Combining an Aurora Kinase Inhibitor and a Death Receptor Ligand/Agonist Antibody Triggers Apoptosis in Melanoma Cells and Prevents Tumor Growth in Preclinical Mouse Models.

PURPOSE: Preclinical studies show that inhibition of aurora kinases in melanoma tumors induces senescence and reduces tumor growth, but does not cause tumor regression. Additional preclinical models are needed to identify agents that will synergize with aurora kinase inhibitors to induce tumor regression. EXPERIMENTAL DESIGN: We combined treatment with an aurora kinase A inhibitor, MLN8237, with agents that activate death receptors (Apo2L/TRAIL or death receptor 5 agonists) and monitored the ability of this treatment to induce tumor apoptosis and melanoma tumor regression using human cell lines and patient-derived xenograft (PDX) mouse models. RESULTS: We found that this combined treatment led to apoptosis and markedly reduced cell viability. Mechanistic analysis showed that the induction of tumor cell senescence in response to the AURKA inhibitor resulted in a decreased display of Apo2L/TRAIL decoy receptors and increased display of one Apo2L/TRAIL receptor (death receptor 5), resulting in enhanced response to death receptor ligand/agonists. When death receptors were activated in senescent tumor cells, both intrinsic and extrinsic apoptotic pathways were induced independent of BRAF, NRAS, or p53 mutation status. Senescent tumor cells exhibited BID-mediated mitochondrial depolarization in response to Apo2L/TRAIL treatment. In addition, senescent tumor cells had a lower apoptotic threshold due to decreased XIAP and survivin expression. Melanoma tumor xenografts of one human cell line and one PDX displayed total blockage of tumor growth when treated with MLN8237 combined with DR5 agonist antibody. CONCLUSIONS: These findings provide a strong rationale for combining senescence-inducing therapeutics with death receptor agonists for improved cancer treatment.

Quercetin induces the apoptosis of human ovarian carcinoma cells by upregulating the expression of microRNA-145.

Ovarian cancer is one of the most malignant types of cancer of the female human reproductive track, posing a severe threat to the health of the female population. Numerous previous studies have demonstrated that microRNA (miR)-145 is downregulated in ovarian cancer, and that quercetin can inhibit the growth of cancer cells via regulating the expression of miRs. Therefore, the present study investigated the effect of quercetin on the expression of miR-145 in SKOV-3 and A2780 human ovarian cancer cell lines. The results revealed that the expression levels of cleaved caspase-3 in the SKOV-3 and A2780 cells were significantly increased following treatment to induce overexpression of miR-145 compared with treatment with quercetin alone (P<0.01). However, the expression of cleaved caspase-3 in the anti-miR-145 (miR-145 inhibitor) group of cells was markedly decreased compared with that in the miR-145 overexpression group (P<0.01). Taken together, the results suggested that treatment with quercetin induced the apoptosis of human ovarian carcinoma cells through activation of the extrinsic death receptor mediated and intrinsic mitochondrial apoptotic pathways.

Targeting death receptors for TRAIL by agents designed by Mother Nature.

Selective killing of cancer cells is one of the major goals of cancer therapy. Although chemotherapeutic agents are being used for cancer treatment, they lack selectivity toward tumor cells. Among the six different death receptors (DRs) identified to date, DR4 and DR5 are selectively expressed on cancer cells. Therefore, unlike chemotherapeutic agents, these receptors can potentially mediate selective killing of tumor cells. In this review we outline various nutraceuticals derived from 'Mother Nature' that can upregulate DRs and thus potentiate apoptosis. These nutraceuticals increase tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis of cancer cells through different mechanisms. First, nutraceuticals have been found to induce DRs through the upregulation of various signaling molecules. Second, nutraceuticals can downregulate tumor cell-survival pathways. Third, nutraceuticals alone have been found to activate cell-death pathways. Although both TRAIL and agonistic antibodies against DR4 and DR5 are in clinical trials, combination with nutraceuticals is likely to boost their anticancer potential.

Death receptor agonist therapies for cancer, which is the right TRAIL?

The activation of cell-surface death receptors represents an attractive therapeutic strategy to promote apoptosis of tumor cells. Several investigational therapeutics that target this extrinsic pathway, including recombinant human Apo2L/TRAIL and monoclonal agonist antibodies directed against death receptors-4 (DR4) or -5 (DR5), have been evaluated in the clinic. Although Phase 1/1b studies provided encouraging preliminary results, findings from randomized Phase 2 studies failed to demonstrate significant clinical benefit. This has raised multiple questions as to why pre-clinical data were not predictive of clinical response. Results from clinical studies and insight into why current agents have failed to yield robust responses are discussed. In addition, new strategies for the development of next generation death receptor agonists are reviewed.

