Beta-amyloid interacts with and activates the long-form phosphodiesterase PDE4D5 in neuronal cells to reduce cAMP availability.

Inhibition of the cyclic-AMP degrading enzyme phosphodiesterase type 4 (PDE4) in the brains of animal models is protective in Alzheimer's disease (AD). We show for the first time that enzymes from the subfamily PDE4D not only colocalize with beta-amyloid (Aß) plaques in a mouse model of AD but that Aß directly associates with the catalytic machinery of the enzyme. Peptide mapping suggests that PDE4D is the preferential PDE4 subfamily for Aß as it possesses a unique binding site. Intriguingly, exogenous addition of Aß to cells overexpressing the PDE4D5 longform caused PDE4 activation and a decrease in cAMP. We suggest a novel mechanism where PDE4 longforms can be activated by Aß, resulting in the attenuation of cAMP signalling to promote loss of cognitive function in AD.

NF1 mutation-driven neuronal hyperexcitability sets a threshold for tumorigenesis and therapeutic targeting of murine optic glioma.

BACKGROUND: With the recognition that noncancerous cells function as critical regulators of brain tumor growth, we recently demonstrated that neurons drive low-grade glioma initiation and progression. Using mouse models of neurofibromatosis type 1 (NF1)-associated optic pathway glioma (OPG), we showed that Nf1 mutation induces neuronal hyperexcitability and midkine expression, which activates an immune axis to support tumor growth, such that high-dose lamotrigine treatment reduces Nf1-OPG proliferation. Herein, we execute a series of complementary experiments to address several key knowledge gaps relevant to future clinical translation. METHODS: We leverage a collection of Nf1-mutant mice that spontaneously develop OPGs to alter both germline and retinal neuron-specific midkine expression. Nf1-mutant mice harboring several different NF1 patient-derived germline mutations were employed to evaluate neuronal excitability and midkine expression. Two distinct Nf1-OPG preclinical mouse models were used to assess lamotrigine effects on tumor progression and growth in vivo. RESULTS: We establish that neuronal midkine is both necessary and sufficient for Nf1-OPG growth, demonstrating an obligate relationship between germline Nf1 mutation, neuronal excitability, midkine production, and Nf1-OPG proliferation. We show anti-epileptic drug (lamotrigine) specificity in suppressing neuronal midkine production. Relevant to clinical translation, lamotrigine prevents Nf1-OPG progression and suppresses the growth of existing tumors for months following drug cessation. Importantly, lamotrigine abrogates tumor growth in two Nf1-OPG strains using pediatric epilepsy clinical dosing. CONCLUSIONS: Together, these findings establish midkine and neuronal hyperexcitability as targetable drivers of Nf1-OPG growth and support the use of lamotrigine as a potential chemoprevention or chemotherapy agent for children with NF1-OPG.

Disruption of the pro-oncogenic c-RAF-PDE8A complex represents a differentiated approach to treating KRAS-c-RAF dependent PDAC.

Pancreatic ductal adenocarcinoma (PDAC) is considered the third leading cause of cancer mortality in the western world, offering advanced stage patients with few viable treatment options. Consequently, there remains an urgent unmet need to develop novel therapeutic strategies that can effectively inhibit pro-oncogenic molecular targets underpinning PDACs pathogenesis and progression. One such target is c-RAF, a downstream effector of RAS that is considered essential for the oncogenic growth and survival of mutant RAS-driven cancers (including KRASMT PDAC). Herein, we demonstrate how a novel cell-penetrating peptide disruptor (DRx-170) of the c-RAF-PDE8A protein-protein interaction (PPI) represents a differentiated approach to exploiting the c-RAF-cAMP/PKA signaling axes and treating KRAS-c-RAF dependent PDAC. Through disrupting the c-RAF-PDE8A protein complex, DRx-170 promotes the inactivation of c-RAF through an allosteric mechanism, dependent upon inactivating PKA phosphorylation. DRx-170 inhibits cell proliferation, adhesion and migration of a KRASMT PDAC cell line (PANC1), independent of ERK1/2 activity. Moreover, combining DRx-170 with afatinib significantly enhances PANC1 growth inhibition in both 2D and 3D cellular models. DRx-170 sensitivity appears to correlate with c-RAF dependency. This proof-of-concept study supports the development of DRx-170 as a novel and differentiated strategy for targeting c-RAF activity in KRAS-c-RAF dependent PDAC.

