Intraventricular SHH inhibition proves efficient in SHH medulloblastoma mouse model and prevents systemic side effects

BACKGROUND

Medulloblastoma (MB) is the most common malignant brain tumor in children and requires intensive multimodal therapy. Long-term survival is still dissatisfying and, most importantly, survivors frequently suffer from severe treatment-associated morbidities. The sonic hedgehog pathway (SHH) in SHH MB provides a promising target for specific therapeutic agents. The small molecule Vismodegib allosterically inhibits SMO, the main upstream activator of SHH. Vismodegib has proven effective in the treatment of MB in mice and in clinical studies. However, due to irreversible premature epiphyseal growth plate fusions after systemic application to infant mice and children, its implementation to pediatric patients has been limited. Intraventricular Vismodegib application might provide a promising novel treatment strategy for pediatric medulloblastoma patients.

METHODS

Infant medulloblastoma-bearing Math1-cre::Ptch1Fl/Fl mice were treated with intraventricular Vismodegib in order to evaluate efficacy on tumor growth and systemic side effects.

RESULTS

We show that intraventricular Vismodegib treatment of Math1-cre::Ptch1Fl/Fl mice leads to complete or partial tumor remission only 2 days after completed treatment. Intraventricular treatment also significantly improved symptom-free survival in a dose-dependent manner. At the same time, intraventricular application prevented systemic side effects in the form of anatomical or histological bone deformities.

CONCLUSIONS

We conclude that intraventricular application of a SHH pathway inhibitor combines the advantages of a specific treatment agent with precise drug delivery and might evolve as a promising new way of targeted treatment for SHH MB patients.

MODL-03. Establishment of intraventricular Shh inhibition as a therapeutic option for young patients with medulloblastoma

The prognosis of pediatric medulloblastoma is still dissatisfying today and tumor survivors often suffer from severe treatment-related morbidities. This poses an urgent need for more efficient therapies. Shh medulloblastoma is characterized by mutations in the Sonic Hedgehog (Shh) pathway, providing an elegant way of targeted therapy. The small molecule Vismodegib allosterically inhibits Smoothened (SMO), an upstream activator of Shh, and shows promising anti-tumor effects against Shh medulloblastoma. Unfortunately, Vismodegib caused severe bone deformities in preclinical studies and clinical trials, preventing its systemic application in children. In a mouse model, we established an intraventricular therapy with Vismodegib combining the benefits of targeted drug delivery and minimal systemic side effects. We compare intraventricular, oral, and placebo treatment regarding effects on survival, tumor biology, and bone morphology.Math1-cre::Ptch^1Fl/Fl mice show a homozygous loss of Ptch1 in Math1-positive cells, resulting in Shh pathway overactivation and development of Shh medulloblastomas. At postnatal day 11-13, Math1-cre::Ptch1^Fl/Fl mice were randomized in four treatment arms: Group A (n=14) received intraventricular placebo, B (n=12) received 200 mg/kd/d oral Vismodegib, C (n=16) received 0.2 mg/kg/d intraventricular Vismodegib, and D (n=9) received 1.6 mg/kg/d intraventricular Vismodegib. Kaplan-Meier survival curves show a significant survival benefit of 1.6 mg/kg/d intraventricular Vismodegib over placebo (p=0.003). While all intraventricular treated animals develop proliferative tumors at end of observation, investigations at an early time point after completed treatment show promising anti-tumor effects with reduced or absent proliferation in the cerebellum compared to placebo. Bone histology and X-ray analysis of intraventricular treated mice show intact femoral and tibial growth plates, in contrast to orally treated mice that develop severe skeletal malformations. Based on these preliminary experimental results, we conclude that intraventricular application of a SMO-inhibitor might evolve as a promising new way of targeted treatment of Shh medulloblastoma in children.

EXTH-70. ESTABLISHMENT OF INTRAVENTRICULAR SHH INHIBITION AS A THERAPEUTIC OPTION IN YOUNG PATIENTS WITH MEDULLOBLASTOMA

Medulloblastoma is the most common malignant brain tumor in children. The embryonal tumor arises in the posterior fossa and disseminates via the cerebrospinal fluid. Medulloblastoma divides in four molecular subgroups, one of which is characterized by mutations in the sonic-hedgehog (SHH) -pathway. SHH inhibition provides an elegant way of targeted therapy. The small molecule Vismodegib allosterically inhibits Smoothened (SMO), an upstream activator of SHH. Unfortunately, Vismodegib has shown to cause irreversible premature epiphyseal growth plate fusions in preclinical studies and clinical trials, preventing its systemic application in children (Kimura et al. 2008; Robinson et al. 2017). We established an intraventricular therapy with Vismodegib, combining the benefits of targeted drug delivery and minimizing systemic side effects. In a mouse model for SHH medulloblastoma, we compare intraventricular, oral and placebo treatment regarding effects on survival, tumor biology, and bone morphology. Math1-cre::Ptch1 Fl/Fl mice show a homozygous loss of PTCH1 in Math1-positive cells, resulting in SHH-pathway overactivation and development of SHH medulloblastomas. At postnatal day 11-13, Math1-cre::Ptch1 Fl/Fl mice were randomized in four treatment arms: group A (n= 9) received placebo intrathecally, B (n= 9) received Vismodegib 200 mg/kd/d orally, C (n= 19) received Vismodegib 0.2 mg/kg/d intrathecally, and D (n= 8) received Vismodegib 1.6 mg/kg/d intrathecally. Kaplan-Meier survival analysis showed a significant survival benefit for 1.6 mg/kg/d intraventricular Vismodegib compared to placebo (p= 0.012). Bone histology and X-ray analysis of intraventricular treated mice showed intact femoral and tibial growth plates, in contrast to orally treated mice that developed skeletal malformations. Further analyses such as DNA sequencing, gene expression analysis, and histological evaluation are ongoing and will add to the picture of the anti-tumor effects of intraventricular SHH-inhibition. Based on the preliminary experimental results, we conclude that intrathecal application of a SMO-inhibitor might evolve as a promising new way of targeted treatment of SHH medulloblastomas.