IMPDH2 and cancer: Shikonin is a reversible competitive inhibitor of IMPDH that binds to IMPDH2 with higher affinity than IMPDH149, and AVN-944 is a noncompetitive IMPDH inhibitor that has reached phase 1 clinical trial for advanced hematologic malignancies (NCT00273936), keeping the quest for IMPDH2 inhibitors as cancer treatment still going.