Manipulating the apoptotic pathway: potential therapeutics for cancer patients.

This review summarizes the current state of scientific understanding of the apoptosis pathway, with a focus on the proteins involved in the pathway, their interactions and functions. This forms the rationale for detailing the preclinical and clinical pharmacology of drugs that modulate the pivotal proteins in this pathway, with emphasis on drugs that are furthest advanced in clinical development as anticancer agents. There is a focus on describing drugs that modulate three of the most promising targets in the apoptosis pathway, namely antibodies that bind and activate the death receptors, small molecules that inhibit the anti-apoptotic Bcl-2 family proteins, and small molecules and antisense oligonucleotides that inactivate the inhibitors of apoptosis, all of which drive the equilibrium of the apoptotic pathway towards apoptosis. These structurally different yet functionally related groups of drugs represent a promising novel approach to anticancer therapeutics whether used as monotherapy or in combination with either classical cytotoxic or other molecularly targeted anticancer agents.

Biology and medicinal chemistry approaches towards various apoptosis inducers.

Apoptosis is a genetically in-built process whereby organisms remove unwanted cells. Apoptosis can serve as a regulatory and defense mechanism in the formation of the shape and size of the human body and also to eradicate surplus amount of cells. The regulation of apoptosis is relevant and differentiates between a normal cells of body and cancer cells by loss of control. Apoptosis being an intricate process regulated by much more than just a biological mechanism. The induction of the apoptosis manifests the control on the tumour size and number of tumour cells hence establishing the application of apoptotic inducers as vital components in the treatment of cancer. During apoptosis, cells die in a controlled and regulated fashion which makes apoptosis distinct from necrosis (uncontrolled cell death). Protein components and regulators for apoptosis signaling pathways can involve the mitochondria (intrinsic pathway) or signal through death receptors (extrinsic pathway). Many different drug and gene therapy approaches are being tested for initiating apoptosis. Resistance to apoptosis is considered a hallmark of cancer. Therapeutic approaches attempted to date include traditional small molecules, antisense oligonucleotides, monoclonal antibodies, recombinant proteins and several classes of chemical compounds discussed in this review. These compounds may serve as precursor molecules for more effective drugs, all aimed at developing clinically effective therapeutics, targeting key apoptosis regulatory mechanism. This review will discuss the current understanding of apoptosis induced by various chemical agents and highlighting the role of apoptosis inducing agents as emerging opportunities for cancer therapy.

Targeting the apoptotic pathway in chondrosarcoma using recombinant human Apo2L/TRAIL (dulanermin), a dual proapoptotic receptor (DR4/DR5) agonist.

Recombinant human Apo2L/TRAIL (dulanermin) is based on the ligand for death receptors (DR4 and DR5), which promotes apoptosis. We report a patient with refractory chondrosarcoma who showed a prolonged response to dulanermin and explore mechanisms of response and resistance. This heavily pretreated patient had progressive metastatic chondrosarcoma to the lung. On dulanermin (8 mg/kg i.v. on days 1-5 in a 21-day cycle), the patient achieved a sustained partial response with only subcentimeter nodules remaining. After 62 months of dulanermin treatment, progressive disease in the lungs was noted, and the patient underwent a resection that confirmed chondrosarcoma. DR4 was detected (immunohistochemistry) in the patient's tumor, which may have enabled the response. However, upregulation of prosurvival proteins, namely, phosphorylated (p)-NF-κBp65 (Ser 536), p-STAT3 (Tyr 705), p-ERK 1/2 (Thr 202/Tyr 204), p-mTOR (Ser 2448), FASN, and Bcl-2, were also detected, which may have provided the underlying mechanisms for acquired dulanermin resistance. The patient was restarted on dulanermin and has continued on this treatment for an additional 16 months since surgery (78 months since initiation of treatment), with his most recent computed tomography (CT) scans showing no evidence of disease.

Sensitization of tumor cells by targeting histone deacetylases.

