Insights into the mitochondrial signaling pathway: what lessons for chemotherapy?

Comparative anti-proliferative activity of some new 2-(arylazo)phenolate-palladium (II) complexes and cisplatin against some human cancer cell lines

In this study, we report the synthesis of four 2-(arylazo)phenol-Pd(II) complexes and their anti-proliferative property against the human lung cancer (A549), cervical cancer (HeLa), and ovarian teratocarcinoma (PA-1) cell lines with cisplatin as the gold standard. One of the complexes, [Pd(L(2))2], induced robust apoptosis in all the chosen cells, as revealed by annexin-V-positive/propidium iodide dual staining, increased sub-G1 cell cycle population, and significant morphological changes in the treated cells. The Pd complex inflicted mitochondrial dysfunction leading to mitochondrial membrane potential loss, reactive oxygen species generation and release of cytosolic cytochrome c that activated caspase-9 and caspase-3 proteins which finally caused programmed cell death.

Quantitative proteomics analysis identifies mitochondria as therapeutic targets of multidrug-resistance in ovarian cancer

Doxorubicin is a widely used chemotherapeutic agent for the treatment of a variety of solid tumors. However, resistance to this anticancer drug is a major obstacle to the effective treatment of tumors. As mitochondria play important roles in cell life and death, we anticipate that mitochondria may be related to drug resistance. Here, stable isotope labeling by amino acids in cell culture (SILAC)-based quantitative proteomic strategy was applied to compare mitochondrial protein expression in doxorubicin sensitive OVCAR8 cells and its doxorubicin-resistant variant NCI_ADR/RES cells. A total of 2085 proteins were quantified, of which 122 proteins displayed significant changes in the NCI_ADR/RES cells. These proteins participated in a variety of cell processes including cell apoptosis, substance metabolism, transport, detoxification and drug metabolism. Then qRT-PCR and western blot were applied to validate the differentially expressed proteins quantified by SILAC. Further functional studies with RNAi demonstrated TOP1MT, a mitochondrial protein participated in DNA repair, was involved in doxorubicin resistance in NCI_ADR/RES cells. Besides the proteomic study, electron microscopy and fluorescence analysis also observed that mitochondrial morphology and localization were greatly altered in NCI_ADR/RES cells. Mitochondrial membrane potential was also decreased in NCI_ADR/RES cells. All these results indicate that mitochondrial function is impaired in doxorubicin-resistant cells and mitochondria play an important role in doxorubicin resistance. This research provides some new information about doxorubicin resistance, indicating that mitochondria could be therapeutic targets of doxorubicin resistance in ovarian cancer cells.

Apicidin-resistant HA22T hepatocellular carcinoma cells massively promote pro-survival capability via IGF-IR/PI3K/Akt signaling pathway activation

Despite rapid advances in the diagnostic and surgical procedures, hepatocellular carcinoma (HCC) remains one of the most difficult human malignancies to treat. This may be due to the chemoresistant behaviors of HCC. It is believed that acquired resistance could be overcome and improve the overall survival of HCC patients by understanding the mechanisms of chemoresistance in HCC. A stable HA22T cancer line, which is chronically resistant to a histone deacetylase inhibitor, was established. After comparing the molecular mechanism of apicidin-R HA22T cells to parental ones by Western blotting, cell cycle-regulated proteins did not change in apicidin-R cells, but apicidin-R cells were more proliferative and had higher tumor growth (wound-healing assay and nude mice xenograft model). Moreover, apicidin-R cells displayed increased levels of p-IGF-IR, p-PI3K, p-Akt, Bcl-xL, and Bcl-2 but also significantly inhibited the tumor suppressor PTEN protein and apoptotic pathways when compared to the parental strain. Therefore, the highly proliferative effect of apicidin-R HA22T cells was blocked by Akt knockdown. For all these findings, we believe that novel strategies to attenuate IGF-IR/PI3K/Akt signaling could overcome chemoresistance toward the improvement of overall survival of HCC patients.

