Current status of MEK inhibitors in the treatment of plexiform neurofibromas

Unraveling neuronal and metabolic alterations in neurofibromatosis type 1

Neurofibromatosis type 1 (OMIM 162200) affects ~ 1 in 3,000 individuals worldwide and is one of the most common monogenetic neurogenetic disorders that impacts brain function. The disorder affects various organ systems, including the central nervous system, resulting in a spectrum of clinical manifestations. Significant progress has been made in understanding the disorder's pathophysiology, yet gaps persist in understanding how the complex signaling and systemic interactions affect the disorder. Two features of the disorder are alterations in neuronal function and metabolism, and emerging evidence suggests a potential relationship between them. This review summarizes neurofibromatosis type 1 features and recent research findings on disease mechanisms, with an emphasis on neuronal and metabolic features.

Mucocutaneous toxicities from MEK inhibitors: a scoping review of the literature

BACKGROUND

MEK inhibitors cause a wide spectrum of mucocutaneous toxicities which can delay or interrupt life-saving therapy.

PURPOSE

To summarize the morphology, incidence, and clinical presentation of mucocutaneous toxicities from MEK inhibitors via a scoping review of the literature.

METHODS

We conducted a scoping review of the published literature, including clinical trials, retrospective and prospective studies, reviews, and case reports and series. All included literature was analyzed by a panel of pediatric and adult oncodermatologists.

RESULTS

Of 1626 initial citations, 227 articles met final inclusion criteria. Our review identified follicular reactions, ocular toxicities, xerosis, eczematous dermatitis, edema, and paronychia as the most common mucocutaneous side effects from MEK inhibitor therapy. Grade 1 and 2 reactions were the most prevalent and were typically managed while continuing treatment; however, grade 3 toxicities requiring dose reductions or treatment interruptions were also reported.

CONCLUSION

Mucocutaneous toxicities to MEK inhibitor therapy are common and most often mild in severity. Early recognition and treatment can mitigate disruptions in oncologic therapy.

Precision Drug Repurposing: A Deep Learning Toolkit for Identifying 34 Hyperpigmentation-Associated Genes and Optimizing Treatment Selection

BACKGROUND

Hyperpigmentation is a skin disorder characterized by a localized darkening of the skin due to increased melanin production. When patients fail first line topical treatments, secondary treatments such as chemical peels and lasers are offered. However, these interventions are not devoid of risks and are associated with postinflammatory hyperpigmentation. In the quest for novel therapeutic potentials, this study aims to investigate computational methods in the identification of new targeted therapies in the treatment of hyperpigmentation.

METHODS

We used a comprehensive approach, which integrated text mining, interpreting gene lists through enrichment analysis and integration of diverse biological information (GeneCodis), protein-protein association networks and functional enrichment analyses (STRING), and plug-in network centrality parameters (Cytoscape) to pinpoint genes closely associated with hyperpigmentation. Subsequently, analysis of drug-gene interactions to identify potential drugs (Cortellis) was utilized to select drugs targeting these identified genes. Lastly, we used Deep Learning Based Drug Repurposing Toolkit (DeepPurpose) to conduct drug-target interaction predictions to ultimately identify candidate drugs with the most promising binding affinities.

RESULTS

Thirty-four hyperpigmentation-related genes were identified by text mining. Eight key genes were highlighted by utilizing GeneCodis, STRING, Cytoscape, gene enrichment, and protein-protein interaction analysis. Thirty-five drugs targeting hyperpigmentation-associated genes were identified by Cortellis, and 29 drugs, including 16 M2PK1 inhibitors, 11 KRAS inhibitors, and 2 BRAF inhibitors were recommended by DeepPurpose.

CONCLUSIONS

The study highlights the promise of advanced computational methodology for identifying potential treatments for hyperpigmentation.

A guide to ERK dynamics, part 2: downstream decoding

Signaling by the extracellular signal-regulated kinase (ERK) pathway controls many cellular processes, including cell division, death, and differentiation. In this second installment of a two-part review, we address the question of how the ERK pathway exerts distinct and context-specific effects on multiple processes. We discuss how the dynamics of ERK activity induce selective changes in gene expression programs, with insights from both experiments and computational models. With a focus on single-cell biosensor-based studies, we summarize four major functional modes for ERK signaling in tissues: adjusting the size of cell populations, gradient-based patterning, wave propagation of morphological changes, and diversification of cellular gene expression states. These modes of operation are disrupted in cancer and other related diseases and represent potential targets for therapeutic intervention. By understanding the dynamic mechanisms involved in ERK signaling, there is potential for pharmacological strategies that not only simply inhibit ERK, but also restore functional activity patterns and improve disease outcomes.

