Calcipotriol and Betamethasone Dipropionate Cream Based on PAD Technology for the Treatment of Plaque Psoriasis: A Narrative Review.

Topical treatment plays a crucial role in psoriasis management, with non-adherence being a major barrier to treatment success. The fixed-dose combination of calcipotriol (CAL) and betamethasone dipropionate (BDP) represents the first-line choice in topical psoriasis treatment. A CAL/BDP cream based on polyaphron dispersion (PAD) Technology has emerged as a novel formulation for a more convenient topical treatment of psoriasis. This article aims to summarize the most relevant published evidence about CAL/BDP PAD-cream and its underlying PAD Technology. The PAD Technology enables CAL and BDP stability in an aqueous cream through a multimolecular shell structure, as well as it increases the penetration of both active ingredients into the epidermis and dermis. This technology also demonstrated to increase the cosmetic acceptability and to provide the desirable sensory properties for a topical psoriasis treatment. Two phase III clinical trials have been conducted so far with CAL/BDP PAD-cream. Findings from both trials revealed high efficacy with a fast onset of action, a favourable safety and tolerability profile and convenience for CAL/BDP PAD-cream compared to CAL/BDP gel. In the trial including patients with psoriasis affecting the scalp (MC2-01-C7), results support the use of CAL/BDP PAD-cream in scalp psoriasis. An anchored matching-adjusted indirect comparison (MAIC) was conducted to compare CAL/BDP PAD-cream and CAL/BDP foam, as both products had been previously compared to CAL/BDP gel. CAL/BDP PAD-cream and CAL/BDP foam showed equivalent efficacy and quality of life at their recommended treatment duration, whereas greater treatment satisfaction for CAL/BDP PAD-cream was found after one week of treatment. Overall, the high patient acceptability and treatment satisfaction observed with CAL/BDP PAD-cream in clinical trials may lead to improved adherence and hence higher efficacy in clinical practice.

Calcipotriene and Betamethasone Dipropionate PAD-Cream Demonstrates Greater Treatment Efficacy in Patients with Moderate-to-Severe Psoriasis Compared to Topical Suspension/Gel: A Subgroup Analysis of Two Phase 3 Studies.

INTRODUCTION: Psoriasis ranges from mild to severe with the majority of patients having mild disease. Mild to moderate disease is often treated with topical therapies while photo-, oral, and biologic therapies are generally reserved for moderate-to-severe disease. There is a strong scientific rationale for the combination of calcipotriene (CAL) and betamethasone dipropionate (BDP) with respect to mode of action, efficacy, and safety and CAL/BDP has shown an inhibitory effect on key pathogenic cytokines in psoriasis including tumor necrosis factor-α, interleukin (IL)-17, and IL-23. METHODS: The objective of this pooled post hoc analysis is to investigate the efficacy of CAL/BDP polyaphron dispersion (PAD)-cream in subgroups of patients with moderate-to-severe psoriasis from two completed phase 3 studies conducted in the USA and Europe. RESULTS: The proportion of patients achieving Physician Global Assessment (PGA) treatment success as well as a modified Psoriasis Area and Severity Index (mPASI)75 response was higher in the subgroup with a body surface area > 10% and mPASI > 10 and Dermatology Life Quality Index > 10 at baseline compared to the overall patient population. Furthermore, the numerical difference in treatment efficacy between CAL/BDP PAD-cream and CAL/BDP topical suspension/gel increased in patient subgroups with higher baseline severity. Similar patterns were shown for the patient-reported outcomes. CONCLUSION: In this subgroup analysis, patients who had higher disease severity at baseline achieved greater efficacy than the total patient population when treated with 8 weeks of CAL/BDP PAD-cream as compared to a currently marketed active comparator. Additionally, as indicated by this analysis, CAL/BDP PAD-cream treatment may also be more convenient and less greasy, which may reduce the burden of daily treatment and improve adherence to therapy. TRIAL REGISTRATION: NCT03308799 and NCT03802344.

Enhanced Skin Deposition of Betamethasone Dipropionate from a Novel Formulation and Drug Delivery Technology.

