PIM kinases have important pro-tumorigenic roles and mediate several oncogenic traits, including cell proliferation, survival, and chemotherapeutic resistance. As a result, multiple PIM inhibitors have been pursued as
investigational new drugs in
cancer; however, response to PIM inhibitors in solid
tumors has fallen short of expectations. We found that inhibition of PIM
kinase activity stabilizes
protein levels of all three PIM
isoforms (PIM1/2/3), and this can promote resistance to PIM inhibitors and
chemotherapy. To overcome this effect, we designed PIM
proteolysis targeting chimeras (
PROTACs) to target PIM for degradation. PIM
PROTACs effectively downmodulated PIM levels through the
ubiquitin-
proteasome pathway. Importantly, degradation of
PIM kinases was more potent than inhibition of catalytic activity at inducing apoptosis in
prostate cancer cell line models. In conclusion, we provide evidence of the advantages of degrading
PIM kinases versus inhibiting their catalytic activity to target the oncogenic functions of
PIM kinases.