Smac mimetic increases chemotherapy response and improves survival in mice with pancreatic cancer

Xevinapant Combined with Pembrolizumab in Patients with Advanced, Pretreated, Colorectal and Pancreatic Cancer: Results of the Phase Ib/II CATRIPCA Trial

PURPOSE

Xevinapant is an orally available inhibitor of apoptosis proteins (IAP) inhibitor. Preclinical data suggest that IAP antagonism may synergize with immune checkpoint blockers by modulating the NFκB pathway in immune cells.

PATIENTS AND METHODS

Adult patients with non-high microsatellite instability advanced/metastatic pancreatic ductal adenocarcinoma (PDAC) or colorectal cancer were enrolled in this phase Ib/II study and received pembrolizumab 200 mg every 3 weeks intravenously, and ascending doses of oral xevinapant (100, 150, and 200 mg daily for 14 days on/7 days off). Dose escalation followed a 3+3 design with a 21-day dose-limiting toxicity (DLT) evaluation period. Following the determination of the recommended phase II dose (RP2D), 14 patients with PDAC and 14 patients with colorectal cancer were enrolled in expansion cohorts to assess preliminary efficacy.

RESULTS

Forty-one patients (26 males) with a median age of 64 years were enrolled: 13 in the dose escalation and 28 in the two expansion cohorts. No DLT was observed during dose escalation. The RP2D was identified as xevinapant 200 mg/day + pembrolizumab 200 mg every 3 weeks. The most common adverse events (AE) were fatigue (37%), gastrointestinal AE (decreased appetite in 37%, nausea in 24%, stomatitis in 12%, and diarrhea and vomiting in 10% each), and cutaneous AE (pruritus, dry skin, and rash seen in 20%, 15%, and 15% of patients, respectively). The best overall response according to RECIST1.1 was partial response (confirmed) in 1 (3%), stable disease in 4 (10%), and progressive disease in 35 (88%).

CONCLUSIONS

Xevinapant combined with pembrolizumab was well tolerated with no unexpected AEs. However, antitumor activity was low.

Learning and Investigation of the Role of Angiotensin-Converting Enzyme in Radiotherapy for Nasopharyngeal Carcinoma

Ionizing radiation (IR) is an important treatment for nasopharyngeal carcinoma (NPC) that mainly kills tumor cells by producing large amounts of reactive oxygen species (ROS). Intracellular ROS levels affect the sensitivity of tumor cells to IR. Recently, angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin-converting enzyme (ACE) have been found to affect the intracellular levels of ROS. Therefore, we performed a health informatics assessment of ACE in the TCGA database. We explored the effect of ACE in NPC cells. We found that either knockdown of ACE or inhibition of ACE by enalaprilat could decrease ROS levels in NPC cells. Furthermore, knockdown of ACE or inhibition of ACE by enalaprilat could reduce IR-induced ROS levels. ACE knockdown or inhibition reduced IR-induced DNA damage and apoptosis. ACE overexpression increased the level of ROS in NPC cells and further increased sensitivity to IR. These findings indicate that ACE influences the effect of IR by regulating the level of ROS in NPC cells.

Modulatory role of BV6 and chloroquine on the regulation of apoptosis and autophagy in non-small cell lung cancer cells

Aims

Non-small cell lung cancer (NSCLC) is one of the aggressive tumors mostly diagnosed in the advanced stage. Therapeutic failure and drug resistance pose a major problem in NSCLC treatment primarily due to alterations in autophagy and loss of apoptosis. Therefore, the present study aimed to investigate the importance of the second mitochondria-derived activator of caspase mimetic BV6 and autophagy inhibitor chloroquine (CQ) on the regulation of apoptosis and autophagy, respectively.

Subjects and Methods

Study was conducted on NCI-H23 and NCI-H522 cell lines to evaluate the effect of BV6 and CQ on the transcription and translation level of LC3-II, caspase-3, and caspase-9 genes by quantitative real-time-polymerase chain reaction and western blotting techniques.

Results

In NCI-H23 cell line, BV6 and CQ treatments showed increased mRNA and protein expression of caspase-3, and caspase-9 compared to its untreated counterpart. BV6 and CQ treatments also caused downregulation of LC3-II protein expression compared to its counterpart. In NCI-H522 cell line, BV6 treatment showed a significantly increased expression of caspase-3 and caspase-9 mRNA and protein expression levels whereas BV6 treatment downregulated the expression level of LC3-II protein. A similar pattern was also observed in CQ treatment when compared with the respective controls. Both BV6 and CQ modulated in vitro expression of caspases and LC3-II which have critical regulatory roles in apoptosis and autophagy, respectively.

Conclusions

Our findings suggest that BV6 and CQ could be promising candidates in NSCLC treatment and there is a need to explore them in vivo and in clinical applications.

Inhibiting the inhibitors: Development of the IAP inhibitor xevinapant for the treatment of locally advanced squamous cell carcinoma of the head and neck

Standard of care for patients with locally advanced squamous cell carcinoma of the head and neck (LA SCCHN) is surgery followed by chemoradiotherapy (CRT) or definitive CRT. However, approximately 50 % of patients with LA SCCHN develop disease recurrence or metastasis within 2 years of completing treatment, and the outcome for these patients is poor. Despite this, the current treatment landscape for LA SCCHN has remained relatively unchanged for more than 2 decades, and novel treatment options are urgently required. One of the key causes of disease recurrence is treatment resistance, which commonly occurs due to cancer cells' ability to evade apoptosis. Evasion of apoptosis has been in part attributed to the overexpression of inhibitor of apoptosis proteins (IAPs). IAPs, including X-linked IAP (XIAP) and cellular IAP 1 and 2 (cIAP1/2), are a class of proteins that regulate apoptosis induced by intrinsic and extrinsic apoptotic pathways. IAPs have been shown to be overexpressed in SCCHN, are associated with poor clinical outcomes, and are, therefore, a rational therapeutic target. To date, several IAP inhibitors have been investigated; however, only xevinapant, a potent, oral, small-molecule IAP inhibitor, has shown clinical proof of concept when combined with CRT. Specifically, xevinapant demonstrated superior efficacy in combination with CRT vs placebo + CRT in a randomized, double-blind, phase 2 trial in patients with unresected LA SCCHN. Here, we describe the current treatment landscape in LA SCCHN and provide the rationale for targeting IAPs and the clinical data reported for xevinapant.

SMAC mimetics inhibit human T cell proliferation and fail to augment type 1 cytokine responses

Second mitochondria-derived activator of caspases (SMAC) mimetics are small molecule drugs that mimic the activity of the endogenous SMAC protein. SMAC and SMAC mimetics antagonize inhibitors of apoptosis proteins (IAPs), thereby sensitizing cells to apoptosis. As such, SMAC mimetics are being tested in numerous clinical trials for cancer. In addition to their direct anti-cancer effect, it has been suggested that SMAC mimetics may activate T cells, thereby promoting anti-tumor immunity. Here, we tested the effect of three clinically relevant SMAC mimetics on activation of primary human T cells. As previously reported, SMAC mimetics killed tumor cells and activated non-canonical NF-κB in T cells at clinically relevant doses. Surprisingly, none of the SMAC mimetics augmented T cell responses. Rather, SMAC mimetics impaired T cell proliferation and decreased the proportion of IFNγ/TNFα double-producing T cells. These results question the assumption that SMAC mimetics are likely to boost anti-tumor immunity in cancer patients.

