Targeting the CRKL/Src Family Kinases in Rhabdomyosarcoma


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Lee Helman
National Cancer Institute, Bethesda, USA

Abstract

Rhabdomyosarcoma (RMS) is the most common soft-tissue sarcoma of childhood. There are two major histologic and molecular subtypes of RMS, including embryonal RMS and alveolar RMS. Although progress has been made in treating localized tumours, metastatic tumours and alveolar tumours continue to have poor outcome with current treatment approaches. To identify novel signaling pathways necessary for rhabdomyosarcoma (RMS) survival, we performed a loss-of-function screen using an inducible shRNA library in an alveolar and an embryonal RMS cell line. This screen identified CRKL expression as necessary for growth of alveolar RMS and embryonal RMS both in vitro and in vivo. We also found that CRKL was uniformly highly expressed in both RMS cell lines and tumour tissue. Since CRKL is a member of the CRK adapter protein family that contains an SH2 and 2 SH3 domains, involved in signal transduction from multiple tyrosine kinase receptors, we evaluated CRKL interaction with multiple tyrosine kinase receptor signaling pathways in RMS cells. While we saw no interaction of CRKL with IGFIR, MET or PI3KAKT/mTOR pathways, we determined that CRKL signaling was associated with SRC family kinase (SFK) signaling, and specifically with downstream YES signaling. Inhibition of SFK signaling with dasatinib or another SFK inhibitor, sarcatinib, suppressed RMS cell growth in vitro and in vivo.

Since previous data have shown RMS cells to be dependent on IGFIR signaling, and we saw no interaction between CRKL and IGFIR, we asked whether inhibition of the non-overlapping IGFIR and CRKL/SFK pathways might be additive or synergistic. There was enhanced cell growth inhibition using a combination of IGFIR Ab plus dasatinib in both embryonal and alveolar RMS cell lines. These data identify CRKL as a novel critical component of RMS growth. This study also demonstrates the use of functional screening to identify a potentially novel therapeutic target and treatment approach for these highly aggressive paediatric cancers.