The neonatal Fc receptor (FcRn) plays an important role in regulating the serum half-lives of IgG antibodies. A correlation has been established between the pH-dependent binding affinity of IgG antibodies to FcRn and their serum half-lives in mice. In this study, molecular modeling was used to identify Fc positions near the FcRn binding site in a human IgG antibody that, when mutated, might alter the binding affinity of IgG to FcRn. Following mutagenesis, several IgG2 mutants with increased binding affinity to human FcRn at pH 6.0 were identified at Fc positions 250 and 428. These mutants do not bind to human FcRn at pH 7.5. A pharmacokinetics study of two mutant IgG2 antibodies with increased FcRn binding affinity indicated that they had serum half-lives in rhesus monkeys ∼2-fold longer than the wild-type antibody.
Breast cancer is the most prevalent malignancy affecting women and ranks second in cancer-related deaths, in which death occurs primarily from metastatic disease. Triple-negative breast cancer (TNBC) is a more aggressive and metastatic subtype of breast cancer that is initially responsive to treatment of microtubule-targeting agents (MTA) such as taxanes. Recently, we reported the characterization of AMG 900, an orally bioavailable, potent, and highly selective pan-Aurora kinase inhibitor that is active in multidrug-resistant cell lines. In this report, we investigate the activity of AMG 900 alone and in combination with two distinct classes of MTAs (taxanes and epothilones) in multidrug-resistant TNBC cell lines and xenografts. In TNBC cells, AMG 900 inhibited phosphorylation of histone H3 on Ser(10), a proximal substrate of Aurora-B, and induced polyploidy and apoptosis. Furthermore, AMG 900 potentiated the antiproliferative effects of paclitaxel and ixabepilone at low nanomolar concentrations. In mice, AMG 900 significantly inhibited the growth of MDA-MB-231 (F(11); parental), MDA-MB-231 (F(11)) PTX-r (paclitaxel-resistant variant), and DU4475 xenografts. The combination of AMG 900 with docetaxel enhanced tumor inhibition in MDA-MB-231 (F(11)) xenografts compared with either monotherapy. Notably, combining AMG 900 with ixabepilone resulted in regressions of MDA-MB-231 (F(11)) PTX-r xenografts, in which more than 50% of the tumors failed to regrow 75 days after the cessation of drug treatment. These findings suggest that AMG 900, alone and in combination with MTAs, may be an effective intervention strategy for the treatment of metastatic breast cancer and provide potential therapeutic options for patients with multidrug-resistant tumors.
<p>Supplementary Materials and Methods; Supplementary Figure 1: Effects of AMG 900 on nuclear morphology and centrosome features are consistent with aurora-B inhibition in MDA-MB-231 cell line; Supplementary Figure 2: Elevated expression of ABC transporter gene ABCB1 and ABCB4 in MDA-MB-231 (F11) PTX-r cell line; Supplementary Figure 3: Cell-cycle profiles of TNBC cell lines treated with paclitaxel or ixabepilone.</p>
<div>Abstract<p>Aurora kinase A and B have essential and non-overlapping roles in mitosis, with elevated expression in a subset of human cancers, including acute myeloid leukemia (AML). In this study, pan-aurora kinase inhibitor (AKI) AMG 900 distinguishes itself as an anti-leukemic agent that is more uniformly potent against a panel of AML cell lines than are isoform-selective AKIs and classic AML drugs. AMG 900 inhibited AML cell growth by inducing polyploidization and/or apoptosis. AMG 900 and aurora-B–selective inhibitor AZD1152-hQPA showed comparable cellular effects on AML lines that do not harbor a <i>FLT3</i>-ITD mutation. AMG 900 was active against P-glycoprotein–expressing AML cells resistant to AZD1152-hQPA and was effective at inducing expression of megakaryocyte-lineage markers (CD41, CD42) on human CHRF-288-11 cells and mouse <i>Jak2</i><sup>V617F</sup> cells. In MOLM-13 cells, inhibition of p-histone H3 by AMG 