Purpose: Novel strategies are needed to prevent the high mortality rates of several types of cancer. These high rates stem from tumor resistance to radiation therapy, which is thought to result from the induction of matrix metalloproteinases (MMP) and plasminogen activators. In the present study, we show that the modulation of MMP-9 expression, using adenoviral-mediated transfer of the antisense MMP-9 gene (MMP-9 adenoviral construct, Ad-MMP-9), affects breast cancer sensitivity to radiation.
Experimental design: In the present study, we used antisense Ad-MMP-9 to down-regulate the expression of MMP-9 in MDA MB 231 breast cancer cell lines in vitro before irradiation and subsequently incubated cells in hypoxic condition. In vivo studies were done with orthotopic breast tumors, and radiosensitivity was evaluated both in vitro and in vivo.
Results: Ad-MMP-9 infection resulted in down-regulation of radiation-induced levels of hypoxia-inducible factor 1 alpha and MMP-9 under hypoxic conditions in MDA MB 231 breast cancer cells. In addition, Ad-MMP-9, in combination with radiation, decreased levels of the transcription factors nuclear factor-kappaB and activator protein 1, both of which contribute to the radioresistance of breast tumors. Finally, the triggering of the Fas-Fas ligand apoptotic cascade, which resulted in the cleavage of PARP-1 and caspase-10, caspase-3, and caspase-7, signifies the efficiency of combined treatment of Ad-MMP-9 and radiation. Treatment with Ad-MMP-9 plus radiation completely regressed tumor growth in orthotopic breast cancer model.
Conclusions: In summary, integrating gene therapy (adenovirus-mediated inhibition of MMP-9) with radiotherapy could have a synergistic effect, thereby improving the survival of patients with breast cancer.