Treatment decisions and the use of MEK inhibitors for children with neurofibromatosis type 1-related plexiform neurofibromas

Neurofibromatosis type 1 (NF1), the most common tumor predisposition syndrome, occurs when NF1 gene variants result in loss of neurofibromin, a negative regulator of RAS activity. Plexiform neurofibromas (PN) are peripheral nerve sheath tumors that develop in patients with NF1 and are associated with substantial morbidity and for which, until recently, the only treatment was surgical resection. However, surgery carries several risks and a proportion of PN are considered inoperable. Understanding the genetic underpinnings of PN led to the investigation of targeted therapies as medical treatment options, and the MEK1/2 inhibitor selumetinib has shown promising efficacy in pediatric patients with NF1 and symptomatic, inoperable PN. In a phase I/II trial, most children (approximately 70%) achieved reduction in tumor volume accompanied by improvements in patient-reported outcomes (decreased tumor-related pain and improvements in quality of life, strength, and range of motion). Selumetinib is currently the only licensed medical therapy indicated for use in pediatric patients with symptomatic, inoperable NF1-PN, with approval based on the results of this pivotal clinical study. Several other MEK inhibitors (binimetinib, mirdametinib, trametinib) and the tyrosine kinase inhibitor cabozantinib are also being investigated as medical therapies for NF1-PN. Careful consideration of multiple aspects of both disease and treatments is vital to reduce morbidity and improve outcomes in patients with this complex and heterogeneous disease, and clinicians should be fully aware of the risks and benefits of available treatments. There is no single treatment pathway for patients with NF1-PN; surgery, watchful waiting, and/or medical treatment are options. Treatment should be individualized based on recommendations from a multidisciplinary team, considering the size and location of PN, effects on adjacent tissues, and patient and family preferences. This review outlines the treatment strategies currently available for patients with NF1-PN and the evidence supporting the use of MEK inhibitors, and discusses key considerations in clinical decision-making.

Diagnosis and Treatment of Peripheral and Cranial Nerve Tumors with Expert Recommendations: An EUropean Network for RAre CANcers (EURACAN) Initiative

The 2021 WHO classification of the CNS Tumors identifies as "Peripheral nerve sheath tumors" (PNST) some entities with specific clinical and anatomical characteristics, histological and molecular markers, imaging findings, and aggressiveness. The Task Force has reviewed the evidence of diagnostic and therapeutic interventions, which is particularly low due to the rarity, and drawn recommendations accordingly. Tumor diagnosis is primarily based on hematoxylin and eosin-stained sections and immunohistochemistry. Molecular analysis is not essential to establish the histological nature of these tumors, although genetic analyses on DNA extracted from PNST (neurofibromas/schwannomas) is required to diagnose mosaic forms of NF1 and SPS. MRI is the gold-standard to delineate the extension with respect to adjacent structures. Gross-total resection is the first choice, and can be curative in benign lesions; however, the extent of resection must be balanced with preservation of nerve functioning. Radiotherapy can be omitted in benign tumors after complete resection and in NF-related tumors, due to the theoretic risk of secondary malignancies in a tumor-suppressor syndrome. Systemic therapy should be considered in incomplete resected plexiform neurofibromas/MPNSTs. MEK inhibitor selumetinib can be used in NF1 children ≥2 years with inoperable/symptomatic plexiform neurofibromas, while anthracycline-based treatment is the first choice for unresectable/locally advanced/metastatic MPNST. Clinical trials on other MEK1-2 inhibitors alone or in combination with mTOR inhibitors are under investigation in plexiform neurofibromas and MPNST, respectively.

Neurofibromatosis type 1 system-based manifestations and treatments: a review

INTRODUCTION

Neurofibromatosis type 1 (NF1) is a genetic disorder caused by a mutation in the NF1 gene. This disease presents with various system-based manifestations, including cardiac, musculoskeletal, and neuronal issues, which have been well-studied in previous research and have prompted the development of current and emerging treatments. These treatments, mainly medications targeting specific manifestations of NF1, aim to mitigate the negative impacts of the disease on patients' lives. NF1 is associated with an increased risk of malignancy and a significant decrease in life expectancy. In this paper, we review the current and emerging treatments for NF1 in relation to its system-based manifestations.

METHODS

We conducted an extensive literature search using specific keywords through databases such as PubMed, Scopus, and Cochrane. The articles we found were compiled and subjected to strict inclusion and exclusion criteria.

RESULTS

Pharmacological advances have led to the development of products that hold promise as future treatments for NF1. Given the diverse manifestations that can affect multiple organ systems in patients with NF1, it is important to consider a variety of treatment options to achieve optimal results. However, one of the major challenges in diagnosing and treating NF1 is that patients present asymptomatically, making it necessary to rely on clinical features for diagnosis.

CONCLUSION

In conclusion, NF1 is a complex disease with varying manifestations and a growing field of pharmacologic treatments. The information presented in this article synthesizes current knowledge and available therapies for NF1.

