THYROTROPIN RECEPTOR ANTAGONISM BY A NOVEL SMALL MOLECULE: PRE-CLINICAL IN VITRO OBSERVATIONS

BACKGROUND

Treatment of Graves' hyperthyroidism (GH) and Graves' orbitopathy (GO) is far from adequate, hence new substances, which specifically target the autoantigens in GH/GO are warranted. This study determined the preclinical in vitro efficacy of SYD5115, a novel low molecular weight compound, which inhibits the thyrotropin receptor (TSH-R).

METHODS

The TSH-R inhibiting capability of SYD5115 was tested through stimulation of wild type and chimeric TSH-R expressed in Chinese hamster ovary (CHO) cells using-two functional (stimulatory and blocking) cell-based TSH-R-Ab bioassays. TSH-R expressing human orbital fibroblasts, collected from GH+GO patients (GOF), were stimulated with the monoclonal antibody M22 or with stimulatory TSH-R-Ab (TSAb)-positive sera with cyclic adenosine monophosphate (cAMP) or hyaluronic acid (HA) release as read-outs. The effect of SYD5115 on the viability of GOF was tested in 4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium bromide and scratch cell growth assays.

RESULTS

SYD5115 significantly and dose-dependently inhibited the TSH-R activation through M22 or TSAb-positive sera in all performed bioassays. Inhibition showed similar levels in the TSAb reporter bioassay and in the cAMP assay with GOF. The % inhibition and compound concentration showed a sigmoidal relationship, with all seven TSAb positive sera markedly inhibited by SYD5115. A SYD5115 dose-dependent inhibition of M22 (10 ng/ml, 6 hours)-stimulated HA and/or cAMP-release from GOF was observed. Strong SYD5115-induced inhibitions of M22-stimulated cAMP production in GOF were registered with SYD5115 concentrations of 1 (p=0.0029), 10 (p<0.0001), 100 (p<0.0001), 1,000 (p<0.0001), and 10,000 (p<0.0001) nM, respectively. SYD5115-induced inhibition of M22-stimulated HA production was noted with SYD5115 concentrations of 100 (p=0.0392), 1,000 (p=0.0431), and 10,000 (p=0.0245) nM, respectively. The inhibitory activity of SYD5115 was confirmed in a human osteosarcoma U2OS cell line stably expressing human TSH-R with cAMP as read-out. SYD5115 induced 100% inhibition of the M22-induced cAMP levels with a potency of 193 nM. Compared to control, SYD5115 did neither impact the growth nor the migration of cultivated GOF. In addition, SYD5115 did not alter the viability of GOF.

CONCLUSIONS

SYD5115 blocked M22- and TSAb-induced TSH-R activity with a nanomolar potency in TSH-R overexpressed CHO cells as well as primary GOF, which demonstrates the ability of this small molecule to block TSH-R overactivity.

BYON4228 is a pan-allelic antagonistic SIRPα antibody that potentiates destruction of antibody-opsonized tumor cells and lacks binding to SIRPγ on T cells

BACKGROUND

Preclinical studies have firmly established the CD47-signal-regulatory protein (SIRP)α axis as a myeloid immune checkpoint in cancer, and this is corroborated by available evidence from the first clinical studies with CD47 blockers. However, CD47 is ubiquitously expressed and mediates functional interactions with other ligands as well, and therefore targeting of the primarily myeloid cell-restricted inhibitory immunoreceptor SIRPα may represent a better strategy.

METHOD

We generated BYON4228, a novel SIRPα-directed antibody. An extensive preclinical characterization was performed, including direct comparisons to previously reported anti-SIRPα antibodies.

RESULTS

BYON4228 is an antibody directed against SIRPα that recognizes both allelic variants of SIRPα in the human population, thereby maximizing its potential clinical applicability. Notably, BYON4228 does not recognize the closely related T-cell expressed SIRPγ that mediates interactions with CD47 as well, which are known to be instrumental in T-cell extravasation and activation. BYON4228 binds to the N-terminal Ig-like domain of SIRPα and its epitope largely overlaps with the CD47-binding site. BYON4228 blocks binding of CD47 to SIRPα and inhibits signaling through the CD47-SIRPα axis. Functional studies show that BYON4228 potentiates macrophage-mediated and neutrophil-mediated killing of hematologic and solid cancer cells in vitro in the presence of a variety of tumor-targeting antibodies, including trastuzumab, rituximab, daratumumab and cetuximab. The silenced Fc region of BYON4228 precludes immune cell-mediated elimination of SIRPα-positive myeloid cells, implying anticipated preservation of myeloid immune effector cells in patients. The unique profile of BYON4228 clearly distinguishes it from previously reported antibodies representative of agents in clinical development, which either lack recognition of one of the two SIRPα polymorphic variants (HEFLB), or cross-react with SIRPγ and inhibit CD47-SIRPγ interactions (SIRPAB-11-K322A, 1H9), and/or have functional Fc regions thereby displaying myeloid cell depletion activity (SIRPAB-11-K322A). In vivo, BYON4228 increases the antitumor activity of rituximab in a B-cell Raji xenograft model in human SIRPα_BIT transgenic mice. Finally, BYON4228 shows a favorable safety profile in cynomolgus monkeys.

