IGF1R as druggable target mediating PI3K-δ inhibitor resistance in a murine model of chronic lymphocytic leukemia

Annika Scheffold, Billy Michael Chelliah Jebaraj, Eugen Tausch, Johannes Bloehdorn, Paolo Ghia, Anella Yahiaoui, Anna Dolnik, Tamara Jacqueline Blätte, Lars Bullinger, Rashmi Priyadharshini Dheenadayalan, Li Li, Christof Schneider, Shih-Shih Chen, Nicholas Chiorazzi, Sascha Dietrich, Martina Seiffert, Stacey Tannheimer, Hartmut Döhner, Daniel Mertens and Stephan Stilgenbauer

Key Points

  • Murine in vivo modelling of PI3K-δ inhibitor resistance identifies hyperactivation of IGF1R signalling in resistant cells

  • Targeting IGF1R offers efficacious salvage treatment for PI3K-δ inhibitor resistant tumors


Targeted therapy is currently revolutionizing the treatment of cancers, but resistance evolves against these therapies and derogates their success. The PI3K-δ inhibitor idelalisib has been approved for CLL and NHL treatment, but the mechanisms conferring resistance in a subset of patients are unknown. Here, we modelled resistance to PI3K-δ inhibitor in vivo using a serial tumor transfer and treatment scheme in mice. Whole exome sequencing identified no recurrent mutation explaining resistance to PI3K-δ inhibitor. In the murine model resistance to PI3K-δ inhibitor occurred due to a signalling switch mediated by consistent and functionally relevant activation of Insulin-like growth factor 1 receptor (IGF1R), resulting in enhanced MAPK signalling in the resistant tumors. Overexpression of IGF1R in vitro demonstrated its prominent role in PI3K-δ inhibitor resistance. IGF1R upregulation in PI3K-δ inhibitor resistant tumors was mediated by functional activation and enhanced nuclear localization of forkhead box protein O1 (FOXO1) transcription factors and glycogen synthase kinase 3 beta (GSK3B). In human CLL, high IGF1R expression was associated with trisomy-12. CLL cells from an idelalisib treated patient showed decreased sensitivity to idelalisib in vitro concomitant with enhanced MAPK signalling and strong upregulation of IGF1R upon idelalisib exposure. Our results thus highlight that alternative signalling cascades are playing a predominant role in the resistance and survival of cancer cells under PI3K-δ inhibition. We also demonstrate that these pathway alterations can serve as therapeutic targets, as inhibition of IGF1R offered efficacious salvage treatment for PI3K-δ inhibitor resistant tumors in vitro and in vivo.

  • Submitted November 1, 2018.
  • Revision received April 8, 2019.
  • Accepted April 5, 2019.