View metadata, citation and similarDownloaded papers at core.ac.uk from http://esmoopen.bmj.com/ on March 23, 2016 - Published by group.bmj.com brought to you by CORE provided by AIR Universita degli studi di Milano Open Access Review NTRK gene fusions as novel targets of cancer therapy across multiple tumour types Alessio Amatu,1 Andrea Sartore-Bianchi,1 Salvatore Siena1,2 To cite: Amatu A, Sartore- ABSTRACT for unbiased gene fusion discovery. In this NTRK Bianchi A, Siena S. The tropomyosin receptor kinase (Trk) receptor family article, we review the role of NTRK gene gene fusions as novel targets comprises 3 transmembrane proteins referred to as Trk fusions across several tumour histologies, and of cancer therapy across A, B and C (TrkA, TrkB and TrkC) receptors that are multiple tumour types. ESMO the promises and challenges of targeting such encoded by the NTRK1, NTRK2 and NTRK3 genes, Open 2016;1:e000023. genetic alterations for cancer therapy. doi:10.1136/esmoopen-2015- respectively. These receptor tyrosine kinases are 000023 expressed in human neuronal tissue and play an essential role in the physiology of development and TROPOMYOSIN RECEPTOR KINASE (TRK) function of the nervous system through activation by ▸ Prepublication history and FAMILY OF RECEPTORS neurotrophins. Gene fusions involving NTRK genes additional material for this The Trk receptor family comprises three lead to transcription of chimeric Trk proteins with paper is available online. To transmembrane proteins referred to as Trk A, constitutively activated or overexpressed kinase view these files please visit B and C (TrkA, TrkB and TrkC) receptors, the journal online function conferring oncogenic potential. These genetic (http://dx.doi.org/10.1136/ abnormalities have recently emerged as targets for and are encoded by the NTRK1, NTRK2 and esmoopen-2015-000023). cancer therapy, because novel compounds have been NTRK3 genes, respectively. These receptor developed that are selective inhibitors of the tyrosine kinases (TK) are expressed in Received 3 February 2016 constitutively active rearranged proteins. Developments human neuronal tissue, and play an essential Accepted 4 February 2016 in this field are being aided by next generation role in both the physiology of development sequencing methods as tools for unbiased gene and function of the nervous system through fusions discovery. In this article, we review the role of activation by neurotrophins (NTs).1 The NTRK gene fusions across several tumour histologies, latter are specific ligands known as nerve and the promises and challenges of targeting such growth factor (NGF) for TrkA, brain-derived genetic alterations for cancer therapy. growth factor (BDGF), and NT-4/5 for TrkB and NT3 for TrkC, respectively.2 All three Trk receptors are structured with an extracellular INTRODUCTION domain for ligand binding, a transmembrane The treatment of solid tumours is dramatic- region and an intracellular domain with a ally changing in recent years thanks to the kinase domain. The binding of the ligand to Find the Fact Sheet on enhancement of molecular diagnostic tech- the receptor triggers the oligomerisation of NTRK/TrkB here: http:// nologies leading to identification of an the receptors and phosphorylation of specific oncologypro.esmo.org/ fi Publications/Glossary-of- increasing number of speci c actionable tyrosine residues in the intracytoplasmic Molecular-Biology/ oncogenic abnormalities such as gene activat- kinase domain. This event results into the Glossary-in-Molecular- ing point mutations, in-frame insertions/dele- activation of signal transduction pathways Biology tions and amplification or rearrangements. leading to proliferation, differentiation and The concept of precision medicine consists in survival in normal and neoplastic neuronal the accomplishment of therapy individualised cells1 (figure 1). The binding of TrkA recep- 1Niguarda Cancer Center, to each tumour by exploiting these alterations tor by NGF causes the activation of the Ras/ Grande Ospedale as predictive biomarkers as well as targets of Mitogen activated protein kinase (MAPK) Metropolitano Niguarda, therapy. Neurotrophic tropomyosin receptor pathway, which leads to increased prolifer- Milan, Italy 2Dipartimento di Oncologia kinase (NTRK) gene rearrangements have ation and cellular growth through extracellu- e Emato-Oncologia, recently emerged as targets for cancer lar signal-regulated kinase (ERK) signalling. Università degli Studi di therapy, because novel compounds have been Other pathways such as phospholipase C-γ Milano, Milan, Italy developed that are selective inhibitors of the (PLCγ) and PI3K are also activated. TrkC constitutively active fusion proteins that coupling with NT3 causes preferential activa- Correspondence to