Characterization of a Hedgehog pathway antagonist in a mouse medulloblastoma allograft model.

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Constitutive activation of the Hedgehog pathway accounts for 25% of sporadic medulloblastoma, the most common childhood brain cancer. It has been demonstrated previously that treatment of a medulloblastoma mouse model (Ptch1 P53−/−) with a Hh pathway antagonist, leads to complete eradication of tumors. In order to further characterize the mechanism of action of Cur-691, we have established an allograft model derived from Ptch1 p53 mice and observed total regression of established subcutaneous medulloblastoma allografts following 28 days treatment with Cur-691. Importantly, this effect was found to be durable as no tumor regrowth was noted during 60-day following cessation of treatment. In the current study, we characterized pharmacokinetic pharmacodynamic (PK/PD) profile of Cur-691 within the tumor, evaluated changes in apoptosis and cell proliferation, and performed gene expression microarray analysis to identify the molecular pathways altered by Cur-691 treatment. PK/PD analysis demonstrated that concentrations of Cur-691 found in the tumor correlated with repression of the Hh pathway with trough values of less than 1mM. Immuno-fluorescence analysis detected a rapid and progressive increase in cell death and inhibition of cell proliferation confined within the tumor component of the allograft following Cur-691 treatment, indicating that the drug specifically targets Ptch1 tumor cells, while leaving the stromal and vasculature components of the allograft intact. In addition to down-regulation of several well-characterized Hh target genes, we also observed profound changes in cell cycle regulation and DNA replication following Cur-691 treatment by microarrays. Many signature genes upregulated in desmoplastic (Hh driven) medulloblastoma are immediately modulated by Cur-691 treatment, further confirming that transcription of these signature genes are driven by Hh signaling. Together these data support targeting the Shh pathway for the treatment of desmoplastic medulloblastoma or other cancer where activation of the Hh pathway has been implicated.