The role of the immune response and inflammatory pathways in TNF-related apoptosis-inducing ligand (TRAIL) resistance in triple-negative breast cancer cells.

Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer, and the majority of TNBC lacks targeted therapies. Previous studies have shown that TNBC cells are highly sensitive to TNF-related apoptosis-inducing ligand (TRAIL), making it a potentially viable treatment option for TNBC. However, the development of TRAIL resistance limits its potential for clinical use, and the underlying mechanisms are not fully understood. To better understand the mechanism of resistance to TRAIL, we performed RNA sequencing to identify the candidates that are responsible for resistance to TRAIL in two previously established TRAIL-resistant MDA231 and SUM159 cells. This approach led us to identify differentially expressed genes (DEGs) and pathways in TRAIL-resistant MDA231 and SUM159 cells compared to their TRAIL-sensitive counterparts. We showed that several DEGs and pathways were associated with inflammation in TRAIL-resistant cells, including IL-1α and IL6. By downregulating IL-1α and IL6 expression, we showed that TRAIL sensitivity can be significantly restored in TRAIL-resistant cells. Therefore, this study identifies a mechanism by which the inflammation pathway promotes TRAIL resistance, which could be targeted for enhancing TRAIL-based therapies in TNBC cells.

The Role of TRAIL in Apoptosis and Immunosurveillance in Cancer.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that selectively induces apoptosis in tumor cells without harming normal cells, making it an attractive agent for cancer therapy. TRAIL induces apoptosis by binding to and activating its death receptors DR4 and DR5. Several TRAIL-based treatments have been developed, including recombinant forms of TRAIL and its death receptor agonist antibodies, but the efficacy of TRAIL-based therapies in clinical trials is modest. In addition to inducing cancer cell apoptosis, TRAIL is expressed in immune cells and plays a critical role in tumor surveillance. Emerging evidence indicates that the TRAIL pathway may interact with immune checkpoint proteins, including programmed death-ligand 1 (PD-L1), to modulate PD-L1-based tumor immunotherapies. Therefore, understanding the interaction between TRAIL and the immune checkpoint PD-L1 will lead to the development of new strategies to improve TRAIL- and PD-L1-based therapies. This review discusses recent findings on TRAIL-based therapy, resistance, and its involvement in tumor immunosurveillance.

Regulation of programmed death ligand 1 (PD-L1) expression by TNF-related apoptosis-inducing ligand (TRAIL) in triple-negative breast cancer cells.

Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer that lacks targeted therapies. Previous studies have shown that TNBC cells are highly sensitive to tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), making it a promising agent for treating TNBC. However, the development of TRAIL resistance limits its further clinical development, and the underlying mechanisms are not fully understood. In this study, we report the role of PD-L1 in TRAIL resistance. Specifically, we found that TRAIL treatment increases PD-L1 expression in TRAIL-sensitive cells and that basal PD-L1 expression is increased in acquired TRAIL-resistant cells. Mechanistically, we found that increased PD-L1 expression was accompanied by increased extracellular signal-regulated kinase (ERK) activation. Using both genetic and pharmacological approaches, we showed that knockdown of ERK by siRNA or inhibition of ERK activation by the mitogen-activated protein kinase kinase inhibitor U0126 decreased PD-L1 expression and increased TRAIL-induced cell death. Furthermore, we found that knockout or knockdown of PD-L1 enhances TRAIL-induced apoptosis, suggesting that PD-L1-mediated TRAIL resistance is independent of its ability to evade immune suppression. Therefore, this study identifies a noncanonical mechanism by which PD-L1 promotes TRAIL resistance, which can be potentially exploited for immune checkpoint therapy.

Proteomic Analysis Identifies p62/SQSTM1 as a Critical Player in PARP Inhibitor Resistance.

