Patterns of cell death have been divided into apoptosis, which is actively executed by specific proteases, the caspases, and accidental necrosis. However, there is now accumulating evidence indicating that cell death can occur in a programmed fashion but in complete absence and independent of caspase activation. Alternative models of programmed cell death (PCD) have therefore been proposed, including autophagy, paraptosis, mitotic catastrophe, and the descriptive model of apoptosis-like and necrosis-like PCD. Caspase-independent cell death pathways are important safeguard mechanisms to protect the organism against unwanted and potential harmful cells when caspase-mediated routes fail but can also be triggered in response to cytotoxic agents or other death stimuli. As in apoptosis, the mitochondrion can play a key role but also other organelles such as lysosomes and the endoplasmic reticulum have an important function in the release and activation of death factors such as cathepsins, calpains, and other proteases. Here we review the various models of PCD and their death pathways at molecular and organelle level and discuss the relevance of the growing knowledge of caspase-independent cell death pathways for cancer.

Purpose: Epigenetic modifications may contribute to the development and progression of cancer. We investigated whether epigenetic changes involving multiple histones influence prognosis of non–small-cell lung cancer (NSCLC) patients. Patients and Methods: We used immunohistochemistry to assess histone 3 lysine 4 dimethylation (H3K4diMe), and acetylation of histone 2A lysine 5 (H2AK5Ac), histone 2B lysine 12, histone 3 lysine 9 (H3K9Ac), and histone 4 lysine 8 in resected tumor samples of 138 NSCLC patients. Data were analyzed using a recursive partitioning analysis (RPA). Results: The RPA classified the patients into seven distinct prognostic groups based on TNM stage (first node), histology, and histone modifications: H3K4diMe (< or ≥ 85% tumor cells), H3K9Ac (< or ≥ 68% tumor cells), and H2AK5Ac (< or ≥ 5% tumor cells). The seven groups were associated with significantly different disease-free (P < .0001) and overall survival (P < .0001). Interestingly, the four groups determined by stage I patients (below the first node) displayed dramatic differences in survival (median, 10 months in adenocarcinoma patients with H3K9Ac ≥ 68% v 147 months in nonadenocarcinoma patients with H3K4diMe ≥ 85%). A Cox model retained age and RPA groups as the sole independent factors significantly influencing overall survival. Conclusion: The prognostic influence of epigenetic changes involving multiple histones, in particular H2A and H3, is greater in early NSCLC, and evaluation of these changes may help in selecting early-stage NSCLC patients for adjuvant treatment. Our observations provide a rationale for the use of a combination of standard chemotherapy with drugs interacting with histone modifications, such as histone deacetylase inhibitors.

Initial response of small-cell lung cancer (SCLC) to chemotherapy is high, and recurrences occur frequently, leading to early death. This study investigated the prognostic value of circulating tumor cells (CTCs) in patients with SCLC and whether changes in CTCs can predict response to chemotherapy. In this multicenter prospective study, blood samples for CTC analysis were obtained from 59 patients with SCLC before, after one cycle, and at the end of chemotherapy. CTCs were measured using CellSearch^® systems. At baseline, lower numbers of CTCs were observed for 21 patients with limited SCLC (median = 6, range 0–220) compared with 38 patients with extensive stage (median = 63, range 0–14 040). Lack of measurable CTCs (27% of patients) was associated with prolonged survival (HR 3.4; P ≤ 0.001). CTCs decreased after one cycle of chemotherapy; this decrease was not associated with tumor response after four cycles of chemotherapy. CTC count after the first cycle of chemotherapy was the strongest predictor for overall survival (HR 5.7; 95% CI 1.7–18.9; P = 0.004). Absolute CTCs after one cycle of chemotherapy in patients with SCLC is the strongest predictor for response on chemotherapy and survival. Patients with low initial CTC numbers lived longer than those with higher CTCs.

Different molecular subtypes of glioblastoma (GBM) have been recently identified, of which the mesenchymal subtype is associated with worst prognoses. Here, we report that transforming growth factor-β (TGF-β) is able to induce a mesenchymal phenotype in GBM that involves activation of SMAD2 and ZEB1, a known transcriptional inducer of mesenchymal transition in epithelial cancers. TGF-β exposure of established and newly generated GBM cell lines was associated with morphological changes, enhanced mesenchymal marker expression, migration and invasion in vitro and in an orthotopic mouse model. TGF-β-induced mesenchymal differentiation and invasive behavior was prevented by chemical inhibition of TGF-β signaling as well as small interfering RNA (siRNA)-dependent silencing of ZEB1. Furthermore, TGF-β-responding and -nonresponding GBM neurospheres were identified in vitro. Interestingly, nonresponding cells displayed already high levels of pSMAD2 and ZEB1 that could not be suppressed by inhibition of TGF-β signaling, suggesting the involvement of yet unknown mechanisms. These different GBM neurospheres formed invasive tumors in mice as well as revealed mesenchymal marker expression in immunohistochemical analyses. Moreover, we also detected distinct zones with overlapping pSMAD2, elevated ZEB1 and mesenchymal marker expression in GBM patient material, suggestive of the induction of local, microenvironment-dependent mesenchymal differentiation. Overall, our findings indicate that GBM cells can acquire mesenchymal features associated with enhanced invasive potential following stimulation by secretory cytokines, such as TGF-β. This property of GBM contributes to heterogeneity in this tumor type and may blur the boundaries between the proposed transcriptional subtypes. Targeting TGF-β or downstream targets like ZEB1 might be of potential benefit in reducing the invasive phenotype of GBM in a subpopulation of patients.