Weakened APC/C activity at mitotic exit drives cancer vulnerability to KIF18A inhibition

The efficacy of current antimitotic cancer drugs is limited by toxicity in highly proliferative healthy tissues. A cancer-specific dependency on the microtubule motor protein KIF18A therefore makes it an attractive therapeutic target. Not all cancers require KIF18A, however, and the determinants underlying this distinction remain unclear. Here, we show that KIF18A inhibition drives a modest and widespread increase in spindle assembly checkpoint (SAC) signaling from kinetochores which can result in lethal mitotic delays. Whether cells arrest in mitosis depends on the robustness of the metaphase-to-anaphase transition, and cells predisposed with weak basal anaphase-promoting complex/cyclosome (APC/C) activity and/or persistent SAC signaling through metaphase are uniquely sensitive to KIF18A inhibition. KIF18A-dependent cancer cells exhibit hallmarks of this SAC:APC/C imbalance, including a long metaphase-to-anaphase transition, and slow mitosis overall. Together, our data reveal vulnerabilities in the cell division apparatus of cancer cells that can be exploited for therapeutic benefit.

Small-molecule inhibition of kinesin KIF18A reveals a mitotic vulnerability enriched in chromosomally unstable cancers

Chromosomal instability (CIN) is a hallmark of cancer, caused by persistent errors in chromosome segregation during mitosis. Aggressive cancers like high-grade serous ovarian cancer (HGSOC) and triple-negative breast cancer (TNBC) have a high frequency of CIN and TP53 mutations. Here, we show that inhibitors of the KIF18A motor protein activate the mitotic checkpoint and selectively kill chromosomally unstable cancer cells. Sensitivity to KIF18A inhibition is enriched in TP53-mutant HGSOC and TNBC cell lines with CIN features, including in a subset of CCNE1-amplified, CDK4-CDK6-inhibitor-resistant and BRCA1-altered cell line models. Our KIF18A inhibitors have minimal detrimental effects on human bone marrow cells in culture, distinct from other anti-mitotic agents. In mice, inhibition of KIF18A leads to robust anti-cancer effects with tumor regression observed in human HGSOC and TNBC models at well-tolerated doses. Collectively, our results provide a rational therapeutic strategy for selective targeting of CIN cancers via KIF18A inhibition.

Combined inhibition of BCL-2 and MCL-1 overcomes BAX deficiency-mediated resistance of TP53-mutant acute myeloid leukemia to individual BH3 mimetics

TP53-mutant acute myeloid leukemia (AML) respond poorly to currently available treatments, including venetoclax-based drug combinations and pose a major therapeutic challenge. Analyses of RNA sequencing and reverse phase protein array datasets revealed significantly lower BAX RNA and protein levels in TP53-mutant compared to TP53-wild-type (WT) AML, a finding confirmed in isogenic CRISPR-generated TP53-knockout and -mutant AML. The response to either BCL-2 (venetoclax) or MCL-1 (AMG176) inhibition was BAX-dependent and much reduced in TP53-mutant compared to TP53-WT cells, while the combination of two BH3 mimetics effectively activated BAX, circumventing survival mechanisms in cells treated with either BH3 mimetic, and synergistically induced cell death in TP53-mutant AML and stem/progenitor cells. The BH3 mimetic-driven stress response and cell death patterns after dual inhibition were largely independent of TP53 status and affected by apoptosis induction. Co-targeting, but not individual targeting of BCL-2 and MCL-1 in mice xenografted with TP53-WT and TP53-R248W Molm13 cells suppressed both TP53-WT and TP53-mutant cell growth and significantly prolonged survival. Our results demonstrate that co-targeting BCL-2 and MCL-1 overcomes BAX deficiency-mediated resistance to individual BH3 mimetics in TP53-mutant cells, thus shifting cell fate from survival to death in TP53-deficient and -mutant AML. This concept warrants clinical evaluation.

Abstract 3867: Chromatin modification driving sub-clonal resistance to KRAS G12C combination therapies in KRAS mutant non-small cell lung cancer

The FDA approval of the KRAS G12C inhibitor (G12Ci) sotorasib and the advancement of similar drugs into clinical trials marks a major milestone in treating KRAS G12C non-small cell lung cancer (NSCLC). However, not all patients respond (sotorasib - ORR = 37.1%, adagrasib - 43%, JDQ443 - 35%), motivating preclinical and clinical investigation into mechanisms of intrinsic and acquired resistance. For instance, clinical studies have reported on-target KRAS mutations and preclinical studies have demonstrated mitogen-activated protein kinase (MAPK) feedback reactivation including EGFP, SHP2, and WT RAS signaling. In response to targeted therapies, sub-populations of cells can enter quiescence or specific epigenetic-driven states that confer drug tolerance. However, epigenetic states defining drug-tolerant persister populations and contributing to adaptive resistance to KRAS G12Ci have not been reported. Using a lineage tracing barcoded system, we identify distinct and reversible subpopulations defined by specific chromatin and transcriptional states in KRAS NSCLC cell lines that contribute to KRAS G12Ci resistance in vitro, even prior to drug treatment. We observed that specific states, including activation of histone demethylation and SWI/SNF complex, may contribute to MAPK reactivation-driven resistance. These results suggest potential epigenetic vulnerabilities that can be exploited to improve the response to KRAS G12Ci. Moreover, we observed distinct persister subpopulations with resistance to KRAS G12Ci combination co-targeting orthogonal pathways (SHP2, CDK4/6, PI3K, and MCL-1), raising the possibility that distinct epigenetic-transcriptional states contribute to differential drug response and clonal evolution of persisters. Collectively, these results suggest that more complete tumor regression may be achieved by orthogonal strategies that target different resistant populations within the same tumor.

Citation Format: Chendi Li, Qian Qin, Mohammed Usman Syed, Anahita Nimbalkar, Barbara Karakyriakou, Sarah E. Clark, Anne Y. Saiki, Paul E. Hughes, Chris Ott, Luca Pinello, Aaron N. Hata. Chromatin modification driving sub-clonal resistance to KRAS G12C combination therapies in KRAS mutant non-small cell lung cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3867.

Abstract 6246: The MTA-cooperative PRMT5 inhibitor AM-9747 exhibits robust antitumor activity in combination with clinically relevant chemotherapies and targeted agents in MTAP null tumor models

Homozygous deletion of chr9p21, containing genes CDKN2A and MTAP, occurs in about 15% of cancers. MTAP loss, a key enzyme in the methionine and adenine salvage pathways, leads to the accumulation of its substrate MTA. MTA competes with the methyl donor SAM for binding to type II arginine methyltransferase PRMT5, placing PRMT5 in a hypomorphic state and vulnerable to further PRMT5 inhibition. MTA-cooperative PRMT5 inhibitors are an emerging class of therapeutics targeting MTAP null tumors. AMG 193, currently in Phase 1 trials, and its representative analog AM-9747 have broad spectrum activity in MTAP null tumor models across hematologic and solid tumor indications. Mechanistically, AM-9747 induces DNA damage, shown by increased phosphorylated H2AX, resulting in cell cycle arrest and senescence. Exploration of clinically relevant therapeutic combinations with standard of care (SOC) chemotherapies or targeted agents that could potentiate this DNA damage or target orthogonal pathways is a rational therapeutic approach. Here, we evaluated AM-9747 in combination with SOC chemotherapies and assessed synergy using the Chou-Talalay Method to generate Combination Index (CI) scores. SOC agents representing a variety of mechanisms of action (paclitaxel, carboplatin, gemcitabine, pemetrexed, irinotecan, 5-FU) were evaluated and results ranged from strongly synergistic (CI<0.3) to additive (CI=1) in a panel of non-small cell lung carcinoma (NSCLC) and pancreatic cancer cell lines. The SOC combinations augmented AM-9747 induced DNA damage resulting in increased cell cycle arrest and nuclear count assays confirmed the synergistic antiproliferative effects of the combinations. Combinations of AM-9747 and one strongly synergistic agent (carboplatin) and one moderately synergistic agent (paclitaxel) were evaluated in H292 NSCLC xenografts. Significant reductions in tumor burden compared to single agent treatments were observed with AM-9747 + paclitaxel (67% TGI) and AM-9747 + carboplatin (82% TGI). Additionally, roughly 2-3% of NSCLC tumors harbor both MTAP loss and a KRAS G12C mutation. To target both pathways we combined the FDA-approved KRAS G12C inhibitor sotorasib with AM-9747 and observed synergy (CI<0.6) in MIAPACA2 cells. Nuclear counts confirmed a greater cell growth inhibition in the combination and immunoblots confirmed on target inhibition of both pathways. Combination treatment of AM-9747 and sotorasib in LU99 NSCLC xenografts resulted in significant tumor regression compared to each single agent with 10/10 mice tumor free. This combination is being tested in additional MTAP null KRAS G12C mutant models. Overall, our data suggests that combining MTA-cooperative inhibitor AM-9747 with SOC or clinically relevant targeted agents is a compelling therapeutic strategy for the treatment of MTAP null cancers.

Citation Format: Katherine Slemmons, Brian Belmontes, Siyuan Liu, Jodi Moriguchi, Antonia Policheni, Paul E. Hughes. The MTA-cooperative PRMT5 inhibitor AM-9747 exhibits robust antitumor activity in combination with clinically relevant chemotherapies and targeted agents in MTAP null tumor models. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6246.