CONCLUSIONS

Collectively, this defines BYON4228 as a preclinically highly differentiating pan-allelic SIRPα antibody without T-cell SIRPγ recognition that promotes the destruction of antibody-opsonized cancer cells. Clinical studies are planned to start in 2023.

A Platform for the Generation of Site-Specific Antibody-Drug Conjugates That Allows for Selective Reduction of Engineered Cysteines

Engineering cysteines at specific sites in antibodies to create well-defined ADCs for the treatment of cancer is a promising approach to increase the therapeutic index and helps to streamline the manufacturing process. Here, we report the development of an in silico screening procedure to select for optimal sites in an antibody to which a hydrophobic linker-drug can be conjugated. Sites were identified inside the cavity that is naturally present in the Fab part of the antibody. Conjugating a linker-drug to these sites demonstrated the ability of the antibody to shield the hydrophobic character of the linker-drug while resulting ADCs maintained their cytotoxic potency in vitro. Comparison of site-specific ADCs versus randomly conjugated ADCs in an in vivo xenograft model revealed improved efficacy and exposure. We also report a selective reducing agent that is able to reduce the engineered cysteines while leaving the interchain disulfides in the oxidized state. This enables us to manufacture site-specific ADCs without introducing impurities associated with the conventional reduction/oxidation procedure for site-specific conjugation.

SYD985, a Novel Duocarmycin-Based HER2-Targeting Antibody-Drug Conjugate, Shows Antitumor Activity in Uterine Serous Carcinoma with HER2/Neu Expression

Uterine serous carcinoma (USC) is an aggressive form of endometrial cancer. Up to 35% of USC may overexpress the HER2/neu oncogene at strong (i.e., 3+) levels by IHC while an additional 40% to 50% express HER2/neu at moderate (2+) or low (1+) levels. We investigated the efficacy of SYD985, (Synthon Biopharmaceuticals), a novel HER2-targeting antibody-drug conjugate (ADC) composed of the mAb trastuzumab linked to a highly potent DNA-alkylating agent (i.e., duocarmycin) in USC. We also compared the antitumor activity of SYD985 in head-to-head experiments to trastuzumab emtansine (T-DM1), a FDA-approved ADC, against multiple primary USC cell lines expressing different levels of HER2/neu in in vitro and in vivo experiments. Using antibody-dependent cellular cytotoxicity (ADCC), proliferation, viability, and bystander killing assays as well as propidium iodide-based flow cytometry assays and multiple in vivo USC mouse xenograft models, we demonstrate for the first time that SYD985 is a novel ADC with activity against USC with strong (3+) as well as low to moderate (i.e., 1+/2+) HER2/neu expression. SYD985 is 10- to 70-fold more potent than T-DM1 in comparative experiments and, unlike T-DM1, it is active against USC demonstrating moderate/low or heterogeneous HER2/neu expression. Clinical studies with SYD985 in patients harboring chemotherapy-resistant USC with low, moderate, and high HER2 expression are warranted. Mol Cancer Ther; 15(8); 1900-9. ©2016 AACR.

The Preclinical Profile of the Duocarmycin-Based HER2-Targeting ADC SYD985 Predicts for Clinical Benefit in Low HER2-Expressing Breast Cancers

SYD985 is a HER2-targeting antibody-drug conjugate (ADC) based on trastuzumab and vc-seco-DUBA, a cleavable linker-duocarmycin payload. To evaluate the therapeutic potential of this new ADC, mechanistic in vitro studies and in vivo patient-derived xenograft (PDX) studies were conducted to compare SYD985 head-to-head with T-DM1 (Kadcyla), another trastuzumab-based ADC. SYD985 and T-DM1 had similar binding affinities to HER2 and showed similar internalization. In vitro cytotoxicity assays showed similar potencies and efficacies in HER2 3+ cell lines, but in cell lines with low HER2 expression, SYD985 was 3- to 50-fold more potent than T-DM1. In contrast with T-DM1, SYD985 efficiently induced bystander killing in vitro in HER2-negative (HER2 0) cells mixed with HER2 3+, 2+, or 1+ cell lines. At pH conditions relevant for tumors, cathepsin-B cleavage studies showed efficient release of the active toxin by SYD985 but not by T-DM1. These in vitro data suggest that SYD985 might be a more potent ADC in HER2-expressing tumors in vivo, especially in low HER2-expressing and/or in heterogeneous tumors. In line with this, in vivo antitumor studies in breast cancer PDX models showed that SYD985 is very active in HER2 3+, 2+, and 1+ models, whereas T-DM1 only showed significant antitumor activity in HER2 3+ breast cancer PDX models. These properties of SYD985 may enable expansion of the target population to patients who have low HER2-expressing breast cancer, a patient population with still unmet high medical need.