Epigenetic mechanisms may contribute to drug resistance by interfering with tumor growth regulatory pathways and pro-apoptotic programs. Since gene expression is regulated by acetylation status of histones, a large variety of histone deacetylase (HDAC) inhibitors have been studied as antitumor agents. On the basis of their pro-apoptotic activity, HDAC inhibitors have been combined with conventional antitumor agents or novel target-specific agents to increase susceptibility to apoptosis and drug sensitivity of cancer cells. Several combination strategies including HDAC inhibitors have been explored in preclinical studies. Promising therapeutic effects have been reported in combination with DNA damaging agents, taxanes, targeted agents, death receptor agonists and hormonal therapies. Some histone deacetylases, such as HDAC6, can also modulate the function of non-histone proteins involved in critical regulatory processes which may be relevant as therapeutic targets. Given the pleiotropic effects of most of the available inhibitors, the mechanisms of the sensitization are not completely elucidated. A better understanding of the involved mechanisms will provide a rational basis to improve the therapeutic outcome of the available antitumor agents.

Death receptor pathway activation and increase of ROS production by the triple epigenetic inhibitor UVI5008.

Deregulation of the epigenome is recognized as cause of cancer and epigenetic factors are receiving major attention as therapeutic targets; yet, the molecular mode of action of existing epi-drugs is largely elusive. Here, we report on the decryption of the mechanism of action of UVI5008, a novel epigenetic modifier, that inhibits histone deacetylases, sirtuins, and DNA methyltransferases. UVI5008 highly efficiently induces cancer cell-selective death in a variety of models and exerts its activities in several human tumor xenografts and genetic mouse models of human breast cancer in vivo. Its anticancer activity involves independent activation of death receptors and reactive oxygen species production. Importantly, UVI5008 action is not critically dependent on p53, Bcl-2 modifying factor, and/or TNF-related apoptosis-inducing ligand as cell death is efficiently induced in cells mutated or deficient for these factors limiting the risk of drug resistance development and maximizing its application spectrum. The simultaneous modulation of multiple (epigenetic) targets promises to open new avenues with unanticipated potential against cancer.

Mechanisms of Cell Death and Disease: Advances in Therapeutic Intervention and Drug Discovery--ESH's Eighth International Conference. October 14-17, 2010, Cascais, Portugal.

The Mechanisms of Cell Death and Disease: Advances in Therapeutic Intervention and Drug Discovery--ESH's Eighth International Conference, held in Cascais, Portugal, included topics covering new therapeutic developments in the field of cell death and cancer. This conference report highlights selected presentations on inhibiting the inhibitor of apoptosis (IAP) proteins, activating death receptors (DRs), and targeting ubiquitins and the Bcl-2 family. Investigational drugs discussed include LCL-161 (Novartis) and navitoclax (Abbott Laboratories/Genentech).

Quercetin induced apoptosis in association with death receptors and fludarabine in cells isolated from chronic lymphocytic leukaemia patients.

BACKGROUND: Quercetin is a flavonoid naturally present in food and beverages belonging to the large class of phytochemicals with potential anti-cancer properties. Here, we investigated the ability of quercetin to sensitise primary cells from chronic lymphocytic leukaemia (CLL) to death receptor (DR) agonists, recombinant TNF-related-apoptosis-inducing ligand (rTRAIL) and anti-CD95, and to fludarabine, a widely used chemotherapeutic drug against CLL. METHODS: Peripheral white blood cells were isolated from patients and incubated with medium containing 50 ng ml anti-CD95 agonist antibody; 10 ng ml recombinant TRAIL; 10-25 microM quercetin and 3.5-14 microM fludarabine. Neutral Red assay was used to measure cell viability, where as apoptosis was assessed by determining caspase-3 activity, exposure to Annexin V and PARP fragmentation. RESULTS: Quercetin significantly enhanced anti-CD95- and rTRAIL-induced cell death as shown by decreased cell viability, increased caspase-3 and -9 activities, and positivity to Annexin V. In addition, association of quercetin with fludarabine increases the apoptotic response in CLL cells of about two-fold compared with quercetin monotreatment. CONCLUSION: This work shows that resistance to DR- and fludarabine-induced cell death in leukaemic cells isolated from CLL patients can be ameliorated or bypassed by the combined treatment with quercetin. Considering the low toxicity of the molecule, our study results are in favour of a potential use of quercetin in adjuvant chemotherapy in combination with other drugs.

Death receptor agonists as a targeted therapy for cancer.

Apoptosis is integral to normal, physiologic processes that regulate cell number and results in the removal of unnecessary or damaged cells. Apoptosis is frequently dysregulated in human cancers, and recent advancements in our understanding of the regulation of programmed cell death pathways has led to the development of novel agents to reactivate apoptosis in malignant cells. The activation of cell surface death receptors by tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) and death receptor agonists represent an attractive therapeutic strategy to promote apoptosis of tumor cells through the activation of the extrinsic pathway. The observation that Apo2L/TRAIL can eliminate tumor cells preferentially over normal cells has resulted in several potential therapeutics that exploit the extrinsic pathway, in particular, the soluble recombinant human (rh)Apo2L/TRAIL protein and agonist monoclonal antibodies that target death receptors 4 or 5. Many of these agents are currently being evaluated in phase 1 or 2 trials, either as a single agent or in combination with cytotoxic chemotherapy or other targeted agents. The opportunities and challenges associated with the development of death receptor agonists as cancer therapeutics, the status of ongoing clinical evaluations, and the progress toward identifying predictive biomarkers for patient selection and pharmacodynamic markers of response are reviewed.