Poly (ADP-ribose) polymerase (PARP) inhibitors (PARPis) are currently being used for treating breast cancer patients with deleterious or suspected deleterious germline BRCA-mutated, HER2-negative locally advanced or metastatic diseases. Despite durable responses, almost all patients receiving PARPis ultimately develop resistance and succumb to their illness, but the mechanism of PARPi resistance is not fully understood. To better understand the mechanism of PARPi resistance, we established two olaparib-resistant SUM159 and MDA468 cells by chronically exposing olaparib-sensitive SUM159 and MDA468 cells to olaparib. Olaparib-resistant SUM159 and MDA468 cells displayed 5-fold and 7-fold more resistance over their corresponding counterparts. Despite defects in PARPi-induced DNA damage, these olaparib-resistant cells are sensitive to cisplatin-induced cell death. Using an unbiased proteomic approach, we identified 6 447 proteins, of which 107 proteins were differentially expressed between olaparib-sensitive and -resistant cells. Ingenuity pathway analysis (IPA) revealed a number of pathways that are significantly altered, including mTOR and ubiquitin pathways. Among these differentially expressed proteins, p62/SQSTM1 (thereafter p62), a scaffold protein, plays a critical role in binding to and delivering the ubiquitinated proteins to the autophagosome membrane for autophagic degradation, was significantly downregulated in olaparib-resistant cells. We found that autophagy inducers rapamycin and everolimus synergistically sensitize olaparib-resistant cells to olaparib. Moreover, p62 protein expression was correlated with better overall survival in estrogen receptor-negative breast cancer. Thus, these findings suggest that PARPi-sensitive TNBC cells hyperactivate autophagy as they develop acquired resistance and that pharmacological stimulation of excessive autophagy could lead to cell death and thus overcome PARPi resistance.

Correction: Discovery and clinical introduction of first-in-class imipridone ONC201.

[This corrects the article DOI: 10.18632/oncotarget.11814.].

Pharmacological Inhibition of PP2A Overcomes Nab-Paclitaxel Resistance by Downregulating MCL1 in Esophageal Squamous Cell Carcinoma (ESCC).

Paclitaxel-based chemotherapy is a treatment option for advanced esophageal squamous cell carcinoma (ESCC). However, the development of chemoresistance leads to treatment failure, and the underlying mechanism remains elusive. We investigated the mechanisms of nanoparticle albumin-bound paclitaxel (nab-PTX) resistance by establishing three nab-PTX resistant ESCC cell lines. Proteomics analysis revealed higher oxidative phosphorylation (OXPHOS) in resistant cell line DR150 than in its parental cell line KYSE150, which is likely caused by stabilized anti-apoptotic protein MCL1. Additionally, we discovered the elevated activity of protein phosphatase 2A (PP2A), the phosphatase that dephosphorylates and stabilizes MCL1, in nab-PTX resistant cell lines. Pharmacological inhibition of PP2A with small molecule compound LB-100 decreased MCL1 protein level, caused more apoptosis in nab-PTX resistant ESCC cell lines than in the parental cells in vitro, and significantly inhibited the tumor growth of nab-PTX resistant xenografts in vivo. Moreover, LB-100 pretreatment partially restored nab-PTX sensitivity in the resistant cell lines and synergistically inhibited the tumor growth of nab-PTX resistant xenografts with nab-PTX. In summary, our study identifies a novel mechanism whereby elevated PP2A activity stabilizes MCL1 protein, increases OXPHOS, and confers nab-PTX resistance, suggesting that targeting PP2A is a potential strategy for reversing nab-PTX resistance in patients with advanced ESCC.

Analysis of Adaptive Olaparib Resistance Effects on Cisplatin Sensitivity in Triple Negative Breast Cancer Cells.

Poly-(ADP)-ribose polymerase inhibitors (PARPi) and platinum-based drugs are promising therapies for triple negative breast cancers (TNBC) with BRCA1 or BRCA2 loss. PARPi(s) show better efficacies when combined with platinum-based therapy, however, acquisition of PARPi resistance has been linked with co-resistance to platinum-based drugs. Here, we show that TNBCs with constitutively hyperactivated PARP-1 display greater tolerances for the PARPi olaparib and cisplatin, and respond synergistically to olaparib/cisplatin combinations with increased cytotoxicity. Regardless of BRCA1 and PARP-1 activity status, upon gaining olaparib resistance (OlaR), OlaR MDA-MB-468 (BRCA1 wild-type) and SUM1315 (BRCA1 mutant) TNBC cells retain cisplatin sensitivities of their isogenic parental counterparts. OlaR TNBC cells express decreased levels of PARP-1 and Pol η, a translesion-synthesis polymerase important in platinum-induced interstrand crosslink repair. Although native RAD51 recombinase levels are unaffected, anti-RAD51 immunoreactive low molecular weight sbands are exclusively detected in OlaR cells. Despite normal BRCA1, RAD51 foci formation/recruitment to double-strand breaks are impaired in OlaR MDA-MB-468 cells, suggesting homologous-recombination impairment. RNA-seq and pathway analysis of cisplatin-affected genes revealed enrichment of G2/M cell cycle regulation and DNA repair pathways in parental and OlaR MDA-MB-468 cells whereas parental and OlaR SUM1315 cells showed enrichment of inflammatory stress response pathways associated with TNFR1/2, TWEAK and IL-17 signaling. These data show that TNBC models with wild type versus mutant BRCA1 exhibit differences in CDDP-induced cellular response pathways, however, the CDDP-induced signaling responses remain stable across the isogenic models of OlaR from the same lineage. These data also show that adaptive OlaR does not automatically promote cisplatin resistance, implicating the potential benefit of platinum-based therapy for OlaR TNBCs.