INTRODUCTION: Effective topical drug delivery is the essence of dermatologic treatment. The drug must be applied to the skin surface, be released from the vehicle, enter the stratum corneum, traverse the epidermis, and enter the dermis pharmacologically intact. New advances have improved emulsion-type formulation and drug delivery technology by encapsulating dispersed oil droplets in a robust multimolecular aqueous film of surfactants, oil, and water, enabling a multifold decrease in surfactant concentration compared to conventional creams. In the research reported here, we studied this new concept, termed polyaphron dispersion (PAD) technology, by comparing skin delivery of betamethasone dipropionate from a novel oil-in-water emulsion system of calcipotriene and betamethasone dipropionate (CAL/BDP) cream to that from a traditional topical suspension (CAL/BDP TS) utilizing in vitro and in vivo detection methods. METHODS: The amount of BDP released from the CAL/BDP cream and CAL/BDP TS was evaluated using both in vitro Franz cell analysis and in vivo human tape stripping from ten female human volunteers after a single application of CAL/BDP cream or CAL/BDP TS. For the tape stripping analysis, 20 circular tape strips were taken from forearm application sites at 1, 2, 4, and 8 h after application and analyzed for the amount of BDP in the tape strip using liquid chromatography-mass spectrometry (LC-MS). RESULTS: The in vitro Franz cell analysis demonstrated that the cumulative amount of BDP that diffused through the epidermis was statistically significantly greater for the CAL/BDP cream compared to the CAL/BDP TS at all time points. In addition, consistently higher amounts of BDP were recovered following CAL/BDP cream application than following CAL/BDP TS application at 1, 2, 4, and 8 h following application utilizing the in vivo tape stripping technique. CONCLUSION: The novel PAD technology-based cream formulation delivered more BDP into the upper stratum corneum and lower epidermis than a traditional topical suspension.

Sensory properties analysis of a calcipotriol and betamethasone dipropionate cream vehicle formulated with an innovative PAD Technology for the treatment of plaque psoriasis on the skin and scalp.

Background: In psoriasis, poor treatment adherence is frequently related to low efficacy and limited cosmetic acceptability from the patients' perspective. This study aimed to characterize the sensorial attributes of a calcipotriol (CAL) and betamethasone dipropionate (BDP)-cream vehicle based on polyaphron dispersion (PAD) Technology and to compare them with the conventional ointment and oleogel formulations for psoriasis. Methods: A panel of 16 experts assessed sensory properties at four different stages: appearance, pick up, rub out and afterfeel. Descriptive sensory analysis was used to evaluate relevant attributes. Each attribute was rated on a line scale (range 0-100%). Active ingredients were not used because panellists were healthy volunteers, and vehicle formulations needed to be used instead. Results: CAL/BDP PAD-cream vehicle was evaluated as having a low stickiness, low grease behaviour, good wetness, and good spreadability. Ointment showed the least desirable behaviour regarding these properties. Moreover, once CAL/BDP PAD-cream vehicle was absorbed, the gloss disappeared quickly, leaving low stickiness and a low amount of residue. This afterfeel behaviour was not observed with ointment. The oleogel formulation had good sensory properties, similar to CAL/BDP PAD-cream vehicle, but with lower integrity of shape, lower wetness and higher greasiness. Conclusion: Overall, CAL/BDP PAD-cream vehicle has the desirable requirements for a topical product for the treatment of psoriasis, with better sensory properties than ointment and easier manipulation than oleogel, which may lead to greater acceptance and adherence.

A novel, fixed-dose calcipotriol and betamethasone dipropionate cream for the topical treatment of plaque psoriasis: Direct and indirect evidence from phase 3 trials discussed at the 30th EADV Congress 2021.