Abstract 1644: Dual inhibition of MAT2A and PRMT5 delivers synergistic anti-tumor responses in preclinical models of MTAP-deleted cancer

Approximately 15% of all tumors harbor deletions in the 9p21 locus that encompass CDKN2A and MTAP. MTAP fuels the adenine and methionine salvage pathways by converting MTA into precursors of building blocks for protein and DNA production. In MTAP-deleted (MTAPdel) tumors, cellular MTA accumulates and partially inhibits the essential protein methyl transferase, PRMT5, through direct displacement of the cofactor S-adenosyl methionine (SAM) from the PRMT5 active site. This context provides therapeutic opportunities, currently under clinical evaluation, to selectively extinguish PRMT5 activity in tumor cells with MAT2A inhibitors that limit SAM synthesis or with direct PRMT5 inhibitors that are MTA-cooperative. Preclinical modeling of these synthetic lethal relationships, and elucidation of their cellular mechanisms of action, suggests efficacy can vary depending upon the extent of MTA accumulation and/or adaptive compensation to PRMT5 inhibition. To potentially maximize therapeutic activity among mechanistically heterogenous MTAPdel tumors, we evaluated combinatorial pathway suppression with MAT2A and PRMT5 inhibitors in MTAPWT and MTAPdel tumor models in vitro and in vivo. We noted synergistic antiproliferative effects when the potent and selective MAT2A inhibitor IDE397 was combined with any of multiple MTA-cooperative PRMT5 inhibitors in MTAPdel cell lines that exhibit sensitivity to each single agent. In vivo, the combination of IDE397 and MTA-cooperative PRMT5 inhibitors were well tolerated, and induced durable tumor regressions, including complete responses, at dose levels well below the maximally efficacious preclinical dose of each individual agent in MTAPdel lung adenocarcinoma and pancreas cancer models H838 and BXPC3. Pharmacodynamic target engagement in the tumor was evaluated by quantitative assessment of symmetric dimethyl arginine (SDMA), as detected by IHC, and indicated earlier onset and greater extent of PRMT5 inhibition by combination treatment as compared to either agent alone. The potentiation of the antitumor response with the combination did not occur in the MTAPWT setting. Thus, combined inhibition of MAT2A and PRMT5 potentially offers a compelling dual synthetic lethal opportunity to address unmet need for the many patients afflicted with MTAPdel cancers.

Citation Format: Marcus M. Fischer, Kimberline Gerrick, Brian Belmontes, Katherine Slemmons, Yevgeniy Freyman, Jay Jain, Steve Federowicz, Isaac Bishof, Arjun A. Rao, Melissa Fleury, Zineb Mounir, Mark R. Lackner, Paul E. Hughes, Mike White, Claire L. Neilan. Dual inhibition of MAT2A and PRMT5 delivers synergistic anti-tumor responses in preclinical models of MTAP-deleted cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1644.

Abstract LB202: Discovery and preclinical characterization of novel small molecule inhibitors of kinesin KIF18A motor protein with potent activity against chromosomally unstable cancers

KIF18A is a mitotic kinesin that localizes to the plus-end tips of kinetochore microtubule (MT) spindle fibers during metaphase, where it regulates chromosome alignment, and promotes the viability of chromosomally unstable cancer cells. KIF18A is overexpressed in a subset of human cancers, and its elevated expression is associated with tumor aggressiveness.

Chromosomal instability (CIN) is a hallmark of human cancers and is caused by persistent errors in chromosome segregation during mitosis. Aggressive types of human cancer such as high-grade serous ovarian cancer (HGSOC) and triple-negative breast cancer (TNBC) have elevated levels of CIN and frequently harbor alterations in TP53 tumor suppressor gene. These two CIN+ cancer subtypes share molecular similarities but have limited treatment options at present. The rationale of pharmacological inhibition of KIF18A motor activity is to selectively target a tumor-specific mitotic spindle vulnerability in CIN+ cancer cells while largely sparing normal diploid dividing somatic cells.

Here, we describe the identification of a novel series of potent and selective small molecule inhibitors of KIF18A MT-ATPase motor activity exemplified by AM-1882, that disrupt the mitotic spindle and selectively kill chromosomally unstable cancer cells. Our KIF18A inhibitors phenocopy genetic ablation of KIF18A and trigger spindle assembly checkpoint activation, multipolarity, and apoptosis in sensitive CIN+ cancer cell lines. The sensitivity profile of AM-1882 is focal-in-nature with cell potency in the low double-digit nanomolar range across a panel of breast and ovarian cancer cell lines, including lines that harbor genetic alterations (e.g., TP53, CCNE1, RB1, BRCA1, whole genome doubling) frequently enriched in CIN+ cancers and in HGSOC and TNBC tumor subtypes. Furthermore, the sensitivity profile of AM-1882 is distinct from comparator test agents ispinesib (Eg5, pan cytotoxic) and palbociclib (CDK4/6, focal cytostatic). The combination of AM-1882 with PARP inhibitor olaparib is synergistic in BRCA1-deficient cancer cell lines, with evidence of increased double-strand DNA breaks (p-H2AX) and apoptosis (cl-PARP). Importantly, KIF18A inhibitors have minimal toxicity on normal dividing somatic cell types in vitro, including proliferating human bone marrow mononuclear cells, distinct from paclitaxel and small molecule inhibitors of essential mitotic kinases and kinesins. In vivo, we demonstrate that administration of KIF18A inhibitors AM-1882 and AM-5308 induce a robust pharmacodynamic response (pH3, mitotic marker) and frank tumor regressions in two TP53 mutant human HGSOC xenograft models (OVCAR-3, OVCAR-8) at well-tolerated doses.

Collectively, our preclinical data provides the first example of a therapeutic strategy to selectively target CIN+ cancers through inhibition of KIF18A motor protein.

Citation Format: Jan Sun, Brain Belmontes, Jodi Moriguchi, Grace Chung, Kui Chen, John D. McCarter, Upendra P. Dahal, Andrew S. Boghossian, Matthew G. Rees, Melissa M. Ronan, Jennifer A. Roth, Sheroy Minocherhomji, Matthew P. Bourbeau, Jennifer R. Allen, Angela Coxon, Paul E. Hughes, Nuria Tamayo, Marc N. Payton. Discovery and preclinical characterization of novel small molecule inhibitors of kinesin KIF18A motor protein with potent activity against chromosomally unstable cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr LB202.

Abstract 1807: The discovery and preclinical characterization of the MTA cooperative PRMT5 inhibitor AM-9747

Homozygous deletion of the tumor suppressor gene CDKN2A and the neighboring MTAP gene located at chr9p21 occurs in 10-15% of human cancers. Deletion of MTAP, an enzyme in methionine and adenine salvage pathways, results in accumulation of its substrate MTA, which is structurally similar to SAM, the substrate methyl donor for the type II methyltransferase PRMT5. In MTAP deleted cells, MTA competes with SAM for binding to PRMT5, placing PRMT5 in a partially inhibited or hypormorphic state. Multiple studies using shRNAi knockdown have shown that tumor cell lines harboring MTAP deletions are vulnerable to PRMT5 inhibition. PRMT5 inhibitors that have advanced to clinical studies do not selectively target the MTA-bound form of PRMT5, and the preclinical activity of these molecules is not enriched in MTAP-deleted tumor cells lines. Moreover, the therapeutic window of these molecules is narrow, presumably due to the inhibition of PRMT5 in normal cells. We set out to identify PRMT5 inhibitors that bind cooperatively with MTA, with the goal of selectively targeting PRMT5 in MTAP-deleted tumors. A DNA encoded library screen was conducted to identify small molecules that preferentially bind to PRMT5 in the presence of MTA. The subsequent optimization of screening hits to improve potency, MTA-cooperativity, and pharmacokinetic properties led to the identification of AM-9747. The nature of the MTA cooperativity of AM-9747 was interrogated by multiple biophysical methods and structural biology experiments. Following treatment with AM-9747, the levels of SDMA marks were lower in HCT116 MTAP-deleted cells (IC50 = 0.0002 μM) compared to HCT116 MTAP-WT cells (IC50 = 0.050 μM). AM-9747 selectively inhibited the proliferation of HCT116 MTAP-deleted cells (IC50 = 0.027 μM) compared to HCT116 MTAP-WT cells (IC50 = 0.63 μM). The profiling of AM-9747 in an expanded panel of tumor cell lines demonstrated that AM-9747 inhibited the proliferation of most MTAP-deleted cells, with minimal effects on MTAP-WT cells. In vitro mechanism of action studies demonstrated that treatment with AM-9747 induces DNA damage, as illustrated by increased phosphorylation of H2AX, and an arrest in the G2/M phase of the cell cycle in MTAP-deleted cells. In vivo, oral administration of AM-9747 selectively inhibits SDMA and tumor growth in HCT116 MTAP-deleted tumor xenografts, compared to HCT116 MTAP-WT xenografts. Furthermore, treatment with AM-9747 inhibits the growth of multiple MTAP-deleted tumor xenograft models, including BXPC3 (PDAC) and DOHH2 (DLBCL). AM-9747 was profiled against a panel of over twenty PDX models, with greater than 50% tumor growth inhibition observed in the majority of PDX models harboring deletion of the MTAP gene. Our data with AM-9747 indicates that PRMT5 inhibitors that selectively target PRMT5 in cooperation with MTA may represent a novel and compelling therapeutic strategy for the treatment of MTAP-deleted cancers.

Citation Format: Brian Belmontes, Antonia Policheni, Siyuan Liu, Katherine Slemmons, Jodi Moriguchi, Hayley Ma, Daniel Aiello, Yajing Yang, Mikkel Vestergaard, Sanne Cowland, Jan Anderson, Ian Sarvary, Nuria Tamayo, Liping Pettus, Susmith Mukund, Leszek Pope, Jennifer R. Allen, Sanne Glad, Matthew Bourbeau, Paul E. Hughes. The discovery and preclinical characterization of the MTA cooperative PRMT5 inhibitor AM-9747 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1807.