BH3-mimetics: recent developments in cancer therapy

The hopeful outcomes from 30 years of research in BH3-mimetics have indeed served a number of solid paradigms for targeting intermediates from the apoptosis pathway in a variety of diseased states. Not only have such rational approaches in drug design yielded several key therapeutics, such outputs have also offered insights into the integrated mechanistic aspects of basic and clinical research at the genetics level for the future. In no other area of medical research have the effects of such work been felt, than in cancer research, through targeting the BAX-Bcl-2 protein-protein interactions. With these promising outputs in mind, several mimetics, and their potential therapeutic applications, have also been developed for several other pathological conditions, such as cardiovascular disease and tissue fibrosis, thus highlighting the universal importance of the intrinsic arm of the apoptosis pathway and its input to general tissue homeostasis. Considering such recent developments, and in a field that has generated so much scientific interest, we take stock of how the broadening area of BH3-mimetics has developed and diversified, with a focus on their uses in single and combined cancer treatment regimens and recently explored therapeutic delivery methods that may aid the development of future therapeutics of this nature.

Advances in Cancer Treatment by Targeting the Neddylation Pathway

Developmental down-regulation protein 8 (NEDD8), expressed by neural progenitors, is a ubiquitin-like protein that conjugates to and regulates the biological function of its substrates. The main target of NEDD8 is cullin-RING E3 ligases. Upregulation of the neddylation pathway is closely associated with the progression of various tumors, and MLN4924, which inhibits NEDD8-activating enzyme (NAE), is a promising new antitumor compound for combination therapy. Here, we summarize the latest progress in anticancer strategies targeting the neddylation pathway and their combined applications, providing a theoretical reference for developing antitumor drugs and combination therapies.

Caspase-8 loss radiosensitizes head and neck squamous cell carcinoma to SMAC mimetic-induced necroptosis

Caspase-8 (CASP8) is one of the most frequently mutated genes in head and neck squamous carcinomas (HNSCCs), and CASP8 mutations are associated with poor survival. The distribution of these mutations in HNSCCs suggests that they are likely to be inactivating. Inhibition of CASP8 has been reported to sensitize cancer cells to necroptosis, a regulated cell death mechanism. Here, we show that knockdown of CASP8 renders HNSCCs susceptible to necroptosis by a second mitochondria-derived activator of caspase (SMAC) mimetic, birinapant, in combination with pan-caspase inhibitors Z-VAD-FMK or emricasan and radiation. In a syngeneic mouse model of oral cancer, birinapant, particularly when combined with radiation, delayed tumor growth and enhanced survival under CASP8 loss. Exploration of molecular underpinnings of necroptosis sensitivity confirmed that the level of functional receptor-interacting serine/threonine protein kinase 3 (RIP3) determines susceptibility to this mode of death. Although an in vitro screen revealed that low RIP3 levels rendered many HNSCC cell lines resistant to necroptosis, patient tumors maintained RIP3 expression and should therefore remain sensitive. Collectively, these results suggest that targeting the necroptosis pathway with SMAC mimetics, especially in combination with radiation, may be relevant therapeutically in HNSCC with compromised CASP8 status, provided that RIP3 function is maintained.

Potency and Selectivity of SMAC/DIABLO Mimetics in Solid Tumor Therapy

Aiming to promote cancer cell apoptosis is a mainstream strategy of cancer therapy. The second mitochondria-derived activator of caspase (SMAC)/direct inhibitor of apoptosis protein (IAP)-binding protein with low pI (DIABLO) protein is an essential and endogenous antagonist of inhibitor of apoptosis proteins (IAPs). SMAC mimetics (SMs) are a series of synthetically chemical compounds. Via database analysis and literature searching, we summarize the potential mechanisms of endogenous SMAC inefficiency, degradation, mutation, releasing blockage, and depression. We review the development of SMs, as well as preclinical and clinical outcomes of SMs in solid tumor treatment, and we analyze their strengths, weaknesses, opportunities, and threats from our point of view. We also highlight several questions in need of further investigation.

Convergence of pathway analysis and pattern recognition predicts sensitization to latest generation TRAIL therapeutics by IAP antagonism

Second generation TRAIL-based therapeutics, combined with sensitising co-treatments, have recently entered clinical trials. However, reliable response predictors for optimal patient selection are not yet available. Here, we demonstrate that a novel and translationally relevant hexavalent TRAIL receptor agonist, IZI1551, in combination with Birinapant, a clinically tested IAP antagonist, efficiently induces cell death in various melanoma models, and that responsiveness can be predicted by combining pathway analysis, data-driven modelling and pattern recognition. Across a panel of 16 melanoma cell lines, responsiveness to IZI1551/Birinapant was heterogeneous, with complete resistance and pronounced synergies observed. Expression patterns of TRAIL pathway regulators allowed us to develop a combinatorial marker that predicts potent cell killing with high accuracy. IZI1551/Birinapant responsiveness could be predicted not only for cell lines, but also for 3D tumour cell spheroids and for cells directly isolated from patient melanoma metastases (80–100% prediction accuracies). Mathematical parameter reduction identified 11 proteins crucial to ensure prediction accuracy, with x-linked inhibitor of apoptosis protein (XIAP) and procaspase-3 scoring highest, and Bcl-2 family members strongly represented. Applied to expression data of a cohort of n = 365 metastatic melanoma patients in a proof of concept in silico trial, the predictor suggested that IZI1551/Birinapant responsiveness could be expected for up to 30% of patient tumours. Overall, response frequencies in melanoma models were very encouraging, and the capability to predict melanoma sensitivity to combinations of latest generation TRAIL-based therapeutics and IAP antagonists can address the need for patient selection strategies in clinical trials based on these novel drugs.

Key necroptotic proteins are required for Smac mimetic-mediated sensitization of cholangiocarcinoma cells to TNF-α and chemotherapeutic gemcitabine-induced necroptosis

Cholangiocarcinoma (CCA), a malignant tumor originating in the biliary tract, is well known to be associated with adverse clinical outcomes and high mortality rates due to the lack of effective therapy. Evasion of apoptosis is considered a key contributor to therapeutic success and chemotherapy resistance in CCA, highlighting the need for novel therapeutic strategies. In this study, we demonstrated that the induction of necroptosis, a novel regulated form of necrosis, could potentially serve as a novel therapeutic approach for CCA patients. The RNA sequencing data in The Cancer Genome Atlas (TCGA) database were analyzed and revealed that both receptor-interacting protein kinase 3 (RIPK3) and mixed lineage kinase domain-like (MLKL), two essential mediators of necroptosis, were upregulated in CCA tissues when compared with the levels in normal bile ducts. We demonstrated in a panel of CCA cell lines that RIPK3 was differentially expressed in CCA cell lines, while MLKL was more highly expressed in CCA cell lines than in nontumor cholangiocytes. We therefore showed that treatment with both tumor necrosis factor-α (TNF-α) and Smac mimetic, an inhibitor of apoptosis protein (IAP) antagonist, induced RIPK1/RIPK3/MLKL-dependent necroptosis in CCA cells when caspases were blocked. The necroptotic induction in a panel of CCA cells was correlated with RIPK3 expression. Intriguingly, we demonstrated that Smac mimetic sensitized CCA cells to a low dose of standard chemotherapy, gemcitabine, and induced necroptosis in an RIPK1/RIPK3/MLKL-dependent manner upon caspase inhibition but not in nontumor cholangiocytes. We further demonstrated that Smac mimetic and gemcitabine synergistically induced an increase in TNF-α mRNA levels and that Smac mimetic reversed gemcitabine-induced cell cycle arrest, leading to cell killing. Collectively, our present study demonstrated that TNF-α and gemcitabine induced RIPK1/RIPK3/MLKL-dependent necroptosis upon IAP depletion and caspase inhibition; therefore, our findings have pivotal implications for designing a novel necroptosis-based therapeutic strategy for CCA patients.

