Bruton's tyrosine kinase as anti-cancer drug target

Abstract

Receptor protein tyrosine kinases (RPTKs) transmit extracellular signals across the plasma membrane to cytosolic proteins, stimulating the formation of complexes that regulate key cellular functions. Over half of the 90 tyrosine kinases have been implicated in human cancers and are for this reason considered highly promising drug targets. To gain insight into the tyrosine kinases that contribute to breast cancer related cellular mechanisms, we carried out a large-scale loss-of-function analysis of the tyrosine kinases, using RNA interference, in the clinically relevant Erb-B2 positive, BT474 breast cancer cell line. The cytosolic, non-receptor tyrosine kinase Bruton's tyrosine kinase (BTK), which has been extensively studied for its role in B cell development, was among those tyrosine kinase genes required for BT474 breast cancer cell survival. The BTK protein identified was an alternative form containing an amino-terminal extension. This alternative form of the Btk message is also present in tumorigenic breast cells at significantly higher levels than in normal breast cells.

1 . A method of treating cancer, comprising:
 a. providing a subject with breast cancer cells and an inhibitor of a gene encoding a cytoplasmic tyrosine kinase;   b. treating said subject with said inhibitor.   
     
     
         2 . The method of  claim 1 , wherein said cytoplasmic tyrosine kinase is a member of the Tec family of cytoplasmic tyrosine kinases. 
     
     
         3 . The method of  claim 2 , wherein said cytoplasmic tyrosine kinase is Bruton's Tyrosine Kinase. 
     
     
         4 . The method of  claim 2 , wherein said cytoplasmic tyrosine kinase is a variant of Bruton's Tyrosine Kinase comprising an amino-terminal extension. 
     
     
         5 . The method of  claim 4 , wherein said extension comprises an additional 34 amino acids. 
     
     
         6 . The method of  claim 1 , wherein said inhibitor comprises an interfering RNA. 
     
     
         7 . The method of  claim 6 , wherein treating with said RNA results in reduced proliferation of said breast cancer cells. 
     
     
         8 . A method of diagnosing cancer, comprising:
 a. providing cells suspected to be breast cancer cells and a ligand capable of binding to a variant of Bruton's Tyrosine Kinase, said variant comprising an amino-terminal extension;   b. contacting said cells with said ligand under conditions wherein said variant is detected.   
     
     
         9 . The method of  claim 8 , wherein said extension comprises an additional 34 amino acids. 
     
     
         10 . The method of  claim 9 , wherein said ligand binds to a portion of said 34 amino acid extension. 
     
     
         11 . The method of  claim 10 , wherein said ligand comprises an antibody or fragment thereof. 
     
     
         12 . A composition, comprising a variant of Bruton's Tyrosine Kinase comprising an amino-terminal extension. 
     
     
         13 . The composition of  claim 12 , wherein said extension comprises an additional 34 amino acids. 
     
     
         14 . A ligand-protein complex comprising antibody bound to said variant of  claim 12 . 
     
     
         15 . A kit for use in the method of  claim 8 , the kit comprising a ligand capable of binding to a variant of Bruton's Tyrosine Kinase and instructions for its use.