Novel effects of Ras-MAPK pathogenic variants on the developing human brain and their link to gene expression and inhibition abilities

The RASopathies are genetic syndromes associated with pathogenic variants causing dysregulation of the Ras/mitogen-activated protein kinase (Ras-MAPK) pathway, essential for brain development, and increased risk for neurodevelopmental disorders. Yet, the effects of most pathogenic variants on the human brain are unknown. We examined: 1. How Ras-MAPK activating variants of PTPN11 / SOS1 protein-coding genes affect brain anatomy. 2. The relationship between PTPN11 gene expression levels and brain anatomy, and 3. The relevance of subcortical anatomy to attention and memory skills affected in the RASopathies. We collected structural brain MRI and cognitive-behavioral data from 40 pre-pubertal children with Noonan syndrome (NS), caused by PTPN11 ( n  = 30) or SOS1 ( n  = 10) variants (age 8.53 ± 2.15, 25 females), and compared them to 40 age- and sex-matched typically developing controls (9.24 ± 1.62, 27 females). We identified widespread effects of NS on cortical and subcortical volumes and on determinants of cortical gray matter volume, surface area (SA) and cortical thickness (CT). In NS, we observed smaller volumes of bilateral striatum, precentral gyri, and primary visual area ( d 's<-0.8), and extensive effects on SA ( d 's>|0.8|) and CT ( d 's>|0.5|) relative to controls. Further, SA effects were associated with increasing PTPN11 gene expression, most prominently in the temporal lobe. Lastly, PTPN11 variants disrupted normative relationships between the striatum and inhibition functioning. We provide evidence for effects of Ras-MAPK pathogenic variants on striatal and cortical anatomy as well as links between PTPN11 gene expression and cortical SA increases, and striatal volume and inhibition skills. These findings provide essential translational information on the Ras-MAPK pathway's effect on human brain development and function.

Selumetinib - a potential small molecule inhibitor for osteoarthritis treatment

Objectives: Osteoarthritis (OA) is a common disease that mainly manifests as inflammation and destruction of cartilage and subchondral bone. Recently, necroptosis has been reported to play an important role in the development of OA. Selumetinib displays a contrasting expression pattern to necroptosis-related proteins. The present study aimed to investigate the potential therapeutic effects of selumetinib in OA process.

Methods:In vitro experiments, interleukin-1β (IL-1β) was used to induce necroptosis of chondrocytes. We used high-density cell culture, Western Blot and PT-PCR to observe the effect of different concentrations of selumetinib on the extracellular matrix of cartilage. Afterwards, we visualized the effect of selumetinib on osteoclast formation by TRAP staining and F-actin rings. In vivo experiment, we induced experimental osteoarthritis in mice by surgically destabilizing the medial meniscus (DMM) while administering different concentrations of selumetinib intraperitoneally.

Results: Selumetinib promoted cartilage matrix synthesis and inhibited matrix decomposition. We found that selumetinib exerted a protective function by inhibiting the activation of RIP1/RIP3/MLKL signaling pathways in chondrocytes. Selumetinib also inhibited the activation of RANKL-induced NF-κB and MAPK signaling pathways in BMMs, thereby interfering with the expression of osteoclast marker genes. In the DMM-induced OA model, a postsurgical injection of selumetinib inhibited cartilage destruction and lessened the formation of TRAP-positive osteoclasts in subchondral bone.

Conclusion: Selumetinib can protect chondrocytes by regulating necroptosis to prevent the progression of OA and reduce osteoclast formation. In summary, our findings suggest that selumetinib has potential as a therapeutic agent for OA.

[Progress in diagnosis and treatment of neurofibromatosis in children]

Neurofibromatosis type 1（NF1） is an autosomal dominant genetic disease in which a mutation in the NF1 gene on chromosome 17q11.2 results in inactivation or down-regulation of neurofibromin. This results in a series of neurocutaneous lesions characterized by neurofibromatosis. Patients with plexiform neurofibromas（PN）, as one of the main manifestations of NF1, often experience pain, dysfunction, skeletal deformities, changes in appearance and other symptoms. In severe cases, compression of the airways and vital organs occurs, and the PN is at risk of malignancy progression. At present, its treatment is still challenging. Surgery is the primary treatment for PN, but complete resection is often difficult. In recent years, chemotherapy for PN has become a hot topic. This article reviews the research progress in the pathogenesis, diagnosis and treatment of PN in recent years.

Expanding the Reach of Precision Oncology by Drugging All KRAS Mutants

KRAS is the most frequently mutated oncogene, harboring mutations in approximately one in seven cancers. Allele-specific KRASG12C inhibitors are currently changing the treatment paradigm for patients with KRASG12C-mutated non-small cell lung cancer and colorectal cancer. The success of addressing a previously elusive KRAS allele has fueled drug discovery efforts for all KRAS mutants. Pan-KRAS drugs have the potential to address broad patient populations, including KRASG12D-, KRASG12V-, KRASG13D-, KRASG12R-, and KRASG12A-mutant or KRAS wild-type-amplified cancers, as well as cancers with acquired resistance to KRASG12C inhibitors. Here, we review actively pursued allele-specific and pan-KRAS inhibition strategies and their potential utility.