Heparanase Inhibition by Pixatimod (PG545): Basic Aspects and Future Perspectives

Pixatimod is an inhibitor of heparanase, a protein which promotes cancer via its regulation of the extracellular environment by enzymatic cleavage of heparan sulfate (HS) and non-enzymatic signaling. Through its inhibition of heparanase and other HS-binding signaling proteins, pixatimod blocks a number of pro-cancerous processes including cell proliferation, invasion, metastasis, angiogenesis and epithelial-mesenchymal transition. Several laboratories have found that these activities have translated into potent activity using a range of different mouse cancer models, including approximately 30 xenograft and 20 syngeneic models. Analyses of biological samples from these studies have confirmed the heparanase targeting of this agent in vivo and the broad spectrum of anti-cancer effects that heparanase blockade achieves. Pixatimod has been tested in combination with a number of approved anti-cancer drugs demonstrating its clinical potential, including with gemcitabine, paclitaxel, sorafenib, platinum agents and an anti-PD-1 antibody. Clinical testing has shown pixatimod to be well tolerated as a monotherapy, and it is currently being investigated in combination with the anti-PD-1 drug nivolumab in a pancreatic cancer phase I trial.

Understanding Apoptosis and Apoptotic Pathways Targeted Cancer Therapeutics

Various physiological processes involve appropriate tissue developmental process and homeostasis - the pathogenesis of several diseases connected with deregulatory apoptosis process. Apoptosis plays a crucial role in maintaining a balance between cell death and division, evasion of apoptosis results in the uncontrolled multiplication of cells leading to different diseases such as cancer. Currently, the development of apoptosis targeting anticancer drugs has gained much interest since cell death induced by apoptosis causes minimal inflammation. The understanding of complexities of apoptosis mechanism and how apoptosis is evolved by tumor cells to oppose cell death has focused research into the new strategies designed to induce apoptosis in cancer cells. This review focused on the underlying mechanism of apoptosis and the dysregulation of apoptosis modulators involved in the extrinsic and intrinsic apoptotic pathway, which include death receptors (DRs) proteins, cellular FLICE inhibitory proteins (c-FLIP), anti-apoptotic Bcl-2 proteins, inhibitors of apoptosis proteins (IAPs), tumor suppressor (p53) in cancer cells along with various current clinical approaches aimed to selectively induce apoptosis in cancer cells.

HTiP: High-Throughput Immunomodulator Phenotypic Screening Platform to Reveal IAP Antagonists as Anti-cancer Immune Enhancers

Protein- and cell-based immunotherapeutic agents have revolutionized cancer treatment. However, small-molecule immunomodulators with favorable pharmacological properties for reaching intracellular targets remain to be developed. To explore the vast chemical space, a robust method that recapitulates the complex cancer-immune microenvironment in a high-throughput format is essential. To address this critical gap, we developed a high-throughput immunomodulator phenotypic screening platform, HTiP, which integrates the immune and cancer cell co-culture system with imaging- and biochemical-based multiplexed readouts. Using the HTiP platform, we have demonstrated its capability in modeling an oncogenic KRAS mutation-driven immunosuppressive phenotype. From a bioactive chemical library, multiple structurally distinct compounds were identified, all of which target the same class of proteins, inhibitor of apoptosis protein (IAP). IAP has demonstrated roles in cancer immunity. Identification of IAP antagonists as potent anti-tumor immune enhancers provides strong validating evidence for the use of the HTiP platform to discover small-molecule immunomodulators.

Temporal Effects of Combined Birinapant and Paclitaxel on Pancreatic Cancer Cells Investigated via Large-Scale, Ion-Current-Based Quantitative Proteomics (IonStar)

Despite decades of effort, pancreatic adenocarcinoma (PDAC) remains an intractable clinical challenge. An insufficient understanding of mechanisms underlying tumor cell responses to chemotherapy contributes significantly to the lack of effective treatment regimens. Here, paclitaxel, a first-line chemotherapeutic agent, was observed to interact synergistically with birinapant, a second mitochondrial-derived activator of caspases mimetic. Therefore, we investigated molecular-level drug interaction mechanisms using comprehensive, reproducible, and well-controlled ion-current-based MS1 quantification (IonStar). By analyzing 40 biological samples in a single batch, we compared temporal proteomic responses of PDAC cells treated with birinapant and paclitaxel, alone and combined. Using stringent criteria (e.g. strict false-discovery-rate (FDR) control, two peptides/protein), we quantified 4069 unique proteins confidently (99.8% without any missing data), and 541 proteins were significantly altered in the three treatment groups, with an FDR of <1%. Interestingly, most of these proteins were altered only by combined birinapant/paclitaxel, and these predominantly represented three biological processes: mitochondrial function, cell growth and apoptosis, and cell cycle arrest. Proteins responsible for activation of oxidative phosphorylation, fatty acid β-oxidation, and inactivation of aerobic glycolysis were altered largely by combined birinapant/paclitaxel compared with single drugs, suggesting the Warburg effect, which is critical for survival and proliferation of cancer cells, was alleviated by the combination treatment. Metabolic profiling was performed to confirm substantially greater suppression of the Warburg effect by the combined agents compared with either drug alone. Immunoassays confirmed proteomic data revealing changes in apoptosis/survival signaling pathways, such as inhibition of PI3K/AKT, JAK/STAT, and MAPK/ERK signal transduction, as well as induction of G2/M arrest, and showed the drug combination induced much more apoptosis than did single agents. Overall, this in-depth, large-scale proteomics study provided novel insights into molecular mechanisms underlying synergy of combined birinapant/paclitaxel and describes a proteomics/informatics pipeline that can be applied broadly to the development of cancer drug combination regimens.

Therapeutic opportunities based on caspase modulation

Caspases are a family of proteolytic enzymes that play a critical role in the regulation of programmed cell death via apoptosis. Activation of caspases is frequently impaired in human cancers, contributing to cancer formation, progression and therapy resistance. A better understanding of the molecular mechanisms regulating caspase activation in cancer cells is therefore highly important. Thus, targeted modulation of caspase activation and apoptosis represents a promising approach for the development of new therapeutic options to elucidate cancer cell death.

Detection of phosphatidylserine-positive exosomes for the diagnosis of early-stage malignancies

Background:

There has been increasing interest in the detection of tumour exosomes in blood for cancer diagnostics. Most studies have focussed on miRNA and protein signatures that are surrogate markers for specific tumour types. Because tumour cells and tumour-derived exosomes display phosphatidylserine (PS) in their outer membrane leaflet, we developed a highly sensitive ELISA-based system that detects picogram amounts of exosomal phospholipid in plasma as a cancer biomarker.

Methods:

This report describes the development of a highly specific and sensitive ELISA for the capture of PS-expressing tumour exosomes in the blood of tumour-bearing mice. To monitor the relationship between tumour burden and tumour exosome plasma concentrations, plasma from one transplantable breast cancer model (MDA-MB-231) and three genetic mouse models (MMTV-PyMT; breast and KIC and KPC; pancreatic) were screened for captured exosomal phospholipid.

Results:

We show that quantitative assessment of PS-expressing tumour exosomes detected very early-stage malignancies before clinical evidence of disease in all four model systems. Tumour exosome levels showed significant increases by day 7 after tumour implantation in the MDA-MB-231 model while palpable tumours appeared only after day 27. For the MMTV-PyMT and KIC models, tumour exosome levels increased significantly by day 49 (P⩽0.0002) and day 21 (P⩽0.001) while tumours developed only after days 60 and 40, respectively. For the KPC model, a significant increase in blood exosome levels was detected by day 70 (P=0.023) when only preinvasive lesions are microscopically detectable.

Conclusions:

These data indicate that blood PS exosome levels is a specific indicator of cancer and suggest that blood PS is a biomarker for early-stage malignancies.

