C-kit Inhibitor Research Articles

Real-world evidence on efficacy and toxicity of targeted therapy in older melanoma patients treated in a tertiary-hospital setting.

Melanoma is the deadliest form of skin cancer. The median age at diagnosis is 66. While most patients are treated with immunotherapy, the use of targeted therapy is a valid alternative for patients whose tumors harbor a BRAF or c-KIT driver mutation. These agents, while effective, come with a variety of side effects which limit their use, especially in older patients. We sought to assess the efficacy and toxicity of these agents in older melanoma patients. Melanoma patients over 65 treated with BRAF/MEK or c-KIT inhibitors were retrospectively identified, and their data were analyzed for treatment efficacy and toxicity. All data were compared using the Chi-square test for categorical comparisons and the Kruskal-Wallis method for median comparisons. One hundred and sixteen patients were identified. One hundred and six patients were treated with BRAF/MEK inhibitors. The assessed response rate (RR) was 83% and was comparable across different subgroups, including advanced line patients and those with a more aggressive disease. The median progression free survival (PFS) was 7.9 months, and the median overall survival (OS) was 15.7 months. Twenty-seven percent experienced grade 3-4 toxicity leading to a 24% treatment discontinuation rate. Another 10 patients were treated with the c-KIT inhibitor imatinib, for whom the assessed RR was 55%. The median PFS was 4.3 months, and the median OS was 22.6 months. Forty percent needed dose reductions, yet none had to stop treatment due to adverse effects. The use of targeted therapy in older patients is effective yet challenging due to toxicity. Deploying mitigation strategies can help maximizing their usefulness.

NK Cell Degranulation Triggered by Rituximab Identifies Potential Markers of Subpopulations with Enhanced Cytotoxicity toward Malignant B Cells.

A promising strategy in cancer immunotherapy is to restore or enhance the cytotoxicity of NK cells, among others, by activating the mechanism of antibody-dependent cellular cytotoxicity (ADCC). Monoclonal antibodies targeting tumor antigens, such as rituximab (targeting CD20), induce NK cell-mediated ADCC and have been used to treat B cell malignancies, such as non-Hodgkin lymphoma, but not always successfully. The aim of this study was to analyze the gene expression profile of the NK cells involved in the cytolytic response stimulated by rituximab. NK cells were co-cultured with rituximab-opsonized Raji cells. Sorting into responder and non-responder groups was based on the presence of CD107a, which is a degranulation marker. RNA-seq results showed that the KIT and TNFSF4 genes were strongly down-regulated in the degranulating population of NK cells (responders); this was further confirmed by qRT-PCR. Both genes encode surface proteins with cellular signaling abilities, namely c-KIT and the OX40 ligand. Consistent with our findings, c-KIT was previously reported to correlate inversely with cytokine production by activated NK cells. The significance of these findings for cancer immunotherapy seems essential, as the pharmacological inhibition of c-KIT and OX40L, or gene ablation, could be further tested for the enhancement of the anti-tumor activity of NK cells in response to rituximab.

Covalent-103: A phase 1, open-label, dose-escalation and expansion study of BMF-500, an oral covalent FLT3 inhibitor, in adults with acute leukemia (AL).

TPS6589 Background: FLT3 mutations occur in 25-35% of AML and result from an internal tandem duplication (ITD) of amino acids in the juxtamembrane domain of FLT3 kinase or point mutations in the tyrosine kinase domain (TKD). FLT3-ITD mutations are associated with increased relapse, shorter remission, and decreased disease-free and overall survival. BMF-500 is a novel oral, highly potent and selective covalent inhibitor of FLT3 including wild-type (WT), ITD, TKD, and resistance mutations (e.g., gatekeeper F691). BMF-500 has high affinity for FLT3, lack of cKIT inhibition, and sustained cell-killing despite drug washout (Law et al., ASH 2022 Abst 2756). BMF-500 shows sustained tumor regression and improved survival in subcutaneous and disseminated xenografts of FLT3-m AML. Methods: COVALENT-103 (NCT05918692) is a multicenter, first-in-human study evaluating the safety, tolerability, and antileukemic activity of escalating doses of daily BMF-500 in patients with relapsed or refractory (R/R) AL, including AML, ALL, or MPAL, with or without FLT3-m. The trial has 2 arms that dose escalate in parallel: Arm A (without) and Arm B (with) concomitant use of a CYP3A4 inhibitor. Using an accelerated titration design (ATD), doses of BMF-500 are escalated in single-subject cohorts until one subject experiences ≥Grade 2 related adverse event or dose-limiting toxicity (DLT). At that point, the cohort will switch to a classical “3 +3” design. Patients with WT FLT3 AL may enroll up to 33% per arm. Treatment continues in 28-day cycles until progression or intolerability. Expansion cohorts will enroll additional patients to obtain further safety and efficacy data. Patients must be refractory, relapsed or have progressed on or following discontinuation of the most recent anti-cancer therapy or be ineligible for any approved standard of care, including hematopoietic stem cell transplant (HSCT). FLT3-positive AML patients must have received a FLT3 inhibitor approved for R/R FLT3-m AML. Additional inclusion criteria include ECOG PS ≤2, adequate organ function, and documented FLT3 mutation status. Key exclusion criteria include known CNS disease, clinically significant cardiovascular disease, and WBC >50,000/µL (uncontrollable with cytoreductive therapy). The primary objective is to evaluate safety and tolerability and determine the optimal biological dose (OBD)/ recommended Phase 2 dose (RP2D) of BMF-500 monotherapy based on available pharmacokinetic/pharmacodynamic (PK/PD), safety and efficacy data. Secondary objectives include characterization of the PK/PD of BMF-500, and assessment of its antitumor activity per modified Cheson (2003) criteria or NCCN Clinical Practice Guidelines (ALL Version 1.2022) as determined by the investigator. The study was initiated in July 2023, is currently in dose escalation, and we plan to enroll approximately 110 patients total. Clinical trial information: NCT05918692 .

