Large-scale Analysis of PDGFRA Mutations in Melanomas and Evaluation of Their Sensitivity to Tyrosine Kinase Inhibitors Imatinib and Crenolanib

“Platelet-derived growth factor receptor alpha (PDGFRA) is a target for tyrosine kinase inhibitors (TKIs)-based targeted therapy. Dysregulation of PDGFRA has been reported in many cancers. However, PDGFRA mutations in melanomas have not been well studied. We analyzed the genetic mutations of PDGFRA in Chinese melanoma patients, and determined the inhibitory potency of TKIs such as imatinib and crenolanib on mutant PDGFRA. Experimental Design: 351 melanoma tissue samples were examined for genetic mutations in exons 12, 14 and 18 of PDGFRA. Activities of mutations in response to imatinib and crenolanib were analyzed by western blotting of tyrosine-phosphorylated PDGFRA and cell proliferation assays. Results: PDGFRA mutations were observed in 4.6% (16/351) of melanomas, and these mutations were mainly detected in acral and mucosal melanomas. PDGFRA mutations appear to be mutually exclusive with KIT mutations, but may coexist with BRAF and NRAS mutations. The genetic mutations of PDGFRA were unrelated to the age, thickness and ulceration status of primary melanomas. Thirteen mutations were not reported before, and five (P577S, V658A, R841K, H845Y and G853D) of them resulted in strong autophosphorylation of PDGFRA. Crenolanib showed higher potency than imatinib in inhibiting the kinase activity of PDGFRA. Except that V658A mutation was imatinib-resistant, all the other mutations were sensitive to both imatinib and crenolanib. Conclusions: PDGFRA mutations are detected in a small population of melanoma patients. Our study suggests that melanoma patients harboring certain PDGFRA mutations may benefit from imatinib and crenolanib treatment.”

BRD4 Sustains Melanoma Proliferation and Represents a New Target for Epigenetic Therapy

“Metastatic melanoma remains a mostly incurable disease. Although newly approved targeted therapies are efficacious in a subset of patients, resistance and relapse rapidly ensue. Alternative therapeutic strategies to manipulate epigenetic regulators and disrupt the transcriptional program that maintains tumor cell identity are emerging. Bromodomain and extraterminal domain (BET) proteins are epigenome readers known to exert key roles at the interface between chromatin remodeling and transcriptional regulation. Here, we report that BRD4, a BET family member, is significantly upregulated in primary and metastatic melanoma tissues compared with melanocytes and nevi. Treatment with BET inhibitors impaired melanoma cell proliferation in vitro and tumor growth and metastatic behavior in vivo, effects that were mostly recapitulated by individual silencing of BRD4. RNA sequencing of BET inhibitor–treated cells followed by Gene Ontology analysis showed a striking impact on transcriptional programs controlling cell growth, proliferation, cell-cycle regulation, and differentiation. In particular, we found that, rapidly after BET displacement, key cell-cycle genes (SKP2ERK1, and c-MYC) were downregulated concomitantly with the accumulation of cyclin-dependent kinase (CDK) inhibitors (p21 and p27), followed by cell-cycle arrest. Importantly, BET inhibitor efficacy was not influenced by BRAF or NRAS mutational status, opening the possibility of using these small-molecule compounds to treat patients for whom no effective targeted therapy exists. Collectively, our study reveals a critical role for BRD4 in melanoma tumor maintenance and renders it a legitimate and novel target for epigenetic therapy directed against the core transcriptional program of melanoma.”

A Switch in the Expression of Embryonic EMT-Inducers Drives the Development of Malignant Melanoma

“Aberrant expression of embryonic epithelial-mesenchymal transition-inducing transcription factors (EMT-TFs) in epithelial cells triggers EMT, neoplastic transformation, stemness, and metastatic dissemination. We found that regulation and functions of EMT-TFs are different in malignant melanoma. SNAIL2 and ZEB2 transcription factors are expressed in normal melanocytes and behave as tumor-suppressor proteins by activating an MITF-dependent melanocyte differentiation program. In response to NRAS/BRAF activation, EMT-TF network undergoes a profound reorganization in favor of TWIST1 and ZEB1. This reversible switch cooperates with BRAF in promoting dedifferentiation and neoplastic transformation of melanocytes. We detected EMT-TF reprogramming in late-stage melanoma in association with enhanced phospho-ERK levels. This switch results in E-cadherin loss, enhanced invasion, and constitutes an independent factor of poor prognosis in melanoma patients.”

Clinical Characteristics and Outcomes with Specific BRAF and NRAS Mutations in Patients with Metastatic Melanoma

“Hotspot mutations in BRAF and NRAS are the most common somatic events in patients with melanoma. These mutations occur at highly conserved residues, but include several different substitutions. To determine whether specific mutations are clinically important to differentiate, tumor characteristics and clinical outcomes were compared among patients with advanced melanoma with 1) BRAF V600E versus V600K mutations and 2) NRAS exon 1 versus exon 2 mutations.”

NRAS Mutation in Melanoma: A Challenging Target

Among melanomas, BRAF-mutated disease gets the vast majority of attention. Fifty percent of melanomas harbor BRAF mutations, which can be targeted with BRAF inhibitors. However, despite its notoriety, BRAF is not the only important melanoma mutation.

Another melanoma-linked mutation can be found in the NRAS gene. Like BRAF mutations, NRAS mutations are ‘driver mutations’—a tumor with an NRAS mutation is dependent on the mutation for its growth and survival. Continue reading…

BRAF/NRAS Wild-Type Melanomas Have a High Mutation Load Correlating with Histological and Molecular Signatures of UV Damage

“The mutation load in melanoma is generally high compared to other tumor types due to extensive UV damage. Translation of exome sequencing data into clinically relevant information is therefore challenging. This study sought to characterize mutations identified in primary cutaneous melanomas and correlate these with clinico-pathologic features.”

Imatinib for Melanomas Harboring Mutationally Activated or Amplified KIT Arising on Mucosal, Acral, and Chronically Sun-Damaged Skin

“Amplifications and mutations in the KIT proto-oncogene in subsets of melanomas provide therapeutic opportunities…We conducted a multicenter phase II trial of imatinib in metastatic mucosal, acral, or chronically sun-damaged (CSD) melanoma with KIT amplifications and/or mutations…Melanomas that arise on mucosal, acral, or CSD skin should be assessed for KIT mutations. Imatinib can be effective when tumors harbor KIT mutations, but not if KIT is amplified only. NRAS mutations and KIT copy number gain may be mechanisms of therapeutic resistance to imatinib.

Vesicular Stomatitis Virus Variants Selectively Infect and Kill Human Melanomas but Not Normal Melanocytes

“Metastatic malignant melanoma remains one of the most therapeutically challenging forms of cancer. Here we test replication-competent vesicular stomatitis viruses (VSV) on 19 primary human melanoma samples and compare these infections with those of normal human melanocyte control cells. Even at a low viral concentration, we found a strong susceptibility to viral oncolysis in over 70% of melanomas. In contrast, melanocytes displayed strong resistance to virus infection and showed complete protection by interferon.”

Conjunctival Melanomas Harbor BRAF and NRAS Mutations and Copy Number Changes Similar to Cutaneous and Mucosal Melanomas

“Conjunctival melanoma is a rare but potentially deadly tumor of the eye. Despite effective local therapies, recurrence and metastasis remain frequent. Once the tumor has metastasized, treatment options are limited and the prognosis is poor. To date, little is known of the genetic alterations in conjunctival melanomas.”