Combinatorial Screening of Pancreatic Adenocarcinoma Reveals Sensitivity to Drug Combinations Including Bromodomain Inhibitor Plus Neddylation Inhibitor

Pancreatic adenocarcinoma (PDAC) is the fourth most common cause of cancer-related death in the United States. PDAC is difficult to manage effectively, with a five-year survival rate of only 5%. PDAC is largely driven by activating KRAS mutations, and as such, cannot be directly targeted with therapeutic agents that affect the activated protein. Instead, inhibition of downstream signaling and other targets will be necessary to effectively manage PDAC. Here, we describe a tiered single-agent and combination compound screen to identify targeted agents that impair growth of a panel of PDAC cell lines. Several of the combinations identified from the screen were further validated for efficacy and mechanism. Combination of the bromodomain inhibitor JQ1 and the neddylation inhibitor MLN4294 altered the production of reactive oxygen species in PDAC cells, ultimately leading to defects in the DNA damage response. Dual bromodomain/neddylation blockade inhibited in vivo growth of PDAC cell line xenografts. Overall, this work revealed novel combinatorial regimens, including JQ1 plus MLN4294, which show promise for the treatment of RAS-driven PDAC. Mol Cancer Ther; 16(6); 1041-53. ©2017 AACR.

Dabigatran potentiates gemcitabine-induced growth inhibition of pancreatic cancer in mice

Pancreatic cancer is one of the most lethal solid malignancies with little treatment options. We have recently shown that expression of protease activated receptor (PAR)-1 in the tumor microenvironment drives progression and induces chemoresistance of pancreatic cancer. As thrombin is the prototypical PAR-1 agonist, here we addressed the effect of the direct thrombin inhibitor dabigatran on pancreatic cancer growth and drug resistance in an orthotropic pancreatic cancer model. We show that dabigatran treatment did not affect primary tumor growth whereas it significantly increased tumor dissemination throughout the peritoneal cavity. Increased dissemination was accompanied by intratumoral bleeding and increased numbers of aberrant and/or collapsed blood vessels in the primary tumors. In combination with gemcitabine, dabigatran treatment limited primary tumor growth, did not induce bleeding complications and prevented tumor cell dissemination. Dabigatran was however not as efficient as genetic ablation of PAR-1 in our previous study suggesting that thrombin is not the main PAR-1 agonist in the setting of pancreatic cancer. Overall, we show that dabigatran potentiates gemcitabine-induced growth inhibition of pancreatic cancer but does not affect primary tumor growth when used as a monotherapy.

Smac Mimetics to Therapeutically Target IAP Proteins in Cancer

Inhibitor of Apoptosis (IAP) proteins are overexpressed in a variety of human cancers. Therefore, they are considered as promising targets for the design of therapeutic strategies. Smac mimetics mimic the endogenous mitochondrial protein Smac that antagonizes IAP proteins upon its release into the cytosol. Multiple preclinical studies have documented the ability of Smac mimetics to either directly induce cell death of cancer cells or to prime them to agents that trigger cell death. At present, several Smac mimetics are being evaluated in early clinical trials. The current review provides an overview on the potential of Smac mimetics as cancer therapeutics to target IAP proteins for cancer therapy.

The Targeted SMAC Mimetic SW IV-134 is a strong enhancer of standard chemotherapy in pancreatic cancer

Background

Pancreatic cancer is a lethal malignancy that frequently acquires resistance to conventional chemotherapies often associated with overexpression of inhibitors of apoptosis proteins (IAPs). We have recently described a novel means to deliver second mitochondria-derived activator of caspases (SMAC) mimetics selectively to cancer cells employing the sigma-2 ligand/receptor interaction. The intrinsic death pathway agonist SMAC offers an excellent opportunity to counteract the anti-apoptotic activity of IAPs. SMAC mimetics have been used to sensitize several cancer types to chemotherapeutic agents but cancer-selective delivery and appropriate cellular localization have not yet been considered. In our current study, we tested the ability of the sigma-2/SMAC drug conjugate SW IV-134 to sensitize pancreatic cancer cells to gemcitabine.

Methods

Using the targeted SMAC mimetic SW IV-134, inhibition of the X-linked inhibitor of apoptosis proteins (XIAP) was induced pharmacologically and its impact on cell viability was studied alone and in combination with gemcitabine. Pathway analyses were performed by assessing caspase activation, PARP cleavage and membrane blebbing (Annexin-V), key components of apoptotic cell death. Single-agent treatment regimens were compared with combination therapy in a preclinical mouse model of pancreatic cancer.

Results

The sensitizing effect of XIAP interference toward gemcitabine was confirmed via pharmacological intervention using our recently designed, targeted SMAC mimetic SW IV-134 across a wide range of commonly used pancreatic cancer cell lines at concentrations where the individual drugs showed only minimal activity. On a mechanistic level, we identified involvement of key components of the apoptosis machinery during cell death execution. Furthermore, combination therapy proved superior in decreasing the tumor burden and extending the lives of the animals in a preclinical mouse model of pancreatic cancer.

Conclusion

We believe that the strong sensitizing capacity of SW IV-134 in combination with clinically relevant doses of gemcitabine represents a promising treatment option that warrants clinical evaluation.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-016-0470-4) contains supplementary material, which is available to authorized users.

An inhibitor of apoptosis protein antagonist T-3256336 potentiates the antitumor efficacy of the Nedd8-activating enzyme inhibitor pevonedistat (TAK-924/MLN4924)

Inhibitors of apoptosis proteins (IAPs) are antiapoptotic regulators that block cell death, and are frequently overexpressed in several human cancers, where they facilitate evasion of apoptosis and promote cell survival. IAP antagonists are also known as second mitochondria-derived activator of caspase (SMAC)-mimetics, and have recently been considered as novel therapeutic agents for inducing apoptosis, alone and in combination with other anticancer drugs. In this study, we showed that T-3256336, the orally available IAP antagonist has synergistically enhances the antiproliferative effects of the NEDD8-activating enzyme (NAE) inhibitor pevonedistat (TAK-924/MLN4924), and these effects were attenuated by a TNFα-neutralizing antibody. In the present mechanistic analyses, pevonedistat induced TNFα mRNA and triggered IAP antagonist-dependent extrinsic apoptotic cell death in cancer cell lines. Furthermore, synergistic effects of the combination of T-3256336 and pevonedistat were demonstrated in a HL-60 mouse xenograft model. Our findings provide mechanistic evidence of the effects of IAP antagonists in combination with NAE inhibitors, and demonstrate the potential of a new combination therapy for cancer.

Promises and Challenges of Smac Mimetics as Cancer Therapeutics

Inhibitor of Apoptosis (IAP) proteins block programmed cell death and are expressed at high levels in various human cancers, thus making them attractive targets for cancer drug development. Second mitochondrial activator of caspases (Smac) mimetics are small-molecule inhibitors that mimic Smac, an endogenous antagonist of IAP proteins. Preclinical studies have shown that Smac mimetics can directly trigger cancer cell death or, even more importantly, sensitize tumor cells for various cytotoxic therapies, including conventional chemotherapy, radiotherapy, or novel agents. Currently, several Smac mimetics are under evaluation in early clinical trials as monotherapy or in rational combinations (i.e., GDC-0917/CUDC-427, LCL161, AT-406/Debio1143, HGS1029, and TL32711/birinapant). This review discusses the promise as well as some challenges at the translational interface of exploiting Smac mimetics as cancer therapeutics.