Cancer: Phosphodiesterase type 4C (PDE4C), the forgotten subfamily as a therapeutic target.

Phosphodiesterase type 4 (PDE4) enzymes specifically hydrolyse cAMP in many cell signalling systems that are transduced by hormones and other primary messengers. The physiological function of the four PDE4 subfamilies (A, B, C and D) are numerous and varied due to the differentially localised plethora of isoforms that can be detected in cardiovascular, CNS and immune systems. Of the four subfamilies, least is known about PDE4C probably due to its restricted distribution pattern, scarcity of selective inhibitors and the lack of developed research tools. Here, for the first time, we chart the discovery of PDE4C, describe its regulation and highlight cancers where future development of PDE4C selective small molecules may have potential.

Ablation of specific long PDE4D isoforms increases neurite elongation and conveys protection against amyloid-ß pathology.

Inhibition of phosphodiesterase 4D (PDE4D) enzymes has been investigated as therapeutic strategy to treat memory problems in Alzheimer's disease (AD). Although PDE4D inhibitors are effective in enhancing memory processes in rodents and humans, severe side effects may hamper their clinical use. PDE4D enzymes comprise different isoforms, which, when targeted specifically, can increase treatment efficacy and safety. The function of PDE4D isoforms in AD and in molecular memory processes per se has remained unresolved. Here, we report the upregulation of specific PDE4D isoforms in transgenic AD mice and hippocampal neurons exposed to amyloid-ß. Furthermore, by means of pharmacological inhibition and CRISPR-Cas9 knockdown, we show that the long-form PDE4D3, -D5, -D7, and -D9 isoforms regulate neuronal plasticity and convey resilience against amyloid-ß in vitro. These results indicate that isoform-specific, next to non-selective, PDE4D inhibition is efficient in promoting neuroplasticity in an AD context. Therapeutic effects of non-selective PDE4D inhibitors are likely achieved through actions on long isoforms. Future research should identify which long PDE4D isoforms should be specifically targeted in vivo to both improve treatment efficacy and reduce side effects.

Structural basis of CBP/p300 recruitment by the microphthalmia-associated transcription factor.

The microphthalmia-associated transcription factor (MITF) is a master regulator of the melanocyte cell lineage. Aberrant MITF activity can lead to multiple malignancies including skin cancer, where it modulates the progression and invasiveness of melanoma. MITF-regulated gene expression requires recruitment of the transcriptional co-regulator CBP/p300, but details of this process are not fully defined. In this study, we investigate the structural and functional interaction between the MITF N-terminal transactivation domain (MITFTAD) and CBP/p300. Using pulldown assays and nuclear magnetic resonance spectroscopy we determined that MITFTAD is intrinsically disordered and binds to the TAZ1 and TAZ2 domains of CBP/p300 with moderate affinity. The solution-state structure of the MITFTAD:TAZ2 complex reveals that MITF interacts with a hydrophobic surface of TAZ2, while remaining somewhat dynamic. Peptide array and mutagenesis experiments determined that an acidic motif is integral to the MITFTAD:TAZ2 interaction and is necessary for transcriptional activity of MITF. Peptides that bind to the same surface of TAZ2 as MITFTAD, such as the adenoviral protein E1A, are capable of displacing MITF from TAZ2 and inhibiting transactivation. These findings provide insight into co-activator recruitment by MITF that are fundamental to our understanding of MITF targeted gene regulation and melanoma biology.

Raising the Dead Volume: Analysis of Microsamples Diluted and Corrected with Near Infrared Tracer.

BACKGROUND: Sample processing robotics require large liquid volumes to operate efficiently. Robotics are impractical in settings that deal in small specimen volumes such as pediatric laboratories. Short of manual sample handling, remedies for the current state include a redesign of current hardware or specialized adaptation for submilliliter specimens. METHODS: We blindly increased the volume of plasma specimens with diluent containing a near infrared dye, IR820, to assess the change to the original specimen volume. Diluted specimens were analyzed using a variety of assay formats/wavelengths (sodium, calcium, alanine aminotransferase, creatine kinase, cholesterol, HDL cholesterol, triglyceride, glucose, total protein, creatinine), and results were compared to neat specimens. Recovery of analyte in the diluted specimens vs neat was the primary outcome measure. RESULTS: Mean analytic recovery from the diluted specimens across all assays ranged from 93% to 110% after correction using IR820 absorbance. Absorbance correction compared favorably to mathematical correction using known volumes of specimens and diluents (93%-107%). Pooled mean analytic imprecision across all assays ranged from 2% using the neat specimen pool to 8% when plasma pool was diluted to 30% of its original concentration. No interference from dye addition was noted, indicating the diluent was broadly applicable and chemically inert. The greatest variability in recovery was observed when respective analyte concentrations were present near the lower limits of assay detectability. CONCLUSIONS: Addition of a chemically inert diluent containing a near-infrared tracer is a feasible way to raise specimen dead volume and potentially automate processing and measurement of clinical analytes in microsamples.

