IGF1R signalling in testicular germ cell tumour cells impacts on cell survival and acquired cisplatin resistance

Abstract

Testicular germ cell tumours (TGCTs) are the most frequent malignancy and cause of death from solid tumours in the 20‐ to 40‐year age group. Although most cases show sensitivity to cis‐platinum‐based chemotherapy, this is associated with long‐term toxicities and chemo‐resistance. Roles for receptor tyrosine kinases other than KIT are largely unknown in TGCT. We therefore conducted a phosphoproteomic screen and identified the insulin growth factor receptor‐1 (IGF1R) as both highly expressed and activated in TGCT cell lines representing the nonseminomatous subtype. IGF1R was also frequently expressed in tumour samples from patients with nonseminomas. Functional analysis of cell line models showed that long‐term shRNA‐mediated IGF1R silencing leads to apoptosis and complete ablation of nonseminoma cells with active IGF1R signalling. Cell lines with high levels of IGF1R activity also showed reduced AKT signalling in response to decreased IGF1R expression as well as sensitivity to the small‐molecule IGF1R inhibitor NVP‐AEW541. These results were in contrast to those in the seminoma cell line TCAM2 that lacked IGF1R signalling via AKT and was one of the two cell lines least sensitive to the IGF1R inhibitor. The dependence on IGF1R activity in the majority of nonseminomas parallels the known role of IGF signalling in the proliferation, migration, and survival of primordial germ cells, the putative cell of origin for TGCT. Upregulation of IGF1R expression and signalling was also found to contribute to acquired cisplatin resistance in an in vitro nonseminoma model, providing a rationale for targeting IGF1R in cisplatin‐resistant disease. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

IGF signalling in germ cells and testicular germ cell tumours: roles and therapeutic approaches

“…Expression of IGF1R or even presence of activated IGF1R does not always signify cells that are susceptible to IGF1R inhibition. This is seen in the case of the seminoma cell line, TCAM2 (Selfe et al ., ), which despite comparatively high basal levels of activated IGF1R among TGCT cell lines was among the least responsive to an IGF1R TKI. Expression of other components of the IGF axis such as IRS2 and IGFBP5 has been shown to be important for determining sensitivity to an IGF1R mAb (Pavlicek et al ., ).…”

“…Increased serum levels of IGF2 and IGFBP2 have been found in non‐seminomatous TGCT, decreasing upon successful therapy and increasing again in cases of recurrence (Fottner et al ., ). Our group has recently shown that IGF1R is expressed in approximately half of non‐seminomas and influences survival of non‐seminoma cells in vitro (Selfe et al ., ).…”

“…Mutations in the TP53 gene and amplification of its regulatory protein MDM2 are over‐represented in cisplatin‐resistant TGCT but do not explain all cases (Bagrodia et al ., ). We have recently described increased IGF1R copy number, expression and activation (with increased phospho‐AKT levels) in a model of acquired cisplatin resistance (Selfe et al ., ) which could subsequently be resensitized to cisplatin upon reduction of IGF1R. IGF1R hyperactivation has been specifically linked to cisplatin refractory ovarian cancer (Eckstein et al ., ).…”

“…The clinical utility of blocking this pathway may therefore lie in combining newly designed IGF ligand‐targeted therapies with existing or new treatments. TGCT cells commonly exhibit aberrant IGF axis activation through elevated IGF1R activity (Selfe et al ., ) and/or increased IGF2 expression through loss of imprinting (Van Gurp et al ., ). We have shown that cells with high levels of IGF1R activation are vulnerable to IGF1R inhibition.…”

Functions of genes related to testicular germ cell tumour development

“…Schlueter et al ., () showed that in zebrafish, knockdown of one of two functional copies of IGF1R gene resulted in disturbed migration and reduced number of PGCs colonizing the genital ridges. In a recent study, phosphorylation of IGF1R was detected in TGCT cell lines of non‐seminoma type and at highest levels of the RTKs (Selfe et al ., ). The insulin receptor, which can heterodimerize with IGF1R, was also found highly phosphorylated, in support of an active IGF pathway in TGCT.…”