A novel small-molecule IAP antagonist, AZD5582, draws Mcl-1 down-regulation for induction of apoptosis through targeting of cIAP1 and XIAP in human pancreatic cancer

Inhibitor of apoptosis proteins (IAPs) plays an important role in controlling cancer cell survival. IAPs have therefore attracted considerable attention as potential targets in anticancer therapy. In this study, we investigated the anti-tumor effect of AZD5582, a novel small-molecule IAP inhibitor, in human pancreatic cancer cells. Treating human pancreatic cancer cells with AZD5582 differentially induced apoptosis, dependent on the expression of p-Akt and p-XIAP. Moreover, the knockdown of endogenous Akt or XIAP via RNA interference in pancreatic cancer cells, which are resistant to AZD5582, resulted in increased sensitivity to AZD5582, whereas ectopically expressing Akt or XIAP led to resistance to AZD5582. Additionally, AZD5582 targeted cIAP1 to induce TNF-α-induced apoptosis. More importantly, AZD5582 induced a decrease of Mcl-1 protein, a member of the Bcl-2 family, but not that of Bcl-2 and Bcl-xL. Interestingly, ectopically expressing XIAP and cIAP1 inhibited the AZD5582-induced decrease of Mcl-1 protein, which suggests that AZD5582 elicits Mcl-1 decrease for apoptosis induction by targeting of XIAP and cIAP1. Taken together, these results indicate that sensitivity to AZD5582 is determined by p-Akt-inducible XIAP phosphorylation and by targeting cIAP1. Furthermore, Mcl-1 in pancreatic cancer may act as a potent marker to analyze the therapeutic effects of AZD5582.

Hypoxia and Transforming Growth Factor β Cooperate to Induce Fibulin-5 Expression in Pancreatic Cancer

The deposition of extracellular matrix (ECM) is a defining feature of pancreatic ductal adenocarcinoma (PDA), where ECM signaling can promote cancer cell survival and epithelial plasticity programs. However, ECM signaling can also limit PDA tumor growth by producing cytotoxic levels of reactive oxygen species. For example, excess fibronectin stimulation of α5β1 integrin on stromal cells in PDA results in reduced angiogenesis and increased tumor cell apoptosis because of oxidative stress. Fibulin-5 (Fbln5) is a matricellular protein that blocks fibronectin-integrin interaction and thus directly limits ECM-driven reactive oxygen species production and supports PDA progression. Compared with normal pancreatic tissue, Fbln5 is expressed abundantly in the stroma of PDA; however, the mechanisms underlying the stimulation of Fbln5 expression in PDA are undefined. Using in vitro and in vivo approaches, we report that hypoxia triggers Fbln5 expression in a TGF-β- and PI3K-dependent manner. Pharmacologic inhibition of TGF-β receptor, PI3K, or protein kinase B (AKT) was found to block hypoxia-induced Fbln5 expression in mouse embryonic fibroblasts and 3T3 fibroblasts. Moreover, tumor-associated fibroblasts from mouse PDA were also responsive to TGF-β receptor and PI3K/AKT inhibition with regard to suppression of Fbln5. In genetically engineered mouse models of PDA, therapy-induced hypoxia elevated Fbln5 expression, whereas pharmacologic inhibition of TGF-β signaling reduced Fbln5 expression. These findings offer insight into the signaling axis that induces Fbln5 expression in PDA and a potential strategy to block its production.

Potential of apoptotic pathway-targeted cancer therapeutic research: Where do we stand?

Underneath the intricacy of every cancer lies mysterious events that impel the tumour cell and its posterity into abnormal growth and tissue invasion. Oncogenic mutations disturb the regulatory circuits responsible for the governance of versatile cellular functions, permitting tumour cells to endure deregulated proliferation, resist to proapoptotic insults, invade and erode normal tissues and above all escape apoptosis. This disruption of apoptosis has been highly implicated in various malignancies and has been exploited as an anticancer strategy. Owing to the fact that apoptosis causes minimal inflammation and damage to the tissue, apoptotic cell death-based therapy has been the centre of attraction for the development of anticancer drugs. Increased understanding of the molecular pathways underlying apoptosis has enabled scientists to establish unique approaches targeting apoptosis pathways in cancer therapeutics. In this review, we reconnoitre the two major pathways (intrinsic and extrinsic) targeted cancer therapeutics, steering toward chief modulators of these pathways, such as B-cell lymphoma 2 protein family members (pro- and antiapoptotic), inhibitor of apoptosis proteins, and the foremost thespian of extrinsic pathway regulator, tumour necrosis factor-related apoptosis-inducing agent. Together, we also will have a look from clinical perspective to address the agents (drugs) and therapeutic strategies adopted to target these specific proteins/pathways that have entered clinical trials.

Molecular mechanisms of apoptosis and roles in cancer development and treatment

Programmed cell death (PCD) or apoptosis is a mechanism which is crucial for all multicellular organisms to control cell proliferation and maintain tissue homeostasis as well as eliminate harmful or unnecessary cells from an organism. Defects in the physiological mechanisms of apoptosis may contribute to different human diseases like cancer. Identification of the mechanisms of apoptosis and its effector proteins as well as the genes responsible for apoptosis has provided a new opportunity to discover and develop novel agents that can increase the sensitivity of cancer cells to undergo apoptosis or reset their apoptotic threshold. These novel targeted therapies include those targeting anti-apoptotic Bcl-2 family members, p53, the extrinsic pathway, FLICE-inhibitory protein (c-FLIP), inhibitor of apoptosis (IAP) proteins, and the caspases. In recent years a number of these novel agents have been assessed in preclinical and clinical trials. In this review, we introduce some of the key regulatory molecules that control the apoptotic pathways, extrinsic and intrinsic death receptors, discuss how defects in apoptotic pathways contribute to cancer, and list several agents being developed to target apoptosis.

Curcumin Induces Pancreatic Adenocarcinoma Cell Death Via Reduction of the Inhibitors of Apoptosis

OBJECTIVES

The inhibitor of apoptosis (IAP) proteins are critical modulators of chemotherapeutic resistance in various cancers. To address the alarming emergence of chemotherapeutic resistance in pancreatic cancer, we investigated the efficacy of the turmeric derivative curcumin in reducing IAP protein and mRNA expression resulting in pancreatic cancer cell death.

METHODS

The pancreatic adenocarcinoma cell line PANC-1 was used to assess curcumin's effects in pancreatic cancer. Curcumin uptake was measured by spectral analysis and fluorescence microscopy. AlamarBlue and Trypan blue exclusion assays were used to determine PANC-1 cell viability after curcumin treatment. Visualization of PANC-1 cell death was performed using Hoffman Modulation Contrast microscopy. Western blot, and polymerase chain reaction analyses were used to evaluate curcumin's effects on IAP protein and mRNA expression.

RESULTS

Curcumin enters PANC-1 cells and is ubiquitously present within the cell after treatment. Furthermore, curcumin reduces cell viability and induces morphological changes characteristic of cell death. Additionally, curcumin decreases IAP protein and mRNA expression in PANC-1 cells.

CONCLUSIONS

These data demonstrate that PANC-1 cells are sensitive to curcumin treatment. Futthermore, curcumin is a potential therapeutic tool for overcoming chemotherapeutic resistance mediated by IAPs. Together, this data supports a role for curcumin as part of the therapeutic approach for the treatment of pancreatic cancer.

