Non-apoptotic Mechanisms Research Articles

Pan-caspase peptide inhibitor to induce primary chronic lymphocytic leukemia (CLL) cell death through a non-apoptotic and non-necroptotic mechanism.

e13536 Background: It is thought that CLL cells are poised on the brink of apoptosis. Recent advances in the understanding of the balance of BCL2 family proteins in CLL biology have led to the deve...

Nonapoptotic and extracellular activity of granzyme B mediates resistance to regulatory T cell (Treg) suppression by HLA-DR-CD25hiCD127lo Tregs in multiple sclerosis and in response to IL-6.

In autoimmune patients, regulatory T cells (Tregs) are increasingly found to be unable to suppress patient-derived T cells, an outcome referred to as Treg resistance. In this study, we show that CD4 T cells from patients with multiple sclerosis resist suppression by patient-derived or healthy donor-derived ex vivo Tregs. Importantly, we report that granzyme B (GzmB) contributes to this Treg resistance via a novel, apoptosis-independent mechanism. We show that memory CD4(+)CD127(lo)FOXP3(+) Treg subsets do not express GzmB, whereas activated, nonregulatory CD4 T cells isolated from patients with multiple sclerosis express higher levels of GzmB than do cells from healthy donors. In contrast to the intracellular GzmB that mediates apoptosis, GzmB can be found in extracellular fluids where it is hypothesized to regulate other cellular processes. In this study, we show that providing extracellular GzmB strongly inhibits Treg suppression, without altering Treg viability. However, when GzmB and GzmB-specific inhibitor are both provided to the cocultures, Treg suppression occurs. Thus, these data suggest that a novel activity of extracellular GzmB is to regulate Treg suppression. Additionally, we find that the suppression-abrogating cytokine IL-6 augments GzmB expression by human CD4 T cells, and it inhibits Treg suppression via this nonapoptotic GzmB-mediated mechanism. Lastly, in examining the mechanism whereby GzmB inhibits Treg function, we show that extracellular GzmB reduces Treg expression of CD39 and programmed death ligand 1. Collectively, these data indicate that extracellular GzmB plays an unexpected, nonapoptotic role in regulating Treg suppression and suggest that inactivation of specifically the extracellular activity of GzmB may be an efficacious therapeutic in autoimmunity.

Adenovirus expressing dual c-Met-specific shRNA exhibits potent antitumor effect through autophagic cell death accompanied by senescence-like phenotypes in glioblastoma cells.

c-Met, a cognate receptor tyrosine kinase of hepatocyte growth factor, is overexpressed and/or mutated in number of tumors. Therefore, abrogation of c-Met signaling may serve as potential therapeutic targets. In this study, we generated Ads expressing single shRNA specific to c-Met (shMet) (dl/shMet4 and dl/shMet5) or dual shRNAs specific to c-Met (dl/shMet4+5); and examined the therapeutic potential of these newly engineered Ads in targeting c-Met, and delineated their mechanism of action in vitro and in vivo. Ads expressing shMet induced knock-down in c-Met, and phenotypically resulted in autophagy-like features including appearance of membranousvacuoles, formation of acidic vesicular organelles, and cleavage and recruitment of microtubule-associated protein1 light chain 3 to autophagosomes. Ads expressing shMet also suppressed Akt phosphorylation and increased number of senescence-related gene products including SM22, TGase II, and PAI-1. These changes resulted in inhibition of cell proliferation and G2/M arrest of U343 cells. In vivo, intratumoral injection with dl/shMet4+5 resulted in a significant reduction of tumor growth with corresponding increasing overall survival. Histopathological analysis of these treated tumors revealed that Atg5 was highly up-regulated, indicating the therapeutic induction of autophagy. In sum, these results reveal that autophagic cell death induced by shMet-expressing Ads provide a novel strategy for targeting c-Met-expressing tumors through non-apoptotic mechanism of cell death.

Effects of Chinese herbal medicine in combination with mitomycin C on gastric cancer cells.

