Abuse and dependence potential of sphingosine-1-phosphate (S1P) receptor modulators used in the treatment of multiple sclerosis: a review of literature and public data.

Abuse and misuse of prescription drugs remains an ongoing concern in the USA and worldwide; thus, all centrally active new drugs must be assessed for abuse and dependence potential. Sphingosine-1-phosphate (S1P) receptor modulators are used primarily in the treatment of multiple sclerosis. Among the new S1P receptor modulators, siponimod, ozanimod, and ponesimod have recently been approved in the USA, European Union (EU), and other countries. This review of literature and other public data has been undertaken to assess the potential for abuse of S1P receptor modulators, including ozanimod, siponimod, ponesimod, and fingolimod, as well as several similar compounds in development. The S1P receptor modulators have not shown chemical or pharmacological similarity to known drugs of abuse; have not shown abuse or dependence potential in animal models for subjective effects, reinforcement, or physical dependence; and do not have adverse event profiles demonstrating effects of interest to individuals who abuse drugs (such as sedative, stimulant, mood-elevating, or hallucinogenic effects). In addition, no reports of actual abuse, misuse, or dependence were identified in the scientific literature for fingolimod, which has been on the market since 2010 (USA) and 2011 (EU). Overall, the data suggest that S1P receptor modulators are not associated with significant potential for abuse or dependence, consistent with their unscheduled status in the USA and internationally.

A Pooled Analysis of Three Randomized Phase I/IIa Clinical Trials Confirms Absence of a Clinically Relevant Effect on the QTc Interval by Umibecestat.

Umibecestat, an orally active ß-secretase inhibitor, reduces the production of amyloid beta-peptide that accumulates in the brain of patients with Alzheimer's disease. The echocardiogram effects of umibecestat, on QTcF (Fridericia-corrected QT), on PR and QRS and heart rate (HR), were estimated by concentration-effect modeling. Three phase I/II studies with durations up to 3 months, with 372 healthy subjects over a wide age range, including both sexes and 2 ethnicities, were pooled, providing a large data set with good statistical power. No clinically relevant effect on QTcF, PR interval, QRS duration, or HR were observed up to supratherapeutic doses. The upper bound of 90% confidence intervals of the ∆QTcF was below the 10 ms threshold of regulatory concern for all concentrations measured. Prespecified sensitivity analysis confirmed the results in both sexes, in those over and below 60 years, and in Japanese subjects. All conclusions were endorsed by the US Food and Drug Administration (FDA).

The BACE-1 inhibitor CNP520 for prevention trials in Alzheimer's disease.

The beta-site amyloid precursor protein cleaving enzyme-1 (BACE-1) initiates the generation of amyloid-ß (Aß), and the amyloid cascade leading to amyloid plaque deposition, neurodegeneration, and dementia in Alzheimer's disease (AD). Clinical failures of anti-Aß therapies in dementia stages suggest that treatment has to start in the early, asymptomatic disease states. The BACE-1 inhibitor CNP520 has a selectivity, pharmacodynamics, and distribution profile suitable for AD prevention studies. CNP520 reduced brain and cerebrospinal fluid (CSF) Aß in rats and dogs, and Aß plaque deposition in APP-transgenic mice. Animal toxicology studies of CNP520 demonstrated sufficient safety margins, with no signs of hair depigmentation, retina degeneration, liver toxicity, or cardiovascular effects. In healthy adults ≥ 60 years old, treatment with CNP520 was safe and well tolerated and resulted in robust and dose-dependent Aß reduction in the cerebrospinal fluid. Thus, long-term, pivotal studies with CNP520 have been initiated in the Generation Program.

Induction of hemangiosarcoma in mice after chronic treatment with S1P-modulator siponimod and its lack of relevance to rat and human.

