NUMB as a Therapeutic Target for Melanoma.

The upregulation of the adaptor protein NUMB triggers melanocytic differentiation from multipotent skin stem cells, which share many properties with aggressive melanoma cells. Although NUMB acts as a tumor suppressor in various human cancer types, little is known about its role in melanoma. In this study, we investigated the role of NUMB in melanoma progression and its regulatory mechanism. Analysis of The Cancer Genome Atlas melanoma datasets revealed that high NUMB expression in melanoma tissues correlates with improved patient survival. Moreover, NUMB expression is downregulated in metastatic melanoma cells. NUMB knockdown significantly increased the invasion potential of melanoma cells in a three-dimensional collagen matrix in vitro and in the lungs of a mouse model in vivo; it also significantly upregulated the expression of the NOTCH target gene CCNE. Previous studies suggested that Wnt signaling increases NUMB expression. By mimicking Wnt stimulation through glycogen synthase kinase-3 inhibition, we increased NUMB expression in melanoma cells. Furthermore, a glycogen synthase kinase-3 inhibitor reduced the invasion of melanoma cells in a NUMB-dependent manner. Together, our results suggest that NUMB suppresses invasion and metastasis in melanoma, potentially through its regulation of the NOTCH‒CCNE axis and that the inhibitors that upregulate NUMB can exert therapeutic effects in melanoma.

Neural Crest-Like Stem Cell Transcriptome Analysis Identifies LPAR1 in Melanoma Progression and Therapy Resistance.

Metastatic melanoma is challenging to clinically address. Although standard-of-care targeted therapy has high response rates in patients with BRAF-mutant melanoma, therapy relapse occurs in most cases. Intrinsically resistant melanoma cells drive therapy resistance and display molecular and biologic properties akin to neural crest-like stem cells (NCLSC) including high invasiveness, plasticity, and self-renewal capacity. The shared transcriptional programs and vulnerabilities between NCLSCs and cancer cells remains poorly understood. Here, we identify a developmental LPAR1-axis critical for NCLSC viability and melanoma cell survival. LPAR1 activity increased during progression and following acquisition of therapeutic resistance. Notably, genetic inhibition of LPAR1 potentiated BRAFi ± MEKi efficacy and ablated melanoma migration and invasion. Our data define LPAR1 as a new therapeutic target in melanoma and highlights the promise of dissecting stem cell-like pathways hijacked by tumor cells. SIGNIFICANCE: This study identifies an LPAR1-axis critical for melanoma invasion and intrinsic/acquired therapy resistance.

Tumor-infiltrating mast cells are associated with resistance to anti-PD-1 therapy.

Anti-PD-1 therapy is used as a front-line treatment for many cancers, but mechanistic insight into this therapy resistance is still lacking. Here we generate a humanized (Hu)-mouse melanoma model by injecting fetal liver-derived CD34+ cells and implanting autologous thymus in immune-deficient NOD-scid IL2Rγnull (NSG) mice. Reconstituted Hu-mice are challenged with HLA-matched melanomas and treated with anti-PD-1, which results in restricted tumor growth but not complete regression. Tumor RNA-seq, multiplexed imaging and immunohistology staining show high expression of chemokines, as well as recruitment of FOXP3+ Treg and mast cells, in selective tumor regions. Reduced HLA-class I expression and CD8+/Granz B+ T cells homeostasis are observed in tumor regions where FOXP3+ Treg and mast cells co-localize, with such features associated with resistance to anti-PD-1 treatment. Combining anti-PD-1 with sunitinib or imatinib results in the depletion of mast cells and complete regression of tumors. Our results thus implicate mast cell depletion for improving the efficacy of anti-PD-1 therapy.

Amivantamab (JNJ-61186372), an Fc Enhanced EGFR/cMet Bispecific Antibody, Induces Receptor Downmodulation and Antitumor Activity by Monocyte/Macrophage Trogocytosis.

Small molecule inhibitors targeting mutant EGFR are standard of care in non-small cell lung cancer (NSCLC), but acquired resistance invariably develops through mutations in EGFR or through activation of compensatory pathways such as cMet. Amivantamab (JNJ-61186372) is an anti-EGFR and anti-cMet bispecific low fucose antibody with enhanced Fc function designed to treat tumors driven by activated EGFR and/or cMet signaling. Potent in vivo antitumor efficacy is observed upon amivantamab treatment of human tumor xenograft models driven by mutant activated EGFR, and this activity is associated with receptor downregulation. Despite these robust antitumor responses in vivo, limited antiproliferative effects and EGFR/cMet receptor downregulation by amivantamab were observed in vitro Interestingly, in vitro addition of isolated human immune cells notably enhanced amivantamab-mediated EGFR and cMet downregulation, leading to antibody dose-dependent cancer cell killing. Through a comprehensive assessment of the Fc-mediated effector functions, we demonstrate that monocytes and/or macrophages, through trogocytosis, are necessary and sufficient for Fc interaction-mediated EGFR/cMet downmodulation and are required for in vivo antitumor efficacy. Collectively, our findings represent a novel Fc-dependent macrophage-mediated antitumor mechanism of amivantamab and highlight trogocytosis as an important mechanism of action to exploit in designing new antibody-based cancer therapies.

