Simultaneous quantitation of topoisomerase II alpha and beta isoform mRNAsin lung tumor cells and normal and malignant lung tissue

Certain drugs used in the treatment of lung cancer and other human malignan cies are cytotoxic because of their ability to interact with the two isofor ms of topoisomerase It (topo II), topo II alpha and topo II beta. As part o f an effort to evaluate the contribution of topo II alterations to drug sen sitivity and resistance in lung cancer, we have developed a semi-quantitati ve reverse transcriptase-polymerase chain reaction (RT-PCR) assay to measur e levels of topo II alpha and beta mRNAs simultaneously using a single pair of primers with sequences common to both isoforms. The PGR products derive d from the topo II alpha and beta mRNAs are both 446 bp but have different electrophoretic mobilities in a nondenaturing polyacrylamide gel, allowing sensitive, rapid quantitation when the products are radiotabeled with [S-35 ]-dATP. Using this RT-PCR method, poly(A+) RNA from 13 non-small cell lung cancer (NSCLC) cell lines was analyzed. The results obtained indicated that the cell lines express a wide range of topo II alpha mRNA levels (12-fold) and topo II beta mRNA levels (5.5-fold). Tumor and normal lung tissues fro m 25 patients with NSCLC were also examined. In the tumor samples, the leve ls of the topo II alpha and beta mRNAs were similar. However, mean topo II alpha mRNA levels in the tumors were approximately 7-fold higher than those of the paired normal lung tissues. In contrast, topo II beta mRNA levels w ere similar in both tumor and normal lung. Topo II alpha and beta mRNA reve ls were both significantly lower in the squamous cell tumors than in the ad enocarcinoma samples. Topo II beta mRNA levels in the squamous cell tumors were also significantly lower than those in paired normal lung tissue. The RT-PCR method described is reliable and convenient, and for the first time, makes the rapid simultaneous direct comparison of topo II alpha and topo I I beta mRNA levels feasible in targe numbers of clinical samples.