This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Pinski, J. Articles by Isaacs, J. T. Search for Related Content PubMed PubMed Citation Articles by Pinski, J. Articles by Isaacs, J. T.

Trk Receptor Inhibition Induces Apoptosis of Proliferating but not Quiescent Human Osteoblasts¹

Johns Hopkins Oncology Center, Baltimore, Maryland 21231-1000

Prostate cancer frequently metastasizes to the skeleton, producing painful osteoblastic lesions, which are associated with significant morbidity and mortality. This bone tropism involves the bidirectional paracrine interactions between prostate cancer cells and osteoblasts. These interactions enhance prostate cancer cell survival and proliferation of osteoblasts. Therefore, agents that can induce apoptosis of prostate cancer cells and proliferating osteoblasts would be highly advantageous. Previously, we have documented that the unique survival pathway for prostate cancer cells involves a neurotrophin/Trk receptor autocrine pathway. The indocarbazole compounds, CEP-701 and CEP-751, are potent inhibitor of this Trk receptor survival signaling and thus selectively induces apoptosis of prostate cancer cells in various in vitro and in vivo models. In this study, we documented the effects of CEP-751 on the conditionally immortalized osteoblastic cell line, hFOB, in vitro. At the permissive temperature of 34°C, these cells express large T antigen, inducing their continuous proliferation, whereas at 39°C, T antigen is degraded and the cells stop proliferating without undergoing apoptosis. Trk receptors are expressed in hFOB cells, as determined both by reverse transcription-PCR and Western blots. These osteoblasts were shown to produce nerve growth factor and brain-derived neurotrophic factor but not neurotrophin-3, as measured by ELISA. hFOB osteoblasts, cultured at 34°C, secreted significantly (P < 0.01) more brain-derived neurotrophic factor and nerve growth factor into the medium than hFOB cells cultured at 39°C. Because the Trk/neurotrophin axis is present in both proliferating and quiescent (i.e., nonproliferating) osteoblasts, the effects of 48 h of exposure to various doses of CEP-751 on cell viability and apoptosis of hFOB cells were assessed by trypan blue exclusion assays and 4',6-diamidino-2-phenylindole nuclear staining. Cell viability and apoptosis of hFOB cells at 34°C were significantly and dose-dependently decreased compared with untreated proliferating cells. In contrast, even the highest concentration of CEP-751 (200 nM) did not affect cell viability and apoptosis of quiescent hFOB cells cultured at 39°C. This trk inhibition-induced cytotoxicity was confirmed using early-passage, proliferating normal (i.e., non-SV40-transformed) human osteoblasts, which also express Trk receptor protein. These combined results demonstrate that proliferating osteoblasts acquire a sensitivity to trk inhibition- induced apoptosis not shared with normally quiescent osteoblasts.

This article has been cited by other articles:

				S. R. Denmeade, C. M. Jakobsen, S. Janssen, S. R. Khan, E. S. Garrett, H. Lilja, S. B. Christensen, and J. T. Isaacs Prostate-Specific Antigen-Activated Thapsigargin Prodrug as Targeted Therapy for Prostate Cancer J Natl Cancer Inst, July 2, 2003; 95(13): 990 - 1000. [Abstract] [Full Text] [PDF]