Corrigendum: Rare cell variability and drug-induced reprogramming as a mode of cancer drug resistance.

This corrects the article DOI: 10.1038/nature22794.

MSX1-Induced Neural Crest-Like Reprogramming Promotes Melanoma Progression.

Melanoma cells share many biological properties with neural crest stem cells. Here we show that the homeodomain transcription factor MSX1, which is significantly correlated with melanoma disease progression, reprograms melanocytes and melanoma cells toward a neural crest precursor-like state. MSX1-reprogrammed normal human melanocytes express the neural crest marker p75 and become multipotent. MSX1 induces a phenotypic switch in melanoma, which is characterized by an oncogenic transition from an E-cadherin-high nonmigratory state toward a ZEB1-high invasive state. ZEB1 up-regulation is responsible for the MSX1-induced migratory phenotype in melanoma cells. Depletion of MSX1 significantly inhibits melanoma metastasis in vivo. These results show that neural crest-like reprogramming achieved by a single factor is a critical process for melanoma progression.

Genetic and Genomic Characterization of 462 Melanoma Patient-Derived Xenografts, Tumor Biopsies, and Cell Lines.

Tumor-sequencing studies have revealed the widespread genetic diversity of melanoma. Sequencing of 108 genes previously implicated in melanomagenesis was performed on 462 patient-derived xenografts (PDXs), cell lines, and tumors to identify mutational and copy number aberrations. Samples came from 371 unique individuals: 263 were naive to treatment, and 108 were previously treated with targeted therapy (34), immunotherapy (54), or both (20). Models of all previously reported major melanoma subtypes (BRAF, NRAS, NF1, KIT, and WT/WT/WT) were identified. Multiple minor melanoma subtypes were also recapitulated, including melanomas with multiple activating mutations in the MAPK-signaling pathway and chromatin-remodeling gene mutations. These well-characterized melanoma PDXs and cell lines can be used not only as reagents for a large array of biological studies but also as pre-clinical models to facilitate drug development.

A Comprehensive Patient-Derived Xenograft Collection Representing the Heterogeneity of Melanoma.

Therapy of advanced melanoma is changing dramatically. Following mutational and biological subclassification of this heterogeneous cancer, several targeted and immune therapies were approved and increased survival significantly. To facilitate further advancements through pre-clinical in vivo modeling, we have established 459 patient-derived xenografts (PDX) and live tissue samples from 384 patients representing the full spectrum of clinical, therapeutic, mutational, and biological heterogeneity of melanoma. PDX have been characterized using targeted sequencing and protein arrays and are clinically annotated. This exhaustive live tissue resource includes PDX from 57 samples resistant to targeted therapy, 61 samples from responders and non-responders to immune checkpoint blockade, and 31 samples from brain metastasis. Uveal, mucosal, and acral subtypes are represented as well. We show examples of pre-clinical trials that highlight how the PDX collection can be used to develop and optimize precision therapies, biomarkers of response, and the targeting of rare genetic subgroups.

Tumor-associated B-cells induce tumor heterogeneity and therapy resistance.

In melanoma, therapies with inhibitors to oncogenic BRAFV600E are highly effective but responses are often short-lived due to the emergence of drug-resistant tumor subpopulations. We describe here a mechanism of acquired drug resistance through the tumor microenvironment, which is mediated by human tumor-associated B cells. Human melanoma cells constitutively produce the growth factor FGF-2, which activates tumor-infiltrating B cells to produce the growth factor IGF-1. B-cell-derived IGF-1 is critical for resistance of melanomas to BRAF and MEK inhibitors due to emergence of heterogeneous subpopulations and activation of FGFR-3. Consistently, resistance of melanomas to BRAF and/or MEK inhibitors is associated with increased CD20 and IGF-1 transcript levels in tumors and IGF-1 expression in tumor-associated B cells. Furthermore, first clinical data from a pilot trial in therapy-resistant metastatic melanoma patients show anti-tumor activity through B-cell depletion by anti-CD20 antibody. Our findings establish a mechanism of acquired therapy resistance through tumor-associated B cells with important clinical implications.Resistance to BRAFV600E inhibitors often occurs in melanoma patients. Here, the authors describe a potential mechanism of acquired drug resistance mediated by tumor-associated B cells-derived IGF-1.

