The aromatase inhibitor letrozole and inhibitors of insulin-like growth factor I receptor synergistically induce apoptosis in in vitro models of estrogen-dependent breast cancer

INTRODUCTION: Endocrine-dependent, estrogen receptor positive breast cancer cells proliferate in response to estrogens, synthesized by the cytochrome p450 aromatase enzyme. Letrozole is a potent nonsteroidal aromatase inhibitor that is registered for the treatment of postmenopausal women with advanced metastatic breast cancers and in the neoadjuvant, early, and extended adjuvant indications. Because crosstalk exists between estrogen receptor and insulin-like growth factor I receptor (IGF-IR), the effect of combining a selective IGF-IR inhibitor (NVP-AEW541) with letrozole was assessed in two independent in vitro models of estrogen-dependent breast cancer. METHODS: MCF7 and T47D cells stably expressing aromatase (MCF7/Aro and T47D/Aro) were used as in vitro models of aromatase-driven breast cancer. The role of the IGF-IR pathway in breast cancer cells stimulated only by 17ß-estradiol or androstenedione was assessed by proliferation assays. The combination of letrozole and NVP-AEW541 was assessed for synergy in inhibiting cell proliferation using Chou-Talalay derived equations. Finally, combination or single agent effects on proliferation and apoptosis were assessed using proliferation assays, flow cytometry, and immunoblotting. RESULTS: Both MCF7 and T47D cells, as well as MCF7/Aro and T47D/Aro, exhibited sensitivity to inhibition of 17ß-estradiol dependent proliferation by NVP-AEW541. Letrozole combined with NVP-AEW541 synergistically inhibited androstenedione-dependent proliferation in aromatase-expressing cells with combination index values of 0.6 or less. Synergistic combination effects correlated with higher levels of apoptosis as compared with cells treated with the single agent alone. Treatment with either agent also appeared to inhibit IGF-IR signalling via phosphoinositide 3-kinase. Notably, IGF-IR inhibition had limited effect on estrogen-dependent proliferation in the cell lines, but was clearly required for survival, suggesting that the combination of letrozole and IGF-IR inhibition sensitizes cells to apoptosis. CONCLUSION: Inhibition of the IGF-IR pathway and aromatase was synergistic in two independent estrogen-dependent in vitro models of breast cancer. Moreover, synergism of NVP-AEW541 and letrozole correlated with induction of apoptosis, but not cell cycle arrest, in the cell lines tested. Combination of IGF-IR inhibitors and letrozole may hold promise for the treatment of patients with estrogen-dependent breast cancers

The aromatase inhibitor letrozole and inhibitors of insulin-like growth factor I receptor synergistically induce apoptosis in in vitro models of estrogen-dependent breast cancer.

INTRODUCTION: Endocrine-dependent, estrogen receptor positive breast cancer cells proliferate in response to estrogens, synthesized by the cytochrome p450 aromatase enzyme. Letrozole is a potent nonsteroidal aromatase inhibitor that is registered for the treatment of postmenopausal women with advanced metastatic breast cancers and in the neoadjuvant, early, and extended adjuvant indications. Because crosstalk exists between estrogen receptor and insulin-like growth factor I receptor (IGF-IR), the effect of combining a selective IGF-IR inhibitor (NVP-AEW541) with letrozole was assessed in two independent in vitro models of estrogen-dependent breast cancer. METHODS: MCF7 and T47D cells stably expressing aromatase (MCF7/Aro and T47D/Aro) were used as in vitro models of aromatase-driven breast cancer. The role of the IGF-IR pathway in breast cancer cells stimulated only by 17beta-estradiol or androstenedione was assessed by proliferation assays. The combination of letrozole and NVP-AEW541 was assessed for synergy in inhibiting cell proliferation using Chou-Talalay derived equations. Finally, combination or single agent effects on proliferation and apoptosis were assessed using proliferation assays, flow cytometry, and immunoblotting. RESULTS: Both MCF7 and T47D cells, as well as MCF7/Aro and T47D/Aro, exhibited sensitivity to inhibition of 17beta-estradiol dependent proliferation by NVP-AEW541. Letrozole combined with NVP-AEW541 synergistically inhibited androstenedione-dependent proliferation in aromatase-expressing cells with combination index values of 0.6 or less. Synergistic combination effects correlated with higher levels of apoptosis as compared with cells treated with the single agent alone. Treatment with either agent also appeared to inhibit IGF-IR signalling via phosphoinositide 3-kinase. Notably, IGF-IR inhibition had limited effect on estrogen-dependent proliferation in the cell lines, but was clearly required for survival, suggesting that the combination of letrozole and IGF-IR inhibition sensitizes cells to apoptosis. CONCLUSION: Inhibition of the IGF-IR pathway and aromatase was synergistic in two independent estrogen-dependent in vitro models of breast cancer. Moreover, synergism of NVP-AEW541 and letrozole correlated with induction of apoptosis, but not cell cycle arrest, in the cell lines tested. Combination of IGF-IR inhibitors and letrozole may hold promise for the treatment of patients with estrogen-dependent breast cancers