Melatonin inhibits cell proliferation and induces caspase activation and apoptosis in human malignant lymphoid cell lines

Melatonin exerts strong anti-tumour activity via several mechanisms, including anti-proliferative and pro-apoptotic effects in addition to its potent antioxidant activity. Several studies have investigated the effects of melatonin on haematological malignancies. However, the previous studies investigating lymphoid malignancies have been largely restricted to a single type of malignancy, Burkitt's lymphoma (BL). Thus, we examined the actions of melatonin on the growth and apoptosis in a small panel of cell lines representing different human lymphoid malignancies including Ramos (Epstein-Barr virus-negative BL), SU-DHL-4 (diffuse large B cell lymphoma), DoHH2 (follicular B non-Hodgkin lymphoma) and JURKAT (acute T cell leukaemia). We showed that melatonin promotes cell cycle arrest and apoptosis in all these cells, although there was marked variations in responses among different cell lines (sensitivity; Ramos/DoHH2 > SU-DHL-4 > JURKAT). Melatonin-induced apoptosis was relatively rapid, with increased caspase 3 and PARP cleavage detected within 0.5-1 h following melatonin addition. Moreover, there was evidence for rapid processing of both caspase 9, as well as a breakdown of the mitochondrial inner transmembrane potential. On the contrary, caspase activation was detected only in SU-DHL-4 and Ramos cells following melatonin treatment suggesting that the extrinsic pathway does not make a consistent contribution to melatonin-induced apoptosis in malignant lymphocytes. Although all cell lines expressed the high-affinity melatonin receptors, MT1 and MT2, melatonin-induced caspase activation appeared to be independent these receptors. Our findings confirm that melatonin could be a potential chemotherapeutic/preventive agent for malignant lymphocytes. However, it is necessary to take into account that different lymphoid malignancies may differ in their response to melatonin.

Aromatase deficiency inhibits the permeability transition in mouse liver mitochondria

Lack of estrogens affects male physiology in a number of ways, including severe changes in liver metabolism that result in lipid accumulation and massive hepatic steatosis. Here we investigated whether estrogen deficiency may alter the functionality and permeability properties of liver mitochondria using, as an experimental model, aromatase knockout (ArKO) male mice, which cannot synthesize endogenous estrogens due to a disruption of the Cyp19 gene. Liver mitochondria isolated from ArKO mice displayed increased activity of the mitochondrial respiratory complex IV compared with wild-type mice and were less prone to undergo cyclosporin A-sensitive mitochondrial permeability transition (MPT) induced by calcium loading. The altered permeability properties of the mitochondrial membranes were not due to changes in reactive oxygen species, ATP levels, or mitochondrial membrane potential but were associated with increased content of the phospholipid cardiolipin, structural component of the mitochondrial membranes and regulator of the MPT pore, and with increased mitochondrial protein levels of Bcl-2 and the adenine nucleotide translocator (ANT), regulator and component of the MPT pore, respectively. Real-time RT-PCR demonstrated increased mRNA levels for Bcl-2 and ANT2 but not for the ANT1 isoform in ArKO livers. Supplementation of 17beta-estradiol retrieved ArKO mice from massive hepatic steatosis and restored mitochondrial permeability properties, cardiolipin, Bcl-2, and ANT2 levels. Overall, our findings demonstrate an important role of estrogens in the modulation of hepatic mitochondrial function and permeability properties in males and suggest that estrogen deficiency may represent a novel positive regulator of Bcl-2 and ANT2 proteins, two inhibitors of MPT occurrence and powerful antiapoptotic molecules.

Pim-1 expression and monoclonal antibody targeting in human leukemia cell lines

OBJECTIVE

Based on our previous findings that Pim-1 was expressed on the cell surface and could be targeted with a highly specific anti-Pim-1 monoclonal antibody (P9), this study aims to evaluate the possibility that Pim-1 could be targeted for the treatment of human leukemia.

