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High throughput screen identifies two FDA drugs that suppress non-SHH and non-WNT Medulloblastoma proliferation

Marie Morfouace, Anang Shelat, Megan Jaccus, Burgess Freeman, Frederique Zindy, Giles Robinson, Kiplin Guy, Clinton Stewart, Amar Gajjar, Martine Roussel
St Jude Children's Research Hospital, Memphis, TN, USA

Introduction

Medulloblastomas, the most common malignant pediatric brain tumors, are molecularly divided into 4 major groups: SHH, WNT, Group 3 and Group 4.  Group 3 tumors, which overexpress and frequently amplify MYC, are the most aggressive and least curable.  Our recently described mouse model recapitulates Group 3 medulloblastoma by overexpressing Myc in Trp53-null granule neural progenitors.   Myc-induced mouse medulloblastoma cells can be grown as neurospheres and recapitulate primary tumors after transplantation into the brain of nude recipient mice. These properties provide an ideal platform on which to conduct high throughput screens and then test the “hits” in the live model system.

Method

A library of 830 FDA-approved drugs was screened against Myc-induced mouse medulloblastoma neurospheres (hereon Myc-neurospheres) by measuring ATP consumption.  Drugs active against Myc-neurospheres (primary screen, single point at 10 μM) were moved to a secondary screen (dose response from 1 nm to 10 μM) in order to assess their selectivity. Wash out experiments were performed on 21 compounds.  Drugs that efficiently inhibited Myc-neurosphere proliferation and that were selective (i.e., inactive against Trp53-null neurospheres) were moved forward and subjected to pharmacokinetic and in vivo studies.

Results

Pemetrexed (an inhibitor of the folate pathway) and gemcitabine (an inhibitor of nucleotide synthesis), were active and selective against the Myc-neurospheres.  Pharmacokinetic modeling of these compounds demonstrated they were detectable in tumor extracellular fluid at concentrations that exceeded the in vitro IC50 values for 6 hours.  When administered as single agents to mice orthotopically transplanted with Myc-neurospheres, each increased the survival by 6 and 10 days, respectively.   However, when administered in combination survival doubled from 15 to 30 days.  Importantly, they also inhibited the proliferation of several primary neurosphere lines derived from non-SHH/non-WNT human medulloblastomas.

Conclusions

Group 3 medulloblastomas grow robustly as neurospheres allowing for the unbiased high throughput screening of vast drug libraries.  Using a library of FDA-approved drugs and preclinical studies we have identified pemetrexed and gemcitabine as candidate drugs for the treatment of patients with this most aggressive form of medulloblastoma.

 

This work is funded in part by The V-foundation (MFR, AG), NIH Grants CA-096832 (MFR), a Core Grant CA-021765and the American Lebanese-Syrian Associated Charities (ALSAC) of St. Jude Children’s Research Hospital.