Four posters about the novel, fixed-dose calcipotriol and betamethasone dipropionate cream (CAL/BDP cream) based on Poly-Aphron Dispersion (PAD) Technology were presented at the 30th European Academy of Dermatology and Venereology (EADV) Congress 2021 and are summarized here. CAL/BDP cream was compared in two randomized, phase 3 trials to vehicle and active comparator (CAL/BDP gel/topical suspension [TS]) in adults with plaque psoriasis (NCT03802344 and NCT03308799). Pooled data from both trials demonstrated significant greater efficacy in favour of CAL/BDP cream for all efficacy endpoints, including PGA treatment success, mPASI, and mPASI75 compared to CAL/BDP gel/TS. CAL/BDP cream was well tolerated and comparable to CAL/BDP gel/TS with no adverse drug reactions with a frequency >1%. In the NCT03308799 study, CAL/BDP cream demonstrated a substantial improvement in the proportion of participants achieving a minimum 4-point improvement on the peak pruritus numeric rating scale (NRS) score compared with vehicle at Weeks 1, 4 and 8. CAL/BDP cream also improved quality of life (QoL), as assessed through the Dermatology Life Quality Index (DLQI), and the EQ-VAS at Week 8 compared with active comparator. Treatment convenience of CAL/BDP cream, as measured by the Psoriasis Treatment Convenience Scale, was superior to CAL/BDP gel/TS at all studied timepoints, including questions addressing formulation's greasiness and overall treatment satisfaction. Finally, an indirect comparison following the Bucher's method of adjusted indirect comparison and the difference-in-differences method was conducted to compare CAL/BDP cream and CAL/BDP foam, as both therapies have been compared to CAL/BDP gel/TS. Indirect evidence showed that treatment with CAL/BDP cream was associated with a trend for greater QoL improvement than CAL/BDP foam when DLQI improvement was assessed at the recommended treatment duration of 8 weeks for CAL/BDP cream and 4 weeks for CAL/BDP foam. CAL/BDP cream was statistically superior versus CAL/BDP foam in four out of five treatment satisfaction domains.

Polyaphron Dispersion Technology, A Novel Topical Formulation and Delivery System Combining Drug Penetration, Local Tolerability and Convenience of Application.

Topical formulation and delivery technologies for pharmaceutical application should simultaneously address efficacy, safety and convenience of therapy. This has historically proven to be challenging, since formulation features that drive efficacy often have undesirable consequences for safety and convenience and vice versa. Polyaphron dispersion (PAD) technology is a novel topical formulation and drug delivery system developed with the purpose of preserving these key attributes. PAD formulations are typically oil-in-water dispersions consisting of oil droplets encapsulated in a multi-molecular shell structure. This shell structure protects potentially unstable active molecules solubilized in the oil from hydrolytic degradation. Example data are presented of enhanced drug penetration from PAD formulations, including dermal delivery of calcipotriene, betamethasone dipropionate and tacrolimus as well as ocular delivery of ciclosporin A. Local tolerability is an important safety parameter for topical formulations, where high levels of surfactants can cause skin irritation. In this regard, a key benefit of PAD formulations is the inherent reduced requirement for surfactants to generate stable formulations compared to conventional emulsion systems. Patients with chronic diseases with topical manifestations such as psoriasis or atopic dermatitis have been reported to miss up to 70% of planned topical applications, mainly due to a lack of satisfaction with their therapy. Patients generally prefer light, moisturizing, non-greasy and quickly absorbed vehicles that are simple to use on all body parts. PAD formulations can generally be designed to meet these criteria. In conclusion, PAD technology provides high flexibility in topical drug design and can be applied to several body locations without compromising efficacy, safety or convenience of therapy.Clinical Trial Register: Clinicaltrials.gov: NCT03802344.

An anchored matching-adjusted indirect comparison of fixed-dose combination calcipotriol and betamethasone dipropionate (Cal/BDP) cream versus Cal/BDP foam for the treatment of psoriasis.