Chinese herbal medicine (CHM) is frequently used by cancer patients in Chinese community. It remains largely unknown about the interaction between CHM and chemotherapeutic agents. Herein, we evaluated 3 commonly used CHM formulas for cancer patients: Bu-Zhong-Yi-Qi-Tang (BZYQT), Bao-Yuan-Tang (BYT), and Ju-Yuan-Jian (JYJ). We examined the effects of these 3 formulas in human gastric cancer cells MKN-74, in terms of cytotoxicity and apoptosis induction when used alone or in combination with mitomycin C (MMC). Cytotoxicity was determined by tetrazolium dye colorimetric assay. The 10% inhibitory concentration of CHM was used in this study. Cells were first exposed to CHM or phosphate buffered saline (as control) for 48 h. Then MMC at final concentration of 0.25 μg/ml was added to media for another 24-h. Among these 3 CHM formulas, BZYQT showed the most pronounced effect in augmenting MMC-induced cytotoxicity. The viability of MKN-74 cells was decreased to 43.1% when treated with BZYQT and MMC, compared to 94.9% with MMC alone. We subsequently examined apoptosis induction by quantitative florescent microscopy and single-strand DNA enzyme-linked immunosorbent assay, and found BZYQT did not enhance MMC-induced apoptosis. Our findings indicate BZYQT in combination with MMC induces cell death in gastric cancer cells via non-apoptotic mechanism. Our results provide a rationale for further investigation in the interaction of CHM and anti-cancer treatment.

The small molecule C-6 is selectively cytotoxic against breast cancer cells and its biological action is characterized by mitochondrial defects and endoplasmic reticulum stress.

IntroductionThe establishment of drug resistance following treatment with chemotherapeutics is strongly associated with poor clinical outcome in patients, and drugs that target chemoresistant tumors have the potential to increase patient survival. In an effort to identify biological pathways of chemoresistant breast cancers that can be targeted therapeutically, a small molecule screen utilizing metastatic patient-derived breast cancer cells was conducted; from this previous report, the cytotoxic small molecule, C-6, was identified for its ability to selectively kill aggressive breast cancer cells in a caspase-independent manner. Here, we describe the cellular and molecular pathways induced following C-6 treatment in both normal and breast cancer cell lines.MethodsTranscriptome analyses and protein expression experiments were used to measure endoplasmic reticulum (ER) stress following C-6 treatment. Studies utilizing transmission electron microscopy and metabolomic profiling were conducted to characterize mitochondrial morphology and function in C-6-treated cells. Oxygen consumption rates and oxidative stress were also measured in breast cancer and normal mammary epithelial cells following treatment with the small molecule. Finally, structural modifications were made to the molecule and potency and cancer selectivity were evaluated.ResultsTreatment with C-6 resulted in ER stress in both breast cancer cells and normal mammary epithelial cells. Gross morphological defects were observed in the mitochondria and these aberrations were associated with metabolic imbalances and a diminished capacity for respiration. Following treatment with C-6, oxidative stress was observed in three breast cancer cell lines but not in normal mammary epithelial cells. Finally, synthetic modifications made to the small molecule resulted in the identification of the structural components that contribute to C-6’s cancer-selective phenotype.ConclusionsThe data reported here implicate mitochondrial and ER stress as a component of C-6’s biological activity and provide insight into non-apoptotic cell death mechanisms; targeting biological pathways that induce mitochondrial dysfunction and ER stress may offer new strategies for the development of therapeutics that are effective against chemoresistant breast cancers.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-014-0472-0) contains supplementary material, which is available to authorized users.

Identification of a common non-apoptotic cell death mechanism in hereditary retinal degeneration.

Cell death in neurodegenerative diseases is often thought to be governed by apoptosis; however, an increasing body of evidence suggests the involvement of alternative cell death mechanisms in neuronal degeneration. We studied retinal neurodegeneration using 10 different animal models, covering all major groups of hereditary human blindness (rd1, rd2, rd10, Cngb1 KO, Rho KO, S334ter, P23H, Cnga3 KO, cpfl1, Rpe65 KO), by investigating metabolic processes relevant for different forms of cell death. We show that apoptosis plays only a minor role in the inherited forms of retinal neurodegeneration studied, where instead, a non-apoptotic degenerative mechanism common to all mutants is of major importance. Hallmark features of this pathway are activation of histone deacetylase, poly-ADP-ribose-polymerase, and calpain, as well as accumulation of cyclic guanosine monophosphate and poly-ADP-ribose. Our work thus demonstrates the prevalence of alternative cell death mechanisms in inherited retinal degeneration and provides a rational basis for the design of mutation-independent treatments.