Abstract 2150: LKB1 loss rewires JNK-induced apoptotic protein dynamics through NUAKs and sensitizes KRAS-mutant non-small cell lung cancers to combined KRAS G12C + MCL-1 blockade

The recent approval of the KRAS G12C inhibitor sotorasib (AMG 510) for non-small cell lung cancer (NSCLC) marked a milestone in the development of targeted therapies for KRAS mutant cancers. While sotorasib and other KRAS G12C inhibitors have demonstrated rapid and durable responses in the clinic, some patients do not achieve responses. The identification of specific vulnerabilities conferred by recurrent co-occurring mutations may enable the development of biomarker-driven combination therapies with enhanced activity in distinct subsets of patients. We screened a panel of KRAS-mutant NSCLC cell lines as well as patient-derived xenograft (PDX) mouse models and observed that loss of the tumor suppressor STK11/LKB1 is associated with increased sensitivity to combined MAPK (either the KRAS G12C inhibitor sotorasib or MEK inhibitor trametinib) and MCL-1 inhibition (AMG 176). Restoration of LKB1 expression in LKB1-deficient cell lines and PDX tumors blunted the apoptotic response to MAPK + MCL-1 inhibition; conversely, deletion of LKB1 in LKB1 wild-type models increased sensitivity. Mitochondrial apoptotic cell death is regulated by interactions between pro- (e.g., BIM) and anti-apoptotic (e.g., MCL-1, BCL-XL) BCL-2 family members. MAPK inhibition increases BIM, while MCL-1 inhibition prevents BIM sequestration by MCL-1, resulting in apoptosis. LKB1 deficient cells exhibit increased association of BIM and MCL-1 upon MAPK inhibition, effectively priming cells for death upon inhibition of MCL-1. Mechanistically, LKB1 deficiency and associated loss of NUAK phosphorylation leads to hyperactivation of the JNK phospho-kinase network. JNK phosphorylates MCL-1 at S64 and T163, which enhances BIM: MCL-1 protein-protein interaction. Conversely, JNK phosphorylates BCL-XL at S62 and prevents sequestration of BIM. This series of phosphorylation events increases MCL-1 dependence and creates a specific vulnerability of KRAS-LKB1 tumors to MAPK + MCL-1 inhibition. Consistent with this mechanism, ex vivo treatment of tumor tissue from a KRAS-LKB1 mutant NSCLC patient with sotorasib or trametinib increased MCL-1 dependent priming. These results reveal a novel link between LKB1 and the regulation of BCL-2 family proteins and provide preclinical rationale for evaluation of combined KRAS G12C + MCL-1 inhibitors for KRAS-LKB1 mutant NSCLC.

Citation Format: Chendi Li, Mohammed Usman Syed, Yi Shen, Audris Oh, Cameron Fraser, Johannes Kreuzer, Christopher Nabel, Kaitlyn Webster, Robert Morris, Sean Caenepeel, Anne Y. Saiki, Karen Rex, J. Russell Lipford, Wilhelm Hass, Kristopher Sarosiek, Paul E. Hughes, Aaron Hata. LKB1 loss rewires JNK-induced apoptotic protein dynamics through NUAKs and sensitizes KRAS-mutant non-small cell lung cancers to combined KRAS G12C + MCL-1 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2150.

Maximal activation of apoptosis signaling by co-targeting anti-apoptotic proteins in BH3 mimetic-resistant AML and AML stem cells

MCL-1 is known to play a major role in resistance to BCL-2 inhibition, but the contribution of other BCL-2 family proteins has not been fully explored. We here demonstrate ineffectiveness of MCL-1 inhibitor AMG176 in venetoclax-resistant, and conversely, of venetoclax in AMG176-resistant AML. Like cells with acquired resistance to venetoclax, cells with acquired resistance to AMG176 express increased MCL-1. Both cells with acquired resistance to venetoclax and to AMG176 express increased levels of BCL-2 and BCL-2A1, decreased BAX, and/or altered levels of other BCL-2 proteins. Co-targeting BCL-2 and MCL-1 was highly synergistic in AML cell lines with intrinsic or acquired resistance to BH3 mimetics or engineered to genetically-overexpress BCL-2 or BCL-2A1 or downregulate BAX. The combination effectively eliminated primary AML blasts and stem/progenitor cells resistant to or relapsed after venetoclax-based therapy irrespective of mutations and cytogenetic abnormalities. Venetoclax and AMG176 combination markedly suppressed anti-apoptotic BCL-2 proteins and AML stem/progenitor cells and dramatically extended mouse survival (median 336 vs control 126 d, P<0.0001) in a PDX model developed from a venetoclax/hypomethylating agent therapy-resistant AML patient. However, decreased BAX levels in the bone marrow residual leukemia cells after 4-wk combination treatment may represent a resistance mechanism that contributed to their survival. Enhanced anti-leukemia activity was also observed in a PDX model of monocytic AML, known to be resistant to venetoclax therapy. Our results support co-dependence on multiple anti-apoptotic BCL-2 proteins and suppression of BAX as mechanisms of AML resistance to individual BH3 mimetics. Co-targeting of MCL-1 and BCL-2 eliminates otherwise apoptosis-resistant cells.

Abstract 982: LKB1 loss rewires stress signaling-induced apoptotic protein dynamics and sensitizes KRAS-mutant non-small cell lung cancers to combined MAPK + MCL-1 blockade

Background: There are currently no approved targeted therapies for KRAS-mutant non-small cell lung cancers (NSCLC), which represent 25-30% of lung adenocarcinomas. The development of mutant-specific covalent inhibitors of KRAS G12C has invigorated hope that clinically effective KRAS-targeted therapies are within reach. While these agents have shown activity in early phase clinical trials, identification of specific vulnerabilities conferred by common co-occurring mutations in KRAS-mutant NSCLC may enable development of combination therapies with enhanced activity in distinct subsets of patients.

Results: We screened a panel of KRAS-mutant NSCLC cell lines and observed that loss of the tumor suppressor STK11/LKB1 is associated with increased MCL-1 dependence and sensitivity to combined MAPK (either MEK inhibitor or KRAS G12C inhibitor AMG 510) and MCL-1 inhibition (AMG 176). Restoration of LKB1 expression in LKB1-deficient cell lines and mouse xenograft tumors blunted the apoptotic response to MAPK + MCL-1 inhibition; conversely, deletion of LKB1 in LKB1 wild-type models restored the sensitivity. Mechanistically, LKB1 deficiency is associated with an altered phosphoproteome and increased MCL-1-dependent apoptotic priming. LKB1 loss increased cellular stress leading to hyperactivation of JNK1, phosphorylation and stabilization of MCL-1 protein, and increased BIM sequestration by MCL-1. Upon suppression of MAPK signaling, LKB1-deficient cells exhibited greater levels of BIM bound to MCL-1 that could be liberated by AMG 176 to induce apoptosis. Consistent with these results, ex vivo treatment of tumor tissue from a KRAS-LKB1 mutant NSCLC patient with MEK inhibitor or AMG 510 increased MCL-1 dependent priming.

Conclusion: These results uncover a novel link between LKB1, cellular stress, and the regulation of MCL-1. LKB1 loss confers a dependency on MCL-1 that can be exploited therapeutically. Moreover, our study provides preclinical rationale for the exploration of combined KRAS G12C + MCL-1 inhibitors, particularly for KRAS-LKB1 mutant patients who respond poorly to standard-of-care checkpoint inhibitor therapy.

Citation Format: Chendi Li, Yi Shen, Mohammed Usman Syed, Audris Oh, Cameron Fraser, Johannes Kreuzer, Kaitlyn Webster, Robert Morris, Sean Caenepeel, Anne Y. Saiki, Karen Rex, James Lipford, Wilhelm Hass, Kristopher Sarosiek, Paul E. Hughes, Aaron N. Hata. LKB1 loss rewires stress signaling-induced apoptotic protein dynamics and sensitizes KRAS-mutant non-small cell lung cancers to combined MAPK + MCL-1 blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 982.

AMG 757, a Half-Life Extended, DLL3-Targeted Bispecific T-Cell Engager, Shows High Potency and Sensitivity in Preclinical Models of Small-Cell Lung Cancer

PURPOSE

Small-cell lung cancer (SCLC) is an aggressive neuroendocrine tumor with a high relapse rate, limited therapeutic options, and poor prognosis. We investigated the antitumor activity of AMG 757, a half-life extended bispecific T-cell engager molecule targeting delta-like ligand 3 (DLL3)-a target that is selectively expressed in SCLC tumors, but with minimal normal tissue expression.

EXPERIMENTAL DESIGN

AMG 757 efficacy was evaluated in SCLC cell lines and in orthotopic and patient-derived xenograft (PDX) mouse SCLC models. Following AMG 757 administration, changes in tumor volume, pharmacodynamic changes in tumor-infiltrating T cells (TILs), and the spatial relationship between the appearance of TILs and tumor histology were examined. Tolerability was assessed in nonhuman primates (NHPs).

RESULTS

AMG 757 showed potent and specific killing of even those SCLC cell lines with very low DLL3 expression (<1,000 molecules per cell). AMG 757 effectively engaged systemically administered human T cells, induced T-cell activation, and redirected T cells to lyse tumor cells to promote significant tumor regression and complete responses in PDX models of SCLC and in orthotopic models of established primary lung SCLC and metastatic liver lesions. AMG 757 was well tolerated with no AMG 757-related adverse findings up to the highest tested dose (4.5 mg/kg weekly) in NHP. AMG 757 exhibits an extended half-life in NHP, which is projected to enable intermittent administration in patients.