Abstract 5117: CK2 inhibiton exhibits synergistic effect in acute lymphoblastic leukemia

Abstract Survival for pre-B cell Acute lymphoblastic leukemia (B ALL) has improved greatly, however. High risk (HR) subgroups continue to result in significant mortality and morbidity of pediatric oncology patients. Pediatric T-cell acute lymphoblastic leukemia (T-ALL) is a lethal disease, often associated with high-risk clinical features. T-ALL therapy has made less improvement than B ALL and continues to represent a significant number of high-risk outcomes. Novel treatment strategies are required to overcome chemotherapy resistance and improve morbidity for HR B ALL. The development of treatments that can overcome chemotherapy resistance is essential for improving survival in T-ALL. Deletions of IKZF1, resulting in decreased IKAROS function, are present in High-risk ALL patients. Casein kinase 2 (CK2), a protein kinase upregulated in ALL, phosphorylates IKAROS preventing DNA binding reducing transcriptional regulation in ALL patients. Past studies have shown that pharmacologic inhibition of CK2 with CX-4945 rescues IKAROS function as a transcriptional regulator. Receptor tyrosine kinase c-KIT is transcriptionally regulated by IKAROS and is often upregulated in cancer. The purpose of this study was to determine whether restoration of IKAROS via CX-4945 would act in a synergistic manner with c-KIT inhibitor imatinib in ALL.Methods/results B-ALL Nalm6 cells were treated with imatinib over 72-hours to establish the half-maximal inhibitory concentration (IC50). The IC50 was used to determine the concentration range of imatinib to be used in combination with CX-4945 in a 72-hour synergy analysis of cytotoxicity.. Cell viability was measured using WST-1 cell proliferation assay. The data were analyzed using Calcusyn and synergy was defined as a combination index below 0.85. The study was repeated to determine a more precise range of synergy. The cytotoxicity of single drug c-KIT inhibitor, Imatinib, in Nalm6 B-ALL yielded an IC50 of 25uM while CK2 inhibitor CX-4945 resulted in 4uM. When a combination was administered with a constant dose of CX-4945 at 4uM and varying concentrations of imatinib, synergy was observed at multiple dose combinations. Conclusion: The data shows that CK2 inhibitor, CX-4945, and c-KIT inhibitor, imatinib, exhibit a synergistic therapeutic effect. Imatinib is indicated for use in Philadelphia positive (Ph+) acute lymphoblastic leukemia so future studies will include testing CX-4945/imatinib synergy in Ph+ BALL where we expect to see more potent synergistic effect. Citation Format: Daniel Gary Bogush, Joseph Schramm, Katarina Dovat, Yali Ding, Chingakham Singh, Sinisa Dovat. CK2 inhibiton exhibits synergistic effect in acute lymphoblastic leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5117.

Abstract 3142: NN3201, a novel c-Kit targeting ADC, exhibits robust preclinical anti-tumor efficacy in SCLC and GIST models

Abstract c-Kit (CD117) is a type III receptor tyrosine kinase (RTK), which is known to be activated upon binding to its cognate ligand stem cell factor (SCF) to induce critical signaling pathways involved in cell proliferation, survival, and differentiation. Indicative of poor prognosis, overexpression and activating mutations of c-Kit have been implicated in a variety of human cancers including small cell lung cancer (SCLC), gastrointestinal stromal tumors (GIST), and acute myelogenous leukemia (AML). While imatinib, a small molecule c-Kit inhibitor, has been a beneficial treatment for GIST, resistance eventually develops to the drug, moreover, shows limited efficacy in c-Kit overexpressing tumors such as SCLC. Herein, we developed NN3201, a novel c-Kit targeting antibody-drug conjugate (ADC), comprised of fully human 2G4 antibody with a picomolar binding affinity to c-Kit and cytotoxic monomethyl auristatin E (MMAE) as the payload. NN3201 displayed potent in vitro cytotoxicity in various wild-type and mutant c-Kit positive SCLC and GIST cell lines with IC50 in the nanomolar range. In addition, NN3201 was rapidly internalized and inhibited c-Kit-mediated signaling., NN3201 treatment resulted in the increased proportions of the sub G1 and G2/M in the c-Kit positive cancer cell lines, indicating that release of MMAE induced cell cycle arrest. Moreover, bystander effect was confirmed by co-culturing c-Kit high and negative cell lines. Most importantly, in mouse xenograft models, NN3201 showed a remarkable tumor growth inhibition of several wild type, mutant c-Kit positive, and imatinib resistant SCLC and GIST cell lines. Enhanced anti-tumor activity and delayed tumor growth were observed in an SOC-treated (etoposide and carboplatin) SCLC xenograft model, by NN3201 in comparison to second line SOC (topotecan or irinotecan). In the GLP study, repeated intravenous administration of NN3201 was well tolerated at all doses (0.5, 1, 2 mg/kg Q3Wx3) without unscheduled death. Dose-dependent, yet transient, cytotoxicity of NN3201 was observed in the bone marrow. We confirmed HNSTD (Highest Non-Severely Toxic Dose) of NN3201 to be 2 mg/kg through exploratory and GLP repeat dose toxicity studies as no serious irreversible toxicity was observed. Accumulating data suggest that NN3201 is a promising therapeutic alternative for the treatment of SCLC and GIST regardless of wild-type or activating mutations in c-Kit. Citation Format: Chansik Kim, Jin Gu Cho, TaeMin Wi, Jiwoo Moon, Han-Jik Ko, Jina Lee, Jin Woo Park, Yeonjy Lee, Sanghee Kim, Jin-Ock Kim, Jaeyoung Song, Sun-Hwa Lee, Sang Gyu Park. NN3201, a novel c-Kit targeting ADC, exhibits robust preclinical anti-tumor efficacy in SCLC and GIST models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3142.

