Production of insulin-like growth factor binding proteins by small-cell lung cancer cell lines

Disruption of insulin receptor function inhibits proliferation in endocrine-resistant breast cancer cells

The insulin-like growth factor (IGF) system is a well-studied growth regulatory pathway implicated in breast cancer biology. Clinical trials testing monoclonal antibodies directed against the type I IGF receptor (IGF1R) in combination with estrogen receptor-α (ER) targeting have been completed, but failed to show benefits in patients with endocrine resistant tumors compared to ER targeting alone. We have previously shown that the closely related insulin receptor (InsR) is expressed in tamoxifen resistant breast cancer cells. Here we examined if inhibition of InsR affected tamoxifen-resistant (TamR) breast cancer cells. InsR function was inhibited by three different mechanisms: InsR shRNA, a small InsR blocking peptide, S961 and an InsR monoclonal antibody (mAb). Suppression of InsR function by these methods in TamR cells successfully blocked insulin-mediated signaling, monolayer proliferation, cell cycle progression and anchorage-independent growth. This strategy was not effective in parental cells likely due to the presence of IGFR/InsR hybrid receptors. Down-regulation of IGF1R in conjunction with InsR inhibition was more effective in blocking IGF- and insulin-mediated signaling and growth in parental cells compared to single receptor targeting alone. Our findings show TamR cells were stimulated by InsR and were not sensitive to IGF1R inhibition, whereas in tamoxifen-sensitive parental cancer cells, the presence of both receptors, especially hybrid receptors, allowed cross-reactivity of ligand-mediated activation and growth. To suppress the IGF system, targeting of both IGF1R and InsR is optimal in endocrine sensitive and resistant breast cancer.

Neuroendocrine cancer-specific up-regulating mechanism of insulin-like growth factor binding protein-2 in small cell lung cancer

Small cell lung cancer (SCLC) exhibits insulin-like growth factor-dependent growth. SCLC is the most aggressive among known in vivo lung cancers, whereas in vitro growth of SCLC is paradoxically slow as compared with that of non-SCLC (NSCLC). In this study, we demonstrate that SCLC cells overexpress insulin-like growth factor binding protein (IGFBP)-2 via NeuroD, a neuroendocrine cell-specific transcription factor. Chromatin immunoprecipitation, electrophoretic mobility shift, and IGFBP-2 promoter assays all revealed that NeuroD binds to the E-box in the 5'-untranslated region of IGFBP-2. A NeuroD transgene in both airway epithelial and NSCLC cells up-regulated the transcription of IGFBP-2 and retarded cell growth. Recombinant IGFBP-2 repressed the growth of both airway epithelial and NSCLC cells in a dose-dependent manner. A NeuroD-specific small interfering RNA repressed IGFBP-2 expression in SCLC, and neutralization of IGFBP-2 and an IGFBP-2-specific small interfering RNA increased SCLC cell growth. Pathological samples of SCLC also expressed IGFBP-2 abundantly, as compared with NSCLC, and showed only rare (8%) IGFBP-2 promoter methylation, whereas the IGFBP-2 promoter was methylated in 71% of adenocarcinomas and 29% of squamous cell carcinomas. These findings suggest that 1) SCLC has an IGFBP-2 overexpression mechanism distinct from NSCLC, 2) secreted IGFBP-2 contributes to the slow growth of SCLC in vitro, and 3) the epigenetic alterations in the IGFBP-2 promoter contribute to the striking differences in IGFBP-2 expression between SCLC and NSCLC in vivo.

The insulin-like growth factor-I receptor kinase inhibitor, NVP-ADW742, sensitizes small cell lung cancer cell lines to the effects of chemotherapy

PURPOSE

Insulin-like growth factor-I (IGF-I) is a potent growth factor for small cell lung cancer (SCLC) in both the autocrine and endocrine context. It also inhibits chemotherapy-induced apoptosis through activation of the phosphatidylinositol 3-kinase (PI3K)-Akt pathway and we have previously shown that inhibition of this signaling pathway enhances sensitivity of SCLC cell lines to chemotherapy. The purpose of this study was to determine whether the novel IGF-I receptor (IGF-IR) kinase inhibitor, NVP-ADW742, sensitizes SCLC cell lines to etoposide and carboplatin, which are commonly used in the treatment of SCLC.

