Background: Rather than a Janus Kinase 2 inhibitor (ruxolitinib), a
specific thrombopoietin receptor (TpoR) inhibitor would be more specific for the
treatment of myeloproliferative neoplasms due to TpoR mutations.
Objective: A cell-based phenotypic approach to identify specific TpoR inhibitors
was implemented and a library of 505,483 small molecules was screened for
inhibitory effects on cells transformed by TpoR mutants.
Results: Among the identified hits are two analogs of 3-(4-piperidinyl) indole. The
analogs showed about five-fold preferential inhibition of cell viability towards
Ba/F3 cells expressing the TpoR W515L mutation compared to the parental cells.
There was no significant difference in inhibition of cell viability between the TpoR
wild type and the TpoR W515L mutant cells. Preferential inhibition of viability was observed in Ba/F3
cells expressing erythropoietin receptor (EpoR) when stimulated with Epo compared to stimulation
with interleukin-3 (IL3). The indole analog inhibited ex vivo colony formations of primary bone
marrow cells from heterozygous JAK2 V617F knock-in mice. Drug combination treatment study was
performed using ruxolitinib and the indole analog. Drug synergistic effects were observed when cells
were stimulated to proliferate through both the IL3 and TpoR pathways. Our compound specifically
targets monoamine receptors in the rhodopsin-like receptor family of G protein-coupled receptor.
Conclusion: This screen has identified a monoamine receptor inhibitor that can inhibit viability of cells
with active TpoR or EpoR signalings. Drug synergism with ruxolitib is demonstrated.