900 was associated with polyploidy, extra centrosomes, accumulation of p53 protein, apoptosis, and cleavage of Bcl-2 protein. Co-administration of cytarabine (Ara-C) with AMG 900 potentiated cell killing in a subset of AML lines, with evidence of attenuated polyploidization. AMG 900 inhibited the proliferation of primary human bone marrow cells in culture, with a better proliferation recovery profile relative to classic antimitotic drug docetaxel. <i>In vivo</i>, AMG 900 significantly reduced tumor burden in a systemic MOLM-13 xenograft model where we demonstrate the utility of 3′-deoxy-3′-<sup>18</sup>F-fluorothymidine [<sup>18</sup>F]FLT positron emission tomographic (PET)–CT imaging to measure the antiproliferative effects of AMG 900 in skeletal tissues in mice.</p></div>
<p>Supplementary Figure S1 shows the cellular effects of AKIs and anti-leukemic agents across a panel of human AML cell lines. Supplementary Figure S2 shows expression of aurora-A and aurora-B protein levels in four AML cell lines. Supplementary Figure S3 shows AMG 900 induces a dose-dependent increase in polyploidy, apoptosis, and p53 protein levels in MOLM-13 cells. Supplementary Figure S4 shows AMG 900 plus Ara-C combination matrix and CI determination in MOLM-13 cells. Supplementary Figure S5 shows AMG 900 induced apoptosis is attenuated by peptide inhibitors of caspases in MOLM-13 cells. Supplementary Figure S6 shows FC gating strategy for annexin-V coupled JC-1 assay. Supplementary Figure S7 shows the anti-proliferative effects of AMG 900 and AZD1152-hQPA on primary human bone marrow mononuclear cells in culture. Supplementary Figure S8 shows a moderate reduction in mouse body weight after AMG 900 treatment.</p>
Abstract 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 and triple-negative breast cancer have elevated levels of CIN and frequently harbor TP53 gene alterations and are poorly served by current treatment options. These two CIN+ cancer types also share mutually exclusive genetic alterations in BRCA1 and CCNE1 cancer genes. KIF18A is a mitotic kinesin motor protein that localizes to the plus-end tips of kinetochore microtubule (MT) spindle fibers, where it regulates chromosome alignment during cell division. KIF18A is overexpressed in a subset of human cancers, and its elevated expression is associated with tumor aggressiveness. Recent reports provide compelling evidence that genetic ablation of KIF18A reduced the viability of CIN cancer cells (Marquis et al. Nature Com 2021, Quinton et al. Nature 2021, Cohen-Sharir et al. Nature 2021). Here, we report the discovery and preclinical characterization of AMG 650, a potent and selective inhibitor of KIF18A with a compelling anti-cancer profile distinct from other cell cycle and anti-mitotic drug targets. Structural insights gained by cryo-EM illustrate the unique binding mode of AMG 650 to an allosteric pocket at the interface of KIF18A motor α4 and α6 helices and α-tubulin. AMG 650 selectively inhibits KIF18A MT-ATPase motor activity (IC50 = 48 nM) and exhibits specificity against a panel of diverse motor proteins. In cells, AMG 650 is active at double-digit nM concentrations and phenocopies KIF18A genetic KD/KO dependencies across a panel of DNA-barcoded cancer cell lines. AMG 650 selectively activates the mitotic checkpoint resulting in multipolarity and apoptosis in breast and ovarian cancer cell lines enriched with CIN features. Notably, AMG 650 has minimal effects on proliferating human bone marrow mononuclear cells in culture at concentrations active on sensitive cancer cells (>100X window). In vivo, AMG 650 has low clearance, long half-life, and good oral bioavailability across preclinical species. In mice, oral administration of AMG 650 induces a dose-dependent pharmacodynamic response (pH3 mitotic marker) that is sustained for 24 hours in OVCAR-3 tumor model. Importantly, continuous once-daily dosing with AMG 650 shows robust anti-cancer