Topoisomerase I inhibitors in the combined-modality therapy of lung cancer.

Locally advanced non-small-cell lung cancer represents 30% to 40% of all pulmonary malignancies. Most patients will die of the disease after aggressive contemporary treatments. Therefore, significant improvement in therapeutic methods must be implemented to improve overall survival rates. The arrival of a new generation of chemotherapeutic agents--including the taxanes, gemcitabine (Gemzar), and topoisomerase inhibitors such as irinotecan (Camptosar) and topotecan (Hycamtin)--offers the hope of significant advances in the treatment of lung cancer. Irinotecan and topotecan are camptothecin derivatives that inhibit topoisomerase I enzyme. It is believed that topoisomerase I inhibitors stabilize a DNA/topoisomerase I complex and interact with replication machinery to cause cell death. A significant amount of data demonstrates that these topoisomerase I inhibitors also act as radiosensitizers. With the increasing data that support concurrent chemoradiation treatment for malignancies, including lung cancer and head and neck cancers, there is an impetus to pursue the additional drugs that may potentially improve local control and survival. Irinotecan is undergoing early clinical trials in the combined-modality setting in several different disease sites. This paper will review the data on the role of camptothecin derivatives as a radiosensitizer and as a component of combined-modality therapy for lung cancer. It is hoped that newer treatment strategies, like the combination of radiation and topoisomerase I inhibitors, will have a significant impact on cure rates in the future.