Fibulin-5 Blocks Microenvironmental ROS in Pancreatic Cancer

Elevated oxidative stress is an aberration seen in many solid tumors, and exploiting this biochemical difference has the potential to enhance the efficacy of anticancer agents. Homeostasis of reactive oxygen species (ROS) is important for normal cell function, but excessive production of ROS can result in cellular toxicity, and therefore ROS levels must be balanced finely. Here, we highlight the relationship between the extracellular matrix and ROS production by reporting a novel function of the matricellular protein Fibulin-5 (Fbln5). We used genetically engineered mouse models of pancreatic ductal adenocarcinoma (PDAC) and found that mutation of the integrin-binding domain of Fbln5 led to decreased tumor growth, increased survival, and enhanced chemoresponse to standard PDAC therapies. Through mechanistic investigations, we found that improved survival was due to increased levels of oxidative stress in Fbln5-mutant tumors. Furthermore, loss of the Fbln5-integrin interaction augmented fibronectin signaling, driving integrin-induced ROS production in a 5-lipooxygenase-dependent manner. These data indicate that Fbln5 promotes PDAC progression by functioning as a molecular rheostat that modulates cell-ECM interactions to reduce ROS production, and thus tip the balance in favor of tumor cell survival and treatment-refractory disease.

A rapid in vivo screen for pancreatic ductal adenocarcinoma therapeutics

Pancreatic ductal adenocarcinoma (PDA) is the fourth leading cause of cancer-related deaths in the United States, and is projected to be second by 2025. It has the worst survival rate among all major cancers. Two pressing needs for extending life expectancy of affected individuals are the development of new approaches to identify improved therapeutics, addressed herein, and the identification of early markers. PDA advances through a complex series of intercellular and physiological interactions that drive cancer progression in response to organ stress, organ failure, malnutrition, and infiltrating immune and stromal cells. Candidate drugs identified in organ culture or cell-based screens must be validated in preclinical models such as KIC (p48(Cre);LSL-Kras(G12D);Cdkn2a(f/f)) mice, a genetically engineered model of PDA in which large aggressive tumors develop by 4 weeks of age. We report a rapid, systematic and robust in vivo screen for effective drug combinations to treat Kras-dependent PDA. Kras mutations occur early in tumor progression in over 90% of human PDA cases. Protein kinase and G-protein coupled receptor (GPCR) signaling activates Kras. Regulators of G-protein signaling (RGS) proteins are coincidence detectors that can be induced by multiple inputs to feedback-regulate GPCR signaling. We crossed Rgs16::GFP bacterial artificial chromosome (BAC) transgenic mice with KIC mice and show that the Rgs16::GFP transgene is a Kras(G12D)-dependent marker of all stages of PDA, and increases proportionally to tumor burden in KIC mice. RNA sequencing (RNA-Seq) analysis of cultured primary PDA cells reveals characteristics of embryonic progenitors of pancreatic ducts and endocrine cells, and extraordinarily high expression of the receptor tyrosine kinase Axl, an emerging cancer drug target. In proof-of-principle drug screens, we find that weanling KIC mice with PDA treated for 2 weeks with gemcitabine (with or without Abraxane) plus inhibitors of Axl signaling (warfarin and BGB324) have fewer tumor initiation sites and reduced tumor size compared with the standard-of-care treatment. Rgs16::GFP is therefore an in vivo reporter of PDA progression and sensitivity to new chemotherapeutic drug regimens such as Axl-targeted agents. This screening strategy can potentially be applied to identify improved therapeutics for other cancers.

Mechanism-based mathematical modeling of combined gemcitabine and birinapant in pancreatic cancer cells

Combination chemotherapy is standard treatment for pancreatic cancer. However, current drugs lack efficacy for most patients, and selection and evaluation of new combination regimens is empirical and time-consuming. The efficacy of gemcitabine, a standard-of-care agent, combined with birinapant, a pro-apoptotic antagonist of Inhibitor of Apoptosis Proteins (IAPs), was investigated in pancreatic cancer cells. PANC-1 cells were treated with vehicle, gemcitabine (6, 10, 20 nM), birinapant (50, 200, 500 nM), and combinations of the two drugs. Temporal changes in cell numbers, cell cycle distribution, and apoptosis were measured. A basic pharmacodynamic (PD) model based on cell numbers, and a mechanism-based PD model integrating all measurements, were developed. The basic PD model indicated that synergistic effects occurred in both cell proliferation and death processes. The mechanism-based model captured key features of drug action: temporary cell cycle arrest in S phase induced by gemcitabine alone, apoptosis induced by birinapant alone, and prolonged cell cycle arrest and enhanced apoptosis induced by the combination. A drug interaction term Ψ was employed in the models to signify interactions of the combination when data were limited. When more experimental information was utilized, Ψ values approaching 1 indicated that specific mechanisms of interactions were captured better. PD modeling identified the potential benefit of combining gemcitabine and birinapant, and characterized the key interaction pathways. An optimal treatment schedule of pretreatment with gemcitabine for 24-48 h was suggested based on model predictions and was verified experimentally. This approach provides a generalizable modeling platform for exploring combinations of cytostatic and cytotoxic agents in cancer cell culture studies.

Smac therapeutic Peptide nanoparticles inducing apoptosis of cancer cells for combination chemotherapy with Doxorubicin

Smac-conjugated nanoparticle (Smac-NP) was designed to induce the apoptosis of cancer cells and as a drug carrier for combination therapy. It contained three parts, a SmacN7 peptide which could induce apoptosis of cancer cells by interacting with XIAPs, the cell penetrating domain rich in arginine, and four hydrophobic tails for self-assembled Smac-NP. We demonstrated that Smac-NPs exerted an antitumor effect in breast cancer cell MDA-MB-231 and nonsmall lung cancer (NSCLC) cell H460, which efficiently inhibited cancer cells proliferation without influencing normal liver cell lines LO2. Smac-NPs also significantly induced apoptosis of MDA-MB-231 and H460 cells through activating pro-caspase-3, down-regulating the expression of antiapoptotic protein Bcl-2 and up-regulating the pro-apoptotic protein Bax. Furthermore, Smac-NPs could be explored as a drug delivery system to load hydrophobic drug such as DOX for combination therapy. The DOX-loaded nanoparticles (DOX-Smac-NPs) exhibited higher cellular uptake efficiency and antitumor effect. Our work provided a new insight into therapeutic peptides integrated with drug simultaneously in one system for cancer combination treatment.

Smac mimetics as IAP antagonists

As the Inhibitor of Apoptosis (IAP) proteins are expressed at high levels in human cancers, they represent promising targets for therapeutic intervention. Small-molecule inhibitors of IAP proteins mimicking the endogenous IAP antagonist Smac, called Smac mimetics, neutralize IAP proteins and thereby promote the induction of cell death. Smac mimetics have been shown in preclinical models of human cancer to directly trigger cancer cell death or to sensitize for cancer cell death induced by a variety of cytotoxic stimuli. Smac mimetics are currently undergoing clinical evaluation in phase I/II trials, demonstrating that therapeutic targeting of IAP proteins has reached the clinical stage.

Debio 1143, an antagonist of multiple inhibitor-of-apoptosis proteins, activates apoptosis and enhances radiosensitization of non-small cell lung cancer cells in vitro

Inhibitors of apoptosis (IAPs) limit the effectiveness of radiation in non-small cell lung cancer (NSCLC). Debio 1143 (D1143) is an antagonist of IAPs. The purpose of this study was to investigate the potential of D1143 as a radiosensitizer in NSCLC. MTS assays were performed in two NSCLC cell lines: HCC193 and H460. Extent of apoptotic cell death was characterized by Annexin V assay and Western blot for cleaved caspase-3, -8, and IAPs. TNF-α release was determined by ELISA. Radiosensitivities were compared with dose enhancement ratios (DERs). HCC193 cells D1143 IC50 was 1 μM. HCC193 cells demonstrated noticeable cleaved caspase-3, -8, and a decrease in IAP levels with 2.5 μM D1143; H460 cells, with 10 μM; both in a time-dependent manner. Additionally, HCC193 cells exhibited an increase in TNF-α. D1143 radiosensitized cells: HCC193, 2.5 μM D1143, 24 h incubation, DER of 2.19, p = 0.001; H460 cells, 10 μM D1143, 48 h incubation, DER of 1.29, p = 0.082. Treatment of H460 cells with radiation therapy, TNF-α, and D1143 further radiosensitized the cells (DER of 1.92, p = 0.026). D1143 significantly enhanced the radiosensitization of HCC193 and H460 cells in vitro. TNF-α contributed to the sensitization in the more sensitive cell line (HCC193). More research is warranted to test the mechanism of D1143, and to assess its potential in vivo in the clinical setting.