Fibroblast growth factor receptors as novel therapeutic targets in malignant rhabdoid tumors

Malignant rhabdoid tumors (MRTs) are highly aggressive pediatric cancers arising in brain, kidney and soft tissues, which are characterized by loss of the tumor suppressor SNF5. MRTs are poorly responsive to chemotherapy and thus a high unmet clinical need exists for novel therapies for MRT patients. SNF5 is a core subunit of the SWI/SNF chromatin remodeling complex which affects gene expression by nucleosome remodeling. In this study, we report that loss of SNF5 function correlates with increased expression of fibroblast growth factor receptors (FGFRs) in MRT cell lines and primary tumor samples and that re-expression of SNF5 in MRT cell lines causes a striking repression of FGFR expression. Conversely, siRNA-mediated impairment of SWI/SNF function leads to elevated levels of FGFR2 in human fibroblast. In vivo, treatment with NVP-BGJ398, a novel selective, pan-specific FGFR inhibitor, blocks progression of a MRT allograft derived from a SNF5-deficient mouse model. Hence, we identify FGFR signaling as an aberrantly activated oncogenic pathway in MRTs and propose pharmacological inhibition of FGFRs as a potential novel clinical therapy for MRTs

FGFR inhibition with NVP-BGJ398 impairs MRT growth <i>in vivo</i>.

<p>(A) <i>In vivo</i> efficacy of NVP-BGJ398 in a primary mouse MRT allograft model. MRT bearing nude mice received vehicle or NVP-BGJ398 at 50 mg/kg body weight for 13 consecutive days and tumor volumes were monitored. Date are given as average with SEM (n = 4) and were compared by unpaired Student’s t test; *p<0.05. (B) Immunohistochemistry (IHC, upper panel) and immunoblot (lower panel) analysis of p-ERK1/2 levels in MRT allograft samples from mice treated with a single dose of vehicle or NVP-BGJ398 (50 mg/kg body weight) for 2 h. β-Tubulin expression was used to monitor equal loading.</p

FGFR expression levels of the MRT cell lines A204, G401 and G402.

<p>(A) Scatter plot showing expression and copy number levels for <i>FGFR1</i> (left panel) and <i>FGFR2</i> (right panel) within the CCLE. MRT lines A204, G401 and G402 are indicated in red. (B) Quantitative RT-PCR (qRT-PCR) analysis of <i>FGFR1</i> and <i>FGFR2</i> mRNA expression in MRT cell lines and soft tissue cancer lines SKLMS1 and SKUT1. Expression values are given as average with standard errors of the mean (SEM) (n≥3) with respect to <i>GAPDH</i> mRNA levels (arbitrarily set as 100). (C) qRT-PCR and immunoblot analysis of SNF5-deficiency in MRT lines. SKLMS1 and SKUT1 cells were used as positive controls for SNF5 expression. <i>SNF5</i> mRNA expression is given as average with SEM (n≥3) with respect to <i>GAPDH</i> mRNA levels (arbitrarily set as 100). β-Tubulin expression was used to monitor equal loading.</p