Tinggui Yin

Inhibition of RAF Isoforms and Active Dimers by LY3009120 Leads to Anti-tumor Activities in RAS or BRAF Mutant Cancers

LY3009120 is a pan-RAF and RAF dimer inhibitor that inhibits all RAF isoforms and occupies both protomers in RAF dimers. Biochemical and cellular analyses revealed that LY3009120 inhibits ARAF, BRAF, and CRAF isoforms with similar affinity, while vemurafenib or dabrafenib have little or modest CRAF activity compared to their BRAF activities. LY3009120 induces BRAF-CRAF dimerization but inhibits the phosphorylation of downstream MEK and ERK, suggesting that it effectively inhibits the kinase activity of BRAF-CRAF heterodimers. Further analyses demonstrated that LY3009120 also inhibits various forms of RAF dimers including BRAF or CRAF homodimers. Due to these unique properties, LY3009120 demonstrates minimal paradoxical activation, inhibits MEK1/2 phosphorylation, and exhibits anti-tumor activities across multiple models carrying KRAS, NRAS, or BRAF mutation.

Cdk1 Activity Is Required for Mitotic Activation of Aurora A during G2/M Transition of Human Cells

In mammalian cells entry into and progression through mitosis are regulated by multiple mitotic kinases. How mitotic kinases interact with each other and coordinately regulate mitosis remains to be fully understood. Here we employed a chemical biology approach using selective small molecule kinase inhibitors to dissect the relationship between Cdk1 and Aurora A kinases during G2/M transition. We find that activation of Aurora A first occurs at centrosomes at late G2 and is required for centrosome separation independently of Cdk1 activity. Upon entry into mitosis, Aurora A then becomes fully activated downstream of Cdk1 activation. Inactivation of Aurora A or Plk1 individually during a synchronized cell cycle shows no significant effect on Cdk1 activation and entry into mitosis. However, simultaneous inactivation of both Aurora A and Plk1 markedly delays Cdk1 activation and entry into mitosis, suggesting that Aurora A and Plk1 have redundant functions in the feedback activation of Cdk1. Together, our data suggest that Cdk1, Aurora A, and Plk1 mitotic kinases participate in a feedback activation loop and that activation of Cdk1 initiates the feedback loop activity, leading to rapid and timely entry into mitosis in human cells. In addition, live cell imaging reveals that the nuclear cycle of cells becomes uncoupled from cytokinesis upon inactivation of both Aurora A and Aurora B kinases and continues to oscillate in a Cdk1-dependent manner in the absence of cytokinesis, resulting in multinucleated, polyploidy cells.

A Novel CDK9 Inhibitor Shows Potent Antitumor Efficacy in Preclinical Hematologic Tumor Models

DNA-dependent RNA polymerase II (RNAP II) largest subunit RPB1 C-terminal domain (CTD) kinases, including CDK9, are serine/threonine kinases known to regulate transcriptional initiation and elongation by phosphorylating Ser 2, 5, and 7 residues on CTD. Given the reported dysregulation of these kinases in some cancers, we asked whether inhibiting CDK9 may induce stress response and preferentially kill tumor cells. Herein, we describe a potent CDK9 inhibitor, LY2857785, that significantly reduces RNAP II CTD phosphorylation and dramatically decreases MCL1 protein levels to result in apoptosis in a variety of leukemia and solid tumor cell lines. This molecule inhibits the growth of a broad panel of cancer cell lines, and is particularly efficacious in leukemia cells, including orthotopic leukemia preclinical models as well as in ex vivo acute myeloid leukemia and chronic lymphocytic leukemia patient tumor samples. Thus, inhibition of CDK9 may represent an interesting approach as a cancer therapeutic target, especially in hematologic malignancies. Mol Cancer Ther; 13(6); 1442–56. ©2014 AACR.

A Novel Eg5 Inhibitor (LY2523355) Causes Mitotic Arrest and Apoptosis in Cancer Cells and Shows Potent Antitumor Activity in Xenograft Tumor Models

Intervention of cancer cell mitosis by antitubulin drugs is among the most effective cancer chemotherapies. However, antitubulin drugs have dose-limiting side effects due to important functions of microtubules in resting normal cells and are often rendered ineffective by rapid emergence of resistance. Antimitotic agents with different mechanisms of action and improved safety profiles are needed as new treatment options. Mitosis-specific kinesin Eg5 represents an attractive anticancer target for discovering such new antimitotic agents, because Eg5 is essential only in mitotic progression and has no roles in resting, nondividing cells. Here, we show that a novel selective Eg5 inhibitor, LY2523355, has broad target-mediated anticancer activity in vitro and in vivo. LY2523355 arrests cancer cells at mitosis and causes rapid cell death that requires sustained spindle-assembly checkpoint (SAC) activation with a required threshold concentration. In vivo efficacy of LY2523355 is highly dose/schedule-dependent, achieving complete remission in a number of xenograft tumor models, including patient-derived xenograft (PDX) tumor models. We further establish that histone-H3 phosphorylation of tumor and proliferating skin cells is a promising pharmacodynamic biomarker for in vivo anticancer activity of LY2523355. Mol Cancer Ther; 14(11); 2463–72. ©2015 AACR.