Targeting PP2A inhibits the growth of triple-negative breast cancer cells.

Triple-negative breast cancer (TNBC) does not respond to widely used targeted/endocrine therapies because of the absence of progesterone and estrogen receptors and HER2 amplification. It has been shown that the majority of TNBC cells are highly sensitive to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis, but the development of TRAIL resistance limits its efficacy. We previously found that protein phosphatase 2A (PP2A) plays an important role in TRAIL resistance. In this study, we evaluated the effects of PP2A inhibition on cell death in TRAIL-resistant TNBC cells. We found that the PP2A inhibitor LB-100 effectively inhibits the growth of a panel of TNBC cell lines including lines that are intrinsically resistant to TRAIL. Using two TRAIL-resistant cell lines generated from TRAIL-sensitive parental cells (MDA231 and SUM159), we found that both TRAIL-sensitive and -resistant cell lines are equally sensitive to LB-100. We also found that LB-100 sensitizes TNBC cells to clinically used chemotherapeutical agents, including paclitaxel and cisplatin. Importantly, we found that LB-100 effectively inhibits the growth of MDA468 tumors in mice in vivo without apparent toxicity. Collectively, these data suggest that pharmacological inhibition of PP2A activity could be a novel therapeutic strategy for treating patients with TNBC in a clinical setting.

GP78 Cooperates with Dual-Specificity Phosphatase 1 To Stimulate Epidermal Growth Factor Receptor-Mediated Extracellular Signal-Regulated Kinase Signaling.

GP78 is an autocrine motility factor (AMF) receptor (AMFR) with E3 ubiquitin ligase activity that plays a significant role in tumor cell proliferation, motility, and metastasis. Aberrant extracellular signal-regulated kinase (ERK) activation via receptor tyrosine kinases promotes tumor proliferation and invasion. The activation of GP78 leads to ERK activation, but its underlying mechanism is not fully understood. Here, we show that GP78 is required for epidermal growth factor receptor (EGFR)-mediated ERK activation. On one hand, GP78 interacts with and promotes the ubiquitination and subsequent degradation of dual-specificity phosphatase 1 (DUSP1), an endogenous negative regulator of mitogen-activated protein kinases (MAPKs), resulting in ERK activation. On the other hand, GP78 maintains the activation status of EGFR, as evidenced by the fact that EGF fails to induce EGFR phosphorylation in GP78-deficient cells. By the regulation of both EGFR and ERK activation, GP78 promotes cell proliferation, motility, and invasion. Therefore, this study identifies a previously unknown signaling pathway by which GP78 stimulates ERK activation via DUSP1 degradation to mediate EGFR-dependent cancer cell proliferation and invasion.

Erratum: Functional analysis of MKP-1 and MKP-2 in breast cancer tamoxifen sensitivity.

[This corrects the article DOI: 10.18632/oncotarget.1795.].

Metabolic vulnerability of cisplatin-resistant cancers.