SIGNIFICANCE

Mutant-selective KRASG12C inhibitors target a fraction (approximately 13.6%) of all KRAS-driven cancers. A broad arsenal of KRAS drugs is needed to comprehensively conquer KRAS-driven cancers. Conceptually, we foresee two future classes of KRAS medicines: mutant-selective KRAS drugs targeting individual variant alleles and pan-KRAS therapeutics targeting a broad range of KRAS alterations.

Value of a café-au-lait macules screening clinic: Experience from The Hospital for Sick Children in Toronto

BACKGROUND/OBJECTIVES

Café-au-lait macules (CALMs) are a characteristic feature of neurofibromatosis type 1 (NF1), but also occur in other genetic disorders. Differential diagnosis of CALMs remains challenging and can be stressful for families. We sought to examine the role of an established CALMs screening clinic in diagnosing CALMs-related disorders.

METHOD

We retrospectively reviewed patients seen between July 2012 and January 2019 in a CALMs screening clinic at The Hospital for Sick Children, a tertiary pediatric hospital in Toronto, Canada. Pediatric patients were referred because of multiple CALMs or suspected NF1. Selection was based on a chronological referral sample with no exclusions. A pediatric dermatologist examined all patients for CALMs and NF1 manifestations. Genetic testing was offered to confirm a clinical diagnosis or when clinical findings were inconclusive.

RESULTS

Three hundred patients, of which 152 (50.7%) were female and had a mean age of 5.6 ± 4.8 years were seen during the study period. NF1 was diagnosed in 76 (25.3%) patients, mosaic NF1 in 38 (12.7%) patients, and 8 (2.7%) patients received other genetic diagnoses. One hundred and twelve (37.3%) patients were diagnosed with isolated CALMs not associated with an underlying genetic disease. Furthermore, 36 (12%) of our patients did not have CALMs.

CONCLUSIONS

The CALMs screening clinic aided in the early diagnosis of genetic disorders such as NF1 and distinguished CALMs from other hyperpigmented lesions. We encourage the adoption of this clinic model in referral centers to streamline and optimize care of patients with presumptive diagnosis of CALMs.

Treatment of Plexiform Neurofibromas with MEK Inhibitors: First Results with a New Therapeutic Option

Neurofibromatosis type-1 (NF1)-associated plexiform neurofibromas (PN) are peripheral nerve sheath tumors that can significantly affect the quality of life. Until recently, surgery was the only treatment for these tumors. However, in most cases, surgery cannot achieve complete tumor removal and carries a high risk of postoperative deficits. Therefore, the recent approval of the MEK inhibitor selumetinib for the treatment of NF1-associated PN provides a long-awaited novel therapeutic option. Here, we report our experience with MEK inhibitor treatment in 12 pediatric NF1 patients with inoperable symptomatic PN. Eight patients received trametinib (median therapy duration 12.13 months and range 4-29 months), and four patients received selumetinib (median therapy duration 6.25 months and range 4-11 months). Volumetric magnetic resonance imaging (MRI) after 6 months of treatment was available for seven trametinib patients (median tumor volume reduction of 26.5% and range 11.3-55.7%) and two selumetinib patients (21.3% tumor volume reduction in one patient and +3% tumor volume change in the other one). All patients reported clinical benefits such as improved range of motion or reduced disfigurement. Therapy-related adverse events occurred in 58.3% of patients and mainly consisted of skin toxicity, paronychia, and gastrointestinal symptoms. Two patients discontinued trametinib treatment after 14 and 29 months when severe skin toxicity occurred and no further reduction of tumor size was observed. In one patient, discontinuation of therapy resulted in a 27.2% tumor volume increase as demonstrated on volumetric MRI 6 months later. Our data show that MEK inhibition is a novel therapeutic approach for inoperable PN with promising results and a manageable safety profile.

Current concepts of neurofibromatosis type 1: pathophysiology and treatment

Neurofibromatosis type 1 is the most common tumor predisposition syndrome inherited in an autosomal dominant (100% penetrance) fashion with a wide variety of expressivity. From the perspective of plastic surgery, the most significant clinical symptoms, including disfiguration, peripheral neurologic symptoms, and skeletal abnormalities, are caused by various tumors originating from the affected nerves. Surgical removal is the standard of care for these tumors. However, the outcome is frequently unsatisfactory, facilitating the search for additional therapeutic adjuvants. Current trials of molecularly targeted therapies are promising. Abbreviations: CALMs, café-au-lait macules; CNs, cutaneous neurofibromas; FDG, 18F-fluoro-deoxy-glucose; MAPK, mitogen-activated protein kinase; MPNSTs, malignant peripheral nerve sheath tumors; MRI, magnetic resonance imaging; NF1, neurofibromatosis type 1; NIH, National Institutes of Health; PET, positron emission tomography; PN, plexiform neurofibromas; TME, tumor microenvironment.