CONCLUSIONS

AMG 757 has a compelling safety and efficacy profile in preclinical studies making it a viable option for targeting DLL3-expressing SCLC tumors in the clinical setting.

Abstract 4558: Antitumor activity of AMG757, a half-life extended (HLE) bispecific T-cell engager (BiTE®) immune therapy targeting DLL3, in human PDX and orthotopic mouse models of small cell lung cancer (SCLC)

SCLC is a highly aggressive neuroendocrine tumor with poor prognosis and limited therapeutic options. Delta-like ligand 3 (DLL3) is a tumor-associated antigen that is highly specific for SCLC; expression is elevated in tumors but minimal and mainly cytoplasmic in normal tissues. AMG 757 is an HLE BiTE® immune therapy that is designed to redirect T-cell cytotoxicity to cancer cells by binding to DLL3 on the surface of cancer cells and CD3 on T cells. AMG 757 is being evaluated in a phase 1 clinical trial in patients with relapsed/refractory SCLC (NCT03319940). We evaluated the efficacy and pharmacodynamic (PD) effects of AMG 757 in three preclinical models of SCLC that express DLL3. We used the LXFS 1129 patient-derived xenograft (PDX) model to assess AMG 757 efficacy in established, subcutaneously implanted tumors similar to human SCLC tumors with their associated stroma. We also developed two orthotopic models of SCLC (SHP-77 and H82) to assess AMG 757 efficacy and PD at biologically relevant sites. In the SHP-77 orthotopic model, cells injected intravenously trafficked to the lungs where they formed diffuse tumors similar to primary SCLC tumors. In the H82 orthotopic model, cells injected intravenously formed discrete metastatic lesions in the liver, mimicking a major site for SCLC metastasis. In each model, mice bearing established tumors received a single infusion of human T cells and were then dosed with AMG 757 or a control HLE BiTE molecule. In the LXFS 1129 PDX model, treatment with AMG 757 induced complete tumor regression in 8 out of 10 mice, whereas treatment with the control HLE BiTE molecule showed no tumor growth inhibition. In the orthotopic SHP-77 model, treatment with AMG 757 led to significant tumor growth inhibition in the lungs relative to treatment with a control HLE BiTE molecule; the bioluminescence (BLI) signal decreased to near the limit of detection 22 days after start of treatment. AMG 757 antitumor activity was associated with increased T-cell trafficking and expansion in tumors; a single dose of AMG 757 significantly increased the number of human CD4+ and CD8+ cells in lungs as assessed by flow cytometry. In the orthotopic H82 model, AMG 757 treatment completely cleared visible lesions from the liver, as assessed by a decrease in BLI to near-background levels and macroscopic analysis of the liver tissue. AMG 757 antitumor activity was associated with increased CD8+ T-cell infiltration as assessed by flow cytometry and IHC and upregulation of the T cell surface activation markers CD25, CD69, PD-1, and 4-1BB as assessed by flow cytometry. Together, these preclinical data demonstrate that AMG 757 can recruit and engage T cells to tumors, consistent with the BiTE® mechanism of action, and that AMG 757-mediated redirected T-cell lysis can drive significant antitumor activity in established SCLC tumor models.

Citation Format: Keegan Cooke, Juan Estrada, Jinghui Zhan, Jonathan Werner, Sean Caenepeel, Mike Giffin, Julie M. Bailis, Angela Coxon, Paul E. Hughes, Jude Canon. Antitumor activity of AMG757, a half-life extended (HLE) bispecific T-cell engager (BiTE®) immune therapy targeting DLL3, in human PDX and orthotopic mouse models of small cell lung cancer (SCLC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4558.

Mixing Sows into Alternative Lactation Housing Affects Sow Aggression at Mixing, Future Reproduction and Piglet Injury, with Marked Differences between Multisuckle and Sow Separation Systems

Simple Summary

Alternative lactation housing could reduce aggression when sows are mixed. We aimed to compare the effects of mixing sows during lactation (with or without piglets) at weaning and after insemination and determine the effects of mixing strategies and lactation housing on the piglet. Sows in the multisuckle treatment were the least aggressive, had the fewest injuries around mixing, and gave birth to the most piglets at the subsequent litter, with multisuckle housing having no apparent ill effects on the piglets. There was greater aggression in sows separated from their piglets for seven hours daily in lactation (SEP) than any other method. Multisuckle housing appears to be an effective way of decreasing aggression at the point of mixing, whilst optimizing sow reproduction. The behavioural response to mixing was similar when it occurred at weaning or after insemination, with the highest incidence of aggression observed in sows mixed without their piglets during lactation.

Abstract

Alternative lactation housing could reduce aggression when sows are mixed. We aimed to compare the effects of mixing sows in lactation (with or without piglets), at weaning or after insemination, and determine the effects of lactation housing on the piglet. This study used 120 multiparous Large White × Landrace sows and 54 focal litters. The sows were mixed into groups of six and allocated to multisuckle from day 21 lactation (MS), separated from litter and housed in groups, with piglets left in the crate for seven hours daily from day 21 lactation (SEP), mixed at weaning (day 28 lactation) (WEAN) and mixed after artificial insemination (AI) (MAI; 4 ± 1 day after last AI). Behaviour, saliva for free salivary cortisol concentration and injury counts were taken on M-1 (before mixing), M0 (mixing), M1 and M6. Piglets were weighed, injury-scored and bloods taken for cortisol. There was reduced aggression, seen as fights, bites and knocks in MS compared to the other treatments on all days (p < 0.05). MS sows had no fights on M1 and M6 and had more piglets born in the subsequent farrowing. Piglet weight, cortisol and mortality were unaffected by treatment (p > 0.05). MS piglets had greater injury scores immediately after moving to multisuckle and lower injuries around weaning (p > 0.001). Multisuckle housing could decrease aggression and stress at mixing in sows, with changes in the time of peak piglet injury (at mixing rather than at weaning) but overall no negative effects on the piglets.

Provision Point-Source Materials Stimulates Play in Sows but Does Not Affect Aggression at Regrouping

When sows are mixed into groups, hierarchies form and resulting aggression and stress can affect production and welfare. This study determined the effect of providing point-source materials on aggressive and play behaviors in gestating sows. Large white cross Landrace sows were mixed after insemination; six pens of 12 sows were housed in 'standard' pens, and six pens of 12 sows were housed in 'enhanced' pens. The 'enhanced' pens each contained two rubber mats, eight strands of 24 mm-thick sisal rope and two yellow plastic disks, suspended from the roof. The sows remained in these pens until pregnancy confirmation. Salivary cortisol concentration, injury counts, and sow behaviors were recorded the day before mixing (day 1), mixing (day 0) and post-mixing day 1, day 4, day 7 and day 20. At farrowing, reproductive outcomes were obtained. Play was observed (including locomotor and object play) in the 'enhanced' pen, and percentage of time spent playing was greater on d4 (1.48 ± 0.3 Square root transformed data (2.84% non-transformed adjusted mean)), d7 (1.43 ± 0.3 (2.97%)) and d20 (1.64 ± 0.3 (3.84%)), compared to d0 (0.56 ± 0.3 (0.70%)) and d1 (0.87 ± 0.3 (1.67%) (p < 0.05)). No play was observed in standard housing. Aggression, salivary free cortisol concentrations and injuries were unaffected (p > 0.05). The provision of materials had no impact on aggression, although their presence maintained sow interest and play behavior, suggesting a positive effect.

Magnetic perturbation diagnostics in the high-temperature lithiated environment of LTX-β

Magnetic perturbation measurements will be invaluable for characterizing Lithium Tokamak Experiment Beta (LTX-β) plasmas due to the time-evolving 3D nature of the magnetic fields generated by eddy currents in the vessel and copper shell segments, as well as enhanced MHD instability drive due to newly introduced neutral beam heating. The LTX-β upgrade includes two new arrays of Mirnov coils: a shell eddy sensor array of two-axis coils distributed over the back surface of one shell segment and a toroidal array of poloidal field coils at the low-field side midplane gap. Evaporative lithium wall-coating and the high temperatures required for liquid lithium wall operation both complicate the implementation of in-vessel diagnostics. While the shell array is protected from lithium exposure, the shell segment to which it is mounted will at times exceed 300 °C. The toroidal array, however, will experience direct line-of-sight exposure to the lithium evaporator as well as close proximity to the hot shell and may also be subject to poorly confined beam-driven fast ions. We describe how the two new Mirnov coil arrays meet these environmental challenges and enhance the LTX-β diagnostic suite.

Exploiting MCL1 Dependency with Combination MEK + MCL1 Inhibitors Leads to Induction of Apoptosis and Tumor Regression in KRAS-Mutant Non-Small Cell Lung Cancer

BH3 mimetic drugs, which inhibit prosurvival BCL2 family proteins, have limited single-agent activity in solid tumor models. The potential of BH3 mimetics for these cancers may depend on their ability to potentiate the apoptotic response to chemotherapy and targeted therapies. Using a novel class of potent and selective MCL1 inhibitors, we demonstrate that concurrent MEK + MCL1 inhibition induces apoptosis and tumor regression in KRAS-mutant non-small cell lung cancer (NSCLC) models, which respond poorly to MEK inhibition alone. Susceptibility to BH3 mimetics that target either MCL1 or BCL-xL was determined by the differential binding of proapoptotic BCL2 proteins to MCL1 or BCL-xL, respectively. The efficacy of dual MEK + MCL1 blockade was augmented by prior transient exposure to BCL-xL inhibitors, which promotes the binding of proapoptotic BCL2 proteins to MCL1. This suggests a novel strategy for integrating BH3 mimetics that target different BCL2 family proteins for KRAS-mutant NSCLC. SIGNIFICANCE: Defining the molecular basis for MCL1 versus BCL-xL dependency will be essential for effective prioritization of BH3 mimetic combination therapies in the clinic. We discover a novel strategy for integrating BCL-xL and MCL1 inhibitors to drive and subsequently exploit apoptotic dependencies of KRAS-mutant NSCLCs treated with MEK inhibitors.See related commentary by Leber et al., p. 1511.This article is highlighted in the In This Issue feature, p. 1494.

