Email updates

Keep up to date with the latest news and content from Radiation Oncology and BioMed Central.

Open Access Research

Preclinical evaluation of sunitinib, a multi-tyrosine kinase inhibitor, as a radiosensitizer for human prostate cancer

Colin Brooks14, Tommy Sheu1, Kathleen Bridges1, Kathy Mason1, Deborah Kuban2, Paul Mathew3 and Raymond Meyn1*

Author Affiliations

1 Department of Experimental Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA

2 Department of Radiation Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, USA

3 Department of Hematology-Oncology, Tufts Medical Center, Boston, MA, USA

4 National University of Galway (NUIGalway), Galway, Ireland

For all author emails, please log on.

Radiation Oncology 2012, 7:154  doi:10.1186/1748-717X-7-154

Published: 11 September 2012

Abstract

Background

Many prostate cancers demonstrate an increased expression of growth factor receptors such as vascular endothelial growth factor receptor (VEGFR) and platelet derived growth factor receptor (PDGFR) which have been correlated with increased resistance to radiotherapy and poor prognosis in other tumors. Therefore, response to radiation could potentially be improved by using inhibitors of these abnormally activated pathways. We have investigated the radiosensitizing effects of sunitinib, a potent, multi-tyrosine kinase inhibitor of the VEGFR and PDGFR receptors, on human prostate cancer cells.

Methods

The radiosensitizing effects of sunitinib were assessed on human prostate cancer cell lines DU145, PC3 and LNCaP by clonogenic assay. Sunitinib’s ability to inhibit the activities of its key targets was determined by immunoblot analysis. The radiosensitizing effects of sunitinib in vivo were tested on human tumor xenografts growing in nude mice where response was assessed by tumor growth delay.

Results

Clonogenic survival curve assays for both DU145 and PC3 cells showed that the surviving fraction at 2 Gy was reduced from 0.70 and 0.52 in controls to 0.44 and 0.38, respectively, by a 24 hr pretreatment with 100 nM sunitinib. LNCaP cells were not radiosensitized by sunitinib. Dose dependent decreases in VEGFR and PDGFR activation were also observed following sunitinib in both DU145 and PC3 cells. We assessed the ability of sunitinib to radiosensitize PC3 xenograft tumors growing in the hind limb of nude mice. Sunitinib given concurrently with radiation did not prolong tumor growth delay. However, when animals were treated with sunitinib commencing the day after fractionated radiation was complete, tumor growth delay was enhanced compared to radiation alone.

Conclusions

We conclude, based on the in vivo results, that sunitinib and radiation do not interact directly to radiosensitize the PC3 tumor cells in vivo as they did in vitro. The fact that tumor growth delay was enhanced when sunitinib was given after radiotherapy was completed suggests that sunitinib may be acting on the irradiated tumor stroma and suppressing its ability to sustain regrowth of the irradiated tumor. Based on these preclinical findings, we suggest that the combination of sunitinib and radiation for the treatment of prostate cancer deserves further development.

Keywords:
Sunitinib; Combinational therapy; Targeted therapy; Prostate cancer; Tyrosine kinase inhibitor; Radiation