Role of RIP1 in physiological enterocyte turnover in mouse small intestine via nonapoptotic death.

Enterocyte shedding in the small intestine is often referred as an example of programmed cell death. However, little is known about the underlying mechanisms, although both apoptotic and nonapoptotic cell death have been suggested to play an important role. Here, we show by electron microscope that the majority of cells dying in the mouse small intestine do not display apoptotic characteristics. Chemical biological approach in vivo and in an organ culture showed that necrostatin-1 (Nec-1), an inhibitor of receptor-interacting protein 1 (RIP1, also called RIPK1), inhibited the shedding/nonapoptotic death of enterocyte, resulting in suppression of physiological enterocyte turnover. Moreover, RIP1 knockdown in vivo and RIP1 haploinsufficiency significantly suppressed physiological enterocyte turnover. Unlike Nec-1-sensitive (RIP1-dependent) cell death, so called necroptosis, which is also dependent on RIP3, physiological enterocyte turnover in RIP3-deficient mice was executed normally and still inhibited by Nec-1. As inhibition of the shedding/nonapoptotic death of enterocyte by Nec-1 resulted in suppression of crypt cell proliferation, the shedding process plays a dominant role over cell proliferation in maintaining homeostasis of enterocyte turnover. These results indicate that RIP1 plays a major role in physiological enterocyte turnover through a RIP3-independent nonapoptotic death mechanism in the mouse small intestine.

Autophagy and apoptosis in hepatocellular carcinoma induced by EF25-(GSH)2: a novel curcumin analog.

Curcumin, a spice component as well as a traditional Asian medicine, has been reported to inhibit proliferation of a variety of cancer cells but is limited in application due to its low potency and bioavailability. Here, we have assessed the therapeutic effects of a novel and water soluble curcumin analog, 3,5-bis(2-hydroxybenzylidene)tetrahydro-4H-pyran-4-one glutathione conjugate [EF25-(GSH)2], on hepatoma cells. Using the MTT and colony formation assays, we determined that EF25-(GSH)2 drastically inhibits the proliferation of hepatoma cell line HepG2 with minimal cytotoxicity for the immortalized human hepatic cell line HL-7702. Significantly, EF25-(GSH)2 suppressed growth of HepG2 xenografts in mice with no observed toxicity to the animals. Mechanistic investigation revealed that EF25-(GSH)2 induces autophagy by means of a biphasic mechanism. Low concentrations (<5 µmol/L) induced autophagy with reversible and moderate cytoplasmic vacuolization, while high concentrations (>10 µmol/L) triggered an arrested autophagy process with irreversible and extensive cytoplasmic vacuolization. Prolonged treatment with EF25-(GSH)2 induced cell death through both an apoptosis-dependent and a non-apoptotic mechanism. Chloroquine, a late stage inhibitor of autophagy which promoted cytoplasmic vacuolization, led to significantly enhanced apoptosis and cytotoxicity when combined with EF25-(GSH)2. Taken together, these data imply a fail-safe mechanism regulated by autophagy in the action of EF25-(GSH)2, suggesting the therapeutic potential of the novel curcumin analog against hepatocellular carcinoma (HCC), while offering a novel and effective combination strategy with chloroquine for the treatment of patients with HCC.

