghaus, Annette O. Walter, Ray Valencia, Stuart Ince, Franz von Nussbaum, Dominik Mumberg, Michael Brands, Karl Ziegelbauer. BAY 1143572: A first-in-class, highly selective, potent and orally available inhibitor of PTEFb/CDK9 currently in Phase I, inhibits MYC and shows convincing anti-tumor activity in multiple xenograft models by the induction of apoptosis. [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 DDT02-02. doi:10.1158/1538-7445.AM2015-DDT02-02
Inhibition of monopolar spindle 1 (MPS1) kinase represents a novel approach to cancer treatment: instead of arresting the cell cycle in tumor cells, cells are driven into mitosis irrespective of DNA damage and unattached/misattached chromosomes, resulting in aneuploidy and cell death. Starting points for our optimization efforts with the goal to identify MPS1 inhibitors were two HTS hits from the distinct chemical series "triazolopyridines" and "imidazopyrazines". The major initial issue of the triazolopyridine series was the moderate potency of the HTS hits. The imidazopyrazine series displayed more than 10-fold higher potencies; however, in the early project phase, this series suffered from poor metabolic stability. Here, we outline the evolution of the two hit series to clinical candidates BAY 1161909 and BAY 1217389 and reveal how both clinical candidates bind to the ATP site of MPS1 kinase, while addressing different pockets utilizing different binding interactions, along with their synthesis and preclinical characterization in selected in vivo efficacy models.
Abstract The family of cyclin-dependent kinase (CDK) proteins consists of multiple cell cycle regulating CDK members as well as members involved in the regulation of gene transcription like CDK9/PTEFb (positive transcription elongation factor b). Inhibition of PTEFb and its direct downstream target RNA polymerase II is thought to cause rapid depletion of short-lived mRNA transcripts of important survival proteins like c-myc and Mcl-1 and thereby to induce growth delay and apoptosis in addicted tumor cells. In contrast to pan-CDK inhibitiors which are currently evaluated in Phase I and II clinical trials, PTEFb selective inhibitors have not been explored for clinical utility. BAY 1112054 is a potent and highly selective PTEFb-kinase inhibitor with low nanomolar activity against PTEFb/CDK9 and an at least 50-fold selectivity against other CDKs in enzymatic assays. Furthermore, BAY 1112054 shows a favourable selectivity against non-CDK kinases in vitro. The compound exhibits broad anti-proliferative activity against a panel of tumor cell lines with sub-micromolar IC-50 values. In line with the proposed mode of action, a concentration-dependent inhibition of the phosphorylation of the RNA polymerase II was observed in A549 tumor cells. This inhibition was accompanied by a reduction of intracellular Mcl-1 protein levels. Furthermore, BAY 1112054 increased DNA fragmentation in synchronized HeLa cells upon compound treatment for 24 hours. BAY 1112054 showed convincing in vivo efficacy at tolerated doses in two xenograft models in mice. Once daily oral treatment led to complete tumor stasis in established MOLM-13 AML xenografts. Pharmacokinetic analysis revealed that unbound plasma levels were 8 to 12 hours above the cellular IC50 in this model. In vivo efficacy and tolerability of the once daily po schedule of BAY 1112054 was confirmed in NCI-H82 SCLC xenografts. Xenografted tumors of this model showed lower levels of RNA polymerase II phosphorylation and Mcl-1 upon treatment with BAY 1112054. In conclusion, our data provides in vitro and in vivo proof of concept for BAY 1112054, a potent and highly selective inhibitor of PTEFb/CDK9 with first-in-class potential, and warrant further clinical evaluation of PTEFb selective inhibitors for the treatment of cancers addicted to the transcription of short-lived anti-apoptotic survival proteins. Citation Format: Arne Scholz, Ulrich Lücking, Gerhard Siemeister, Philip Lienau, Knut Eis, Antje Wengner, Kirstin Petersen, Ulf Bömer, Peter Nussbaumer, Axel Choidas, Gerd Rühter, Jan Eickhoff, Carsten Schultz-Fademrecht, Bert Klebl, Stuart Ince, Franz von Nussbaum, Dominik Mumberg, Michael Brands, Karl Ziegelbauer. BAY 1112054, a highly selective, potent and orally available inhibitor of PTEFb/CDK9, shows convincing anti-tumor activity. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4538. doi:10.1158/1538-7445.AM2014-4538
ORIGINAL RESEARCH article Front. Oncol., 16 November 2011Sec. Molecular and Cellular Oncology Volume 1 - 2011 | https://doi.org/10.3389/fonc.2011.00044
Purpose: Targeted alpha therapy (TAT) represents an emerging treatment approach attempting to deliver systemic radiation selectively to cancer cells and bypassing mechanisms of acquired resistance while minimizing systemic toxic effects. Radium-223 dichloride (Ra-223) is a first-in-class TAT shown to prolong survival in patients with metastatic castration-resistant prostate cancer and bone metastases. Yet, the understanding of the biological effects of α-particle irradiation is still limited. Here, we used a novel in vitro assay designed to assess alpha irradiation specific effects to investigate the biological effects of Ra-223 in various cancer cell lines. Furthermore, the combination of α-particle irradiation with DNA repair inhibitors was tested.Methods: The following cancer cell lines were used: lung (H460), ovarian (OVCAR-3, COV362, COV644, ES2) and prostate (22Rv1, LNCaP). The effects of different radiation doses and exposure times of Ra-223 on various biological parameters were analyzed using a Transwell® system where cells grow on a 10 µm membrane located on top of an underlying Ra-223 coating.Results: After 4 hours of exposure to α-particle irradiation (5, 10 and 20 kBq/3.8 cm2), a dose-dependent induction of DNA double strand breaks (DSB) as assessed by 53BP1 positivity was observed. Exposure to α-particle irradiation (10 and 20 kBq/3.8 cm2) for 1 hour dose-dependently induced DNA damage in a comet assay. Exposure to α-particle irradiation (5 kBq/3.8 cm2) for 1, 4 and 8 hours time-dependently reduced the surviving fraction in the subsequent colony formation assay. The frequency of micronuclei formation was increased in an activity- and time-dependent manner after α-particle exposure at 5, 10, 20, 40 kBq/3.8 cm2 for 1, 4 and 8 hours. In the same assay, the number of dead cells was significantly increased after an 8-hour exposure in all dose groups tested. Pre-incubation with the ATR inhibitor BAY 1895344 (5 nM for 2 hours prior to radiation) synergistically enhanced micronuclei formation (< 5% vs 12% vs 42% in ATR inhibitor only vs α-particle irradiation only vs ATR inhibitor + α-particle irradiation, respectively).Conclusion: Using several cancer cell lines, we demonstrated that short term exposure to α-particle irradiation in the range of 1 to 8 hours is sufficient to induce DNA damage including DNA DSB which leads to cellular damage and cell death. Synergistic effects were observed when Ra-223 was combined with the ATR inhibitor BAY 1895344 .Citation Format: Kristina Bannik, Sabine Zitzmann-Kolbe, Arne Scholz, Sabrina Jarke, Marco Jarzombek, Andreas Sutter, Gerhard Siemeister, Dominik Mumberg. Radium-223 α-particle radiation: Characterization of the in vitro effects on cancer cells in monotherapy and in combination with DNA repair inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3927.
