Design and Evaluation of Phosphonamidate-Linked Exatecan Constructs for Highly Loaded, Stable, and Efficacious Antibody-Drug Conjugates.

Topoisomerase I (TOP1) Inhibitors constitute an emerging payload class to engineer antibody-drug conjugates (ADC) as next-generation biopharmaceutical for cancer treatment. Existing ADCs are using camptothecin payloads with lower potency and suffer from limited stability in circulation. With this study, we introduce a novel camptothecin-based linker-payload platform based on the highly potent camptothecin derivative exatecan. First, we describe general challenges that arise from the hydrophobic combination of exatecan and established dipeptidyl p-aminobenzyl-carbamate (PAB) cleavage sites such as reduced antibody conjugation yields and ADC aggregation. After evaluating several linker-payload structures, we identified ethynyl-phosphonamidates in combination with a discrete PEG24 chain to compensate for the hydrophobic PAB-exatecan moiety. Furthermore, we demonstrate that the identified linker-payload structure enables the construction of highly loaded DAR8 ADCs with excellent solubility properties. Head-to-head comparison with Enhertu, an approved camptothecin-based ADC, revealed improved target-mediated killing of tumor cells, excellent bystander killing, drastically improved linker stability in vitro and in vivo and superior in vivo efficacy over four tested dose levels in a xenograft model. Moreover, we show that ADCs based on the novel exatecan linker-payload platform exhibit antibody-like pharmacokinetic properties, even when the ADCs are highly loaded with eight drug molecules per antibody. This ADC platform constitutes a new and general solution to deliver TOP1 inhibitors with highest efficiency to the site of the tumor, independent of the antibody and its target, and is thereby broadly applicable to various cancer indications.

Global site-specific neddylation profiling reveals that NEDDylated cofilin regulates actin dynamics.

Neddylation is the post-translational protein modification most closely related to ubiquitination. Whereas the ubiquitin-like protein NEDD8 is well studied for its role in activating cullin-RING E3 ubiquitin ligases, little is known about other substrates. We developed serial NEDD8-ubiquitin substrate profiling (sNUSP), a method that employs NEDD8 R74K knock-in HEK293 cells, allowing discrimination of endogenous NEDD8- and ubiquitin-modification sites by MS after Lys-C digestion and K-εGG-peptide enrichment. Using sNUSP, we identified 607 neddylation sites dynamically regulated by the neddylation inhibitor MLN4924 and the de-neddylating enzyme NEDP1, implying that many non-cullin proteins are neddylated. Among the candidates, we characterized lysine 112 of the actin regulator cofilin as a novel neddylation event. Global inhibition of neddylation in developing neurons leads to cytoskeletal defects, altered actin dynamics and neurite growth impairments, whereas site-specific neddylation of cofilin at K112 regulates neurite outgrowth, suggesting that cofilin neddylation contributes to the regulation of neuronal actin organization.

Publisher Correction: Global site-specific neddylation profiling reveals that NEDDylated cofilin regulates actin dynamics.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Chronic CRH depletion from GABAergic, long-range projection neurons in the extended amygdala reduces dopamine release and increases anxiety.

The interplay between corticotropin-releasing hormone (CRH) and the dopaminergic system has predominantly been studied in addiction and reward, while CRH-dopamine interactions in anxiety are scarcely understood. We describe a new population of CRH-expressing, GABAergic, long-range-projecting neurons in the extended amygdala that innervate the ventral tegmental area and alter anxiety following chronic CRH depletion. These neurons are part of a distinct CRH circuit that acts anxiolytically by positively modulating dopamine release.

Neddylation inhibition impairs spine development, destabilizes synapses and deteriorates cognition.

Neddylation is a ubiquitylation-like pathway that controls cell cycle and proliferation by covalently conjugating Nedd8 to specific targets. However, its role in neurons, nonreplicating postmitotic cells, remains unexplored. Here we report that Nedd8 conjugation increased during postnatal brain development and is active in mature synapses, where many proteins are neddylated. We show that neddylation controls spine development during neuronal maturation and spine stability in mature neurons. We found that neddylated PSD-95 was present in spines and that neddylation on Lys202 of PSD-95 is required for the proactive role of the scaffolding protein in spine maturation and synaptic transmission. Finally, we developed Nae1(CamKIIα-CreERT2) mice, in which neddylation is conditionally ablated in adult excitatory forebrain neurons. These mice showed synaptic loss, impaired neurotransmission and severe cognitive deficits. In summary, our results establish neddylation as an active post-translational modification in the synapse regulating the maturation, stability and function of dendritic spines.

MicroRNA-9 controls dendritic development by targeting REST.

MicroRNAs (miRNAs) are conserved noncoding RNAs that function as posttranscriptional regulators of gene expression. miR-9 is one of the most abundant miRNAs in the brain. Although the function of miR-9 has been well characterized in neural progenitors, its role in dendritic and synaptic development remains largely unknown. In order to target miR-9 in vivo, we developed a transgenic miRNA sponge mouse line allowing conditional inactivation of the miR-9 family in a spatio-temporal-controlled manner. Using this novel approach, we found that miR-9 controls dendritic growth and synaptic transmission in vivo. Furthermore, we demonstrate that miR-9-mediated downregulation of the transcriptional repressor REST is essential for proper dendritic growth.