Stem cell factor restrains endoplasmic reticulum stress-associated apoptosis through c-Kit receptor activation of JAK2/STAT3 axis in hippocampal neuronal cells.

Alzheimer's disease (AD) is a common elderly disorder characterized by cognitive decline. Endoplasmic reticulum (ER) stress has been implicated in various neurodegenerative diseases, including AD. Stem cell factor (SCF) performs its biological functions by binding to and activating receptor tyrosine kinase c-Kit. We aimed to investigate the effects of SCF/c-Kit and JAK2/STAT3 on ER stress and apoptosis in AD. The study employed L-glutamic acid (L-Glu)-treated HT22 cells as sporadic AD cell model and APP/PS1 mice as an animal model of familiar AD. SCF, c-Kit inhibitor ISCK03 or JAK2/STAT3 inhibitor WP1066 was treated to verify the effects of SCF/c-Kit and JAK2/STAT3 on ER stress and apoptosis of L-Glu-exposed HT22 cells. Cell viability was assessed by MTT. BrdU detected cell proliferation. Flow cytometry measured cell apoptosis. The expression levels of ER stress markers GRP78, PERK, CHOP, and apoptosis protein caspase3 were determined by western blot. The effect on the mRNA of ER stress markers GRP78, PERK, CHOP and apoptotic caspase3 were quantified by RT-qPCR in primary cultured hippocampal neurons from APP/PS1 transgenic mice. Administration of SCF significantly augmented the activity and proliferation of hippocampal neuronal cells, protecting cells against L-Glu induced ER stress-associated apoptosis. Moreover, the addition of ISCK03 (c-Kit inhibitor) or WP1066 (JAK2/STAT3 inhibitor) reversed SCF effects on ER stress and apoptosis in vitro. We found that SCF inhibits L-Glu-induced ER stress-associated apoptosis via JAK2/STAT3 axis in HT22 hippocampal neuronal cells, as well as in primary hippocampal neurons from APP/PS1 mice, which provides valuable insights into the molecular mechanisms underlying the pathogenesis of AD and explores novel therapeutic targets for both sporadic and familial AD.

C-kit controls blood-brain barrier permeability by regulating caveolae-mediated transcytosis after chronic cerebral hypoperfusion

Blood-brain barrier (BBB) dysfunction plays a pivotal role in the pathology of chronic cerebral hypoperfusion (CCH)-related neurodegenerative diseases. Continuous endothelial cells (EC) that line the blood vessels of the brain are important components of the BBB to strictly control the flow of substances and maintain the homeostatic environment of the brain. However, the molecular mechanisms from the perspective of EC-induced BBB dysfunction after CCH are largely unknown. In this study, the BBB function was assessed using immunostaining and transmission electron microscopy. The EC dysfunction profile was screened by using EC enrichment followed by RNA sequencing. After identified the key EC dysfunction factor, C-kit, we used the C-kit inhibition drug (imatinib) and C-kit down-regulation method (AAV-BR1-C-kit shRNA) to verify the role of C-kit on BBB integrity and EC transcytosis after CCH. Furthermore, we also activated C-kit with stem cell factor (SCF) to observe the effects of C-kit on BBB following CCH. We explored that macromolecular proteins entered the brain mainly through EC transcytosis after CCH and caused neuronal loss. Additionally, we identified receptor tyrosine kinase C-kit as a key EC dysfunction molecule. Furthermore, the pharmacological inhibition of C-kit with imatinib counteracted BBB leakage by reducing caveolae-mediated transcytosis. Moreover, treatment with AAV-BR1-C-kit shRNA, which targets brain EC to inhibit C-kit expression, also ameliorated BBB leakage by reducing caveolae-mediated transcytosis. Furthermore, the SCF increased the permeability of the BBB by actively increasing caveolae-mediated transcytosis. This study provides evidence that C-kit is a key BBB permeability regulator through caveolae-mediated transcytosis in EC after CCH.

