Production of immunoreactive insulin-like growth factor-I (IGF-I) and IGF-I binding proteins by human lung tumours

Abstract

Summary The production of insulin-like growth factor I (IGF-I) and IGF-I binding proteins (BPs) by human lung tumour cell lines in vitro has been examined and the levels of these substances in the serum of lung cancer patients investigated. While small cell lung cancer (SCLC) cell lines secreted both IGF-I and BPs, non-small cell lung cancer (NSCLC) cell lines secreted BPs only. No evidence of increased serum IGF-I levels was obtained in a cohort of 52 lung cancer patients having SCLC and NSCLC histologies. In contrast, serum levels of low molecular weight BPs were markedly elevated in the majority of lung cancer patients.The detection of elevated immunoreactive insulin-like growth factor-I (IGF-I) in human lung tumours (Minuto et al., 1986;Macaulay et al., 1988a) Healthy adult male and female non-smokers (n = 32), and male and female normal smokers (n = 31) were included in the study as controls. The age range for controls was 23-81 years and for lung cancer patients 39-79 years.Pre-treatment serum samples were prepared immediately after collection and stored at -70'C before assay. IGF-I determinationsA radioimmunoassay (RIA) kit (Amersham International, Aylesbury, UK) and a somatomedin C (SM-C) immunoradiometric (IRMA) kit (Immunodiagnostics Ltd, Tyne and Wear, UK) were used for the quantitative measurement of IGF-I in conditioned media and serum samples. Recombinant human IGF-I was used as standards in both assays. The rabbit antiserum used in the competitive RIA was raised against a recombinant analogue of IGF-I, shows 100% cross-reactivity with human IGF-I and 0.5% crossreactivity with human IGF-II. Fifty per cent displacement of tracer occurs with insulin at 2,000 ftunits ml-' (normal range of insulin in fasting individuals is 4-30 gunits ml-' in serum). Phase separation was achieved using Amerlex-M donkey anti-rabbit reagent (Amersham UK). Assay sensitivity is 100pg per tube.The non-competitive SM-C IRMA employed a two site immunoradiometric assay. Briefly standards/samples were incubated simultaneously with a mouse monoclonal anti-SM-C lgG immobilised on the inside walls of test tubes and a '25I-labelled mouse monoclonal antibody directed against a second IGF-I epitope. Unbound materials were then removed by decanting and washing the tubes. The antisera show 3% cross-reactivity with IGF-II and did not cross-react at all with insulin or pro-insulin. The lowest detectable level of SM-C that could be distinguished from the zero standard was 8 mU ml' at the 95% confidence limit.To separate binding protein from IGF-I, serum samples and cell conditioned media were extracted by incubation in 50 of acid extraction solution (supplied by Immunodiagnostics Ltd) for 10min at room temperature. Neutralising solution (500pl) (supplied by Immunodiagnostics Ltd) was then added to each sample. This extraction procedure yields aproximately 100% recovery of SM-C in patient samples. The neutralised, extracted conditioned media and serum samples, and unextracted serum samples were then used in the Amersham RIA and the IRMA.

Elevated serum levels of IGFBP-2 found in children suffering from acute leukaemia is accompanied by the occurrence of IGFBP-2 mRNA in the tumour clone

“…This finding is in accordance with other reports describing elevated IGFBP-2 levels in various malignant diseases, such as prostate cancer (Kanety et al, 1993), Wilms' tumour (Zumkeller et al, 1993) and lung cancer (Reeve and Payne, 1990). Whereas the stimulation of cell proliferation by IGFs is well established (Camacho-Hubner et al, 1991;Jones and Clemmons, 1995) the functions of IGFBP-2 on tumour and normal cells are still unknown.…”

Serum insulin-like growth factor binding protein-2 levels as an indicator of functional ability in elderly men

“…As IGFBP-2 concentrations have been reported to be elevated in patients with several malignant tumors (42,43), in particular prostate carcinoma (39), one might hypothesize that the association between IGFBP-2 and functional ability is dependent on the presence of prostate malignancies. However, even within the group of individuals with elevated PSA levels, there was no relation between IGFBP-2 and PSA, or other prostate abnormalities.…”

Serum-based protein biomarkers for detection of lung cancer

“…Macauly et al [142] measured serum IGF-I concentrations in 42 SCLC patients and concluded that IGF-I levels do not correlate with tumor bulk or with the therapeutic responsiveness of SCLC. Reeve et al [143] observed that IGFs were highly upregulated in the sera of SCLC as well as NSCLC patients and the levels of these proteins in blood correlate with course of treatment in such patients. Further studies are needed for better evaluation of these substances.…”