Plexiform neurofibroma: shedding light on the investigational agents in clinical trials

INTRODUCTION

Neurofibromatosis Type 1 (NF1) is an autosomal dominant genetic condition, which predisposes individuals to the development of plexiform neurofibromas (PN), benign nerve sheath tumors seen in 30-50% of patients with NF1. These tumors may cause significant pain and disfigurement or may compromise organ function. Given the morbidity associated with these tumors, therapeutic options for patients with NF1-related PN are necessary.

AREAS COVERED

We searched the www.clinicaltrials.gov database for 'plexiform neurofibroma.' This article summarizes completed and ongoing trials involving systemic therapies for PN.

EXPERT OPINION

Surgery is the mainstay treatment; however, complete resection is not possible in many cases. Numerous systemic therapies have been evaluated in patients with NF1, with MEK inhibitors (MEKi) showing the greatest efficacy for volumetric reduction and improvement in functional and patient-reported outcomes. The MEKi selumetinib is now FDA approved for the treatment of inoperable, symptomatic PN in pediatric NF1 patients. Questions remain regarding the use of this drug class in terms of when to initiate therapy, overall duration, reduced dosing schedules, and side effect management. Future studies are needed to fully understand the clinical application of MEKi and to evaluate other potential therapies through appropriate trial designs for this potentially devastating, manifestation in NF1.

Targeted Therapies for the Neurofibromatoses

Over the past several years, management of the tumors associated with the neurofibromatoses has been recognized to often require approaches that are distinct from their spontaneous counterparts. Focus has shifted to therapy aimed at minimizing symptoms given the risks of persistent, multiple tumors and new tumor growth. In this review, we will highlight the translation of preclinical data to therapeutic trials for patients with neurofibromatosis, particularly neurofibromatosis type 1 and neurofibromatosis type 2. Successful inhibition of MEK for patients with neurofibromatosis type 1 and progressive optic pathway gliomas or plexiform neurofibromas has been a significant advancement in patient care. Similar success for the malignant NF1 tumors, such as high-grade gliomas and malignant peripheral nerve sheath tumors, has not yet been achieved; nor has significant progress been made for patients with either neurofibromatosis type 2 or schwannomatosis, although efforts are ongoing.

Updated Approach to Patients with Multiple Café au Lait Macules

Café au lait macules (CALMs) are a normal and frequent finding in the general population, but multiple CALMs raise the possibility of an underlying neurocutaneous disease like neurofibromatosis type I. Certain features of CALMs like number, size, shape, and distribution are important in identifying children at higher risk of having a neurocutaneous disorder or another genetic disorder. Genetic testing can be especially helpful in establishing a diagnosis in atypical presentations, or when the child is young and other features of the disease aside from CALMs have not manifested.

New Medical Device and Therapeutic Approvals in Otolaryngology: State of the Art Review 2020

Objectives

To evaluate new drugs and devices relevant to otolaryngology–head and neck surgery that were approved by the US Food and Drug Administration (FDA) in 2020.

Data Sources

Publicly available device and therapeutic approvals from ENT (ear, nose, and throat), anesthesia, neurology (neurosurgery), and plastic and general surgery FDA committees.

Review Methods

Members of the American Academy of Otolaryngology–Head and Neck Surgery’s Medical Devices and Drugs Committee reviewed new therapeutics and medical devices from a query of the FDA’s device and therapeutic approvals. Two independent reviewers assessed the drug’s or device’s relevance to otolaryngology, classified to subspecialty field, with a critical review of available scientific literature.

Conclusions

The Medical Devices and Drugs Committee reviewed 53 new therapeutics and 1094 devices (89 ENT, 140 anesthesia, 511 plastic and general surgery, and 354 neurology) approved in 2020. Ten drugs and 17 devices were considered relevant to the otolaryngology community. Rhinology saw significant improvements around image guidance systems; indications for cochlear implantation expanded; several new monoclonal therapeutics were added to head and neck oncology’s armamentarium; and several new approvals appeared for facial plastics surgery, pediatric otolaryngology, and comprehensive otolaryngology.

Implications for Practice

New technologies and pharmaceuticals offer the promise of improving how we care for otolaryngology patients. However, judicious introduction of innovations into practice requires a nuanced understanding of safety, advantages, and limitations. Working knowledge of new drugs and medical devices approved for the market helps clinicians tailor patient care accordingly.

A Review of Selumetinib in the Treatment of Neurofibromatosis Type 1-Related Plexiform Neurofibromas

OBJECTIVE

To evaluate the safety and efficacy of selumetinib, a novel MEK inhibitor, for the treatment of plexiform neurofibromas (PN) in patients with neurofibromatosis type 1 (NF1).