Phosphodiesterase type 4 anchoring regulates cAMP signaling to Popeye domain-containing proteins.

Cyclic AMP is a ubiquitous second messenger used to transduce intracellular signals from a variety of Gs-coupled receptors. Compartmentalisation of protein intermediates within the cAMP signaling pathway underpins receptor-specific responses. The cAMP effector proteins protein-kinase A and EPAC are found in complexes that also contain phosphodiesterases whose presence ensures a coordinated cellular response to receptor activation events. Popeye domain containing (POPDC) proteins are the most recent class of cAMP effectors to be identified and have crucial roles in cardiac pacemaking and conduction. We report the first observation that POPDC proteins exist in complexes with members of the PDE4 family in cardiac myocytes. We show that POPDC1 preferentially binds the PDE4A sub-family via a specificity motif in the PDE4 UCR1 region and that PDE4s bind to the Popeye domain of POPDC1 in a region known to be susceptible to a mutation that causes human disease. Using a cell-permeable disruptor peptide that displaces the POPDC1-PDE4 complex we show that PDE4 activity localized to POPDC1 modulates cycle length of spontaneous Ca2+ transients firing in intact mouse sinoatrial nodes.

Peptides derived from the SARS-CoV-2 receptor binding motif bind to ACE2 but do not block ACE2-mediated host cell entry or pro-inflammatory cytokine induction.

SARS-CoV-2 viral attachment and entry into host cells is mediated by a direct interaction between viral spike glycoproteins and membrane bound angiotensin-converting enzyme 2 (ACE2). The receptor binding motif (RBM), located within the S1 subunit of the spike protein, incorporates the majority of known ACE2 contact residues responsible for high affinity binding and associated virulence. Observation of existing crystal structures of the SARS-CoV-2 receptor binding domain (SRBD)-ACE2 interface, combined with peptide array screening, allowed us to define a series of linear native RBM-derived peptides that were selected as potential antiviral decoy sequences with the aim of directly binding ACE2 and attenuating viral cell entry. RBM1 (16mer): S443KVGGNYNYLYRLFRK458, RBM2A (25mer): E484GFNCYFPLQSYGFQPTNGVGYQPY508, RBM2B (20mer): F456NCYFPLQSYGFQPTNGVGY505 and RBM2A-Sc (25mer): NYGLQGSPFGYQETPYPFCNFVQYG. Data from fluorescence polarisation experiments suggested direct binding between RBM peptides and ACE2, with binding affinities ranging from the high nM to low µM range (Kd = 0.207-1.206 µM). However, the RBM peptides demonstrated only modest effects in preventing SRBD internalisation and showed no antiviral activity in a spike protein trimer neutralisation assay. The RBM peptides also failed to suppress S1-protein mediated inflammation in an endogenously expressing ACE2 human cell line. We conclude that linear native RBM-derived peptides are unable to outcompete viral spike protein for binding to ACE2 and therefore represent a suboptimal approach to inhibiting SARS-CoV-2 viral cell entry. These findings reinforce the notion that larger biologics (such as soluble ACE2, 'miniproteins', nanobodies and antibodies) are likely better suited as SARS-CoV-2 cell-entry inhibitors than short-sequence linear peptides.

Stapled ACE2 peptidomimetics designed to target the SARS-CoV-2 spike protein do not prevent virus internalization.