activity with evidence of durable tumor regressions in a subset of human ovarian and breast CDX/PDX tumor models at well-tolerated doses. Lastly, the combination of AMG 650 with PARP inhibitor Olaparib enhances anti-cancer activity relative to single agent alone in BRCA1- and CCNE1-altered tumor models at well-tolerated doses. Collectively, our results provide a rational therapeutic strategy for selective targeting of CIN cancers via AMG 650, a first-in-class KIF18A inhibitor. Citation Format: Brian Belmontes, Jodi Moriguchi, Grace Chung, Jan Sun, Maria Stefania S. Ninniri, Kelly Hanestad, Kui Chen, John D. McCarter, Upendra P. Dahal, Sudipa Ghimire-Rijal, Yue Hao, Christopher P. Mohr, Xinchao Yu, Matthew G. Rees, Melissa Ronan, Jennifer Roth, Sheroy Minocherhomji, Jennifer R. Allen, Matthew P. Bourbeau, Paul E. Hughes, Nuria A Tamayo, Marc N. Payton. Discovery and preclinical characterization of AMG 650, a first-in-class inhibitor of kinesin KIF18A motor protein with potent activity against chromosomally unstable cancers [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 516.
<div>Abstract<p>Aurora kinase A and B have essential and non-overlapping roles in mitosis, with elevated expression in a subset of human cancers, including acute myeloid leukemia (AML). In this study, pan-aurora kinase inhibitor (AKI) AMG 900 distinguishes itself as an anti-leukemic agent that is more uniformly potent against a panel of AML cell lines than are isoform-selective AKIs and classic AML drugs. AMG 900 inhibited AML cell growth by inducing polyploidization and/or apoptosis. AMG 900 and aurora-B–selective inhibitor AZD1152-hQPA showed comparable cellular effects on AML lines that do not harbor a <i>FLT3</i>-ITD mutation. AMG 900 was active against P-glycoprotein–expressing AML cells resistant to AZD1152-hQPA and was effective at inducing expression of megakaryocyte-lineage markers (CD41, CD42) on human CHRF-288-11 cells and mouse <i>Jak2</i><sup>V617F</sup> cells. In MOLM-13 cells, inhibition of p-histone H3 by AMG 900 was associated with polyploidy, extra centrosomes, accumulation of p53 protein, apoptosis, and cleavage of Bcl-2 protein. Co-administration of cytarabine (Ara-C) with AMG 900 potentiated cell killing in a subset of AML lines, with evidence of attenuated polyploidization. AMG 900 inhibited the proliferation of primary human bone marrow cells in culture, with a better proliferation recovery profile relative to classic antimitotic drug docetaxel. <i>In vivo</i>, AMG 900 significantly reduced tumor burden in a systemic MOLM-13 xenograft model where we demonstrate the utility of 3′-deoxy-3′-<sup>18</sup>F-fluorothymidine [<sup>18</sup>F]FLT positron emission tomographic (PET)–CT imaging to measure the antiproliferative effects of AMG 900 in skeletal tissues in mice.</p></div>
Efforts to improve upon the physical properties and metabolic stability of Aurora kinase inhibitor 14a revealed that potency against multidrug-resistant cell lines was compromised by increased polarity. Despite its high in vitro metabolic intrinsic clearance, 23r (AMG 900) showed acceptable pharmacokinetic properties and robust pharmacodynamic activity. Projecting from in vitro data to in vivo target coverage was not practical due to disjunctions between enzyme and cell data, complex and apparently contradictory indicators of binding kinetics, and unmeasurable free fraction in plasma. In contrast, it was straightforward to relate pharmacokinetics to pharmacodynamics and efficacy by following the time above a threshold concentration. On the basis of its oral route of administration, a selectivity profile that favors Aurora-driven pharmacology and its activity against multidrug-resistant cell lines, 23r was identified as a potential best-in-class Aurora kinase inhibitor. In phase 1 dose expansion studies with G-CSF support, 23r has shown promising single agent activity.
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