Endocrine Abstracts

Malignant pleural mesothelioma (MPM) is an asbestos-related tumour which is highly resistant to standard treatments, thus continuing to present a therapeutically challenge. Insulin-like growth factor system (IGFs), play an important role in the regulation of solid tumour cell growth. IGFBP-3, the most abundant circulating IGF binding protein, inhibits cell growth by both IGF-I dependent and independent pathways.

The aim of our study was to evaluate the effects of rhIGFBP-3 treatment in regulating MPM cell growth in vitro.

Methods

Two MPM cells (NCI-H28 and NCI-H2052) were used. Western ligand, immunoblot analysis and PCR methods were performed to characterise the various components of the IGF system. Cell proliferation was determined by a colorimetric MTS assay, anchorage-independent growth was examined in a methylcellulose-based clonogenic assay and cytotoxicity effect of rhIGFBP-3 was assessed by clonogenic assay using crystal violet staining. Cells were treated with rhIGF-I (50–100 ng/ml), rhIGFBP-3 (0.5, 1 and 5 μg/ml) and des-IGF-I (100 ng/ml) for 24 hrs, alone or in combination.

Results

MPM cell lines express IGFBP-2, -3, and -5, IGF-I and IGF-II mRNA and secrete IGFBP-3 and IGFBP-2 in conditioned medium. RhIGF-I and des-IGF-I treatment increased MPM cell proliferation by 61% and 49%, respectively compared to serum free media (SFM, P<0.05). In contrast, rhIGFBP-3 treatment significantly decreased proliferation in NCI-H2052 cells (12%). One of the best indicators of tumorigenicity in vitro is the anchorage independence of tumour cells, which was examined using methylcellulose assay. Treatment of cells with rhIGFBP-3 markedly decreased colony formation in both MPM cell lines. We have also showed that in NCI-H2052 cell lines colony formation was significantly decreased with rhIGFBP-3 (1 μg/ml) by 30% and in NCI-H28 cell lines by 52% compared to non treated cells.

In conclusion, rhIGFBP-3 decreased proliferation and tumorigenicity in MPM cells in vitro.