OBJECTIVES: To undertake a comparison of Cal/BDP cream versus foam for the treatment of plaque psoriasis, with cross-trial population differences accounted for. MATERIALS AND METHODS: An anchored matching-adjusted indirect comparison was undertaken, using individual patient data for Cal/BDP cream and published aggregated data for Cal/BDP foam. Altogether, 11 outcomes were analyzed, including PGA success, mPASI75, DLQI-related outcomes and treatment satisfaction across numerous domains. For each outcome an odds ratio or mean difference was calculated to represent the relative efficacy of Cal/BDP cream versus foam. Methods were guided by NICE Decision Support Unit recommendations. RESULTS: After adjustment, baseline characteristics were balanced across treatment arms in each analysis. There were no statistically significant differences in PGA success, mPASI75 or DLQI outcomes between Cal/BDP cream and foam when they were compared after their recommended treatment durations (8 weeks for cream and 4 weeks for foam). For treatment satisfaction after 1 week of treatment, Cal/BDP cream was significantly superior to the Cal/BDP foam in all but one domain of the questionnaire. CONCLUSIONS: Cal/BDP cream and Cal/BDP foam have equivalent efficacy and HRQoL (measured in DLQI) outcomes when used for the topical treatment of plaque psoriasis at their recommended treatment durations. A comparison of treatment satisfaction assessments after 1 week of treatment demonstrated that patients find Cal/BDP cream to be more convenient than foam.

Pooled Analysis Demonstrating Superior Patient- Reported Psoriasis Treatment Outcomes for Calcipotriene/ Betamethasone Dipropionate Cream Versus Suspension/Gel.

BACKGROUND: Calcipotriene and betamethasone dipropionate (CAL/BDP) cream is a novel treatment of plaque psoriasis based on PAD™ Technology (PAD-cream) designed to improve patient reported treatment satisfaction and quality of life (QoL). METHOD: A pooled analysis of patient reported outcomes from two phase 3, multicenter, randomized, investigator-blind, active, and vehicle-controlled trials evaluating a total of 1271 patients with mild to moderate plaque psoriasis according to the Physician Global Assessment (PGA) scale. Products were applied once daily for 8 weeks. RESULTS: The proportion of patients evaluating their treatment to have improved by 2 grades to clear or very mild disease on the 5-grade Subject Global Assessment (SGA) scale, defined as SGA Success, was significantly higher in the CAL/BDP PAD-cream group compared to active comparator (CAL/BDP suspension/gel) (week 8, 44.2% vs 27.9%, P<0.0001). A Dermatology Life Quality Index (DLQI) score of 0 or 1, indicating no impact of disease on the patient's life, was obtained by 43.8% of patients at week 8 in the CAL/BDP cream group versus 34.2% in the CAL/BDP suspension/gel group (P=0.0005). CAL/BDP PAD-cream demonstrated significantly greater psoriasis treatment convenience compared to CAL/BDP suspension/gel at all studied time points, including questions addressing greasiness of the formulation and overall satisfaction of treatment. CONCLUSION: CAL/BDP PAD-cream is a novel topical treatment for psoriasis, which through PAD™ Technology offers substantial improvement in QoL and treatment satisfaction for patients. Given these data, CAL/BDP PAD-cream may lead to better adherence to treatment, which ultimately could result in better treatment outcomes in clinical practice. CLINICALTRIALS: gov: NCT03308799 and NCT03802344. J Drugs Dermatol. 2022;21(3):242-248. doi:10.36849/JDD.6611.

Validation of the Self-Reported Psoriasis Treatment Convenience Scale (PTCS).

INTRODUCTION: Adherence to topical treatments for psoriasis is reported to be poor. One key contributing factor is the inconvenience associated with formulations that may be greasy, time consuming to apply, and slow to absorb. There is a paucity of patient-reported outcome measures that evaluate psoriasis patients' perceptions of treatment convenience. The Psoriasis Treatment Convenience Scale (PTCS) was therefore developed and validated. METHODS: Following a literature review of issues relating to convenience of topical treatments, important items were identified and a draft version of the PTCS was developed and underwent content validity testing (n = 20). The revised scale was included in a clinical trial of topical therapy (n = 794; NCT03308799), and psychometric testing was performed. RESULTS: The final questionnaire included five core items and one overall satisfaction question. In psychometric testing, the scale demonstrated stability across trial population, and good validity, reliability, and sensitivity. CONCLUSION: The PTCS is a new, reliable, sensitive, validated tool for the assessment of patient-reported treatment convenience. Use of the PTCS will facilitate evaluation of convenience as part of the clinical development of topical therapies, and thus may help to improve patient adherence and, therefore, treatment outcomes.

A Phase 3, Randomized Trial Demonstrating the Improved Efficacy and Patient Acceptability of Fixed Dose Calcipotriene and Betamethasone Dipropionate Cream.