DATA SOURCES

An English-based literature search of PubMed, EMBASE, and ClinicalTrials.gov was conducted using the terms selumetinib AND neurofibromatosis from inception to August 1, 2021.

STUDY SELECTION AND DATA EXTRACTION

Relevant prescribing information, abstracts, and articles identified through the search were considered for inclusion in this review.

DATA SYNTHESIS

The open-label, multicenter, single-arm, phase II SPRINT trial demonstrated clinically significant improvements in PN-related complications. Of 50 symptomatic patients, 68% experienced a partial response, with a median change in tumor volume of -27.9% from baseline. Estimated progression-free survival at 3 years was 84%. Additionally, clinically meaningful improvements were seen on patient- and parent-reported assessments evaluating pain, range of motion, disfigurement, and quality of life. Overall, the adverse effect profile for selumetinib appears mild and manageable.

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE

Selumetinib is the first FDA-approved treatment for inoperable PN in patients with NF1, demonstrating that MEK inhibition is a promising therapeutic strategy. Studies are ongoing to assess the effect of selumetinib on other NF1-associated tumor types and to determine the optimal dosing schedule and treatment duration. Cost and treatment burden must be considered when selecting selumetinib therapy.

CONCLUSION

Selumetinib exhibits impressive antitumor activity and sustained clinical benefit in patients lacking other viable treatment options. Further studies are warranted to determine the optimal age of initiation, treatment duration, and overall cost-effectiveness of selumetinib.

MEK inhibitors in RASopathies

PURPOSE OF REVIEW

An early understanding of the role of the Ras/Raf/MEK/ERK signalling pathway in regulating cell proliferation has set the stage for the development of several potent and selective MEK inhibitors (MEKi). MEKi represent promising therapies for RAS-driven neoplasias and RASopathies associated with increased Ras/MAPK activity.

RECENT FINDINGS

Neurofibromatosis 1 (NF1) is a prototypic RASopathy in which early-phase clinical trials with MEKi have been successful in the treatment of plexiform neurofibromas (pNF) and low-grade gliomas (LGGs). The phase 2 trial (SPRINT) of selumetinib in pNF resulted in at least 20% reduction in the size of pNF from baseline in 71% of patients and was associated with clinically meaningful improvements. On the basis of this trial, selumetinib (Koselugo) received FDA approval for children 2 years of age and older with inoperable, symptomatic pNF. The phase 2 trial of selumetinib in LGG resulted in 40% partial response and 96% of patients had 2 years of progression-free survival.

SUMMARY

Given the potential of MEK inhibition as an effective and overall well tolerated medical treatment, the use of targeted agents in the NF1 population is likely to increase considerably. Future work on non-NF1 RASopathies should focus on developing preclinical models and defining endpoints for measurement of efficacy in order to conduct clinical trials.

Novel molecular targeted therapies for patients with neurofibromatosis type 1 with inoperable plexiform neurofibromas: a comprehensive review

Neurofibromatosis type 1 (NF1) is a genetic disorder that carries a higher risk of tumor development. Plexiform neurofibromas (PNs) are present in 50% of NF1 and cause significant morbidity when surgery is not feasible. Systemic therapies had not succeeded to reduce PN tumor volume until 2016 when the first trial with an MAPK/extracellular-signal-regulated kinase (MEK) inhibitor was published. We performed a systematic research on novel targeted therapies for patients with NF1 and PNs in PubMed, EMBASE, and conference abstracts with the last update in February 2021. Since 2016, seven trials have reported positive results with MEK inhibitors and other molecular targeted therapies (cabozantinib). Selumetinib has shown an overall response rate of 68% in children with NF1 and symptomatic inoperable PNs, and was associated with pain improvement and a manageable adverse events profile. This led to Food and Drug Administration (FDA) approval of selumetinib in May 2020. Recently, cabozantinib and mirdametinib have also proven their efficacy in adult population. Other MEK inhibitors such as trametinib and binimetinib have also communicated promising preliminary results. Ongoing trials in different populations and with intermittent dosing strategies are underway.

Mesenteric Plexiform Neurofibroma as a Cause of Weight Loss and Chronic Diarrhea in a Patient with YPEL3 Variant

Mesenteric plexiform neurofibroma is a subtype of plexiform neurofibroma that involves the mesentery and causes a variety of gastrointestinal complaints. Plexiform neurofibroma is classically found in patients with neurofibromatosis type 1, although genetic contributions to plexiform neurofibroma pathogenesis are heterogeneous. We report the first case of mesenteric plexiform neurofibroma in a patient with a YPEL3 pathogenic variant. This patient presented with growth failure, generalized abdominal pain and chronic diarrhea. She was confirmed to have mesenteric plexiform neurofibroma on histopathology and targeted sequencing on affected tissue confirmed that there were no neurofibromatosis type 1 variants present. Given that this patient's mesenteric plexiform neurofibroma is associated with YPEL3 dysfunction, she is unlikely to benefit from MEK inhibitors, which are the newly approved treatment for inoperable plexiform neurofibroma in patients with neurofibromatosis type 1.