Covalent-103: A Phase 1, Open-Label, Dose-Escalation, and Dose-Expansion Study of Bmf-500, an Oral Covalent FLT3 Inhibitor, in Adults with Acute Leukemia (AL)

Background: FLT3 mutations occur in 25-35% of patients with AML and are associated with poor prognosis. FLT3 mutations are most frequently the result of an internal tandem duplication (ITD) of amino acids in the juxtamembrane region of FLT3 or point mutations in the tyrosine kinase domain (TKD). FLT3-ITD mutations are associated with increased incidence of relapse, shorter duration of remission, and decreased disease-free and overall survival. BMF-500 is a novel orally bioavailable, highly potent and selective covalent inhibitor of FLT3 including wildtype (WT), ITD, TKD, as well as a variety of additional resistance-conferring mutations such as the gatekeeper F691. BMF-500 has demonstrated high affinity for FLT3, lack of cKIT inhibition, and sustained cell-killing capacity despite drug washout (Law et al., ASH 2022 Abstract 2756). BMF-500 has shown sustained tumor regression and improved survival in both subcutaneous and disseminated xenograft models of mutant FLT3-driven AML. Study Design: COVALENT-103 (NCT05918692) is an open-label, non-randomized, multicenter, first-in-human Phase I study evaluating the safety, tolerability, and clinical activity of escalating doses of twice daily oral BMF-500 in patients with relapsed or refractory (R/R) AL, including AML, ALL, or MPAL, with or without FLT3 mutations. The trial has 2 arms that will undergo dose escalation in parallel: Arm A (without) and Arm B (with) concomitant use of a moderate or strong CYP3A4 inhibitor. Utilizing an accelerated titration design (ATD), doses of BMF-500 will be escalated in single-subject cohorts until 1 subject experiences either a Grade 2 or higher related-adverse event or dose-limiting toxicity (DLT). At that point, the cohort will switch to a classical “3 +3” design. Patients with WT FLT3 AL may be enrolled, up to a limit of 33% per arm. Treatment will continue in 28-day cycles until progression or intolerability. Expansion cohorts will enroll additional patients to obtain further safety and efficacy data. Patients must be refractory, relapsed or must have progressed on or following discontinuation of the most recent anti-cancer therapy or be ineligible for any approved standard of care therapies, including HSCT. Participants with FLT3-mutant AML must have received treatment with a FLT3 inhibitor approved for treatment of relapsed or refractory FLT3-mutant AML. Key inclusion criteria include ECOG PS ≤ 2, adequate organ function, and documented FLT3 mutation status. Key exclusion criteria include known CNS disease involvement, clinically significant cardiovascular disease, and WBC count >50,000/µL (uncontrollable with cytoreductive therapy). Objectives: The primary objective of the study is to evaluate safety and tolerability and to determine the optimal biological dose (OBD)/ recommended Phase 2 dose (RP2D) of BMF-500 oral monotherapy based on evaluation of available PK/ PD, safety and efficacy data. Secondary objectives include characterization of the pharmacodynamics and pharmacokinetics of BMF-500, and assessment of its antitumor activity per modified Cheson (2003) criteria or the NCCN Clinical Practice Guidelines (ALL Version 1.2022) as determined by the investigator. Endpoints include best overall response rate (ORR), complete remission (CRc), duration of response (DOR), relapse-free survival (RFS) and overall survival (OS). The study was initiated in July 2023 and will enroll ~110 participants at approximately 30 sites.

Efficacy and safety profile of pimicotinib (ABSK021) in tenosynovial giant cell tumor (TGCT): Phase 1b update.

11559 Background: TGCT is a rare type of locally aggressive neoplasm that is mainly caused by overexpression of colony-stimulating factor 1 (CSF1) gene. Pimicotinib is an oral, highly potent, and selective small-molecule antagonist of CSF-1R with minimum inhibition of c-Kit and PDGFR, and has been granted Breakthrough Therapy Designation for TGCT by FDA in Jan 2023. Here, we report the updates from 50 mg QD cohort as well as the preliminary data from 25 mg QD cohort in TGCT pts. Methods: The study (NCT04192344) is to evaluate the safety and preliminary antitumor activity of Pimicotinib at 50 mg QD and 25 mg QD in TGCT pts not amenable to surgical resection. Results: As of December 31, 2022, 49 TGCT pts were enrolled, including 37 pts treated with 50 mg QD and 12 pts with 25 mg QD. Median age was 39 y (range: 19-76) and 40.8% were male. The tumor location was mainly in knee (53.1%), hip (18.4%) or ankle (12.2%). Thirty-one pts received at least one prior surgery, and 1 pt received prior exploratory systemic therapy (Anlotinib). Median treatment duration was 7.9 mos (range: 0.4-12.5), and 89.8% remained on treatment. The ORR was 77.4% (24/31, including 2 CR) in 50 mg QD and 40% (4/10, including 1 CR) in 25 mg QD by IRC based on RECIST 1.1. Most responses were achieved within 25 wks and median DOR in both cohorts was not reached. Average improvement of flexion range of knee at wk 13 from baseline was 30.2 degrees (n = 13, range: 2, 105) in 50 mg QD and 4.8 degrees (n = 5, range: -12, 24) in 25 mg QD. Proportion of responders based on BPI-30 at wk 25 was 66.7% (16/24) in 50 mg QD and 60% (3/5) in 25 mg QD, along with a similar trend of stiffness. Most TEAEs were Gr 1 or 2. Four Gr 3/4 TEAEs were reported (2 drug-related), including 1 Gr 3 serious TEAE. Most common TEAEs (≥20%) include LDH increase (75.5%), CPK increase (67.3%), α-HBDH increase (63.3%), AST increase (42.9%), amylase increase (26.5%), ALT increase (24.5%), pruritus (20.4%) and rash (20.4%). No hair color changes or serious liver injuries were reported. CPK and transaminase elevations were asymptomatic, on-target and quickly recovered after drug interruptions. nder steady-state, 50 mg QD resulted in ~ 2-fold higher Cmax and Ctrough compared to 25 mg QD, in sync with findings from escalation phase. Significant PD changes were observed in both cohorts, such as increase in plasma CSF-1 levels, decrease in non-classical monocytes and C-terminal telopeptide(CTx). Changes from baselines in both CSF-1 and CTx showed a correlation with pimocetinib plasma concentrations. Conclusions: Pimicotinib has demonstrated a significant antitumor activity, favorable safety, and PK profiles at both 50 mg QD and 25 mg QD with no apparent hepatotoxicity. The changes in PD biomarkers indicate significant CSF-1R inhibition in TGCT pts. Updated data from 50 mg QD cohort showed higher ORR and continuous improvement over a longer treatment time, which supports the further evaluation of Pimicotinib in a phase 3 study. Clinical trial information: NCT04192344 .

