In 2014, Ibrutinib the irreversible inhibitor of Bruton’s tyrosine kinase (Btk) was approved for use as the therapeutics for treating chronic lymphocytic leukemia (CLL). In addition to CLL, Btk overactivation also contributes to other B-cell malignancies such as multiple myeloma (MM). Thus, ibrutinib has been trialled in combination with other drugs for the treatment of MM. Since MM is a bone marrow disease and little is known about the oncogenic mechanism of Btk, we aim to use quantitative phosphoproteomics approach to chart the signalling pathways mediating the oncogenic action of Btk.

Bruton’s tyrosine kinase (Btk), a member of the Tec family protein tyrosine kinases, was first discovered by genetic studies as the defective gene product that caused X-linked agammaglobulinemia. Further studies revealed that Btk is important in directing the development of mature B cell from pre-B cell. In addition, Btk is also involved in maintaining cell survival, promoting cell proliferation, and regulating cell migration and adhesion, presumably via the B-cell receptor (BCR) signalling pathway. Its constitutive activation contributes to B cell malignancies. Therefore, we embark on deciphering the oncogenic signalling mechanism of Btk in MM cells.  We aim to study how inhibition of Btk by Ibrutinib affects cell survival, cell proliferation and cell signalling pathways in cultured MM cells. Specifically, I proposed to use quantitative global proteomics and phosphoproteomics approach to unveil new cellular proteins that are regulated by Btk. Some of these downstream signalling proteins could be potential targets for the development of new therapeutic strategy of B cell malignancies. In addition, the project so far had successfully identified ibrutinib bound tryptic fragment of Btk. Incorporation of the identified fragment with Selected Reaction Monitoring (SRM) could provide us a new strategy in studying efficiency of ibrutinib in inhibiting endogenous Btk in vivo.