BACKGROUND: The fixed dose combination of calcipotriene and betamethasone dipropionate (CAL/BDP) is a well-established, efficacious, and safe topical treatment of psoriasis. METHOD: A Phase 3, multicenter, randomized, investigator-blind, active, and vehicle-controlled trial enrolling 796 patients with moderate to severe psoriasis according to the Physician Global Assessment (PGA) scale. Products were applied once daily for 8 weeks. RESULTS: The proportion of patients achieving PGA treatment success after 8 weeks was statistically significantly greater for CAL/BDP cream (37.4%) compared to CAL/BDP TS (22.8%, P<0.0001), and vehicle (3.7%, P<0.0001). A similar statistically significant difference in favor of CAL/BDP cream at week 8 was demonstrated for the percentage change in mPASI from baseline and the proportion of patients obtaining mPASI75. Patient reported treatment convenience for CAL/BDP cream was rated superior to CAL/BDP TS. Safety assessments during the trial demonstrated that CAL/BDP cream was well-tolerated with no adverse reactions with a frequency greater than 1%. CONCLUSION: CAL/BDP cream is a novel topical treatment of psoriasis, which in a single product, offers a unique combination of high efficacy combined with favorable safety and excellent treatment convenience. For these reasons, CAL/BDP cream offers a distinctive advantage for the topical treatment of plaque psoriasis. ClinicalTrials.gov: NCT03308799J Drugs Dermatol. 20(4):420-425. doi:10.36849/JDD.5653.

Profiling of multiple signal pathway activities by multiplexing antibody and GFP-based translocation assays.

Multiplexing of GFP based and immunofluorescence translocation assays enables easy acquisition of multiple readouts from the same cell in a single assay run. Immunofluorescence assays monitor translocation, phosphorylation, and up/down regulation of endogenous proteins. GFP-based assays monitor translocation of stably expressed GFP-fusion proteins. Such assays may be multiplexed along (vertical), across (horizontal), and between (branch) signal pathways. Examples of these strategies are presented: 1) The MK2-GFP assay monitors translocation of MK2-GFP from the nucleus to the cytoplasm in response to stimulation of the p38 pathway. By applying different immunofluorescent assays to the MK2 assay, a multiplexed HCA system is created for deconvolution of p38 pathway activation including assay readouts for MK2, p38, NFkappaB, and c-Jun. 2) A method for evaluating GPCR activation and internalization in a single assay run has been established by multiplexing GFP-based internalization assays with immunofluorescence assays for downstream transducers of GPCR activity: pCREB (cAMP sensor), NFATc1 (Ca(2+) sensor), and ERK (G-protein activation). Activation of the AT1 receptor is given as an example. 3) Cell toxicity readouts can be linked to primary readouts of interest via acquisition of secondary parameters describing cellular morphology. This approach is used to flag cytotoxic compounds and deselect false positives. The ATF6 Redistribution assay is provided as an example. These multiplex strategies provide a unique opportunity to enhance HCA data quality and save time during drug discovery. From a single assay run, several assay readouts are obtained that help the user to deconvolute the mode of action of test compounds.

High content translocation assays for pathway profiling.

This chapter describes the design and development of cell-based assays, in which quantitation of the intracellular translocation of a target protein--rather than binding or catalytic activity--provides the primary assay readout. These are inherently high content assays, and they provide feedback on cellular response at the systems level, rather than data on activities of individual, purified molecules. Multiple protein translocation assays can be used to profile cellular signaling pathways and they can play a key role in determination of mechanism of action for novel classes of compounds with therapeutic potential. This assay technology has developed from laboratory curiosity into main stream industrial research over the past decade, and its promise is beginning to be realized as data acquisition and analysis technology evolve to take advantage of the rich window into systems biology provided by translocation assays.

Protein translocation assays: key tools for accessing new biological information with high-throughput microscopy.

Redistribution technology is a cell-based assay technology that uses protein translocation as the primary readout for the activity of cellular signaling pathways and other intracellular events. Protein targets are labeled with the green fluorescent protein, and stably transfected cell lines are generated. The assays are read using a high-throughput, optical microscope-based instrument, several of which have become available commercially. Protein translocation assays can be formatted as agonist assays, in which compounds are tested for their ability to promote protein translocation, or as antagonist assays, in which compounds are tested for their ability to inhibit protein translocation caused by a known agonist. Protein translocation assays are high-content, high-throughput assays primarily used for profiling of lead series, primary screening of compound libraries, and as readouts for gene-silencing studies using siRNAs. This chapter describes two novel high-content Redistribution assay technologies: (1) The p53:hdm2 GRIP interaction assay, in which one high-content image feature is used for detection of primary hits, whereas a different feature is used to deselect compounds with unwanted mode of action, and (2) application of siRNAs to Redistribution assays, exemplified by knockdown of Akt isoforms in a FKHR translocation assay reporting on the PI3 kinase signaling pathway.

Identification of RAS-mitogen-activated protein kinase signaling pathway modulators in an ERF1 redistribution screen.

The RAS-mitogen-activated protein kinase (MAPK) signaling pathway has a central role in regulating the proliferation and survival of both normal and tumor cells. This pathway has been 1 focus area for the development of anticancer drugs, resulting in several compounds, primarily kinase inhibitors, in clinical testing. The authors have undertaken a cell-based, high-throughput screen using a novel ERF1 Redistribution assay to identify compounds that modulate the signaling pathway. The hit compounds were subsequently tested for activity in a functional cell proliferation assay designed to selectively detect compounds inhibiting the proliferation of MAPK pathway-dependent cancer cells. The authors report the identification of 2 cell membrane-permeable compounds that exhibit activity in the ERF1 Redistribution assay and selectively inhibit proliferation of MAPK pathway-dependent malignant melanoma cells at similar potencies (IC(50)=< 5 microM). These compounds have drug-like structures and are negative in RAF, MEK, and ERK in vitro kinase assays. Drugs belonging to these compound classes may prove useful for treating cancers caused by excessive MAPK pathway signaling. The results also show that cell-based, high-content Redistribution screens can detect compounds with different modes of action and reveal novel targets in a pathway known to be disease relevant.

A simple cell-based HTS assay system to screen for inhibitors of p53-Hdm2 protein-protein interactions.

Green fluorescent protein-assisted readout for interacting proteins (GRIP) is a universal protein interaction discovery system that can be used to generate truly high throughput screening-compatible cellular assays to be used to screen for inhibitors of protein-protein interactions. The technology uses a "bait and prey" principle based on the distinct translocation behavior of the human cyclic AMP phosphodiesterase 4A4. Here we use the p53-Hdm2 Redistribution assay (Fisher BioImage ApS, Søborg, Denmark) as an example to describe the GRIP technology. The p53-Hdm2 Redistribution assay is a high content imaging assay based on the GRIP technology that is designed to measure the interaction between Hdm2 and the tumor suppressor p53. Hdm2 regulates p53 and inhibits its function by modulating its transcriptional activity and stability. Activation of p53 in tumor cells through inhibition of its physical interaction with Hdm2 is therefore a focus of cancer drug discovery. We have performed a pilot screen by screening 3,165 compounds from a diverse small-molecule library for inhibitors of the p53-Hdm2 interaction by using the p53-Hdm2 Redistribution assay. Here we show that by taking advantage of the translocation behavior of nonbound p53, it is possible to identify true inhibitors of the p53-Hdm2 interaction by extracting high content information from the acquired images.

Identification of Akt pathway inhibitors using redistribution screening on the FLIPR and the IN Cell 3000 analyzer.

The PI3-kinase/Akt pathway is an important cell survival pathway that is deregulated in the majority of human cancers. Despite the apparent druggability of several kinases in the pathway, no specific catalytic inhibitors have been reported in the literature. The authors describe the development of a fluorometric imaging plate reader (FLIPR)-based Akt1 translocation assay to discover inhibitors of Akt1 activation. Screening of a diverse chemical library of 45,000 compounds resulted in identification of several classes of Akt1 translocation inhibitors. Using a combination of classical in vitro assays and translocation assays directed at different steps of the Akt pathway, the mechanisms of action of 2 selected chemical classes were further defined. Protein translocation assays emerge as powerful tools for hit identification and characterization.

