Utilizing a Novel Giant Congenital Melanocytic Nevus Murine Model to Investigate Therapeutic Strategies and Model Tumorigenesis

Giant congenital melanocytic nevi (gCMN) are oncogene-driven proliferations of melanocytes present since birth that are greater than 20 cm in projected adult size, and have a melanoma conversion frequency of ranging from 5-15%. Patients with gCMN typically develop melanoma in early childhood that is extremely aggressive and almost universally fatal. Therefore, targeted therapies to induce nevus regression would be enormously beneficial. NRAS activating mutations are postulated to be the driver mutation gCMN. Described here are two novel gCMN preclinical murine models that harbor an NrasQ61R mutation. Evaluation of both the constitutive nevus model (Dct promoter-driven constitutive Cre with NrasQ61R mutation) and the inducible nevus model (Tyr promoter-driven tamoxifen-inducible CreERT2 with NrasQ61R mutation) demonstrate that both models recapitulate human gCMN histological architecture and model spontaneous tumorigenesis. Of the various drug candidates tested, topical administration of a combination of the MEK inhibitor binimetinib and the c-KIT inhibitor imatinib was superior in causing almost complete nevus regression, as measured by a reduction of melanin deposition and melanocytes in the dermal layer. This may represent a potential topical treatment strategy for the regression of gCMN that avoids both the more deleterious side effects of either systemic drug administration or large-scale surgical procedures. Ultimately, this preclinical murine model may help generate new information about the rare, but deadly gCMN that may aid in improving daily symptoms from these lesions as well as hopefully reduce overall melanoma risk

Scoring Assessments in Stevens-Johnson Syndrome and Toxic Epidermal Necrolysis

Epidermal necrolysis, the unifying term for Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), is a severe cutaneous drug reaction associated with high morbidity and mortality. Given the rarity of this disease, large-scale prospective research studies are limited. Significant institutional and geographical variations in treatment practices highlight the need for standardization of clinical assessment scores and prioritization of research outcome measures in epidermal necrolysis. At the present, clinical assessment is typically simplified to total body surface area (BSA) involvement, with little focus on morphology. Validated clinical scoring systems are used as mortality prognostication tools, with SCORTEN being the best-validated tool thus far, although the ABCD-10 has also been recently introduced. These tools are imperfect in that they tend to either overestimate or underestimate mortality in certain populations and are not designed to monitor disease progression. Although mortality is often used as a primary endpoint for epidermal necrolysis studies, this outcome fails to capture more nuanced changes in skin disease such as arrest of disease progression while also lacking a validated skin-directed inclusion criterion to stratify patients based on the severity of skin disease at study entry. In addition to mortality, many studies also use BSA stabilization or time to re-epithelialization as endpoints, although these are not clearly defined morphologically, and inter- and intra-rater reliability are unclear. More specific, validated cutaneous assessment scores are necessary in order advance therapeutic options for epidermal necrolysis. In this review, we summarize the strengths and weaknesses of current clinical assessment practices in epidermal necrolysis and highlight the need for standardized research tools to monitor cutaneous involvement throughout the hospitalization

High-performance genetically targetable optical neural silencing by proton pumps

The ability to silence the activity of genetically specified neurons in a temporally precise fashion would provide the opportunity to investigate the causal role of specific cell classes in neural computations, behaviours and pathologies. Here we show that members of the class of light-driven outward proton pumps can mediate powerful, safe, multiple-colour silencing of neural activity. The gene archaerhodopsin-3 (Arch)1 from Halorubrum sodomense enables near-100% silencing of neurons in the awake brain when virally expressed in the mouse cortex and illuminated with yellow light. Arch mediates currents of several hundred picoamps at low light powers, and supports neural silencing currents approaching 900 pA at light powers easily achievable in vivo. Furthermore, Arch spontaneously recovers from light-dependent inactivation, unlike light-driven chloride pumps that enter long-lasting inactive states in response to light. These properties of Arch are appropriate to mediate the optical silencing of significant brain volumes over behaviourally relevant timescales. Arch function in neurons is well tolerated because pH excursions created by Arch illumination are minimized by self-limiting mechanisms to levels comparable to those mediated by channelrhodopsins2, 3 or natural spike firing. To highlight how proton pump ecological and genomic diversity may support new innovation, we show that the blue–green light-drivable proton pump from the fungus Leptosphaeria maculans4 (Mac) can, when expressed in neurons, enable neural silencing by blue light, thus enabling alongside other developed reagents the potential for independent silencing of two neural populations by blue versus red light. Light-driven proton pumps thus represent a high-performance and extremely versatile class of ‘optogenetic’ voltage and ion modulator, which will broadly enable new neuroscientific, biological, neurological and psychiatric investigations.National Institutes of Health (U.S.) (NIH Director's New Innovator Award (DP2 OD002002-01))National Institutes of Health (U.S.) (grant 0835878)National Science Foundation (U.S.) (grant 0848804)McGovern Institute for Brain Research at MIT (Neurotechnology Award Program)National Institutes of Health (U.S.) (NIH 1K99MH085944)Alfred P. Sloan FoundationUnited States. Dept. of DefenseDr. Gerald Burnett and Marjorie BurnettSFN Research Award for Innovation in NeuroscienceMassachusetts Institute of Technology. Media LaboratoryBenesse FoundationWallace H. Coulter FoundationHelen Hay Whitney FoundationBrain & Behavior Research Foundatio

The Koebner phenomenon may contribute to the development of calciphylaxis: A case series

Calciphylaxis is characterized by calcific occlusion of vessels and subsequent tissue ischemia due to thrombosis. The precise pathogenetic mechanism behind calciphylaxis remains unclear. In the original experiment by Hans Selye and colleagues, soft-tissue calcification was induced in rats by applying a sensitizing agent, followed by a “challenger” agent after a specific time period. Trauma may represent one of these “challenger” agents, serving as an inducer of endothelial dysfunction and subsequent thrombosis, leading from tissue calcification to calciphylaxis. Koebnerization, a term used to describe the appearance of isomorphic lesions in areas of trauma, has been postulated to be a feature of calciphylaxis. This hypothesis arose from reports of patients who developed calciphylaxis following mild skin trauma, such as that caused by chronic resting of elbows on thighs, placement of ice packs, and injections involving various medications such as iron dextran, tobramycin, and especially insulin. Rigorous studies demonstrating the relationship between calciphylaxis and Koebnerization and an underlying mechanism are limited. To better understand this association, this study retrospectively identified characteristics of patients who presented with calciphylaxis in areas of trauma, suggesting the presence of Koebnerization