Human zygotes respond to sperm DNA damage by slowing DNA replication

OBJECTIVE: Some authors describe similar and high fertilization and pregnancy rates in non-obstructive azoospermia (NOA) patients whereas others report lower outcomes in NOA than in obstructive azoospermia (OA) patients. Sperm DNA damage is associated with reduced fertilization rates, embryo quality and pregnancy rates and higher rates of spontaneous miscarriage and childhood disease. Meanwhile, mouse zygotes respond to spermDNA damage through a non-apoptoticmechanism that acts by slowing paternal DNA replication and embryonic development. In this study, we compared the early development of embryos fertilized with NOA and OA spermatozoa by using time-lapse monitoring system. DESIGN: This is a retrospective study. MATERIALS AND METHODS: Six oocytes with ICSI using testicular spermatozoa from NOA and 35 oocytes with OA from 2013 to 2014 were used. The exact times for each embryo division and developmental parameters were calculated in hours after ICSI. Time-lapse images of each embryo were retrospectively analyzed by PrimoVision software. The developmental events observed in each embryo were at the time of the visibility of two pronuclei (2PN), syngamy, two cells and four cells. These parameters were compared between the NOA group and the OA group. RESULTS: The time of the visibility of 2PN in the NOA group (9.5 1.4 hours) was significantly earlier than that in the OA group (12.1 2.3 hours). However, the time from the visibility of 2PN to the syngamy in the NOA group (13.2 3.4 hours) was significantly longer than that in the OA group (10.6 2.7 hours). The time between the syngamy and the two cells in the NOA group (12.2 1.3 hours) was comparable with that in the OA group (16.6 10.2 hours). The time from the two cells to the four cells in the NOA group (13.5 3.5 hours) was also comparable with that in the OA group (10.0 4.2 hours). CONCLUSION: The time from the visibility of 2PN to the pronuclear fading (syngamy) after ICSI with testicular spermatozoa from NOAwas prolonged compared to that after ICSI with testicular spermatozoa from OA.

Cold atmospheric plasma treatment selectively targets head and neck squamous cell carcinoma cells.

The treatment of locoregional recurrence (LRR) of head and neck squamous cell carcinoma (HNSCC) often requires a combination of surgery, radiation therapy and/or chemotherapy. Survival outcomes are poor and the treatment outcomes are morbid. Cold atmospheric plasma (CAP) is an ionized gas produced at room temperature under laboratory conditions. We have previously demonstrated that treatment with a CAP jet device selectively targets cancer cells using in vitro melanoma and in vivo bladder cancer models. In the present study, we wished to examine CAP selectivity in HNSCC in vitro models, and to explore its potential for use as a minimally invasive surgical approach that allows for specific cancer cell or tumor tissue ablation without affecting the surrounding healthy cells and tissues. Four HNSCC cell lines (JHU-022, JHU-028, JHU-029, SCC25) and 2 normal oral cavity epithelial cell lines (OKF6 and NOKsi) were subjected to cold plasma treatment for durations of 10, 30 and 45 sec, and a helium flow of 20 l/min−1 for 10 sec was used as a positive treatment control. We showed that cold plasma selectively diminished HNSCC cell viability in a dose-response manner, as evidenced by MTT assays; the viability of the OKF6 cells was not affected by the cold plasma. The results of colony formation assays also revealed a cell-specific response to cold plasma application. Western blot analysis did not provide evidence that the cleavage of PARP occurred following cold plasma treatment. In conclusion, our results suggest that cold plasma application selectively impairs HNSCC cell lines through non-apoptotic mechanisms, while having a minimal effect on normal oral cavity epithelial cell lines.

Sorafenib in advanced hepatocellular carcinoma: current status and future perspectives.

The approval of sorafenib, a multikinase inhibitor targeting primarily Raf kinase and the vascular endothelial growth factor receptor, in 2007 for treating advanced hepatocellular carcinoma (HCC) has generated considerable enthusiasm in drug development for this difficult-to-treat disease. However, because several randomized Phase III studies testing new multikinase inhibitors failed, sorafenib remains the standard of first-line systemic therapy for patients with advanced HCC. Field practice studies worldwide have suggested that in daily practice, physicians are adopting either a preemptive dose modification or a ramp-up strategy to improve the compliance of their patients. In addition, accumulating data have suggested that patients with Child–Pugh class B liver function can tolerate sorafenib as well as patients with Child–Pugh class A liver function, although the actual benefit of sorafenib in patients with Child–Pugh class B liver function has yet to be confirmed. Whether sorafenib can be used as an adjunctive therapy to improve the outcomes of intermediate-stage HCC patients treated with transcatheter arterial chemoembolization or early-stage HCC patients after curative therapies is being investigated in several ongoing randomized Phase III studies. An increasing number of studies have reported that sorafenib exerts “off-target” effects, including the modulation of signaling pathways other than Raf/MEK/ERK pathway, nonapoptotic cell death mechanisms, and even immune modulation. Finally, although sorafenib in combination with chemotherapy or other targeted therapies has the potential to improve therapeutic efficacy in treating HCC, it also increases toxicity. Additional clinical studies are warranted to determine useful sorafenib-based combinations for the treatment of advanced HCC.