Nuclear export inhibitors and kinase inhibitors identified using a MAPK-activated protein kinase 2 redistribution screen.

Redistribution (BioImage) A/S, Søborg, Denmark) is a novel high-throughput screening technology that monitors translocation of specific protein components of intracellular signaling pathways within intact mammalian cells, using green fluorescent protein as a tag. A single Redistribution assay can be used to identify multiple classes of compounds that act at, or upstream of, the level of the protein target used in the primary screening assay. Such compounds may include both conventional and allosteric enzyme inhibitors, as well as protein-protein interaction modulators. We have developed a series of Redistribution assays to discover and characterize compounds that inhibit tumor necrosis factor-alpha biosynthesis via modulation of the p38 mitogen-activated protein kinase (MAPK) pathway. A primary assay was designed to identify low-molecular-weight compounds that inhibit the activation-dependent nuclear export of the p38 kinase substrate MAPK-activated protein kinase 2 (MK2). Hits from the primary screen were categorized, using secondary assays, either as direct inhibitors of MK2 nuclear export, or as inhibitors of the upstream p38 MAPK pathway. Activity profiles are presented for a nuclear export inhibitor, and a compound that structurally and functionally resembles a known p38 kinase inhibitor. These results demonstrate the utility of Redistribution technology as a pathway screening method for the identification of diverse and novel compounds that are active within therapeutically important signaling pathways.

Occupancy of the catalytic site of the PDE4A4 cyclic AMP phosphodiesterase by rolipram triggers the dynamic redistribution of this specific isoform in living cells through a cyclic AMP independent process.

In cells transfected to express wild-type PDE4A4 cAMP phosphodiesterase (PDE), the PDE4 selective inhibitor rolipram caused PDE4A4 to relocalise so as to form accretion foci. This process was followed in detail in living cells using a PDE4A4 chimera formed with Green Fluorescent Protein (GFP). The same pattern of behaviour was also seen in chimeras of PDE4A4 formed with various proteins and peptides, including LimK, RhoC, FRB and the V5-6His tag. Maximal PDE4A4 foci formation, occurred over a period of about 10 h, was dose-dependent on rolipram and was reversible upon washout of rolipram. Inhibition of protein synthesis, using cycloheximide, but not PKA activity with H89, inhibited foci generation. Foci formation was elicited by Ro20-1724 and RS25344 but not by either Ariflo or RP73401, showing that not all PDE4 selective inhibitors had this effect. Ariflo and RP73401 dose-dependently antagonised rolipram-induced foci formation and dispersed rolipram pre-formed foci as did the adenylyl cyclase activator, forskolin. Foci formation showed specificity for PDE4A4 and its rodent homologue, PDE4A5, as it was not triggered in living cells expressing the PDE4B2, PDE4C2, PDE4D3 and PDE4D5 isoforms as GFP chimeras. Altered foci formation was seen in the Deltab-LR2-PDE4A4 construct, which deleted a region within LRZ, showing that appropriate linkage between the N-terminal portion of PDE4A4 and the catalytic unit of PDE4A4 was needed for foci formation. Certain single point mutations within the PDE4A4 catalytic site (His505Asn, His506Asn and Val475Asp) were shown to ablate foci formation but still allow rolipram inhibition of PDE4A4 catalytic activity. We suggest that the binding of certain, but not all, PDE4 selective inhibitors to PDE4A4 induces a conformational change in this isoform by 'inside-out' signalling that causes it to redistribute in the cell. Displacing foci-forming inhibitors with either cAMP or inhibitors that do not form foci can antagonise this effect. Specificity of this effect for PDE4A4 and its homologue PDE4A5 suggests that interplay between the catalytic site and the unique N-terminal region of these isoforms is required. Thus, certain PDE4 selective inhibitors may exert effects on PDE4A4 that extend beyond simple catalytic inhibition. These require protein synthesis and may lead to redistribution of PDE4A4 and any associated proteins. Foci formation of PDE4A4 may be of use in probing for conformational changes in this isoform and for sub-categorising PDE4 selective inhibitors.