FDA Approval Summary: Midostaurin for the Treatment of Advanced Systemic Mastocytosis

Kinase inhibitors: 20 years of success and many new challenges and recent trends in their patents

INTRODUCTION

Protein kinases (PKs) play key roles in cellular signaling and regulation cascades and therefore are listed among the most investigated enzymes with the intent to develop drugs that are able to modulate their catalytic features. Specifically, PKs are involved in chronic diseases of large impact in the society such as cancers and neurodegeneration. Since the approval of Fasudil for the management of cerebral vasospasm, frantic efforts are currently ongoing for the development of selective PK-modulating agents.

AREAS COVERED

A selection of the most relevant patents in the European Patent Office for biomedical innovation and/or industrial development covering the years 2020-2023 on PK modulators either of the antibody and small-molecule type is reported. In addition to the examined patents, we also reported the contributions claiming the use of antibody-targeted PKs for lab bench identification kits.

EXPERT OPINION

The field of PK modulators for biomedical purposes is particularly crowded with contributions, making it rich in valuable information for the development of potential drugs. An emerging frontier is represented by PK activators that aims to complement the use of PK inhibitors with the final intent of finely adjusting any PK-related disruption responsible for triggering any disease.

Comprehensive biomarker diagnostics of unfavorable cancer of unknown primary to identify patients eligible for precision medical therapies

PURPOSE

Current guidelines recommend combination chemotherapy for treatment of patients with unfavorable cancer of unknown primary (CUP). Biomarker-guided targeted therapies may offer additional benefit. Data on the feasibility and effectiveness of comprehensive genomic biomarker profiling of CUP in a standard clinical practice setting are limited.

METHODS

This analysis included 156 patients with confirmed unfavorable CUP diagnosis according to ESMO guidelines, who were treated at the West German Cancer Center, Essen, Germany, from 2015 to 2021. Clinical parameters and outcome data were retrieved from the electronic hospital information system. Genomic biomarker analyses were performed in formalin-fixed paraffin-embedded tumor tissue whenever possible using the QIAseq Multimodal-Pancancer-Panel.

RESULTS

Non-squamous histologies, high tumor burden, and age above 60 years associated with poor survival outcome. Tissue availability restricted comprehensive biomarker analyses to 50 patients (32%), reflecting a major limitation in the real-world setting. In those patients a total of 24 potentially actionable alterations were identified in 17 patients (34% of profiled patients, 11% of total population). The most prevalent biomarkers were high tumor mutational burden and BRCA-mutations.

CONCLUSION

In a real-world setting precision medicine for patients with CUP is severely restricted by tissue availability, and a limited spectrum of actionable alterations. Progress for patients may require emphasizing the need for sufficient biopsies, and prospective exploration of blood-based biomarker profiling.

Kidney and urinary tract involvement in systemic mastocytosis

Systemic mastocytosis (SM) is a disorder of excessive mast cell accumulation in tissues due to a somatic gain-of-function mutation, commonly in the KIT gene, which prevents apoptosis of mast cells. Whereas bone marrow, skin, lymph nodes, spleen and gastrointestinal tract are commonly involved, kidneys are rarely involved directly by SM. However, there are increasing reports of indirect kidney involvement in patients with SM. Novel anti-neoplastic agents to treat advanced forms of SM include non-specific tyrosine kinase inhibitors, which are reported to be associated with kidney dysfunction in some patients. SM is also associated with immune-mediated glomerulonephritis (GN) such as mesangioproliferative GN, membranous nephropathy and diffuse proliferative GN. Kidney injury, in the form of monoclonal deposition disease and primary light chain amyloidosis, is reported in SM associated with plasma cell dyscrasia. In this narrative review we discuss the various ways kidneys (and the urinary tract) are involved in patients with SM.