RAF inhibitor LY3009120 sensitizes RAS or BRAF mutant cancer to CDK4/6 inhibition by abemaciclib via superior inhibition of phospho-RB and suppression of cyclin D1

KRAS, NRAS and BRAF mutations are among the most important oncogenic drivers in many major cancer types, such as melanoma, lung, colorectal and pancreatic cancer. There is currently no effective therapy for the treatment of RAS mutant cancers. LY3009120, a pan-RAF and RAF dimer inhibitor advanced to clinical study has been shown to inhibit both RAS and BRAF mutant cell proliferation in vitro and xenograft tumor growth in vivo. Abemaciclib, a CDK4/6-selective inhibitor, is currently in phase III studies for ER-positive breast cancer and KRAS mutant lung cancer. In this study, we found that combinatory treatment with LY3009120 and abemaciclib synergistically inhibited proliferation of tumor cells in vitro and led to tumor growth regression in xenograft models with a KRAS, NRAS or BRAF mutation at the doses of two drugs that were well tolerated in combination. Further in vitro screen in 328 tumor cell lines revealed that tumor cells with KRAS, NRAS or BRAF mutation, or cyclin D activation are more sensitive, whereas tumor cells with PTEN, PIK3CA, PIK3R1 or retinoblastoma (Rb) mutation are more resistant to this combination treatment. Molecular analysis revealed that abemaciclib alone inhibited Rb phosphorylation partially and caused an increase of cyclin D1. The combinatory treatment cooperatively demonstrated more complete inhibition of Rb phosphorylation, and LY3009120 suppressed the cyclin D1 upregulation mediated by abemaciclib. These results were further verified by CDK4/6 siRNA knockdown. Importantly, the more complete phospho-Rb inhibition and cyclin D1 suppression by LY3009120 and abemaciclib combination led to more significant cell cycle G0/G1 arrest of tumor cells. These preclinical findings suggest that combined inhibition of RAF and d-cyclin-dependent kinases might provide an effective approach to treat patients with tumors harboring mutations in RAS or RAF genes.

Distinct mobilization of leukocytes and hematopoietic stem cells by CXCR4 peptide antagonist LY2510924 and monoclonal antibody LY2624587

Stromal cell-derived factor-1 (SDF-1) and its receptor CXCR4 play a critical role in mobilization and redistribution of immune cells and hematopoietic stem cells (HSCs). We evaluated effects of two CXCR4-targeting agents, peptide antagonist LY2510924 and monoclonal antibody LY2624587, on mobilizing HSCs and white blood cells (WBCs) in humans, monkeys, and mice. Biochemical analysis showed LY2510924 peptide blocked SDF-1/CXCR4 binding in all three species; LY2624587 antibody blocked binding in human and monkey, with minimal activity in mouse. Cellular analysis showed LY2624587 antibody, but not LY2510924 peptide, down-regulated cell surface CXCR4 and induced hematological tumor cell death; both agents have been shown to inhibit SDF-1/CXCR4 interaction and downstream signaling. In animal models, LY2510924 peptide induced robust, prolonged, dose- and time-dependent WBC and HSC increases in mice and monkeys, whereas LY2624587 antibody induced only moderate, transient increases in monkeys. In clinical trials, similar pharmacodynamic effects were observed in patients with advanced cancer: LY2510924 peptide induced sustained WBC and HSC increases, while LY2624587 antibody induced only minimal, transient WBC changes. These distinct pharmacodynamic effects in two different classes of CXCR4 inhibitors are clinically important and should be carefully considered when designing combination studies with immune checkpoint inhibitors or other agents for cancer therapy.

Abstract DDT02-02: Identification of LY3009120 as a pan inhibitor of Raf isoforms and dimers with minimal paradoxical activation and activities against BRaf or Ras mutant tumor cells

