Evaluation of IGF1R and phosphorylated IGF1R as targets in HER2-positive breast cancer cell lines and tumours

Abstract

Insulin-like growth factor-1 receptor (IGF1R) signalling is implicated in resistance to trastuzumab. However, the benefit of co-targeting HER2 and IGF1R has not been extensively studied, and the relationship between activated IGF1R and clinical response to trastuzumab has not been reported. This study aimed to evaluate the combination of trastuzumab with IGF1R tyrosine kinase inhibitors (TKIs) in a panel of HER2-positive breast cancer cell lines, and to examine the relationship between IGF1R expression and activation and response to trastuzumab in HER2-positive breast cancer patients. The anti-proliferative effects of trastuzumab combined with IGF1R TKIs BMS-536924 or NVP-AEW541 were measured in nine HER2-positive cell lines. IGF1R and phosphorylated IGF1R/insulin receptor (pIGF1R/IR) were measured by immunohistochemistry in 160 tumour samples from trastuzumab-treated patients (ICORG 06-22). The HER2-positive cell lines displayed varying sensitivity to IGF1R TKIs alone (IC(50)s: 0.7 to >10 μM). However, when combined with trastuzumab, a significantly enhanced effect was observed in five cell lines treated with BMS-536924, and three with NVP-AEW541. While IGF1R levels correlated with reduced response to NVP-AEW541 alone, neither IGF1R nor pIGF1R were predictive of response to BMS-536924 or NVP-AEW541 in combination with trastuzumab. Low HER2 levels correlated with response to BMS-536924 in combination with trastuzumab. Akt levels correlated with improved response to trastuzumab and NVP-AEW541 (P = 0.039). Cytoplasmic IGF1R staining was observed in all tumours, membrane IGF1R was detected in 13.8 %, and pIGF1R/IR was detected in 48.8 %. Although membrane IGF1R staining was associated with larger tumour size (P = 0.041), and lower tumour grade (P = 0.024), no association between IGF1R or pIGF1R/IR and patient survival was observed. In conclusion, while neither IGF1R expression nor activation was predictive of response to trastuzumab, these pre-clinical data provide evidence that co-targeting HER2 and IGF1R may be beneficial in some HER2-amplified breast cancers.

Combination therapy approaches to target insulin-like growth factor receptor signaling in breast cancer

“…In recent years, IGF1R activity has been shown to play a role in driving HER2 therapy trastuzumab resistance, and co-targeting HER2 and IGF1R is thought to be a viable therapeutic approach to overcome resistance (Browne et al 2012). Mechanisms associated with IGF1R-driven HER2 therapy resistance are not well defined; however, there are studies suggesting that it is mediated via de-regulation of the PTEN/PI3K/AKT signaling pathway (Gallardo et al 2012).…”

“…Thus, co-targeting strategies using Src inhibitors in conjunction with HER2-targeted therapies may be clinically effective for HER2-amplified cancers to eliminate IGF1R-mediated HER2 therapy resistance (Browne et al 2012). At present, there are no clinical trials testing this type of combination therapy for breast cancer; however, a phase 2 trial testing the safety of IMC-A12 and the Src inhibitor, sorafenib, in combination for advanced liver cancer may give some further insight into the potential of combination therapy (Tables 1 and 2: Ref #27, NCT00906373).…”

IGF1R Protein Expression Is Not Associated with Differential Benefit to Concurrent Trastuzumab in Early-Stage HER2+ Breast Cancer from the North Central Cancer Treatment Group (Alliance) Adjuvant Trastuzumab Trial N9831

“…A study that utilized the same polyclonal antibody as our study (directed against the β subunit of IGF1R) showed that 65% of 297 unselected breast cancers did not have IGF1R protein expression and 3% of the cases had 3+ staining(39). This same antibody detected membrane IGF1R (when exceeded cytoplasmic staining) in 13.8% of 160 HER2+ breast cancers(25). In addition, our results are in alignment with recent findings that demonstrated that IGF1R protein expression was associated with HER2-negativity, and reduced IGF1R expression (compared to moderate expression observed in normal breast epithelial elements) was observed consistently in ER−/PR−/HER2+ breast tumors(38).…”

“…IGF1R has been linked to resistance to chemo/hormonal/biological/radio-therapy(19) and particularly implicated in therapeutic resistance to trastuzumab(8, 20, 21). Preclinical evidence has demonstrated that increased IGF1R signaling interferes with trastuzumab action(8, 22, 23), and synergy has been observed between trastuzumab and anti-IGF1R agents in inhibiting HER2+ tumor cell growth(24, 25). A unique interaction/heterodimerization of IGF1R and HER2 has been observed in trastuzumab-resistant cells but not in sensitive parental cells (26–28).…”

“…However, clinical evidence suggested that IGF1R expression alone (as determined by immunohistochemistry) was not associated with trastuzumab resistance in patients with HER2+ metastatic breast cancer(29–31), but only the combination of low protein expression of IGF1R and high protein expression of the downstream phospho-ribosomal 6 (pS6) protein was associated with a favorable patient response outcome to trastuzumab in patients with HER2+ metastatic breast cancer(30). Three small retrospective analyses (<70 patients) in the neo-adjuvant and adjuvant settings produced inconsistent results regarding the association between IGF1R expression and trastuzumab benefit(25, 31, 32). …”