A human monoclonal antibody targeting the stem cell factor receptor (c-Kit) blocks tumor cell signaling and inhibits tumor growth

Drug delivery targets and strategies to address mast cell diseases

INTRODUCTION

Current and developing mast cell therapeutics are reliant on small molecule drugs and biologics, but few are truly selective for mast cells. Most have cellular and disease-specific limitations that require innovation to overcome longstanding challenges to selectively targeting and modulating mast cell behavior. This review is designed to serve as a frame of reference for new approaches that utilize nanotechnology or combine different drugs to increase mast cell selectivity and therapeutic efficacy.

AREAS COVERED

Mast cell diseases include allergy and related conditions as well as malignancies. Here, we discuss the targets of existing and developing therapies used to treat these disease pathologies, classifying them into cell surface, intracellular, and extracellular categories. For each target discussed, we discuss drugs that are either the current standard of care, under development, or have indications for potential use. Finally, we discuss how novel technologies and tools can be used to take existing therapeutics to a new level of selectivity and potency against mast cells.

EXPERT OPINION

There are many broadly and very few selectively targeted therapeutics for mast cells in allergy and malignant disease. Combining existing targeting strategies with technology like nanoparticles will provide novel platforms to treat mast cell disease more selectively.

c-Kit Induces Migration of Triple-Negative Breast Cancer Cells and Is a Promising Target for Tyrosine Kinase Inhibitor Treatment

Triple-negative breast cancer (TNBC) is associated with a poor prognosis and the absence of targeted therapy. c-Kit, a receptor tyrosine kinase (RTK), is considered a molecular target for anticancer drugs. Tyrosine kinase inhibitors (TKIs) recognizing c-Kit are used for the treatment of c-Kit-expressing tumors. However, the expression, function, and therapeutic potential of c-Kit have been little explored in TNBC. Here, we studied the expression and effects of c-Kit in TNBC through in vitro and in silico analysis, and evaluated the response to TKIs targeting c-Kit. Analysis of TNBC cells showed the expression of functional c-Kit at the cell membrane. The stimulation of c-Kit with its ligand induced the activation of STAT3, Akt, and ERK1/2, increasing cell migration, but had no effect on cell proliferation or response to Doxorubicin. Analysis of public datasets showed that the expression of c-Kit in tumors was not associated with patient survival. Finally, TNBC cells were susceptible to TKIs, in particular the effect of Nilotinib was stronger than Doxorubicin in all cell lines. In conclusion, TNBC cells express functional c-Kit, which is a targetable molecule, and show a strong response to Nilotinib that may be considered a candidate drug for the treatment of TNBC.

Anti-CD117 immunotherapy to eliminate hematopoietic and leukemia stem cells

Precise replacement of diseased or dysfunctional organs is the goal of regenerative medicine and has appeared to be a distant goal for a long time. In the field of hematopoietic stem cell transplantation, this goal is now becoming tangible as gene-editing technologies and novel conditioning agents are entering the clinical arena. Targeted immunologic depletion of hematopoietic stem cells (HSCs), which are at the very root of the hematopoietic system, will enable more selective and potentially more effective hematopoietic stem cell transplantation in patients with hematological diseases. In contrast to current conditioning regimes based on ionizing radiation and chemotherapy, immunologic conditioning will spare mature hematopoietic cells and cause substantially less inflammation and unspecific collateral damage to other organs. Biological agents that target the stem cell antigen CD117 are the frontrunners for this purpose and have exhibited preclinical activity in depletion of healthy HSCs. The value of anti-CD117 antibodies as conditioning agents is currently being evaluated in early clinical trials. Whereas mild, antibody-based immunologic conditioning concepts might be appropriate for benign hematological disorders in which incomplete replacement of diseased cells is sufficient, higher efficacy will be required for treatment and elimination of hematologic stem cell malignancies such as acute myeloid leukemia and myelodysplastic syndrome. Antibody-drug conjugates, bispecific T-cell engaging and activating antibodies (TEAs), or chimeric antigen receptor (CAR) T cells might offer increased efficacy compared with naked antibodies and yet higher tolerability and safety compared with current genotoxic conditioning approaches. Here, we summarize the current state regarding immunologic conditioning concepts for the treatment of HSC disorders and outline potential future developments.

