Ciliobrevin A (HPI-4) is a hedgehog (Hh) signaling pathway inhibitor with median inhibitory concentration (IC₅₀) less than 10 μM.

Ciliobrevin A (HPI-4) also prevents an increase in the FLAG-Gli2 full-length/repressor ratio upon Shh stimulation, but HPI-2 and HPI-3 have no significant effect. Ciliobrevin A decreases FLAG-Gli1 stability in these cells, revealing another mechanism by which this small molecule can inhibit Hh target gene expression, while neither HPI-2 or HPI-3 has any significant effect on FLAG-Gli1 levels. Ciliobrevin A increases ciliary levels of FLAG-Gli2 in a manner disproportionate to their effects on total FLAG-Gli2 levels. In addition, Shh-EGFP^FLAG-Gli2 cells cultured with Ciliobrevin A have truncated primary cilia, and this cellular organelle is absent in a significant fraction of Ciliobrevin A-treated cells. Ciliobrevin A also perturbs primary cilia formation in the Shh-LIGHT2^FLAG-Gli1 cells and promotes accumulation of FLAG-Gli1 at the distal tip of this organelle. Ciliobrevin A significantly inhibits the proliferation of these neuronal progenitors, as measured by histone H3 phosphorylation (pH3) levels, and reduces cellular levels of cyclin D1 protein and Gli1, Gli2, and N-Myc transcripts in the CGNPs. Ciliobrevin A can block the proliferation of SmoM2-expressing CGNPs and should be equally potent against CGNPs lacking Su(fu) function, whereas the Smo inhibitor Cyclopamine is ineffective against either oncogenic lesion.

西域 has not independently confirmed the accuracy of these methods. They are for reference only.

• . Hyman JM, et al. Small-molecule inhibitors reveal multiple strategies for Hedgehog pathway blockade. Proc Natl Acad Sci U S A. 2009 Aug 18;106(33):14132-7.  [Content Brief]