Association of caspase-8 mutation with chemoresistance to cisplatin in HOC313 head and neck squamous cell carcinoma cells.

Caspase-8 is a critical upstream mediator of apoptosis in the death receptor pathway. However, the relationship between caspase-8 mutation and chemosensitivity remain unclear in head and neck squamous cell carcinoma (HNSCC) carrying p53 mutation. In this study, we identified a caspase-8 nonsense mutation, accompanied by the loss of the second allele, in a drug-resistant HOC313 HNSCC cell line. The nonsense mutation (R68X) leads to truncation of all defined functional domains. Reconstitution of caspase-8 by stable transfection of wild-type caspase-8 sensitized the cells to cisplatin-, but not etoposide-induced apoptosis. Consistent with this, cisplatin, but not etoposide, induced TNF-alpha and TRAIL mRNA in caspase-8 reconstituted HOC313 cells, accompanied by activation of the reconstituted caspase-8 and its downstream caspase-3. These results indicate that the loss of caspase-8 plays an important role in acquisition of chemoresistance to cisplatin in HOC313 cells.

Apomab, a fully human agonistic antibody to DR5, exhibits potent antitumor activity against primary and metastatic breast cancer.

Apomab, a fully human agonistic DR5 monoclonal antibody, triggers apoptosis through activation of the extrinsic apoptotic signaling pathway. In this study, we assessed the cytotoxic effect of Apomab in vitro and evaluated its antitumor activity in murine models of breast cancer development and progression. MDA-MB-231-TXSA breast cancer cells were transplanted into the mammary fat pad or directly into the tibial marrow cavity of nude mice. Apomab was administered early, postcancer cell transplantation, or after tumors progressed to an advanced stage. Tumor burden was monitored progressively using bioluminescence imaging, and the development of breast cancer-induced osteolysis was measured using microcomputed tomography. In vitro, Apomab treatment induced apoptosis in a panel of breast cancer cell lines but was without effect on normal human primary osteoblasts, fibroblasts, or mammary epithelial cells. In vivo, Apomab exerted remarkable tumor suppressive activity leading to complete regression of well-advanced mammary tumors. All animals transplanted with breast cancer cells directly into their tibiae developed large osteolytic lesions that eroded the cortical bone. In contrast, treatment with Apomab following an early treatment protocol inhibited both intraosseous and extraosseous tumor growth and prevented breast cancer-induced osteolysis. In the delayed treatment protocol, Apomab treatment resulted in the complete regression of advanced tibial tumors with progressive restoration of both trabecular and cortical bone leading to full resolution of osteolytic lesions. Apomab represents a potent immunotherapeutic agent with strong activity against the development and progression of breast cancer and should be evaluated in patients with primary and metastatic disease.

Enhancing the apoptotic and therapeutic effects of HDAC inhibitors.

Histone deacetylase inhibitors (HDACi) are anti-cancer drugs that have moved rapidly through clinical development and in 2006 vorinostat (SAHA, Zolinza) was given FDA approval for the treatment of cutaneous T cell lymphoma. Class I, II and IV HDACs that are targets for these compounds deacetylate histone proteins, resulting in chromatin remodelling and altered gene transcription. In addition, numerous non-histone proteins are modified by acetylation and the inhibition of HDAC activity can therefore affect various molecular processes. This broad effect on protein function may account for the pleiotropic anti-tumor responses elicited by HDACi that include induction of tumor cell apoptosis, cell cycle arrest, differentiation and senescence, modulation of immune responses and altered angiogenesis. The ability of HDACi to selectively induce tumor cells to undergo apoptosis is important for the therapeutic efficacy observed in pre-clinical models. Moreover, HDACi can augment the apoptotic effects of other anti-cancer agents that have diverse molecular targets. While HDACi are promising anti-cancer drugs, particularly given the scope to combine HDACi with other agents, identifying the key molecular events that determine the biological response of cells to HDACi treatment remains a challenge. Herein we focus on HDACi-induced apoptosis and discuss the various proteins and pathways that are affected by HDACi to mediate this programmed cell death response. In addition, we highlight the ability of HDACi to synergise with other anti-cancer agents to potently kill tumor cells and discuss the possible molecular processes that underpin the combination effect.

