The novel JAK inhibitor CYT387 suppresses multiple signalling pathways, prevents proliferation and induces apoptosis in phenotypically diverse myeloma cells

Janus kinases (JAKs) are involved in various signalling pathways exploited by malignant cells. In multiple myeloma (MM), the interleukin-6/JAK/signal transducers and activators of transcription (IL-6/JAK/STAT) pathway has been the focus of research for a number of years and IL-6 has an established role in MM drug resistance. JAKs therefore make a rational drug target for anti-MM therapy. CYT387 is a novel, orally bioavailable JAK1/2 inhibitor, which has recently been described. This preclinical evaluation of CYT387 for treatment of MM demonstrated that CYT387 was able to prevent IL-6-induced phosphorylation of STAT3 and greatly decrease IL-6- and insulin-like growth factor-1-induced phosphorylation of Akt and extracellular signal-regulated kinase in human myeloma cell lines (HMCL). CYT387 inhibited MM proliferation in a time- and dose-dependent manner in 6/8 HMCL, and this was not abrogated by the addition of exogenous IL-6 (3/3 HMCL). Cell cycling was inhibited with a G(2)/M accumulation of cells, and Apoptosis was induced by CYT387 in all HMCL tested (3/3). CYT387 synergised in killing HMCL when used in combination with the conventional anti-MM therapies melphalan and bortezomib. Importantly, Apoptosis was also induced in primary patient MM cells (n=6) with CYT387 as a single agent, and again synergy was seen when combined with conventional therapies.