Rare cell variability and drug-induced reprogramming as a mode of cancer drug resistance.

Therapies that target signalling molecules that are mutated in cancers can often have substantial short-term effects, but the emergence of resistant cancer cells is a major barrier to full cures. Resistance can result from secondary mutations, but in other cases there is no clear genetic cause, raising the possibility of non-genetic rare cell variability. Here we show that human melanoma cells can display profound transcriptional variability at the single-cell level that predicts which cells will ultimately resist drug treatment. This variability involves infrequent, semi-coordinated transcription of a number of resistance markers at high levels in a very small percentage of cells. The addition of drug then induces epigenetic reprogramming in these cells, converting the transient transcriptional state to a stably resistant state. This reprogramming begins with a loss of SOX10-mediated differentiation followed by activation of new signalling pathways, partially mediated by the activity of the transcription factors JUN and/or AP-1 and TEAD. Our work reveals the multistage nature of the acquisition of drug resistance and provides a framework for understanding resistance dynamics in single cells. We find that other cell types also exhibit sporadic expression of many of these same marker genes, suggesting the existence of a general program in which expression is displayed in rare subpopulations of cells.

Personalized Preclinical Trials in BRAF Inhibitor-Resistant Patient-Derived Xenograft Models Identify Second-Line Combination Therapies.

PURPOSE: To test second-line personalized medicine combination therapies, based on genomic and proteomic data, in patient-derived xenograft (PDX) models. EXPERIMENTAL DESIGN: We established 12 PDXs from BRAF inhibitor-progressed melanoma patients. Following expansion, PDXs were analyzed using targeted sequencing and reverse-phase protein arrays. By using multi-arm preclinical trial designs, we identified efficacious precision medicine approaches. RESULTS: We identified alterations previously described as drivers of resistance: NRAS mutations in 3 PDXs, MAP2K1 (MEK1) mutations in 2, BRAF amplification in 4, and aberrant PTEN in 7. At the protein level, re-activation of phospho-MAPK predominated, with parallel activation of PI3K in a subset. Second-line efficacy of the pan-PI3K inhibitor BKM120 with either BRAF (encorafenib)/MEK (binimetinib) inhibitor combination or the ERK inhibitor VX-11e was confirmed in vivo Amplification of MET was observed in 3 PDX models, a higher frequency than expected and a possible novel mechanism of resistance. Importantly, MET amplification alone did not predict sensitivity to the MET inhibitor capmatinib. In contrast, capmatinib as single agent resulted in significant but transient tumor regression in a PDX with resistance to BRAF/MEK combination therapy and high pMET. The triple combination capmatinib/encorafenib/binimetinib resulted in complete and sustained tumor regression in all animals. CONCLUSIONS: Genomic and proteomic data integration identifies dual-core pathway inhibition as well as MET as combinatorial targets. These studies provide evidence for biomarker development to appropriately select personalized therapies of patients and avoid treatment failures. See related commentary by Hartsough and Aplin, p. 1550.

miR-200c/Bmi1 axis and epithelial-mesenchymal transition contribute to acquired resistance to BRAF inhibitor treatment.

Resistance to BRAF inhibitors (BRAFi) is one of the major challenges for targeted therapies for BRAF-mutant melanomas. However, little is known about the role of microRNAs in conferring BRAFi resistance. Herein, we demonstrate that miR-200c expression is significantly reduced whereas miR-200c target genes including Bmi1, Zeb2, Tubb3, ABCG5, and MDR1 are significantly increased in melanomas that acquired BRAFi resistance compared to pretreatment tumor biopsies. Similar changes were observed in BRAFi-resistant melanoma cell lines. Overexpression of miR-200c or knock-down of Bmi1 in resistant melanoma cells restores their sensitivities to BRAFi, leading to deactivation of the PI3K/AKT and MAPK signaling cascades, and acquisition of epithelial-mesenchymal transition-like phenotypes, including upregulation of E-cadherin, downregulation of N-cadherin, and ABCG5 and MDR1 expression. Conversely, knock-down of miR-200c or overexpression of Bmi1 in BRAFi-sensitive melanoma cells activates the PI3K/AKT and MAPK pathways, upregulates N-cadherin, ABCG5, and MDR1 expression, and downregulates E-cadherin expression, leading to BRAFi resistance. Together, our data identify miR-200c as a critical signaling node in BRAFi-resistant melanomas impacting the MAPK and PI3K/AKT pathways, suggesting miR-200c as a potential therapeutic target for overcoming acquired BRAFi resistance.