We therefore investigated whether the CPT and NPOA cotreatment increased proapoptotic proteins of H1299 cells, including Bax, cleaved caspase 9 and cleaved caspase 3, and mitochondrial depolarization (Figure 3), suggesting that Bax may play a role in contributing to the synergism of CPT and NPOA combination, and the low cytotoxicity of NPOA could be a promising chemosensitizer of CPT-based lung cancer treatment. Here, CASP9 is linked to lung cancer.