Non small cell lung carcinoma (NSCLC) is a highly lethal malignancy that often becomes resistant to chemotherapy. To determine whether alterations in apoptotic signaling might contribute to such resistance, we established in vitro and in vivo models for sensitive and resistant human NSCLC. We found that resistance is due to multiple defects found in expression of CD95-L, CD95 and members of the Bcl-2 and IAP family, as well as caspase-8, -9 and -3 as examined by immunohistochemistry, Western blot analysis, gene array analysis and functional assays. Failure to activate death receptor, as well as mitochondrial apoptosis signaling, points to a central role of caspases. To restore apoptosis signaling we transfected NSCLC xenografts on nude mice with caspase-8 and -9. This treatment strongly induced apoptosis per se and sensitized the tumors to cisplatin-induced cell death. Thus, these findings indicate that re-expression of caspases might be an effective strategy to restore sensitivity for chemotherapy in NSCLC in vivo. © The most common cancer in the world today is lung cancer, with a mortality rate of more than 90%, and its incidence continues to rise worldwide. 1 Lung cancer is classified clinically into 2 major histologic types, small cell lung cancer (SCLC), which accounts for approximately 25% of cases, and non small cell lung cancer (NSCLC), which accounts for the remaining 75%, usually associated with poor prognosis. 2 NSCLC is normally sensitive to the first cycle of chemotherapy. However, in almost all patients chemotherapy-resistant NSCLC cells are selected, which resist further chemotherapy leading to rapid death of the respective patient. 3,4 Besides physiologic factors, such as pharmacokinetics, drug metabolism, drug delivery, drug location and tumor size, resistance has also been associated with decreased susceptibility to apoptosis. [5][6][7] Identifying the molecular determinants of apoptosis sensitivity and resistance to chemotherapy in NSCLC as well as in other solid tumor types may help improve its efficacy.Apoptosis is a physiologic mode of cell death that can be induced by adverse conditions, such as cellular stress, crosslinking of death receptors and exposure to anticancer agents. Apoptosis signaling converges in the activation of initiator caspases (procaspase-8, -9, -10), which leads to the proteolytic activation of downstream effector caspases (caspase-3, -6, -7) that cleave specific substrates. 8 -10 Two independent initiator pathways perform their action immediately upstream of these effector events: cross-linking of death receptors by their ligands and the release of apoptogenic factors from mitochondria. 10 -12 Chemotherapeutic agents and ␥-irradiation facilitate opening of the mitochondrial permeability transition pore and release of pro-apoptotic molecules such as cytochrome c. These molecules together with Apaf-1 and procaspase-9 form a holoenzyme complex termed "apoptosome." Caspase-9 in combination with this holoenzyme activates downstream caspases, which results in DNA fragmen...

The human leukemic T-cell line Jurkat was used to define the role of the cellular stress pathway with its key player kinase JNK in cancer therapy-induced apoptosis. JNK activity was inhibited by stable transfection with a dominant negative mutant of the upstream kinase JNKK/MKK4 or with the novel, potent and selective JNK1, -2 and -3 inhibitor SP600125. Inhibition of JNK activity delayed the onset of apoptosis induced by cisplatin, doxorubicin, ␥-irradiation and CD95-L but did not prevent apoptosis per se. Early events during apoptosis such as induction of CD95-L, activation of caspase-8 and exposure of phosphatidylserine on the cell surface were strongly inhibited. Also, at early time points of apoptosis, loss of the mitochondrial membrane potential and release of cytochrome c were markedly impaired. However, late signaling events during apoptosis such as cleavage of PARP and DNA fragmentation apoptosis were only marginally affected. These findings are in accordance with the activity of initiator and effector caspases. Whereas activity of the initiator caspase-8 was strongly inhibited early and late after induction, an inhibition of caspase-3 activity was only observed early after induction of apoptosis. We therefore suggest that cellular stress signaling contributes to the initiation of apoptosis, whereas it might be dispensable for the progression of apoptosis. Dysfunction of this pathway under pathological conditions might contribute to therapy resistance of cancer cells.