A high incidence of hemangiosarcoma (HSA) was observed in mice treated for 2 years with siponimod, a sphingosine-1-phosphate receptor 1 (S1P1) functional antagonist, while no such tumors were observed in rats under the same treatment conditions. In 3-month rat (90 mg/kg/day) and 9-month mouse (25 and 75 mg/kg/day) in vivo mechanistic studies, vascular endothelial cell (VEC) activation was observed in both species, but VEC proliferation and persistent increases in circulating placental growth factor 2 (PLGF2) were only seen in the mouse. In mice, these effects were sustained over the 9-month study duration, while in rats increased mitotic gene expression was present at day 3 only and PLGF2 was induced only during the first week of treatment. In the mouse, the persistent VEC activation, mitosis induction, and PLGF2 stimulation likely led to sustained neo-angiogenesis which over life-long treatment may result in HSA formation. In rats, despite sustained VEC activation, the transient mitotic and PLGF2 stimuli did not result in the formation of HSA. In vitro, the mouse and rat primary endothelial cell cultures mirrored their respective in vivo findings for cell proliferation and PLGF2 release. Human VECs, like rat cells, were unresponsive to siponimod treatment with no proliferative response and no release of PLGF2 at all tested concentrations. Hence, it is suggested that the human cells also reproduce a lack of in vivo response to siponimod. In conclusion, the molecular mechanisms leading to siponimod-induced HSA in mice are considered species specific and likely irrelevant to humans.

Longitudinal noninvasive magnetic resonance imaging of brain microhemorrhages in BACE inhibitor-treated APP transgenic mice.

Currently, several immunotherapies and BACE (Beta Site APP Cleaving Enzyme) inhibitor approaches are being tested in the clinic for the treatment of Alzheimer's disease. A crucial mechanism-related safety concern is the exacerbation of microhemorrhages, which are already present in the majority of Alzheimer patients. To investigate potential safety liabilities of long-term BACE inhibitor therapy, we used aged amyloid precursor protein (APP) transgenic mice (APP23), which robustly develop cerebral amyloid angiopathy. T2*-weighted magnetic resonance imaging (MRI), a translational method applicable in preclinical and clinical studies, was used for the detection of microhemorrhages throughout the entire brain, with subsequent histological validation. Three-dimensional reconstruction based on in vivo MRI and serial Perls' stained sections demonstrated a one-to-one matching of the lesions thus allowing for their histopathological characterization. MRI detected small Perls' positive areas with a high spatial resolution. Our data demonstrate that volumetric assessment by noninvasive MRI is well suited to monitor cerebral microhemorrhages in vivo. Furthermore, 3 months treatment of aged APP23 with the potent BACE-inhibitor NB-360 did not exacerbate microhemorrhages in contrast to Aß-antibody ß1. These results substantiate the safe use of BACE inhibitors regarding microhemorrhages in long-term clinical studies for the treatment of Alzheimer's disease.

Pharmacological BACE1 and BACE2 inhibition induces hair depigmentation by inhibiting PMEL17 processing in mice.

Melanocytes of the hair follicle produce melanin and are essential in determining the differences in hair color. Pigment cell-specific MELanocyte Protein (PMEL17) plays a crucial role in melanogenesis. One of the critical steps is the amyloid-like functional oligomerization of PMEL17. Beta Site APP Cleaving Enzyme-2 (BACE2) and γ-secretase have been shown to be key players in generating the proteolytic fragments of PMEL17. The ß-secretase (BACE1) is responsible for the generation of amyloid-ß (Aß) fragments in the brain and is therefore proposed as a therapeutic target for Alzheimer's disease (AD). Currently BACE1 inhibitors, most of which lack selectivity over BACE2, have demonstrated efficacious reduction of amyloid-ß peptides in animals and the CSF of humans. BACE2 knock-out mice have a deficiency in PMEL17 proteolytic processing leading to impaired melanin storage and hair depigmentation. Here, we confirm BACE2-mediated inhibition of PMEL17 proteolytic processing in vitro in mouse and human melanocytes. Furthermore, we show that wildtype as well as bace2(+/-) and bace2(-/-) mice treated with a potent dual BACE1/BACE2 inhibitor NB-360 display dose-dependent appearance of irreversibly depigmented hair. Retinal pigmented epithelium showed no morphological changes. Our data demonstrates that BACE2 as well as additional BACE1 inhibition affects melanosome maturation and induces hair depigmentation in mice.

Proliferative and non-proliferative lesions of the rat and mouse integument.