Professor Salvatore Siena; arise from these molecular alterations. tion of the PI3/AKT pathway preventing salvatore.siena@ Developments in this field are being aided by apoptosis and increasing cell survival, ospedaleniguarda.it next generation sequencing methods as tools whereas TrkB transduces the BDNF signal via Amatu A, et al. ESMO Open 2016;1:e000023. doi:10.1136/esmoopen-2015-000023 1 Downloaded from http://esmoopen.bmj.com/ on March 23, 2016 - Published by group.bmj.com Open Access Figure 1 Schematic view of Trk receptors signalling, showing the three major pathways involved in cell differentiation and survival. AKT, v-akt murine thymoma viral oncogene homologue; BDGF, brain-derived growth factor; DAG, diacyl-glycerol; ERK, extracellular signal-regulated kinase; GAB1, GRB2-associated-binding protein 1; GRB2, growth factor receptor-bound protein 2; IP3, inositol trisphosphate; MEK, mitogen-activated protein kinase; NGF, nerve growth factor; NTF-3, neurotrophin 3; PI3K, phosphatidylinositol-4,5-bisphosphate 3-kinase; PIP2, phosphatidylinositol 4,5-bisphosphate; PKC, protein kinase C; PLC, phospholipase C; RAF, rapidly accelerated fibrosarcoma kinase; RAS, rat sarcoma kinase; SHC, Src homology 2 domain containing. Ras-ERK, PI3K and PLCγ pathway, resulting in neuronal amino acid residues (TrkB receptor). The full-length differentiation and survival.1 The Trk receptor kinases TrkB receptor contains an N-terminal signal sequence, play a key role in central and peripheral nervous system followed by a cysteine-rich domain, a leucine-rich development as well as in cell survival. The proper regu- domain, a second cysteine-rich domain, 2 immunoglobu- lation of Trk receptor levels and their activation is critic- lin (Ig)-like domains that make up the BDNF-binding ally important in cell functioning, and the upregulation region, a transmembrane domain, a Src homology 2 of Trk receptors has been reported in several central domain containing (SHC)-binding motif, a TK domain nervous system-related disorders (eg, TrkB in epilepsy, near the C terminus and a C-terminal PLCγ-docking site. neuropathic pain, or depression).3 The NTRK3 gene is located on chromosome 15q25,9 The NTRK1 gene is located on chromosome and its transcription product known as TrkC was isolated 1q21-q22,4 and its mutations disrupting the function of and characterised by Lamballe et al10 in 1991. TrkC the TrkA protein are found in patients affected by con- receptor is a glycoprotein of 145 kD preferentially genital insensitivity to pain with anhidrosis (CIPA) syn- expressed in the human hippocampus, cerebral cortex drome.5 In 1999 Indo et al cloned the full-length NTRK1 and in the granular cell layer of the cerebellum. human gene encoding a 790-residue or 796-residue protein (TrkA receptor) with an intracellular domain containing a juxtamembrane region, a TK domain and a MOLECULAR ALTERATIONS OF NTRK GENES IN VARIOUS short C terminal tail.6 MALIGNANCIES ACROSS HISTOLOGIES The NTRK2 gene is mapped on chromosome 9q22.17 Gene fusions of NTRK genes represent the main molecu- and contains 24 exons,8 coding for a protein of 822 lar alterations with known oncogenic and transforming 2 Amatu A, et al. ESMO Open 2016;1:e000023. doi:10.1136/esmoopen-2015-000023 Downloaded from http://esmoopen.bmj.com/ on March 23, 2016 - Published by group.bmj.com Open Access potential.11 Less common oncogenic mechanisms that previously occurred with ALK (Anaplastic Lymphoma have been described are in-frame deletion of NTRK1 in Kinase) gene fusions in non-small cell lung cancer acute myeloid leukaemia12 and a TrkA alternative spli- (NSCLC), in which despite evidence of ALK fusions cing in neuroblastoma.13 In all reported Trk oncogenic since 2007,16 the scientific interest was raised only after gene fusions, the 3’ region of the NTRK gene is joined synthesis of compounds with ALK-specific inhibitory with a 5’ sequence of a fusion partner gene by an intra- activity.17 In particular, in 2014, Ardini et al reported the chromosomal or interchromosomal rearrangement, and characterisation of the TPM3-NTRK1 gene rearrange- the oncogenic chimaera is typically a constitutively acti- ment as a recurring, although rare, event in CRC, and vated or overexpressed kinase (figure 2). Table 1 shows also discovered entrectinib (NMS-P626; RXDX-101) as a the NTRK fusions reported to date and their associated novel, highly potent and selective pan-Trk inhibitor. cancer types. Entrectinib suppressed TPM3-TRKA phosphorylation Colorectal adenocarcinoma: It has been believed for more and downstream signalling in KM12 cells and showed than three decades since the seminal work of Fearon remarkable antitumour activity in mice bearing KM12 and Vogelstein14 on molecular carcinogenesis of colorec- tumours. Also, in 2015,