Cisplatin is the most widely used chemotherapeutic agent, and resistance of neoplastic cells against this cytoxicant poses a major problem in clinical oncology. Here, we explored potential metabolic vulnerabilities of cisplatin-resistant non-small human cell lung cancer and ovarian cancer cell lines. Cisplatin-resistant clones were more sensitive to killing by nutrient deprivation in vitro and in vivo than their parental cisplatin-sensitive controls. The susceptibility of cisplatin-resistant cells to starvation could be explained by a particularly strong dependence on glutamine. Glutamine depletion was sufficient to restore cisplatin responses of initially cisplatin-resistant clones, and glutamine supplementation rescued cisplatin-resistant clones from starvation-induced death. Mass spectrometric metabolomics and specific interventions on glutamine metabolism revealed that, in cisplatin-resistant cells, glutamine is mostly required for nucleotide biosynthesis rather than for anaplerotic, bioenergetic or redox reactions. As a result, cisplatin-resistant cancers became exquisitely sensitive to treatment with antimetabolites that target nucleoside metabolism.

Developing TRAIL/TRAIL death receptor-based cancer therapies.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can initiate the apoptosis pathway by binding to its associated death receptors DR4 and DR5. The activation of the TRAIL pathway in inducing tumor-selective apoptosis leads to the development of TRAIL-based cancer therapies, which include recombinant forms of TRAIL, TRAIL receptor agonists, and other therapeutic agents. Importantly, TRAIL, DR4, and DR5 can all be induced by synthetic and natural agents that activate the TRAIL apoptosis pathway in cancer cells. Thus, understanding the regulation of the TRAIL apoptosis pathway can aid in the development of TRAIL-based therapies for the treatment of human cancer.

ONC201 activates ER stress to inhibit the growth of triple-negative breast cancer cells.

ONC201 was previously identified as a first-in-class antitumor agent and small-molecule inducer of the TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) gene that induces apoptosis in cancer cells. ONC201 has a safety profile and is currently in phase II clinical trials for the treatment of various malignancies. In the current study, we examine the effect of ONC201 on triple-negative breast cancer cells (TNBC), a subtype of breast cancer that is sensitive to TRAIL. We find that ONC201 inhibits the growth of TNBC cells including TNBC cells that have developed acquired TRAIL resistance. However, TNBC cells that have developed acquired ONC201 resistance are cross-resistant to TRAIL. Mechanistically, ONC201 triggers an integrated stress response (ISR) involving the activation of the transcription factor ATF4. Knockdown of ATF4 impairs ONC201-induced apoptosis of TNBC cells. Importantly, the activation of ATF4 is compromised in ONC201-resistant TNBC cells. Thus, our results indicate that ONC201 induces an ISR to cause TNBC cell death and suggest that TNBC patients may benefit from ONC201-based therapies.

Discovery and clinical introduction of first-in-class imipridone ONC201.

ONC201 is the founding member of a novel class of anti-cancer compounds called imipridones that is currently in Phase II clinical trials in multiple advanced cancers. Since the discovery of ONC201 as a p53-independent inducer of TRAIL gene transcription, preclinical studies have determined that ONC201 has anti-proliferative and pro-apoptotic effects against a broad range of tumor cells but not normal cells. The mechanism of action of ONC201 involves engagement of PERK-independent activation of the integrated stress response, leading to tumor upregulation of DR5 and dual Akt/ERK inactivation, and consequent Foxo3a activation leading to upregulation of the death ligand TRAIL. ONC201 is orally active with infrequent dosing in animals models, causes sustained pharmacodynamic effects, and is not genotoxic. The first-in-human clinical trial of ONC201 in advanced aggressive refractory solid tumors confirmed that ONC201 is exceptionally well-tolerated and established the recommended phase II dose of 625 mg administered orally every three weeks defined by drug exposure comparable to efficacious levels in preclinical models. Clinical trials are evaluating the single agent efficacy of ONC201 in multiple solid tumors and hematological malignancies and exploring alternative dosing regimens. In addition, chemical analogs that have shown promise in other oncology indications are in pre-clinical development. In summary, the imipridone family that comprises ONC201 and its chemical analogs represent a new class of anti-cancer therapy with a unique mechanism of action being translated in ongoing clinical trials.

CD44 correlates with clinicopathological characteristics and is upregulated by EGFR in breast cancer.

