Cytotoxic chemotherapy targets elements common to all nucleated human cells, such as DNA and microtubules, yet it selectively kills tumor cells. Here we show that clinical response to these drugs correlates with, and may be partially governed by, the pre-treatment proximity of tumor cell mitochondria to the apoptotic threshold, a property called mitochondrial priming. We used BH3 profiling to measure priming in tumor cells from patients with multiple myeloma, acute myelogenous and lymphoblastic leukemia, and ovarian cancer. This assay measures mitochondrial response to peptides derived from pro-apoptotic BH3 domains of proteins critical for death signaling to mitochondria. Patients with highly primed cancers exhibited superior clinical response to chemotherapy. In contrast, chemoresistant cancers and normal tissues were poorly primed. Manipulation of mitochondrial priming might enhance the efficacy of cytotoxic agents.

Cancer cells exhibit many abnormal phenotypes that induce apoptotic signaling via the intrinsic, or mitochondrial, pathway. That cancer cells nonetheless survive implies that they select for blocks in apoptosis. Identifying cancer-specific apoptotic blocks is necessary to rationally target them. Using a panel of 18 lymphoma cell lines, we show that a strategy we have developed, BH3 profiling, can identify apoptotic defects in cancer cells and separate them into three main classes based on position in the apoptotic pathway. BH3 profiling identifies cells that require BCL-2 for survival and predicts sensitivity to the BCL-2 antagonist ABT-737. BCL-2 dependence correlates with high levels of proapoptotic BIM sequestered by BCL-2. Strikingly, BH3 profiling can also predict sensitivity to conventional chemotherapeutic agents like etoposide, vincristine, and adriamycin.

Numerous stressful conditions activate kinases that phosphorylate the alpha subunit of translation initiation factor 2 (eIF2␣), thus attenuating mRNA translation and activating a gene expression program known as the integrated stress response. It has been noted that conditions associated with eIF2␣ phosphorylation, notably accumulation of unfolded proteins in the endoplasmic reticulum (ER), or ER stress, are also associated with activation of nuclear factor kappa B (NF-B) and that eIF2␣ phosphorylation is required for NF-B activation by ER stress. We have used a pharmacologically activable version of pancreatic ER kinase (PERK, an ER stress-responsive eIF2␣ kinase) to uncouple eIF2␣ phosphorylation from stress and found that phosphorylation of eIF2␣ is both necessary and sufficient to activate both NF-B DNA binding and an NF-B reporter gene. eIF2␣ phosphorylation-dependent NF-B activation correlated with decreased levels of the inhibitor IB␣ protein. Unlike canonical signaling pathways that promote IB␣ phosphorylation and degradation, eIF2␣ phosphorylation did not increase phosphorylated IB␣ levels or affect the stability of the protein. Pulse-chase labeling experiments indicate instead that repression of IB␣ translation plays an important role in NF-B activation in cells experiencing high levels of eIF2␣ phosphorylation. These studies suggest a direct role for eIF2␣ phosphorylation-dependent translational control in activating NF-B during ER stress.

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Introduction Recent studies have provided conflicting data regarding the role of dyslipidemia in amyotrophic lateral sclerosis (ALS). The aim of this study was to determine whether cholesterol level are an independent predictor of survival in ALS. Methods Cholesterol levels were measured in 427 ALS subjects from three clinical trial databases. Results The LDL/HDL ratio did not decrease over time, despite significant declines in body mass index (BMI), forced vital capacity (FVC), and ALSFRS-R. After adjusting for BMI, FVC, and age, the lipid ratio was not associated with survival. There was a “U”-shaped association between BMI and mortality, with the highest survival at 30–35 kg/m2. The adjusted hazard ratio for the linear association between BMI and survival was 0.860 (95% CI 0.80–0.93, P = 0.0001). Conclusions We found that dyslipidemia is not an independent predictor of survival in ALS. BMI is an independent prognostic factor for survival after adjusting for markers of disease severity.

SUMMARY It is not understood why healthy tissues can exhibit varying levels of sensitivity to the same toxic stimuli. Using BH3 Profiling, we find that mitochondria of many adult somatic tissues, including brain, heart and kidneys, are profoundly refractory to pro-apoptotic signaling, leading to cellular resistance to cytotoxic chemotherapies and ionizing radiation. In contrast, mitochondria from these tissues in young mice and humans are primed for apoptosis, predisposing them to undergo cell death in response to genotoxic damage. While expression of the apoptotic protein machinery is nearly absent by adulthood, in young tissues its expression is driven by c-Myc, linking developmental growth to cell death. These differences may explain why pediatric cancer patients have a higher risk of developing treatment-associated toxicities.

These results provide a mechanism for translation inhibition by UV irradiation and identify a hitherto unrecognized role for mammalian GCN2 as a mediator of the cellular response to UV stress.

• Venetoclax potently induces rapid onset apoptosis of CLL cells in vitro and in vivo, independently of TP53 function.• Objective responses in patients with del(17p) and/or TP53-mutated CLL are as deep as patients with no perturbation of TP53.BCL2 blunts activation of the mitochondrial pathway to apoptosis, and high-level expression is required for chronic lymphocytic leukemia (CLL) survival. Venetoclax (ABT-199) is a small-molecule selective inhibitor of BCL2 currently in clinical trials for CLL and other malignancies. In conjunction with the phase 1 first-in-human clinical trial of venetoclax in patients with relapsed or refractory CLL (M12-175), we investigated the mechanism of action of venetoclax in vivo, explored whether in vitro sensitivity assays or BH3 profiling correlated with in vivo responses in patients, and determined whether loss of TP53 function affected responses in vitro and in vivo. In all samples tested, venetoclax induced death of CLL cells in vitro at concentrations achievable in vivo, with cell death evident within 4 hours. Apoptotic CLL cells were detected in vivo 6 or 24 hours after a single 20-mg or 50-mg dose in some patients. The extent of mitochondrial depolarization by a BIM BH3 peptide in vitro was correlated with percentage reduction of CLL in the blood and bone marrow in vivo, whereas the half lethal concentration derived from standard cytotoxicity assays was not. CLL cell death in vitro and the depth of clinical responses were independent of deletion of chromosome 17p, TP53 mutation, and TP53 function. These data provide direct evidence that venetoclax kills CLL cells in a TP53-independent fashion by inhibition of BCL2 in patients and support further assessment of BH3 profiling as a predictive biomarker for this drug. (Blood. 2016;127(25):3215-3224)