Strategies for the discovery of potential anticancer agents from plants collected from Southeast Asian tropical rainforests as a case study

Covering up to early 2023The present review summarizes recent accomplishments made as part of a multidisciplinary, multi-institutional anticancer drug discovery project, wherein samples comprising higher plants were collected primarily from Southeast Asia, and also from Central America, and the West Indies. In the introductory paragraphs, a short perspective is provided on the current importance of plants in the discovery of cancer therapeutic agents, and the contributions of other groups working towards this objective are mentioned. For our own investigations, following their collection, tropical plants have been subjected to solvent extraction and biological evaluation for their antitumor potential. Several examples of purified plant lead bioactive compounds were obtained and characterized, and found to exhibit diverse structures, including those of the alkaloid, cardiac glycoside, coumarin, cucurbitacin, cyclobenzofuran (rocaglate), flavonoid, lignan, and terpenoid types. In order to maximize the efficiency of work on drug discovery from tropical plant species, strategies to optimize various research components have been developed, including those for the plant collections and taxonomic identification, in accordance with the requirements of contemporary international treaties and with a focus on species conservation. A major component of this aspect of the work is the development of collaborative research agreements with representatives of the source countries of tropical rainforest plants. The phytochemical aspects have included the preparation of plant extracts for initial screening and the selection of promising extracts for activity-guided fractionation. In an attempt to facilitate this process, a TOCSY-based NMR procedure has been applied for the determination of bioactive rocaglate derivatives in samples of Aglaia species (Meliaceae) collected for the project. Preliminary in vitro and in vivo mechanistic studies carried out by the authors are described for two tropical plant-derived bioactive lead compounds, corchorusoside C and (+)-betulin, including work conducted with a zebrafish (Danio rerio) model. In the concluding remarks, a number of lessons are summarized that our group has learned as a result of working on anticancer drug discovery using tropical plants, which we hope will be of interest to future workers.

Recalcitrant Cutaneous Mastocytosis Treated With Genetically Informed Targeted Therapy: A Case Report

Mastocytosis, a clonal proliferation of mast cells commonly involving the skin and bone marrow, has a varied clinical presentation ranging from cutaneous lesions to systemic disease. Cutaneous mastocytosis is managed symptomatically, but systemic mastocytosis is treated with targeted therapy against the mutated receptor tyrosine kinase c-KIT, the pathogenic driver of mastocytosis. However, there are no guidelines for the treatment of cutaneous mastocytosis refractory to symptomatic management. We herein report a method to select genetically informed therapy for symptomatic and recalcitrant cutaneous mastocytosis.

Case presentation

We performed a mutational analysis of dermal mast cells after enrichment by laser capture in a 23-year-old woman with recalcitrant cutaneous mastocytosis. The analysis revealed a aspartic acid to valine substitution at codon 816 (D816V) mutation in the protein c-KIT. Based on these results, we initiated treatment with the multi-kinase/KIT inhibitor midostaurin, a treatment effective against the D816V c-KIT mutation. After 3 months of treatment, the patient exhibited a reduction in the number and size of cutaneous lesions and reported resolution of pruritus and decreased severity of other mast cell-related symptoms.

Discussion

The treatment of mastocytosis relies heavily on whether the disease is limited to the skin or systemic. However, there are no guidelines for cutaneous mastocytosis that does not respond to symptomatic management. In the present report describing a patient with recalcitrant cutaneous mastocytosis, we describe a strategy in which skin mutational analysis is used to guide the selection of targeted therapy.

Conclusion

Performing mast cell mutational analyses in the skin provides a means to select targeted therapy for symptomatic and refractory cutaneous mastocytosis.