EXPERIMENTAL DESIGN

Cell growth in the presence of various combinations of NVP-ADW742, imatinib (STI571; Gleevec/Glivec), and chemotherapeutic agents was monitored using a 3-(4,5 dimethylthiazol-2yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay and analyzed using the Chou-Talalay multiple-drug-effect equation. Induction of apoptosis was assessed using terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL) and Western blot analysis of procaspase 3 and poly(ADP-ribose)polymerase cleavage. IGF-I-induced vascular endothelial cell growth factor expression was monitored by Northern blot and ELISA.

RESULTS

NVP-ADW742 synergistically enhanced sensitivity of multiple SCLC cell lines to etoposide and carboplatin. Maximal enhancement occurred at concentrations of NVP-ADW742 that eliminated basal PI3K-Akt activity in individual cell lines. In the WBA cell line, in which the c-Kit receptor tyrosine kinase is partly responsible for basal PI3K-Akt activity, the combination of NVP-ADW742 and imatinib was superior to NVP-ADW742 alone in sensitizing the cells to etoposide. Enhancement of the sensitivity of SCLC cell lines to etoposide, as determined by MTT assay, correlated closely with sensitization to the induction of apoptosis as measured by TUNEL and caspase activation assays. Treatment with NVP-ADW742 also eliminated IGF-I-mediated expression of vascular endothelial cell growth factor, suggesting that in addition to enhancing sensitivity of SCLC to chemotherapy, this kinase inhibitor could potentially inhibit angiogenesis in vivo.

CONCLUSIONS

Inhibition of IGF-IR signaling synergistically enhances the sensitivity of SCLC to etoposide and carboplatin. This enhancement in sensitivity to chemotherapy tightly correlates with inhibition of PI3K-Akt activation. Future SCLC clinical trials incorporating IGF-IR inhibitors alone or in combination with other kinase inhibitors should include assessment of PI3K-Akt activity as a pharmacodynamic end-point.

The insulin-like growth factor-I (IGF-I) receptor kinase inhibitor NVP-ADW742, in combination with STI571, delineates a spectrum of dependence of small cell lung cancer on IGF-I and stem cell factor signaling

Stem cell factor (SCF)/Kit and insulin-like growth factor-I (IGF-I)/IGF-I receptor (IGF-IR) autocrine loops play a prominent role in the growth of small cell lung cancer (SCLC). Previous data suggested that IGF-I protects cells from apoptosis induced by STI571, an efficient inhibitor of Kit signal transduction, by activating the critical phosphatidylinositol 3-kinase-Akt pathway. To determine if inhibition of IGF-IR signaling would be therapeutically relevant in SCLC, the activity of a novel kinase inhibitor of IGF-IR, NVP-ADW742 (Novartis Pharma AG, Basel, Switzerland), was characterized. Pretreatment of the H526 cell line with NVP-ADW742 inhibited IGF-IR signaling and growth with IC50 values between 0.1 and 0.4 μm. SCF-mediated Kit phosphorylation and Akt activation were inhibited with IC50 values in the 1–5 μm range. However, NVP-ADW742 affected neither hepatocyte growth factor-mediated Akt activation nor activity of constitutively active Akt. The therapeutic potential of NVP-ADW742 was assessed by determining its effect on growth of several SCLC cell lines in serum. These studies clearly delineated two populations of cell lines as determined by differential sensitivity to NVP-ADW742. One population, which lacks active SCF/Kit autocrine loops, was inhibited with IC50 values between 0.1 and 0.5 μm. A second population, which has active SCF/Kit autocrine loops, was inhibited with IC50 values in the 4–7 μm range. When these cell lines were treated with a combination of STI571 and NVP-ADW742, no advantage was seen in the former group, whereas, in the latter group, a clearly synergistic response to the combination was seen when growth, apoptosis, or Akt activation was assessed. These data demonstrate that NVP-ADW742 is a potent and selective IGF-IR kinase inhibitor that can efficiently inhibit the growth of cells that are highly dependent on IGF-I signaling. However, for optimal growth inhibition of SCLC cells with an active SCF/Kit autocrine loop, a combination of a Kit inhibitor (STI571) and an IGF-IR inhibitor (NVP-ADW742) appears to be necessary. These observations suggest that, in tumors in which critical signal transduction pathways can be activated by alternative receptors, optimal therapy may require inhibition of multiple receptors.