Small Molecule c-KIT Inhibitors for the Treatment of Gastrointestinal Stromal Tumors: A Review on Synthesis, Design Strategies, and Structure-Activity Relationship (SAR).

The proto-oncogenic protein, c-KIT, plays a crucial role in regulating cellular transformation and differentiation processes, such as proliferation, survival, adhesion, and chemotaxis. The overexpression of, and mutations, in c-KIT can lead to its dysregulation and promote various human cancers, particularly gastrointestinal stromal tumors (GISTs); approximately 80-85% of cases are associated with oncogenic mutations in the KIT gene. Inhibition of c-KIT has emerged as a promising therapeutic target for GISTs. However, the currently approved drugs are associated with resistance and significant side effects, highlighting the urgent need to develop highly selective c-KIT inhibitors that are not affected by these mutations for GISTs. Herein, the recent research efforts in medicinal chemistry aimed at developing potent small-molecule c-KIT inhibitors with high kinase selectivity for GISTs are discussed from a structure-activity relationship perspective. Moreover, the synthetic pathways, pharmacokinetic properties, and binding patterns of the inhibitors are also discussed to facilitate future development of more potent and pharmacokinetically stable small-molecule c-KIT inhibitors.

Discovery and optimization of natural-based nanomolar c-Kit inhibitors via in silico and in vitro studies

c-Kit is a receptor tyrosine kinase which is involved in intracellular signaling and mutations of c-Kit have been associated with various types of cancers. Investigations have shown that inhibition of c-Kit, using tyrosine kinase inhibitors, yielded promising results in cancer treatment marking it as a promising target for cancer therapy. However, the emerging resistance for the current therapy necessitates the development of more potent inhibitors which are not affected by these mutations. Herein, virtual screening of a library of natural-based compounds yielded three hits (2, 5 and 6) which possessed nanomolar inhibitory (2.02, 4.33 and 2.80 nM, respectively) activity when tested in vitro against c-Kit. Single point mutation docking studies showed the hits to be unaffected by the most common resistance mutation in imatinib-resistant cells, mutation of Val654. Although, the top hits exhibited around 3000 higher inhibitory potency toward c-Kit when compared to imatinib (5.4 µM), previous studies have shown that they are metabolically unstable. Fragment-based drug design approaches were then employed to enhance binding affinity of the top hit and make it more metabolically stable. Screening of the generated fragments yielded a new derivative, F1, which demonstrated stronger binding affinity, stability and binding free energy when compared to the hit compound 2. Communicated by Ramaswamy H. Sarma

Age-related liver endothelial zonation triggers steatohepatitis by inactivating pericentral endothelium-derived C-kit.

Aging leads to systemic metabolic disorders, including steatosis. Here we show that liver sinusoidal endothelial cell (LSEC) senescence accelerates liver sinusoid capillarization and promotes steatosis by reprogramming liver endothelial zonation and inactivating pericentral endothelium-derived C-kit, which is a type III receptor tyrosine kinase. Specifically, inhibition of endothelial C-kit triggers cellular senescence, perturbing LSEC homeostasis in male mice. During diet-induced nonalcoholic steatohepatitis (NASH) development, Kit deletion worsens hepatic steatosis and exacerbates NASH-associated fibrosis and inflammation. Mechanistically, C-kit transcriptionally inhibits chemokine (C-X-C motif) receptor (CXCR)4 via CCAAT enhancer-binding protein α (CEBPA). Blocking CXCR4 signaling abolishes LSEC-macrophage-neutrophil cross-talk and leads to the recovery of C-kit-deficient mice with NASH. Of therapeutic relevance, infusing C-kit-expressing LSECs into aged mice or mice with diet-induced NASH counteracts age-associated senescence and steatosis and improves the symptoms of diet-induced NASH by restoring metabolic homeostasis of the pericentral liver endothelium. Our work provides an alternative approach that could be useful for treating aging- and diet-induced NASH.

C-kit inhibitor masitinib induces reactive oxygen species-dependent apoptosis in c-kit-negative HepG2 cells

Tumor-specific growth signal inhibition is a major anticancer strategy. Receptor tyrosine kinases (RTKs) are the most upstream receptors for growth signaling in cancer. Therefore, inhibition of RTKs has been proposed as an efficient therapeutic target. Masitinib, a c-kit inhibitor of the c-kit RTK, was developed to treat mastocytoma in dogs. In humans, however, the antitumor efficacy of masitinib was found to be attenuated against tumor cells with mutations of the c-kit gene. Here, we report that masitinib induced cell death via the intrinsic apoptotic pathway in HepG2, a c-kit-negative hepatocellular carcinoma cell line. In masitinib-treated HepG2 cells, increases in intracellular reactive oxygen species levels, loss of mitochondrial membrane potential, and cleavage of caspase-9 were observed, activating the intrinsic apoptotic pathway. Moreover, the cytotoxicity of masitinib to HepG2 cells was suppressed by treatment with the antioxidant N-acetyl-L-cysteine or a c-Jun N-terminal kinase/stress-activated protein kinase (JNKs) inhibitor. Thus, we demonstrated that the anticancer effects of masitinib are not due to its targeting c-kit, but rather to its targeting the redox balance via the JNK pathway in HepG2 cells. These results suggest that masitinib has the potential to provide a robust antitumor effect in tumor lesions and could also be applied to a broad range of other anticancer therapies.