Abstract 3632: BiTE® antibody constructs for the treatment of SCLC

Small cell lung cancer (SCLC) is a highly aggressive neuroendocrine tumor with a poor prognosis and limited therapeutic options. Most patients present with extensive stage disease, where recent advances in immunotherapies, including bi-specific T cell engager (BiTE®) antibody constructs, represent a promising new therapeutic approach. BiTE® molecules have demonstrated durable complete responses in the clinic in hematological malignancies. Similar to hematological malignancies, SCLC is also a widely-disseminated malignancy that shows very high response rate to first line therapies with high rates of disease recurrence, features which may support efficacy of the BiTE® modality. Next generation sequencing (NGS) identified Delta-like Ligand 3 (DLL3) as a highly specific tumor associated antigen for SCLC, with consistent expression in tumors and very low expression in normal tissues. Tumor expression of DLL3 protein was confirmed by IHC, with 30 of 35 SCLC tumors staining positive for DLL3. DLL3 BiTE® antibody constructs showed low pM potency in vitro and also demonstrated significant inhibition of tumor growth in vivo in an orthotopic model of SCLC. A half-life extended (HLE) BiTE® targeting DLL3 demonstrated antibody-like pharmacokinetic properties in single-dose studies in non-human primates (NHP), with a half-life of 11 days. This is predicted to support every other week dosing in humans. The combination of high potency and excellent PK properties suggests that HLE BiTE® molecules may provide a useful tool for targeting residual disease in SCLC patients whose tumors express DLL3.

Citation Format: Michael J. Giffin, Ed K. Lobenhofer, Keegan Cooke, Tobias Raum, Jennitte Stevens, Pedro J. Beltran, Angela Coxon, Paul E. Hughes. BiTE® antibody constructs for the treatment of SCLC [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 3632. doi:10.1158/1538-7445.AM2017-3632

Controlling lactation oestrus: The final frontier for breeding herd management

Lactation anoestrus limits the flexibility of modern pig production systems such that any increase in lactation length reduces farrowing frequency, and thus profit. This review focuses on post-partum development of the sow's reproductive system, the physiology of lactation anoestrus and how it can be overcome, as well as the fertility of sows mated while lactating. The propensity for sows to ovulate spontaneously while lactating is high (24-31%), and a high proportion of sows will ovulate rapidly and synchronously in response to combinations of altered suckling (split weaning, interrupted suckling), daily boar contact, exogenous gonadotrophins, and group housing. The apparent ease with which lactation anoestrus can be overcome represents an opportunity to uncouple sow mating from weaning, thus reducing the impact of lactation length on productivity. This is especially true when considering the benefits of the described stimulation methods on the reproductive performance (i.e., shorter weaning to oestrus intervals and higher litter sizes) of the low proportion of sows that maintain lactation anoestrus.

Group and individual sow behavior is altered in early gestation by space allowance in the days immediately following grouping

Aggression between domestic sows is greatest when sows are first introduced to each other and hierarchies form. The aim of this study was to determine the effect of a spacious "mixing pen" on sow aggression and stress. Sows were mixed into groups of 6 and allowed 2 (LOW; 8 groups and 48 sows), 4 (MED; 7 groups and 42 sows), or 6 m/sow (HIGH; 7 groups and 42 sows) for 4 d after mixing, at which point all pens were equalized to 2 m/sow. Salivary cortisol concentration and injury counts were measured on d -1, 0, 1, 3, and 4 relative to mixing, and behavior was also recorded on each of these days following mixing. Reproductive performance was assessed at farrowing. A linear mixed model was applied to the data. Data are presented as least squares means and standard error of the mean. Where transformations occurred, nontransformed adjusted means are presented in parentheses following the presentation of transformed data. In the primary analyses where measures were considered at the pen level, there were no effect of space allowance on fight number per sow, duration of fights, percentage of total time spent fighting, displacements, bites, knocks, and lunges ( > 0.05). These measures were higher on d 0 (i.e., fight number 1.0 ± 0.1 [13.8]) compared with d 1 (0.4 ± 0.1 [4.2]), 3 (0.7 ± 0.1 [5.3]), and 4 (0.7 ± 0.1 [5.5]; < 0.05), with no increase in aggression on d 4 when pen sizes were standardized ( > 0.05). There was increased percentage of time spent active (1.5 ± 0.02 [33.7] for LOW, 1.5 ± 0.02 [36.5] for MED, and 1.6 ± 0.02 [43.4] for HIGH) and time spent exploring (1.8 ± 0.1 [3.5] for LOW, 2.0 ± 0.1 [4.0] for MED, and 2.3 ± 0.1 [5.7] for HIGH) and number of nonaggressive sow-sow contacts (0.3 ± 0.09 [2.2] for LOW, 0.4 ± 0.07 [3.2] for MED, and 0.5 ± 0.07 [4.5] for HIGH) in HIGH compared with LOW ( < 0.05). Farrowing rate and total piglets born were not affected by treatment ( > 0.05). A secondary analysis was conducted that examined individual sow behavior within each pen, and this identified increased injury number in the lowest ranked sows (involved in no fights on d 0 and no displacements on d0 to d4) in LOW (9.3 ± 1.2 [107.9] for LOW, 6.2 ± 0.8 [53.0] for MED, and 5.1 ± 0.8 [28.1] for HIGH) and also decreased fight number and duration in HIGH compared with LOW on d 0 and 1 ( < 0.05). Our primary data analysis demonstrates positive exploratory and social behaviors with increased space and suggests that a reduction in space following hierarchy formation is not a significant stressor. Additionally, there is some evidence at an individual sow level that increased space at mixing benefits sow welfare parameters, especially for low-ranked sows.

Dietary ractopamine supplementation during the first lactation affects milk composition, piglet growth and sow reproductive performance

Excessive mobilization of body reserves during lactation delays the return to reproductive function in weaned primiparous sows. This study tested the hypothesis that supplementing the lactation diets of first-parity sows with ractopamine hydrochloride would reduce maternal weight loss and improve subsequent reproductive performance. Gestating gilts were allocated to one of two treatment groups (n=30 sows/treatment), with one group fed a standard lactation diet (2.5g/Mcal LYS: DE) throughout lactation (CTRL), whereas the treatment group received the standard lactation diet supplemented with 10mg/kg ractopamine hydrochloride (RAC) from d 1 to 13 of lactation and 20mg/kg RAC from d 14 of lactation until artificial insemination (AI). Weaning occurred on d 21 of lactation, with AI occurring at the first post-weaning estrus. Compared to CTRL, RAC supplementation decreased (P<0.05) liveweight loss between d 13 and 20 of lactation (4.3±0.90 versus 1.3±0.96kg), and tended to increase (P=0.06) the number of second litter piglets born alive (9.5±0.52 versus 8.1±0.74). Treatment (RAC versus CTRL) reduced milk protein levels on d 13 and 20 of lactation (P<0.05), and piglet weight gain between d 13 and 20 of lactation (260±0.01 versus 310±0.01g/day, P<0.01). In conclusion, it is evident that dietary RAC altered milk composition and stimulated conservation of maternal body reserves during the third week of lactation, resulting in a beneficial effect on subsequent reproductive performance.

In Vitro and In Vivo Activity of AMG 337, a Potent and Selective MET Kinase Inhibitor, in MET-Dependent Cancer Models

The MET receptor tyrosine kinase is involved in cell growth, survival, and invasion. Clinical studies with small molecule MET inhibitors have shown the role of biomarkers in identifying patients most likely to benefit from MET-targeted therapy. AMG 337 is an oral, small molecule, ATP-competitive, highly selective inhibitor of the MET receptor. Herein, we describe AMG 337 preclinical activity and mechanism of action in MET-dependent tumor models. These studies suggest MET is the only therapeutic target for AMG 337. In an unbiased tumor cell line proliferation screen (260 cell lines), a closely related analogue of AMG 337, Compound 5, exhibited activity in 2 of 260 cell lines; both were MET-amplified. Additional studies examining the effects of AMG 337 on the proliferation of a limited panel of cell lines with varying MET copy numbers revealed that high-level focal MET amplification (>12 copies) was required to confer MET oncogene addiction and AMG 337 sensitivity. One MET-amplified cell line, H1573 (>12 copies), was AMG 337 insensitive, possibly because of a downstream G12A KRAS mutation. Mechanism-of-action studies in sensitive MET-amplified cell lines demonstrated that AMG 337 inhibited MET and adaptor protein Gab-1 phosphorylation, subsequently blocking the downstream PI3K and MAPK pathways. AMG 337 exhibited potency in pharmacodynamic assays evaluating MET signaling in tumor xenograft models; >90% inhibition of Gab-1 phosphorylation was observed at 0.75 mg/kg. These findings describe the preclinical activity and mechanism of action of AMG 337 in MET-dependent tumor models and indicate its potential as a novel therapeutic for the treatment of MET-dependent tumors. Mol Cancer Ther; 15(7); 1568-79. ©2016 AACR.