Proceedings: AACR Annual Meeting 2014; April 5-9, 2014; San Diego, CA Mutations in KRas, NRas, BRaf and NF-1 that activate the Ras and mitogen-activated protein kinase (MAPK) pathway are among the most common oncogenic drivers in many cancers, including melanoma, lung, colorectal, and pancreatic cancer. Two BRaf selective inhibitors, vemurafenib and dabrafenib, have been approved for the treatment of melanoma patients harboring the BRaf V600E/K mutation. However, both compounds have been reported to promote paradoxical MAPK pathway activation in BRaf wild-type cells through induction of active Raf dimers. Therefore, they are believed to be contraindicated for treatment of cancers with BRaf wild type background. In this study, we have identified and characterized a pyrido-pyrimidine derivative inhibitor of all three Raf isoforms. A whole-cell mass spectrum-based analysis revealed that LY3009120 binds to ARaf, BRaf and CRaf isoforms with similar affinity in cells with activating mutations of BRaf or KRas, while vemurafenib or dabrafenib have little or modest CRaf activity. Additionally, LY3009120 induces BRaf-CRaf heterodimerization, but inhibits the phosphorylation of downstream MEK and ERK, indicating that it effectively inhibits the kinase activity of BRaf-CRaf heterodimer. Due to its activity against the three Raf isoforms and dimer, LY3009120 induces minimal paradoxical pathway activation in NRas or KRas mutant cells. These unique pharmacological properties of LY3009120 further distinguish it from selective BRaf inhibitors by its physiologically-relevant activities against tumor cells with NRas or KRas mutations. LY3009120 inhibits MEK phosphorylation and cell proliferation in vitro, and exhibits anti-tumor activity in multiple xenograft models carrying mutations in BRaf, NRas or KRas. LY3009120 is also active against melanoma cells with acquired resistance to vemurafenib or dabrafenib in the setting of MAPK reactivation and cyclin D1 upregulation caused by RTK/Ras activation, BRaf splice variants, or NRas Q61K mutation. Collectively, our findings identify LY3009120 as a potentially best-in-class inhibitor of three Raf isoforms and Raf dimer, with activity against tumor cells with BRaf, NRas or KRas mutations, as well as melanoma cells with acquired resistance to current BRaf therapies. These unique features support investigation of LY3009120 in clinical studies. Citation Format: Sheng-Bin Peng, James Henry, Michael Kaufman, Wei-Ping Lu, Bryan D. Smith, Subha Vogeti, Scott Wise, Youyan Zhang, Robert Van Horn, Xiaoyi Zhang, Tinggui Yin, Vipin Yadav, Lysiane Huber, Lisa Kays, Jennie Walgren, Denis McCann, Phenil Patel, Sean Buchanan, Ilaria Conti, James J. Starling, Daniel L. Flynn. Identification of LY3009120 as a pan inhibitor of Raf isoforms and dimers with minimal paradoxical activation and activities against BRaf or Ras mutant tumor cells. [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 DDT02-02. doi:10.1158/1538-7445.AM2014-DDT02-02

Abstract A62: A novel Eg5 inhibitor that causes mitotic arrest leading to rapid cancer cell death shows broad‐spectrum antitumor activity in preclinical xenograft tumor models

Antitubulin agents including taxanes and vincas that target mitosis of rapidly dividing cancer cells are among the most effective cancer therapies in current clinical use. However, these antitubulin agents also have debilitating side effects that are dose‐limiting, such as neuropathy, due to their disruption of the normal microtubule functions in resting cells including neuronal cells. Eg5 is an evolutionarily conserved mitosis‐specific kinesin essential for bipolar mitotic spindle formation and has no roles in microtubule functions of resting cells. Inactivation of Eg5 causes mitotic arrest of proliferating cells, resulting in formation of monopolar spindles. Targeting Eg5 for cancer treatment thus represents an attractive strategy that has the potential to maximize the anticancer efficacy by inhibiting cancer cell mitosis while minimizing debilitating side effects associated with antitubulins. Here we describe a selective ATP‐non competitive small molecule inhibitor of human Eg5 kinesin. The Eg5 inhibitor shows no effects on microtubule dynamics in cell‐free assays and arrests cells specifically at mitosis with monopolar spindles, resulting in rapid cancer cell death. Growth inhibition assays against a panel of 21 cancer cell lines shows that the Eg5 inhibitor has potent and broad‐spectrum activity with IC50 values ranged from 0.55 nM to 14.2 nM. Quantitative live cell imaging and high content imaging reveal that the Eg5 inhibitor has a threshold concentration activity and kills cancer cells specifically at mitosis in a time/cell cycle, but not concentration above the threshold,‐dependent manner. Consistent with the in vitro activities, the Eg5 inhibitor shows broad‐spectrum antitumor activity in preclinical xenograft tumor models representing major human cancer histologies also including drug resistant tumors and demonstrates superiority as compared to several chemotherapeutic agents targeting G2/M. Furthermore, its in vivo antitumor activity is highly schedule‐dependent with a clear threshold dose effect, as expected from in vitro observations. Indeed, the Eg5 inhibitor exhibits a robust PK/PD relationship in antitumor activity and its antitumor activity is associated with mitotic arrest of cancer cells and subsequent cell death. The Eg5 inhibitor is currently being evaluated in Phase I studies. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A62.