Cluster of differentiation 44 (CD44), a well-known transmembrane glycoprotein, serves as a promoting factor in the carcinogenesis and progression of a variety of neoplasms. Previous studies have demonstrated that aberrant expression of CD44 was associated with the initiation, invasion, metastasis, and therapy-resistance of breast cancer, but whether there was any association between CD44 and pathological characteristics of breast cancer or epidermal growth factor receptor (EGFR) has not been clearly elucidated. In this study, we utilized public microarray data analysis and tissue microarray technologies to display that CD44 level was enhanced in breast cancer and was significantly correlated with histological grade and the status of estrogen receptor, progesterone receptor and human epidermal growth factor receptor-2 (HER2) and EGFR. Furthermore, mRNA expression of CD44 in breast tumors was positively correlated with basal cytokeratin markers KRT5 and KRT17, but inversely associated with luminal marker FOXA1. Besides, Kaplan-Meier analysis showed that high CD44 mRNA level had adverse impact on the progression-free survival of patients with HER2-expressing or basal-like breast cancer. Functionally, inhibition of EGFR activity by erlotinib impaired the invasion and migration ability of breast cancer cell lines. Western blot assays demonstrated that erlotinib treatment decreased the expression of CD44, accompanied with the reduced protein levels of mesenchymal and cancer stem cell markers. Collectively, this study suggested that the expression of CD44 was upregulated by EGFR pathway and CD44 had a robust impact on the development of breast cancer.

Role for DUSP1 (dual-specificity protein phosphatase 1) in the regulation of autophagy.

Accumulating evidence suggests that mitogen-activated protein kinases (MAPKs) regulate macroautophagy/autophagy. However, the involvement of dual-specificity protein phosphatases (DUSPs), endogenous inhibitors for MAPKs, in autophagy remains to be determined. Here we report that DUSP1/MKP-1, the founding member of the DUSP family, plays a critical role in regulating autophagy. Specifically, we demonstrate that DUSP1 knockdown by shRNA in human ovarian cancer CAOV3 cells and knockout in murine embryonic fibroblasts, increases both basal and rapamycin-increased autophagic flux. Overexpression of DUSP1 had the opposite effect. Importantly, knockout of Dusp1 promoted phosphorylation of ULK1 at Ser555, and BECN1/Beclin 1 at Ser15, and the association of PIK3C3/VPS34, ATG14, BECN1 and MAPK, leading to the activation of the autophagosome-initiating class III phosphatidylinositol 3-kinase (PtdIns3K) complex. Furthermore, knockdown and pharmacological inhibitor studies indicated that DUSP1-mediated suppression of autophagy reflected inactivation of the MAPK1-MAPK3 members of the MAPK family. Knockdown of DUSP1 sensitized CAOV3 cells to rapamycin-induced antigrowth activity. Moreover, CAOV3-CR cells, a line that had acquired cisplatin resistance, exhibited an elevated DUSP1 level and were refractory to rapamycin-induced autophagy and cytostatic effects. Knockdown of DUSP1 in CAOV3-CR cells restored sensitivity to rapamycin. Collectively, this work identifies a previously unrecognized role for DUSP1 in regulating autophagy and suggests that suppression of DUSP1 may enhance the therapeutic activity of rapamycin.

Expression profile of SIX family members correlates with clinic-pathological features and prognosis of breast cancer: A systematic review and meta-analysis.

Sineoculis homeobox homolog (SIX) family proteins, including SIX1, SIX2, SIX3, SIX4, SIX5, and SIX6, have been implicated in the initiation and progression of breast cancer, but the role of each member in breast tumor is not fully understood. We conducted a systematic review and meta-analysis to evaluate the association between the mRNA levels of all 6 members and clinic-pathological characteristics and clinical outcome of breast cancer patients based on the PRISMA statement criteria.ArrayExpress and Oncomine were searched for eligible databases published up to December 10, 2015. The association between the mRNA expression of SIX family members and clinic-pathological features and prognosis was measured by the odds ratio (OR), hazard ratio (HR), and the corresponding 95% confidence interval (CI), respectively. All statistical analyses were performed using STATA software.In total, 20 published Gene Expression Omnibus (GEO) databases with 3555 patients were analyzed. Our analysis revealed that patients with SIX1 overexpression had worse overall survival (OS) (HR: 1.28, 95% CI: 1.03-1.58) and shorter relapse-free survival (RFS) (HR: 1.28, 95% CI: 1.05-1.56), and much worse prognosis for luminal breast cancer patients with SIX1 overexpression (OS: HR: 1.64, 95% CI: 1.13-2.39; RFS: HR: 1.43, 95% CI: 1.06-1.93). We found that patients with higher SIX2 level had shorter time to both relapse and metastasis. However, high SIX3 mRNA level was a protective factor for OS and RFS of basal-like breast cancer patients.Our study suggested that members of SIX family played distinct roles in breast cancer. Detailed analysis of the expression of the SIX family members might provide useful information to predict breast cancer progression and prognosis.