Neurofibromin Deficiency and Extracellular Matrix Cooperate to Increase Transforming Potential through FAK-Dependent Signaling

Simple Summary

Neurofibromatosis type 1 is a genetic disease that predisposes to tumors of the nervous system, primarily the neurofibroma. Plexiform neurofibromas (Pnfs) are of the greatest concern because of location, size, and frequent progression to malignancy. Although research is making great progress, the lack of in-depth understanding of the molecular mechanisms driving neoplastic progression results in the absence of prognostic indicators and therapeutic targets. We document that cell–cell cooperativity and the dynamics of the extracellular matrix play important roles in the growth and transformation of Pnf cells, directly through the cooperation of RAS and focal adhesion kinase (FAK) signaling. In turn, we found that treatment of Pnf cells with both MEK and FAK inhibitors is effective in abolishing the transforming ability of these cells.

Abstract

Plexiform neurofibromas (Pnfs) are benign peripheral nerve sheath tumors that are major features of the human genetic syndrome, neurofibromatosis type 1 (NF1). Pnfs are derived from Schwann cells (SCs) undergoing loss of heterozygosity (LOH) at the NF1 locus in an NF1^+/− milieu and thus are variably lacking in the key Ras-controlling protein, neurofibromin (Nfn). As these SCs are embedded in a dense desmoplastic milieu of stromal cells and abnormal extracellular matrix (ECM), cell–cell cooperativity (CCC) and the molecular microenvironment play essential roles in Pnf progression towards a malignant peripheral nerve sheath tumor (MPNST). The complexity of Pnf biology makes treatment challenging. The only approved drug, the MEK inhibitor Selumetinib, displays a variable and partial therapeutic response. Here, we explored ECM contributions to the growth of cells lacking Nfn. In a 3D in vitro culture, NF1 loss sensitizes cells to signals from a Pnf-mimicking ECM through focal adhesion kinase (FAK) hyperactivation. This hyperactivation correlated with phosphorylation of the downstream effectors, Src, ERK, and AKT, and with colony formation. Expression of the GAP-related domain of Nfn only partially decreased activation of this signaling pathway and only slowed down 3D colony growth of cells lacking Nfn. However, combinatorial treatment with both the FAK inhibitor Defactinib (VS-6063) and Selumetinib (AZD6244) fully suppressed colony growth. These observations pave the way for a new combined therapeutic strategy simultaneously interfering with both intracellular signals and the interplay between the various tumor cells and the ECM.

Population pharmacokinetics and exposure-response of selumetinib and its N-desmethyl metabolite in pediatric patients with neurofibromatosis type 1 and inoperable plexiform neurofibromas

PURPOSE

Selumetinib (ARRY-142886) is a potent, selective, MEK1/2 inhibitor approved in the US for the treatment of children (≥ 2 years) with neurofibromatosis type 1 (NF1) and symptomatic, inoperable plexiform neurofibromas (PN). We characterized population pharmacokinetics (PK) of selumetinib and its active N-desmethyl metabolite, evaluated exposure-safety/efficacy relationships, and assessed the proposed therapeutic dose of 25 mg/m² bid based on body surface area (BSA) in this patient population.

METHODS

Population PK modeling and covariate analysis (demographics, formulation, liver enzymes, BSA, patients/healthy volunteers) were based on pooled PK data from adult healthy volunteers (n = 391), adult oncology patients (n = 83) and pediatric patients with NF1-PN (n = 68). Longitudinal selumetinib/metabolite exposures were predicted with the final model. Exposure-safety/efficacy analyses were applied to pediatric patients (dose levels: 20, 25, 30 mg/m² bid).

RESULTS

Selumetinib and metabolite concentration-time courses were modeled using a joint compartmental model. Typical selumetinib plasma clearance was 11.6 L/h (95% CI 11.0-12.2 L/ h). Only BSA had a clinically relevant (> 20%) impact on exposure, supporting BSA-based administration in children. Selumetinib and metabolite exposures in responders (≥ 20% PN volume decrease from baseline) and non-responders were largely overlapping, with medians numerically higher in responders. No clear relationships between exposure and safety events were established; exposure was not associated with key adverse events (AEs) including rash acneiform, diarrhea, vomiting, and nausea.

CONCLUSION

Findings support continuous selumetinib 25 mg/m² bid in pediatric patients. Importantly, the updated dosing nomogram ensures that patients will receive a clinically active, yet tolerable, dose regardless of differences in BSA and allows dose reductions, if necessary.

