title: Understanding the Interplay between Expression, Mutation and Activity of ALK Receptor in Rhabdomyosarcoma Cells for Clinical Application of Small-Molecule Inhibitors.
abstract: BACKGROUND
  Receptor tyrosine kinases (RTKs) have a central role in cancer initiation and progression, since changes in their expression and activity potentially results in cell transformation. This concept is essential from a therapeutic standpoint, as clinical evidence indicates that tumours carrying deregulated RTKs are particularly susceptible to their activity but also to their inhibition. Rhabdomyosarcoma (RMS) is an aggressive childhood cancer where emerging therapies rely on the use kinase inhibitors, and among druggable kinases ALK represents a potential therapeutic target to commit efforts against. However, the functional relevance of ALK in RMS is not known, likewise the multi-component deregulated RTK profile to which ALK belongs.
  
  
  METHODS
  In this study we used RMS cell lines representative of the alveolar and embrional histotype and looked at ALK intracellular localization, activity and cell signalling.
  
  
  RESULTS
  We found that ALK was properly located at the plasma membrane of RMS cells, though in an unphosphorylated and inactive state due to intracellular tyrosine phosphatases (PTPases) activity. Indeed, increase of ALK phosphorylation was observed upon PTPase inhibition, as well as after ligand binding or protein overexpression. In these conditions, ALK signalling proceeded through the MAPK/ERK and PI3K/AKT pathways, and it was susceptible to ATP-competitive inhibitors exposure. However, drug-induced growth inhibition, cell cycle arrest and apoptosis did not correlate with ALK expression only, but relied also on the expression of other RTKs with akin drug binding affinity. Indeed, analysis of baseline and inducible RTK phosphorylation confirmed that RMS cells were susceptible to ALK kinase inhibitors even in the absence of the primary intended target, due to the presence of compensatory RTKs signalling pathways.
  
  
  CONCLUSIONS
  These data, hence, provided evidences of a potentially active role of ALK in RMS cells, but also suggest caution in considering ALK a major therapeutic target in this malignancy, particularly if expression and activity cannot be accurately determined.
authors.affiliation: Clinica di Oncoematologia Pediatrica di Padova, Azienda Ospedaliera-Università di Padova, Padua, Italy.
authors.forename: Marica
authors.initials: M
authors.lastname: Peron
authors.affiliation: Clinica di Oncoematologia Pediatrica di Padova, Azienda Ospedaliera-Università di Padova, Padua, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Lovisa
authors.affiliation: Clinica di Oncoematologia Pediatrica di Padova, Azienda Ospedaliera-Università di Padova, Padua, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Poli
authors.affiliation: Clinica di Oncoematologia Pediatrica di Padova, Azienda Ospedaliera-Università di Padova, Padua, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Basso
authors.affiliation: Clinica di Oncoematologia Pediatrica di Padova, Azienda Ospedaliera-Università di Padova, Padua, Italy; Istituto di Ricerca Pediatrica Città della Speranza, Padova, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Bonvini
mesh_terms: D000077548:Anaplastic Lymphoma Kinase; D045744:Cell Line, Tumor; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D057809:HEK293 Cells; D006801:Humans; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012208:Rhabdomyosarcoma / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D009363:Neoplasm Proteins; D047428:Protein Kinase Inhibitors; C000626173:ALK protein, human; D000077548:Anaplastic Lymphoma Kinase; D020794:Receptor Protein-Tyrosine Kinases; D017027:Protein Tyrosine Phosphatases