FADD regulates thymocyte development at the β-selection checkpoint by modulating Notch signaling.

Non-apoptotic functions of Fas-associated protein with death domain (FADD) have been implicated in T lineage lymphocytes, but the nature of FADD-dependent non-apoptotic mechanism in early T-cell development has not been completely elucidated. In this study, we show that tissue-specific deletion of FADD in immature (CD44–CD25+) thymocytes results in severe perturbation of αβ lineage development. Meanwhile, loss of FADD signaling at a later (CD44–CD25–) developmental stage does not affect subsequent T-cell development. Collectively, our work presents that FADD deficiency induces failed survival in double-negative 4 (DN4) cells, while pre-T-cell receptor (TCR) signal remains intact. In addition, Notch signaling is positive regulated on DN4 and double-positive thymocytes in T-cell-specific FADD-knockout mice, which express higher levels of a subset of Notch-target genes, including Hes1, Deltex1 and CD25. Moreover, a transcriptional repressor of Notch1, NKAP is downregulated coupled with the loss of FADD in thymocytes and is found to associate with FADD. These data suggest that as a death receptor, FADD is also required for cell survival in β-selection as a regulator of Notch1 expression.

Die another way--non-apoptotic mechanisms of cell death.

Regulated, programmed cell death is crucial for all multicellular organisms. Cell death is essential in many processes, including tissue sculpting during embryogenesis, development of the immune system and destruction of damaged cells. The best-studied form of programmed cell death is apoptosis, a process that requires activation of caspase proteases. Recently it has been appreciated that various non-apoptotic forms of cell death also exist, such as necroptosis and pyroptosis. These non-apoptotic cell death modalities can be either triggered independently of apoptosis or are engaged should apoptosis fail to execute. In this Commentary, we discuss several regulated non-apoptotic forms of cell death including necroptosis, autophagic cell death, pyroptosis and caspase-independent cell death. We outline what we know about their mechanism, potential roles in vivo and define outstanding questions. Finally, we review data arguing that the means by which a cell dies actually matters, focusing our discussion on inflammatory aspects of cell death.

AKT Inhibitors Promote Cell Death in Cervical Cancer through Disruption of mTOR Signaling and Glucose Uptake

BackgroundPI3K/AKT pathway alterations are associated with incomplete response to chemoradiation in human cervical cancer. This study was performed to test for mutations in the PI3K pathway and to evaluate the effects of AKT inhibitors on glucose uptake and cell viability.Experimental DesignMutational analysis of DNA from 140 pretreatment tumor biopsies and 8 human cervical cancer cell lines was performed. C33A cells (PIK3CAR88Q and PTENR233*) were treated with increasing concentrations of two allosteric AKT inhibitors (SC-66 and MK-2206) with or without the glucose analogue 2-deoxyglucose (2-DG). Cell viability and activation status of the AKT/mTOR pathway were determined in response to the treatment. Glucose uptake was evaluated by incubation with 18F-fluorodeoxyglucose (FDG). Cell migration was assessed by scratch assay.ResultsActivating PIK3CA (E545K, E542K) and inactivating PTEN (R233*) mutations were identified in human cervical cancer. SC-66 effectively inhibited AKT, mTOR and mTOR substrates in C33A cells. SC-66 inhibited glucose uptake via reduced delivery of Glut1 and Glut4 to the cell membrane. SC-66 (1 µg/ml-56%) and MK-2206 (30 µM-49%) treatment decreased cell viability through a non-apoptotic mechanism. Decreases in cell viability were enhanced when AKT inhibitors were combined with 2-DG. The scratch assay showed a substantial reduction in cell migration upon SC-66 treatment.ConclusionsThe mutational spectrum of the PI3K/AKT pathway in cervical cancer is complex. AKT inhibitors effectively block mTORC1/2, decrease glucose uptake, glycolysis, and decrease cell viability in vitro. These results suggest that AKT inhibitors may improve response to chemoradiation in cervical cancer.

