In vitro and in vivo studies on the effects of bone morphogenetic protein-7 on human kidney and lung tumor cells

Abstract

Breast, kidney, lung, and prostate cancers are among the human cancers that show high propensity to form bone metastasis. Bone morphogenetic protein (BMP) -2 and -7 are two members of the BMP superfamily which show the most potent biological activity in stimulating bone differentiation and repair. These proteins have been used in clinical treatment of orthopedic diseases and have also been studied in different types of cancer. We report here detection of mRNA coding for three type I and one type II BMP receptors in G-402 kidney tumor cells and A-549 lung tumor cells, suggesting that these cells are responsive to BMPs. We then observed that BMP-7 inhibited cell proliferation of both cell lines in a protein concentration dependent manner in vitro. Additionally, when BMP-7-treated cells were implanted into the flank region of male nude mice, smaller tumors, compared to those formed with the untreated cells, were observed. Histological analysis showed that the masses formed at the site of implantation displayed significantly less number of tumors than the control and exhibited significant ectopic bone formation. These findings raise the possibility of BMP-7 as a therapeutic agent for kidney and lung cancers.

Keywords: BMP receptors; BMP-7; cell proliferation; human kidney and lung tumor cell lines; tumor growth in vivo.

Figure 1

Messenger RNA expression of BMP receptors in kidney G-402 and lung A-549 cells in culture. Total RNA was isolated from cells and the levels of mRNA coding for the different BMP receptors were determined by Northern blot analysis. (A) Representative autoradiogram of Northern blots; (B) Quantitative values of ActR-I, BMPR-IA, -IB, and –II. Values represent the mean ± SD of 4 independent measurements.

Figure 2

Effects of BMP-7 on thymidine incorporation in G-402 (●) and A-549 (■) in culture. Cell cultures were treated with different concentrations of BMP-7 for 18 h and 6 additional hour in the presence of [³H]thymidine. Level of radioactivity incorporated into TCA insoluble materials was measured and normalized to the vehicle-treated control experiment. Values represent mean±SD of 4 independent determinations.

Figure 3

Sections from subcutaneous mass in the flank of nude mouse implanted with tumor cells G-402 or A-549 were stained with Hematoxylin and Eosin. Representative photographs of the sections are shown (200X magnification). (A) implanted with G-402, section contained neoplastic renal leiomyosarcoma cells; (B) implanted with G-402 treated BMP-7, mass comprised mainly of bone, bone marrow and foci of tumor cells; (C) implanted with A-549 cells, section contained neoplastic bronchiolar epithelial cells; (D) implanted with A-549 cells treated BMP-7, section showed neoplastic bronchiolar epithelial cells containing a focus of bone.