Behavioral phenotyping of Nestin-Cre mice: implications for genetic mouse models of psychiatric disorders.

Genetic mouse models based on the Cre-loxP system have been extensively used to explore the influence of specific gene deletions on different aspects of behavioral neurobiology. However, the interpretation of the effects attributed to the gene deletion might be obscured by potential side effects secondary to the Cre recombinase transgene insertion or Cre activity, usually neither controlled nor reported. Here, we performed a comprehensive behavioral analysis of endophenotypes of neuropsychiatric disorders in the extensively used Nestin(Cre) mouse line, commonly employed to restrict genetic modifications to the CNS. We observed no alterations in locomotion, general exploratory activity, learning and memory, sociability, startle response and sensorimotor gating. Although the overall response to stimuli triggering anxiety-like behaviors remained unaltered in Nestin(Cre) mice, a strong impairment in the acquisition of both contextual- and cued-conditioned fear was observed. These results underline the importance of adequately controlling the behavioral performance of the employed Cre-lines per-se in pre-clinical neurobehavioral research.

Glutamatergic and dopaminergic neurons mediate anxiogenic and anxiolytic effects of CRHR1.

The corticotropin-releasing hormone receptor 1 (CRHR1) critically controls behavioral adaptation to stress and is causally linked to emotional disorders. Using neurochemical and genetic tools, we determined that CRHR1 is expressed in forebrain glutamatergic and γ-aminobutyric acid-containing (GABAergic) neurons as well as in midbrain dopaminergic neurons. Via specific CRHR1 deletions in glutamatergic, GABAergic, dopaminergic, and serotonergic cells, we found that the lack of CRHR1 in forebrain glutamatergic circuits reduces anxiety and impairs neurotransmission in the amygdala and hippocampus. Selective deletion of CRHR1 in midbrain dopaminergic neurons increases anxiety-like behavior and reduces dopamine release in the prefrontal cortex. These results define a bidirectional model for the role of CRHR1 in anxiety and suggest that an imbalance between CRHR1-controlled anxiogenic glutamatergic and anxiolytic dopaminergic systems might lead to emotional disorders.

Urocortin 3 modulates social discrimination abilities via corticotropin-releasing hormone receptor type 2.

Urocortin 3 (UCN3) is strongly expressed in specific nuclei of the rodent brain, at sites distinct from those expressing urocortin 1 and urocortin 2, the other endogenous ligands of corticotropin-releasing hormone receptor type 2 (CRH-R2). To determine the physiological role of UCN3, we generated UCN3-deficient mice, in which the UCN3 open reading frame was replaced by a tau-lacZ reporter gene. By means of this reporter gene, the nucleus parabrachialis and the premammillary nucleus were identified as previously unknown sites of UCN3 expression. Additionally, the introduced reporter gene enabled the visualization of axonal projections of UCN3-expressing neurons from the superior paraolivary nucleus to the inferior colliculus and from the posterodorsal part of the medial amygdala to the principal nucleus of the bed nucleus of the stria terminalis, respectively. The examination of tau-lacZ reporter gene activity throughout the brain underscored a predominant expression of UCN3 in nuclei functionally connected to the accessory olfactory system. Male and female mice were comprehensively phenotyped but none of the applied tests provided indications for a role of UCN3 in the context of hypothalamic-pituitary-adrenocortical axis regulation, anxiety- or depression-related behavior. However, inspired by the prevalent expression throughout the accessory olfactory system, we identified alterations in social discrimination abilities of male and female UCN3 knock-out mice that were also present in male CRH-R2 knock-out mice. In conclusion, our results suggest a novel role for UCN3 and CRH-R2 related to the processing of social cues and to the establishment of social memories.

Immunology, signal transduction, and behavior in hypothalamic-pituitary-adrenal axis-related genetic mouse models.

A classical view of the neuroendocrine-immune network assumes bidirectional interactions where pro-inflammatory cytokines influence hypothalamic-pituitary-adrenal (HPA) axis-derived hormones that subsequently affect cytokines in a permanently servo-controlled circle. Nevertheless, this picture has been continuously evolving over the last years as a result of the discovery of redundant expression and extended functions of many of the molecules implicated. Thus, cytokines are not only expressed in cells of the immune system but also in the central nervous system, and many hormones present at hypothalamic-pituitary level are also functionally expressed in the brain as well as in other peripheral organs, including immune cells. Because of this intermingled network of molecules redundantly expressed, the elucidation of the unique roles of HPA axis-related molecules at every level of complexity is one of the major challenges in the field. Genetic engineering in the mouse offers the most convincing method for dissecting in vivo the specific roles of distinct molecules acting in complex networks. Thus, various immunological, behavioral, and signal transduction studies performed with different HPA axis-related mutant mouse lines to delineate the roles of beta-endorphin, the type 1 receptor of corticotropin-releasing hormone (CRHR1), and its ligand CRH will be discussed here.