Cytotoxic properties of d-gluco-, d-galacto- and d-manno-configured 2-amino-2-deoxy-glycerolipids against epithelial cancer cell lines and BT-474 breast cancer stem cells

Glycosylated antitumor ether lipids (GAELs) 6 and 7 containing a α- or β-d-gluco-configured 2-amino-2-deoxy (2-NH2-Glc) sugar moiety linked to a glycerolipid aglycone kill cancer cell lines via a non-apoptotic mechanism that could be exploited to kill cancer stem cells. To test this hypothesis and develop novel potent GAEL analogs, we synthesized GAELS which contain d-galacto- and d-manno-configured 2-amino-2-deoxy sugar moieties (2-NH2-Gal or 2-NH2-Man) and investigated their cytotoxicity against human epithelial cancer cell lines and cancer stem cells derived from BT-474 breast cancer cells. Within the class of d-galacto-configured GAELs, we prepared both O- and S-glycosidic linkages as well as their corresponding α- and β-anomers and screened against breast (BT-474, JIMT-1 and BT-549), pancreas (MiaPaCa2) and prostate cancer (DU145, PC3) cancer cell lines. The α-anomeric 2-NH2-Gal-based lipid 1 was the most active of all the compounds tested with CC50 values of 4.4–8 μM and is the most active GAEL synthesized to date. The β-anomer 2 was 4–>5-fold less active than 1. Replacement of the α-O-glycosidic by an α-S-glycosidic linkage resulted in a 2–4-fold reduction in activity, while the β-S-glycolipid 4 was inactive. In comparison, α-configured 2-NH2-Man-based glycerolipid 5 displayed very little activity with CC50 > 30 μM. The effect of the most active GAELs, 1, 6, or 7, on cancer stem cell viability revealed that all three inhibited the formation of tumorspheres from BT-474 cancer stem cell lines, caused the disintegration of preformed tumorspheres and resulted in total loss of cell viability of the cancer stem cells at concentrations of 20 μM. In contrast, the related antitumor ether lipid gold standard, edelfosine that is in clinical development was much less effective in preventing tumorsphere formation and affecting the viability of the cancer stem cells. Taken together our study demonstrates that α-GAEL anomers are more potent than their corresponding β-anomers and that the nature of the CHO moiety as well as the glycosidic bond significantly affects activity. The study also showed that GAELs are effective in killing CSCs while the apoptosis-inducing edelfosine is not.

Sodium iodate induced retinal degeneration: new insights from an old model.

Studies on the selective retinal degeneration induced by sodium iodate (NaIO3) date back to 1941; Sorsby (1941) described the effect of intravenously injected NaIO3 solution on the rabbit retina. Since then, NaIO3-induced retinal degeneration has been described in different mammalian species including sheep, rabbit, rat and mouse with varying doses and routes of administration. At the present time, the murine NaIO3 model is the most widely used because it results in reproducible, patchy retinal degeneration (Figure 1) and can be studied in a wide variety of wild type and genetic knockout strains. Many studies reporting the pathologic changes in retinal structure at specific time points and electrophysiological changes in retinal function over time have followed (Franco et al., 2009; Redfern et al., 2011). More recently, the model has gained a resurgence of interest because of the ability to utilize high resolution in vivo imaging to study structural changes in the retina in live animals. Techniques such as spectral domain optical coherence tomography (OCT) and confocal scanning laser ophthalmoscopy (cSLO) allow longitudinal evaluation of retinal structure (Machalinska et al., 2014; Yang et al., 2014); thus making this model amenable to evaluation of novel therapeutic approaches to retinal degeneration such as cellular therapies.