The INHAND (International Harmonization of Nomenclature and Diagnostic Criteria for Lesions in Rats and Mice) project is a joint initiative of the societies of toxicological pathology from Europe (ESTP), Great Britain (BSTP), Japan (JSTP) and North America (STP). Its aim is to develop an internationally-accepted nomenclature for proliferative and non-proliferative lesions in laboratory rodents. A widely accepted international harmonization of nomenclature in laboratory animals will decrease confusion among regulatory and scientific research organizations in different countries and will provide a common language to increase and enrich international exchanges of information among toxicologists and pathologists. The purpose of this publication is to provide a standardized nomenclature for classifying microscopical lesions observed in the integument of laboratory rats and mice. Example colour images are provided for most lesions. The standardized nomenclature presented in this document and additional colour images are also available electronically at http://www.goreni.org. The nomenclature presented herein is based on histopathology databases from government, academia, and industrial laboratories throughout the world, and covers lesions that develop spontaneously as well as those induced by exposure to various test materials. (DOI: 10.1293/tox.26.27S; J Toxicol Pathol 2013; 26: 27S-57S).

LRRK2 protein levels are determined by kinase function and are crucial for kidney and lung homeostasis in mice.

Mutations in leucine-rich repeat kinase 2 (LRRK2) cause late-onset Parkinson's disease (PD), but the underlying pathophysiological mechanisms and the normal function of this large multidomain protein remain speculative. To address the role of this protein in vivo, we generated three different LRRK2 mutant mouse lines. Mice completely lacking the LRRK2 protein (knock-out, KO) showed an early-onset (age 6 weeks) marked increase in number and size of secondary lysosomes in kidney proximal tubule cells and lamellar bodies in lung type II cells. Mice expressing a LRRK2 kinase-dead (KD) mutant from the endogenous locus displayed similar early-onset pathophysiological changes in kidney but not lung. KD mutants had dramatically reduced full-length LRRK2 protein levels in the kidney and this genetic effect was mimicked pharmacologically in wild-type mice treated with a LRRK2-selective kinase inhibitor. Knock-in (KI) mice expressing the G2019S PD-associated mutation that increases LRRK2 kinase activity showed none of the LRRK2 protein level and histopathological changes observed in KD and KO mice. The autophagy marker LC3 remained unchanged but kidney mTOR and TCS2 protein levels decreased in KD and increased in KO and KI mice. Unexpectedly, KO and KI mice suffered from diastolic hypertension opposed to normal blood pressure in KD mice. Our findings demonstrate a role for LRRK2 in kidney and lung physiology and further show that LRRK2 kinase function affects LRRK2 protein steady-state levels thereby altering putative scaffold/GTPase activity. These novel aspects of peripheral LRRK2 biology critically impact ongoing attempts to develop LRRK2 selective kinase inhibitors as therapeutics for PD.

Outside-in signaling through integrins and cadherins: a central mechanism to control epidermal growth and differentiation?

The process of epidermal renewal persists throughout the entire life of an organism. It begins when a keratinocyte progenitor leaves the stem cell compartment, undergoes a limited number of mitotic divisions, exits the cell cycle, and commits to terminal differentiation. At the end of this phase, the postmitotic keratinocytes detach from the basement membrane to build up the overlaying stratified epithelium. Although highly coordinated, this sequence of events is endowed with a remarkable versatility, which enables the quiescent keratinocyte to reintegrate into the cell cycle and become migratory when necessary, for example after wounding. It is this versatility that represents the Achilles heel of epithelial cells allowing for the development of severe pathologies. Over the past decade, compelling evidence has been provided that epithelial cancer cells achieve uncontrolled proliferation following hijacking of a "survival program" with PI3K/Akt and a "proliferation program" with growth factor receptor signaling at its core. Recent insights into adhesion receptor signaling now propose that integrins, but also cadherins, can centrally control these programs. It is suggested that the two types of adhesion receptors act as sensors to transmit extracellular stimuli in an outside-in mode, to inversely modulate epidermal growth factor receptor signaling and ensure cell survival. Hence, cell-matrix and cell-cell adhesion receptors likely play a more powerful and wide-ranging role than initially anticipated. This Perspective article discusses the relevance of this emerging field for epidermal growth and differentiation, which can be of importance for severe pathologies such as tumorigenesis and invasive metastasis, as well as psoriasis and Pemphigus vulgaris.

Keratinocyte transcriptional regulation of the human c-Myc promoter occurs via a novel Lef/Tcf binding element distinct from neoplastic cells.