A new monoclonal antibody that blocks dimerisation and inhibits c-kit mutation-driven tumour growth

PURPOSE

Imatinib, a small-molecule tyrosine kinase inhibitor, has shown good clinical activity by inhibiting adenosine triphosphate (ATP) binding to the receptor. Unfortunately, majority of patients eventually develop drug resistance, which limits the long-term benefits of the tyrosine kinase inhibitors and poses a significant challenge in the clinical management of GIST. The aim of our study was to explore the feasibility of blocking KIT dimerisation upstream of the phosphorylation in imatinib-resistant GIST.

METHOD

KITMAb was prepared using hybridoma technique. The biological function of KITMAb was examined in KIT-dimer-expressing cells constructed by transfecting with liposomes using enzyme linked immunosorbent assay (ELISA), immunohistochemistry, western blot, MTT, Annexin V/FITC, and flow cytometry assay, respectively.

RESULTS

KIT-dimer was expressed in 293 cells transfected with c-kit mutated-type pcDNA3.1. Treatment of KIT-dimer-expressing cells with the KITMAb significantly decreased the expression of both KIT-dimer and other phosphorylated proteins of KIT downstream signalling pathway. Furthermore, KITMAb slowed down cell growth and reduced the proportion of cells in the proliferative phase (S + G2-M). Finally, we also found that KITMAb treatment accelerated cell apoptosis. These results indicate that KITMAb strongly inhibits KIT receptor dimerisation-mediated signalling pathway and cell growth responses in vitro.

CONCLUSIONS

We demonstrate c-kit mutation-driven KIT auto-dimerisation prior to tyrosine kinase phosphorylation as same as the procedure in ligand-dependent signalling pathway and describe a monoclonal antibody, KITMAb, with strong affinity to the dimerisation domain of KIT that blocks the important step in both the KIT signalling pathways. Further, the results suggest that treatment with KITMAb may be potentially therapeutic in imatinib-resistant GIST.

Elevated CELSR3 expression is associated with hepatocarcinogenesis and poor prognosis

Cadherin EGF LAG seven-pass G-type receptor 3 (CELSR3) has been reported to exhibit a cancer-specific pattern. The present study aimed to investigate the clinical value and functional role of CELSR3 in hepatocellular carcinoma (HCC), and determine the underlying molecular mechanism in patients with HCC. CELSR3 expression in tumor and paracancerous HCC tissues was obtained from The Cancer Genome Atlas. Differential expression analysis was performed using the edgeR package. Pearson correlation analysis was used to analyze the correlation between methylation and mRNA levels of CELSR3. Pathways affected by aberrant CELSR3 expression were identified through Gene Set Enrichment Analysis. The results demonstrated that CELSR3 was highly expressed in the early stage of cancer and was present throughout the entire cancer process, which suggested that CELSR3 may serve a key role in the carcinogenesis of HCC. In addition, upregulation of CELSR3 was associated with its methylation level; high CELSR3 expression indicated a shorter overall survival time. Multiple candidate genes were screened by integrating differentially expressed (DE) mRNAs and target genes of DE microRNAs (miRs). Subsequent pathway enrichment analysis demonstrated that the upregulated genes were predominantly enriched in the ‘Neuroactive ligand-receptor interaction’ and ‘Cell cycle’ pathways, whereas the downregulated genes were primarily enriched in ‘Cytokine-cytokine receptor interaction’ and ‘Metabolic pathways’. CELSR3 and its connected nodes and edges were initially removed from the miRNA-mRNA regulatory network in order to prevent bias and compared with the network containing CELSR3 alone. The frequently dysregulated miRNAs were identified as miR-181 family members, and the results suggested that miR-181 and the Wnt/β-catenin signaling pathway influenced CELSR3 expression.

Targeting KIT on innate immune cells to enhance the antitumor activity of checkpoint inhibitors

Innate immune cells such as mast cells and myeloid-derived suppressor cells are key components of the tumor microenvironment. Recent evidence indicates that levels of myeloid-derived suppressor cells in melanoma patients are associated with poor survival to checkpoint inhibitors. This suggests that targeting both the innate and adaptive suppressive components of the immune system will maximize clinical benefit and elicit more durable responses in cancer patients. Preclinical data suggest that targeting signaling by the receptor tyrosine kinase KIT, particularly on mast cells, may modulate innate immune cell numbers and activity in tumors. Here, we review data highlighting the importance of the KIT signaling in regulating antitumor immune responses and the potential benefit of combining selective KIT inhibitors with immune checkpoint inhibitors.