Insulin-like growth factor expression in human cancer cell lines

The insulin-like growth factors (IGFs), IGF-I and IGF-II, are potent mitogens for human lung and other epithelial cancer cell lines. Previous studies in defined medium lacking added IGF or insulin suggest that an IGF-related ligand can act as an autocrine growth factor for many cancer cell lines through action via the type I IGF receptor (IGF-R). Analysis of RNA isolated from human lung and breast cancer cell lines by reverse transcription of mRNA and polymerase chain reaction reveal that IGF-I and IGF-II mRNAs were co-expressed with IGF-R in the majority of cell lines. IGF-I mRNA was detected in 11/12 small cell lung cancer cell lines (SCLC), 13/14 nonsmall cell lung cancer (NSCLC) cell lines, and 1/2 breast cancer cell lines. IGF-II mRNA was detected in 8/10 SCLC, 11/12 NSCLC cell lines, and 2/2 breast lines. All cell lines expressed IGF-R. For analysis of IGF peptide secretion, cell lines were adapted to growth in serum/hormone-free culture medium (R0), and to avoid interference by IGF-binding proteins, secreted IGF peptides were isolated under acidic conditions and analyzed by Western blotting. Based upon measurement of the sensitivity of the anti-IGF antibodies for detection of recombinant human IGFs, IGF peptides accumulated in conditioned medium at greater than picomolar concentrations should have been readily detected. In three cell lines (two lung and one breast) secreted IGF immunoreactivity was detected as three molecular mass species of 23, 14, and 6 kDa. Isolation and NH2-terminal sequencing of each of these species definitively identified them as differentially processed forms of the IGF-II prohormone. Despite the high frequency of IGF-I gene expression detected by reverse transcription-polymerase chain reaction analysis, only one lung cancer cell line, NCI-N417d, was found that unequivocally secreted IGF-I peptide. This direct sequence determination unambiguously identifies IGF-II as the predominant IGF involved in the autocrine growth stimulation of human lung and breast epithelial tumor cell lines and supports a growing body of literature that implicates IGF-II/IGF-R autocrine loops as a common growth mechanism in epithelial carcinogenesis.

Monoclonal antibody alpha IR-3 inhibits non-small cell lung cancer growth in vitro and in vivo

The ability of monoclonal antibody (mAb) alpha IR-3 to interact with non-small cell lung cancer (NSCLC) cells was investigated. MAb alpha IR-3 inhibited specific binding of 125I-IGF-I and 125I-alpha IR-3 to a panel of 8 NSCLC cell lines with high affinity (IC50 = 200 and 50 ng/ml, respectively). 125I-alpha IR-3 bound with high affinity (Kd = 40 ng/ml) to a single class of sites (Bmax = 8,000/cell) using NCI-H838 cells. 125I-alpha IR-3 was internalized when exposed to NCI-H838 or H1299 cells at 37 degrees C but not 4 degrees C. alpha IR-3 immunoprecipitated major 90 and 130 kD proteins. IGF-I stimulated and alpha IR-3 inhibited the clonal growth of NCI-H1299 cells. alpha IR-3 slowed the growth of NCI-H157 and H838 xenografts in nude mice. In a biodistribution study 125I-alpha IR-3 was preferentially localized to the tumor as opposed to other organs. These data suggest that IGF-I may be a regulatory agent in NSCLC.

Production of insulin-like growth factor binding proteins by human ovarian carcinoma cells

Cells of the human ovarian carcinoma lines EFO-21, EFO-27, MFO-35 and MFO-36 secrete binding proteins for insulin-like growth factors (IGFBPs) into their culture media. By sodium dodecyl sulfate/polyacrylamide gel electrophoresis (SDS-PAGE) and ligand blotting, seven groups of IGFBPs with molecular masses of 25, 30 (doublet), 34, 37, 40, 45, and 50 kDa were observed, depending on the cell line under investigation. By Northern blot analyses using cDNAs or oligonucleotides specific for the six types of IGFBP (IGFBP-1 to IGFBP-6), mRNA for all IGFBPs tested except for IGFBP-1 could be detected in the ovarian carcinoma cell extracts. In detail, analysis of EFO-21 protein products by SDS-PAGE yielded IGFBPs of 25, 34, and 50 kDa; extracts of EFO-21 cells contained mRNAs for IGFBP-2, -3, -4, and -6. EFO-27 cells produced IGFBPs of 40 kDa and 45 kDa as determined by SDS-PAGE, and mRNAs for IGFBP-3, -4, and -6 were detected. In the conditioned medium of MFO-35 cells, IGFBPs of 25, 30 (doublet), 34, 37, 40, and 45 kDa were observed by SDS-PAGE, while mRNAs for the five proteins IGFBP-2 to IGFBP-6 were found. MFO-36 cells produced IGFBPs of 34 kDa and 50 kDa as determined by SDS-PAGE, and the cells expressed mRNAs for IGFBP-2, -3, -4, and -6. In relation to published molecular mass data of the known IGFBPs, the size of the secreted proteins could be correlated to the mRNA patterns expressed by the ovarian carcinoma cells. It is concluded that ovarian carcinoma cells frequently express IGFBP-3, -4, and -6 and, to a lesser extent, IGFBP-2; the expression of IGFBP-5 appears as a rather rare event, while IGFBP-1 was not found to be expressed in ovarian carcinoma cells.