Drugging Hijacked Kinase Pathways in Pediatric Oncology: Opportunities and Current Scenario

Childhood cancer is considered rare, corresponding to ~3% of all malignant neoplasms in the human population. The World Health Organization (WHO) reports a universal occurrence of more than 15 cases per 100,000 inhabitants around the globe, and despite improvements in diagnosis, treatment and supportive care, one child dies of cancer every 3 min. Consequently, more efficient, selective and affordable therapeutics are still needed in order to improve outcomes and avoid long-term sequelae. Alterations in kinases' functionality is a trademark of cancer and the concept of exploiting them as drug targets has burgeoned in academia and in the pharmaceutical industry of the 21st century. Consequently, an increasing plethora of inhibitors has emerged. In the present study, the expression patterns of a selected group of kinases (including tyrosine receptors, members of the PI3K/AKT/mTOR and MAPK pathways, coordinators of cell cycle progression, and chromosome segregation) and their correlation with clinical outcomes in pediatric solid tumors were accessed through the R2: Genomics Analysis and Visualization Platform and by a thorough search of published literature. To further illustrate the importance of kinase dysregulation in the pathophysiology of pediatric cancer, we analyzed the vulnerability of different cancer cell lines against their inhibition through the Cancer Dependency Map portal, and performed a search for kinase-targeted compounds with approval and clinical applicability through the CanSAR knowledgebase. Finally, we provide a detailed literature review of a considerable set of small molecules that mitigate kinase activity under experimental testing and clinical trials for the treatment of pediatric tumors, while discuss critical challenges that must be overcome before translation into clinical options, including the absence of compounds designed specifically for childhood tumors which often show differential mutational burdens, intrinsic and acquired resistance, lack of selectivity and adverse effects on a growing organism.

Nitrogen Containing Heterocycles as Anticancer Agents: A Medicinal Chemistry Perspective

Cancer is one of the major healthcare challenges across the globe. Several anticancer drugs are available on the market but they either lack specificity or have poor safety, severe side effects, and suffer from resistance. So, there is a dire need to develop safer and target-specific anticancer drugs. More than 85% of all physiologically active pharmaceuticals are heterocycles or contain at least one heteroatom. Nitrogen heterocycles constituting the most common heterocyclic framework. In this study, we have compiled the FDA approved heterocyclic drugs with nitrogen atoms and their pharmacological properties. Moreover, we have reported nitrogen containing heterocycles, including pyrimidine, quinolone, carbazole, pyridine, imidazole, benzimidazole, triazole, β-lactam, indole, pyrazole, quinazoline, quinoxaline, isatin, pyrrolo-benzodiazepines, and pyrido[2,3-d]pyrimidines, which are used in the treatment of different types of cancer, concurrently covering the biochemical mechanisms of action and cellular targets.

Roles of Phosphorylation of N-Methyl-D-Aspartate Receptor in Chronic Pain

Phosphorylation of N-methyl-D-aspartate receptor (NMDAR) is widely regarded as a vital modification of synaptic function. Various protein kinases are responsible for direct phosphorylation of NMDAR, such as cyclic adenosine monophosphate-dependent protein kinase A, protein kinase C, Ca²⁺/calmodulin-dependent protein kinase II, Src family protein tyrosine kinases, cyclin-dependent kinase 5, and casein kinase II. The detailed function of these kinases on distinct subunits of NMDAR has been reported previously and contributes to phosphorylation at sites predominately within the C-terminal of NMDAR. Phosphorylation underlies both structural and functional changes observed in chronic pain, and studies have demonstrated that inhibitors of kinases are significantly effective in alleviating pain behavior in different chronic pain models. In addition, the exploration of drugs that aim to disrupt the interaction between kinases and NMDAR is promising in clinical research. Based on research regarding the modulation of NMDAR in chronic pain models, this review provides an overview of the phosphorylation of NMDAR-related mechanisms underlying chronic pain to elucidate molecular and pharmacologic references for chronic pain management.