MATERIALS AND METHODS

Pim-1 expression was investigated in a series of human leukemia cell lines with immunohistochemistry and flow cytometry. The inhibitory effect of P9 on cell proliferation was evaluated with (3)H-thymidine incorporation assay. Cell apoptosis was assayed with Annexin-V/propidium iodide dual staining. The in vivo effect of P9 was evaluated with xenograft tumor models in severe combined immunodeficient mice.

RESULTS

Pim-1 expression varied depending on the cell lines and correlated with the inhibitory effects mediated by P9. An association between Pim-1 expression and drug resistance was observed. Although the drug-resistant CEM/A7R cells were highly resistant to cytotoxic P-glycoprotein substrates, their growth was inhibited by P9 as demonstrated by in vitro proliferation assay and in vivo inhibition of xenograft tumors. P9 had little effect on P-glycoprotein expression and intracellular Rhodamine 123 accumulation, but it inhibited the phosphorylation of Bad and induced apoptosis.

CONCLUSIONS

Pim-1 is variably expressed in leukemia cell lines and associated with drug resistance. Targeting Pim-1 with monoclonal antibody could be explored for the treatment of leukemia and may represent a novel strategy to overcome drug resistance.

A double hit to kill tumor and endothelial cells by TRAIL and antiangiogenic 3TSR

As tumor development relies on a coordination of angiogenesis and tumor growth, an efficient antitumor strategy should target both the tumor and its associated vessels. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces apoptosis in a tumor-selective manner. Additionally, thrombospondin-1, a naturally occurring inhibitor of angiogenesis, and a recombinant protein containing functional domains of thrombospondin-1, 3TSR, have been shown to be necessary and sufficient to inhibit tumor angiogenesis. Here, we show that a combination of a TRAIL receptor 2 agonist antibody, Lexatumumab, and 3TSR results in a significantly enhanced and durable tumor inhibition. We further observed that 3TSR induces apoptosis in primary endothelial cells by up-regulating the expression of TRAIL receptors 1 and 2 in a CD36 and Jun NH(2)-terminal kinase-dependent manner leading to the activation of both intrinsic and extrinsic apoptotic machineries. The modulation of these pathways is critical for 3TSR-induced apoptosis as disrupting either via specific inhibitors reduced apoptosis. Moreover, 3TSR attenuates the Akt survival pathway. These studies indicate that 3TSR plays a critical role in regulating the proapoptotic signaling pathways that control growth and death in endothelial cells and that a combination of TRAIL and 3TSR acts as a double hit against tumor and tumor-associated vessels.

Targeting the apoptotic pathway with BCL-2 inhibitors sensitizes primary chronic lymphocytic leukemia cells to vesicular stomatitis virus-induced oncolysis

Chronic lymphocytic leukemia (CLL) is characterized by clonal accumulation of CD5(+) CD19(+) B lymphocytes that are arrested in the G(0)/G(1) phase of the cell cycle and fail to undergo apoptosis because of overexpression of the antiapoptotic B-cell CLL/lymphoma 2 (BCL-2) protein. Oncolytic viruses, such as vesicular stomatitis virus (VSV), have emerged as potential anticancer agents that selectively target and kill malignant cells via the intrinsic mitochondrial pathway. Although primary CLL cells are largely resistant to VSV oncolysis, we postulated that targeting the apoptotic pathway via inhibition of BCL-2 may sensitize CLL cells to VSV oncolysis. In the present study, we examined the capacity of EM20-25--a small-molecule antagonist of the BCL-2 protein--to overcome CLL resistance to VSV oncolysis. We demonstrate a synergistic effect of the two agents in primary ex vivo CLL cells (combination index of 0.5; P < 0.0001). In a direct comparison of peripheral blood mononuclear cells from healthy volunteers with primary CLL, the two agents combined showed a therapeutic index of 19-fold; furthermore, the combination of VSV and EM20-25 increased apoptotic cell death in Karpas-422 and Granta-519 B-lymphoma cell lines (P < 0.005) via the intrinsic mitochondrial pathway. Mechanistically, EM20-25 blocked the ability of the BCL-2 protein to dimerize with proapoptotic BAX protein, thus sensitizing CLL to VSV oncolytic stress. Together, these data indicate that the use of BCL-2 inhibitors may improve VSV oncolysis in treatment-resistant hematological malignancies, such as CLL, with characterized defects in the apoptotic response.