Insulin-like growth factor binding protein production and regulation in fetal rat lung cells

Insulin-like growth factor binding proteins (IGFBPs) are expressed in lung from early in gestation and may modulate IGF-stimulated fetal lung cell proliferation and/or differentiation. To begin to define IGFBP production and regulation in lung cells during development, we prepared primary cultures of 19 day gestation fetal rat lung fibroblasts and epithelial cells and identified IGFBPs secreted into medium. Ligand blot analysis of conditioned media (CM) from both cell types demonstrated IGFBP bands of approximately 39,000-45,000, 32,000, 24,000, and 22,000 M(r). These migration characteristics allowed the identification of the 39,000-45,000 M(r) bands as IGFBP-3 and the 24,000 M(r) band as IGFBP-4, while Western immunoblot analyses localized IGFBP-2 to the 32,000 M(r) band and IGFBP-5 to the 22,000 M(r) band. Polymerase chain reaction amplification of cDNAs generated by reverse transcription of fibroblast and epithelial cell RNA using specific oligodeoxynucleotide primers for IGFBPs 1 through 6, demonstrated the presence of amplified products for IGFBP-2, -3, -4, -5, and -6. In both cell types, IGFBP-2 and -3 production was sustained during 48 h of incubation in serum-free medium, whereas IGFBP-4 abundance increased only during the first 6 to 12 h of incubation. CM from fibroblasts and epithelial cells plated at low densities contained a high abundance of IGFBP-2 per microgram cellular DNA compared with cells at higher densities. In contrast, IGFBP-3 and -4 abundance normalized to cell DNA did not change with differing cell densities.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular cloning of IGFBP-5 from SCLC cell lines and expression of IGFBP-4, IGFBP-5 and IGFBP-6 in lung cancer cell lines and primary tumours

We showed recently that insulin-like growth factor binding protein (IGFBP)-1, -2 and -3 are differentially expressed in lung cancer and permanent lung cancer cell lines. Elevated levels of IGF binding capacity in serum of lung cancer patients were also reported. The function and tissue specificity of IGFBP are still obscure but they are probably local regulators of IGF action. Here we show the expression of IGFBP-4 transcripts in 11/11 small cell lung cancer (SCLC) cell lines, in nine out of 11 non-small cell lung cancer (NSCLC) cell lines, in 11/11 lung tumour specimens (10 derived from patients with NSCLC and one from SCLC origin) and in normal lung. In addition we isolated IGFBP-5 cDNA from lambda gt10 libraries of SCLC cell lines. With this IGFBP-5 cDNA we detected transcripts of different lengths in seven out of 11 SCLC cell lines, in 11/11 lung cancer specimens but only in one out of 11 NSCLC cell lines and in normal lung. IGFBP-6 was not detected in northern analysis of any tested SCLC cell line but it was expressed in nine out of 11 NSCLC cell lines and in nine out of 11 human lung cancer specimens and in normal lung.