Enrichment of CD44 in basal-type breast cancer correlates with EMT, cancer stem cell gene profile, and prognosis.

Cluster of differentiation 44 (CD44) is a transmembrane glycoprotein that serves as the receptor for the extracellular matrix component hyaluronic acid. CD44 has been reported to play key roles in cell proliferation, motility, and survival, but its role in breast cancer remains controversial. In this study, we conducted a meta-analysis. A total of 23 published Gene Expression Omnibus databases were included to evaluate the association between CD44 mRNA expression and clinicopathological characteristics or prognosis of the patients with breast cancer. Our analysis revealed that CD44 expression was associated with clinicopathological features, including the histological grade, estrogen receptor status, progesterone receptor status, and human epidermal growth factor receptor-2 status. Higher levels of CD44 expression were observed in the basal subtype of breast cancer both at the mRNA and protein levels (odds ratio [OR] =2.08, 95% confidence interval [CI]: 1.72-2.52; OR =2.11, 95% CI: 1.67-2.68). Patients with CD44 overexpression exhibited significantly worse overall survival (hazard ratio =1.27; 95% CI: 1.04-1.55). Whole gene profile analysis revealed that CD44 expression was enriched in basal-type breast cancer and correlated with epithelial-mesenchymal transition and cancer stem cell gene profiles. In summary, our analyses indicated that CD44 potentially might be a prognostic marker for breast cancer and thus can serve as a therapeutic target for basal-type breast cancer.

Notch signaling: an emerging therapeutic target for cancer treatment.

The Notch pathway is involved in cell proliferation, differentiation and survival. The Notch signaling pathway is one of the most commonly activated signaling pathways in cancer. Alterations include activating mutations and amplification of the Notch pathway, which play key roles in the progression of cancer. Accumulating evidence suggests that the pharmacological inhibition of this pathway can overcome chemoresistance. Efforts have been taken to develop Notch inhibitors as a single agent or in combination with clinically used chemotherapeutics to treat cancer. Some Notch inhibitors have been demonstrated to have therapeutic efficacy in preclinical studies. This review summarizes the recent studies and clinical evaluations of the Notch inhibitors in cancer.

Identification of TRAIL-inducing compounds highlights small molecule ONC201/TIC10 as a unique anti-cancer agent that activates the TRAIL pathway.

BACKGROUND: We previously reported the identification of ONC201/TIC10, a novel small molecule inducer of the human TRAIL gene that improves efficacy-limiting properties of recombinant TRAIL and is in clinical trials in advanced cancers based on its promising safety and antitumor efficacy in several preclinical models. METHODS: We performed a high throughput luciferase reporter screen using the NCI Diversity Set II to identify TRAIL-inducing compounds. RESULTS: Small molecule-mediated induction of TRAIL reporter activity was relatively modest and the majority of the hit compounds induced low levels of TRAIL upregulation. Among the candidate TRAIL-inducing compounds, TIC9 and ONC201/TIC10 induced sustained TRAIL upregulation and apoptosis in tumor cells in vitro and in vivo. However, ONC201/TIC10 potentiated tumor cell death while sparing normal cells, unlike TIC9, and lacked genotoxicity in normal fibroblasts. Investigating the effects of TRAIL-inducing compounds on cell signaling pathways revealed that TIC9 and ONC201/TIC10, which are the most potent inducers of cell death, exclusively activate Foxo3a through inactivation of Akt/ERK to upregulate TRAIL and its pro-apoptotic death receptor DR5. CONCLUSION: These studies reveal the selective activity of ONC201/TIC10 that led to its selection as a lead compound for this novel class of antitumor agents and suggest that ONC201/TIC10 is a unique inducer of the TRAIL pathway through its concomitant regulation of the TRAIL ligand and its death receptor DR5.