Mitochondrial membrane permeabilization in cell death

Irrespective of the morphological features of end-stage cell death (that may be apoptotic, necrotic, autophagic, or mitotic), mitochondrial membrane permeabilization (MMP) is frequently the decisive event that delimits the frontier between survival and death. Thus mitochondrial membranes constitute the battleground on which opposing signals combat to seal the cell's fate. Local players that determine the propensity to MMP include the pro- and antiapoptotic members of the Bcl-2 family, proteins from the mitochondrialpermeability transition pore complex, as well as a plethora of interacting partners including mitochondrial lipids. Intermediate metabolites, redox processes, sphingolipids, ion gradients, transcription factors, as well as kinases and phosphatases link lethal and vital signals emanating from distinct subcellular compartments to mitochondria. Thus mitochondria integrate a variety of proapoptotic signals. Once MMP has been induced, it causes the release of catabolic hydrolases and activators of such enzymes (including those of caspases) from mitochondria. These catabolic enzymes as well as the cessation of the bioenergetic and redox functions of mitochondria finally lead to cell death, meaning that mitochondria coordinate the late stage of cellular demise. Pathological cell death induced by ischemia/reperfusion, intoxication with xenobiotics, neurodegenerative diseases, or viral infection also relies on MMP as a critical event. The inhibition of MMP constitutes an important strategy for the pharmaceutical prevention of unwarranted cell death. Conversely, induction of MMP in tumor cells constitutes the goal of anticancer chemotherapy.

Sanguinarine induces apoptosis of human pancreatic carcinoma AsPC-1 and BxPC-3 cells via modulations in Bcl-2 family proteins

Pancreatic cancer is associated with low responsiveness to conventional chemotherapies and its incidence nearly equals its death rate. This warrants the development of novel mechanism-based approaches for the management of pancreatic cancer. This study was designed to determine the potential of sanguinarine, a plant alkaloid known to possess strong antimicrobial, anti-inflammatory, and antioxidant activities, against human pancreatic carcinoma cells. Employing human pancreatic carcinoma AsPC-1 and BxPC-3 cells, we specifically evaluated the pro-apoptotic and cell cycle deregulatory effects of sanguinarine and evaluated the involvement of Bcl-2 family proteins and p53 as the mechanism of the biological effects of sanguinarine. Our data demonstrated that sanguinarine (at low concentrations of 0.1-10 microM; for 24 h) treatment to AsPC-1 and BxPC-3 cells resulted in a dose dependent (i) inhibition of viability and growth, (ii) colony formation ability, (iii) induction of apoptosis, and (iv) G0-G1 phase cell cycle arrest. Further, sanguinarine-treatment to AsPC-1 and BxPC-3 cells resulted in a dose dependent (i) increase in pro-apoptotic Bax, Bid and Bak proteins; (ii) decrease in anti-apoptotic Bcl-2 and Bcl-X(L) proteins; and (iii) decrease in p53 with an increase in its phosphorylation. Based on our study, we suggest that sanguinarine may be developed as an agent for the management of pancreatic cancer. Indeed, more in depth studies both in vitro as well as in vivo in appropriate relevant animal models are needed to strengthen this suggestion.

