Selective inhibition of exclusively transcription‐regulating PTEFb/CDK9 is a promising new approach in cancer therapy. Starting from lead compound BAY‐958, lead optimization efforts strictly focusing on kinase selectivity, physicochemical and DMPK properties finally led to the identification of the orally available clinical candidate atuveciclib (BAY 1143572). Structurally characterized by an unusual benzyl sulfoximine group, BAY 1143572 exhibited the best overall profile in vitro and in vivo, including high efficacy and good tolerability in xenograft models in mice and rats. BAY 1143572 is the first potent and highly selective PTEFb/CDK9 inhibitor to enter clinical trials for the treatment of cancer.

Aberrant activation in fibroblast growth factor signaling has been implicated in the development of various cancers, including squamous cell lung cancer, squamous cell head and neck carcinoma, colorectal and bladder cancer. Thus, fibroblast growth factor receptors (FGFRs) present promising targets for novel cancer therapeutics. Here, we evaluated the activity of a novel pan‐FGFR inhibitor, rogaratinib, in biochemical, cellular and in vivo efficacy studies in a variety of preclinical cancer models. In vitro kinase activity assays demonstrate that rogaratinib potently and selectively inhibits the activity of FGFRs 1, 2, 3 and 4. In line with this, rogaratinib reduced proliferation in FGFR‐addicted cancer cell lines of various cancer types including lung, breast, colon and bladder cancer. FGFR and ERK phosphorylation interruption by rogaratinib treatment in several FGFR‐amplified cell lines suggests that the anti‐proliferative effects are mediated by FGFR/ERK pathway inhibition. Furthermore, rogaratinib exhibited strong in vivo efficacy in several cell line‐ and patient‐derived xenograft models characterized by FGFR overexpression. The observed efficacy of rogaratinib strongly correlated with FGFR mRNA expression levels. These promising results warrant further development of rogaratinib and clinical trials are currently ongoing (http://clinicaltrials.gov Identifiers: NCT01976741, NCT03410693, NCT03473756).

Selective inhibition of exclusively transcription-regulating positive transcription elongation factor b/CDK9 is a promising new approach in cancer therapy. Starting from atuveciclib, the first selective CDK9 inhibitor to enter clinical development, lead optimization efforts aimed at identifying intravenously (iv) applicable CDK9 inhibitors with an improved therapeutic index led to the discovery of the highly potent and selective clinical candidate VIP152. The evaluation of various scaffold hops was instrumental in the identification of VIP152, which is characterized by the underexplored benzyl sulfoximine group. VIP152 exhibited the best preclinical overall profile in vitro and in vivo, including high efficacy and good tolerability in xenograft models in mice and rats upon once weekly iv administration. VIP152 has entered clinical trials for the treatment of cancer with promising longterm, durable monotherapy activity in double-hit diffuse large B-cell lymphoma patients.

The PI3K-AKT-mTOR signaling cascade is activated in the majority of human cancers, and its activation also plays a key role in resistance to chemo and targeted therapeutics. In particular, in both breast and prostate cancer, increased AKT pathway activity is associated with cancer progression, treatment resistance and poor disease outcome. Here, we evaluated the activity of a novel allosteric AKT1/2 inhibitor, BAY 1125976, in biochemical, cellular mechanistic, functional and in vivo efficacy studies in a variety of tumor models. In in vitro kinase activity assays, BAY 1125976 potently and selectively inhibited the activity of full-length AKT1 and AKT2 by binding into an allosteric binding pocket formed by kinase and PH domain. In accordance with this proposed allosteric binding mode, BAY 1125976 bound to inactive AKT1 and inhibited T308 phosphorylation by PDK1, while the activity of truncated AKT proteins lacking the pleckstrin homology domain was not inhibited. In vitro, BAY 1125976 inhibited cell proliferation in a broad panel of human cancer cell lines. Particularly high activity was observed in breast and prostate cancer cell lines expressing estrogen or androgen receptors. Furthermore, BAY 1125976 exhibited strong in vivo efficacy in both cell line and patient-derived xenograft models such as the KPL4 breast cancer model (PIK3CA mutant), the MCF7 and HBCx-2 breast cancer models and the AKT mutant driven prostate cancer (LAPC-4) and anal cancer (AXF 984) models. These findings indicate that BAY 1125976 is a potent and highly selective allosteric AKT1/2 inhibitor that targets tumors displaying PI3K/AKT/mTOR pathway activation, providing opportunities for the clinical development of new, effective treatments.

PTEFb/CDK9 mediated transcription of short-lived anti-apoptotic survival proteins like Mcl-1 and Myc plays a critical role in cancer cell growth and survival in various tumor entities including AML. In addition, these survival proteins play important roles in the development of resistance to chemotherapy. We previously disclosed the preclinical profile of BAY 1143572, the first selective, orally available PTEFb/CDK9 inhibitor that entered clinical development [1-3]. BAY 1143572 had low nanomolar activity against PTEFb/CDK9, an at least 50-fold selectivity against other CDKs in enzymatic assays and broad anti-proliferative activity against a panel of tumour cell lines with sub-micromolar IC50 values. BAY 1143572 also showed single agent in vivo efficacy at tolerated doses in various xenograft tumour models in mice and rats upon once daily oral administration. To fully explore future treatment options using selective PTEFb/CDK9 inhibitors we initiated a follow-up program to identify novel PTEFb/CDK9 inhibitors for treatment of cancer with increased potency enabling i.v. treatment of patients. Extensive lead optimisation efforts, including various scaffold hops, led to the identification of BAY 1251152. In comparison to oral BAY 1143572, BAY 1251152 shows significantly increased biochemical (IC50 CDK9 = 3 nM) and cellular potency (IC50 MOLM13 = 29 nM), increased selectivity against CDK2 as well as high permeability and no efflux. The significantly reduced therapeutic dose and high solubility of BAY 1251152 enable the desired i.v. application. BAY 1251152 demonstrated excellent efficacy upon i.v. treatment in xenograft models (e.g. MOLM13) in mice and rats. BAY 1251152 is currently being evaluated in Phase I studies (NCT02635672; NCT02745743) 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/CDK9 i.v. lead optimization program and disclose the structure of BAY 1251152 for the first time. [1]: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3022. [2]: 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. [3]: 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 Citation Format: Ulrich T. Luecking, Arne Scholz, Dirk Kosemund, Rolf Bohlmann, Hans Briem, Philip Lienau, Gerhard Siemeister, Ildiko Terebesi, Kirstin Meyer, Katja Prelle, Ray Valencia, Stuart Ince, Franz von Nussbaum, Dominik Mumberg, Karl Ziegelbauer, Michael Brands. Identification of potent and highly selective PTEFb inhibitor BAY 1251152 for the treatment of cancer: from p.o. to i.v. application via scaffold hops [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 984. doi:10.1158/1538-7445.AM2017-984