PKC412 Effectively Inhibits Constitutively Activated FGFR3 Mutants in Murine Leukemia Models and t(4;14) Myeloma Cell Lines.

Reccurent translocation t(4;14) associated ectopic expression of FGFR3, sometimes containing the activation mutation K650E (TDII), has been identified in 25% of human multiple myeloma (MM) patients and cell lines. However, current empirically-derived cytotoxic chemotherapy does not effectively treat this disease. One potential therapeutic strategy of treating MM is to inhibit the tyrosine kinase activity of FGFR3. In this report, we evaluated the efficacy of PKC412 (N-benzoyl-staurosporine), a small molecule tyrosine kinase inhibitor, for the treatment of FGFR3 mutants induced diseases. PKC412 effectively inhibits the tyrosine kinase activity and activation of downstream effector pathways of FGFR3 TDII or the constitutively activated TEL-FGFR3 fusion that was reported in a subtype of human peripheral T-cell lymphoma (PTCL), as well as proliferation of hematopoietic Ba/F3 cells transformed by the FGFR3 mutants. Furthermore, PKC412 drastically inhibits proliferation of four different multiple myeloma-derived primary cell lines that are associated with t(4;14) and expression of dysregulated FGFR3. Moreover, oral-gavage treatment with PKC412 resulted in statistically significant prolongation of survival in the murine bone marrow transplant (BMT) models of FGFR3 TDII-induced pre-B cell lymphoma or TEL-FGFR3 fusion-induced myeloproliferative disease, which suggests suitable pharmacokinetic and toxicity profiles of PKC412 for clinical use. Together, our data establish the small molecule inhibitor PKC412 as a molecularly targeted therapy for multiple myeloma and other human malignancies expressing activated FGFR3.