Antineoplastic efficacy profiles of avapritinib and nintedanib in KIT D816V+ systemic mastocytosis: a preclinical study

Systemic mastocytosis (SM) is a hematopoietic neoplasm with a complex pathology and a variable clinical course. Clinical symptoms result from organ infiltration by mast cells (MC) and the effects of pro-inflammatory mediators released during MC activation. In SM, growth and survival of MC are triggered by various oncogenic mutant-forms of the tyrosine kinase KIT. The most prevalent variant, D816V, confers resistance against various KIT-targeting drugs, including imatinib. We examined the effects of two novel promising KIT D816V-targeting drugs, avapritinib and nintedanib, on growth, survival, and activation of neoplastic MC and compared their activity profiles with that of midostaurin. Avapritinib was found to suppress growth of HMC-1.1 cells (KIT V560G) and HMC-1.2 cells (KIT V560G + KIT D816V) with comparable IC₅₀ values (0.1-0.25 µM). In addition, avapritinib was found to inhibit the proliferation of ROSA^{KIT WT} cells, (IC₅₀: 0.1-0.25 µM), ROSA^{KIT D816V} cells (IC₅₀: 1-5 µM), and ROSA^{KIT K509I} cells (IC₅₀: 0.1-0.25 µM). Nintedanib exerted even stronger growth-inhibitory effects in these cells (IC₅₀ in HMC-1.1: 0.001-0.01 µM; HMC-1.2: 0.25-0.5 µM; ROSA^{KIT WT}: 0.01-0.1 µM; ROSA^{KIT D816V}: 0.5-1 µM; ROSA^{KIT K509I}: 0.01-0.1 µM). Avapritinib and nintedanib also suppressed the growth of primary neoplastic cells in most patients with SM examined (avapritinib IC₅₀: 0.5-5 µM; nintedanib IC₅₀: 0.1-5 µM). Growth-inhibitory effects of avapritinib and nintedanib were accompanied by signs of apoptosis and decreased surface expression of the transferrin receptor CD71 in neoplastic MC. Finally, we were able to show that avapritinib counteracts IgE-dependent histamine secretion in basophils and MC in patients with SM. These effects of avapritinib may explain the rapid clinical improvement seen during treatment with this KIT inhibitor in patients with SM. In conclusion, avapritinib and nintedanib are new potent inhibitors of growth and survival of neoplastic MC expressing various KIT mutant forms, including D816V, V560G, and K509I, which favors the clinical development and application of these new drugs in advanced SM. Avapritinib is of particular interest as it also blocks mediator secretion in neoplastic MC.

Discovery of Anticancer Agents of Diverse Natural Origin

Research progress from mainly over the last five years is described for a multidisciplinary collaborative program project directed toward the discovery of potential anticancer agents from a broad range of taxonomically defined organisms. Selected lead compounds with potential as new antitumor agents that are representative of considerable structural diversity have continued to be obtained from each of tropical plants, terrestrial and aquatic cyanobacteria, and filamentous fungi. Recently, a new focus has been on the investigation of the constituents of U.S. lichens and their fungal mycobionts. A medicinal chemistry and pharmacokinetics component of the project has optimized structurally selected lead natural products, leading to enhanced cytotoxic potencies against selected cancer cell lines. Biological testing has shown several compounds to have in vivo activity, and relevant preliminary structure-activity relationship and mechanism of action studies have been performed. Several promising lead compounds worthy of further investigation have been identified from the most recent collaborative work performed.

Indirect treatment comparisons of avapritinib versus midostaurin for patients with advanced systemic mastocytosis

Objective: This research aimed to compare the relative efficacy of avapritinib versus midostaurin for patients with advanced systemic mastocytosis. Method: A systematic literature review was performed to identify relevant evidence. Unanchored matching-adjusted indirect comparisons were conducted for overall survival (OS), overall response rate (ORR) and complete remission (CR). Results: The systematic literature review identified the clinical trials EXPLORER and PATHFINDER (investigating avapritinib) and D2201 and A2213 (investigating midostaurin). The avapritinib versus midostaurin adjusted hazard ratio for OS was 0.44 (95% CI: 0.25-0.76), and the adjusted odds ratios for ORR and CR were 4.06 (95% CI: 3.09-5.33) and 9.56 (95% CI: 0.97-93.81), respectively. Conclusion: The results suggest that avapritinib improves survival and response (ORR and CR) compared with midostaurin.