Immunohistochemical Study of Cancer Stem Cell marker, Tight Junction Protein, and Lymphatic Density in Malignant Salivary Gland Tumors

Background: CD117/c-kit, is a powerful stem cell marker for malignant salivary gland tumors in which dysregulation of c-kit is closely associated with impairment of cell adhesion molecules and cancer metastasis.
 Objective: The main purpose of this work is to evaluate the immunohistochemical expression of c-kit, and claudin-1 and measure the density of lymph vessels (LVD) in common malignant salivary gland tumors by using podoplanin (D2-40) antibody.
 Materials and Methods: Immunohistochemical staining with streptavidin peroxidase was used to analysis the expression of c-kit, claudin-1 and stained podoplanin (D2-40) lymphatic vessels on fifty archival paraffin blocks of malignant salivary gland tumor (MSGTs) cases included 20 cases of AdCC, 11 cases of MEC, 10 cases of CXPA, 6 cases of AcCC, and 3 cases of PAC.
 Results: The immunopositivity of c-kit (CD117) was detected in 44/50 (88%) of studied cases, whereas, claudin-1 protein was observed in 35 (70%) of our specimens of MSGTs. Count down of stained lymph vessels between examined cases was, MEC on the top, followed by CXPA, AdCC, PAC and AcCC. A direct correlation was observed between c-kit and lymphatic density, on the other hand, the inverse correlation was found d between c-kit and cld-1, as well as, between cld-1 and lymphatic density
 Conclusion: Up regulation of cancer stem cell marker c-kit (CD117) expression is associated with decrease of tight junction protein cld-1 and increase the density of stained lymphatic vessels by podoplanin (D2-40) antibody which confirms the using of c-kit inhibitor to improve treatment strategy of malignant salivary gland tumors.

Effects of Stem Cell Factor/c-Kit Signaling on In Vitro Maturation of Porcine Oocytes and Subsequent Developmental Competence After Fertilization.

Stem cell factor (SCF), also known as c-Kit ligand, plays an important role in the proliferation of primordial germ cells and the survival of oocytes during follicular development. The aim of this study was to investigate the effect of SCF/c-Kit signaling on in vitro maturation (IVM) of porcine oocytes by analyzing nuclear and cytoplasmic maturation, oocyte size, cumulus cell expansion, and developmental competence to the blastocyst stage. Moreover, mRNA expression patterns of porcine cumulus cells and oocytes were evaluated using qRT-PCR. Following 42 h of IVM, 10 and 50 ng/mL SCF-treated groups exhibited significantly (P < 0.05) increased polar body extrusion rates and intracellular glutathione levels compared with the control group. The cumulus expansion index significantly (P < 0.05) increased in all SCF-treated groups compared with the control samples. mRNA levels of the proapoptotic gene Bax and apoptosis-related cysteine peptidase Caspase3 were lower in SCF-treated cumulus cells than in the control group. Notably, the diameter of oocytes after IVM, the mRNA expression of well-known oocyte-secreted factors (GDF9 and BMP15), and an oocyte-specific protein essential for ovulation and oocyte health (YBX2) were significantly (P < 0.05) higher in SCF-treated than in non-treated oocytes. Inhibition of c-Kit during porcine IVM using ACK2, an antagonistic blocker of c-Kit, significantly (P < 0.05) decreased the polar body extrusion rate compared with the control, as well as blastocyst formation rate compared with the 10 ng/mL SCF-treated group. In conclusion, the effect of SCF/c-Kit-mediated signaling during porcine IVM could be ascribed to the reduced expression of apoptosis-related genes and higher expression of oocyte-specific/secreted factors.

Beyond the Driver Mutation: Immunotherapies in Gastrointestinal Stromal Tumors.

Gastrointestinal stromal tumors (GISTs) are a subtype of soft tissue sarcoma (STS), and have become a concept of oncogenic addiction and targeted therapies.The large majority of these tumors develop after a mutation in KIT or platelet derived growth factor receptor α (PDGFRα), resulting in uncontrolled proliferation. GISTs are highly sensitive to imatinib. GISTs are immune infiltrated tumors with a predominance of tumor-associated macrophages (TAMs) and T-cells, including many CD8+ T-cells, whose numbers are prognostic. The genomic expression profile is that of an inhibited Th1 response and the presence of tertiary lymphoid structures and B cell signatures, which are known as predictive to response to ICI. However, the microtumoral environment has immunosuppressive attributes, with immunosuppressive M2 macrophages, overexpression of indoleamine 2,3-dioxygenase (IDO) or PD-L1, and loss of major histocompatibility complex type 1. In addition to inhibiting the KIT oncogene, imatinib appears to act by promoting cytotoxic T-cell activity, interacting with natural killer cells, and inhibiting the expression of PD-L1. Paradoxically, imatinib also appears to induce M2 polarization of macrophages. There have been few immunotherapy trials with anti-CTLA-4 or anti-PD-L1drugs and available clinical data are not very promising. Based on this comprehensive analysis of TME, we believe three immunotherapeutic strategies must be underlined in GIST. First, patients included in clinical trials must be better selected, based on the identified driver mutation (such as PDGFRα D842V mutation), the presence of tertiary lymphoid structures (TLS) or PD-L1 expression. Moreover, innovative immunotherapeutic agents also provide great interest in GIST, and there is a strong rationale for exploring IDO targeting after disease progression during imatinib therapy. Finally and most importantly, there is a strong rationale to combine of c-kit inhibition with immune checkpoint inhibitors.