Design and installation of a ferromagnetic wall in tokamak geometry

Low-activation ferritic steels are leading material candidates for use in next-generation fusion development experiments such as a prospective component test facility and DEMO power reactor. Understanding the interaction of plasmas with a ferromagnetic wall will provide crucial physics for these facilities. In order to study ferromagnetic effects in toroidal geometry, a ferritic wall upgrade was designed and installed in the High Beta Tokamak-Extended Pulse (HBT-EP). Several material options were investigated based on conductivity, magnetic permeability, vacuum compatibility, and other criteria, and the material of choice (high-cobalt steel) is characterized. Installation was accomplished quickly, with minimal impact on existing diagnostics and overall machine performance, and initial results demonstrate the effects of the ferritic wall on plasma stability.

MDM2 antagonists synergize broadly and robustly with compounds targeting fundamental oncogenic signaling pathways

While MDM2 inhibitors hold great promise as cancer therapeutics, drug resistance will likely limit their efficacy as single agents. To identify drug combinations that might circumvent resistance, we screened for agents that could synergize with MDM2 inhibition in the suppression of cell viability. We observed broad and robust synergy when combining MDM2 antagonists with either MEK or PI3K inhibitors. Synergy was not limited to cell lines harboring MAPK or PI3K pathway mutations, nor did it depend on which node of the PI3K axis was targeted. MDM2 inhibitors also synergized strongly with BH3 mimetics, BCR-ABL antagonists, and HDAC inhibitors. MDM2 inhibitor-mediated synergy with agents targeting these mechanisms was much more prevalent than previously appreciated, implying that clinical translation of these combinations could have far-reaching implications for public health. These findings highlight the importance of combinatorial drug targeting and provide a framework for the rational design of MDM2 inhibitor clinical trials.

Melatonin implants do not alter estrogen feedback or advance puberty in gilts

Puberty in pigs is often delayed during late summer and autumn, with long daylength the most likely cause. We hypothesised (1) that gilts born around the shortest day would have a later release from the negative feedback actions of estradiol than gilts born around the spring equinox and (2) melatonin treatment would result in an earlier release from estradiol negative feedback and advance the onset of puberty in gilts born around the spring equinox. We first determined the optimal number of estradiol implants required to monitor the release from estradiol negative feedback in ovariectomised gilts. Secondly we determined whether melatonin implants altered negative feedback in 4 cohorts of ovariectomised gilts born between the winter solstice and spring equinox, and in the following year whether melatonin altered the time of the first ovulation in 5 cohorts of intact gilts born between the winter solstice and spring equinox. Plasma LH and FSH increased between 126 and 210d of age (P<0.001) in each cohort (season), but there was no effect of cohort, melatonin treatment or interactions (P>0.05). Age at first detection of elevated plasma progesterone in untreated, intact gilts decreased across the 4 cohorts (P<0.05). Melatonin treatment of intact gilts failed to advance the age of puberty irrespective of their season of birth (P>0.05). In conclusion, while we confirmed that estradiol sensitivity is decreased as gilts age, we failed to demonstrate any effects of season or melatonin on estradiol feedback or melatonin on puberty.

Abstract 3712: HGF mediated resistance to BRAF inhibition in BRAF V600E mutant melanoma xenograft models

Background: A key obstacle in the treatment of cancer is resistance to targeted therapy. Recent reports suggest that growth factors and their receptors may play a role in mediating this resistance. HGF/MET signaling has been shown to play a role in mediating resistance to BRAF inhibitors in BRAF mutant melanoma. We studied the role of HGF/MET in mediating resistance to BRAF inhibition in BRAF mutant melanoma xenografts, comparing models of systemic and local HGF expression and evaluating the ability of a MET inhibitor to reverse HGF mediated resistance. The underlying mechanisms of this resistance were evaluated by monitoring changes in PI3K and MAPK signaling. Our data suggest that elevated local HGF expression may be required for resistance to BRAF inhibition in vivo and that resistance can be reversed by treatment with a MET inhibitor.

Methods: To model systemic HGF expression, mice bearing G361 melanoma xenografts were treated with recombinant adeno-associated virus containing an expression cassette for human HGF (AAV-HGF) or GFP as control. Mice were treated with C-1 (10 mg/kg, QD, PO), a BRAF inhibitor, or vehicle, and tumor growth was monitored. Local HGF expression was modeled using G361 xenografts engineered to express HGF under the control of an inducible promoter (tet-HGF). Mice bearing G361 tet-HGF xenografts, with or without doxycycline, were treated and monitored as described above. A follow up study was performed in G361 tet-HGF xenografts to measure the ability of AMG 337 (20 mg/kg, BID, PO), a selective MET inhibitor, to attenuate the HGF mediated rescue of BRAF inhibition. To monitor effects on the PI3K and MAPK pathways, pAKT and pERK levels were measured in tumors. Plasma and tumor HGF levels were also measured.

Results: Systemic expression of HGF via AAV-HGF treatment failed to rescue G361 xenografts from the growth inhibitory effects of C1. In contrast, local doxycycline-induced expression of HGF in mice harboring G361 tet-HGF xenografts conveyed significant (p&lt;0.001) rescue of tumor growth, suggesting that local HGF expression may be required to mediate BRAF inhibitor resistance. Elevated pAKT and pERK levels were detected in HGF rescued tumors, suggesting that PI3K and MAPK signaling pathways play a role in conveying HGF mediated resistance. Combined treatment with AMG 337 prevented the HGF mediated rescue of BRAF inhibition, confirming the role of MET signaling in this rescue mechanism. Plasma HGF levels in mice from the systemic HGF expression groups exceeded those in the local groups (3,049 and 195 pg/mL). However, tumor HGF levels were higher in the local expression groups compared to the systemic groups (26,400 and 477 pg/mL).

Conclusion: Here we demonstrate the role for HGF/MET signaling in mediating resistance to BRAF inhibitors in melanoma and suggest that monitoring HGF levels may be of clinical utility for predicting response to BRAF inhibition and in defining the opportunity for combination therapy with MET inhibitors.

Citation Format: Keegan Cooke, Guo Huang, Sean Caenepeel, Hong Ma, Cherylene Plewa, Ki Jeong Lee, Angela Coxon, Paul E. Hughes, Pedro Beltran. HGF mediated resistance to BRAF inhibition in BRAF V600E mutant melanoma xenograft models. [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 3712. doi:10.1158/1538-7445.AM2014-3712

Human and bovine viruses in the Milwaukee River watershed: hydrologically relevant representation and relations with environmental variables

To examine the occurrence, hydrologic variability, and seasonal variability of human and bovine viruses in surface water, three stream locations were monitored in the Milwaukee River watershed in Wisconsin, USA, from February 2007 through June 2008. Monitoring sites included an urban subwatershed, a rural subwatershed, and the Milwaukee River at the mouth. To collect samples that characterize variability throughout changing hydrologic periods, a process control system was developed for unattended, large-volume (56-2800 L) filtration over extended durations. This system provided flow-weighted mean concentrations during runoff and extended (24-h) low-flow periods. Human viruses and bovine viruses were detected by real-time qPCR in 49% and 41% of samples (n=63), respectively. All human viruses analyzed were detected at least once including adenovirus (40% of samples), GI norovirus (10%), enterovirus (8%), rotavirus (6%), GII norovirus (1.6%) and hepatitis A virus (1.6%). Three of seven bovine viruses analyzed were detected including bovine polyomavirus (32%), bovine rotavirus (19%), and bovine viral diarrhea virus type 1 (5%). Human viruses were present in 63% of runoff samples resulting from precipitation and snowmelt, and 20% of low-flow samples. Maximum human virus concentrations exceeded 300 genomic copies/L. Bovine viruses were present in 46% of runoff samples resulting from precipitation and snowmelt and 14% of low-flow samples. The maximum bovine virus concentration was 11 genomic copies/L. Statistical modeling indicated that stream flow, precipitation, and season explained the variability of human viruses in the watershed, and hydrologic condition (runoff event or low-flow) and season explained the variability of the sum of human and bovine viruses; however, no model was identified that could explain the variability of bovine viruses alone. Understanding the factors that affect virus fate and transport in rivers will aid watershed management for minimizing human exposure and disease transmission.

Lactation estrus induction in multi- and primiparous sows in an Australian commercial pork production system

This study evaluated the effect of full physical boar exposure and split weaning on the incidence of lactation estrus within a large commercial piggery. A total of 299 multiparous (MP; parity 2.5 ± 0.03) and 303 primiparous (PP) sows of Large White × Duroc × Landrace genetics were individually housed in conventional farrowing crates from 1 wk before expected farrowing until weaning on Day 30.7 ± 0.05 postparturition. Before shed entry, sows were allocated randomly within parity to receive either boar exposure (BE; n = 454) or no BE (No BE; n = 149). Sows assigned to receive BE were then allocated to 1 of 2 litter size treatments: litter size unchanged (BE; n = 302) or BE and the litter permanently reduced (split weaned) to 7 piglets (BESPW7; n = 152) on Day 18 of lactation. From Day 18 of lactation until weaning, sows in both BE treatments were taken daily to a detection mating area where they received 15 min of full physical BE and were artificially inseminated at the first observed estrus. Providing sows with BE increased the incidence of lactation estrus, with a further increase observed when litter size was reduced to 7 piglets (16% No BE vs. 62% BE and 75% BESPW7; P < 0.05). Multiparous sows exhibited a greater incidence of lactation estrus than PP sows irrespective of treatment (81 compared to 52%, respectively; P < 0.05). Both MP and PP sows exhibited an increased incidence of lactation estrus when a portion of the litter was removed (MP: 76 vs. 89% and PP: 47 vs. 61%; P < 0.05). Farrowing rates were higher in BE MP sows mated postweaning and all BESPW7 sows mated postweaning when compared to their counterparts mated in lactation (P < 0.05). Percentage live weight loss over the course of lactation was greatest for sows in the No BE compared to the BE and BESPW7 treatments (7.7% ± 0.5 vs. 5.4% ± 0.3 and 4.5% ± 0.4, respectively; P < 0.05). Between Day 17 and weaning, piglets suckling sows in the BESPW7 treatment had a higher average weight gain than piglets suckling sows with a full litter (3.5 ± 0.06 vs. 3.1 ± 0.05 kg; P < 0.05). In conclusion these data suggest that providing MP sows with BE is effective at stimulating a synchronous lactation estrus while PP sows require, in addition to BE, a reduction in suckled litter size to 7 piglets.