Trends in kinase drug discovery: targets, indications and inhibitor design

The FDA approval of imatinib in 2001 was a breakthrough in molecularly targeted cancer therapy and heralded the emergence of kinase inhibitors as a key drug class in the oncology area and beyond. Twenty years on, this article analyses the landscape of approved and investigational therapies that target kinases and trends within it, including the most popular targets of kinase inhibitors and their expanding range of indications. There are currently 71 small-molecule kinase inhibitors (SMKIs) approved by the FDA and an additional 16 SMKIs approved by other regulatory agencies. Although oncology is still the predominant area for their application, there have been important approvals for indications such as rheumatoid arthritis, and one-third of the SMKIs in clinical development address disorders beyond oncology. Information on clinical trials of SMKIs reveals that approximately 110 novel kinases are currently being explored as targets, which together with the approximately 45 targets of approved kinase inhibitors represent only about 30% of the human kinome, indicating that there are still substantial unexplored opportunities for this drug class. We also discuss trends in kinase inhibitor design, including the development of allosteric and covalent inhibitors, bifunctional inhibitors and chemical degraders.

Avapritinib in the Treatment of Systemic Mastocytosis: an Update

PURPOSE OF REVIEW

Patients with systemic mastocytosis, a dangerous and rare myeloid neoplasm, have long had few therapies available to them and, historically, rarely achieved from significant disease control. However, research and translational developments over the last decade have led to promising new options for disease management. In this review, we briefly outline the history of treatment for systemic mastocytosis and subsequently focus on the clinical development and potential applications of avapritinib (previously known as BLU-285), a potent and selective oral inhibitor of the tyrosine kinase most commonly mutated in this condition.

RECENT FINDINGS

Phase I data and recent phase II data have demonstrated both safety and efficacy of this agent used as monotherapy, even in patients who have progressed on other targeted therapy. Studies to date have focused on patients with the most aggressive disease, but new trials in indolent mastocytosis are accruing currently. Over the next several years, one may anticipate finalized, peer-reviewed, and formally published data for this agent in both advanced systemic and indolent mastocytosis. Evidence from these early studies will also likely highlight where more research is needed.

The Protein Kinase Inhibitor Midostaurin Improves Functional Neurological Recovery and Attenuates Inflammatory Changes Following Traumatic Cervical Spinal Cord Injury

Traumatic spinal cord injury (SCI) impairs neuronal function and introduces a complex cascade of secondary pathologies that limit recovery. Despite decades of preclinical and clinical research, there is a shortage of efficacious treatment options to modulate the secondary response to injury. Protein kinases are crucial signaling molecules that mediate the secondary SCI-induced cellular response and present promising therapeutic targets. The objective of this study was to examine the safety and efficacy of midostaurin—a clinically-approved multi-target protein kinase inhibitor—on cervical SCI pathogenesis. High-throughput analyses demonstrated that intraperitoneal midostaurin injection (25 mg/kg) in C6/7 injured Wistar rats altered the local inflammasome and downregulated adhesive and migratory genes at 24 h post-injury. Treated animals also exhibited enhanced recovery and restored coordination between forelimbs and hindlimbs after injury, indicating the synergistic impact of midostaurin and its dimethyl sulfoxide vehicle to improve functional recovery. Furthermore, histological analyses suggested improved tissue preservation and functionality in the treated animals during the chronic phase of injury. This study serves as a proof-of-concept experiment and demonstrates that systemic midostaurin administration is an effective strategy for mitigating cervical secondary SCI damage.