Targeting Son of Sevenless 1: The pacemaker of KRAS

Son of Sevenless (SOS) is a guanine nucleotide exchange factor that activates the important cell signaling switch KRAS. SOS acts as a pacemaker for KRAS, the beating heart of cancer, by catalyzing the "beating" from the KRAS(off) to the KRAS(on) conformation. Activating mutations in SOS1 are common in Noonan syndrome and oncogenic alterations in KRAS drive 1 in seven human cancers. Promising clinical efficacy has been observed for selective KRAS^G12C inhibitors, but the vast majority of oncogenic KRAS alterations remain undrugged. The discovery of a druggable pocket on SOS1 has led to potent SOS1 inhibitors such as BI-3406. SOS1 inhibition leads to antiproliferative effects against all major KRAS mutants. The first SOS1 inhibitor has entered clinical trials for KRAS-mutated cancers. In this review, we provide an overview of SOS1 function, its association with cancer and RASopathies, known SOS1 activators and inhibitors, and a future perspective is provided.

Neurofibromatosis in the Era of Precision Medicine: Development of MEK Inhibitors and Recent Successes with Selumetinib

PURPOSE OF REVIEW

Patients with neurofibromatosis type 1 (NF1) are at increased risk for benign and malignant neoplasms. Recently, targeted therapy with the MEK inhibitor class has helped address these needs. We highlight recent successes with selumetinib while acknowledging ongoing challenges for NF1 patients and future directions.

RECENT FINDINGS

MEK inhibitors have demonstrated efficacy for NF1-related conditions, including plexiform neurofibromas and low-grade gliomas, two common causes of NF1-related morbidity. Active investigations for NF1-related neoplasms have benefited from advanced understanding of the genomic and cell signaling alterations in these conditions and development of sound preclinical animal models. Selumetinib has become the first FDA-approved targeted therapy for NF1 following its demonstrated efficacy for inoperable plexiform neurofibroma. Investigations of combination therapy and the development of a representative NF1 swine model hold promise for translating therapies for other NF1-associated pathology.

Increased nuclear translation of YAP might act as a potential therapeutic target for NF1-related plexiform neurofibroma

Plexiform neurofibroma (pNF) in the head and neck is a characteristic feature in patients with neurofibromatosis type 1 (NF1) and is associated with significant disfigurement and psychological distress. Yes-associated protein (YAP), the key molecule involved in the Hippo pathway, is a vital transductor that regulates the proliferation and remyelinating of Schwann cells. The functional status of YAP and its feasibility as a potential target are still unknown in pNF. A total of 17 pNF tumor tissue specimens from the head and neck were collected at the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine. Histologically, diagnosis of the Schwann cell region in pNF was achieved with hematoxylin-eosin staining, positive reactions for S100, SOX10, ERK and p-ERK, and low identification of Ki67 and SMA. Compared with normal nerve tissue, obviously increased nuclear YAP was detected in the Schwann cell region of pNF, with a mean nuclear staining rate of 67.11%. Based on the shNF1 Schwann cell model (the RSC96 cell line), with upregulated expression of RAS, ERK and p-ERK, p-YAP (Ser127) and p-YAP (Ser397) were significantly decreased and total YAP and nuclear YAP were increased. According to a confocal assay, the interference of shNF1 substantially promoted YAP nuclear translocation. Compared with control Schwann cells, the YAP inhibitor CA3 might have a more sensitive effect (IC₅₀: NC=0.96±0.04, shNF1=0.71±0.02, P<0.05) on the shNF1 Schwann cell model than the classic MEK1/2 inhibitor selumetinib (IC₅₀: NC=14.36±0.95, shNF1=24.83±0.98, P>0.05). For in vivo inhibition, the CA3 group and the selumetinib group displayed a similar inhibition effect with no significant difference. Increased nuclear translation and the functional state of YAP implies that the YAP-Hippo pathway might play an important role in the formation and remyelination of pNF. Compared with selumetinib, the YAP inhibitor can exhibit a similar but more sensitive effect on NF1^-/- Schwann cells. These observations imply that YAP as a novel or adjuvant therapy target in the treatment of pNF.

Neurofibromin Structure, Functions and Regulation

Neurofibromin is a large and multifunctional protein encoded by the tumor suppressor gene NF1, mutations of which cause the tumor predisposition syndrome neurofibromatosis type 1 (NF1). Over the last three decades, studies of neurofibromin structure, interacting partners, and functions have shown that it is involved in several cell signaling pathways, including the Ras/MAPK, Akt/mTOR, ROCK/LIMK/cofilin, and cAMP/PKA pathways, and regulates many fundamental cellular processes, such as proliferation and migration, cytoskeletal dynamics, neurite outgrowth, dendritic-spine density, and dopamine levels. The crystallographic structure has been resolved for two of its functional domains, GRD (GAP-related (GTPase-activating protein) domain) and SecPH, and its post-translational modifications studied, showing it to be localized to several cell compartments. These findings have been of particular interest in the identification of many therapeutic targets and in the proposal of various therapeutic strategies to treat the symptoms of NF1. In this review, we provide an overview of the literature on neurofibromin structure, function, interactions, and regulation and highlight the relationships between them.