The expression of matrix metalloproteinases (MMPs) plays crucial roles in cancer progression and metastasis. This study is to clarify whether MMP associates with radiation-accelerated pulmonary metastasis of Lewis lung carcinoma (LLC-LM) in C57BL/6 mouse model. By using in vitro matrigel-coated Boyden chamber invasion assay, non-cytotoxic dose of radiation (7.5 Gy) significantly enhanced LLC-LM cell invasiveness. Irradiated LLC-LM cells showed the increased intravasation capability in the chicken chorioallantoic membrane assay. To test MMP family protein gene expression in irradiated LLC-LM cells, MMP-9 gene expression was significantly enhanced in both transcriptional and translational levels, so was the enzyme activity in the culture supernatant. The use of anti-sense MMP-9 oligonucleotides significantly inhibited the in vitro radiation-enhanced invasiveness. With 1 x 106 MMP-9 RNAi stably transfected LLC-LM cells injected subcutaneously in the right thighs of C57BL/6 mice and irradiated to the primary tumor, the number of radiation-accelerated pulmonary metastases was significantly reduced (4.3 versus 23.0, p<0.001). The inhibitory effect of 1-benzyl-3-(5'-hydroxymethyl-2'-furyl) indazole (YC-1), through interrupting eIF-4E phosphorylation and MMP-9 expression, was shown on radiation-enhanced LLC cell invasiveness in vitro. YC-1 was further tested in the irradiated LLC-LM injected C57BL/6 mouse model for pulmonary metastasis. The number of radiation-accelerated pulmonary metastases was significantly reduced by pretreatment with YC-1 (daily dose of 10 mg/kg orally) starting 3 days before radiotherapy (1.6 versus 21.2, p<0.001). The serial urinary gelatin zymography demonstrated the therapeutic effect of YC-1 was likely to be through the inhibition of MMP-9 activity. We conclude that MMP-9 crucially involves the radiation-enhanced LLC-LM cell invasiveness in vitro and radiation-accelerated pulmonary metastasis in vivo.
98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA