LMTK3 is essential for oncogenic KIT expression in KIT-mutant GIST and melanoma.

Certain cancers, including gastrointestinal stromal tumor (GIST) and subsets of melanoma, are caused by somatic KIT mutations that result in KIT receptor tyrosine kinase constitutive activity, which drives proliferation. The treatment of KIT-mutant GIST has been revolutionized with the advent of KIT-directed cancer therapies. KIT tyrosine kinase inhibitors (TKI) are superior to conventional chemotherapy in their ability to control advanced KIT-mutant disease. However, these therapies have a limited duration of activity due to drug-resistant secondary KIT mutations that arise (or that are selected for) during KIT TKI treatment. To overcome the problem of KIT TKI resistance, we sought to identify novel therapeutic targets in KIT-mutant GIST and melanoma cells using a human tyrosine kinome siRNA screen. From this screen, we identified lemur tyrosine kinase 3 (LMTK3) and herein describe its role as a novel KIT regulator in KIT-mutant GIST and melanoma cells. We find that LMTK3 regulated the translation rate of KIT, such that loss of LMTK3 reduced total KIT, and thus KIT downstream signaling in cancer cells. Silencing of LMTK3 decreased cell viability and increased cell death in KIT-dependent, but not KIT-independent GIST and melanoma cell lines. Notably, LMTK3 silencing reduced viability of all KIT-mutant cell lines tested, even those with drug-resistant KIT secondary mutations. Furthermore, targeting of LMTK3 with siRNA delayed KIT-dependent GIST growth in a xenograft model. Our data suggest the potential of LMTK3 as a target for treatment of patients with KIT-mutant cancer, particularly after failure of KIT TKIs.

Using molecular diagnostic testing to personalize the treatment of patients with gastrointestinal stromal tumors.

INTRODUCTION: The diagnosis and treatment of gastrointestinal stromal tumor (GIST) has emerged as a paradigm for modern cancer treatment ('precision medicine'), as it highlights the importance of matching molecular defects with specific therapies. Over the past two decades, the molecular classification and diagnostic work up of GIST has been radically transformed, accompanied by the development of molecular therapies for specific subgroups of GIST. This review summarizes the developments in the field of molecular diagnosis of GIST, particularly as they relate to optimizing medical therapy. Areas covered: Based on an extensive literature search of the molecular and clinical aspects of GIST, the authors review the most important developments in this field with an emphasis on the differential diagnosis of GIST including mutation testing, therapeutic implications of each molecular subtype, and emerging technologies relevant to the field. Expert commentary: The use of molecular diagnostics to classify GIST has been shown to be successful in optimizing patient treatment, but these methods remain under-utilized. In order to facilitate efficient and comprehensive molecular testing, the authors have developed a decision tree to aid clinicians.

Biochemical, Molecular, and Clinical Characterization of Succinate Dehydrogenase Subunit A Variants of Unknown Significance.

Purpose: Patients who inherit a pathogenic loss-of-function genetic variant involving one of the four succinate dehydrogenase (SDH) subunit genes have up to an 86% chance of developing one or more cancers by the age of 50. If tumors are identified and removed early in these high-risk patients, they have a higher potential for cure. Unfortunately, many alterations identified in these genes are variants of unknown significance (VUS), confounding the identification of high-risk patients. If we could identify misclassified SDH VUS as benign or pathogenic SDH mutations, we could better select patients for cancer screening procedures and remove tumors at earlier stages.Experimental Design: In this study, we combine data from clinical observations, a functional yeast model, and a computational model to determine the pathogenicity of 22 SDHA VUS. We gathered SDHA VUS from two primary sources: The OHSU Knight Diagnostics Laboratory and the literature. We used a yeast model to identify the functional effect of a VUS on mitochondrial function with a variety of biochemical assays. The computational model was used to visualize variants' effect on protein structure.Results: We were able to draw conclusions on functional effects of variants using our three-prong approach to understanding VUS. We determined that 16 (73%) of the alterations are actually pathogenic, causing loss of SDH function, and six (27%) have no effect upon SDH function.Conclusions: We thus report the reclassification of the majority of the VUS tested as pathogenic, and highlight the need for more thorough functional assessment of inherited SDH variants. Clin Cancer Res; 23(21); 6733-43. ©2017 AACR.