Is the Canonical RAF/MEK/ERK Signaling Pathway a Therapeutic Target in SCLC?

The activity of the RAF/MEK/ERK signaling pathway is critical for the proliferation of normal and cancerous cells. Oncogenic mutations driving the development of lung adenocarcinoma often activate this signaling pathway. In contrast, pathway activity levels and their biological roles are not well established in small cell lung cancer (SCLC), a fast-growing neuroendocrine lung cancer subtype. Here we discuss the function of the RAF/MEK/ERK kinase pathway and the mechanisms leading to its activation in SCLC cells. In particular, we argue that activation of this pathway may be beneficial to the survival, proliferation, and spread of SCLC cells in response to multiple stimuli. We also consider evidence that high levels of RAF/MEK/ERK pathway activity may be detrimental to SCLC tumors, including in part by interfering with their neuroendocrine fate. On the basis of these observations, we examined when small molecules targeting kinases in the RAF/MEK/ERK pathway may be useful therapeutically in patients with SCLC, including in combination with other therapeutic agents.

Therapeutic Efficacy Assessment of CK6, a Monoclonal KIT Antibody, in a Panel of Gastrointestinal Stromal Tumor Xenograft Models

We evaluated the efficacy of CK6, a KIT monoclonal antibody, in a panel of human gastrointestinal stromal tumor (GIST) xenograft models. Nude mice were bilaterally transplanted with human GIST xenografts (four patient derived and two cell line derived), treated for 3 weeks, and grouped as follows: control (untreated); CK6 (40 mg/kg, 3 × weekly); imatinib (50 mg/kg, twice daily); sunitinib (40 mg/kg, once daily); imatinib + CK6; sunitinib + CK6 (same doses and schedules as in the single-agent treatments). Tumor volume assessment, Western blot analysis, and histopathology were used for evaluation of efficacy. Statistical analysis was performed using Mann-Whitney U (MWU) and Wilcoxon matched-pairs tests. CK6 as a single agent only reduced tumor growth rate in the UZLX-GIST3 model (P = .053, MWU compared to control), while in none of the other GIST models an effect on tumor growth rate was observed. CK6 did not result in significant anti-proliferative or pro-apoptotic effects in any of the GIST models, and moreover, CK6 did not induce a remarkable inhibition of KIT activation. Furthermore, no synergistic effect of combining CK6 with tyrosine kinase inhibitors (TKIs) was observed. Conversely, in certain GIST xenografts, anti-tumor effects seemed to be inferior under combination treatment compared to single-agent TKI treatment. In the GIST xenografts tested, the anti-tumor efficacy of CK6 was limited. No synergy was observed on combination of CK6 with TKIs in these GIST models. Our findings highlight the importance of using relevant in vivo human tumor xenograft models in the preclinical assessment of drug combination strategies.

c-Kit Expression is Rate-Limiting for Stem Cell Factor-Mediated Disease Progression in Adenoid Cystic Carcinoma of the Salivary Glands

Adenoid cystic carcinoma (ACC) is an aggressive malignant neoplasm of the salivary glands in which c-Kit is overexpressed and activated, although the mechanism for this is as yet unclear. We analyzed 27 sporadic ACC tumor specimens to examine the biologic and clinical significance of c-Kit activation. Mutational analysis revealed expression of wild-type c-Kit in all, eliminating gene mutation as a cause of activation. Because stem cell factor (SCF) is c-Kit's sole ligand, we analyzed its expression in the tumor cells and their environment. Immunohistochemistry revealed its presence in c-Kit–positive tumor cells, suggesting an activation of autocrine signaling. We observed a significant induction of ERK1/2 in the cells. SCF staining was also found in other types of non-cancerous cells adjacent to tumors within salivary glands, including stromal fibroblasts, neutrophils, peripheral nerve, skeletal muscle, vascular endothelial cells, mucous acinar cells, and intercalated ducts. Quantitative PCR showed that the top quartile of c-Kit mRNA expression distinguished ACCs from normal salivary tissues and was cross-correlated with short-term poor prognosis. Expression levels of SCF and c-Kit were highly correlated in the cases with perineural invasion. These observations suggest that c-Kit is potentially activated by receptor dimerization upon stimulation by SCF in ACC, and that the highest quartile of c-Kit mRNA expression could be a predictor of poor prognosis. Our findings may support an avenue for c-Kit-targeted therapy to improve disease control in ACC patients harboring the top quartile of c-Kit mRNA expression.