The inhibitory effect of cisplatin in combination with irradiation on lungtumor cell growth is due to induction of tumor cell apoptosis

Chemoradiation is becoming an important method of treatment of advanced lun g cancer. Although many studies have demonstrated the efficacy of chemoradi ation against lung tumors, the mechanism of its effect is still poorly unde rstood. In this study, we analyzed the combined effect of cisplatin (CDDP) and irradiation on human lung cancer cell lines (PC-9 and Lu 134A) in vitro using MTT assay and isobologrnm analysis. To study whether the combined ef fect is due to induction of tumor cell apoptosis, we further quantified the nuclear fragmentation of tumor cells by flow cytometric analysis. Our stud y revealed that a combination of cisplatin and irradiation had an additive inhibitory effect on both PC-9 (adenocarcinoma) and Lu 134A (small cell car cinoma) tumor cell growth. Cisplatin improved the sensitivity of tumor cell s to irradiation. The use of both cisplatin and irradiation doses could be reduced without decreasing the inhibitory effect. The additive inhibitory e ffect was correlated positively with the levels of tumor cell nuclear fragm entation. We concluded that combination treatment with cisplatin and irradi ation is effective against lung tumors, not only small cell carcinoma but a lso non-small cell carcinoma, and the inhibitory effect was due to inductio n of tumor cell apoptosis.