The pathogenic role of c-Kit+ mast cells in the spinal motor neuron-vascular niche in ALS

Degeneration of motor neurons, glial cell reactivity, and vascular alterations in the CNS are important neuropathological features of amyotrophic lateral sclerosis (ALS). Immune cells trafficking from the blood also infiltrate the affected CNS parenchyma and contribute to neuroinflammation. Mast cells (MCs) are hematopoietic-derived immune cells whose precursors differentiate upon migration into tissues. Upon activation, MCs undergo degranulation with the ability to increase vascular permeability, orchestrate neuroinflammation and modulate the neuroimmune response. However, the prevalence, pathological significance, and pharmacology of MCs in the CNS of ALS patients remain largely unknown. In autopsy ALS spinal cords, we identified for the first time that MCs express c-Kit together with chymase, tryptase, and Cox-2 and display granular or degranulating morphology, as compared with scarce MCs in control cords. In ALS, MCs were mainly found in the niche between spinal motor neuron somas and nearby microvascular elements, and they displayed remarkable pathological abnormalities. Similarly, MCs accumulated in the motor neuron-vascular niche of ALS murine models, in the vicinity of astrocytes and motor neurons expressing the c-Kit ligand stem cell factor (SCF), suggesting an SCF/c-Kit-dependent mechanism of MC differentiation from precursors. Mechanistically, we provide evidence that fully differentiated MCs in cell cultures can be generated from the murine ALS spinal cord tissue, further supporting the presence of c-Kit+ MC precursors. Moreover, intravenous administration of bone marrow-derived c-Kit+ MC precursors infiltrated the spinal cord in ALS mice but not in controls, consistent with aberrant trafficking through a defective microvasculature. Pharmacological inhibition of c-Kit with masitinib in ALS mice reduced the MC number and the influx of MC precursors from the periphery. Our results suggest a previously unknown pathogenic mechanism triggered by MCs in the ALS motor neuron-vascular niche that might be targeted pharmacologically.

Abstract 634: Targeting metastatic brain germinoma using PDOX tumor models with sequential metastases

Abstract Introduction. Intracranial germ cell tumor is an Asian-centric tumor, showing great variation in geographical distribution, with an incidence 5-8 fold greater in Asia/East Asia, than Western countries. Germinoma is one histological subtype of intracranial germ cell tumors. Current standard of care for germinoma, is chemoradiotherapy. Metastatic/recurrent germinoma have poor prognosis. There is currently no targeted therapy. Purpose: To create patient-derived orthotopic xenograft (PDOX) models of distant metastases in brain germinoma beyond brain boundaries to recapitulate sequential metastases of original patient tumors. These tumor models will serve as clinically accurate metastatic models for preclinical testing, replicating patient's pattern of tumor progression/metastases. There is a lack of such metastatic brain tumor models in the field. c-KIT is the most common mutation in germinoma. We evaluated preclinical efficacy of a c-KIT inhibitor. Experimental Procedures. Most PDOX brain tumor models are created by implanting patient-derived tumor cells in cerebrum/cerebellum. Germinoma originates from pineal gland/suprasellar region. We implanted germinoma cells nearer location of tumor origin. We were successful and achieved consistent tumor implantation into this location (100% post-surgery survival, 0% surgical mortality, 0% post-surgical neurological deficits). Summary. We successfully established two models with sequential metastases. Model 1 was created from metastatic cells from spinal recurrence (Patient 1) post-chemo-radiotherapy. This model faithfully created skull base metastases in 100% of murine replicas (n=9). Both tumor cells from brain and skull base metastases (n=7) were serially transplantable. Our findings were replicated (n=5) and consistent. Model 2 was created from metastatic cells of cerebrospinal fluid dissemination (Patient 2). Brain surface metastases were formed recapitulating patient tumor. Both models recapitulated a similar path of metastases in craniospinal axis, corresponding to respective patients. c-KIT inhibitor, was effective in significantly prolonging animal survival in Model 2 (p=0.0046) but not in Model 1 (p=0.0541). In Model 2, c-kit inhibition in-vivo was efficacious and resulted in 3-fold effect, (1) Significantly improved animal survival, (2) Macroscopically reduced frequency, severity of brain surface metastases (Controls=50%, Treated=14%, lesser in severity), (3) Microscopically reduced tumor burden to minimal residual disease limited to cerebrospinal fluid outline. Control mice brains were largely replaced by tumor bulk, while treated mice had minimal residual tumor burden. Conclusions. Understanding metastatic patterns in such aggressive models is relevant in biologic targeting for preclinical studies and clinical decision to extend radiotherapy field in recurrent disease. Citation Format: Shiying Huang, Sekar Karthik, Jack M Su, Qi Lin, YuChen Du, Ching C Lau, Adesina Adekunle, Angela Major, Kam-Man Hui, M. Tarek Elghetany, Xiaonan Li, Wan-Yee Teo. Targeting metastatic brain germinoma using PDOX tumor models with sequential metastases [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 634.