A novel small molecule that induces oxidative stress and selectively kills malignant cells

We have synthesized a novel molecule named XB05 (1-bromo-1,1-difluoro-non-2-yn-4-ol) and evaluated its effects in a variety of human cell lines. XB05 displayed potent antiproliferative activity against cell lines derived from leukemia or solid tumors, but had less effect on nonmalignant cells. To identify factors that contribute to the cancer selectivity of XB05, we chose three cell lines that had high sensitivity to XB05 (U937 leukemia), moderate sensitivity (A549 lung cancer), or low sensitivity (Hs27 nonmalignant skin fibroblasts), and proceeded to assess cell death and oxidative stress in these cells. XB05 was found to induce cell death via both apoptotic and nonapoptotic mechanisms in U937 and A549 cells, whereas it had no cytotoxicity against Hs27 cells at comparable concentrations. Treatment with XB05 caused an increase in reactive oxygen species in all cell lines tested, but levels were higher in malignant compared to nonmalignant cells. XB05 treatment also induced DNA damage exclusively in the malignant cells. Differences in antioxidant responses were observed between cell lines. For example, XB05 caused a decrease in levels of glutathione and nuclear Nrf2 in the most sensitive cells (U937), whereas the least sensitive cells (Hs27) displayed increased glutathione levels and no change in nuclear Nrf2. XB05 could react in vitro with cysteine and glutathione, but had much lower reactivity compared to typical thiol-reactive electrophiles, diethyl maleate and maleimide. In summary, XB05 is a novel compound that selectively kills malignant cells, most likely by disrupting cellular redox homeostasis, making it a promising candidate for development as a chemotherapeutic agent.

Destabilization of the Epidermal Growth Factor Receptor (EGFR) by a Peptide That Inhibits EGFR Binding to Heat Shock Protein 90 and Receptor Dimerization

An eight-amino acid segment is known to be responsible for the marked difference in the rates of degradation of the EGF receptor (ErbB1) and ErbB2 upon treatment of cells with the Hsp90 inhibitor geldanamycin. We have scrambled the first six amino acids of this segment of the EGF receptor (EGFR), which lies in close association with the ATP binding cleft and the dimerization face. Scrambling these six amino acids markedly reduces EGFR stability, EGF-stimulated receptor dimerization, and autophosphorylation activity. Two peptides were synthesized as follows: one containing the wild-type sequence of the eight-amino acid segment, which we call Disruptin; and one with the scrambled sequence. Disruptin inhibits Hsp90 binding to the EGFR and causes slow degradation of the EGFR in two EGFR-dependent cancer cell lines, whereas the scrambled peptide is inactive. This effect is specific for EGFR versus other Hsp90 client proteins. In the presence of EGF, Disruptin, but not the scrambled peptide, inhibits EGFR dimerization and causes rapid degradation of the EGFR. In contrast to the Hsp90 inhibitor geldanamycin, Disruptin inhibits cancer cell growth by a nonapoptotic mechanism. Disruptin provides proof of concept for the development of a new class of anti-tumor drugs that specifically cause EGFR degradation.

The σ2 Receptor: A Novel Protein for the Imaging and Treatment of Cancer

The σ2 receptor is an important target for the development of molecular probes in oncology because of its 10-fold higher density in proliferating tumor cells compared with that in quiescent tumor cells and because of the observation that σ2 receptor agonists are able to kill tumor cells via apoptotic and nonapoptotic mechanisms. Although recent evidence indicates that the σ2 receptor binding site is localized within the progesterone receptor membrane component 1 (PGRMC1), most information regarding this protein has been obtained using either radiolabeled or fluorescent receptor-based probes and from biochemical analysis of the effect of σ2 selective ligands on cells grown in culture. This article reviews the development of σ2 receptor ligands and presents an overview of how they have been used in vitro and in vivo to increase our understanding of the role of the σ2 receptor in cancer and proliferation.

P53 regulates a non-apoptotic death induced by ROS.

DNA damage induced by reactive oxygen species and several chemotherapeutic agents promotes both p53 and poly (ADP-ribose) polymerase (PARP) activation. p53 activation is well known to regulate apoptotic cell death, whereas robust activation of PARP-1 has been shown to promote a necrotic cell death associated with energetic collapse. Here we identify a novel role for p53 in modulating PARP enzymatic activity to regulate necrotic cell death. In mouse embryonic fibroblasts, human colorectal and human breast cancer cell lines, loss of p53 function promotes resistance to necrotic, PARP-mediated cell death. We therefore demonstrate that p53 can regulate both necrotic and apoptotic cell death, mutations or deletions in this tumor-suppressor protein may be selected by cancer cells to provide not only their resistance to apoptosis but also to necrosis, and explain resistance to chemotherapy and radiation even when it kills via non-apoptotic mechanisms.