Oral Presentation 26th Lorne Cancer Conference 2014

Targeting the CHK1-CIP2A axis to treat Glioblastoma (GBM) (#23)

Anchit Khanna 1 , Brett Stringer 2 , Bryan Day 2 , Kathleen Ensbey 2 , Han Shen 1 , Andrew Boyd 2 , Kerrie McDonald 1 , John Pimanda 1
  1. Lowy Cancer Centre, Kensington, NSW, Australia
  2. QIMR-Berghofer Medical Research Institute, University of Queensland, Brisbane,, Queensland, Australia

Checkpoint kinase1 (CHK1) is a DNA damage kinase, which has been observed to be constitutively active in human cancers. Unfortunately a number of new generation CHK1 inhibitors, currently in clinical trials, have shown deleterious effects on normal cells, thus limiting their clinical utility. Therefore, identification and targeting of cancer specific effectors of CHK1 signaling has emerged as an attractive therapeutic alternative.

Analysis of the REMBRANDT and TCGA datasets revealed a strong positive correlation for CHK1 and CIP2A expression in 422/522 and 356/454 glioma patients respectively.  By contrast, there was negligible correlation observed in normal samples. Additionally, high mRNA expression of both CHK1 and CIP2A was associated with reduced overall survival in glioma patients and marked a more aggressive form of the disease. Notably, CIP2A amplification found in 14.72% cases in the Rembrandt study was associated with worse overall survival in GBM patients. Inhibition of CHK1, by siRNA and small molecule inhibitors, resulted in decreased CIP2A expression both in vitro and in vivo. Functionally, both CHK1 and CIP2A promoted viability, clonogenicity and anchorage-independent growth of GBM cells. Importantly, inhibition of cancer cell viability by Chk1 inhibition can be partially rescued by exogenous expression of CIP2A. Higher CIP2A and pCHK1-serine345 levels were observed in de novo and patient-derived GBM, and U251MG cells relative to levels in normal human astrocytes (NHA). Analogously, CHK1 and CIP2A mRNA expression is increased 10 to 15 fold in genetically engineered mouse models of human GBM (Pdgf-Cre-driven Ptenf/f and Pdgf-Cre-driven Ptenf/f;/p53f/f double mutant mice compared with wild-type mice). Finally, using xenograft mouse models we show that both PF477736 (a small molecule inhibitor of CHK1) and CIP2A depletion inhibits tumour growth.

These results highlight CHK1 and CIP2A expression as potential diagnostic and prognostic markers in human GBMs and identify CIP2A as a cancer specific therapeutic target downstream of CHK1.