Abstract 1133: Combined inhibition of cKIT and Lysine-Specific Demethylase 1 as a therapeutic strategy in acute myeloid leukemia

Abstract Responses to kinase inhibitors in AML are short-lived with the inevitable development of resistance. Combination therapy with agents from distinct functional classes is one strategy to overcome this resistance. Using AML cell lines and primary patient samples harboring oncogenic cKIT mutations we demonstrate that inhibition of the epigenetic regulator Lysine-Specific Demethylase 1 (LSD1) markedly augments the cytotoxic effect of the KIT inhibitor avapritinib. Transcriptomic and epigenetic profiling revealed synergistic suppression of Myc activity accompanied by a global loss of acetylation and decreased expression of key leukemia cell cycle genes. This epigenetic reorganization results from disruption of key transcription factor networks responsible for maintaining leukemia cell self-renewal and survival. These findings demonstrate that combined KIT and LSD1 inhibition is an exciting new therapeutic avenue for KIT mutant AML. Previously, we have shown targeting the leukemic epigenome as a possible mechanism to augment the efficacy of kinase inhibitors. Thus, we hypothesize that targeting both the cKIT and CBF mutations with combination therapy will result in a deeper molecular response. Kasumi-1 cells harbor mutant cKIT, making an ideal model to study this combination. We observed a synergistic response to a clinically available KIT inhibitor, avapritinib, and two different LSD1 inhibitors, ORY-1001 and GSK-LSD1. Colony formation of healthy CD34+ cells and cell growth of cKIT WT cells were not significantly altered by the combination, thus showing the specificity of this combination by targeting mutant KIT. Bulk RNA-seq and master regulator analysis revealed greater suppression of Myc target genes with dual inhibition of KIT and LSD1. Using Cleavage Under Targets and Tagmentation (CUT&amp;Tag), we observed synergistic loss of H3K27Ac at the promoters of genes necessary for cell proliferation. Additionally, we used Cleavage Under Targets and Release Using Nuclease (CUT&amp;RUN) to interrogate Myc localization, and found a greater loss of Myc binding with dual inhibition, overlapping with the loss of acetylation at these loci. This study demonstrates the synergistic efficacy of combination therapy and identifies key biomarkers for drug activity, namely loss of histone acetylation and Myc binding. Collectively, combined KIT and LSD1 inhibition may be an effective therapeutic approach for cKIT mutant AML. Citation Format: Brittany M. Smith, Daniel J. Coleman, Lauren Maloney, Cody Coblentz, Zachary Schonrock, Joseph Estabrook, Theresa Lusardi, Brian J. Druker, Julia E. Maxson, Theodore P. Braun. Combined inhibition of cKIT and Lysine-Specific Demethylase 1 as a therapeutic strategy in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1133.

Abstract 1482: M4645 is a potent and highly selective inhibitor of disease relevant cKIT mutations for the treatment of metastatic or recurrent GIST

Abstract Oncogenic mutations in cKIT in exons 9 and 11 are the main driver of gastrointestinal stromal tumors (GIST). Imatinib is standard of care in 1L in unresectable metastatic or recurrent GIST, yet secondary resistance mutations in exons 13/14 and 17/18 of the cKIT kinase domain frequently arise limiting efficacy. Currently approved 2L and 3L therapies sunitinib and regorafenib target these mutations only to some extent and show limited clinical benefit. Even with the recent approval of ripretinib as 4L treatment, a high unmet medical need remains for patients with imatinib resistance mutations in exon13/14. M4645 was designed to particularly inhibit the frequent V654A resistance mutation in exon 13 of cKIT. Based on cKIT inhibitor scaffolds identified within the Merck compound collection, a 3,5,6-substituted indazole-lead was discovered. Substituent optimization in the 5- and 6-positions of the core scaffold resulted in highly selective kinase inhibitors. Through variation at the 3-position, potency and physicochemical properties were optimized, resulting in the candidate molecule M4645 which combined potency, kinase selectivity, and solubility with a good safety profile. The excellent kinase selectivity could be rationalized by the crystal structure of cKIT V654A mutant kinase domain in complex with M4645. M4645 showed potent inhibition of cKIT autophosphorylation and of downstream P-ERK1/2 and P-AKT signaling in cell lines bearing activating and resistance mutations of cKIT. Dose-dependent inhibition of cKIT activation was demonstrated in a GIST xenograft model expressing the cKIT resistance mutation V654A in exon 13. Strong antitumor activity was observed in cell line and patient-derived GIST xenograft models with this imatinib resistance mutation. Compared to imatinib, M4645 induced prolonged anti-tumor response in a GIST model with a primary activating mutation of cKIT. In summary, the favorable profile and strong antitumor activity, particularly in GIST models expressing the V654A resistance mutation, suggests superiority of M4645 compared to currently available &amp;gt; 2L treatment options for unresectable metastatic or recurrent GIST patients. Citation Format: Nina Linde, Andreas Blum, Dieter Dorsch, Ulrich Graedler, Michael Busch, Nina Glaser, Carl Petersson, Aaron Ruff, Eva Sherbetjian, Christina Esdar. M4645 is a potent and highly selective inhibitor of disease relevant cKIT mutations for the treatment of metastatic or recurrent GIST [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1482.