Split weaning increases the incidence of lactation oestrus in boar-exposed sows

This study evaluated the effect of split weaning and fence-line boar exposure during lactation on the incidence of lactation oestrus. Large White and Large White × Landrace sows (parity 2.9 ± 0.17; mean ± SEM) were housed in conventional farrowing crates from day -4 to 30 post-parturition. Four treatments (n = 18) were used: control (SPW0): continuous lactation of 10 piglets with all piglets weaned on day 30 of lactation; and three split wean (SPW) treatments with 3 (SPW3), 5 (SPW5) or 7 (SPW7) of the heaviest piglets removed from the sow on day 18 lactation. From day 18 lactation all sows received 15 min daily, fence-line boar exposure in a detection mating area. Fewer sows in the SPW0 treatment (56% (10/18)) expressed a lactation oestrus compared to the SPW3, SPW5, and SPW7 treatments (83%; 89%; 94%, respectively). SPW0 sows had a lower subsequent total born compared to SPW5 or SPW7 sows (8.9 ± 1.1 vs. 12.5 ± 1.0 and 13.1 ± 1.1, respectively). Between day 18 and 30 of lactation, sows in SPW5 and SPW7 gained weight (4.5 ± 1.4 and 1.9 ± 1.4 kg, respectively) whereas SPW0 and SPW3 sows lost weight (4.9 ± 1.4 and 2.9 ± 1.4 kg, respectively) (P<0.05). Split weaned piglets were heavier at day 17 of age by 1.0 kg however by day 40 of age no weight differences were observed between piglets weaned on day 18 compared to day 30 (P<0.05). In conclusion, split weaning coupled with fence-line boar exposure in late lactation induced lactation oestrus in a higher proportion of sows compared to those suckling a normal litter size.

Selective class I phosphoinositide 3-kinase inhibitors: optimization of a series of pyridyltriazines leading to the identification of a clinical candidate, AMG 511

The phosphoinositide 3-kinase family catalyzes the phosphorylation of phosphatidylinositol-4,5-diphosphate to phosphatidylinositol-3,4,5-triphosphate, a secondary messenger which plays a critical role in important cellular functions such as metabolism, cell growth, and cell survival. Our efforts to identify potent, efficacious, and orally available phosphatidylinositol 3-kinase (PI3K) inhibitors as potential cancer therapeutics have resulted in the discovery of 4-(2-((6-methoxypyridin-3-yl)amino)-5-((4-(methylsulfonyl)piperazin-1-yl)methyl)pyridin-3-yl)-6-methyl-1,3,5-triazin-2-amine (1). In this paper, we describe the optimization of compound 1, which led to the design and synthesis of pyridyltriazine 31, a potent pan inhibitor of class I PI3Ks with a superior pharmacokinetic profile. Compound 31 was shown to potently block the targeted PI3K pathway in a mouse liver pharmacodynamic model and inhibit tumor growth in a U87 malignant glioma glioblastoma xenograft model. On the basis of its excellent in vivo efficacy and pharmacokinetic profile, compound 31 was selected for further evaluation as a clinical candidate and was designated AMG 511.

Abstract 2805: In vitro characterization of AMG 511, a potent and selective class I PI3K inhibitor for the treatment of cancer

The PI3K signaling pathway is frequently activated in cancer and has been implicated in many aspects of tumor growth and survival. Inhibition of this pathway represents a potential therapeutic path for the treatment of cancer. This study evaluated the in vitro characteristics of AMG 511, a potent and selective pan class I PI3K inhibitor exhibiting IC50 values of 8, 11, 2, and 6 nM against the PI3K β, α, β, and ≤ isoforms respectively. AMG 511 was shown to be inactive against members of the closely related phosphoinositide 3 kinase related kinases (PIKK) family of kinases and did not inhibit mTOR, hVPS34, PI4Kα or PI4Kα in-vitro (IC50 values &gt; 1 μM). In addition, AMG 511 was inactive against a majority of protein kinases (372) in the human kinome as measured by in-vitro binding assays. AMG 511 inhibited PI3K pathway signaling in U87 MG glioblastoma cells as determined by dose-dependent reduction in AKT S473 phosphorylation (IC50 = 4 nM). AKT inhibition resulted in a concomitant reduction in PRAS40 phosphorylation (IC50 = 23 nM), a downstream effector of AKT. Reduced phosphorylation of mTORC1 substrates p70S6K (IC50 = 30 nM) and S6 (IC50 = 70 nM) but not 4EBP1 (T37/46), was also detected in U87 MG cells, suggesting that upstream blockade of PI3K pathway signaling with AMG 511 treatment leads to a selective reduction in downstream mTORC1 activity. Given the well documented role of mTORC1 in cap-dependent translation we profiled AMG 511 in a methionine-analog incorporation assay in U87 MG cells. However, no significant inhibition of bulk translation was observed following treatment with AMG 511 in U87 MG cells. Treatment of U87 MG cells with AMG 511 revealed a pronounced G1 arrest with a concurrent reduction in BrdU+ cells, detectable within 8 hours of treatment. This anti-proliferative effect was fully reversible by 18 hours following washout. In line with these anti-proliferative effects, reduced cyclin D1 levels and elevated p27 levels were detected within 4 hours of treatment. Minimal cell killing effects were detected with AMG 511 treatment in U87 MG cells as measured by induction of cleaved caspase-3 and DNA content &lt; 2N. AMG 511 was profiled across a large panel of tumor cell lines encompassing several tumor types including breast and lung. A majority of the cell lines tested exhibited sensitivity to AMG 511 with a subset exhibiting evidence for cell death upon treatment with AMG 511. Breast cancer cell lines harboring activating mutations in PI3Kα, loss of PTEN, or amplification of Her2 tended to show greater sensitivity to AMG 511 treatment. In conclusion, AMG 511 is a potent and selective pan class I PI3K inhibitor, capable of inhibiting PI3K signaling and inducing robust anti-proliferative effects via a G1 arrest in many tumor cell lines, with evidence of cell killing in a subset of lines.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2805. doi:1538-7445.AM2012-2805

Structure-activity relationships of phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dual inhibitors: investigations of various 6,5-heterocycles to improve metabolic stability

N-(6-(6-Chloro-5-(4-fluorophenylsulfonamido)pyridin-3-yl)benzo[d]thiazol-2-yl)acetamide (1) is a potent and efficacious inhibitor of PI3Kα and mTOR in vitro and in vivo. However, in hepatocyte and in vivo metabolism studies, 1 was found to undergo deacetylation on the 2-amino substituent of the benzothiazole. As an approach to reduce or eliminate this metabolic deacetylation, a variety of 6,5-heterocyclic analogues were examined as an alternative to the benzothiazole ring. Imidazopyridazine 10 was found to have similar in vitro potency and in vivo efficacy relative to 1, while only minimal amounts of the corresponding deacetylated metabolite of 10 were observed in hepatocytes.

Phospshoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) dual inhibitors: discovery and structure-activity relationships of a series of quinoline and quinoxaline derivatives

The phosphoinositide 3-kinase (PI3K) family catalyzes the ATP-dependent phosphorylation of the 3'-hydroxyl group of phosphatidylinositols and plays an important role in cell growth and survival. There is abundant evidence demonstrating that PI3K signaling is dysregulated in many human cancers, suggesting that therapeutics targeting the PI3K pathway may have utility for the treatment of cancer. Our efforts to identify potent, efficacious, and orally available PI3K/mammalian target of rapamycin (mTOR) dual inhibitors resulted in the discovery of a series of substituted quinolines and quinoxalines derivatives. In this report, we describe the structure-activity relationships, selectivity, and pharmacokinetic data of this series and illustrate the in vivo pharmacodynamic and efficacy data for a representative compound.

Nutritional restriction of pre-pubertal liveweight gain impairs ovarian follicle growth and oocyte developmental competence of replacement gilts

The objective was to investigate the effects of moderate restriction of pre- and peri-pubertal liveweight gain on ovarian development and oocyte meiotic competence. At 70 d of age, and 27.7 ± 0.4 kg liveweight (LW), 64 Large White/Landrace crossbred gilts were allocated to two treatment groups (n = 32 gilts/treatment); one group was fed to attain a LW of 70 kg at 161 d of age (LIGHT), while the other group was fed to reach 100 kg LW (HEAVY). At 161 d of age, half of the gilts in each group (n = 16) were fed to gain LW at 0.5 kg/d (LOW), while the remaining half (n = 16) were fed to gain LW at 1.0 kg/d (HIGH) between 161 and 175 d of age, at which point they were killed and ovaries collected. For each gilt, surface antral follicles were counted and aspirated according to three size categories: 1-2.9 mm (small); 3-6 mm (medium); and > 6 mm (large). Follicles were pooled for each size class and treatment. Cumulus-oocyte-complexes (COC) recovered from small and medium follicles were matured in vitro (IVM) for 44 to 46 h, and meiotic maturation assessed. There was an effect of treatment (LIGHT versus HEAVY) on the number of medium sized follicles: 25.1 ± 2.59 versus 34.3 ± 2.60 (P < 0.05). The ovaries of LOW gilts had more small follicles and fewer medium follicles compared to those of HIGH gilts: 92.8 ± 8.35 versus 59.8 ± 5.24, and 25.1 ± 2.59 versus 32.5 ± 2.86 (P < 0.05). Target LW at 161 d did not affect meiotic progression of oocytes. However, LOW compared to HIGH LW gain between 161 and 175 d resulted in fewer oocytes reaching MII (0.40 versus 0.54; P < 0.05). In conclusion, moderately restricting feed intake impaired follicle growth beyond 3 mm and reduced oocyte meiotic competence. Further, although a carry-over effect of long-term feed restriction on follicle growth was evident, acute changes in feed intake during the 14 d prior to ovary collection had the greatest effect on oocyte nuclear maturation in vitro.