Growth factor and peptide receptors in small cell lung cancer

In the past decade, over 1000 continuous human cell lines have been established from lung cancer biopsy specimens. Numerous growth factors and receptors have been identified in the small cell lung cancer (SCLC) cell lines. SCLC is a neuroendocrine tumor which contains numerous peptides, including bombesin/gastrin releasing peptide (BN/GRP), and receptors. High levels of GRP mRNA and immunoreactivity are present in SCLC cells. The secretion rate of GRP from SCLC cells is increased by vasoactive intestinal peptide (VIP), which elevates the intracellular cAMP. GRP binds to cell surface receptors, elevates cytosolic calcium and stimulates the growth of SCLC cells. Additional SCLC growth factors include insulin-like growth factor I (IGF-I) and transferrin. IGF-I mRNA and protein is present in SCLC. IGF-I binds with high affinity to SCLC cells and stimulates tyrosine kinase activity and growth. Transferrin is also present in SCLC cells. Transferrin binds with high affinity to SCLC cells and stimulates iron transport and growth. Synthetic peptide antagonists and monoclonal antibodies have been identified which disrupt autocrine growth pathways and inhibit SCLC growth.

Characterization of insulin-like growth factor I receptors and growth effects in human lung cancer cell lines

Small-cell lung cancer (SCLC) and non-small-cell lung cancer (NSCLC) cell lines were studied for insulin-like growth factor I (IGF-I) receptor expression and with regard to the influence of IGF-I on cell proliferation. IGF-I receptors on the cells were characterized by competitive binding assays, chemical crosslinking and northern blot hybridization of IGF-I receptor mRNA. All SCLC and NSCLC cell lines showed specific IGF-I binding sites with an affinity (KD) of 0.69-5.21 nM. The amount of binding sites ranged from 59 fmol/mg to 1230 fmol/mg protein. The IGF-I binding was inhibited by the IGF-I receptor antibody (alpha-IR-3). Northern blot hybridization indicated that IGF-I receptor mRNA was being produced by all SCLC and NSCLC cell lines. We used the soft-agarose clonogenic assay to evaluate the influence of IGF-I on the in vitro proliferation of the cells. Our results have shown that IGF-I stimulates the growth of all tested cell lines ranging from a factor of 1.6 to 4.2 in SCLC and from 1.1 to 2.7 in NSCLC. The data indicate that the IGF-I receptor thus appears to be the common pathway for the mitogenic activity of IGF-I and IGF-II with regard to human lung cancer cells.

Differential expression of insulin-like growth factor binding proteins in human non-small cell lung cancer cell lines

The possible expression and secretion of insulin-like growth factor binding proteins (IGFBPs) by non-small cell lung cancer (NSCLC) cell lines was investigated and compared with possible IGFBP expression by primary NSCLC tumours. Cells growing under serum-free conditions released binding proteins with apparent molecular masses of 26-43 kD when analysed by a ligand blotting method under non-reducing conditions. Additionally, northern blot analysis of total RNA from NSCLC cell lines and tumours was performed using cDNAs coding for each of IGFBP-1, IGFBP-2, and IGFBP-3. This analysis revealed expression of all three mRNAs to varying degrees by all cell lines. In contrast all primary tumours analysed expressed predominantly IGFBP-2 and IGFBP-3 and none showed any evident expression of IGFBP-1. Both NSCLC cell lines and tumours synthesise IGFBPs but the pattern of expression differs significantly between cell lines and primary tumours.

Insulin-like growth factor binding protein expression in human small cell lung cancer cell lines

Insulin-like growth factor binding proteins (IGF-BP) are secreted by several human small cell lung cancer cell lines (SCLC). In order to identify the IGF-BPs from SCLC cell lines the RNA from 10 different SCLC cell lines was analyzed by Northern blot analysis with the probes for three different IGF-BPs, IGFBP-1, IGFBP-2, and IGFBP-3. No hybridization signal could be detected with the probes encoding for IGFBP-1 and IGFBP-3. The hybridization with different IGFBP-2-specific oligodeoxynucleotide probes and with the corresponding full-length cDNA showed that all SCLC cell lines which secreted IGF-BPs express IGFBP-2.

Growth regulation by insulin-like growth factors in lung cancer

Lung cancer is a major health problem, with over 38,000 new cases expected every year in West Germany. A more complete understanding of the biology of lung cancer will hopefully lead to therapeutic modalities. The possible autocrine growth regulation in small-cell lung cancer and non-small-cell lung cancer has been demonstrated for bombesin/GRP, vasopressin, neurotensin, EGF/TGF alpha, transferrin-related peptides and insulin-like growth factors. This contribution concentrates on recent data concerning binding sites, growth promoting effects and secretion of IGFs in lung cancer cell lines. The production of IGF-binding proteins which were also produced by lung cancer cell lines modifies the autocrine/paracrine model for IGFs since then proteins can either enhance or inhibit the effect of IGFs on tumor growth.