Poster Presentation 32nd Lorne Cancer 2020

Inhibition of tumour initiation by a novel small molecule compound through reactivating the death response in MYCN-driven cancer (#176)

Olivia Ciampa 1 , Jessica Koach 1 , Owen Tan 1 , Kacper Jankowski 1 , Toby N Trahair 1 2 , Shizhen Zhu 3 , Daniel R Carter 1 , Belamy B Cheung 1 4 , Glenn M Marshall 1 2 , Mika Herath 1
  1. Children's Cancer Institute, Randwick, NSW, Australia
  2. Kids Cancer Centre, Sydney Children’s Hospital, Randwick, NSW, Australia
  3. Cancer Center and Center for Individualized Medicine, Mayo Clinic, Rochester, MN, USA
  4. School of Women's & Children's Health, UNSW Sydney, Randwick, NSW, Australia

MYCN-driven neuroblastoma is derived from embryonal precancer cells, which persist postnatally due to the loss of the normal death response which follows trophic factor withdrawal, a widespread regulatory process needed for normal organogenesis (1, 2). We performed high-throughput screening to identify novel compounds that restore the death response in MYCN-expressing precursor B lymphocytes. From an initial library of 40,000 compounds screening, we generated a short-list of 5 compounds displaying cytotoxic activity against MYCN-expressing pre-B cells in the absence of interleukin-7 but had a minimal effect on cells in the presence of trophic factor. Ganglia cells harvested from 2-week old wild-type and homozygous TH-MYCN mice were treated with five compounds and only one compound, PB-798, showed significant reduction in ganglia cell growth in the absence of nerve growth factor, evidently restoring death sensitivity following trophic growth factor withdrawal in these MYCN-driven persistent rest cells. PB-798 treatment also resulted in significant reduction of MYCN protein expression levels in MYCN-overexpressing pre-B cells but not in the pre-B cells transfected with the empty vector. The treatment of transgenic MYCN overexpressing zebrafish with PB-798 resulted in significant inhibition of MYCN-induced neuroblastic hyperplasia in the interrenal gland, and a model of the first step towards neuroblastoma initiation, did not show any toxicity in normal zebrafish embryos as measured by no change in their swim bladder size. We commenced a pilot study in the TH-MYCN mice model to test the safety and efficacy of PB-798. We found increased tumour-free survival and inhibition of tumour initiation from 120 mg/kg/day PB-798 treatment compared to the DMSO treated control in TH-MYCN homozygous mice. Transcriptomic comparisons for cells treated with PB798 repressed cholesterol biosynthesis as a mechanism of action. Taken together, a novel small molecule compound PB-798, can restore the death response to trophic factor withdrawal in MYCN-initiated malignant cells, inhibit the initiation of neuroblastoma in MYCN-drive cancer, with little effects on normal cells in vitro and in vivo.