An update of new small-molecule anticancer drugs approved from 2015 to 2020

A high incidence of cancer has given rise to the development of more anti-tumor drugs. From 2015 to 2020, fifty-six new small-molecule anticancer drugs, divided into ten categories according to their anti-tumor target activities, have been approved. These include TKIs (30 drugs), MAPK inhibitors (3 drugs), CDK inhibitors (3 drugs), PARP inhibitors (3 drugs), PI3K inhibitors (3 drugs), SMO receptor antagonists (2 drugs), AR antagonists (2 drugs), SSTR inhibitors (2 drugs), IDH inhibitors (2 drugs) and others (6 drugs). Among them, PTK inhibitors (30/56) have led to a paradigm shift in cancer treatment with less toxicity and more potency. Each of their structures, approval statuses, applications, SAR analyses, and original research synthesis routes have been summarized, giving us a more comprehensive map for further efforts to design more specific targeted agents for reducing cancer in the future. We believe this review will help further research of potential antitumor agents in clinical usage.

Real-World Efficacy of Midostaurin in Aggressive Systemic Mastocytosis

In April 2017 midostaurin was approved by the US Food and Drug Administration for the treatment of patients with aggressive systemic mastocytosis (ASM). So far, very limited real world data on its efficacy is available. Thirteen patients aged from 48 to 79 years, who received midostaurin in the early access program, were included in the study. Midostaurin was used both in first (n = 5) and subsequent lines of treatment (n = 8). The median duration of exposure was 9 months. Most patients (77%, n = 10) had a clinical improvement already as soon as the second month of therapy. Objective response was noted in 4 (50%) of eight evaluated patients. Among responders, we observed a decrease in serum tryptase level (median 74.14%) and bone marrow infiltration by mast cells (median 50%) in the sixth month of treatment. In one case, in the 10th month of treatment, allogenic stem cell transplantation was performed, achieving complete remission. Five patients died, three due to progression of disease, one in the course of secondary acute myeloid leukemia and one due to reasons not related to mastocytosis. Treatment is ongoing in seven patients. We found that midostaurin therapy is beneficial to patients with ASM.

Divergent Mast Cell Responses Modulate Antiviral Immunity During Influenza Virus Infection

Influenza A virus (IAV) is a respiratory pathogen that infects millions of people each year. Both seasonal and pandemic strains of IAV are capable of causing severe respiratory disease with a high risk of respiratory failure and opportunistic secondary infection. A strong inflammatory cytokine response is a hallmark of severe IAV infection. The widespread tissue damage and edema in the lung during severe influenza is largely attributed to an overexuberant production of inflammatory cytokines and cell killing by resident and infiltrating leukocytes. Mast cells (MCs) are a sentinel hematopoietic cell type situated at mucosal sites, including the lung. Poised to react immediately upon detecting infection, MCs produce a vast array of immune modulating molecules, including inflammatory cytokines, chemokines, and proteases. As such, MCs have been implicated as a source of the immunopathology observed in severe influenza. However, a growing body of evidence indicates that MCs play an essential role not only in inducing an inflammatory response but in suppressing inflammation as well. MC-derived immune suppressive cytokines are essential to the resolution of a number of viral infections and other immune insults. Absence of MCs prolongs infection, exacerbates tissue damage, and contributes to dissemination of the pathogen to other tissues. Production of cytokines such as IL-10 and IL-6 by MCs is essential for mitigating the inflammation and tissue damage caused by innate and adaptive immune cells alike. The two opposing functions of MCs—one pro-inflammatory and one anti-inflammatory—distinguish MCs as master regulators of immunity at the site of infection. Amongst the first cells to respond to infection or injury, MCs persist for the duration of the infection, modulating the recruitment, activation, and eventual suppression of other immune cells. In this review, we will discuss the immune modulatory roles of MCs over the course of viral infection and propose that the immune suppressive mediators produced by MCs are vital to minimizing immunopathology during influenza infection.

