Antibody-drug conjugates (ADCs) that are currently on the market or in clinical trials are predominantly based on two drug classes: auristatins and maytansinoids. Both are tubulin binders and block the cell in its progression through mitosis. We set out to develop a new class of linker-drugs based on duocarmycins, potent DNA-alkylating agents that are composed of a DNA-alkylating and a DNA-binding moiety and that bind into the minor groove of DNA. Linker-drugs were evaluated as ADCs by conjugation to the anti-HER2 antibody trastuzumab via reduced interchain disulfides. Duocarmycin 3b, bearing an imidazo[1,2-a]pyridine-based DNA-binding unit, was selected as the drug moiety, notably because of its rapid degradation in plasma. The drug was incorporated into the linker-drugs in its inactive prodrug form, seco-duocarmycin 3a. Linker attachment to the hydroxyl group in the DNA-alkylating moiety was favored over linking to the DNA-binding moiety, as the first approach gave more consistent results for in vitro cytotoxicity and generated ADCs with excellent human plasma stability. Linker-drug 2 was eventually selected based on the properties of the corresponding trastuzumab conjugate, SYD983, which had an average drug-to-antibody ratio (DAR) of about 2. SYD983 showed subnanomolar potencies against multiple human cancer cell lines, was highly efficacious in a BT-474 xenograft model, and had a long half-life in cynomolgus monkeys, in line with high stability in monkey and human plasma. Studies comparing ADCs with a different average DAR showed that a higher average DAR leads to increased efficacy but also to somewhat less favorable physicochemical and toxicological properties. Fractionation of SYD983 with hydrophobic interaction chromatography resulted in SYD985, consisting of about 95% DAR2 and DAR4 species in an approximate 2:1 ratio and having an average DAR of about 2.8. SYD985 combines several favorable properties from the unfractionated ADCs with an improved homogeneity. It was selected for further development and recently entered clinical Phase I evaluation.
SYD985 is a HER2-targeting antibody-drug conjugate (ADC) based on trastuzumab and vc-seco-DUBA, a cleavable linkerduocarmycin payload. To evaluate the therapeutic potential of this new ADC, mechanistic in vitro studies and in vivo patientderived 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 3þ 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 3þ, 2þ, or 1þ 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 3þ, 2þ, and 1þ models, whereas T-DM1 only showed significant antitumor activity in HER2 3þ 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. Mol Cancer Ther; 14(3); 692-703. Ó2015 AACR.
Background: CCX-CKR is considered to be a chemokine decoy receptor that is unable to signal. Results: Chemokines induce -arrestin recruitment to CCX-CKR and pertussis toxin (PTX)-dependent CRE activity. Conclusion: PTX-sensitive G proteins hinder CCX-CKR coupling to other G proteins and consequently keep receptors silent. Significance: Recruitment of -arrestin to CCX-CKR requests re-evaluation of the signaling capacity of this atypical 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
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”. Here, 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, where multiple chemokines are secreted simultaneously.
Carboxylesterase 1c (CES1c) is responsible for linker-drug instability and poor pharmacokinetics (PK) of several antibody-drug conjugates (ADC) in mice, but not in monkeys or humans. Preclinical development of these ADCs could be improved if the PK in mice would more closely resemble that of humans and is not affected by an enzyme that is irrelevant for humans. SYD985, a HER2-targeting ADC based on trastuzumab and linker-drug vc--DUBA, is also sensitive to CES1c. In the present studies, we first focused on the interaction between CES1c and SYD985 by size- exclusion chromatography, Western blotting, and LC/MS-MS analysis, using recombinant CES1c and plasma samples. Intriguingly, CES1c activity not only results in release of the active toxin DUBA but also in formation of a covalent bond between CES1c and the linker of vc--DUBA. Mass spectrometric studies enabled identification of the CES1c cleavage site on the linker-drug and the structure of the CES1c adduct. To assess the impact, CES1c SCID mice were generated that showed stable PK for SYD985, comparable to that in monkeys and humans. Patient-derived xenograft (PDX) studies in these mice showed enhanced efficacy compared with PDX studies in CES1c mice and provided a more accurate prediction of clinical efficacy of SYD985, hence delivering better quality data. It seems reasonable to assume that CES1c SCID mice can increase quality in ADC development much broader for all ADCs that carry linker-drugs susceptible to CES1c, without the need of chemically modifying the linker-drug to specifically increase PK in mice. .
β-Arrestin recruitment assays provide a generic assay platform for drug discovery on G-protein-coupled receptors (GPCRs). The PathHunter™ assay technology developed by DiscoveRx (Fremont, CA) uses enzyme fragment complementation of β-galactosidase to measure receptor-β-arrestin proximity by chemiluminescence. This study describes an agonistic screen on the human endothelial differentiation sphingolipid GPCR 1 (EDG1), also known as S1P1, using PathHunter™ β-arrestin recruitment technology. Screening of a collection of 345,052 compounds yielded 2157 agonistic hits. Only 10 of these compounds showed β-arrestin recruitment activity on a nonrelated receptor, indicating high accuracy and specificity of the assay. The authors show that receptor activation with reference agonists can be detected within the same EDG1 PathHunter™ cell line at the level of β-arrestin recruitment, G i/o protein-mediated inhibition of cyclic adenosine monophosphate (cAMP), and activation of downstream phosphorylation of extracellular signal-regulated protein kinases. The degree of β-arrestin recruitment was largely unaffected upon blockade of G i/o protein signaling with pertussis toxin, whereas kinetic studies demonstrated a lower rate of β-arrestin-receptor association. In contrast, inhibition of cAMP and phosphorylation of extracellular signal-regulated protein kinases were fully G i/o protein regulated. The data indicate that the β-arrestin enzyme fragment complementation cell line can be used not only for agonistic screening of GPCRs but also for the identification of "biased ligands" (i.e., compounds that differ in G-protein coupling and β-arrestin-mediated cellular effects). (Journal of Biomolecular Screening 2008:986-998)
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