Melanoma is one of the most aggressive cancers with extremely poor prognosis, and the median survival time for stage IV patients is approximately 6 to 8 months.,Unlike cutaneous melanoma, mucosal melanoma is a rare melanoma subtype among Caucasian patients but its incidence remains as high as 22.6% among Chinese patients.,Screening specific genetic variations is the guideline to select targeted drugs for the treatment of advanced melanoma, whereas the genetic variation spectrum and potential therapeutic targets for mucosal melanoma are largely unclear.,It is urgent to identify promising genetic variants for mucosal melanoma so as to develop effective targeted therapies for this disease.,Tumor samples from 213 Chinese mucosal melanoma patients were involved in this study.,P16INK4a/Cyclin D1/CDK4 copy number was examined using the QuantiGene Plex DNA assay and the correlation between abnormal copy number and clinicopathological parameters was analyzed.,Patient-derived xenograft models (PDX) were performed to detect the effects of CDK4/6 inhibitors on the proliferation of mucosal melanoma cells with altered copy number of CDK4 pathway (CDK4, Cyclin D1 and P16INK4a).,The molecular mechanisms of CDK4/6 inhibitors on the proliferation of mucosal melanoma were analyzed by RNAseq.,Among the 213 samples, the amplification rate of CDK4 and CCND1 was 47.0% and 27.7%, respectively, and the deletion rate of P16INK4a was 57.7%.,Patients with more than one genetic abnormality were up to 81.7%.,CDK4 pathway gene copy number variation was not associated with the prognosis of patients with mucosal melanoma (P > 0.05).,Drug sensitivity tests showed that AT7519, a broad-spectrum CDK inhibitor, and PD0332991, a specific CDK4/6 inhibitor, exhibited higher inhibitory effect on CDK4 signaling pathway abnormal mucosal melanoma cells-derived PDX tumors growth than CDK4 signaling pathway normal ones.,RNA-seq analysis showed that CDK4 inhibitors may affect tumor proliferation through multiple signaling pathways.,Abnormal copy number of cell cycle related genes is frequently found in mucosal melanoma.,CDK4/6 inhibitors significantly suppress the PDX tumor growth with abnormal CDK4 pathway.,CDK4 signaling variations predict the effectiveness of CDK4 inhibitors in mucosal melanoma.,The online version of this article (10.1186/s12967-019-1987-z) contains supplementary material, which is available to authorized users.
Oncogenic mutations in the serine/threonine kinase B-RAF are found in 50-70% of malignant melanomas1.,Pre-clinical studies have demonstrated that the B-RAFV600E mutation predicts a dependency on the mitogen activated protein kinase (MAPK) signaling cascade in melanoma1-5-an observation that has been validated by the success of RAF and MEK inhibitors in clinical trials6-8.,However, clinical responses to targeted anticancer therapeutics are frequently confounded by de novo or acquired resistance9-11.,Identification of resistance mechanisms in a manner that elucidates alternative ‘druggable’ targets may inform effective long-term treatment strategies12.,Here, we expressed ~600 kinase and kinase-related open reading frames (ORFs) in parallel to functionally interrogate resistance to a selective RAF kinase inhibitor.,We identified MAP3K8 (COT/TPL2) as a MAPK pathway agonist that drives resistance to RAF inhibition in B-RAFV600E cell lines.,COT activates ERK primarily through MEK-dependent mechanisms that do not require RAF signaling.,Moreover, COT expression is associated with de novo resistance in B-RAFV600E cultured cell lines and acquired resistance in melanoma cells and tissue obtained from relapsing patients following treatment with MEK or RAF inhibition.,We further identify combinatorial MAPK pathway inhibition or targeting of COT kinase activity as possible therapeutic strategies for reducing MAPK pathway activation in this setting.,Together, these results provide new insights into resistance mechanisms involving the MAPK pathway and articulate an integrative approach through which high-throughput functional screens may inform the development of novel therapeutic strategies.