Targeting the histone demethylase PHF8-mediated PKCα-Src-PTEN axis in HER2-negative gastric cancer

Targeted treatments for advanced gastric cancer (GC) are needed, particularly for HER2-negative GC, which represents the majority of cases (80 to 88%). In this study, in silico analyses of the lysine histone demethylases (KDMs) involved in diverse biological processes and diseases revealed that PHD finger protein 8 (PHF8, KDM7B) was significantly associated with poor clinical outcome in HER2-negative GC. The depletion of PHF8 significantly reduced cancer progression in GC cells and in mouse xenografts. PHF8 regulated genes involved in cell migration/motility based on a microarray analysis. Of note, PHF8 interacted with c-Jun on the promoter of PRKCA which encodes PKCα. The depletion of PHF8 or PKCα greatly up-regulated PTEN expression, which could be rescued by ectopic expression of a PKCα expression vector or an active Src. These suggest that PTEN destabilization occurs mainly via the PKCα-Src axis. GC cells treated with midostaurin or bosutinib significantly suppressed migration in vitro and in zebrafish models. Immunohistochemical analyses of PHF8, PKCα, and PTEN showed a positive correlation between PHF8 and PKCα but negative correlations between PHF8 and PTEN and between PKCα and PTEN. Moreover, high PHF8-PKCα expression was significantly correlated with worse prognosis. Together, our results suggest that the PKCα-Src-PTEN pathway regulated by PHF8/c-Jun is a potential prognostic/therapeutic target in HER2-negative advanced GC.

Mast cells as a unique hematopoietic lineage and cell system: From Paul Ehrlich's visions to precision medicine concepts

The origin and functions of mast cells (MCs) have been debated since their description by Paul Ehrlich in 1879. MCs have long been considered 'reactive bystanders' and 'amplifiers' in inflammatory processes, allergic reactions, and host responses to infectious diseases. However, knowledge about the origin, phenotypes and functions of MCs has increased substantially over the past 50 years. MCs are now known to be derived from multipotent hematopoietic progenitors, which, through a process of differentiation and maturation, form a unique hematopoietic lineage residing in multiple organs. In particular, MCs are distinguishable from basophils and other hematopoietic cells by their unique phenotype, origin(s), and spectrum of functions, both in innate and adaptive immune responses and in other settings. The concept of a unique MC lineage is further supported by the development of a distinct group of neoplasms, collectively referred to as mastocytosis, in which MC precursors expand as clonal cells. The clinical consequences of the expansion and/or activation of MCs are best established in mastocytosis and in allergic inflammation. However, MCs have also been implicated as important participants in a number of additional pathologic conditions and physiological processes. In this article, we review concepts regarding MC development, factors controlling MC expansion and activation, and some of the fundamental roles MCs may play in both health and disease. We also discuss new concepts for suppressing MC expansion and/or activation using molecularly-targeted drugs.

Turning liabilities into opportunities: Off-target based drug repurposing in cancer

Targeted drugs and precision medicine have transformed the landscape of cancer therapy and significantly improved patient outcomes in many cases. However, as therapies are becoming more and more tailored to smaller patient populations and acquired resistance is limiting the duration of clinical responses, there is an ever increasing demand for new drugs, which is not easily met considering steadily rising drug attrition rates and development costs. Considering these challenges drug repurposing is an attractive complementary approach to traditional drug discovery that can satisfy some of these needs. This is facilitated by the fact that most targeted drugs, despite their implicit connotation, are not singularly specific, but rather display a wide spectrum of target selectivity. Importantly, some of the unintended drug "off-targets" are known anticancer targets in their own right. Others are becoming recognized as such in the process of elucidating off-target mechanisms that in fact are responsible for a drug's anticancer activity, thereby revealing potentially new cancer vulnerabilities. Harnessing such beneficial off-target effects can therefore lead to novel and promising precision medicine approaches. Here, we will discuss experimental and computational methods that are employed to specifically develop single target and network-based off-target repurposing strategies, for instance with drug combinations or polypharmacology drugs. By illustrating concrete examples that have led to clinical translation we will furthermore examine the various scientific and non-scientific factors that cumulatively determine the success of these efforts and thus can inform the future development of new and potentially lifesaving off-target based drug repurposing strategies for cancers that constitute important unmet medical needs.