Chemokine cooperativity is caused by competitive glycosaminoglycan binding

Chemokines comprise a family of secreted proteins that activate G protein-coupled chemokine receptors and thereby control the migration of leukocytes during inflammation or immune surveillance. The positional information required for such migratory behavior is governed by the binding of chemokines to membrane-tethered glycosaminoglycans (GAGs), which establishes a chemokine concentration gradient. An often observed but incompletely understood behavior of chemokines is the ability of unrelated chemokines to enhance the potency with which another chemokine subtype can activate its cognate receptor. This phenomenon has been demonstrated to occur between many chemokine combinations and across several model systems and has been dubbed chemokine cooperativity. In this study, we have used GAG binding-deficient chemokine mutants and cell-based functional (migration) assays to demonstrate that chemokine cooperativity is caused by competitive binding of chemokines to GAGs. This mechanistic explanation of chemokine cooperativity provides insight into chemokine gradient formation in the context of inflammation, in which multiple chemokines are secreted simultaneously.

β-Arrestin recruitment and G protein signaling by the atypical human chemokine decoy receptor CCX-CKR

Chemokine receptors form a large subfamily of G protein-coupled receptors that predominantly activate heterotrimeric Gi proteins and are involved in immune cell migration. CCX-CKR is an atypical chemokine receptor with high affinity for CCL19, CCL21, and CCL25 chemokines, but is not known to activate intracellular signaling pathways. However, CCX-CKR acts as decoy receptor and efficiently internalizes these chemokines, thereby preventing their interaction with other chemokine receptors, like CCR7 and CCR9. Internalization of fluorescently labeled CCL19 correlated with β-arrestin2-GFP translocation. Moreover, recruitment of β-arrestins to CCX-CKR in response to CCL19, CCL21, and CCL25 was demonstrated using enzyme-fragment complementation and bioluminescence resonance energy transfer methods. To unravel why CCX-CKR is unable to activate Gi signaling, CCX-CKR chimeras were constructed by substituting its intracellular loops with the corresponding CCR7 or CCR9 domains. The signaling properties of chimeric CCX-CKR receptors were characterized using a cAMP-responsive element (CRE)-driven reporter gene assay. Unexpectedly, wild type CCX-CKR and a subset of the chimeras induced an increase in CRE activity in response to CCL19, CCL21, and CCL25 in the presence of the Gi inhibitor pertussis toxin. CCX-CKR signaling to CRE required an intact DRY motif. These data suggest that inactive Gi proteins impair CCX-CKR signaling most likely by hindering the interaction of this receptor with pertussis toxin-insensitive G proteins that transduce signaling to CRE. On the other hand, recruitment of the putative signaling scaffold β-arrestin to CCX-CKR in response to chemokines might allow activation of yet to be identified signal transduction pathways.

β-Arrestin-biased signaling of PTH analogs of the type 1 parathyroid hormone receptor

Parathyroid hormone (PTH) is an anabolic agent that mediates bone formation through activation of the Gα(s)-, Gα(q)- and β-arrestin-coupled parathyroid hormone receptor type 1 (PTH1R). Pharmacological evidence based on the effect of PTH(7-34), a PTH derivative that is said to preferentially activate β-arrestin signaling through PTH1R, suggests that PTH1R-activated β-arrestin signaling mediates anabolic effects on bone. Here, we performed a thorough evaluation of PTH(7-34) signaling behaviour using quantitative assays for β-arrestin recruitment, Gα(s)- and Gα(q)-signaling. We found that PTH(7-34) inhibited PTH-induced cAMP accumulation, but was unable to induce β-arrestin recruitment, PTH1R internalization and ERK1/2 phosphorylation in HEK293, CHO and U2OS cells. Thus, the β-arrestin bias of PTH(7-34) is not apparent in every cell type examined, suggesting that correlating in vivo effects of PTH(7-34) to in vitro pharmacology should be done with caution.