A novel antagonist to the inhibitors of apoptosis (IAPs) potentiates cell death in EGFR-overexpressing non-small-cell lung cancer cells

In the effort to develop an efficient chemotherapy drug for the treatment of non-small-cell lung cancer (NSCLC), we analyzed the anti-tumorigenic effects of a novel small molecule targeting the inhibitor of apoptosis (IAPs), HM90822B, on NSCLC cells. HM90822B efficiently decreased IAP expression, especially that of XIAP and survivin, in several NSCLC cells. Interestingly, cells overexpressing epidermal growth factor receptor (EGFR) due to the mutations were more sensitive to HM90822B, undergoing cell cycle arrest and apoptosis when treated. In xenograft experiments, inoculated EGFR-overexpressing NSCLC cells showed tumor regression when treated with the inhibitor, demonstrating the chemotherapeutic potential of this agent. Mechanistically, decreased levels of EGFR, Akt and phospho-MAPKs were observed in inhibitor-treated PC-9 cells on phosphorylation array and western blotting analysis, indicating that the reagent inhibited cell growth by preventing critical cell survival signaling pathways. In addition, gene-specific knockdown studies against XIAP and/or EGFR further uncovered the involvement of Akt and MAPK pathways in HM90822B-mediated downregulation of NSCLC cell growth. Together, these results support that HM90822B is a promising candidate to be developed as lung tumor chemotherapeutics by targeting oncogenic activities of IAP together with inhibiting cell survival signaling pathways.

Putting the pieces together: How is the mitochondrial pathway of apoptosis regulated in cancer and chemotherapy?

In order to solve a jigsaw puzzle, one must first have the complete picture to logically connect the pieces. However, in cancer biology, we are still gaining an understanding of all the signaling pathways that promote tumorigenesis and how these pathways can be pharmacologically manipulated by conventional and targeted therapies. Despite not having complete knowledge of the mechanisms that cause cancer, the signaling networks responsible for cancer are becoming clearer, and this information is serving as a solid foundation for the development of rationally designed therapies. One goal of chemotherapy is to induce cancer cell death through the mitochondrial pathway of apoptosis. Within this review, we present the pathways that govern the cellular decision to undergo apoptosis as three distinct, yet connected puzzle pieces: (1) How do oncogene and tumor suppressor pathways regulate apoptosis upstream of mitochondria? (2) How does the B-cell lymphoma 2 (BCL-2) family influence tumorigenesis and chemotherapeutic responses? (3) How is post-mitochondrial outer membrane permeabilization (MOMP) regulation of cell death relevant in cancer? When these pieces are united, it is possible to appreciate how cancer signaling directly impacts upon the fundamental cellular mechanisms of apoptosis and potentially reveals novel pharmacological targets within these pathways that may enhance chemotherapeutic success.

Small-molecule SMAC mimetics as new cancer therapeutics

Apoptosis is a tightly regulated cellular process and faulty regulation of apoptosis is a hallmark of human cancers. Targeting key apoptosis regulators with the goal to restore apoptosis in tumor cells has been pursued as a new cancer therapeutic strategy. XIAP, cIAP1, and cIAP2, members of inhibitor of apoptosis (IAP) proteins, are critical regulators of cell death and survival and are attractive targets for new cancer therapy. The SMAC/DIABLO protein is an endogenous antagonist of XIAP, cIAP1, and cIAP2. In the last decade, intense research efforts have resulted in the design and development of several small-molecule SMAC mimetics now in clinical trials for cancer treatment. In this review, we will discuss the roles of XIAP, cIAP1, and cIAP2 in regulation of cell death and survival, and the design and development of small-molecule SMAC mimetics as novel cancer treatments.

Therapeutic options for the management of pancreatic cancer

Since its initial characterization, pancreatic ductal adenocarcinoma has remained one of the most devastating and difficult cancers to treat. Pancreatic cancer is the fourth leading cause of death in the United States, resulting in an estimated 38460 deaths annually. With few screening tools available to detect this disease at an early stage, 94% of patients will die within five years of diagnosis. Despite decades of research that have led to a better understanding of the molecular and cellular signaling pathways in pancreatic cancer cells, few effective therapies have been developed to target these pathways. Other treatment options have included more sophisticated pancreatic cancer surgeries and combination therapies. While outcomes have improved modestly for these patients, more effective treatments are desperately needed. One of the greatest challenges in the future of treating this malignancy will be to develop therapies that target the tumor microenvironment and surrounding pancreatic cancer stem cells in addition to pancreatic cancer cells. Recent advances in targeting pancreatic stellate cells and the stroma have encouraged researchers to shift their focus to the role of desmoplasia in pancreatic cancer pathobiology in the hopes of developing newer-generation therapies. By combining novel agents with current cytotoxic chemotherapies and radiation therapy and personalizing them to each patient based on specific biomarkers, the goal of prolonging a patient’s life could be achieved. Here we review the most effective therapies that have been used for the treatment of pancreatic cancer and discuss the future potential of therapeutic options.

Neutralizing murine TGFβR2 promotes a differentiated tumor cell phenotype and inhibits pancreatic cancer metastasis

Elevated levels of TGFβ are a negative prognostic indicator for patients diagnosed with pancreatic cancer; as a result, the TGFβ pathway is an attractive target for therapy. However, clinical application of pharmacologic inhibition of TGFβ remains challenging because TGFβ has tumor suppressor functions in many epithelial malignancies, including pancreatic cancer. In fact, direct neutralization of TGFβ promotes tumor progression of genetic murine models of pancreatic cancer. Here, we report that neutralizing the activity of murine TGFβ receptor 2 using a monoclonal antibody (2G8) has potent antimetastatic activity in orthotopic human tumor xenografts, syngeneic tumors, and a genetic model of pancreatic cancer. 2G8 reduced activated fibroblasts, collagen deposition, microvessel density, and vascular function. These stromal-specific changes resulted in tumor cell epithelial differentiation and a potent reduction in metastases. We conclude that TGFβ signaling within stromal cells participates directly in tumor cell phenotype and pancreatic cancer progression. Thus, strategies that inhibit TGFβ-dependent effector functions of stromal cells could be efficacious for the therapy of pancreatic tumors. Cancer Res; 74(18); 4996-5007. ©2014 AACR.

Pancreatic ductal adenocarcinoma: a review of immunologic aspects

With the continued failures of both early diagnosis and treatment options for pancreatic cancer, it is now time to comprehensively evaluate the role of the immune system on the development and progression of pancreatic cancer. It is important to develop strategies that harness the molecules and cells of the immune system to treat this disease. This review will focus primarily on the role of immune cells in the development and progression of pancreatic ductal adenocarcinoma and to evaluate what is known about the interaction of immune cells with the tumor microenvironment and their role in tumor growth and metastasis. We will conclude with a brief discussion of therapy for pancreatic cancer and the potential role for immunotherapy. We hypothesize that the role of the immune system in tumor development and progression is tissue specific. Our hope is that better understanding of this process will lead to better treatments for this devastating disease.

