Tumor cell-protective catalase as a novel target for rational therapeutic approaches based on specific intercellular ROS signaling.

Reactive oxygen species (ROS) exhibit procarcinogenic effects at multiple stages during multistep oncogenesis. As a hallmark of the transformed state, extracellular superoxide anions generated by NADPH oxidase1 (NOX1) are centrally involved in the control of the transformed state. These pro-carcinogenic effects of ROS are counterbalanced by specific ROS-dependent apoptosis induction in malignant cells, based on four interconnected signaling pathways. Tumor progression selects for a phenotype characterized by resistance to ROS-dependent apoptotic signaling. Resistance is based on membrane-associated catalase in tumor cells, which therefore represents a promising and unique target for specific tumor therapy. Novel approache, developed in vitro, utilize antibody-mediated inhibition of catalase or ROS-driven singlet oxygen generation and subsequent inactivation of tumor cell catalase as initial steps. As a consecutive step, malignant cell-generated superoxide anions then drive apoptotic signaling with high selectivity for malignant cells. We propose to translate this complex but well-established ROS-dependent signaling chemistry into novel approaches for experimental therapy in vivo.