Abstract 282: Pan-RAF inhibitor LY3009120 sensitizes RAS or BRAF mutant cancer to CDK4 and 6 inhibition by abemaciclib via superior inhibition of phospho-RB and suppression of cyclin D1

KRAS, NRAS and BRAF mutations are among the most important oncogenic drivers in many major cancer types, including melanoma, lung, colorectal, and pancreatic cancer. There is currently no effective therapy for the treatment of RAS mutant cancers. LY3009120, a pan-RAF and RAF dimer inhibitor currently in phase I clinical trial, has been shown to inhibit cell proliferation of RAS- or BRAF-mutant tumor cells in vitro and xenograft tumor growth in vivo. An unbiased screen for compounds that synergize with LY3009120 in RAS/BRAF mutant cancers identified inhibitors of CDK4 among the top hits. In this study, we found that combined inhibition of RAF and CDK4 and 6 by LY3009120 and abemaciclib cooperatively reduced viability of tumor cells with KRAS, NRAS or BRAF mutation in vitro. In animal models, the LY3009120 and abemaciclib combination exhibited synergistic regression of tumor growth in multiple xenograft models with KRAS, NRAS, or BRAF mutation. Molecular mechanistic analysis revealed that pan-RAF inhibitor treatment suppressed the cyclin D1 upregulation which was mediated through CDK4 and CDK6 inhibition by abemaciclib, and the combination treatment cooperatively demonstrated more complete inhibition of RB phosphorylation. These results were further verified by CDK4 and CDK6 siRNA knockdown and another CDK4 and CDK6 selective inhibitor palbociclib. Importantly, the more complete phospho-RB inhibition and cyclin D1 suppression by LY3009120 and abemaciclib combinational treatment led to more significant cell cycle G0/G1 arrest and apoptosis of tumor cells. These preclinical findings suggest that the combinational inhibition of RAF and CDK4 and CDK6 signaling by LY3009120 and abemaciclib is synergistic and should be further studied compared to single agents in the treatment of cancer in patients with KRAS, NRAS or BRAF mutations. Citation Format: Shih-Hsun Chen, Youyan Zhang, Robert D. Van Horn, Tinggui Yin, Lysiane Huber, Teresa F. Burke, Xueqian Gong, Wenjuan Wu, Shripad Bhagwat, Sean Buchanan, Richard P. Beckmann, Ramon V. Tiu, Sheng-Bin Peng. Pan-RAF inhibitor LY3009120 sensitizes RAS or BRAF mutant cancer to CDK4 and 6 inhibition by abemaciclib via superior inhibition of phospho-RB and suppression of cyclin D1. [abstract]. In: 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 282.

Abstract B229: TBKI kinase inhibition blocks RANTES secretion and exhibits minimal tumor growth inhibition in oncogenic Ras-driven tumor models.

TANK-binding kinase 1 (TBK1) is a non-canonical IKK family member and plays a critical role in innate immunity by modulating cytokine production, interferon, and NF-kB signaling. It is recently reported that TBK1 directly engages Akt survival signaling to support oncogenic Ras-driven transformation. TBK1 is also identified as a synthetic lethal partner in KRas mutant NSCLC through systematic RNA interference. In this study, we have characterized LSN3090729, a 4-aryl-2-aminopyrimidine derivative as a selective TBK1 kinase inhibitor. Biochemical and cellular analyses demonstrate that LSN3090729 is a potent TBK1 kinase inhibitor, and selectively inhibits TBK1 based on in vitro activities in biochemical assays developed with a panel of protein kinases. In Panc-1, a pancreatic tumor cell line with KRas mutation, LSN3090729 inhibits EGF-induced phosphorylation of AKT at both Thr308 and Ser473 sites. Pharmacokinetic analysis shows that LSN3090729 has an over 70% of oral bioavailability with an acceptable half life in rodents. In a mouse pharmacology model, LSN3090729 blocks LPS-induced RANTES secretion in a dose-dependent manner with 67%, 79%, and 90% inhibition at 10, 30, and 100 mg/kg, respectively. LSN3090729 is assessed for its anti-proliferation activities in vitro in a panel of tumor cells with KRas mutation or other genetic background. The sensitivity of these tumor cells to LSN3090729 in two dimensional proliferation or three dimensional soft agar growth assays appears not correlated with status of KRas mutation. In xenograft models of HCT116 and Panc-1, both with a KRas mutation, treatment of LSN3090729 exhibits minimal anti-tumor growth activities, suggesting that a combination approach might be required for TBK1 kinase inhibition to be effective in cancer settings. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B229. Citation Format: Robert Van Horn, Tinggui Yin, Xiaoyi Zhang, Chunping Yu, Youyan Zhang, Xue-Qian Gong, Sean Buchanan, Xiang S. Ye, William McMillen, David Barda, Sheng-Bin Peng. TBKI kinase inhibition blocks RANTES secretion and exhibits minimal tumor growth inhibition in oncogenic Ras-driven tumor models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B229.