COVID-19 is caused by a novel coronavirus called severe acute respiratory syndrome-coronavirus 2 (SARS-CoV-2). Virus cell entry is mediated through a protein-protein interaction (PPI) between the SARS-CoV-2 spike protein and angiotensin-converting enzyme 2 (ACE2). A series of stapled peptide ACE2 peptidomimetics based on the ACE2 interaction motif were designed to bind the coronavirus S-protein RBD and inhibit binding to the human ACE2 receptor. The peptidomimetics were assessed for antiviral activity in an array of assays including a neutralization pseudovirus assay, immunofluorescence (IF) assay and in-vitro fluorescence polarization (FP) assay. However, none of the peptidomimetics showed activity in these assays, suggesting that an enhanced binding interface is required to outcompete ACE2 for S-protein RBD binding and prevent virus internalization.

Measuring cAMP Specific Phosphodiesterase Activity: A Two-step Radioassay.

Cyclic nucleotide degrading phosphodiesterase (PDE) enzymes are crucial to the fine tuning of cAMP signaling responses, playing a pivotal role in regulating the temporal and spatial characteristics of discrete cAMP nanodomains and hence the activity of cAMP-effector proteins. As a consequence of orchestrating cAMP homeostasis, dysfunctional PDE activity plays a central role in disease pathogenesis. This highlights the need for developing methods that can be used to further understand PDE function and assess the effectiveness of potentially novel PDE therapeutics. Here we describe such an approach, where PDE activity is indirectly measured through the direct quantification of radioactively tagged cAMP (pmol/min-1/mg-1). This method provides a highly sensitive tool for investigating PDE functionality.

Fibrin Breakdown Assay.

Fibrinolysis is an integral part of the matrix remodeling process that contributes to tissue repair. Fibrin clots are broken down during fibrinolysis in a controlled process. Fibrin degradation products (FDPs) have also been shown to have a role in the regulation of cell growth and are implicated in various vascular diseases. This protocol was designed to quantitatively measure the extent of fibrin breakdown and how this can be adapted as a tool to further investigate the pathway involved in fibrinolysis or fibrin degradation products. Until now, we haven't found an alternative method to analysis fibrinolysis.

Reshaping cAMP nanodomains through targeted disruption of compartmentalised phosphodiesterase signalosomes.

Spatio-temporal regulation of localised cAMP nanodomains is highly dependent upon the compartmentalised activity of phosphodiesterase (PDE) cyclic nucleotide degrading enzymes. Strategically positioned PDE-protein complexes are pivotal to the homeostatic control of cAMP-effector protein activity that in turn orchestrate a wide range of cellular signalling cascades in a variety of cells and tissue types. Unsurprisingly, dysregulated PDE activity is central to the pathophysiology of many diseases warranting the need for effective therapies that target PDEs selectively. This short review focuses on the importance of activating compartmentalised cAMP signalling by displacing the PDE component of signalling complexes using cell-permeable peptide disrupters.

Targeting B-Raf inhibitor resistant melanoma with novel cell penetrating peptide disrupters of PDE8A - C-Raf.

BACKGROUND: Recent advances in the treatment of melanoma that involve immunotherapy and B-Raf inhibition have revolutionised cancer care for this disease. However, an un-met clinical need remains in B-Raf inhibitor resistant patients where first-generation B-Raf inhibitors provide only short-term disease control. In these cases, B-Raf inhibition leads to paradoxical activation of the C-Raf - MEK - ERK signalling pathway, followed by metastasis. PDE8A has been shown to directly interact with and modulate the cAMP microdomain in the vicinity of C-Raf. This interaction promotes C-Raf activation by attenuating the PKA-mediated inhibitory phosphorylation of the kinase. METHODS: We have used a novel cell-penetrating peptide agent (PPL-008) that inhibits the PDE8A - C-Raf complex in a human malignant MM415 melanoma cell line and MM415 melanoma xenograft mouse model to investigate ERK MAP kinase signalling. RESULTS: We have demonstrated that the PDE8A - C-Raf complex disruptor PPL-008 increased inhibitory C-Raf-S259 phosphorylation and significantly reduced phospho-ERK signalling. We have also discovered that the ability of PPL-008 to dampen ERK signalling can be used to counter B-Raf inhibitor-driven paradoxical activation of phospho-ERK in MM415 cells treated with PLX4032 (Vemurafenib). PPL-008 treatment also significantly retarded the growth of these cells. When applied to a MM415 melanoma xenograft mouse model, PPL-008C penetrated tumour tissue and significantly reduced phospho-ERK signalling in that domain. CONCLUSION: Our data suggests that the PDE8A-C-Raf complex is a promising therapeutic treatment for B-Raf inhibitor resistant melanoma.