Motesanib inhibits Kit mutations associated with gastrointestinal stromal tumors

Background

Activating mutations in Kit receptor tyrosine kinase or the related platelet-derived growth factor receptor (PDGFR) play an important role in the pathogenesis of gastrointestinal stromal tumors (GIST).

Methods

This study investigated the activity of motesanib, an inhibitor of vascular endothelial growth factor receptors (VEGFR) 1, 2, and 3; PDGFR; and Kit, against primary activating Kit mutants and mutants associated with secondary resistance to imatinib. Single- and double-mutant isoforms of Kit were evaluated for their sensitivity to motesanib or imatinib in autophosphorylation assays and in Ba/F3 cell proliferation assays.

Results

Motesanib inhibited Kit autophosphorylation in CHO cell lines expressing primary activating mutations in exon 9 (AYins503-504, IC₅₀ = 18 nM) and exon 11 (V560 D, IC₅₀ = 5 nM; Δ552-559, IC₅₀ = 1 nM). Motesanib also demonstrated activity against kinase domain mutations conferring imatinib resistance (V560D/V654A, IC₅₀ = 77 nM; V560D/T670I, IC₅₀ = 277 nM; Y823 D, IC₅₀ = 64 nM) but failed to inhibit the imatinib-resistant D816V mutant (IC₅₀ > 3000 nM). Motesanib suppressed the proliferation of Ba/F3 cells expressing Kit mutants with IC₅₀ values in good agreement with those observed in the autophosphorylation assays.

Conclusions

In conclusion, our data suggest that motesanib possesses inhibitory activity against primary Kit mutations and some imatinib-resistant secondary mutations.

Mixing gilts in early pregnancy does not affect embryo survival

There is general acceptance that mixing sows during the first 3 weeks of gestation is detrimental to embryo development and survival. However, there is a paucity of data describing the influence of group housing and remixing during the first 14 days of gestation on pregnancy outcomes. Using 96 purebred maternal (Large White)/terminal (Duroc) line gilts, the current study determined the effects of regrouping, and the timing of regrouping, during the pre-implantation period on embryo mortality. The study was conducted in 2 blocks, with 12 gilts allocated to each of 4 treatments in each block. At 175 days of age, the combination of PG600 and 20 min of daily physical boar contact was used to stimulate puberty, with boar contact resuming 12 days after first detection of oestrus and gilts receiving two artificial inseminations (AIs), 24 h apart, at their second oestrus. After their first AI gilts were allocated to one of four treatment groups (n=12 gilts/treatment). Gilts in one treatment group were housed individually in stalls (STALL). The remaining gilts continued to be housed in their pre-AI groups and were either not remixed (NOMIX), or remixed to form new groups on day 3/4 (RMIXD3/4) or day 8/9 (RMIXD8/9) of gestation (day 0=day of first detection of second oestrus and first insemination). Group-housed gilts were housed in groups of 6, with a space allowance of 2.4 m2/gilt. All gilts were fed once a day (2.2 kg/gilt). Reproductive tracts were collected on day 26.6+/-0.13 of gestation, and the number of corpora lutea (CL) and viable embryos counted. Pregnancy rate was similar across all treatments, averaging 94.5% across the four treatment groups. The number of embryos present on day 26 of gestation was unaffected by housing treatments (P>0.05); gilts in the STALL, NOMIX, RMIXD3/4 and RMIXD8/9 groups possessed 13.2+/-0.67, 12.9+/-0.66, 14.1+/-0.46 and 13.8+/-0.57 embryos, respectively. Similarly, embryo survival rates were 0.91+/-0.04, 0.85+/-0.04, 0.91+/-0.02 and 0.87+/-0.05 for the STALL, NOMIX, RMIXD3.4 and RMIXD8/9 groups, respectively (P>0.05). In conclusion, the current data indicate that individually housing gilts immediately after their first AI does not improve embryo survival. There also appear to be no adverse effects on embryo development or survival when group-housed, mated gilts are remixed during the first 10 days of gestation.

Synthesis, structural analysis, and SAR studies of triazine derivatives as potent, selective Tie-2 inhibitors

A novel class of selective Tie-2 inhibitors was derived from a multi-kinase inhibitor 1. By reversing the amide connectivity and incorporating aminotriazine or aminopyridine hinge-binding moieties, excellent Tie-2 potency and KDR selectivity could be achieved with 3-substituted terminal aryl rings. X-ray co-crystal structure analysis aided inhibitor design. This series was evaluated on the basis of potency, selectivity, and rat pharmacokinetic parameters.

Evolution of a Highly Selective and Potent 2-(Pyridin-2-yl)-1,3,5-triazine Tie-2 Kinase Inhibitor

Inhibition of angiogenesis is a promising and clinically validated approach for limiting tumor growth and survival. The receptor tyrosine kinase Tie-2 is expressed almost exclusively in the vascular endothelium and is required for developmental angiogenesis and vessel maturation. However, the significance of Tie-2 signaling in tumor angiogenesis is not well understood. In order to evaluate the therapeutic utility of inhibiting Tie-2 signaling, we developed a series of potent and orally bioavailable small molecule Tie-2 kinase inhibitors with selectivity over other kinases, especially those that are believed to be important for tumor angiogenesis. Our earlier work provided pyridinyl pyrimidine 6 as a potent, nonselective Tie-2 inhibitor that was designed on the basis of X-ray cocrystal structures of KDR inhibitors 34 (triazine) and 35 (nicotinamide). Lead optimization resulted in pyridinyl triazine 63, which exhibited >30-fold selectivity over a panel of kinases, good oral exposure, and in vivo inhibition of Tie-2 phosphorylation.

Increasing the age of gilts at first boar contact improves the timing and synchrony of the pubertal response but does not affect potential litter size

One hundred and ninety-two Large White/Landrace crossbred gilts were used in this study. The study was conducted in two blocks, with 16 gilts allocated to each of six treatments in each block. The treatments compared the effects on puberty attainment of commencing boar exposure at 161, 182 or 203 days of age, and the effect of first mating gilts at either the pubertal or second oestrus on ovulation rate and early embryo survival. Boar contact took place in a detection-mating area (DMA), and consisted of 20 min/day of full contact with a vasectomized boar greater than ten months of age. Gilts were artificially inseminated at the allocated oestrus, with the reproductive tracts collected at 22.8+/-0.4 days after first mating (mean+/-S.E.M.), and the numbers of corpora lutea and viable embryos recorded. The age at which gilts attained puberty increased with the age at which boar exposure commenced. Mean gilt ages at puberty were 179.5+/-1.6, 191.7+/-1.2 and 210.3+/-0.9 days, respectively, when boar contact commenced at 161, 182 and 203 days of age, P<0.01. Mean days-to-puberty was significantly shorter when boar contact began at 182 and 203 days of age compared to 161 days of age (10.4+/-1.2 and 8.3+/-0.9 days versus 18.9+/-1.5 days, respectively, P<0.01). Similarly, commencing boar exposure at 182 or 203 days of age as opposed to 161 days of age significantly increased the proportion of gilts attaining puberty within 10 days of start of boar exposure (0.67 and 0.70 versus 0.24, P<0.01). Mean days-to-puberty and the synchrony of puberty attainment were similar when boar contact commenced at 182 and 203 days of age. There was no significant effect of mating oestrus or age of gilts at mating on ovulation rate, embryo number or embryo survival. In conclusion, the current data indicate that the timing and synchrony of puberty attainment is significantly improved when first boar exposure of gilts is delayed until 182 days of age. Further, it is evident that within the age range investigated, delaying first mating until the second oestrus does not significantly increase either ovulation rate or embryo number at day 20 post-mating.

C-terminal sequences in R-Ras are involved in integrin regulation and in plasma membrane microdomain distribution

The small GTPases R-Ras and H-Ras are highly homologous proteins with contrasting biological properties, for example, they differentially modulate integrin affinity: H-Ras suppresses integrin activation in fibroblasts whereas R-Ras can reverse this effect of H-Ras. To gain insight into the sequences directing this divergent phenotype, we investigated a panel of H-Ras/R-Ras chimeras and found that sequences in the R-Ras hypervariable C-terminal region including amino acids 175-203 are required for the R-Ras ability to increase integrin activation in CHO cells; however, the proline-rich site in this region, previously reported to bind the adaptor protein Nck, was not essential for this effect. In addition, we found that the GTPase TC21 behaved similarly to R-Ras. Because the C-termini of Ras proteins can control their subcellular localization, we compared the localization of H-Ras and R-Ras. In contrast to H-Ras, which migrates out of lipid rafts upon activation, we found that activated R-Ras remained localized to lipid rafts. However, functionally distinct H-Ras/R-Ras chimeras containing different C-terminal R-Ras segments localized to lipid rafts irrespective of their integrin phenotype.