Pharmacological inhibitors of NF-kappaB accelerate apoptosis in chronic lymphocytic leukaemia cells

Nuclear factor-kappaB (NF-kappaB) is a transcription factor that plays a critical role in the inappropriate survival of various types of malignant cells. Chronic lymphocytic leukaemia (CLL) is the most common B-cell malignancy in the Western world. Although overexpression and regulation of NF-kappaB has been described in CLL, its function remains unclear. Exposure of CLL cells to BAY117082 or Kamebakaurin, potent pharmacological inhibitors of the NF-kappaB pathway, accelerated apoptosis in approximately 70% of cases. Sensitivity to NF-kappaB pathway inhibitors was not related to the prognostic markers VH status, CD38 or Zap70 expression, or to the levels of nuclear NF-kappaB. Normal peripheral B cells were resistant to the apoptosis-inducing effects of these compounds. Cell death induced by the inhibitors was associated with activation of caspase-9 and -3, and loss of mitochondrial membrane polarization, but did not involve changes in the expression of Bcl-2 or Mcl-1. Inhibitors caused an increase in c-jun NH2-terminal kinase activity in CLL, but this did not appear to be important for apoptosis. Microarray analysis identified some potential novel NF-kappaB target genes, including interleukin-16- and the Bcl-2- related survival protein Bcl-w. These results demonstrate that a substantial proportion of CLL are dependent on NF-kappaB for enhanced survival and suggest that inhibition of NF-kappaB may have therapeutic potential.

Death receptor signals to mitochondria

Apoptosis is the best-characterized form of programmed cell death (PCD) and is of fundamental importance in tissue homeostasis. In mammalian systems, there are two major pathways that are involved in the initiation of apoptosis: the "extrinsic" death receptor pathway and the "intrinsic" mitochondrial pathway. Although these pathways act independently to initiate the death machinery in some cellular systems, in many cell types, including numerous tumor cells, there is delicate coordination and cross talk between the extrinsic and intrinsic pathways, which leads to the activation of the executioner caspase cascade. Additionally, there appears to be a fine balance between the caspase-mediated arm of death receptor signaling that engages mitochondria and the caspase-independent arm that promotes vacuole proliferation in many cells. Here, we review our current knowledge about the layers of complexity that are posed by the interactions between death receptor-induced pathways and how they influence mitochondria to regulate cellular life and death decisions.

Dynamic evolution of the adenine nucleotide translocase interactome during chemotherapy-induced apoptosis

The mitochondrial permeability transition pore complex (PTPC) is involved in the control of the mitochondrial membrane permeabilization during apoptosis, necrosis and autophagy. Indeed, the adenine nucleotide translocator (ANT) and the voltage-dependent anion channel (VDAC), two major components of PTPC, are the targets of a variety of proapoptotic inducers. Using co-immunoprecipitation and proteomic analysis, we identified some of the interacting partners of ANT in several normal tissues and human cancer cell lines. During chemotherapy-induced apoptosis, some of these interactions were constant (e.g. ANT-VDAC), whereas others changed strongly concomitantly with the dissipation of the mitochondrial transmembrane potential and until nuclear degradation occurred (e.g. Bax, Bcl-2, subunits of the respiratory chain, a subunit of the phosphatase PP2A, phospholipase PLC beta 4 and IP3 receptor). In addition, a glutathione-S-transferase (GST) interacts with ANT in normal tissue, in colon carcinoma cells and in vitro. This interaction is lost during apoptosis induction, suggesting that GST behaves as an endogenous repressor of PTPC and ANT pore opening. Thus, ANT is connected to mitochondrial proteins as well as to proteins from other organelles such as the endoplasmic reticulum forming a dynamic polyprotein complex. Changes within this ANT interactome coordinate the lethal response of cells to apoptosis induction.

