Oral Presentation Advances in Neuroblastoma Research Congress 2016

The orally bioavailable small molecule CDK9 inhibitors CYC065 and CCT68127 are potent inhibitors of MYCN transcription (#47)

Evon Poon 1 , Yann Jamin 1 , Anne Hakkert 1 , Khin Thway 1 , Karen Barker 1 , Yordan Sbirkov 1 , Lisa Pickard 1 , Zuzanna Urban 1 , Nicolas Tardiff 1 , Hannah Webber 1 , Gary Box 1 , Melanie Valenti 1 , Alexis De Haven Brandon 1 , Kevin Petrie 1 , Marli Ebus 2 , Jan Molenaar 2 , Simon Robinson 1 , Suzanne Eccles 1 , Daniella Zheleva 3 , Paul Workman 1 , Louis Chesler 1
  1. Institute of Cancer Research, London, SURREY, United Kingdom
  2. Department of Oncogenomics M1-130 , Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
  3. Cyclacel Lid, Dundee, Surrey, United Kingdom

Introduction

Amplification of the MYCN oncogene is a common and tumor-specific genomic event in aggressive tumours, but is not effectively targeted by any existing clinical drug. Attempts to target MYC transcription factors using direct approaches have failed. The recent discovery that the CDK7 inhibitor THZ1 targets superenhancer-driven expression of transcription factors such as MYC and MYCN generated much excitement, although this compound is not a clinically viable inhibitor. We explored the ICR med:chem compound library of CDK inhibitors for small-molecules with selective activity against MYCN-dependent neuroblastoma cells. The orally bioavailable, tri-substituted purine CDK inhibitors CCT68127 and CYC065, analogues of CYC202 (celiciclib, Cyclacel, Ltd), a clinical inhibitor of CDK2, exhibited an exquisite selectivity profile concomitant with enhanced potency and selectivity for CDK9, a component of PTEFb (CDK9:cyclinT1), and a rate-limiting regulator of MYC transcription.  The aim of this study was to explore the sensitivity of neuroblastoma cells in vitro and in vivo to CCT68127 and CYC065.

 Methods

Proliferation assays were used to assess the response of neuroblastoma cells in vitro to CCT68127 and CYC065. The efficacy of CYC065 was evaluated in subcutaneous xenograft models of both MYCN amplified (Kelly) and non-amplified neuroblastoma (SKNAS) and a Th-MYCN genetically-engineered murine model of neuroblastoma.

Results

Neuroblastoma cell lines were highly sensitive to both CCT68127 and CYC065 and the cellular increased sensitivity to the inhibitors correlated with MYCN amplification and expression levels.  CCT68127 and CYC065 blocked neuroblastoma cell proliferation, induced apoptosis and depleted MYCN mRNA and protein in a time- and dose-dependent manner. Preclinical evaluation of CCT68127 and CYC065 in MYCN-dependent models of neuroblastoma, resulted in significantly reduced in tumour burdens and prolonged survival. 

 Discussion

We report that CYC065 which exhibits excellent pharmacokinetic characteristics, a low toxicity profile, and which is currently in early phase clinical evaluation for lung cancer, rapidly and selectively killing MYC- or MYCN dependent cancer cells is a powerful clinical tool for treatment of neuroblastoma and other MYC-dependent malignancies.