A phase I/II study of LDE225, a smoothened (Smo) antagonist, in pediatric patients with recurrent medulloblastoma (MB) or other solid tumors

9519 Background: Hedgehog (Hh) signaling is crucial in the development and homeostasis of many human organs and tissues. Aberrant Hh signaling is involved in tumorigenesis through promotion of cell proliferation, survival, and differentiation in wide range of human cancers, including approximately 30% of MBs. LDE225 is a potent and selective inhibitor of Smo, a key positive regulator of Hh signaling. The phase I is exploring the safety and pharmacokinetics of LDE225 in pediatric patients with advanced solid tumors that are potentially dependent on Hh signaling. Preliminary data from the ongoing phase I are presented. Methods: Dose-escalation was performed according to a Bayesian design starting at 372 mg/m2 of continuous once daily oral LDE225. Safety and preliminary efficacy of LDE225 at the maximum tolerated dose will be assessed in pediatric and adult patients with recurrent MB in a phase II expansion part. Pharmacokinetic profiles were performed at Day 1 and 21. Tumor samples were analyzed for Hh pathway activation status using a 5-gene Hh signature assay. Results: Thirty-three patients (24 MB, 3 rhabdomyoscarcoma [RMS], 3 osteosarcoma, and 1 each of neuroblastoma, gliomatosis and oligoastrocytoma) with a median age of 13 years (range, 4–17 y) have enrolled. Dose-limiting toxicity of Grade 4 creatine phosphokinase elevation occurred in 1 RMS patient out of 7 patients treated at 372 mg/m2. No dose-limiting toxicity was observed at 233 and 425 mg /m2. LDE225 at 233 and 372 mg/m2 was absorbed with a median Tmax of 2 h (range, 1–24 h). Systemic exposures were comparable with adults. Two MB patients achieved a confirmed complete response (CR) at doses of 372 and 425 mg/m2. Analysis of 14 available MB tumor samples using the 5-gene Hh signature assay showed that the 2 CR patients have Hh‑activated tumor. The remaining 12 tumor samples were from patients who did not achieve response and were determined to be Hh pathway non-activated. Conclusions: LDE225 is well tolerated in pediatric patients with advanced malignancies. Preliminary data show promising efficacy in medulloblastoma patients and support the use of the 5-gene Hh signature assay as a pre-selection tool in future trials.