The mitochondrial apoptosis-induced channel (MAC) corresponds to a late apoptotic event

We have investigated the mechanism responsible for mitochondria permeabilization occurring during cell apoptosis. We have developed an in vivo model of apoptotic rat liver. Mitochondria appeared as an homogenous population in control liver. On the contrary, mitochondria varied in size, morphology, and the matrical density in apoptotic liver. Mitochondria were purified from control and apoptotic livers. In control conditions, a single mitochondrial population was identified; whereas three populations of mitochondria were purified from apoptotic liver. Our data show that these apoptotic populations correspond to early, intermediate, and late apoptotic mitochondria, which are characterized by an increasing extent of permeabilization of their outer membrane and a gradual enrichment in oligomerized Bax protein. Remarkably, a new ionic channel was observed in apoptotic but not in control mitochondria. The biophysical and pharmacological properties of this channel are in good agreement with those reported for a previously described mitochondrial apoptosis-induced channel (MAC) (Pavlov, E. V., Priault, M., Pietkiewicz, D., Cheng, E. H., Antonsson, B., Manon, S., Korsmeyer, S. J., Mannella, C. A., and Kinnally, K. W. (2001) J. Cell Biol. 155, 725-731). However, MAC activity was only observed in the late apoptotic mitochondrial population. Thus, our study establishes that MAC activity is related to the overall apoptotic process but corresponds to a late event.

Antitumor Activity of 3-Ingenyl Angelate

Options for skin cancer treatment currently include surgery, radiotherapy, topical chemotherapy, cryosurgery, curettage, and electrodessication. Although effective, surgery is costly and unsuitable for certain patients. Radiotherapy can leave a poor cosmetic effect, and current chemotherapy is limited by low cure rates and extended treatment schedules. Here, we describe the preclinical activity of a novel topical chemotherapeutic agent for the treatment of skin cancer, 3-ingenyl angelate (PEP005), a hydrophobic diterpene ester isolated from the plant Euphorbia peplus. Three daily topical applications of 42 nmol (18 micro g) of PEP005 cured a series of s.c. mouse tumors (B16 melanoma, LK2 UV-induced squamous cell carcinoma, and Lewis lung carcinoma; n = >14 tumors/group) and human tumors (DO4 melanoma, HeLa cervical carcinoma, and PC3 and DU145 prostate carcinoma; n = >4 tumors/group) previously established (5-10 mm(3)) on C57BL/6 or Foxn1(nu) mice. The treatment produced a mild, short-term erythema and eschar formation but, ultimately, resulted in excellent skin cosmesis. The LD(90) for PEP005 for a panel of tumor cell lines was 180-220 micro M. Electron microscopy showed that treatment with PEP005 both in vitro (230 micro M) and in vivo (42 nmol) rapidly caused swelling of mitochondria and cell death by primary necrosis. (51)Cr release, uptake of propidium iodide, and staining with the mitochondria dye JC1, revealed that PEP005 (230 micro M) treatment of tumor cells in vitro resulted in a rapid plasma membrane perturbation and loss of mitochondrial membrane potential. PEP005 thus emerges as a new topical anti-skin cancer agent that has a novel mode of action involving plasma membrane and mitochondrial disruption and primary necrosis, ultimately resulting in an excellent cosmetic outcome.

Prospective strategies to enforce selectively cell death in cancer cells

Although induction of apoptosis (cell death mediated by caspases) determines response to cancer therapy, this approach is limited by lack of selectivity in available apoptosis-inducing agents. Furthermore, most cancers, almost by definition, are resistant to apoptosis, growth arrest and cell senescence. Then, how can anticancer agents kill cancer cell without unacceptable toxicity to a patient? The potential therapeutic approaches range from selective inhibition of antiapoptotic pathways, antiangiogenic therapy, tissue-selective therapy (including immunotherapy) to exploitation of, for example, drug resistance, oncoprotein addiction, unrestricted cell cycles, hypermitogenic and hypoxic features of cancer cells. These overlapping and complementary approaches rely on rational drug combinations (at mechanism-based doses and sequences) aimed at matching targets. To ensure killing of cancer cells selectively, we may combine apoptosis- and senescence-inducing agents with inhibitors of apoptosis (to protect normal cells), inhibitors of signal transduction with cell cycle-dependent chemotherapy, antiangiogenic agents with hypoxia-inducible factor-1 inhibitors, tissue-selective therapy with differentiating agents and activators of death receptors with chemotherapy. In theory, consecutive use of these drug combinations may control cancer.