Pharmacological characterization of receptor redistribution and beta-arrestin recruitment assays for the cannabinoid receptor 1

Receptor redistribution and beta-arrestin recruitment assays provide a G-protein-subtype-independent method to measure ligand-stimulated activation of G-protein-coupled receptors. In particular beta-arrestin assays are becoming an increasingly popular tool for drug discovery. The authors have compared a high-content-imaging-based Redistribution assay and 2 nonimaging-based beta-arrestin recruitment assays, Tango and PathHunter, for the cannabinoid receptor 1. Inasmuch as all 3 assays use receptors that are modified at the C-terminus, the authors verified their pharmacology via detection of Galpha(i) coupling of the receptor in cAMP assays using reference ligands. The potencies and efficacies of the cannabinoid receptor agonists CP55,940 and WIN55,212-2 correlated well between the 3 assays, and are comparable with the measured ligand binding affinities. The inverse agonist SR141716 decreased basal signal in all 3 assays, but only in the Tango bla assay a reliable EC50 could be determined for this compound, suggesting that Tango is the most suitable assay for the identification of new inverse agonists. Both the Redistribution and the PathHunter assay could discriminate partial agonists from full agonists, whereas in the Tango assay partial agonists behaved as full agonists. Only the PathHunter cells allowed detection of cannabinoid receptor activation via beta-arrestin recruitment and Galpha(i)-protein-mediated inhibition of cAMP, thus enabling the identification of biased ligands that differ in these cellular effects. The characteristics and limitations of the different assays are discussed.

Nonpeptidergic allosteric antagonists differentially bind to the CXCR2 chemokine receptor

The chemokine receptor CXCR2 is involved in different inflammatory diseases, like chronic obstructive pulmonary disease, psoriasis, rheumatoid arthritis, and ulcerative colitis; therefore, it is considered an attractive drug target. Different classes of small CXCR2 antagonists have been developed. In this study, we selected seven CXCR2 antagonists from the diarylurea, imidazolylpyrimide, and thiazolopyrimidine class and studied their mechanisms of action at human CXCR2. All compounds are able to displace (125)I-CXCL8 and inhibit CXCL8-induced beta-arrestin2 recruitment. Detailed studies with representatives of each class showed that these compounds displace and antagonize CXCL8, most probably via a noncompetitive, allosteric mechanism. In addition, we radiolabeled the high-affinity CXCR2 antagonist SB265610 [1-(2-bromophenyl)-3-(4-cyano-1H-benzo[d] [1,2,3]-triazol-7-yl)urea] and subjected [(3)H]SB265610 to a detailed analysis. The binding of this radioligand was saturable and reversible. Using [(3)H]SB265610, we found that compounds of the different chemical classes bind to distinct binding sites. Hence, the use of a radiolabeled low-molecular weight CXCR2 antagonist serves as a tool to investigate the different binding sites of CXCR2 antagonists in more detail.

Enzyme Fragment Complementation Binding Assay for p38α Mitogen-Activated Protein Kinase to Study the Binding Kinetics of Enzyme Inhibitors

The majority of protein kinase assays used in drug discovery research are enzyme activity assays. These assays are based on the measurement of phosphorylated protein or peptide substrate, which is the end product of the enzyme reaction. Since most kinase inhibitors are ATP competitive, prediction of the activity of compounds in cellular systems based on potency values in enzyme activity assays is complex, as this should take into account the affinity of the enzyme for ATP and the cellular ATP concentration. The fact that some of the most successful kinase inhibitors, such as STI 571 (imatinib mesylate, Gleevec, Novartis Pharmaceuticals, East Hanover, NJ), act through binding to the inactive isoform of the kinase provides another limitation of enzyme activity assays. Binding assays allow separate measurement of compound affinity to active and inactive kinase and do not require ATP or substrate in the reaction. Recently, a non-radioactive kinase binding assay for p38 mitogen-activated protein kinase has become available from DiscoveRx (Fremont, CA). The assay method, called HitHunter, utilizes enzyme fragment complementation of Escherichia coli beta-galactosidase to generate an assay signal by chemiluminescence. We have reconfigured the commercial assay kit to study the binding kinetics of two known reference inhibitors of the alpha-isoform of p38, the pyridinyl imidazole SB 203580 and the diaryl urea BIRB 796. Our data confirm the slow association kinetics of BIRB 796 as compared to SB 203580, which corresponded with the requirement of a relatively long preincubation time to obtain maximal effect in a cellular assay. Although neither of the two compounds showed preference for either active or inactive p38alpha, our data demonstrate that the HitHunter kinase binding assay can be used to select compounds that specifically target inactive kinase.