Death ligands designed to kill: development and application of targeted cancer therapeutics based on proapoptotic TNF family ligands.

The identification of molecular markers associated with cancer development or progression, opened a new era in the development of therapeutics. The successful introduction of a few low molecular weight chemicals and recombinant protein therapeutics with targeted actions into clinical practice have raised great expectations to broadly improve cancer therapy with respect to both overall clinical responses and tolerability. Targeting the apoptotic machinery of malignant cells is an attractive concept to combat cancer, which is currently exploited for the proapoptotic members of the TNF ligand family at various stages of preclinical and clinical development. This review summarizes recent progress in this rapidly progressing field of "biologic" therapies targeting the death receptors of TNF, CD95L, and TRAIL by means of its cognate protein ligands, receptor specific antibodies, and gene therapeutic approaches. Preclinical data on newly derived variants and fusion proteins based on these death ligands, designed to act in a tumor restricted manner, thereby preventing a systemic, potentially harmful action, will also be discussed.

Sensitization by 5-azacytidine toward death receptor-induced hepatic apoptosis.

5-Azacytidine (5-aza-CR) is a DNA-hypomethylating antineoplastic agent used because of its inhibitory activity on DNA methyltransferases. Today, it is approved as an epigenetically active drug therapy for treatment of myelodysplastic disorders, with a contraindication as to pre-existing liver diseases. Because the mechanism of its hepatotoxicity is still unknown, we investigated the pharmacodynamic properties of 5-aza-CR with regard to death receptor/ligand-induced apoptosis and the mode of execution of cell death. In a time- and concentration-dependent manner, primary murine, human hepatocytes and HepG2 cells exposed to 5-aza-CR became highly sensitive toward cell death induced by CD95L, tumor necrosis factor (TNF)-related apoptosis-inducing ligand, or TNF. Cell death was characterized as apoptotic by membrane blebbing, chromatin condensation, and exposure of phosphatidylserine on the outer membrane. Neither 5-aza-2'-deoxycytidine nor the common DNA methyltransferase inhibitors S-(5'-adenosyl)-L-homocysteine or RG 108 showed any significant effects under these conditions. Despite the complete protection of HepG2 by high concentrations of the pan-caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(O-Me) fluoromethyl ketone (z-VAD-fmk), effector caspase-3/7 activity was completely abolished at approximately a 20-fold lower concentration of z-VAD-fmk. Under these conditions, the serine protease inhibitors N,alpha-tosyl-L-phenylalanine chloromethyl ketone, N,p-tosyl-L-lysine chloromethyl ketone, and 4-(2-aminoethyl)-benzenesulfonyl fluoride, respectively, conferred protection against death receptor ligands. We conclude that this caspase-independent apoptosis is executed by a yet-unidentified serine protease.

Immunosensitization with a Bcl-2 small molecule inhibitor.

Several tumor immunotherapy approaches result in a low percentage of durable responses in selected cancers. We hypothesized that the insensitivity of cancer cells to immunotherapy may be related to an anti-apoptotic cancer cell milieu, which could be pharmacologically reverted through the inhibition of antiapoptotic Bcl-2 family proteins in cancer cells. ABT-737, a small molecule inhibitor of the antiapoptotic proteins Bcl-2, Bcl-w and Bcl-x(L), was tested for the ability to increase antitumor immune responses in two tumor immunotherapy animal models. The addition of systemic therapy with ABT-737 to the immunization of BALB/c mice with tumor antigen peptide-pulsed dendritic cells (DC) resulted in a significant delay in CT26 murine colon carcinoma tumor growth and improvement in survival. However, the addition of ABT-737 to either a vaccine strategy involving priming with TRP-2 melanoma antigen peptide-pulsed DC and boosting with recombinant Listeria monocytogenes expressing the same melanoma antigen, or the adoptive transfer of TCR transgenic cells, did not result in superior antitumor activity against B16 murine melanoma. In vitro studies failed to demonstrate increased cytotoxic lytic activity when testing the combination of ABT-737 with lymphokine activated killer (LAK) cells, or the death receptor agonists Fas, TRAIL-ligand or TNF-alpha against the CT26 and B16 cell lines. In conclusion, the Bcl-2 inhibitor ABT-737 sensitized cancer cells to the antitumor effect of antigen-specific immunotherapy in a vaccine model for the CT26 colon carcinoma in vivo but not in two immunotherapy strategies against B16 melanoma.