Targeted pancreatic cancer therapy with the small molecule drug conjugate SW IV-134

Pancreatic adenocarcinoma is highly resistant to conventional therapeutics and has been shown to evade apoptosis by deregulation of the X-linked and cellular inhibitors of apoptosis proteins (XIAP and cIAP). Second mitochondria-derived activator of caspases (Smac) induces and amplifies cell death by reversing the anti-apoptotic activity of IAPs. Thus, Smac-derived peptide analogues (peptidomimetics) have been developed and shown to represent promising cancer therapeutics. Sigma-2 receptors are overexpressed in many proliferating tumor cells including pancreatic cancer. Selected ligands to this receptor are rapidly internalized by cancer cells. These characteristics have made the sigma-2 receptor an attractive target for drug delivery because selective delivery to cancer cells has the potential to increase therapeutic efficacy while minimizing toxicity to normal tissues. Here, we describe the initial characterization of SW IV-134, a chemically linked drug conjugate between the sigma-2 ligand SW43 and the Smac mimetic SW IV-52 as a novel treatment option for pancreatic adenocarcinoma. The tumor killing characteristics of our dual-domain therapeutic SW IV-134 was far greater than either component in isolation or in an equimolar mix and suggests enhanced cellular delivery when chemically linked to the sigma-2 ligand. One of the key findings was that SW IV-134 retained target selectivity of the Smac cargo with the involvement of the NF-κB/TNFα signaling pathway. Importantly, SW IV-134 slowed tumor growth and improved survival in murine models of pancreatic cancer. Our data support further study of this novel therapeutic and this drug delivery strategy because it may eventually benefit patients with pancreatic cancer.

Conjugation to a SMAC mimetic potentiates sigma-2 ligand induced tumor cell death in ovarian cancer

BACKGROUND

Drug resistance is a significant problem in the treatment of ovarian cancer and can be caused by multiple mechanisms. Inhibition of apoptosis by the inhibitor of apoptosis proteins (IAPs) represents one such mechanism, and can be overcome by a mitochondrial protein called second mitochondria-derived activator of caspases (SMAC). We have previously shown that the ligands of sigma-2 receptors effectively induce tumor cell death. Additionally, because sigma-2 receptors are preferentially expressed in tumor cells, their ligands provide an effective mechanism for selective anti-cancer therapy.

METHODS

In the current work, we have improved upon the previously described sigma-2 ligand SW43 by conjugating it to a pro-apoptotic small molecule SMAC mimetic SW IV-52, thus generating the novel cancer therapeutic SW IV-134. The new cancer drug was tested for receptor selectivity and tumor cell killing activity in vitro and in vivo.

RESULTS

We have shown that SW IV-134 retained adequate sigma-2 receptor binding affinity in the context of the conjugate and potently induced cell death in ovarian cancer cells. The cell death induced by SW IV-134 was significantly greater than that observed with either SW43 or SW IV-52 alone and in combination. Furthermore, the intraperitoneal administration of SW IV-134 significantly reduced tumor burden and improved overall survival in a mouse xenograft model of ovarian cancer without causing significant adverse effects to normal tissues. Mechanistically, SW IV-134 induced degradation of cIAP-1 and cIAP-2 leading to NF-қB activation and TNFα-dependent cell death.

CONCLUSIONS

Our findings suggest that coupling sigma-2 ligands to SMAC peptidomimetics enhances their effectiveness while maintaining the cancer selectivity. This encouraging proof-of-principle preclinical study supports further development of tumor-targeted small peptide mimetics via ligands to the sigma-2 receptor for future clinical applications.

Collagen signaling enhances tumor progression after anti-VEGF therapy in a murine model of pancreatic ductal adenocarcinoma

There is growing evidence that antiangiogenic therapy stimulates cancer cell invasion and metastasis. However, the underlying molecular mechanisms responsible for these changes have not been fully defined. Here, we report that anti-VEGF therapy promotes local invasion and metastasis by inducing collagen signaling in cancer cells. We show that chronic VEGF inhibition in a genetically engineered mouse model of pancreatic ductal adenocarcinoma (PDA) induces hypoxia, a less differentiated mesenchymal-like tumor cell phenotype, TGF-β expression, and collagen deposition and signaling. In addition, we show that collagen signaling is critical for protumorigenic activity of TGF-β in vitro. To further model the impact of collagen signaling in tumors, we evaluated PDA in mice lacking Sparc, a protein that reduces collagen binding to cell surface receptors. Importantly, we show that loss of Sparc increases collagen signaling and tumor progression. Together, these findings suggest that collagen actively promotes PDA spread and that enhanced disease progression associated with anti-VEGF therapy can arise from elevated extracellular matrix-mediated signaling.

Smac mimetics induce inflammation and necrotic tumour cell death by modulating macrophage activity

Smac mimetics (SMs) comprise a class of small molecules that target members of the inhibitor of apoptosis family of pro-survival proteins, whose expression in cancer cells hinders the action of conventional chemotherapeutics. Herein, we describe the activity of SM83, a newly synthesised dimeric SM, in two cancer ascites models: athymic nude mice injected intraperitoneally with IGROV-1 human ovarian carcinoma cells and immunocompetent BALB/c mice injected with murine Meth A sarcoma cells. SM83 rapidly killed ascitic IGROV-1 and Meth A cells in vivo (prolonging mouse survival), but was ineffective against the same cells in vitro. IGROV-1 cells in nude mice were killed within the ascites by a non-apoptotic, tumour necrosis factor (TNF)-dependent mechanism. SM83 administration triggered a rapid inflammatory event characterised by host secretion of TNF, interleukin-1β and interferon-γ. This inflammatory response was associated with the reversion of the phenotype of tumour-associated macrophages from a pro-tumoural M2- to a pro-inflammatory M1-like state. SM83 treatment was also associated with a massive recruitment of neutrophils that, however, was not essential for the antitumoural activity of this compound. In BALB/c mice bearing Meth A ascites, SM83 treatment was in some cases curative, and these mice became resistant to a second injection of cancer cells, suggesting that they had developed an adaptive immune response. Altogether, these results indicate that, in vivo, SM83 modulates the immune system within the tumour microenvironment and, through its pro-inflammatory action, leads cancer cells to die by necrosis with the release of high-mobility group box-1. In conclusion, our work provides evidence that SMs could be more therapeutically active than expected by stimulating the immune system.

Anti-cancer IAP antagonists promote bone metastasis: a cautionary tale

The bone microenvironment is complex, containing bone-forming osteoblasts, bone-resorbing osteoclasts, bone-maintaining osteocytes, hematopoietic lineage cells, as well as blood vessels, nerves, and stromal cells. Release of embedded growth factors from the bone matrix via osteoclast resorption has been shown to participate in the alteration of bone microenvironment to facilitate tumor metastasis to this organ. Many types of malignancies including solid tumors and leukemias are associated with elevated levels of inhibitor of apoptosis (IAP) proteins, and IAP antagonists represent an important emerging class of anti-cancer agents. IAPs exert anti-apoptotic roles by inhibiting caspases and upregulating pro-survival proteins, at least in part by activating classical NF-κB signaling. In addition, IAPs act as negative regulators in the alternative NF-κB pathway, so that IAP antagonists stimulate this pathway. The role of the classical NF-κB pathway in IAP antagonist-induced apoptosis has been extensively studied, whereas much less attention has been paid to the role of these agents in the alternative pathway. Thus far, several IAP antagonists have been tested in preclinical and early stage clinical trials, and have shown promise in sensitizing tumor cells to apoptosis without significant side effects. However, recent preclinical evidence suggests an increased risk of bone metastasis caused by IAP antagonists, along with potential for promoting osteoporosis. In this review, the connection between IAP antagonists, the alternative NF-κB pathway, osteoclasts, and bone metastasis are discussed. In light of these effects of IAP antagonists on the bone microenvironment, more attention should be paid to this and other host tissues as these drugs are developed further.