The proto-oncogene c-Myc is involved in early neoplastic transformations. Two consensus Lef/Tcf binding elements (TBE) were found to be prerequisite for transcriptional transactivation by the armadillo proteins beta-catenin and plakoglobin (PG) together with Tcf4 in human neoplastic cells. In epidermal keratinocytes, c-Myc was reported to be repressed by Lef-1 and PG. Using reporter gene assays, here we demonstrate that deletion of the two consensus TBE fails to abrogate transcriptional regulation by Lef-1/PG in wildtype and beta-catenin-/- keratinocytes, while it reduces transcription in pre-neoplastic PG-/- keratinocytes. We identified a TBE sequence variant downstream of the major transcriptional initiation site that binds Lef-1 in vitro and in vivo, and its mutation compromised transcriptional regulation by Lef-1/PG. Collectively, this study demonstrates that the two consensus TBE's reported in neoplastic cells are dispensable for c-Myc regulation in normal keratinocytes, which instead use a novel TBE sequence variant. This unprecedented finding may have important implications for armadillo target genes involved in carcinogenesis.

Consequences of depleted SERCA2-gated calcium stores in the skin.

Sarco(endo)plasmic reticulum Ca2+-ATPase isoform 2 (SERCA2) pumps belong to the family of Ca2+-ATPases responsible for the maintenance of calcium in the endoplasmic reticulum. In epidermal keratinocytes, SERCA2-controlled calcium stores are involved in cell cycle exit and onset of terminal differentiation. Hence, their dysfunction was thought to provoke impaired keratinocyte cohesion and hampered terminal differentiation. Here, we assessed cultured keratinocytes and skin biopsies from a canine family with an inherited skin blistering disorder. Cells from lesional and phenotypically normal areas of one of these dogs revealed affected calcium homeostasis due to depleted SERCA2-gated stores. In phenotypically normal patient cells, this defect compromised upregulation of p21(WAF1) and delayed the exit from the cell cycle. Despite this abnormality it failed to impede the terminal differentiation process in the long term but instead coincided with enhanced apoptosis and appearance of chronic wounds, suggestive of secondary mutations. Collectively, these findings provide the first survey on phenotypic consequences of depleted SERCA-gated stores for epidermal homeostasis that explain how depleted SERCA2 calcium stores provoke focal lesions rather than generalized dermatoses, a phenotype highly reminiscent of the human genodermatosis Darier disease.

Proliferation, cell cycle exit, and onset of terminal differentiation in cultured keratinocytes: pre-programmed pathways in control of C-Myc and Notch1 prevail over extracellular calcium signals.

So far it was reported that a switch from low to high extracellular calcium induces growth arrest and terminal differentiation in cultured human and mouse keratinocytes. We had observed that both canine and mouse keratinocytes proliferate in high (1.8 mM, respectively, 1.2 mM) or low (0.09 and 0.06 mM) calcium-containing medium. In-depth analysis of this phenomenon revealed, as reported here, that the switch between proliferation and terminal differentiation occurred irrespective of calcium conditions when the canine and murine keratinocytes reach confluency. The "confluency switch" coincided with transcriptional upregulation of cell cycle inhibitors p21(WAF1) and p27(KIP1) as well as proteins marking onset of terminal differentiation. It was further accompanied by downregulation and nuclear clearance of c-Myc, and conversely activation of Notch1, which are shown to be critical determinants of this process. Together, this study demonstrates that even in the absence of and similar to their in vivo environment, cultured canine and mouse keratinocytes follow a pre-defined differentiation program. This program is in control of c-Myc and Notch1 and does not require complementary signals for onset of terminal differentiation except those given by cell-cell contact. Once triggered, completion of the terminal differentiation process depends on elevated extracellular calcium to stabilize intercellular junctions and components of the cornified envelope.

Cardiac rhabdomyoma in a juvenile fallow deer (Dama dama).

A cardiac rhabdomyoma is described in a 6-wk-old captive fallow deer (Dama dama) that died suddenly without previous clinical signs. The tumor was characterized by multiple nodules composed of large atypical vacuolated myoblastic cells. As previously reported in humans and other animal species, there is compelling evidence that the cardiac rhabdomyoma is a congenital developmental anomaly rather than a true neoplasm. To our knowledge, this is the first report of a cardiac tumor and a rhabdomyoma in a cervid species.