Unique case of ANCA-negative pauci-immune necrotizing glomerulonephritis with diffuse alveolar hemorrhage, potentially associated with midostaurin

We present a 61-year-old male with FLT3-mutated acute myeloid leukemia treated with midostaurin who developed acute kidney injury requiring hemodialysis and pulmonary renal syndrome. Antibodies to proteinase-3, myeloperoxidase, and glomerular basement membrane were negative. Renal biopsy confirmed acute pauci-immune focal necrotizing glomerulonephritis (GN) with fibrin crescents indicating rapidly progressing glomerulonephritis. He improved with pulse methylprednisolone, intravenous cyclophosphamide, and plasma exchange with resolution of hemoptysis. This case highlights the importance of prompt renal biopsy to guide early initiation of life-saving therapies. To our knowledge, this is the first reported case of ANCA-negative pauci-immune necrotizing GN likely secondary to midostaurin.

Novel approaches to treating advanced systemic mastocytosis

Mastocytosis is a myeloproliferative neoplasm characterized by expansion of abnormal mast cells (MCs) in various tissues, including skin, bone marrow, gastrointestinal tract, liver, spleen, or lymph nodes. Subtypes include indolent systemic mastocytosis, smoldering systemic mastocytosis and advanced systemic mastocytosis (AdvSM), a term collectively used for the three most aggressive forms of the disease: aggressive systemic mastocytosis, mast cell leukemia, and systemic mastocytosis with an associated clonal hematological non-mast cell disease (SM-AHNMD). MC activation and proliferation is physiologically controlled in part through stem cell factor (SCF) binding to its cognate receptor, KIT. Gain-of-function KIT mutations that lead to ligand-independent kinase activation are found in most SM subtypes, and the overwhelming majority of AdvSM patients harbor the KIT^D816V mutation. Several approved tyrosine kinase inhibitors (TKIs), such as imatinib and nilotinib, have activity against wild-type KIT but lack activity against KIT^D816V. Midostaurin, a broad spectrum TKI with activity against KIT^D816V, has a 60% clinical response rate, and is currently the only drug specifically approved for AdvSM. While this agent improves the prognosis of AdvSM patients and provides proof of principle for targeting KIT^D816V as a driver mutation, most responses are partial and/or not sustained, indicating that more potent and/or specific inhibitors are required. Avapritinib, a KIT and PDGFRα inhibitor, was specifically designed to inhibit KIT^D816V. Early results from a Phase 1 trial suggest that avapritinib has potent antineoplastic activity in AdvSM, extending to patients who failed midostaurin. Patients exhibited a rapid reduction in both symptoms as well as reductions of bone marrow MCs, serum tryptase, and KIT^D816V mutant allele burden. Adverse effects include expected toxicities such as myelosuppression and periorbital edema, but also cognitive impairment in some patients. Although considerable excitement about avapritinib exists, more data are needed to assess long-term responses and adverse effects of this novel TKI.

The Role of KIT Mutations in Anaphylaxis

PURPOSE OF REVIEW

Gain of function KIT mutations are detected in clonal mast cell diseases, namely mastocytosis and monoclonal mast cell activation syndrome. Timely diagnosis and treatment of these disorders are crucial because of their association with severe and life-threatening anaphylaxis. KIT mutations also have implications for targeted therapies of mast cell disorders. This review article strives to serve as an overview of the role of clonal mast cell disorders in anaphylaxis while elucidating current and future therapies.

RECENT FINDINGS

Clonal mast cell disease has been increasingly diagnosed in patients with severe hymenoptera allergy and those with recurrent unexplained anaphylaxis. The current state of knowledge of the epidemiology, pathophysiology, diagnosis, and treatment of mastocytosis with a particular focus on anaphylaxis and its triggers which are described in this context. Novel and forthcoming treatments are discussed including the relevance of KIT mutation status. This review provides an overview of the role of KIT mutations in mastocytosis and anaphylaxis, and highlights emerging therapies for mastocytosis, targeting these mutations.